Thermal reactions of 2-alkyl (or aryl)-1-benzoyl-3,4-dihydro-1H-2-thionianaphthalen-1-ides with compounds possessing an acidic hydrogen

Abstract

Thermal reactions of 2-alkyl-1-benzoyl-3,4-dihydro-1H-2-thionianaphthalen-1-ides (1a–d) in ethanol afforded alkyl o-vinylbenzyl sulphides (2a–d) along with ethyl benzoate, whereas that of the 2-phenyl congener (1e) gave o-(ethoxymethyl)phenethyl phenyl sulphide (3) together with the sulphide (2e). The ylides (1a and e) reacted with boiling water to afford the benzoates (9a and e). Reactions of the ylides (1a–e) with carboxylic acids and thiols gave the ring-opening products (11)–(17), cleaving the C(1)–S bond. Reactions of the ylide (1a) with succinimide or phthalimide yielded the ring-expansion product 2-phenyl-4,5-dihydro-3,5-benzoxathionine (19). In the reaction of the ylide (1a) with phenol, the product proportions changed with amounts of phenol. When 2 equiv. of phenol were used, the oxathionine (19) was obtained. However, the ring-opening products (22) and (23) were formed by using 10 or 100 equiv. of phenol.

These reactions are initiated by protonation on the ylidic carbanion to form the sulphonium salt (5). The conjugate base formed concurrently attacks a different reaction site, viz. a carbonyl carbon, C(1), or a methyl proton of the sulphonium salt (5), depending on its character.