Preparation of polyfunctional diorganomercurials and their transmetallation to diorganozincs. Applications to the preparation of optically active secondary alcohols

Article abstract of DOI:10.1016/0022-328X(92)88002-Z

Two new methods of preparation of functionalized diorganomercurials have been developed.The first method involves a substitution reaction of (ICH2)2Hg with zinc-copper reagents FG-RCu(CN)ZnI in THF/DMF at -60 deg C.Functional groups such as an ester, nitrile, ketone, phosphonate, halide, and boronic ester are tolerated in this reaction.The second method involves a reductive transmetallation between polyfunctional organozinc halides and mercurous chloride (Hg2Cl2).This very convenient procedure provides a rapid route to various functionalized diorganomercurials in good yields (61-89percent yield).The synthetic utility of these mercury organometallics is demonstrated.Their transmetallation with zinc dust (toluene, 80 deg C, 3-5 h) affords dialkylzincs which add enantioselectively to aldehydes in the presence of a catalytic amount (20 molpercent) of the norephedrine derivative 13.This transmetallation can also be used to prepare stereoselectively (E)-alkenylzinc halides (> 98percent E).Addition of Cl(H)ZrCp2 to (E)-5-chloropentenylzinc bromide in CH2Cl2 (25 deg C, 1 min) affords a 1,1-bimetallic of zinc and zirconium Cl(CH2)4CH(ZnBr)ZrCp2(Cl) which reacts stereoselectively with an aldehyde providing the (E)-disubstituted olefin (49percent yield; 100percent E).