The Epoxy Lactone Ring of the Coumarin Micromelin: Formation of a New Epimer

Abstract

The five- membered epoxy lactone ring of micromelin opens very readily, without opening of the coumarin ring. Under strongly basic conditions the major product is the methoxy acid isolated by Talapatra et al. Under very mild conditions the five- membered ring may be opened and closed to give either micromelin or isomicromelin [ epimeric at the C4 ( benzylic ) position] according to the nature of the solvent. These studies of isomicromelin confirm the structure previously assigned to micromelin.