Synthesis of the antifungal 1-benzoxepin pterulone

The chlorinated 1-benzoxepin derivative pterulone (1a), a potent antifungal metabolite isolated from a Pterula species, was synthesised from 4,5-dihydro-2H-benzoxepin-3-one 6 by the oxidation of 6 to 3(2H)-oxepinone 7, a Wittig reaction that transformed the keto functionality of 7 to a chlorovinyl group, and a Friedel Craftʹs acetylation. The mixture of E and Z isomers (1a and 1b) obtained could transformed to pure pterulone (1a) by photochemical isomerisation and separation by chromatography. The yield was 23% starting from 6.