Divergent, stereospecific mono- and difluoromethylation of boronic esters

There is considerable interest in incorporating fluorine in agrochemicals and pharmaceuticals to improve their biological properties. Whilst a number of methods have been reported for installing CH 2 F and CHF 2 groups, they are mainly limited to radical reactions which are invariably racemic. Herein, we report the divergent, stereospecific reaction of fluoroiodomethyllithium with boronic esters which give α‐fluoro‐boronic esters. These unique intermediates can be readily transformed into the corresponding mono‐ or difluoromethylated compounds, via proto‐ or fluorodeboronation, respectively. The use of the highly unstable fluoroiodomethyllithium was key to allowing rapid 1,2‐migration over competing decomposition of the carbanion. DFT calculations informed and supported the experimental findings.