Generally Applicable Organocatalytic Tetrahydropyranylation of Hydroxy Functionalities with Very Low Catalyst Loading
作者:Peter Schreiner、Mike Kotke
DOI:10.1055/s-2007-965917
日期:2007.3
This paper presents the first acid-free, organocatalytic tetrahydropyran and 2-methoxypropene protection of alcohols, phenols, and other ROH derivatives utilizing privileged N,N′-bis[3,5-bis(trifluoromethyl)phenyl]thiourea and a polystyrene-bound analogue. The reactions are broadly applicably (also on preparative scale), in particular, to acid-sensitive substrates such as aldol products, hydroxy esters, acetals, silyl-protected alcohols, and cyanohydrins. The catalytic efficiency is truly remarkably with turnover numbers of 100,000 and turnover frequencies of up to 5700 h-1 at catalyst loadings down to 0.001 mol%. The computationally supported mechanistic interpretation emphasizes the hydrogen bond assisted heterolysis of the alcohol and concomitant preferential stabilization of the oxyanion hole in the transition state.
本文介绍了首个无酸、有机催化的四氢吡喃和2-甲氧基丙烯对醇、酚及其他ROH衍生物的保护方法,利用了特权的N,N'-双[3,5-双(三氟甲基)苯基]硫脲及其聚苯乙烯结合类似物。这些反应广泛适用于(包括制备规模)对酸敏感的底物,如醛醇产物、羟基酯、缩醛、硅烷保护的醇和氰醇。催化效率非常高,转化数达到10万,转化频率高达每小时5700次,催化剂负载量低至0.001 mol%。通过计算支持的机理解释强调了氢键辅助的醇异裂和过渡态中氧阴离子穴的优先稳定。