About thirty constitutionally different spiroacetals have been characterised from insects but only three have branched carbon skeletons. Two are based on the 1,7-dioxaspiro[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.

Synthetic approaches to ring-and side-chain hydroxy derivatives of the 2-ethyl-8-methyl-1,7-dioxaspiro-[ S Slundecane system 8 are described. Alkylation reactions of diethyl3-oxopentanedioate, pentane-2,4-dione and acetone N,N-dimethylhydrazone have been employed. Appropriate choices of enantiomeric iodides in the alkylation sequences, sometimes followed by asymmetric dihydroxylation of derived hydroxyenones, have permitted access to key enantiomers of these alcohols, which have been fully characterised by 'H and 3C NMR spectroscopy, gas chromatographic-mass spectrometric methods, and chiral gas chromatography.In previous publications 1-3 we have described the synthesis of a range of spiroacetals, many of which were components of insect secretions and emissions, particularly from Australasian fruit-16 17 902

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