Stereodefined N,O-Acetals: Pd-Catalyzed Synthesis from Homopropargylic Amines and Utility in the Flexible Synthesis of 2,6-Substituted Piperidines

We developed a conceptually new synthetic strategy which exploits the stereochemical information of labile acyclic N,O-acetals. The key to this strategy, chemo- and stereoselective synthesis of N,O-acetals, was achieved by the Pd-catalyzed addition of sulfonyl-protected homopropargylic amines to alkoxyallene. The N,O-acetals generated in this way were combined with Au-catalyzed cycloisomerization to give an access to 2,6-disubstituted piperidines with stereochemical flexibility.