Synthesis of an 11-unsubstituted analogue of (±)-huperzine A

The synthesis of a new analogue of (±)-huperzine A lacking the ethylidene appendage at position 11 has been accomplished. The key steps of the synthesis were: a) the reduction of the keto function of the known methyl 7,7-ethylenedioxy-3-methyl-9-oxobicyclo[3.3.1]non-3-ene-1-carboxylate into a methylene group by reduction to a mixture of stereoisomeric alcohols follwed by alcohol-deoxygenation through a Barton-McCombie proccdure and b) the elaboration of the pyridone ring in a late stage of the synthesis by reaction of a pyrrolidine enamine with propiolamide, which gave a mixture of regioisomeric pyridone derivatives.