Synthesis and Thermal Reactions of New Cyclic Sulfur Ylides possessing 10π. E lectrons, 8-Alkyl-1, 3-diphenyl-2 H dibenzo[b, f] cyclopenta[ d ]thiepinio-2-idse

Abstract

A new cyclic sulfur ylide, 8-methyl-1, 3-diphenyldibenzo[b, f]cyclopenta[d]thiepinio-2-ides [8 a]was synthesized by deprotonation of the thiaazulenium sa [lt [7 a] with sodium hydride. Other 81-alkyl derivatives were generated in situ and subjected to thermal reactions. The ylide [8 a] underwent 1, 4-rearrangement to give 3 a-methyl-1, 3-diphenyl-3 ali-dibenzo[b, cyclopenta[ d ]thiepin [11 a] (64%) together with the demethylated product [ 6 (12%), whereas S-ethyl [8b]and 5-propyl derivative [8 c] afforded the 1, 4-rearranged product 11b] (34%), [11 c] (14%) and the 1, 2-rearranged product [12 b] (29%), [12 c] (47%), respectively.
This 1, 2-rearrangement is unique and interesting because it proceeds at a cost of the benzenoid stabilization of a condensed benzene ring.