Enhanced Selectivities for the Hydroxyl-Directed Methanolysis of Esters Using the 2-Acyl-4-aminopyridine Class of Acyl Transfer Catalysts: Ketones as Binding Sites
作者:Tarek Sammakia、T. Brian Hurley
DOI:10.1021/jo991202k
日期:2000.2.1
compared to that of the previously described catalyst 2-formyl-4-pyrrolidinopyridine (FPP), which contains an aldehyde at the 2-position of the pyridine. The catalysts which contain ketones at the 2-position range in reactivity from 10 times slower to slightly faster than FPP, and certain of these are much more selective for the methanolysis of hydroxy esters than FPP. This increase in selectivity is ascribed
在本文中,我们描述了一系列2-酰基-4-氨基吡啶的制备方法,以及它们作为α-羟基酯(而不是α-甲氧基酯)的羟基定向甲醇分解的催化剂的用途。这些催化剂在吡啶的2-位含有酮的催化剂的羟基方向是通过将羟基酯的醇可逆地加到酮中以提供相应的半缩酮来实现的。将它们的活性与前述催化剂2-甲酰基-4-吡咯烷基二吡啶(FPP)的活性进行比较,该催化剂在吡啶的2-位含有醛。在2位范围内含有酮的催化剂的反应活性比FPP慢10倍至稍快,某些催化剂对羟基酯的甲醇分解的选择性比FPP高得多。选择性的增加归因于与酮衍生的催化剂的非定向甲醇分解反应的速率的降低。证据表明,非定向反应不是通过分子间的通用基本机理进行的,而是通过亲核催化的机理进行的,其中将甲醇添加到FPP的醛中形成的半缩醛的羟基充当亲核剂。由于衍生自半缩酮的羟基比衍生自半缩醛的羟基更受阻且亲核性较小,因此对于以酮为结合位点的催化剂,非定向反应要慢得多。证据表