Diverting Ni‐Catalyzed Direct Benzylic C−H Hydroxylation towards Trifluoroethoxylation

Abstract

AbstractNickel(II) complexes with the simple N4 donor aminopyridine ligands BPMEN (N,N′‐dimethyl‐N,N′‐bis(2‐pyridylmethyl)‐1,2‐diaminoethane) and TPA (tris(2‐pyridylmethyl)amine) have been demonstrated to perform as efficient catalysts for the regioselective oxygenation of benzylic C−H groups with m‐chloroperoxybenzoic acid under mild conditions (at 20 °C), typically ensuring >90 % substrate conversions within 1 h at 1 mol % catalyst loadings. Unprecedentedly, replacing the commonly used mixed reaction solvent CH3CN/CH2Cl2 with 2,2,2‐trifluoroethanol diverts the selectivity of the above Ni‐based catalyst systems from hydroxylation/ketonization to trifluoroalkoxylation, with the formation of 1‐phenylalkyl 2,2,2‐trifluoroethyl ethers. The use of 2,2,2‐trifluoroethanol ensures high substrate conversion values (up to 97 %), as well as high selectivity for the ether formation (up to 92 %). Preliminary discussion of the reaction mechanism is given based on the catalytic and literature data.