Abstract
Reduction of 2-thiaazulenylium salts (2, 3, 5) with lithium aluminum hydride in ether gave only 4H-cyclohepta[c]thiophenes (12, 14, 18) and not the 6H-isomer. Only 6H-cyclohepta[c]thiophene derivative (16) was obtained from 4, not having a phenyl group in 6-position. Reaction with phenylmagnesium bromide also gave 4H-cyclo-hepta[c]thiophenes (13, 15, 19) alone from 2, 3, and 5, and 6H-isomer (17) from 4. These results suggested that selectivity of this reaction was due to the formation of a bulky complex from the nucleophilic reagents, which reacted with 2-thiaazulenylium salts. Reaction of 6 with malononitrile also gave 4H-cyclohepta[c]thiophene derivative (20). 2-Phenyl-2-thiaazulenes (21-24) were synthesized by the reaction of 2-thiaazulenylium salts (1, 2, 3, 7) with phenyllithium. Various physical data of these compounds support the S-phenyl structure, rather than the corresponding 4H- or 6H-cyclohetta[c]thiophenes.
