DIELS-ALDER REACTIONS OF 2,3-BIS-(PHENYLTHIO)-1,3-BUTADIENE - X-RAY AND NMR STRUCTURAL INVESTIGATIONS OF CIS AND S-(PHENYLTHIO)-4,5-DIMETHOXYCARBONYL-1-CYCLOHEXENE

The Diels-Alder reaction of 2,3-bis-(phenyrthio)-1,3-butadiene (4), de rived in situ by thermal extrusion of sulfur dioxide from -bis-(phenyl thio)-2,5-dihydrothiophene-1,1-dioxide (3), with dimethyl fumarate gav e trans-1,2-bis-(phenylthio)-4,5-dimethoxycarbonyl (1). Similarly, the reaction of 4 with maleic anhydride gave 4,5-bis-(phenylthio)4-cycloh exene-1,2-dicarboxylic anhydride (5), which was converted into is-(phe nylthio)4,5-dimethoxycarbonyl-1-cyclohexene (2). The characterization of 1 and 2 included a single-crystal X-ray diffraction study of 1, sim ulations of portions of their H-1 NMR spectra, and homonuclear decoupl ing experiments. The cyclohexene rings of I and 2 are in half-chair co nformations with diequatorial and axial-equatorial diester groups, res pectively.