Branch-Selective and Enantioselective Iridium-Catalyzed Alkene Hydroarylation via Anilide-Directed C-H Oxidative Addition

Tertiary benzylic stereocenters are of recognized value in the design of pharmaceuticals (Scheme 1A). The most powerful methodologies to access these motifs establish the stereocenter via a C–C bond forming fragment union step.(1) Commonly, this is achieved by cross-coupling of a nucleophile with an electrophile;(2) however, effective methods that harness two electrophiles(3) or two nucleophiles have also emerged.(4) Recent methods that allow the direct use of alkenes as a coupling partner are notable.(5) Arguably, the most general approaches exploit arylation of stereodefined secondary alkyl boronic acid derivatives (Scheme 1B).(2a,c,g,h,4) Within this context, Pd-catalyzed Suzuki couplings with aryl halides have been developed; however, isomerization of the alkyl-Pd(II) intermediate often leads to isomeric products.(1a,b,2a,g,h) Metal-free cross-couplings of aryl lithium reagents with alkyl boronic esters, which require external oxidants, circumvent this problem and offer good scope.(4) For all of these approaches, step and atom economy are imperfect because of the requirement for prefunctionalization and/or the need for additional reagents in the coupling step. For example, alkyl boronic esters are often accessed by enantioselective hydroboration of an alkene precursor,(6) whereas aryl halides are usually prepared by regioselective halogenation of an aryl C–H bond.