Selective syntheses of diversely substituted 2-hydroxy-4′-hydroxybenzophenones through [4 + 2] or [3 + 3] annulation of penta-3,4-dien-2-ones with 3-formylchromones

Abstract

A selective synthesis of 2-hydroxy-4′-hydroxybenzophenones or their 3′-acylated counterparts through the cascade reactions of 3-formylchromones with diversely substituted penta-3,4-dien-2-ones is presented. Mechanistically, the formation of the title compounds involves either an unprecedented [4 + 2] annulation or a well defined [3 + 3] cyclization depending on the substitution patterns of the penta-3,4-dien-2-one substrates.