Diastereoselective addition of organozinc reagents to 2-alkyl-3-(arylsulfanyl)propanals

The preparation of compounds incorporating the 3-hydroxy-2-methyl-1-alkyl moiety of high diastereomeric purity is described. Such compounds can serve as potential building blocks for the preparation of several kinds of natural products. Diastereoselective synthesis of two potential pine sawfly pheromone components, one the pure racemic threo-isomer of 3-methylpentadecan-2-ol and the other the racemic erythro-isomer of 3-methyltridecan-2-ol are described. The diastereoselective addition of R₂Zn (R=Me, Et and n-Bu) to several 2-alkyl-3-(arylsulfanyl)propanals in the presence of a Lewis acid and CH₂Cl₂ as solvent was studied. An excellent diastereomeric ratio (95/5 anti-Cram/Cram) was obtained with 2-(phenylsulfanyl)methyl]pentanal, 2-(phenylsulfanyl)methyl]decanal and 2-(phenylsulfanyl)methyl]dodecanal and Me₂Zn in the presence of TiCl₄.