Iron-Catalyzed Asymmetric Haloazidation of α,β-Unsaturated Ketones: Construction of Organic Azides with Two Vicinal Stereocenters

Organic azides play
important roles in synthetic chemistry, chemical
biology, drug discovery, and material science. Azido-functionalization
of alkenes is one of the most efficient procedures for rapid introduction
of azide group into organic compounds. But only a few examples have
been documented in the catalytic asymmetric version of the azidation
of alkenes. Herein, we report an unprecedented highly diastereo- and
enantioselective bromoazidation of α,β-unsaturated ketones
catalyzed by chiral N,N′-dioxide/Fe­(OTf)2 complexes. An array of aryl, heteroaryl, and alkyl substituted
α,β-unsaturated ketones were transformed to the corresponding
α-bromo-β-azido ketones in high yields with excellent
diastereo- and enantioselectivities. The catalytic system was also
applicable for chloroazidation and iodoazidation of chalcone. Kinetic
studies and some control experiments suggested that the reaction might
proceed via a 1,4-addition/halogenation pathway.