Studies related to dihydro-1,4-thiazines. Part VIII. β-Elimination reactions of 7-oxo-8-oxa-4-thia-1-azabicyclo[4.3.0]non-2-ene-3-carboxylates

Abstract

The (6R)-9,9-dimethyl derivative of methyl 7-oxo-8-oxa-4-thia-1-azabicyclo[4.3.0]non-2-ene-3-carboxylate (1) is converted into potassium α-(5-methoxycarbonyl-2,2-dimethyl-Δ⁴-thiazolin-3-yl)acrylate (11) by potassium t-butoxide. When the reaction is conducted in the presence of iodomethane, methyl (Z)-β-(2,2-dimethyl-4-methylene-5-oxo-oxazolidin-3-yl)-α-methylthioacrylate (20) is formed, suggesting that the rearrangement is triggered by a β-elimination process.

A corresponding reorganization, leading to the ββ-dimethylacrylate (17), occurs with the (6S)-5,5,9,9-tetramethyl derivative (14). The (6S,9S)-[or (6S,9R)-] 5,5,9-trimethyl compound (15) affords optically active potassium α-(5-methoxycarbonyl-2-methyl-Δ⁴-thiazolin-3-yl)-ββ-dimethylacrylate (30), implying that the new C–S bond is formed by an S_N2-like pathway.