Synthesis of an 11-unsubstituted analogue of (+/-)-huperzine A

The synthesis of a new analogue of (+/-)-huperzine A lacking the ethylidene appendage at position ii has been accomplished. The key steps of the synth esis were: a) the reduction of the keto function of the known methyl 7.7-et hylenedioxy-3-methyl-9-oxobicyclo[3.3.1]non-3-ene-1 -carboxylate into a met hylene group by reduction to a mixture of stereoisomeric alcohols followed by alcohol-deoxygenation through a Barton-McCombie procedure and b) the ela boration of the pyridone ring in a late stage of the synthesis by reaction of a pyrrolidine enamine with propiolamide, which gave a mixture of regiois omeric pyridone derivatives. (C) 1999 Elsevier Science Ltd. All rights rese rved.