Phosphorus-mediated sp-sp couplings for C-H fluoroalkylation of azines.

Fluoroalkyl groups profoundly affect the physical properties of pharmaceuticals and influence almost all metrics associated with their pharmacokinetic and pharmacodynamic profile. Drug candidates increasingly contain trifluoromethyl (CF) and difluoromethyl (CFH) groups, and the same trend in agrochemical development shows that the effect of fluoroalkylation translates across human, insect and plant life. New fluoroalkylation reactions have undoubtedly stimulated this shift; however, methods that directly convert C-H bonds into C-CFX groups (where X is F or H) in complex drug-like molecules are rare. Pyridines are the most common aromatic heterocycles in pharmaceuticals, but only one approach-via fluoroalkyl radicals-is viable for achieving pyridyl C-H fluoroalkylation in the elaborate structures encountered during drug development. Here we develop a set of bench-stable fluoroalkylphosphines that directly convert the C-H bonds in pyridine building blocks, drug-like fragments and pharmaceuticals into fluoroalkyl derivatives. No preinstalled functional groups or directing groups are required. The reaction tolerates a variety of sterically and electronically distinct pyridines, and is exclusively selective for the 4-position in most cases. The reaction proceeds through initial formation of phosphonium salts followed by sp-sp coupling of phosphorus ligands-an underdeveloped manifold for forming C-C bonds.