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.