Enantioselective Cyclopropanation Catalyzed by Gold(I)-Carbene Complexes

The formation of polysubstituted cyclopropane derivatives in the gold(I)-catalyzed reaction of olefins and propargylic esters is a potentially useful transformation to generate diversity, therefore any method in which its stereoselectivity could be controlled is of significant interest. We prepared and tested a series of chiral gold(I)-carbene complexes as a catalyst in this transformation. With a systematic optimization of the reaction conditions, we were able to achieve high enantioselectivity in the test reaction while the cis:trans selectivity of the transformation was independent of the catalyst. Using the optimized conditions, we reacted a series of various olefins and acetylene derivatives to find that, although the reactions proceeded smoothly and the products were usually isolated in good yield and with good to exclusive cis selectivity, the observed enantioselectivity varied greatly and was sometimes moderate at best. We were unable to establish any structure-property relationship, which suggests that for any given reagent combination, one has to identify individually the best catalyst.

Automated summary

The formation of polysubstituted cyclopropane derivatives in the gold(I)-catalyzed reaction of olefins and propargylic esters is of significant interest due to its potential usefulness in generating diversity. We tested a series of chiral gold(I)-carbene complexes as catalysts and achieved high enantioselectivity in the test reaction. However, the cis:trans selectivity of the transformation was independent of the catalyst. Although the reactions proceeded smoothly, the observed enantioselectivity varied greatly and a structure-property relationship could not be established.