An efficient enantioselective entry to the piperidino-quinolizidine ring system of lupine alkaloids by means of N-acyliminium ion initiated cyclization reactions

An efficient methodology for the enantioselective synthesis of the decahydro-1,5-methano-pyrido[l,2-a][l,5]diazocine skeleton found in tricyclic lupine alkaloids is described, starting from 3,5-disubstituted piperidines as chiral building blocks. Alkyne- or vinylsilane-terminated N-acyliminium ion cyclizations performed on appropriate 3,7-diazabicyclo[3.3.1]nonane derivatives allow for the highly stereoselective construction of piperidino-quinolizidine ring systems, A preliminary application of this methodology results in the synthesis of the quinolizidine alkaloid virgilidone.