Nucleofugality effects in the pyridine promoted formation of esters from 2-substituted ethanesulfonyl chlorides'

JAMES FREDERICK KING, JOHN HENRY HILLHOUSE, TOYANNE MARIE LAURISTON, AND KISHAN CHAND KHEMANI

Department of Chemistry, Universiry of Western Ontario, London, Ont., Canada N6A 5B7

Received October 6, 1987

JAMES FREDERICK KING, JOHN HENRY HILLHOUSE, TOYANNE MARIE LAURISTON, and KISHAN CHAND KHEMANI. Can. J. Chem. 66, 1 109 (1988).

The products of reaction of a series of 10 2-substituted ethanesulfonyl chlorides, X-CH2CH2S02C1 (I) , with neopentyl alcohol and pyridine-d5 in nitromethane-d3 showed three reaction pathways depending on the nucleofugality of the substituent, X. These routes lead, respectively, to (i) the corresponding neopentyl ester (4), via the sulfene (3) (low substituent nucleofugalit- y); (ii) a mixture of ester 4 and neopentyl ethenesulfonate (5), by the same route except for a partial loss of the 2-substituent during trapping of the sulfene (3) (intermediate nucleofugality); and (iii) a mixture of the ethenesulfonate (5) and the pyridino-betylate (4g) esters, arising from initial elimination of HX to form ethenesulfonyl chloride (2) followed by its further reaction (high substituent nucleofugality). A set of nucleofugality values closely related to, and partly complementing, those derived by Stirling and co-workers can be estimated from the product ratios in those reactions proceeding (at least in part) by route (ii) above. Old reports of anomalous products from 1,2-ethanedisulfonyl chloride (li) and 2-chloroethanesulfonyl chloride ( l j ) are simply accounted for on the basis of the initial conversion to ethenesulfonyl chloride (2).

JAMES FREDERICK KING, JOHN HENRY HILLHOUSE, TOYANNE MARIE LAURISTON et KISHAN CHAND KHEMANI. Can. J. Chem. 66, 1109 (1988).

Les produits provenant des rkactions d'une sCrie de 10 chlorures d'tthanesulfonyle substituCs en position 2, X- CH2CH2S02CI (I), avec I'alcool nCopentylique et la pyridine-ds, dans le nitromkthane-d3 proviennent de trois voies differentes qui dtpendent de la nuclCofugacitt du substituant X. Ces voies conduisent respectivement 21 (i) ester nCopentylique correspondant (4), par la biais du sulfene 3 (lorsque la nuclCofugacitC du substituant est faible); (ii) un milange de I'ester 4 et I'tth2nesulfonate de ntopentyle (5) qui proviennent de la m&me voie, except6 pour la perte partielle du substituant en position 2 qui se produit lors du piCgeage du sulf5ne 3 (lorsque la nuclCofugacit6 du substituant est intermkdiaire); et (iii) un melange des esters Cth5nesulfo- nate (5) et pyridinio-Etylate (4g) qui proviennent d'une Climination initiale de HX, conduisant au chlorure d'Cth5nesulfonyle (2), qui est suivie de sa &action (lorsque la nuclCofugacitC du substituant est ClevCe). En se basant sur les rapports des produits qui se foment au cours des rkactions (au moins en partie) qui suivent la voie (ii) mentionnCe plus haut, on peut tvaluer un ensemble de valeurs de nucltofugacitt qui ressemble et qui compl2te celui de Stirling et ses collaborateurs. Des rapports antCrieurs concernant la formation de produits anormaux a partir des chlorures d'Cthanedisulfonyle-1,2 ( l i ) et de chloro-2 Cthanesulfonyle ( l j ) peuvent facilement &tre expliquCs en se basant sur une conversion initiale en chlorure d'eth2nesulfonyle (2).

[Traduit par la revue]

1 I In the course of an extended investigation of the mechanism

of sulfonyl transfer (1-4), we have looked at the reactions of a number of 2-substituted ethanesulfonyl chlorides (1) with water or alcohols in the presence of tertiary amines, and have been struck by the variation in the nature of the reaction products. W e now report a more systematic examination of this reaction with substrates bearing substituents having a sizeable range in nu- cleofugality (or "leaving group ability"). Our results enable us to (a) assign the mechanistic pathways leading to the various observed products, (b) estimate nucleofugality values as defined by Stirling and co-workers (5, 6) for some of these leaving groups, and also (c) to provide insight into some inadequately explained observations with 1,2-ethanedisulfonyl and 2- chloroethanesulfonyl chlorides ( l i and l j ) dating back over many years.

Results and discussion Reaction conditions a n d products

Compounds l a - lj were treated with pyridine-d, and neopentyl alcohol in nitromethane-d3 at room temperature; the 'Hmr spectrum was run within 20 min and the product composi- tion so determined summarized in Table 1. Neopentyl alcohol was chosen because (a) its sulfonic esters are comparatively unreactive and hence less subject to subsequent transformation

than those of other alcohols, and (b) the neopentyl grouping gives characteristic, uncluttered 'Hmr spectra with both starting materials and products; nitromethane was found lo be a suitable solvent capable of keeping both covalent and ionic products in solution. In all cases the products were found to be stable to the conditions of the reaction, i.e., the product composition given in Table 1 is that of the primary, kinetically controlled reaction products.

Reaction pathways to products Inspection of the results in Table 1 reveals three patterns of

reactivity: (i) ordinary formation of the corresponding ester (4), illustrated by the reactions of la-c; (ii) production of a mixture of the corresponding ester (4) and the ethenesulfonate ester (5), exemplified by the reactions of the 2-phenylthio- and 2- acetoxyethanesulfonyl chlorides ( l e and 1 8 ; and (iii) generation of a mixture of the ethenesulfonate (5) and betylate (4g) esters displayed by the disulfonyl chloride ( l i ) and 2- chloroethanesulfonyl chloride ( l j ) . Two of these patterns have been observed previously. The first of these is, of course, just the normal formation of alkanesulfonic esters via the sulfene (3), i.e., the regular "sulfene route". The third set of products, i.e., the -2:l mixture of 5 and 4g, has also been obtained from the reaction of ethenesulfonyl chloride under the same condi-

'part 31 in the series Organic Sulfur Mechanisms. part 30: J. F. tions (1). The simplest expianation of this result is that these King, S. M. Loosmore, and J. H. Hillhouse. In preparation. products arise by initial conversion of the starting sulfonyl

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CAN. J. CHEM. VOL. 66, 1988 ,

TABLE 1 . Relative proportions of esters (4, 4g, and 5) in the reaction of 2-substituted ethanesulfonyl chlorides (1) and related compoundsa

Relative proportions

Substrate 4 4g 5 Mechanistic pathway

l a (X = H) lb (X = HO) l c (X = NpOS02) Id (X = PhS02) l e (X = PhS) If (X = MeCOO)

100 1 OOb Sulfene route

>9SC (1+3+4)

97 -

85 - Sulfene + elimination 40 - 60 route (1 + 3 + 4 + 5)

lg (X = pyridinio) 33 Sulfene + elimination lh (X = 3,5-(N02)2C6H3C00) 9 10 and alkene routesd l i (X = C1SO2) - 33 67f Alkene route lj (X = C1) - (33) 32 68 :7e I ( 1 + 2 + 3 g + 4 g + 5 ) CHFCHSO~CI (2) - 33 67 (2+3g+4g+5)E C1CH2CH2S02Br (6) - 33 67 Alkene route (like li)

"Conditions: sulfonyl halide (-0.3 M), pyridine-d5 (1.5-2.0 M), and neopentyl alcohol (-0.6 M) in nitro- methane-d, at room temperature. Ester ratios were determined from 'Hmr spectra (T-60 or XL-200), which also showed the esters (4,4g, and 5) to be the principal products (usually >go%), often along with small amounts of hydrolysis products.

b ~ c t u a l product composition: 46, 16%, C ~ H ~ N + C H ~ C H ~ S O , - , 84% (see also ref. 4). 'No sign of 4g or 5 in the T-60 'Hrnr spectrum. qncursion of about 20% of the alkene route in the reaction of l g is deduced from labelling experiments described

elsewhere (1). In the reaction of l h the ratio of sulfene to alkene routes is -70:30 with most (87%) of the sulfene (3h) undergoing elimination to give 5 and a small amount (13%) going to 4h (see text).

eActual product composition: 5 , 50%; 4g, 7%; 4h, 7%; neopentyl 3,5-dinitrobenzoate, 13%; pyridinium 2-(3,5-dinitrobenzoyloxy)ethanesulfonate, 7%; pyridinium ethenesulfonate, 16%. The last three probably arise largely by trapping of the sulfene (3h) by the liberated 3,5-dinitrobenzoate anion (cf. ref. 2). followed by further reaction of the resultant mixed anhydrides.

fThe product showed no sign of any 4c, which would have been formed if any 4i ( = l c ) had been produced. T h e assignment of this mechanism is discussed elsewhere (1).

chloride into ethenesulfonyl chloride (2) (the "alkene route"), followed by vinylogous attack of pyridine on 2 to give the cationic sulfene (3g), which in turn forms the characteristic mixture of ethenesulfonate (5) and betylate (4g) (ref. 1, cf. also ref. 3). Reaction of lj with a tertiary amine such as 2,6-lutidine or triethylamine is, in fact, the usual preparative route to 2, and the transitory presence of 2 in the reaction of lj with pyridine is to be expected. In accord with this we found that l i with 2,6-lutidine gave a product with the characteristic 'Hrnr spec- trum of 2.

Except for the special case of lg , the other product composi- tion pattern, namely the mixture of the ethenesulfonate (5) and 2-substituted ethanesulfonate (4), has evidently not been noted before. The normal esters (4) presumably arise from the sulfene (3), since the deuterated alcohol yields a-deuterated esters. The ethenesulfonate esters 4e-f and 4h cannot arise from ethenesul- fonyl chloride (2) because under these conditions 2 always gives aroughly 2: 1 mixture of 5 and 4g (I), and the latter is not present in any detectable amount in the reaction products from le , If, and lh. Accordingly, we propose that 4e-f and 4h are formed from the sulfenes (3e-f and 3h) by elimination of X in the course of the trappng reaction.

Such a proposal requires a mechanistic picture in which it is possible to account for the conversion of 2-acetoxy- ethanesulfonyl chloride (lfi, for example, into the sulfene (3fi without any loss of acetate anion to form 2, and, at the same time, in the sulfene trapping step to lose acetate anion more quickly than protonation to form the acetoxy-ester (4fi. This requirement is nicely consistent with the variable transition state mechanism for elimination reactions, with the conversion of If into 3f proceeding by an ElcB-like E2 reaction, and

the trapping of the sulfene (3fi with the alcohol a stepwise process going via a discrete carbanion (7, X = AcO), which

either eliminates X (AcO- in this case) to give 5 or is protonated by the (unspecified) proton source to give 4; this mechanism has already been discussed in connection with the trapping of 3g in aqueous media (3). With such a picture only apartial negative charge is enough to extrude the comparatively nucleofugal chloride anion from If to give 3f (without any loss of acetate anion to form 2), but, with the formation of the full negative charge on the carbon in 7 in the sulfene trapping step, loss even of the less nucleofugal acetate anion competes successfully with the alternative reaction, the rapid protonation of the a-sulfonyl carbanion.

The reaction of the 3,5-dinitrobenzoyloxy compound (lh) illustrates the particularly delicate balance between the possible pathways in each of the two stages of the reaction. Since forma- tion of the betylate (4g) from the pyridinio-sulfene (3g) is accompanied by roughly twice the quantity of ethenesulfonate ester (5), the 10% yield of 4g indicates that about 30% of the total product is formed via 2, while the remaining 70% arises by direct conversion to the sulfene (3h); the reaction pathways may besummarized as follows: 1 + 3 4 4h, 9%; 1 4 3+ 5,61%; 1 + 2 + 5, 20% (total yield of 5, 81%); 1 4 2 -+ 4g, 10%. Reaction of l h obviously gives the highest yield of 5 of any of the substrates used in this study, but it would appear unlikely

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Np = CH2C(CH3)3 X X

a H f CH3CO-0 b HO g CsHsNf c NpOS02 h 3 ,5-(N02)2C6H3CO-0 d PhS02 i C1S02 e PhS j Cl

that direct quantitative formation of 5 can be obtained (with the present conditions, at least) merely be altering the leaving group (X), since increased reactivity in the leaving group would prob- ably lead to more 2 and so to more betylate (4g), whereas diminished reactivity would likely result in more 4 relative to 5.

In principle, the balance among the different reaction path- ways should be alterable by changing the leaving group on the sulfur atom. The reaction of 2-chloroethanesulfonyl bromide (6) was looked at with an eye to seeing if the more reactive bromide would lead to preferential formation of the sulfene (3, X = C1) rather than the ethenesulfonyl halide, but the product was the same as that from 2 (see Table 1) and therefore presumably arose by way of ethenesulfonyl bromide and the pyridinio-sulfene

Other possible pathways Scheme 1 includes a number of dashed arrows representing

reactions which, though a priori reasonable, may be shown to participate, at most, only to a very limited extent under the conditions of this study. As has already been noted above, interconversion of products under the specified conditions is excluded by control experiments. Much longer intervals than those used in the experiments summarized in Table 1, however, may lead to change; the composition of the mixture of 4g and 5, for example, alters from 33:67 to 88:12 on long standing, thereby providing a convenient route to 4g (1). Also, the re- quired authentic specimen of 4 j was obtained by allowing lj to react for 10 days with neopentyl alcohol in CH2C12 (without added base), i.e., by the direct conversion lj to 4j. That such a direct reaction is not important in the presence of pyridine, however, is shown by the deuteration products observed with neopentyl alcohol-d. With a 10-fold excess of neopentyl alco- hol-d (93% NpOD, 7% NpOH), 2-phenylthioethanesulfonyl chloride (le) gave (in addition to 14% of 5) a mixture of PhSCH2CHDS020Np and PhSCH2CHzSO2ONp (4e) in the

ratio of 87: 13; when one recalls that protons are introduced into the reaction mixture by the formation of the sulfene (1 + 3), it is clear that the reaction products are readily accounted for by the sulfene mechanism (1 + 3 + 4) without any detectable incur- sion of the direct displacement reaction. Similar results were encountered in deuteration experiments with l g and lh . Ethanesulfonyl chloride ( l a ) is the only substrate that shows any sign of the direct displacement process. With a 10-fold excess of NpOD (containing 12% of NpOH) l a gave a 56:44 mixture of the mono- and undeuterated esters, CH3CHDS020Np and CH3CH2S020Np (4a). It seems likely that a portion of this reaction product arises via the direct reaction (1 + 4). It should be noted that l a is much the least reactive of the substrates used in this study, with reaction completion requiring more than 22 h as compared with 5 min for the other substrates (lb-j and 2); with such slow sulfene formation it is perhaps not surprising that another process, such as a general base or possibly a nucleophi- lic catalyzed direct displacement, may enter the picture. The much greater ease of sulfene formation from substrates lb- lg is consistent with the above-mentioned ElcB-like E2 picture, since the substituents b-g are all distinctly electron withdrawing relative to hydrogen and would be expected to facilitate de- velopment of the partial negative charge at C- 1. This expecta- tion is in accord with Thomas and Stirling's observation (7) that the rate of the closely related detritiation of PhS02CHTCH2Z with ethoxide in ethanol correlated with the a* values of the CH2Z grouping ( p* = 4.89).

As has been mentioned elsewhere (1) the interconversion l g $ 2 occurs to a minor extent, leading to some CH4DS020Np in the product. This is not seen in the mate- rial from l e or lh , nor do any of the reactions with NpOD show any sign of the dideuterated product, XCH2CD2S020Np (which would be expected if any XCH2CHDS02C1 had been formed, cf. refs. 3 and 8); hence other 1 2 interconversions are evidently precluded.

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11 12 CAN. J. CHEM. VOL. 66, 1988

The insensitivity of product ratios to changes in concentrations ki[B-I of reagents and the mechanism of trapping of the sulfene G-CH2CH2Z + B- G-CHCH~-Z (3)

k-,[BHl

In the hope of gaining insight into the challenging problem of k2 + G-CH=CH2 + Z-

how sulfenes are converted into the final products, we carried out a series of experiments with 2-phenylthioethanesulfonyl (E1cB)~ Process (i.e., One in which k-l[BHI > k2) the

chloride ( 1 4 in which the various ingredients of the reaction observed rate constant for the overall conversion of G-

mixture were systematically altered. The remarkable result was CH2CH2Z to G--CH=CH2 is given by kobs = klk2/k-l[BH:],

that the product composition changed very little. The ratio of and hence

ethenesulfonate to 2-phenylthioethanesulfonate esters (5:4e) was not altered (from 16:84) by increasing the concentration of NpOH from 0.66 to 1.53 to 2.70 M; changing the pyridine-d5 concentration from - 1.5 to 4.2 M lowered the percentage of 4e slightly (to 76%), but addition to pyridinium chloride (2.0 M, [pyridine] 3.95 M) made no discernible further change (78% 4e). In the presence of NpOD the change in product ratios was less than experimental uncertainty: e.g., with a 5 1 :49 mixture of Np0D:NpOH (in 10-fold excess) the products were 5 (13%), PhSCH2CHDS020Np (4 1 %), and PhSCH2CH2S020Np (46%), and with 93:7 Np0D:NpOH the ratio of the same prod- ucts as 14:75: 11; any isotope effect on either the ratio of 5 to 4e or on the isotopic composition of the phenylthio ester would appear to be minimal (i .e., < 1 .2).

The results would appear to rule out protonation of 7 by NpOH or pyridinium ion from the general body of the solution; uptake of hydrogen ion from the solvent is already excluded by the absence of deuterium in the product from the reaction with NpOH in CD3N03. Recalling our earlier experiments showing that the reaction of phenylsulfene, PHCH=S02, with alcohols is base catalyzed (9), we suggest the following sequence:

XCH2CH=S02 + ROH + B --+ XCH~CHSO~OR 6H 3 7

By this scheme the actual hydrogen ion transfer step is a uni- molecular ion-pair process. One should note that the ion pair (7) as initially formed may be presumed to have the BH+ ion in the vincinity of the RO group, i.e., well away from the other two sulfonyl oxygens and hence not, in the first instance, in the arrangement preferred for protonation of the a-sulfonyl carban- ion (near the (r in the internal bisector of the 0-S--0 angle) (cf. ref. 10). Once this latter "preferred" setup is arrived at, it is likely that the hydrogen ion transfer will be extremely fast; we expect on this basis that kH will not be much influenced by either the particular isotope or the nature of X. It follows that the variation in product ratios from these reactions must be assigned to the intrinsic differences in kE, the rate constant for the elim- ination from 7, and hence that these product ratios may be used to estimate nucleofugalities of the X groups, as discussed in the next section.

Stirling and co-workers define the "leaving group rank or "nucleofugality" of Z by the function log (kob,/kl) + 1 1, i.e., by using the value of log k2 obtained by assigning k-l [BH] equal to 10"; kob, is obtained by measuring the rate of the overall elimination, and kl from the rate of exchange of hydrogens a to G.

In our system it is evident that, if the mechanism in the previous section holds, the product ratio [5]/[4] is simply equal to kE/kH, and hence

If, as we argue above, kH is insensitive to X, then the function log ([5]/[4]) gives a scale of nucleofugalities analogous to Stirling's. The similarities of structure are so great that it is tempting to place our relative results on the same absolute basis by adding the same scaling term, i.e., + 11.

The nucleofugalities thus obtained are listed in Table 2. Comparison with Stirling's results, though limited, suggests a measure of correspondence, and at the same time points up some of the difficulties associated with these procedures. The value 9.5 for the phenylsulfonyl group is between those (8.7 and 9.6) derived by Stirling (from reactions in which G = PhS02 and CN, respectively). That for the acetoxy function (1 1.2) suggests roughly comparable magnitudes for kPl[BH] and k2 in the reac- tion of AcOCH2CH2S02Ph, i.e., a mechanism on the (EICB)~- (ElcB)R borderline, in rough accord with the conclusion (which, though reasonable, was not rigorously proved) that this is an ( E ~ C B ) ~ process (11). It may be noted that the present experiments make it possible to obtain a relative nucleofugality for the acetoxy group, a function for which this is not possible by the Stirling procedure because the appropriate substrates do not react by the requisite (ElcB)R mechanism.

The nucleofugality of the phenylthio function, relative to that of the phenylsulfonyl group, continues to be puzzling. Stirling (6) reported that PhS was less nucleofugal than PhS02 in the reactions of M H 2 C H 2 - - C N and about the same in those of ZCH2CH2S02Ph; we find that PhS is rather more nucleofugal than PhS02 in our system. This anomaly, though by no means fully understood, may well be at least partly steric in origin.

In addition to the above, admittedly approximate, quantita- tive assignments of nucleofugality, we note that the failure of l b to yield any neopentyl ethenesulfonate (5) shows hydroxide to be a weaker nucleofuge than PhS02. We also saw no sign of 5 from the neopentyloxysulfonyl substrate (lc), but the nmr in- strument was less sensitive than that used with the phenylsul- -

Nucleofugalities from product ratios fonyl-sulfonyl chloride ( 1 4 and our results do not prove any real Stirling and co-workers (5,6) have placed the "leaving group difference in nucleofugality between PhS02 and NpOS02.

ability" of nucleofugal groups in alkene-forming reactions on a It is also of interest to look at the other end. of the reactivity quantitative basis by examining a series of olefin-forming elim- scale represented in this study. In a competition experiment inations of the following general type in which G is a carbanion- between the disulfonyl chloride (li) and the chlorosulfonyl stabilizing function like PhS02, CN, or PhCO, and Z is the chloride (lj) we found that l i reacted almost six times faster than "leaving group" or nucleofuge: lj (after inclusion of the statistical factor). The chlorosulfonyl

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KING

TABLE 2. Nucleohgalities of some of the 2-substituents

Group log [5]/[4Ia Nucleofugalityb

Phenylsulfonyl - 1.5 9.5 Phenylthio -0.8 10.2 Acetoxy 0.2 11.2 Pyridinioc 0.3 11.3 3,5-Dinitrobenzoyloxyd 0.8 11.8

"Obtained from the yields of 5 and 4 given in Table 1, except as otherwise noted.

bNucleofugality = log ([5]/[4]) + 11 (see text). 'Calculated from the average of the proportions of 4g and 5 for the five

reactions in Table 1 giving these products (only). '%om the ratio [5]/[4g] = 6119 (the respective percentages from 3g only),

see text.

group, though not commonly regarded as a nucleofuge, has been observed to behave as such in a number of nucleophilic displacements (ref. 12 and refs. cited); the comparative unfamil- iarity of reactions involving the loss of the CIS02 function is due, however, not to low nucleofugality itself but to the ease of other reactions of sulfonyl chlorides such as nucleophilic dis- placement at sulfur, elimination to form the sulfene, or reduc- tion by nueclophilic attack at the chlorine atom. We must note explicitly that our observations do not permit a numerical assignment of the nucleofugalities of the C1 and CIS02 groups as defined by Stirling and co-workers. The lack of deuterium in the neopentyl ethenesulfonate formed from l j , NpOD, and pyridine shows that the conversion of lj to 2 is not an ( E ~ c B ) ~ process, but rather either an E2 or ( E ~ c B ) ~ reaction, and hence, as Stirling has emphasized (6), not capable of providing a nucleo- fugality value as defined.

Our results do, as the following argument shows, lead to the conclusion that both the chloro and chlorosulfonyl functions are the most nucleofugal of the 10 groups examined in this study. If we make the reasonable assumption that the sulfonyl chlorides all have the same possible reaction pathways, the finding that l h and lj reacted only by way of 2 can have only two possible causes: (i) the sulfene formation (1 + 3) is slow for l i and l j , or (ii) the C = C bond formation (1 + 2) is fast for l i and l j . It is very difficult to imagine, however, how the formation of C1CH2CH=S02 or C1S02CH2CH=S02 could be so much slower than the analogous reaction yielding RCOOCH2CH=S02 or, especially, NpOS02CH2CH=S02; this would require a substituent effect leading to quite remark- able differences among similar substi t~ents;~ it is much simpler to conclude that 1 + 2 is fast with l i and l j , i.e., the chloro and chlorosulfonyl groups are more nucleofugal than 3 3 - dinitrobenzoyloxy and the others. The high reactivity of chlor- osulfonyl and bromosulfonyl leaving groups relative to other sulfonyl-containing functions has been noted before and ascribed to a fragmentation process in which the SO2-Hal bond is partly broken in the transition state (14).

Earlier reports of the anomalous reactions of I i and Ij As noted in the introduction there are a number of reports,

some dating back to the previous century, describing unex- pected reactions of 1,2-ethanedisulfonyl and 2-chloro- ethanesulfonyl chlorides ( l i and l j ) (15-22). With nucleo-

'Orthodox substituent effects have been observed in at least one sulfene-generating reaction: the rates of formation of ArCH=S02 from ArCH2S020--C6H3-2,4(N02)2 in an (ElcB), reaction process showed an excellent correlation with u- (with p- 2.38, r = 0.996) (13).

philes of the general formula ZH, such as water, alcohols, or amines, the major products of these reactions were never the orthodox derivatives, ZS02CH2CH2S02Z or C1CH2CH2SO2Z, but rather the ethenesulfonate, CHy==CHS02Z, or the formal product of further addition of ZH, i.e., ZCH2CH2S02Z; thus (a) l i with hot water gives mainly SO2, HCl, and CH-----CHS03H (15, 17, 22), and (b) lj with aniline yields CHF CHS02NHPh (8) and (or) PhNH2+CH2CH2S02NHPh C1- (9) (16-21). In the light of the present work it is highly likely that these products arise by initial formation of ethenesulfonyl chlor- ide (2) followed by vinylogous reaction to form the sulfene 3 (X = Z+). If Clutterbuck and Cohen (20) are correct in their assertion that 8 and 9 are both stable to the reaction conditions, then the different ratios of 8 and 9 found under the various reported conditions arise from different ratios of elimination to protonation in the trapping of 3 (X = Z+). Further work is in order to check aspects of the earlier reports and to sort out the factors that control the variations in product ratios.

Experimental Instrumentation and methods

Where not otherwise indicated, reagent grade chemicals and sol- vents were used as received. Melting points were determined on a Reichert Hot Stage and are uncorrected. Infrared spectra were obtained using Beckman 4250 and Bruker IFS 32 FTIR spectrometers and refer to chloroform solutions except as otherwise noted. The 'Hmr spectra were obtained with Varian T60, XL100, XL200, andXL300 spectrom- eters, with all reported chemical shifts from the latter three instruments. The l3Crnr spectra were run on Varian XL200 and XL300 spectro- meters. Spectra recorded in CDC13 and CD3N02 were calibrated with Me4Si (TMS) and those recorded in D20 either with sodium trimethyl- silylpropionate (TSP) or sodium trimethylsilylpropanesulfonate (DSS). Mass spectra were run on a Varian MAT-31 1A spectrometer. The cold finger distillation apparatus used in microdistillation has been described elsewhere (23). Solvent evaporation on work-up was carried out using a Biichi rotary evaporator connected to a water aspirator.

Reactants (a) Ethanesulfonyl chloride ( la) , commercial sample distilled, bp

54°C (4 Torr; 1 Torr = 133.3 Pa); 'Hmr 6: 1.57 (t, 3H), 3.82 (q, 2H); neopentyl2-(chlorosulfonyl)ethanesulfonate ( l c = 4i) (lo), mp 108°C; 'Hmr (CD3N02) 6: 1.12 (s, 9H), 3.89 (t, 2H), 4.06 (s, 2H), 4.35 (t, 2H); 2-(phenylsulfony1)ethanesulfonyl chloride (Id) (24), mp 172- 174°C (lit. (24) mp 173°C); 'Hmr (CD3N02) 6: 3.75-3.95 and4.1-4.3 (sym A2B2 m, 4H), 7.6-8.05 (m, 5H); 2-(phenylthio)ethanesulfonyl chloride (le) (12); ' ~ m r (CD3N02) 6: 3.45-3.62 and4.15-3.98 (sym m(A2B2), 4H), and 7.3-7.57 (m, 5H); 2-acetoxyethanesulfonyl chlo- ride (lfi (25), bp 72-73°C (0.1 Torr); n 26 1.4639 (lit. (25) n, 1.4633); 'Hmr (CDCI,) 6: 2.13 (s, 3H), 4.07 (t, 2H), 4.65 (t, 2H); N-(2-chloro- sulfonylethyl)pyridinium chloride ( lg , C1-) (3); 2-(3,5-dinitrobenzoyl- oxy)ethanesulfonyl chloride ( lh) , see below; 1,2-ethanedisulfonyl chloride (li) (26), mp 91°C (lit. (26) mp 91°C); 'Hmr (CD3N02) 6: 4.52 (s); 2-chloroethanesulfonyl chloride (lj) (27), bp 58°C (3 Ton); ' ~ m r (CD,NO2) 6: 4.07-4.14 (app t, 2H) and 4.26-4.33 (app t, 2H). Neopentyl alcohol-d was prepared by multiple exchange of a solution of commercial NpOH in organic solution with D20; specifically, NpOH (4 g) in D20 (10 mL) and ether (100 mL), followed by further shaking of the ether layer with three 15-ml D20 portions, then evapora- tion of the ether, dissolution in CH2Clz followed by another D20 wash (15 mL), followed by separation and evaporation of the CH2C12 layer, gave 3.1 g of product; deuterium content was estimated at 93% by comparison of the integral of the OH ' ~ m r peak (6 1.72) with the 13c satellite of the CH2 signal (6 2.95).

(b) 2-(3,s-Dinitrobenzoy1oxy)ethanesulfonyl chloride (Ih) 3,5-Dinitrobenzoyl chloride (freshly prepared from the acid plus

SOC12 and recrystallized from benzene, mp 73°C; 4.4 g, 19.1 mmol) was fused with sodium 2-hydroxyethanesulfonate (2.5 g, 16.9 mmol)

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1114 CAN. J . CHEM. VOL. 66, 1988

in a Pyrex test tube (25 mL) over a microburner for 5 min. The almost clear hot liquid so obtained was cooled to room temperature and quenched with water (250 mL) by grinding the test tube in a mortar and pestle. The aqueous solution was filtered and washed several times with CH2C12 (5 X 100 mL) to remove any dinitrobenzoic acid. The aqueous layer was then concentrated to 50 mL on a rotary evaporator. The white crystals of sodium 2-(3,s-dinitrobenzoyloxy)ethanesulfonate that formed within a few hours were removed by filtration and air-dried, mp 307-310°C (5.6 g, 97%); ir (KBr) v,,,: 3100 (m), 2960, 2900 (w), 1740 (s) 1635 (m), 1540 (s), 1460 (m), 1350 (s), 1280 (s), 1200 (vs), 1050 (m), 1000 (m), 925 (m), 800 (m), 770 (m), 750 (m), 700 (s) cm-'; ' ~ m r (D20) 6: 3.47 (t, 2H), 4.81 (t, 2H), 9.18-9.3 (m, 3H); I3Cmr (D20)6:52.3,64.6, 126.1, 135.8, 151.4,and 166.9.Thesalt(1.22g, 3.57 mmol) was ground with excess PClS (12 g) in a mortar, which was then covered loosely with a watch glass and put in a preheated oven at 210°C for 10 min. The contents of the mortar were then ground again while still hot, whereupon reaction occurred immediately to yield a pasty mass. Water (30 mL) was then added and the aqueous suspension extracted with CH2C12 (5 x 100 mL). The organic extracts were combined, dried with anhydrous MgS04, and evaporated to yield a colorless oil that solidified upon cooling (1.133 g, 94%). Recrystalliza- tion from chloroform afforded 2-(3,5-dinitrobenzoyloxy)ethanesul- fonyl chloride (lh) as white needles (0.909 g, 75%); mp 115- 116°C; ir (CHC13) v,,,: 31 10 (m), 2980 (w), 1750(s), 1630 (m), 1550 (vs), 1380 (s), 1345 (vs), 1275 (vs), 1170 (s), 1155 (s), 1070 (m) cm-'; ' ~ m r (CDC13) 6: 4.19-4.25 and 5.01-5.06 (symmetrical multiplet, 4H) and 9.19-9.3 (m, 3H); '3Crnr(CDC13) 6: 59.4,63.1, 122.9, 129.5, 132.2, 148.6, and 161.7. Exact Mass calcd. for C9H7N2O8SC1: 337.9611; found: 337.9613.

(c) 2-Chloroethanesulfonyl bromide (6) 2-Chloroethanesulfonyl chloride (lj) (719 mg, 4.41 mmol) was

stirred with four equivalents of aqueous (8 mL) sodium sulfite (2.22 g, 17.64 rnmol) at O°C for 18 h. Bromine was then added dropwise until the brownish color of bromine persisted. The reaction mixture was quickly transferred to a separatory funnel and extracted with methylene chloride (5 x 50 mL). The extracts were washed with 5% sodium bisulfite sb~ution until ;he bromine color had disappeared. The CH2C12 layer was dried with MgS04 and the solvent evaporated toy ield crude 6 (624 mg, 68%); cold finger vacuum distillation (bath temperature 1 10°C, 1.4 Torr) gave 6 as a pale yellow liquid (574 mg, 63% yield); ir (film) v,,,: 2992 (w), 2930 (w), 1364 (vs) 13 10 (m), 1 157 (vs), 660 (m)cm-'; ' ~ m r ( C ~ 3 ~ 0 ~ ) 6: 4.40-4.33 and4.11-4.04(m, 4H, A2B2) ppm; I3Cmr (CD3N02) 6: 70.7 and 37.6 ppm; Anal. calcd. for C2H402BrC1: C 11.58, H 1.94, S 15.45, Br 38.51, C1 17.09; found: C11.49,H 1 .89 ,s 15.35,Br38.70,Cl 17.21. Neopentyl esters

(a) Previously reported esters Neopentyl2-hydroxyethanesulfonate (4b) (4), also, see preparation

of 4h. N-[2-(Neopentyloxysulfonyl)ethyl]pyridinium chloride (4g) 1, 23).

(b) Neopentyl ethanesulfonate (4a) Pyridine-ds (0.713 mL, 8.32 mmol) was added to a solution of

ethanesulfonyl chloride ( la) (214 mg, 1.66 mmol) in nitromethane-d3 and the reaction mixture allowed to stand for 22 h; work-up followed by careful removal of the last traces of CH2C12 under reduced presure gave 4a as a pale yellow liquid (280 mg, 93%); ir (CHC13) v,,,: 2970 (s), 1550 (m), 1465 (m), 1350 (vs), 1165 (s), 960 (vs), 840 (vs) cm-'; 'Hmr (CD3N02) 6: 1 .OO (s, 9H), 1.37 (t, 3H), 3.19 (q, 2H), 3.87 (s, 2H); I3Crnr (CD3N02) 6: 8.7, 26.5, 32.7, 45.1, 80.4. Anal: calcd. for C7HI6o3S:C46.64, H8.95, S 17.79;found:C46.84, H9.31, S 17.65.

(c) Dineopentyl 1,2-ethanedisulfonate (4c) Pyridine (0.75 mL, 9.3 mmol) was added to a solution of neopentyl

2-(chlorosulfonyl)ethanesulfonate ( l c = 4i) (10) (0.60 g, 2.15 mmol) and neopentyl alcohol (0.50 g, 5.5 mmol) in methylene chloride (25 mL) and the mixture allowed to stand for 18 h. The diester (4c) was obtained on work-up as a yellowish solid (0.35 g, 50%), which after recrystallization from ethyl acetate - petroleum ether (bp 60-80°C) melted at 150-152°C; ir (CH2C12) v,,,: 3055 (w), 2955 (m), 2860 (w),

1465 (w), 1349 (s), 1215 (w), 1165 (s), 1149 (s), 938 (vs), 915 (s) cm-~. , 1 Hmr (CD3N02) 6: 1.01 (s, 9H), 3.57 (s, 2H), 3.94 (s, 2H).

Anal. calcd. for C12H2606S2: (243.62, H 7.93, S 19.41; found: C 43.73, H 8.10, S 19.62.

(d) Neopentyl2-(phenylsulfony1)ethanesulfonate (4d) A mixture of 2-(phenylsulfonyl)ethanesulfonyl chloride (Id) (202

mg, 0.75 mmol), neopentyl alcohol (132 mg, 1.50 mmol), and pyri- dine (300 mg, 3.79 mmol) in nitromethane (20 mL) was allowed to stand at room temperature for 19 h. Recrystallization from hexanes of the crude product (158 mg, 65%) obtained after work-up gave 4d as white needles, mp 1 10.5- 1 1 1°C; ir (CHCI,) v,,,: 2960 (m), 1360 (s), 1323 (s), 1164 (s), 1145 (s), 950 (s) cm-'; ' ~ m r (CDCl,) 6: 0.98 (s, 9H), 3.63-3.44(symm, 4H), 3.95 (s, 2H), 7.61-8.07 (m, 5H); I3Crnr (CDC13) 6: 25.9, 31.8,43.2,50.2, 80.0, 127.9, 130.0, 134.5, 137.6. Exact Mass calcd. for C13H200sS2: 320.0752; found: 320.0758.

(e) Neopentyl2-(pheny1thio)ethanesulfonate (4e) Recrystallization (hexanes) of the crude product (69% yield)

obtained from l e exactly as 4d was prepared from I d gave needles, mp 71.5-72.5"C; ir (CHC13) v,,: 2960 (m), 1480 (m), 1440 (w), 1350 (s), 1 160 (s), 960 (s), 840 (m) cm-'; ' ~ m r (CDC13) 6: 1.30 (s, 9H), 3.07 (s, 4H), 3.59 (s, 2H), 7.1-7.6 (m, 5H); I3Crnr (CDC13) 6: 26.0, 27.5,31.7,49.7,78.8, 127.3, 129.2, 130.5, 133.1. ExactMasscalcd. for C13H2003S2: 288.0854; found: 288.0853.

If) Neopentyl2-acetoxyethanesulfonate (4f) The mixture of neopentyl ethenesulfonate (5) and neopentyl2-acet-

oxyethanesulfonate (4f) (obtained from reaction of 2-acetoxyethane- sulfonyl chloride (If) with neopentyl alcohol and triethylamine) was placed under reduced pressure (0.2 Torr, oil bath temperature 90°C) to evaporate the 5 (bp 62"C, 0.02 Torr). The colorless oily residue gave the following data: ir (neat) v,,,: 2970 (m), 1750 (s), 1350 (s), 1240 (s), 1 160 (s), 1030 (m), 955 (s), 840 (m) cm-'; 'Hmr (CDC13) 6: 1 .OO (s, 9H), 2.09 (s, 3H), 3.46 (t, 2H), 3.91 (s, 2H), 4.49 (t, 2H); (CD3N02) 6: 1.01 (s, 9H), 2.08 (s, 3H), 3.63 (t, 2H), 3.95 (s, 2H), 4.57 (t, 2H). Anal. calcd. for C9Hl8O5S: C 45.36, H 7.61, S 13.46; found: C45.41, H7.52, S 13.31.

(g) Neopentyl2-(3,5-dinitrobenzoyloxy)ethanesulfonate (4h) A mixture of 2-hydroxyethanesulfonyl chloride (4) (1.99 g, 13.8

mmol), neopentyl alcohol (12.15 g, 137.8 mmol), and trimethylamine (3.25 g, 55.1 mmol) was allowed to stand at room temperature for 2 h. Conventional work-up followed by removal of the excess alcohol over an extended period on the rotary evaporator gave a crude product (2.5 g, 93%) with spectra appropriate to neopentyl 2-hydroxyethane- sulfonate, as follows: ir (CHC13) v,,,: 1352 (vs), 1171 (vs), 967 (vs) cm-'; 'Hmr(CDC13) 6: 1.00(s, 9H), 3.38 (t, 2H), 3.91 (s, 2H),4.06 (t, 2H); I3Cmr (CDC13) 6: 26.0, 52.3, 56.5, 73.2, 79.1. Reaction of 1 g (5.1 mmol) of this material with 3,5-dinitrobenzoyl chloride, as de- scribed above for the preparation of l h followed by work-up gave crude 4h (1.7 g, 85%), which after recrystallization from benzene-pentane gave 4h as white crystals melting at 90-92°C; ir (CHC13) v,,,: 3095 (m), 1735 (vs), 1625 (m), 1540 (s), 1455 (m), 1350 (vs), 1268 (vs), 1150 (vs), 1067 (m), 950 (vs), 840 (m) cm-'; ' ~ m r (CD3N02) 6: 0.99, (s, 9H), 3.77 (s, 2H), 3.99 (s, 2H), 4.87 (t, 2H), 9.09-9.19 (m, 3H); ' 3Cmr(~~3~02)6 :2 .64 ,32 .7 ,49 .6 ,61 .1 ,81 .1 , 124.0, 130.6, 134.4, 150.0, 163.8. Exact Mass calcd. for C14H1809N2S: 390.0733; found: 390.0734.

(h) Neopentyl2-chloroethanesulfonate (4j) A solution of 2-chloroethanesulfonyl chloride ( l j ) (3.5 g, 21.6

mmol) and neopentyl alcohol ( 1 .9 g , 2 1.6 mmol) in methylene chloride (5 mL) was allowed to stand at 50°C for 10 days. The solvent was evaporated and the oily brown residue distilled under reduced pressure in a short-path cold-finger distillation apparatus (bath temperature 120°C, 0.5 Torr) giving a colorless oil (0.6 g, 15%); ir (neat) v: 2960 (m), 1355 (s), 1205 (s), 1 170 (vs), 995 (s), 935 (s), 845 (m) cm-'; 'Hmr (CDC13) 6: 1 .OO (s, 9H), 3.70 (m, 4H), 3.93 (s, 2H); (CD3N02) 6: 1.02 (s, 9H), 3.62 (m, 2H), 3.92 (m, 2H), 3.96 (s, 2H). Anal. calcd. for C7HI5C1O3S: C 39.16, H 7.04, C1 16.51, S 14.93; found: C 39.31, H 7.09, C1 16.42, S 15.03.

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KING ET AL. 1115

Reaction of the 2-substituted ethanesulfonyl chlorides with neopentyl alcohol andpyridine-ds

Pyridine-d5 (50-70 pL, 0.6-0.8 mmol) was injected into a solution of the sulfonyl chloride (1) (0.10-0.16 mmol) and neopentyl alcohol (0.20-0.26 mmol) in CD3N02 (0.25-0.40 mL) at 37°C and contained in an nmr tube. The ' ~ m r spectrum was run (within 5 min), after thorough mixing of the conteilts of the tube. With lc - l j the reaction was then complete, but with l a and 16 the product composition given in Table 1 (determined from integration of Me3CCH20-- singlets) was obtained after 18 and 8 h, respectively. The spectra were in all cases found consistent (by comparison with authentic spectra) with the mix- ture of esters described in Table 1. With l e (which is presumably slightly wet and not readily purified), the spectrum showed peaks corresponding to 18% of the hydrolysis product pyridinium 2- (pheny1thio)ethanesulfonate (as shown by comparison with the spec- trum of an authentic specimen); with the other reactions small amounts (<5%) of the corresponding hydrolysis products were sometimes in evidence.

The following series of experiments with 2-phenylthioethane- sulfonyl chloride (le) was carried out as above (in CD3N02) using the following quantities given in the order l e , NpOH, pyridine-d5, total volume, and forming the relative yields of products 4e:S: (a) 72.5 mg (0.307 mmol, 0.033 M), 54 mg (0.613 mmol, 0.66 M), 131 pL (1.53 mmol, 1.65M), 0.93 mL, gave 84:16; (6) 74.7 mg (0.316 mmol, 0.35 M), 55.7 mg (0.632 mmol, 0.70 M), 135 pL (1.59 mmol, 1.77 M), 0.90mL, gave 82517.5; (c) 75.8 mg (0.321 mmol, 0.305 M), 141 mg (1.60 mmol, 1.53 M), 137.5 pL (1.60 mmol, 1.53 M), 1.05 mL, gave 84.615.4; (4 68.8 mg (0.29 mmol, 0.27 M), 256 mg (2.80 (mrnol, 2.70M), 124 pL(0.145 mmol, 1.35M), 1.08mL, gave82:18; (e) 64.4 mg (0.270 mmol, 0.262 M), 120 mg (1.36 mmol, 1.3 1 M), 374 pL (4.36 mmol, 4.20M), 1.04 mL, gave 7624; V) 58.0 mg (0.245 mmol, 0.245 M), 108 mg (1.23 mmol, 1.23 M), plus a stock solution of pyridinium-d5 chloride and pyridine-d5 in CD3N02 to yield a reaction mixture initially 2.05 M and 3.95 M, respectively, total volume 1.0 mL, gave 78:22.

Deuterium labelling experiments 2-Phenylthioethanesulfonyl chloride (le) (62.3 mg, 0.26 mmol) was

mixed with NpOH and NpOD in CD3N02; 'Hmr integration showed a 4951 ratio of Np0H:NpOD. Pyridine-ds was added quickly; initial concentrations of l e , NpOH-NpOD mixture, pyridine-d5: 0.173, 1.76, 0.88 M; total volume 1.50 mL. The ' ~ m r spectrum after 5 min showed (a) no sign of unreacted le , (6) ratio of 5 to total (deuterated and undeuterated) neopentyl 2-phenylthioethanesulfonate, 1336, (c) no sign of deuteration on the neopentyl ethenesulfonate; the spectrum after a further 15 min was unchanged. The reaction mixture was worked up by pouring into water and extracting with CH2C12, followed by drying and evaporation of the solvent. Integration of the two halves of the A2B2 pattern in the 'Hmr spectrum of the product (CDC13, with E ~ ( f o d ) ~ , 41 mg, 0.092 mmol) gave the ratio of PhSCH2CH2S020Np to PhSCH2CHDS020Np as 53:47. A similar experiment with Np0D:NpOH 93:7, the following initial concentra- tions of the above reagents (same sequence) 0.142,1.42,0.707 M, and total volume 1.50 mL, gave a 14:86 ratio of 5 to the phenylthio-ester, with the latter 88% PhSCH2CHDS020Np.

Pyridine-d5 (47 pL, 0.55 mmol) was added to a solution of l h (37 mg, 0.11 mmol) and NpOD (92% OD, 7% OH) (97.5 mg, 1.09 mmol) in CD3N02 (total volume of solution, 0.86 mL); the C-2 protons of 4g and 4h appeared as doublets at 6 5.31 and 4.89 in the 'Hmr spectrum, showing them to be largely monodeuterated at C-1, but quantitative estimation of deuteration was not feasible.

The 'Hmr spectra of the following reaction mixtures showed signals appropriate to the indicated product composition: (a) from I d (80.4 mg, 0.42 mmol), NpOD (95% OD) (374 mg, 4.20 mmol), pyridine-d5 (180 pL, 2.10 mmol) in CD3N02 (total volume 1.45 mL), PhS02CH2CHDS020Np 90%, PhS02CH2CH2S020Np 8%, 5 -2%; (b) the product (total volume 1.11 mL) from lj (36.7 mg, 0.225 mmol), NpOD (95% OD) (201 mg, 2.25 mmol), pyridine-d5 (97 pL, 1.13 mmol), a roughly 2:l mixture of 5 (with no sign, i.e. estimated <2%,

of CH4DS020Np) and the betylate, with the C-2 proton signal apprearing as a doublet, indicating it to be mostly monodeuterated (C~H~N 'CH~CHDSO~ON~) ; (c) pyridine-d5 (108 pL, 1.26 mmol) with l a (32.3 mg, 0.25 mmol), NpOD (88% OD) (224 mg, 2.5 mmol) in CD3N02 (total volume 0.69 mL), after 22 h at room temperature, CH3CHDS020Np 56% and CH3CH2S020Np 44%.

Reaction of ethane-l,2-disulfonyl chloride (li) with 2,6-lutidine 2.6-Lutidine (25 pL, 0.21 mmol) was injected into a solution of the

disulfonyl chloride (li) (36 mg, 0.16 mmol) in CDC13 (-0.5 mL) in an nrnr tube at 37°C. The 'Hmr spectrum was run immediately after thorough mixing and showed the characteristic signals of ethenesul- fonyl chloride (2) (and the lutidine - lutidinium ion mixture) with no sign of umeacted l i ; addition of authentic 2 enhanced the peaks assigned to 2.

Relative reactivities of l,2-ethanedisulfonyl and2-chlorosulfonyl chlo- rides ( l i and l j )

Pyridine-d5 (44 pL, 0.52 mmol) was added by microsyringe to a mixture of equivalent amounts (0.52 mmol) of l i (1 17 mg) and lj (84 mg) with neopentyl alcohol (91 mg, 1.03 mmol) in CD3N02 (0.5 mL) in an nmr tube. The mixture was shaken vigorously and the ' ~ m r spectrum run immediately. Integration of the singlet at 6 4.65 due to l i and the pair of triplets at 4.40 and 4.13 due to l j , relative to the sum of the neopentyl methylene singlets at 3.98,3.80,3.23 arising from4g, 5, and umeacted neopentyl alcohol, gave the proportions of unreacted l i and lj as 55 and 95%, respectively. Addition of another 44-pL portion of pyridine led to 8 and 80% of umeacted l i and l j . Values for the rate constant ratio were obtained from the expression

and found to be respectively 11.6 and 11.2, from the two sets of results, average, 11.4; the statistically corrected ratio for the rates of elimina- tion to form 2 on a per hydrogen basis from l i vs. l j , 5.7.

Control experiments (a) A solution of 4f (30 mg, 0.13 mmol), neopentyl alcohol (1 8 mg,

0.2 mmol), and pyridine-d5 (50 pL, 0.6 mmol) in CD3N02 (0.4 mL) showed no observable change in 'Hmr spectrum over a 14-h interval. Pyridinium-d5 chloride (20 mg, 0.17 mmol) was added; no change in the spectrum was found after a further 4 h. Similar solutions of 4d, 4e, 4h, and 4j with pyridine-d5 and neopentyl alcohol showed unchanged 'Hmr spectra after, respectively, 10, 10, 10, and 90 min at room temperature; after 5 days the solution of 4j showed a trace (<5%) of 5 but no sign of 4g. (6) Pyridine-d5 (0.1 mL, 0.12 mmol) was added to a solution of 2 (38 mg, 0.3 mmol), neopentyl alcohol (50 mg, 0.57 mrnol), and dry acetic acid (6 pL, 0.1 mmol) at 37°C. The ' ~ m r spectrum showed 5 (72%) and 4g (28%), with no sign of any 4f. (c) A solution of l h (0.14 mmol) and NpOH (0.14 mmol) in CD3N02 showed no change in ' ~ m r spectrum on standing at 50°C for 6 days.

Acknowledgement We thank the Natural Sciences and Engineering Research

Council of Canada for financial support of this work.

1. J. H. HILLHOUSE. Ph.D. thesis, University of Western Ontario, 1982. Chap. 2.

2. J. F. KING. ACC. Chem. Res. 8, 10 (1975). 3. J . F. KING, J. H. HILLHOUSE, and S. SKONIECZNY. Can. J.

Chem. 62, 1977 (1984). 4. J. F. G ~ ~ a n d J. H. HILLHOUSE. Can. J . Chem. 61, 1583 (1983). 5. D. J. MARSHALL, P. J. THOMAS, andC. J. M. STIRLING. J. Chem.

Soc. Perkin Trans. 2, 1898 (1977). 6. C. J. M. STIRLING. ACC. Chem. Res. 12, 198 (1979). 7. P. J. THOMAS and C. J. M. STIRLING. J. Chem. Soc. Perkin Trans.

2, 1909 (1977). 8. J. F. KING, R. P. BEATSON, and J. M. BUCHSHRIBER. Can. J.

Chem. 55,2323 (1977) 9. J. F. KING and Y. I. KANG. J. Chem. Soc. Chem. Commun. 52

(1975).

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1116 CAN. 1. CHEM. VOL. 66, 1988

10. E. BLOCK. Reactions of organosulfur compounds. Academic Press, New York. 1978. pp. 50-53.

11. D. R. MARSHALL, P. J. THOMAS, and C. J. M. STIRLING. J. Chem. Soc. Perkin Trans. 2, 1914 (1977).

12. J. F. KING and K. C. KHEMANI. Can. J. Chem. 63,619 (1985). 13. J. F. KING and R. P. BEATSON. Tetrahedron Lett. 973 (1975). 14. J. F. KING and D. J. H. SMITH. J. Am. Chem. Soc. 89, 4803

(1967). 15. W. KGNIGS. Ber. 7 , 1163 (1874). 16. H. LEYMANN. Ber. 18,870 (1885). 17. E. P. KOHLER. Am. Chem. J. 19,728 (1897), 20,680 (1898). 18. W. AUTENRIETH and P. RUDOLPH. Ber. 34,3470 (1901). 19. W. AUTENRIETH and J. KOBURGER. Ber. 36,3626 (1903).

20. P. W. CLUTTERBUCK and J. B. COHEN. J. Chem. Soc. 121, 120 (1922).

21. A. A. GOLDBERG. J. Chem. Soc. 464 (1945). 22. S. M. MCELVAIN, A. JELINEK, and K. RORIG. J. Am. Chem. Soc.

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