First direct catalytic difluoromethylations from chlorodifluoromethane

Researchers have traditionally prepared difluoromethylated compounds by the deoxyfluorination of aldehydes using harsh electrophilic fluorinating reactions. More recently, chemists have taken a milder approach by using preformed reagents to transfer a CF₂H group to a target molecule. In this case, the preformed reagent is often made from fluoroalkyl halides such as chlorodifluoromethane, ClCF₂H, an inexpensive industrial chemical used for making fluorinated polymers. Xingang Zhang and coworkers at Shanghai Institute of Organic Chemistry wondered if they couldn’t simplify difluoromethylations further by using ClCF₂H directly in a catalytic process. The researchers have found that they indeed can carry out palladium-catalyzed coupling reactions between ClCF₂H and aryl and heteroaryl boronic acids and esters to create an array of aromatic difluoromethyl derivatives, providing new opportunities to develop bioactive compounds used as pharmaceuticals, agrochemicals (one example shown), and flavors and fragrances (Nat. Chem. 2017, DOI: 10.1038/nchem.2746). Zhang says the catalytic process appears to proceed via a metal difluorocarbene intermediate, which could open the door to better knowledge of little-understood metal fluorocarbene reaction chemistry.