Synthesis and stereochemistry of insect derived spiroacetals with branched carbon skeletons

Abstract

About thirty constitutionally different spiroacetals have been characterised from insects but only three have branched carbon skeletons. Two are based on the 1,7-dioxoaspiro[5.5]undecane system and are certain stereoisomers of the 2,4,8-trimethyl derivative, from the aposematic shield bug, Cantao parentum (White), and a 2,2,8-trimethyl derivative from the rove beetle, Ontholestes murinus (L.). The 1,6-dioxaspiro[4.5]decane system is represented by a stereoisomer of the 2,3,7-trimethyl derivative in the Cantao species. The elucidation of their structures and stereochemistry by spectroscopy, synthesis and enantioselective gas chromatography is described.