Indian Journal of Chemistry Vol. 408, September 2001 , pp. 846-849

Note

The behaviour of pyrazole and isoxazole derivatives under electron impact conditions

V Padmavathi*, R P Sumathi, A Padmaja & D Bhaskar Reddy

Department of Chemistry, S. V. University, Tirupati 517 502, India

Received 17 June 2000; accepted (revised) 5 January 2001

The mass spectra of some pyrazole and isoxazole derivatives have been studied under electron impact conditions. It has been observed that the activated olefins and araldehyde phenylhydrazone/araldox ime ions are the precursor ions in the cleavage process of the above molecules.

The chemistry of activated olefins has evoked :.:onsiderable interest because of their utility as building blocks for the development of a number of ~arbocyclic and heterocyclic ring systems. In our ~ndeavour to prepare a new class of heterocycles, Jyrazole and isoxazole derivatives, I ,3-diarylprop-2-~n-1-ones , I-aryl-sulfonyl-2-arylethenes, 1-aroyl-2-lf)'lsulfonylethenes, I ,2-diary lsulfony lethenes and 1,2-iiaroylethenes have been used as synthons. The I ,3-lipolar cycloaddition of dipolarophiles, nitrile imines md nitrile oxides generated in situ from araldehyde >henylhydrazones and araldoximes in the presence of :hloramine-T to the above substrates resulted lyrazole and isoxazole derivatives. The synthesis and tereochemical aspects of these compounds have been liscussed in our earlier communications 14

• The 1ehaviour of some of these compounds under electron mpact conditions were studied to characterize the ompounds unambiguously.

All the compounds exhibited low intense M+. peaks orresponding to their molecular formulae. It is nteresting to observe that the cleavage of these M+. esulted the formation of corresponding activated .Jetins and araldehyde phenylhydrazone/ araldoxime s the principal daughter ions which are the onstituents of five membered heterocycles.

1,3,5-Triphenyl-4-benzoyl-2-pyrazoline 1 and ,5-diphenyl-4-benzoyl-2-isoxazoline 2. The lability f heterocyclic ring in both the compounds is ~fleeted by the cleavage of the bond a- to eteroatoms resulting in the formation of I ,3-iphenylprop-2-en-1-one radical cation (m/z 208). he appearance of this ion has been substantiated by 1e presence of benzaldehyde phenylhydrazone (m/z

PhO)J:hJ~ N -PhC•N.X

Ph X'

1 X= NPh, m/z402 1 X= NHPh, m/z 195

2X=O,m/z327 2X=OH,m/z120 .

+ PhCOCH= CHPhl'

m/,208 \

/ /. \ .. PhCOCH= CHj PhCH= Cl-il PhCOl Pill

m/z131 m/z103 m/z105 m/z77

Scheme I

+

Ph0 2)J_.,phl'

N - PhC :;N.X Ph X'

3X= NPh, m/z438 JX=NHPh, m/z195

4X= 0 , m/z363 4 X= OH, m/z 120

! Phso';-f -- PhS0 2CH=CHPhl'!' ~PhCH= CHf

m/z141 m/z:244 m/z103

1 H ~Ph 'c-c'

Ph-5-0' 'H

/! g]+ ?\ ~

PhS PhC= CH - PhCH 2 ~.,;= 0

m/z 125 m/z119

Scheme II

195) and benzaldoxime (m/z 120) cations in 1 and 2, respectively. The ion at m/z 208 on further disintegration results benzoyl cation (m/z 105). The presence of styryl cation (m/z 103) which is also derived from the same parent ion renders credible

NOTES 847

PhvcoPhM...,~ .... PDPliJ' -m/z 235 PhS02 X"

PhC:N-x:

X= NHPh, m/z 195 X= OH, m/z 120 I 5X= NPh, m/z48~

Ph t COPh.Me-4 6X= 0, m/z405 ~

PhS02CH= N Phj m/z 245 ~34 1

PhSO CH= cHf - 4-Me.PhCOCH= CHS02Ptif

m/~ 167 ~+ I lmlz 286 l 1 1 * PhN=Cf PhS021

ml z 1 41 4-Me.Ph.COCH=CRf 4 -Me. PhC<?f m/z145 m/z119

Phsoilf m/z 142 m/z 103

~ \2) m/z 91

support to such a cleavage pattern. Infact, the benzoyl cation appears as the most abundant ion in 2. The I ,3-diphenylprop-2-en-1-one radical cation in another cleavage process led to benzoylethene cation (rnlz 131) which is also supported by the appearance of phenyl cation. The latter forms the base peak of the spectrum in 1 (Scheme I). Thus, the presence of an ion at rn/z 208 in both 1 and 2 and benzaldehyde phenylhydrazone cation in 1, benzaldoxime cation in 2 clearly shows that these are the important constituents in the frame work of 2-pyrazoline and 2-isoxazoline.

1,3,5-Triphenyl-4-benzenesulfonyl-2-pyrazoline 3 and 3,5-diphenyl-4-benzene- sulfonyl-2-isoxazoline 4. The primary fragmentation pattern observed for the compounds is almost similar to 1 and 2. Thus, the cleavage of heterocyclic ring furnished styrylphenyl­sulfonyl radical cation ( rnlz 244) in both the cases. The appearance of benzaldehyde phenylhydrazone cation (rnlz 195) in 3 and benzaldoxime cation (rnlz 120) in 4 supports such a cleavage pattern. The ion at rnlz 244 undergoes sulfonyl-sulfinate rearrangement5

and further fragments into phenylsulfoxide cation (rnlz 125) in both the cases. The phenylethyleneoxide cation (rnlz 119) evidenced such type of rearrange­ment. The latter can be stabilized by isomerization to benzylcarbonyl cation. Furthermore, the ion at rn/z

1 ~o

Scheme III

244 disintegrates into phenylsulfonyl and styryl cations. The latter ion appears as the base peak of the spectrum in both the cases (Scheme II).

1,3-Diphenyl --4-( 4-methylbenzoyl)-5-benzenesul­fonyl-2-pyrazoline 5 and 3-phenyl-4-(4-methyl­benzoyl)-5-benzenesulfonyl-2-isoxazoline 6. The principal fragmentation route of M+. in both the cases also involves cleavage of heterocyclic ring resulting 1-(4-methylbenzoyl)-2-benzenesulfonylethene radical cation (rnlz 286) along with benzaldehyde phenyl­hydrazone cation in 5 and benzaldoxime cation in 6. In another mode of disintegration of M+. led to 1-( 4-methylbenzoyl)-2-benzylazirine radical cation (rnlz 235). The formation of this ion was substantiated by the appearance of N-phenylbenzenesulfonylmetha­nimine radical cation (rn/z 245) in 5. This ion on further cleavage furnished benzenesulfinic acid (rnlz 142) and benzoisonitrile (rnlz 103) radical cations. The ion at rn/z 286 under different disintegration process i.e. , cleavage a to carbonyl group and sulfonyl group furnished benzenesulfo11ylethene, 4-methylben­zoylethene, benzenesulfonyl and 4-methylbenzoyl cations at rnlz 167, 145, 141 and 119, respectively. The latter ion appeared with high abundance in 6 whereas in 5 it is due to phenyl cation. Ejection of CO from an ion at rnlz 119 led to benzyl cation which gets aromatized to tropylium cation (rnlz 91) (Scheme Ill).

848 INDIAN J CHEM, SEC 8 , SEPTEMBER 2001

_ + 4-Me.PhS:202 -/Ph. C1-4f 4-Me . PhSQ2.~Ph.C1-4f 4-CI .PhC= N-X - . \\ 'N'

X= NHPh, m/z 229 PhSO X'N - m/z 305 X=OH , m/z164 / l

¥ 7X=NPh,m/z550 PhS02CH=NPtf 8x=O,m/z475 4-Me.PhS0

2 .Ph.CI-4

m/z245 Y I~

+ PhS02Al.

+ PhN= Cl

m/z 142 m/z 103

I ~ PhsoJ

ml z 141

4-Me.Phso 2Hf m/z 156

l © .

m/z 91

Scheme IV

m/z 304

l 4-CI.PhC= Nf

m/z 147

4-CI.Ph--..~COPhf_ PhO)C -/. ,NPh.C_14- + 'N' \\ 4-CI. Phc:. N -X

m/z255 4-Me.PhOC X X=NH.Ph,m/z235 ~ X= OH, m/z 155

l gX= NPh, m/z 478 ~ 4-CI.PhC'= ~~ 4-CI.Ph--.,.WCOPh 10X= 0, m/z403 m/z 147

mlz. 2N54 l 4f 4-Me.Ph.cOf

PhCO?/~~~\hM~~- m/z119 PhCOCH= df PhCOl+ 4-Me.PhCOCH= cHf

l +

PhCOC= Nj" ml z 131 m/z131 m/z105 m/z145

Scheme V

1-Phenyl-3-( 4-chlorophenyl)-4-phenylsulfony 1-5-4-methylphenylsulfonyl)-2-pyrazoline 7 and 3-(4-:hlorophenyl)-4-phenylsulfonyl-5-(4-methylphenyl­ulfonyl)-2-isoxazoline 8. The splitting pattern of the teterocyclic ring was observed to be similar to 5 and 6. 'hus, 4-chlorobenzaldehyde phenylhydrazone cation Tllz 229) in 7 and 4-chlorobenzaldoxime cation (rn/z 64) in 8 were the principal fragments . However, a peak

corresponding to 1 ,2-diarylsulfonylethene radical cation was not found in both the cases. Instead, 4-methylbenzenesulfinic acid radical cation (rn/z 156) and benzenesulfonyl cation (m'z 141) were observed. Elision of H" followed by so2 from the former led to tropylium cation. In another mode olf cleavage of the M+. resulted 2-( 4-methylbenzenesulfonyl)-3-( 4-chlorophenyl)azirine radical cation (rn/z 305). The appearance of N-phenyl-

NOTES 849

benzenesulfonylmethanimine radical cation (m/z 245) in 7 supports the type of cleavage pattern. The 4-chloro­benzonitrile radical cation derived either by the cleavage of the ion at m/z 304 or by the M+. forms the base peak of the spectrum in both the cases (Scheme IV).

1-Phenyl-3-( 4-chlorophenyl)-4-benzoyl-5-( 4-chlo­robenzoyl)-2-pyrazoline 9 and 3-(4-chlorophenyl)-4-benzoyl-5-( 4-chlorobenzoyl)-2-isoxazoline 10. The splitting pattern of these compounds is similar to 5, 6, 7 and 8. The different daughter ions observed are shown in the Scheme V. The 4-methylbenzoyl cation (m/z 119) was the base peak in both the cases (Scheme V).

Experimental Section The compounds 1-10 were prepared according to

the literature procedures 14. All the compounds were

characterized by IR, 1 H NMR and 13C NMR spectral

studies. The EI Mass spectra was recorded on a Jeol JMSD-300 mass spectrometer at 70 eV with an emission current of 100 f.! A.

Acknowledgement One of the authors (RPS) is grateful to CSIR, New

Delhi for the award of SRF.

References I Padmavathi V, Sumathi R P, Bhaskar Reddy A V & Bhaskar

Reddy D, Heterocycl Commun , 4, 1998, 163. 2 Padmavathi V, Bhaskar Reddy A V, Sumathi R P, Padmaja A

& Bhaskar Reddy D, Indian J Chem, 37B, 1998, 1286. 3 Padmavathi V, Sumathi R P, Chandrasekhar Babu N &

Bhaskar Reddy D, J Chern Research(S), 1999,610. 4 Padmavathi V, Sumathi R P, Yenugopal Reddy K & Bhaskar

Reddy D, Synth Commun, 30, 2000, 4007. 5 Budzikiewicz H, Dierassi C & Williams D H, Mass

spectrometry of organic compounds, (Holden-Day, San Francisco), 1967, 552.