Padmavathi, V

Reddy, A Somasekhar

Reddy, D Bhaskar

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Indian Journal of ChemistryVol. 378, November 1998, pp. 1194-11962,6-Diaryl pyridinium cation-A precur-sor in the cleavage process of 5,7-diaryl-piperidino[3,4-dl-l,2,3-selenadiazoleslthiadiazolesD Bhaskar Reddy*, A Sornasekhar Reddy &V PadrnavathiDepartment of Chemistry, S.V.University,Tirupati 517 502, IndiaReceived 9 December 1997; accepted (revised)31 August 1998The mass spectra of 5,7-diphenylpiperidino[3,4-d)-1,2,3-selenadiazole 1, 5,7-dif4-methoxyphenyl)piperidino[3,4-d)-1,2,3-selenadiazole 2, '5;7-di(4-chlorophenyl) piperidino [3,4-d)-I ,2,3-selenadiazole 3, 5,7-diphenylpiperidino [3,4-d)-1,2,3-thiadiazole 4, 5,7-di(4-methoxy-phenyl) piperidino [3,4-d)-1,2,3-thiadiazole 5 and 5,7-di (4-chlorophenyl) piperidino[3,4-d)-1,2,3-thiadiazole 6, have been studied under electronimpact by low and high resolution mass spectrometry. It hasbeen observed- that 2,6-diaryl pyridinium cation is the pre-dominant precursor ion in the cleavage process of the abovemolecules.Heterocyclic compounds having nitrogen andsulfur possess potential pharmacological proper-ties 1-4. Since, sulfur and selenium being isosteric,the concept of isosteric exchange would modifythe activity of biologically important molecules.Hence, it was thought of interest that the synthesisand comparative bio-assay of these compoundswould add new dimensions to the existing knowl-edge. In this perspective, 5,7-diarylpiperidino-[3,4-d]selenadiazoles/thiadiazoles 1-6 were pre-pared. The synthesis and stereochemical aspects ofthese compounds have been discussed in our ear-lier communication'. The behaviour of some 5,7-diaryl-piperidino selenadiazoles 1-3 and thiadi-azoles 4-6 under electron impact conditions werestudied to characterize the compounds unambigu-ously.In the mass spectrum of 5,7-diphenylpiperidino[3,4-d]-1,2,3-selenadiazole 1-the M+2 appears with 100% intensity. The accu-rate mass of this is 342.3068 which corresponds toC17HI5N3Se + 2H. The fragmentation process in-volves the expulsion of nitrogen followed by sele-nium resulting a radical cation at rnIz 233. The ap-Notepearance of an ion at rnIz 312 confirms that theejection of selenadiazole unit takes place in a step-wise manner. In fact, this type of fragmentation isanalogous to compounds having selenadiazolering". The arornatization of an ion at rnIz 233 bythe elemination of H followed by hydrogen rear-rangement led to moderate intense pyridiniumcation (rnIz 232).'Cleavage of the bond (l to the heteroatom seemsto be the initiating step for the appearance of vari-ous daughter ions from the ion at rnIz 232. The twopeaks with substantial intensity at rnIz 127 and 103corresponds to I-phenyl-3-buten-l-yne and styrylcations support such a type of fragmentation proc-ess. The former ion gets itself rearranged to a morestable allyl cation. On the other hand, the ~-cleavage led to 2,3-diphenylaziridine cation withmass 'value 192 is another interesting decomposi-tion process observed. In another mode of frag-mentation, the phenyl hydrogen cyanide cation isformed, which by the ejection of H gives phenylcyanide radical cation (Scheme I). The occurrence~AS)Ph N+Ph-C=C=C=CH2x=se/SScheme IPh_C=~tof 2-phenylpyridinium cation at m1z 154 couldalso arise from this ion by the expulsion of H andPh'. This cleavage process is further supported bythe appearance of an ion at m1z 127 with the lossof HCN. Thus, different daughter ions observedindicates that 2,6-diphenyl pyridinium cation isthe stable precursor ion formed in the cleavageprocess of 1. The elemental composition of differ-ent daughter ions formed during the cleavage pro-cess have also been confirmed by the high resolu-tion mass measurements. Chemical composition:C17HI5N3Se, Found: m1z 340.3022 (Calcd340.2892); C17HI5N;m1z 233.3045 (233.3158);CI7HI~' m1z 232.2456 (232.3078); CI4HIIN, m1z192.4002 (192.2425); ClOlh m1z 127.2394(127.1672); CgH7, m1z 103.1564 (103.1449);C7H5N,m1z 103.1365 (103.1246).In the mass spectrum of 5,7-diphenylpiperidino[3,4-d]-1, 2, 3-thiadiazole 4 also the M+2 ion ap-peared with 100% intensity which is confirmed byits chemical composition C17HI5N3S+ 2H (m1z295.2162). The expulsion of N2 and sulfur in astepwise manner' as in 1 leads to the ions at m1z265 and 233. The chemical composition of thedaughter ions is similar to those observed in 1.Thus, the cleavage process and the most abundantions observed are similar to those as in 1(see Ta-ble I). These formulations are in accord with theresults of high resolution mass measurements.Chemical composition; C17HI5N3S,Found m1z293.5246 (Calcd 293.3932); C17HI5N, m1z233.2642 (233.3158); CI7HI~' m1z 232.3246(232.3078);. CI4HIIN, m1z 192.3452 (192.2425);CIOH7, m1z 127.1864 (127.1672); CgH7, "m1z103.1389 (103.1449); C7H5N, m1z 103.1124(103.1246).The mass spectra of 5,7-di(4-methoxyphenyl)piperidino [3,4-d]-1,2,3-selenadiazole 2, 5,7-di (4-chlorophenyl) piperidino [3,4-d]-1,2,3-selenadia-zole 3, 5, 7-di (4-methoxy-phenyl) piperidino [3,4-d]-1,2,3-thiadiazole 5 and 5,7-di (4-chlorophenyl)piperidino[3,4-d] 1,2,3-thiadiazole 6 showed iden-tical fragmentation pattern thus confirming that thesubstituents have rio influence on cleavage process.In all the cases M+2 ion appeared as the base peakof the spectrum. In 3 and 6 M+2, M+4, M+6 areobserved which-substantiate the presence of twochlorine atoms. In 2 and 5, the anisyl cation ejectsHCHO while forming phenyl cation which is acommon process in such systems. All the frag-NOTES 1195Table I-Mass spectral data of compounds 1-6Compd Precursor Principal fragments mlz (relativeions (M+) intensity)1 mlz 340 342 (100.0), 340 (28.4), 312(35.4), 233 (26.0), 232 (36.0), 192(30.0), 154 (76.2), 127 (48.2), 104(17.8), 103 (28.9), 91 (50.1), 77(50.4)2 mlz 400 402 (100.0), 400 (15.8), 372(39.8), 293 (46.0), 292 (34.1), 252(25.9), 184 (34.8), 157 (61.2), 134(38.4), 133 (54.1), 121 (31.8), 107(40.3),77(41.2)3 mlz 409415 (25.5), 413 (45.9), 411(100.0), 409 (18.8), 381 (36.3),302 (54.8), 301 (69.2),261 (68.2),189 (40.6),162 (60.1),138 (34.9),137 (46.5),126 (21.7),112 (55.1)4 mlz 293 295 (100.0), 293 (14.5), 265(29.8),233 (15.1), 232 (26_6),192(46.5), 154 (50.3), 127 (40.2), 104(21.3), 103 (34.5), 91 (56.3), 77(41.8).5 mlz 353 355 (100.0), 353 (24.6), 325(63.5), 293 (72.9), 292 (38.4), 252(56.8), 184 (29.0), 157 (46.9), 133(46.3), 121 (13.7) , 107 (43.8), 77(37.6)6 mlz 362 368 (23.6), 366 (38.9), 364(100.0), 362 (20.2), 334 (39.8),302 (56.2), 301 (72.1),261 (54.6),189 (68.1),162 (29.2),138 (32.0),137 (39.1),126 (18.4),112 (58.2)mented ions encountered in 1-6 are corroboratedby high resolution data.It can be inferred from this study that in thefused ring systems where selenadiazole and thiadi-azole are one of the rings fused to another ring theprimary cleavage process is the expulsion of selen-adiazole or thiadiazole rings. The high resolutionmass spectra of all the compounds indicated theabsence of sulfur and selenium in the chemicalcomposition of different daughter ions formedduring the splitting pattern thus lending support tothe above observation.Experimental SectionThe compounds 1-6 were prepared according toliterature procedures", 1 m.p. 112-113°C; 2, m.p.96-9rC; 3, m.p. 102-103°C; 4, m.p. 150-51°C; 51196 INDIAN J CHEM. SEC. B, NOVEMBER 1998m.p.:114-115°C; 6, m.p. 98°C dec. All the com-pounds were characterised by IR and IH NMRspectral data.The EI mass spectra were measured on JeolJMS-D 300 mass spectrometer at 70 eV with anemission current of 100 !lA. Accurate mass meas-urements were carried out on Krates MS-80 doublefocussing mass spectrometer.Acknowledgement.One of the authors (ASSR) is grateful to Uni-versity Grants Commission (UGC), N6WDelhi forthe award of Junior Research Fellowship.References1 Katritzky A R, Advances in Heterocyclic Chemistry (Aca-demic Press, London), 38, 1985, 135.2 Prota G & Thomson R H, Endevour, 35, 1976, 32.3 Faria C, Priza M, Gamba A & Pifferi G, Eur J Med Chem -Chim Ther, 14,1979,27.4 Shafiee A, Lalezari I, Yazadany S, Shahbazian F M &Pontovi T, J Pharm Sci, 62, 1973, 839.5 Bhaskar Reddy D, Somasekhar Reddy A & Padmavathi V,'phosphorus, Sulfur & Silicon, 122, 1~97, 143.6 Shafiee A, Lalezari I, Mirrashed M & Nercesian D, J Het-erocycl Chem, 14,1977,567.7 Zeller K P, Meier H & Muller E, Tetrahedron, 28, 1972,1353.

2,6-Diaryl pyridinium cation-A precursor in the cleavage process of 5,7-diarylpiperidino[ [3,4-d]-l,2,3-selenadiazolesl thiadiazoles

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2,6-Diaryl pyridinium cation-A precursor in the cleavage process of 5,7-diarylpiperidino[ [3,4-d]-l,2,3-selenadiazolesl thiadiazoles

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