TERPENES IN ORGANIC-SYNTHESIS .15. CHEMOENZYMATIC APPROACH TO THE SYNTHESIS OF ALL 4 STEREOISOMERS OF 2,6-DIMETLHYLOCT-1-YL FORMATE, AN ATTRACTANT OF THE SMALLER FLOUR BEETLE, FROM ENANTIOMERIC BETA-CITRONELLENES

All four stereoisomers of 2,6-dimethyloctan-1-ol, the nearest precurso rs of the title formates, were synthesized in five to eight stages, wi th configurational purity ranging from 41 to 96 %, employing a stereod ivergent scheme based on the partial hydrolysis of two pseudoracemic s ubstrates, (2RS,6R)-2,6-dimethyloct-1-yl formate and (2RS,6S)-2,6-dime thyloct-1-yl acetate, in the presence of porcine pancreatic lipase (PP L). Configurations and diastereomeric compositions of the alcohols thu s obtained were determined by correlating the latter with (S,S)-4,8-di methyldecanal, prepared on the basis of enantioselective biohydrogenat ion of (R)-2,6-dimethylocta-2,7-dienal with bakers' yeast, and by comp aring the [alpha](D) values of the alcohols with their NMR data and/or with those of their (S)-MTPA derivatives. The attractant potency of s tereoisomeric 2,6-dimethyloct-1-yl formates towards Tribolium confusum was found to vary depending on their diastereomeric composition. The configuration at C(6) exerts some influence on the stereoselectivity o f the PPL-catalyzed hydrolysis of pseudoracemic 2,6-dimethyloct-1-yl f ormates.