Naturally occuring lactones and lactames—V: Halogenated β-keto esters as starting materials for the synthesis of tetronic acids

Abstract

In an effort to improve and simplify the synthetic route to tetronic acids 15 differently substituted β-keto esters were investigated as potential starting materials. The β-keto esters were brominated and cyclised with 2·5 N KOH as cyclising agent. Tetronic acid and seven derivatives including the naturally occuring carolinic acid were obtained. In a number of cases products arising from a Favorskii rearrangment were isolated. The NMR spectroscopic data are discussed.