Acid-catalysed rearrangement of a spirocyclohexadienone involving an external nucleophile

Abstract

3,4-Dihydro-3′,8-dimethoxy-2H-benzo[b]pyran-2-spirocyclohexa-2′,5′-dien-4′-one (VI) has been obtained in 13% yield by oxidation of 2′,6-dimethoxy-2,4′-ethylenebisphenol with alkaline ferricyanide. With methanolic hydrogen chloride, the dienone undergoes ring opening to give 2-methoxy-6-(2,4,5-trimethoxyphenethyl)phenol (VIIa), 5′-chloro-2′,6-dimethoxy-2,4′-ethylenebisphenol (VIIb), and 2-(2-chloro-4,5-dimethoxyphenethyl)-6-methoxyphenol (VIIc), whereas with methanol and a trace of concentrated sulphuric acid the product was only (VIIa). Under the conditions used, neither oxygen- nor alkyl-migration occurs. Syntheses of (VIIa) and (VIIc) are described.