Molybdenum-Catalyzed Deoxygenative Cyclopropanation of 1,2-Dicarbonyl or Mono-carbonyl Compounds.

The transition-metal catalyzed cyclopropanation of alkenes via the decomposition of diazo compounds is a powerful and straightforward strategy to produce cyclopropanes. However, the potentially explosive nature of the diazo substrates tempers the appeal of further application of this strategy. Herein we report the first Mo-catalyzed regiospecifically deoxygenative cyclopropanation reaction of the readily available and bench stable 1,2-dicarbonyl compounds, in which one of the two carbonyl groups acts as a carbene equivalent upon deoxygenation, thus engaging in the subsequent cyclopropanation process. With a commercially available molybdenum catalyst, an array of valuable cyclopropanes were obtained in up to 90% yield and exclusive regioselectivity. The synthetic utility of this method is further demonstrated by gram-scale syntheses, late-stage functionalization, and application to the cyclopropanation of a simple mono-carbonyl compound. Preliminary mechanistic studies suggest that phosphine (or silane) is both a mild reductant and a good oxygen acceptor that could efficiently regenerate the catalytically active Mo-catalyst through reduction of the Mo-oxo complexes.