Rearrangement of Substituted 2,4,4,6-Tetraaryl-4H-thiopyrans to Triaryl-3aH-benzo[3,4]cyclopenta[1,2-b]thiophene

Abstract

An intensive bromination of 2,6-diaryl-4,4-diphenyl-4H-thiopyrans can lead through 3,5-dibromo derivatives to unexpected 2,8-diaryl-3-bromo- and 2,8-diaryl-3,5-dibromo-3a-phenyl-3aH-benzo[3,4]cyclopenta[1,2-b]thiophene as demonstrated on examples where the respective aryl groups are phenyl or 4-fluorophenyl. On the other hand, analogous spiro- [fluorene-9,4'-thiopyran]s do not exhibit the rearrangement evidently due to a rigid conformation of the fluorene moiety. The reaction mechanism for the rearrangement is proposed.