Synthesis of substituted tetrahydropyridines by cyclizations of silicon-containing iminium ions

Abstract

Trans-2,6-disubstituted-1,2,5,6-tetrahydropyridines are formed stereoselectively from the cyclization of silicon-containing iminium cations 5 if the nitrogen substituent R 1 is an alkyl group. In contrast, cyclization of the corresponding NH or N-acyl iminium ions occurs in a stereorandom fashion. Nonracemic tetrahydropyridines cannot be prepared in this way, since both iminium ion and N-acyliminium ion intermediates racemize prior to cyclization.