Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA.
J Org Chem. 2011 Mar 18;76(6):1521-37. doi: 10.1021/jo102467j. Epub 2011 Feb 23.
We report a metal-free procedure for transformation of phenols into esters and amides of benzoic acids via a new radical cascade. Diaryl thiocarbonates and thiocarbamates, available in a single high-yielding step from phenols, selectively add silyl radicals at the sulfur atom of the C═S moiety. This addition step, analogous to the first step of the Barton-McCombie reaction, produces a carbon radical which undergoes 1,2 O→C transposition through an O-neophyl rearrangement. The usually unfavorable equilibrium in the reversible rearrangement step is shifted forward via a highly exothermic C-S bond scission in the O-centered radical, which furnishes the final benzoic ester or benzamide product. The metal-free preparation of benzoic acid derivatives from phenols provides a potentially useful alternative to metal-catalyzed carbonylation of aryl triflates.
我们报告了一种无金属的方法，通过新的自由基级联反应将酚转化为苯甲酸的酯和酰胺。二芳基硫代碳酸酯和硫代氨基甲酸酯可通过酚的单步高产反应得到，它们选择性地在 C═S 部分的硫原子上添加硅自由基。这个加成步骤类似于 Barton-McCombie 反应的第一步，生成的碳自由基通过 O-邻基重排经历 1,2 O→C 转换。在通常不利的可逆重排步骤中，通过 O-中心自由基中高度放热的 C-S 键断裂向前转移，从而提供最终的苯甲酸酯或苯甲酰胺产物。从酚制备苯甲酸衍生物的无金属方法为芳基三氟甲磺酸酯的金属催化羰基化提供了一种潜在有用的替代方法。
