Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols

Organic
radicals are generally short-lived intermediates with exceptionally
high reactivity. Strategically, achieving synthetically useful transformations
mediated by organic radicals requires both efficient initiation and
selective termination events. Here, we report a new catalytic strategy,
namely, bimetallic radical redox-relay, in the regio- and stereoselective
rearrangement of epoxides to allylic alcohols. This approach exploits
the rich redox chemistry of Ti and Co complexes and merges reductive
epoxide ring opening (initiation) with hydrogen atom transfer (termination).
Critically, upon effecting key bond-forming and -breaking events,
Ti and Co catalysts undergo proton transfer/electron transfer with
one another to achieve turnover, thus constituting a truly synergistic
dual catalytic system.