Gold(I)-Catalyzed Highly Diastereo- and Enantioselective Alkyne Oxidation/Cyclopropanation of 1,6-Enynes

A highly enantioselective oxidative cyclopropanation of 1,6‐enynes catalyzed by cationic AuI/chiral phophoramidite complexes is presented. The new method provides convenient access to densely functionalized bicyclo[3.1.0]hexanes bearing three contiguous quaternary and tertiary stereogenic centers with high enantioselectivity (up to e.r. 98:2). Control experiments suggest that the quinoline moiety of the β‐gold vinyloxyquinolinium intermediate in the reaction plays an important role in promoting good enantioselectivity through a transitional auxiliary effect in the transition state. Playing it safe: A highly enantioselective oxidative cyclopropanation of 1,6‐enynes with cationic AuI/chiral phosphoramidite catalysts provided convenient access to densely functionalized bicyclo[3.1.0]hexanes with three contiguous quaternary and tertiary stereogenic centers (see scheme; up to 92 % yield, e.r. 98:2). Control experiments suggest that the quinoline moiety in the oxidant plays an essential role in the enantioselective cyclopropanation.