Reaction of Fischer alkynylcarbene complexes with 1-azadiene derivatives: unexpected formation of 3,4-dihydropyridines

Abstract

4-Amino-1-azabutadienes 2 underwent [3 + 3] cyclization with Fischer alkynylcarbene complexes of chromium and tungsten 1 to furnish high yields of substituted 3,4-dihydropyridines 3. The expected pyridine ring formation, which would result from cyclization/aromatization, does not take place. The process is thought to involve a 1,2-imidoyl group shift triggered by a 1,2-metal pentacarbonyl shift as the more characteristic steps. An X-ray diffraction experiment supports the proposed structure for the dihydropyridines.