BHMPO

BHMPO is prepared in one step from 4-hydroxy-2,6-dimethylaniline and oxalyl chloride. It teams with Cu(acac)2 to create an inexpensive, highly active catalyst for the hydroxylation of (hetero)aryl halides. Under optimized conditions—DMSO/H2O (4:1), LiOH or KOH base, 0.5-2 mol % Cu(acac)2/ 0.5-2 mol % BHMPO-aryl chlorides react at 130 ℃, bromides at 80 ℃ and iodides at 40-60 ℃, giving phenols or hydroxylated heteroarenes in 46-99 % isolated yields. The ligand is stable in a hot aqueous base, forms soluble phenolate salts that accelerate turnover, and tolerates a broad scope of electron-donating or withdrawing substituents, ortho-sterics, and heterocycles (pyridine, quinoline, indole, benzothiazole, carbazole, etc.).
Control experiments show that BHMPO outperforms previously reported oxalamides, 8-hydroxyquinoline N-oxide, diketones and oxime ligands. The protocol operates at the lowest Cu loadings yet reported for aryl chloride hydroxylation and provides an economical, phosphine-free alternative to Pd-catalyzed routes.

Fig. 1 BHMPO for hydroxylation of (hetero)aryl halides. (Xia S.; et al. 2016)