Preparation of 8-methyl-2-decanol: General synthesis of diastereomeric mixtures of alkyl branched insect pheromones

Abstract

A general method for synthesis of insect pheromones having alkyl branched carbon skeletons is demonstrated with the preparation of a diastereomeric mixture of 8-methyl-2-decanol, whose propionate is an attractant of someDiabrotica species. The procedure involves reaction of a ketone with lithium acetylide ethylenediamine complex to afford a propargylic alcohol containing the branch of the target molecule. Copper (1) mediated alkylation of the derived propargylic acetate with a primary alkyl halide yields a trisubstituted allene having the desired chain length, and isomerization with an alkali metal amide of either ethylenediamine or 1,3-diaminopropane, affords the alkyl branched terminal acetylene. The triple bond is converted to the methyl ketone and reduced to the methyl carbinol. The reactions proceed in good yield, and can be conveniently carried out on large scale. The method should prove useful for production of pheromone components in cases where diastereomeric mixtures can be employed.