Synthesis of indolizidine from N-chlorooctahydro-1-pyrindine

A model study was undertaken to investigate the rearrangement of N-chloro-octahydro-1-pyrindine. Cyclopenteno-2,3-pyridine was reduced catalytically to a mixture of the cis- and trans-isomers of octahydro-1-pyrindine. The N-chloramines were prepared, and rearrangement was accomplished by stirring these with silver tetrafluoroborate in benzene under a nitrogen atmosphere. The indolizidinium ion which resulted was isolated and reduced with sodium cyanoborohydride. Indolizidine was obtained in 85% yield, based on recovered octahydro-1-pyrindine. Attempts are described to capture the indolizidinium ion with various nucleophiles.