One-Pot Asymmetric Synthesis of Cyclopropanes with Quaternary Centers Starting From Bromonitroalkenes under Aminocatalytic Conditions.

Cyclopropanes with a quaternary center are efficiently synthesized starting from bromonitroalkenes and alkyl aldehydes under aminocatalysis, giving good yield, excellent enantioselectivities, and moderate to excellent diastereoselectivities. This work is a novel approach using bromonitroalkenes as starting material instead of the usual synthesis with bromine-activated methylene derivatives. The cyclization process is analyzed by DFT calculations, which suggests an S 2 mechanism. Theoretical data indicate that diastereoselectivity results from the energetic balance as a consequence of distortion the in trigonal bipyramid transition states and the relative stabilities of both starting rotamers and final products arising from distinct steric repulsions.