Synthesis of functionalized phenolic derivatives via the benzannulation of dienylketenes formed by a thermal wolff rearrangement of α-diazo-β-keto compounds

Abstract

Eleven conjugated dienyl α-diazo-β-keto derivatives were prepared from α,β-unsaturated carbonyl compounds. Their thermolysis induced a Wolff rearrangement generating an intermediate dienyl ketene whose isomer which has the required configuration of the internal double bond underwent a benzannulation thus forming the corresponding phenolic derivatives. When γ-substituted by a methoxy group both stereoisomers of the diazo compounds gave rise to the phenolic derivatives due to the reversible formation of an intermediate cyclobutenone which permitted the isomerization of the nonproductive transient dienylketene into the productive one.