Auxiliary-assisted palladium-catalyzed halogenation of unactivated C(sp3)–H bonds at room temperature†
The direct transformation of unactivated C(sp3)–H bonds into C-halogen bonds was achieved by palladium catalysis at room temperature with good functional group tolerance. Some drugs and natural products were readily modified by this method. Merged with substitution reaction, newly formed C–X bonds can be transformed into diverse C–O, C–S, C–C and C–N bonds. A preliminary mechanism study demonstrates that solvent is crucial for C–H activation and the C–H activation step is involved in the rate-limiting step. An isolated Pd(II) intermediate can be transformed into a halogenated product with the retention of conformation which suggests that concerted reductive elimination from Pd(IV) to form a C–X bond was favored.