Carberioid Transfer to Imines: A New Asymmetric Catalytic Synthesis of Aziridines

摘要

Aziridines are versatile piecuisois for the synthesis of unnatural amino acids and other nitrogen-containing compounds of biological importance. However, the use of aziridines as chiial building blocks in synthesis has been somewhat restricted becausetheir preparation in optically active form typically requires multiple-step transformation of available starting materials. Quite recently, asymmetric metal-catalyzed nkrene transfer to olefins has emerged as the fiist direct method for the enan-tioselective synthesis of aziridines from prochiral 'substrates jEq. (a)r path a). In principle, the catalytic asymmetric transfer of caibenes to imines represents a complementary alternative for the pieparation of these compounds (Eq. (a), path b). Among the potential advantages of the latter approach are the synthetic accessibility of imines and diazocarbonyl compounds, the high reaction efficiency (the only by-product being nitrogen); and the inherent convergence associated with coupling two potentially complex fragments. Although the synthesis of aziridines by metal-mediated reaction of imines with carbenes has some limited precedent, asymmetric variants have not been developed. We report herein the first successful application of this strategy to the catalytic synthesis of aziridines in optically active form.