Synthesis of Optically Active Monoacid Side-Chains of Cephalotaxus Alkaloids
Résumé
The general preparation of enantiopure monoacid sidechains
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 11a 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 organo-cuprate 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.
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