Copper(I)-catalyzed 1,3-Halogen Migration.

摘要

An ongoing challenge in modern catalysis is to identify and understand new modes of reactivity promoted by earth-abundant and inexpensive first-row transition metals. Herein, we describe a new Cu(I)-catalyzed 1,3-halogen migration reaction which effectively recycles an activating group by transferring bromine from a sp2 to a benzylic carbon with concomitant borylation of the Ar-Br bond. Both racemic and enantioselective variants of this transformation have been developed. Computational modelling aids in understanding the outcome of the asymmetric reaction and the benzyl bromide can be displaced with a variety of nucleophiles to produce a wide array of enantioenriched functionalized products. An extensive mechanistic study, which includes a combination of experimental and computational experiments, indicated this reaction does not involve any oxidation state changes at copper; rather, migration occurs through a series of formal sigmatropic shifts. Insight provided from these studies will be used to expand the utility of aryl copper species in synthesis and develop new ligands for enantioselective copper-catalyzed halogenation. Finally, the development of a nickel catalyzed hydroboration is discussed, including the synthesis of new heteroleptic nickel complexes.