Replacing trifluoroacetic acid with it catalytic amount of Lewis acid in the osmium mediated oxidative cyclization results in higher yielding reactions that can proceed nearly an order of magnitude faster. The osmium loading can also be reduced to as little its 0.2 mol %. Furthermore, these mildly acidic conditions are capable of tolerating a wide range of acid sensitive protecting groups that are incompatible with previous cyclization conditions.
Improved Zinc-Catalyzed Simmons–Smith Reaction: Access to Various 1,2,3-Trisubstituted Cyclopropanes
作者:Éric Lévesque、Sébastien R. Goudreau、André B. Charette
DOI:10.1021/ol500267w
日期:2014.3.7
The Simmons–Smith reaction of zinccarbenoids with alkenes is a powerful method to access cyclopropanes containing various substitution patterns. This work exploits the high reactivity of aryldiazomethanes toward zinc halides to generate aryl-substituted carbenoids catalytically. These carbenoids are able to cyclopropanate various alkenes diastereoselectively, including unfunctionalized substrates