Effective methods for the enantiopure formation of substituted piperidine rings are significantly important due to their presence in alkaloid products. A valuable method to form these ring systems would be via an intramolecular heteroatom Michael addition from the corresponding enone or enal. Described herein is a methodolgy that has been developed in order to form piperidine, pyrrolidine and indoline ring systems using organocatalysis. These ring systems have been prepared with yields of 50-87% and ee as high as 95%. This methodology has been utilized in the synthesis of three natural products: homopipecolic acid, homoproline, and pelletierine. Homopipecolic acid was synthesized in 7 steps and 28% yield from commercially available 1-bromo-5-hexene. Homoproline was synthesized in 7 steps and 10% overall yield from commercially available 1-bromo-4-heptene. Pelletierine was synthesized in 8 steps and 26% overall yield from commercially available 1-bromo-5-hexene.
Synthetic efforts toward cermizine D are also disclosed. This synthesis involves the use of our organocatalytic methodology in order to form the initial piperidine ring. Using the Boc protected amine for this reaction gave the desired piperidine ring in 86% yield and 92% ee. One key step is the Ti(O-iPr)₄ mediated coupling to produce the core carbon structure in 68% yield and 1:1 dr. This reaction has not yet been optimized. Another key step is the use of RCM in order to form the second ring in the system with a 94% yield
