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Studies on Unstabilized ^-Sulfuranes: Synthesis of Jrans-l,2-Disubstituted Epoxides

R. S. Tewari, A. K. Awasthi, and S. C. Chaturvedi Department of Chemistry, H. B. Technological Institute, Kanpur 208002, India

Z. Naturforsch. 35 b, 1565-1568 (1980); received April 14/August 25, 1980

4-Nitrobenzylidenedimethylsulfurane 4-Nitrobenzylidenedimethylsulfurane, a semi-stabilized sulfonium ylide has been

generated by the attack of methylsulfinyl carbanion in dimethyl sulfoxide and reacted with a series of substituted benzaldehydes, furfural and benzylideneacetophenone to afford <mns-l,2-disubstituted epoxides in fair to good yields. The structural assignments of the products are based on IR and NMR spectral evidences.

Many routes [1-5] have been devised from time to time to bring about transformation of olefinic as well as carbonyl function [6] into their epoxy derivatives. Two distinct approaches have been utilized for this purpose of which the former involves the controlled oxidation of olefinic systems [7, 8] while latter comprises methylene transfer reaction over carbonyl entities [9]. The former has been proved to be of little worth [7, 8, 10, 11] because of the lower yields of the epoxides possibly due to side reactions. The latter approach, formulated by Corey and Chaykovsky [9] in their attempts to study the reactivity of methylenedimethylsulfurane towards carbonyl compounds was restricted to the synthesis of monosubstituted epoxides i.e. styrene oxides. In the subsequent years, arsonium ylides have also earned the distinction of being epoxidation reagents as investigated by Trippett and Walker [12]. Unlike preceding method, these ylides, though yielded 1,2-diphenylethylene oxides, failed to offer a gen-eralised method as the formation of epoxides was reported to be controlled by the nature of groups present on the ylidic carbanion as well as on the nature of solvent and base [13]. And it was reported that epoxides could only be formed if ylide carbanion carried electron donating groups otherwise olefins were the exclusive products of the reaction and, therefore, idea of synthesizing 1,2-diphenyl ethylene oxide containing electron attracting groups could not be realised. Taking the advantage of the fact that the yr-sulfuranes were the exclusive epoxidation reagents, it was thought to be of interest to enable the synthesis of nitro containing 1,2-diphenyl ethylene oxides through the interaction between a

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new semi-stabilized jr-sulfurane, i.e. 4-nitrobenzyl-idenedimethylsulfurane and carbonyl compounds.

Results and Discussion 4-Nitrobenzyl bromide with dimethyl sulfide at

room temperature afforded 4-nitrobenzyldimethyl-sulfonium bromide (1). Solution of 4-nitrobenzyl-idenedimethylsulfurane (2) was prepared success-fully by addition of solution of 4-nitrobenzyldi-methylsulfonium bromide in dimethylsulfoxide with stirring to a solution of methylsulfinyl carbanion in equimolar amount under N2 at low temperature (0-10 °C in DMSO containing enough THF to prevent freezing) because of the marked thermal instability of 2.

The reaction of 2 with a range of carbonyl compounds (3a-j) were carried out at low tem-peratures to afford trans-1,2-disubstituted epoxides (4a-j) in 50-65% yields (Scheme 1).

(CHjljS-CHj-^^- NOj • [CH2SOCH3] Na* -1 B r ®

(CH3)2S®-CH -(^^-NOj • (CH3)JS0 2

2, A r -c-R DMSO/THF, A r , ? < ! > C H ^ . N 0 2

0 R 3 a - j A a - j

3, 4a: Ar = C6H5 ; R = H b: Ar = 4-CH3 • C6H4; R = H c: Ar - 3,4-02CH2 • C6H3; R = H d: Ar = 4-(CH3)2 • N • C6H4; R = H e: Ar = 3-OC2H5-4-OH • C6H3; R = H f: Ar = 4-OH • C6H4; R = H g: Ar = 4-CHO • C6H4; R = H h: Ar = 3-N02 • C6H4; R = H i: Ar = 2-C4H30; R = H j : Ar = C6H5CH = CH; R = C6H5

Scheme 1.

R. S. Tewari et al. • Studies on Unstabilized rrc-Sulfuranes: Synthesis of trans- 1,2-Disubstituted Epoxides 1566

Table I. Structure and physical properties of frans-1,2-disubstituted epoxides (4a—j).

Elemental analysis [%] Product Yield Recryst. solvent m.p. Found/(Calcd)

[%] Recryst. solvent

[°C] C H N

4a 52 Ethanol-ether 126-127* 69.74 4.60 5.82 (69.70) (4.56) (5.80)

4b 50 Chloroform-benzene 110-112 70.52 5.12 5.44 (70.58) (5.09) (5.49)

4c 65 Chloroform-benzene 151-152 63.20 3.84 4.90 (63.15) (3.85) (4.91)

4d 53 Chloroform-pet. ether 209-210 67.62 5.62 9.88 Chloroform-pet. ether (67.60) (5.63) (9.85)

4e 51 Benzene 65-66 63.81 4.50 4.63 (63.78) (4.98) (4.65)

4f 51 Chloroform-benzene 100-101 65.32 4.25 5.43 (65.36) (4.28) (5.44)

4 g 53 Chloroform-methanol 95-96 66.89 4.12 5.19 4 g

(66.91) (4.08) (5.20)

4h 58 Chloroform-pet. ether 140-141 58.77 3.43 9.72 Chloroform-pet. ether (58.74) (3.49) (9.79)

41 58 Benzene-pet. ether 130-131 62.31 3.85 6.01 Benzene-pet. ether (62.33) (3.89) (6.06)

4j 60 Chloroform-benzene 150-151 76.91 4.91 4.01 4j (76.96) (4.95) (4.08)

a Lit. [14] 126 °C.

The success of the reaction contrasted to the failure to form olefins or cyclopropanes suggested the low potential formation of a sulfur-oxygen bond and high nucleophilicity of the ylidic carbanion.

It was found that the electron withdrawing substituents on the carbonyl group facilitated the reaction as is evident from the yields of 4 a-j .

The trans geometry of the epoxide derivatives (4a-j) was confirmed on the basis of NMR spectra in which the trans coupling constants observed were in the range 2 cps to 4 cps.

All the epoxides (4a-j) synthesized in the present investigations gave satisfactory elemental analysis and all products except 4 a [14] were new. The NMR spectra (CDCI3) in general exhibited epoxy protons in the range of <5 3.0-4.52, aromatic protons at d 6.45-8.5. In IR spectra (KBr) of the products VNC>2 and rOH were exhibited in the expected range (Table II).

Experimental Melting points were determined on a Gallen Kamp

apparatus and are uncorrected. The NMR spectra (CDCI3) were run on a Varian A-60 spectrometer using tetramethylsilane as an internal standard and are reported in (ppm) values. All products were

The course of the reaction seems to have proceeded via the intermediacy of sulfonium betaine (1), in-volving displacement by the oxyanion on the carbon carrying the onium group. Secondly the formation of a sulfur-oxygen bond is not sufficient and thus is unable to provide a considerable driving force for a variety of reactions (Scheme 2). The dimethylsulfide group is known to be an excellent leaving group and this factor also may tend to favour epoxide forma-tion from the betaine 1.

With carbonyl compounds (3a-j), 2 led exclu-sively to epoxides (4a-j). In no case were olefins or cyclopropanes obtained.

(CH3)2S - c

101. •

Schema 2.

I C H 3 ) 2 S - c

© tCH3)2S-0

© 0 - C

H

I C H 3 ) 2 S

H C = C C — C

/

v i a

R. S. Tewari et al. • Studies on Unstabilized rrc-Sulfuranes: Synthesis of trans- 1,2-Disubstituted Epoxides 1567

Table II. IR and NMR spectral data of trans-1,2-disubstituted epoxides (4a-j).

Product IR data [KBr] CH stretching vibrations

v [cm-1] C-C asymmetric ring stretching

Spectral data N M R d a t a (CDCI3) ö ppm

VNC>2 Aliphatic Epoxy Aromatic H H H

Other groups (H)

4a 832 848 1340 — _ _ -

4b 820 848 1340 2.38 S, CH3 3.80, q 7.0 -8.3, m -

4c 856 860 1350 - - - -

4d 820 860 1330 1.30 S, CH3 3.20, q 6.25-8.25, m -

4e 840 850 1280 - - - -

4f 820 856 1350 - 4.65, q 7.0 -8.2, m 6.90 S, OH 4g 820 840 1330 - 3.70, q 7.1 -8.5, m 9.50 S, CHO 4h 832 848 1340 - - - -

4i - - - - 4.0, q 7.41-8.3, m 6.9-7.4, m (furyl)

4j - - - - 2.02, s 6.8 -7.4, m 3.7, q (Olefinic)

purified by column chromatography over neutral alumina. Purity was checked by thin layer chro-matography (tic). Unless otherwise stated all reac-tions were carried out under nitrogen.

Preparation of 4-nitrobenzyldimethylsulfonium bromide (1)

1 was prepared by mixing 4-nitrobenzylbromide (21.6 g, 0.1 mol) and dimethylsulfide (6.2 g, 0.1 mol) in benzene solution (30.0 ml). After stirring for 12 h at room temperature, the reaction mixture was filtered to give a whitish grey solid (hygroscopic). Repeated washings of the residue with acetone afforded the pure product 1, m.p. 140-141 °C, yield 22 g (92%).

Analysis for C^H^BrNO^S Found C 38.80 H 4.32 N5.10, Calcd C 38.84 H 4.31 N 5.03.

IR spectra (KBr) v max. 3380 (ArH), 1600 (C=C), 1350 cm-i (N02).

Preparation of 4-nitrobenzylidenedimethyl-sulfurane (2)

Sodium hydride (0.58 g of 50% mineral oil disper-sion, 12 mmol) was freed of mineral oil by three washings and decantings with petroleum ether (b.p. 40-60 °C) under atmosphere of nitrogen. After the last washing, the system was evacuated to remove the last traces of the petroleum ether. The vacuum was broken by introduction of nitrogen and

100 ml of dimethylsulfoxide (distilled from calcium hydride at 64 °C at 4 mm) was added. An aliquot of this solution was diluted with an equal volume of tetrahydrofuran (distilled from lithium aluminium hydride) and cooled in an ice-salt bath. A solution of 4-nitrobenzyldimethylsulfonium bromide in di-methylsulfoxide (800 ml of solvent per mole of salt), equivalent to the sodium hydride, was added portion wise at such a rate that the internal temperature did not exceed 5 °C. After the addition of the salt was complete, the mixture of 2 was stirred an additional minute longer before adding the accep-tor.

Preparation of trans-1,2-disubstituted epoxides (4a-j) A solution of 0.03 mole of 2 and 0.025 mole of

substituted benzaldehydes, furfural and benzyl-ideneacetophenone in 20 ml of DMSO was stirred for 1 h at 0 °C. The stirring was continued for 30-60 min at room temperature and then 1 h at 60 °C. The reaction mixture was then diluted with three volumes of water and the product extracted with benzene, washed with water and dried over anhydrous sodium sulfate. Evaporative distillation of the product after column chromatography over neutral alumina yielded the substituted epoxides (4a-j) in 50-65% yields as shown in Table I.

Authors thank the Director, H. B. T. I., Kanpur for providing facilities, A. K . A. and S. C. C. thank C. S. I. R., New Delhi, for financial assistance.

R. S. Tewari et al. • Studies on Unstabilized rrc-Sulfuranes: Synthesis of trans- 1,2-Disubstituted Epoxides 1568

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413 (1949). [3] V. A . Pokrovskii, Uspekhi Khim. 21, 785 (1952). [4] M. S. Kharasch and 0 . Reinmuth, Grignard

Reactions of Non-Metallic Substances, pp. 181, Prentice Hall Inc., New Y o r k 1954.

[5] V . A . Pokrovskii, Uspekhi Khim. 25, 1446 (1956).

[6] C. D. Gutsche, Org. React. 8, 364 (1954). [7] D. Swern, Chem. Rev. 45, 1 (1949). [8] D. Swern, Org. React. 7, 121 (1953).

[9] E . J . Corey and M. Chaykovsky, J. Am. Chem. Soc. 84, 3782 (1962).

[10] A. Weissberger, Heterocyclic Compounds, pp. 31, Interscience Publisher, John Wiley, N. Y . 1964.

[11] B. M. Trost and L. S. Melvin (Jr.), Sulfur Ylides, pp. 51, Academic Press, New Y o r k 1975.

[12] S. Trippett and M. J. Walker, J. Chem. Soc. C 1, 1114 (1971).

[13] R . S. Tewari and S. C. Chaturvedi, Tetrahedron Lett . 1977, 3843.

[14] A . W . Johnson and J. O. Martin, Chem. Ind. (London) 1965, 1726.