Complementary enantioselective routes to the quinolizidine alkaloids lupinine and epilupinine

Abstract

Introduction of an α-2-[propenyl] substituent into a chiral 2-piperidineacetate has been effected both by enolate Claisen rearrangement of an allyl ester and by direct allylation of the intermediate lithium enolate [(7) → (8) + (9)] (Scheme 1). These two approaches give largely the opposite stereochemistry at the newly created centre; subsequent hydroboration and cyclisation of ester (9) leads to (+)-lupinine (12).