Catalytic Asymmetric Deoxygenative Cyclopropanation Reactions by a Chiral Salen-Mo Catalyst.

The catalytic asymmetric cyclopropanation reaction of alkenes with diazo compounds is a direct and powerful method to construct chiral cyclopropanes that are essential to drug discovery. However, diazo compounds are potentially explosive and often require hazardous reagents for their preparation. Here, we report on the use of 1,2-dicarbonyl compounds as safe and readily available surrogates for diazo compounds in the direct catalytic asymmetric deoxygenative cyclopropanation reaction. Enabled by a class of simple and readily accessible chiral salen-Mo catalysts, the reaction proceeded with generally good enantioselectivities and yields toward a wide range of substrates (80 examples). Preliminary mechanistic studies suggested that the proposed μ-oxo bridged dinuclear Mo(III)-species was the catalytically active species. This strategy not only provides a promising route for the synthesis of chiral cyclopropanes but also opens a new window for the potential applications of chiral salen-Mo complexes in asymmetric catalysis.