Studies related to dihydro-1,4-thiazines. Part VII. Reaction of methyl (4S,6S)-5,5,9,9-tetramethyl-7-oxo-8-oxa-4-thia-1-azabicyclo-[4.3.0]non-2-ene-3-carboxylate 4-oxide with acetyl chloride

Abstract

The title compound (1) is converted into methyl (6RS)-6-hydroxy-5,5,9,9-tetramethyl-7-oxo-8-oxa-4-thia-1-azabicyclo[4.3.0]non-2-ene-3-carboxylate (4) by acetyl chloride under nitrogen. In the presence of oxygen it is transformed by the reagent into the racemic 6-hydroxy-analogue (2) which reacts further to give methyl 2-chloro-2-[1-methyl-1-(2,2-dimethyl-5-oxo-Δ³-oxazolin-4-yl)ethylthio]-3-oxopropionate (14).

Treatment of the oxopropionate (14) with triphenylphosphine followed by diazomethane yields methyl 3-methoxy-2-[1-methyl-1-(2,2-dimethyl-5-oxo-Δ³-oxazolin-4-yl)ethylthio]acrylate (17). Compound (14) undergoes a silica gel- or triethylamine-induced deformylation to give methyl α-chloro-α-[1-methyl-1-(2,2-dimethyl-5-oxo-Δ³-oxazolin-4-yl)ethylthio]acetate (8). The chlorine atom of compound (8) is replaced by an acetoxy-group with silver(I) perchlorate in acetic acid, by a methoxy-group with either silver(I) perchlorate or sodium methoxide in methanol, and by a hydrogen atom with zinc in acetic acid to give derivatives (9)–(11), respectively. Pyrolysis of the sulphoxide (15), obtained by oxidation of the acetate (11) with m-chloroperbenzoic acid, affords 4-isopropenyl-2,2-dimethyl-Δ³-oxazolin-5-one (16).