Novel rearrangements of cyano-stabilised cyclic sulfur ylides, 2-alkyl-1-cyano-3,4-dihydro-1H-2-thionianaphthalen-1-ides: spiro-compound formation and ring expansion reactions

Abstract

Thermal reaction of 1-cyano-2-methyl-3,4-dihydro-1H-2-thionianaphthaalen-1-ides 1 in ethanol afforded the spiro compounds 3 in good yields, which underwent thermal rearrangement and Diels–Alder reaction to give tetrahydro-3-benzothiepine 4 and a pair of cycloadducts 6 and 7, respectively. Treatment of 1 with succinimide similarly provided 3via the processes of protonation, ylide formation and [2,3]sigmatropic rearrangement. In contrast, treatment of 1a with N-chlorosuccinimide, chloramine B or T formed the chloroketenimine 16via an S→N [2,3]sigmatropic rearrangement of the exo-methanide 15. The exo-ylide 19 generated by deprotonation of the sulfonium salt 18 with sodium hydride underwent a similar [2,3] rearrangement to give the ketenimine 20. Hydrolysis of the ketenimines 16 and 20 with dilute hydrochloric acid produced amides 17 and 21, respectively. Reactions of 1 with dimethyl acetylenedicarboxylate proceeded via Michael addition followed by two different routes of ring-expansion to give the nine-membered cyclic sulfides 30 and the eight-membered cyclic sulfur ylides 32.