Ortho-selectivity in the nucleophilic aromatic substitution (SNAr) reactions of 3-substituted, 2,6-dichloropyridines with alkali metal alkoxides
作者:Jeremy L. Yap、Kellie Hom、Steven Fletcher
DOI:10.1016/j.tetlet.2011.06.007
日期:2011.8
basicities favour substitution of the chlorine ortho to the 3-substituent by alkali metal alkoxides. We present convincing evidence that coordination of the alkali metal counter-ion to the 3-substituent (nitro, ester, amide) is the origin of the ortho-selectivity to give a cyclic, six-membered transition state. Excellent ortho-selectivities (⩾98:2) for secondary and tertiary alkoxides were realized with
3-取代的2,6-二氯吡啶已被广泛用于多种生物学靶标的小分子抑制剂的合成中。因此,氯的区域选择性置换是令人关注的。通过进行广泛的溶剂研究,我们发现低氢键碱性的非极性非质子溶剂有利于用碱金属醇盐将邻氯取代为3-取代基。我们提供令人信服的证据,表明碱金属抗衡离子与3-取代基(硝基,酯,酰胺)的配位是邻位选择性产生环状六元过渡态的起源。优秀的邻钠抗衡离子可实现仲和叔醇盐的选择性(⩾98:2),而反应性较高的伯醇盐则需要更硬,更路易斯的酸性锂抗衡离子。