Significant acceleration of 6 pi-azaelectrocyclization resulting from a remarkable substituent effect and formal synthesis of the ocular age pigment A2-E by a new method for substituted pyridine synthesis.

The remarkable acceleration of 6 pi-azaelectrocyclization due to the combination of the C4-carbonyl and the C6-alkenyl or phenyl substituents in 1-azatrienes was found. This observation was rationalized by considering the remarkable orbital interaction between the HOMO and LUMO of 1-azatrienes, which were obtained by molecular orbital calculations. The formal synthesis of the unusual retinal metabolite, A2-E, was achieved by two types of the new one-pot synthesis of substituted pyridines by utilizing the obtained facile 6 pi-azaelectrocyclization, one of which is compatible with the proposed metabolic pathway of A2-E.