Generation of the First 3,4-Piperidyne and its Cycloaddition Reactions for the Synthesis of Annulated Piperidines

Garg et al. have reported the generation of the first 3,4-piperidyne and its cycloaddition reactions for the synthesis of annulated piperidines. According to their results, silyl triflate 1 is treated with CsF in the presence of several trapping agents to afford the corresponding cycloaddition products via 3,4-piperidyne intermediates. For example, in the case of using N-tert-butyl-α-phenylnitrone as a trapping agent, the cycloaddition reaction proceeds regioselectively to afford the isoxazoline product 2 in good yields. Since the compounds bearing piperidine scaffolds are efficient for the synthesis of pharmaceuticals, this reaction is expected to be a new synthetic method for those compounds.