Asymmetric Copper-Catalyzed Defluoroalkylation
Enantioselective Copper-Catalyzed Defluoroalkylation Using Arylboronate-Activated Alkyl Grignard Reagents.
J. Am. Chem. Soc. 2018;
20 August 2018 (online)
Defluorination of trifluoromethyl alkenes has become a popular strategy in the past few years to introduce a new stereocenter and synthesize gem-difluoroalkenes. gem-Difluoroalkenes are useful handles for further functionalizations and they are also useful moieties in medicinal chemistry. Shi and co-workers report the enantioselective addition of alkyl Grignard reagents to trifluoromethyl alkenes with the assistance of an arylboronate.
The reaction uses alkyl magnesium bromide reagents which initially react with the organoboron species to form a tetraorganoborate. The tetraalkylboron species reacts with the copper catalyst to undergo an enantioselective addition to the trifluromethyl alkene followed by β-fluoride elimination. The reaction was successful with a variety of substituents on the trifluoromethyl alkenes including aryl, alkenyl, alkynyl, and alkyl groups. Unfunctionalized Grignard reagents were most extensively investigated in the reaction.