Stereoselective reactions of acyclic allylic phosphates with organocopper reagents

A series of acyclic allylic alcohols of general structure (RCH)-C-1=CHCH(OH)R-2 were resolved by Sharpless kinetic resolution. The hydroxyl groups of these enantiomerically enriched alcohols were derivatized to diethyl phosphates, and the derivatives were reacted with organocopper reagents. Cleanest substitution reactions were observed with reagents (R2CuCNLi2)-Cu-3. With R-1 = Me and R-3 = n-Bu, the size of R2 affected both the regioselectivity and stereoselectivity of the displacement. Larger R-2 groups gave higher regio- and stereoselectivities: with R-2 = 3-pentyl, > 98% S(N)2', regioselectivity and > 98% anti stereoselectivity were observed. Bn2CuCNLi2 gave stereoselectivities comparable to those observed with n-Bu2CuCNLi2 but t-Bu2CuCNLi2 exhibited much lower diastereofacial preference.