REMOTE ASYMMETRIC INDUCTION USING AXIALLY CHIRAL TWISTED AMIDES

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Chiral 1,4-dihydropyridines have received considerable attention as NAD models and synthetic intermediates for various natural products. In general, chiral 1,4-dihydropyridines are synthesized by the addition of nucleophiles to pyridinium salts under chelation control. However, we synthesized them based on a new concept. Thus, axial chirality of an amide bond was employed for discrimination of pyridinium faces. Addition of various nucleophiles to the pyridinium salts of nicotinic amides bearing chiral 1,3-thiazolidine-2-thiones gave (R)-1,4-dihydropyridines, of which stereochemistry was determined by X-ray analysis. To clarify the mechanism of this reaction, 1H and 13C NMR measurements and ab initio 3-21G* calculations were performed. These studies suggest that C4-C3-CO-N-C=S moiety makes helical structure with twisted amide linkage, moreover, the unusual structure was stabilized by intramolecular HOMO-LUMO interaction.