Diastereoselectivity of Azido-Ugi Reaction with Secondary Amines. Stereoselective Synthesis of Tetrazole Derivatives

The diastereoselectivity of azido-Ugi reaction with cyclic amines was investigated. It was found that the reaction with α-substituted five- to seven-membered cyclic amines proceeds very efficiently to provide high control of diastereoselectivity (≤100% de) under mild conditions. Target tetrazole-derived products were isolated in excellent yields (≤98%). The reaction has a broad scope in terms of its amine, aldehyde, and isocyanide nature. It was found that the diastereoselectivity of the reaction depends on the ring size of the starting cyclic amines. More rigid piperidines provided the highest selectivity of the reaction. Using benzyl isocyanide, the prepared N-benzyl tetrazoles can be deprotected by hydrogenolysis to form the corresponding NH tetrazoles in high yields.