Hydrogen Atom Transfer (HAT)-Mediated Remote Desaturation Enabled by Fe/Cr-H Cooperative Catalysis

An iron/chromium system (Fe(OAc)(v), CpCr(CO)(3)H) catalyzes the preparation of beta,gamma- or gamma,delta-unsaturated amides from 1,4,2-dioxazol-5-ones. An acyl nitrenoid iron complex seems likely to be responsible for C-H activation. A cascade of three H center dot transfer steps appears to be involved: (i) the abstraction of H center dot from a remote C-H bond by the nitrenoid N, (ii) the transfer of H center dot from Cr to N, and (iii) the abstraction of H center dot from a radical substituent by the Cr center dot . The observed kinetic isotope effects are consistent with the proposed mechanism if nitrenoid formation is the rate-determining step. The Fe/Cr catalysts can also desaturate substituted 1,4,2-dioxazol-5-ones to 3,5-dienamides.