Synthesis of Optically Active Monoacid Side-Chains ofCephalotaxusAlkaloids

The general preparation of enantiopure monoacid side-chains of several esters of cephalotaxine is described. The strategy, similar to Weinreb's approach to the synthesis of deoxyharringtonine, used as key intermediate the chiral nonracemic epoxide I la prepared from the commercially available monomethyl itaconate (8). The key step of the strategy was the ring-opening of the epoxide 11a by using different organocuprate nucleophiles. Hydrogenolysis as the final step gave the monacid side-chains of the corresponding esters of cephalotaxine in moderate to good overall yields from epoxide 11a. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)