Preparation and reactions of novel cyclic β-oxosulphonium salts obtained by the acid-induced cyclisation of 1-diazo-ω-phenylthio-2-alkanones

Abstract

With perchloric acid, the diazo-ketones PhS[CH₂]_nCOCHN₂(1a)–(1d) give the corresponding cyclic β-oxosulphonium salts (2a)–(2d); the p-chlorophenyl analogue of (2d) was similarly prepared. The salts (2a), (2c), and (2d) react with triphenylphosphine at C(2) to give the acyclic phosphonium salts (3a), (3c), and (3d) and, analogously, with potassium O-ethyl dithiocarbonate to give the corresponding acyclic O-ethyl dithiocarbonates (3f), (3g), and (3h). All the reactions of the salt (2b) with nucleophiles gave either 1-phenylthiobut-3-en-2-one (11) or products of its Michael addition. Salts (2c) and (2d) with sodium methoxide in methanol provide, respectively, methyl ω-phenylthio-butanoate and -pentanoate in a process that involves the loss of a methylene group. These and other reactions are considered to proceed via ylide intermediates; the intermediate derived by the deprotonation of (2d) being isolated, whereas that from (2c) rearranged to give 3-phenylthiocyclopentanone.