Grob Fragmentation of Norbornyl α-Diketones: A Route to α-Ketoenols and Aromatic Compounds
作者:Faiz Ahmed Khan、Ch. Nageswara Rao
DOI:10.1021/jo200223a
日期:2011.5.6
reactive fused four-membered bicyclo[2.2.0]hexane intermediates. A plausible mechanistic proposal involving the gem-dihalo intermediate, which in one case was actually isolated as its BF2-complex, is outlined. The fragmentation protocol was applied to various norbornyl substrates including bis-α-diketone derivatives. The methodology was successfully utilized for the synthesis of substituted aromatic compounds
报道了对称和不对称取代的降冰片基α-二酮与相应的六元α-酮烯醇的有效酸催化的Grob断裂。研究了C2单取代和二取代的α-二酮的Grob片段的区域和立体化学结果。通常观察到由有利的半椅中间体产生的单一区域异构体。注意到具有外甲基和内甲基的C2二取代α-二酮偏离了正常路线-甲氧基羰基衍生物,由于半缩酮的最初形成,产生相反的区域异构体。C2双取代的α-二酮的溴代类似物提供了一种不寻常的副产物,该副产物似乎是由高反应性的稠合四元双环[2.2.0]己烷中间体形成的。概述了涉及宝石-二卤代中间体的一种可行的机械方案,该方案在一种情况下实际上是作为其BF 2-络合物被分离出来的。将该片段化方案应用于包括双-α-二酮衍生物在内的各种降冰片基底物。该方法已成功用于合成取代的芳族化合物。