Preparation and Reactions of Masked Allylic Organozinc Reagents

Allylic zinc reagents have been prepared from sterically hindered homoallylic alcohols 10 and 13, using a novel fragmentation reaction of the corresponding zinc alkoxide, without any homocoupling products. These allylic zinc reagents react with a range of electrophiles in good to excellent yields. Substituted allylic zinc reagents have also been prepared in this manner. alpha-Substituted homoallylic alcohols 37, 46, and 51 give solely alpha-substituted products after the fragmentation-allylation sequence; these products are obtained not only regioselectively but also with extremely high anti diastereoselectivity. Likewise, gamma-substituted homoallylic alcohols 57 and 58, undergo the fragmentation-allylation reaction to give gamma-substituted products. The reaction has also been demonstrated to be catalytic in zinc salts.