STEREOELECTIVE REACTION BY USING AN INTRAMOLECULAR CATION-π INTERACTION

手性1，4-二氢吡啶类化合物在钙离子激动剂、NADH模型和生物碱合成中间体等方面具有重要的应用价值，这些化合物的立体选择性合成引起了研究者的广泛关注。本文报道了一种新的合成手性1，4-二氢吡啶类化合物的方法，它是通过在阳离子-π络合物上进行表面选择性加成的方式来合成的。我们的策略是将烟酰胺类化合物加入到吡啶盐中，使两个实体之间产生引力，形成阳离子-π络合物；在氯甲酸甲酯存在下，烟酰胺衍生物1a(R=苄基)和1b(R=苯基)分别与硅酮缩醛反应生成相应的1，2-二氢吡啶2a(99%de)和2b(12%de)。立体选择性的显著差异可能归因于中间体吡啶盐之间的几何差异；与苯基相比，苄基更有效地保护了吡啶面的一侧。1H核磁共振研究和X-射线晶体分析证实了反应过程中阳离子-π相互作用的存在。

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.