STEREOELECTIVE REACTION BY USING AN INTRAMOLECULAR CATION-π INTERACTION

点击翻译按钮获取中文摘要

Chiral 1,4-dihydropyridines are continue to be of great interest in relation with calcium agonists, NADH models, and intermediates for alkaloid syntheses, the stereoselective synthesis of these compounds has attracted the attention of researchers. Here we report a new synthetic method of chiral 1,4-dihydropyridines by way of a face-selective addition to a cation-π complex.Our strategy of a nicotinic amide derivative into a pyridinium salt gives rise to an attractive force between the two entities to form a cation-π complex ; (b) The selective shielding of one side of the pyridinium face by the phenyl ring enables nucleophiles to attack the complex only from the non-shielded side, which will result in 1,4-dihydropyridine stereoselectively.The reaction of nicotinic amide derivatives 1a (R=benzyl) and 1b (R=phenyl) with ketene silyl acetals in presence of methyl chloroformate gave corresponding 1,2-dihydroyridines 2a (99%de) and 2b (12%de), respectively. Significant difference in the stereoselectivities would be attributable to the geometrical differences between the intermediary pyridinium salts ; the benzyl group much more effectively shields one side of the pyridinium face than the phenyl group.^1H NMR studies and X-ray crystallographic analysis clarified the existence of a cation-π interaction during the reactions.