Synthesis of ethyl 3-methyl-7-oxo-4-oxo-4-oxa-1-azabicyclo[3.2.0]hept-2-ene-2-carboxylate and the reaction of 4-acetoxyazetidin-2-one with ethyl α-diazoacetoacetate

Abstract

Ethyl 3-methyl-7-oxo-4-oxa-1-azobicylco[3.2.0]-hept-2-ene-2-carboxylate (4) has been obtained by a four-step synthesis from 4-methylthioazetidin-2-one and has been compared with the products obtained from the rhodium(II) acetate-catalysed reaction of 4-acetoxy-azetidin-2-one with ethyl α-diazoacetoacetate; this latter reaction did not give compound (4), as was previously claimed, but yielded ethyl 2-(4-acetoxy-2-oxoazetidinyl)-3-oxobutyrate as the major β-lactam product.