Stereospecific Preparation of Trisubstituted Allylic Alcohols by Alkene Transfer from Boron to Zinc

Article abstract of DOI:10.1016/S0040-4039(00)74350-4

(Z)-Trialkenylboranes, (R¹HC=CR²)3B, easily prepared by hydroboration of the corresponding alkynes with BMS in THF, rapidly react with commercially available diethylzinc in hydrocarbon solvents, in either a 1:3 or 2:3 ratio of organoborane to organozinc, to yield an equilibrium mixture, favoring the migration of alkenyl groups from boron to zinc.Addition of an aldehyde to the 2:3 reaction mixture, in the presence of 10 molpercent N-methylpiperidine, results in the exclusive transfer of both alkenyl groups from zinc, furnishing diastereomerically pure trisubstituted double bonds in allylic alcohols in good to excellent yields.