Enantioselective Brønsted base catalysis with chiral cyclopropenimines.
Jeffrey S Bandar, Tristan H Lambert
文献索引：J. Am. Chem. Soc. 12th ed., 134 , 5552-5555, (2012)
全文：HTML全文
摘要
Cyclopropenimines are shown to be a highly effective new class of enantioselective Brønsted base catalysts. A chiral 2,3-bis(dialkylamino)cyclopropenimine catalyzes the rapid Michael reaction of a glycine imine substrate with high levels of enantioselectivity. A preparative scale reaction to deliver 25 g of product is demonstrated, and a trivial large scale synthesis of the optimal catalyst is shown. In addition, the basicity of a 2,3-bis(dialkylamino)cyclopropenimine is measured for the first time and shown to be approximately equivalent to the P(1)-tBu phosphazene base. An X-ray crystal structure of the protonated catalyst is shown along with a proposed mechanistic and stereochemical rationale.