From p-Xylene to Ibuprofen in Flow: Three-Step Synthesis by a Unified Sequence of Chemoselective C-H Metalations.

Ibuprofen was prepared from an inactive and inexpensive p-xylene by three-step flow functionalizations through chemoselective metalations of benzyl positions in sequence using an in situ generated LICKOR-type superbase. The flow approach in the microreactor facilitated the comprehensive exploration of over 100 conditions in the first-step reaction by varying concentrations, temperatures, solvents, and equivalents of reagents, enabling optimal conditions to be found with 95 % yield by significantly suppressing the formation of byproducts, followed by the second C-H metalation step in 95 % yield. Moreover, gram-scale synthesis of ibuprofen in the final step was achieved by biphasic flow reaction of solution-phase intermediate with CO2 , isolating 2.3 g for 10 min of operation time.