NICKEL-CATALYZED PREPARATIONS OF FUNCTIONALIZED ORGANOZINCS

The reaction of primary alkyl bromides or chlorides with diethylzinc i n the presence of Ni(acac)(2) (5 mol %) furnishes the corresponding al kylzinc halides (X = Br, Cl) via a halogen-zinc exchange reaction. The treatment of terminal alkenes with diethylzinc (neat, 25-60 degrees C ) in the presence of Ni(acac)(2) as a catalyst (1-5 mol %) and 1,5-cyc looctadiene (GOD) affords the corresponding dialkylzincs via a hydrozi ncation reaction. Whereas the conversion for simple alkenes bearing a remote functionality reaches 40 to 63%, the hydrozincation of allylic, homoallylic alcohols and allylic amines proceeds very efficiently (85 -95% conversion). All the zinc organometallics obtained react with var ious electrophiles (allylic halides, enones, acid chlorides, alkynyl h alides, ethyl propiolate) after transmetalation with CuCN . 2LiCl. In the presence of the chiral catalyst 12, the dialkylzincs prepared add to aldehydes with high enantioselectivity.