Photolysis of diterpenoid quinones

Abstract

Photolysis of the diterpene quinone royleanone in benzene gave predominantly products resulting from both side-chain rearrangement and formation of an ether bridge to C-1. It is proposed that these arose by very specific transfer of two hydrogen atoms in a highly oriented complex between ground state royleanone and photo-excited royleanone. In contrast 7α-acetoxyroyleanone gave products of simple side chain rearrangement, with or without loss of acetic acid, probably via a spirocyclopropyl intermediate.Royleanone methyl ether gave mainly an oxetanol in benzene but a methylenedioxy com-pound and an acetoxymethoxy compound in acetic acid. It is suggested that these arise from diradical and zwitterionic intermediates.