Toward a Continuous‐Flow Synthesis of Boscalid®

Abstract A two‐step continuous‐flow protocol for the synthesis of 2‐amino‐4′‐chlorobiphenyl, a key intermediate for the industrial preparation of the fungicide Boscalid ® is described. Initial tetrakis(triphenylphosphine)palladium‐catalyzed high‐temperature Suzuki–Miyaura cross‐coupling of 1‐chloro‐2‐nitrobenzene with 4‐chlorophenylboronic acid in a microtubular flow reactor at 160 °C using the tert ‐butanol/water/potassium tert ‐butoxide solvent/base system provides 4′‐chloro‐2‐nitrobiphenyl in high yield. After in‐line scavenging of palladium metal with the aid of a thiourea‐based resin, subsequent heterogeneous catalytic hydrogenation is performed over platinum‐on‐charcoal in a dedicated continuous‐flow hydrogenation device. The overall two‐step homogeneous/heterogeneous catalytic process can be performed in a single operation providing the desired 2‐amino‐4′‐chlorobiphenyl in good overall yield and high selectivity.