Copper(I)-catalyzed enantioselective hydroboration of cyclopropenes: facile synthesis of optically active cyclopropylboronates

Copper(I)-catalyzed enantioselective hydroboration of 3-aryl substituted cyclopropene-3-carboxylate is described, providing chiral cyclopropylboronates with excellent enantioselectivities (89-95% ee) in moderate to high yields (55-86%). The non-directing effect of the ester group was observed, and the reaction proceeded with solely trans-selectivity. The chiral boronates could be conveniently converted into chiral 1,2-diaryl substituted cyclopropane derivatives.