ORGANIC MASS SPECTROMETRY, VOL. 27, zyxwvuts 615-618 (1992) zyxwvut Mass Spectrometry of Some 2-Styryl- and 2,5-Distyrylfuran and -Thiophene Derivatives Grace Karminski-Zamola,*Miroslav Bajii: and Nikola Blakvii: Department of Organic Chemistry, Faculty of Technology, University of Zagreb, 41000 Zagreb, Croatia zyxw Mass spectra of fourteen 2-styryl- and 2,5-distyrylfuran and -thiophene derivatives are reported. Each styryl sub- stituent has an a-carboxylic acid or methyl carboxylate substituent. Although the parent ion is the zyxw base peak for the styryl and distyryl derivatives, the distyryl species showed less fragmentation than the styryl species. In addition to simple bond cleavages, loss of formic acid or methyl formate was important in many of the species, presumably forming acetylenic fragments. INTRODUCTION There is no information in the literature about the mass spectra of thiophene and especially furan compounds substituted with an unsaturated chain. As 2-styryl- and 2,5-distyrylfuran and -thiophene are the heterocyclic analogues of stilbenes, which are widely used as photo- sensitizers and in various biological and pharmacolo- gical applications, we turned our attention to the synthesis,' photochemical behaviour' and electron impact (EI) mass spectrometry of these compounds. Thiophene itself and alkyl- or halogen-substituted thiophenes show the following fragmentation pat- tern~:~,~ 1 +' zyxwvutsrqponm m/z 39 + zyxwvutsrqpon 9 - HC=CH+ A mlz 58 Furan nuclei show the same type of fragmentation: 1 +f In this study, we examined the fragmentation mode of 24 zyxwvutsrqp E)-( 2-car bomet hoxystyry1)furan (1 ), 24E)-(2-carbo- methoxystyry1)thiophene (2), 2,5-di-(E)-(2-substituted- styry1)furans 3-8 and 2,5-di-(E)-(2-substituted-styryl) thiophenes 9-14. 1 X=O,R=CH, 2 X=S, R=CH, 3 X = zyxwv 0, Ar = Ar' = phenyl, R = R' = H 4 X = 0, Ar = Ar' = phenyl, R = R' = CH , 5 X = 0, Ar = Ar' = phenyl, R = H, R' = CH, 6 X=O, Ar=Ar'=p-OCH,-phenyl, R=H, R'=CH, 7 X = 0, Ar = Ar' =p-OCH,-phenyl, R = R' = CH, 8 X = 0, Ar =m-CI-phenyl, Ar'=p-OCH,-phenyl, R = CH,, R' = H 9 X = S, Ar = Ar' = phenyl, R = R' = H 10 X=S, Ar=Ar'=phenyl, R=R'=CH, 11 X = S, Ar = Ar' = phenyl, R = H, R' = CH, 12 X = S, Ar = phenyl, Ar' =p-OCH,-phenyl, R = CH,, R'= H 13 x = S, Ar = phenyl, Ar' = 2-thienyl, R = R' = H 14 X = S, Ar = phenyl, Ar' = 2-thienyl, R = R' = CH, EXPERIMENTAL All compounds were prepared according to the literature' except 13, which was prepared by the con- densation of formylated 2 (in the 5-position of the thiophene nuclei) and 2-thienylacetic acid in the pres- ence of triethylamine and acetic anhydride and sub- sequent hydrolysis (yield 29%, m.p. 295-298 "C), and 14, which was prepared by esterification of 13 with absolute methanol (yield 67%, m.p. 139-140 "C). All mass spectrometric measurements were performed on a Shimadzu QX lo00 mass spectrometer operating in the EI mode (70 eV, 200 PA). Samples were intro- duced by direct probe at a source temperature of 220 "C. RESULTS AND DISCUSSION The 70 eV EI mass spectra of 1 and 2 are reported in Table I. The features of the mass spectral fragmentation of the molecular ions la and 2a of 1 and 2 are presented in Scheme 1. The molecular ions la and 2a show fragmentation by cleavage of methyl, methoxy and carbomethoxy groups resulting in the fragment ions lb, 2b, zyxw Ic, Id and 2d and loss of methanol producing fragment ions le and 2e. We propose that the intense [M - 601 fragments result from combination of the hydrogen radical on the Received 28 October 1991 Accepted 4 December 1991 0030-493X/92/0506 15-04 $05.00 zyxwvut 0 1992 by John Wiley & Sons, Ltd.