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。