Imine as a linchpin approach for meta -C–H functionalization

Despite the widespread applications of C–H functionalization, controlling site selectivity remains a significant challenge. Covalently attached directing groups (DGs) served as ancillary ligands to ensure ortho -, meta - and para -C–H functionalization over the last two decades. These covalently linked DGs necessitate two extra steps for a single C–H functionalization: introduction of DG prior to C–H activation and removal of DG post-functionalization. Here we report a temporary directing group (TDG) for meta -C–H functionalization via reversible imine formation. By overruling facile ortho -C–H bond activation by imine- N atom, a suitably designed pyrimidine-based TDG successfully delivered selective meta -C–C bond formation. Application of this temporary directing group strategy for streamlining the synthesis of complex organic molecules without any necessary pre-functionalization at the meta position has been explored.