Conversion of benzopyrones into spiro[benzopyran-2,2′-furan]s; a route to 2-(1,3-dioxoalkyl)benzopyrones

Abstract

The reaction of a 5-substituted 4-oxo-1-benzopyran-2-carbonyl chloride with diethyl ethoxymagnesiomalonate gave the required acylmalonate. However, the reaction of the acid chloride with the ethoxymagnesio-derivatives of ethyl acetoacetate and acetylacetone gave spiro[benzopyran-2,2′-furan] derivatives which were identified by n.m.r. and mass spectroscopy. Treatment of these spiro-compounds with either ethanol–concentrated hydrochloric acid or propionic acid–concentrated sulphuric acid gave benzopyrones having 1,3-dicarbonyl substituents at the 2-position.