Synthesis of some C-4 hydroxybenzo[c]pyrans: a new approach.

Abstract

A new synthetic approach to the synthesis of some epimeric C-4-hydroxy-benzo[c]pyrans is described. A key step in their formation is stereoisomerisation of a nonconjugated ortho alkenylphenylketone and -ester using palladium bisacetonitrile [bisacetonitriledichloropalladium(II)] to give the corresponding conjugated E stereo-isomers which cyclize on treatment with meta-chloroperbenzoic acid (m-CPBA) to afford the target compounds.