A General Approach to Deboronative Radical Chain Reaction with Pinacol Alkylboronic Esters
The generation of carbon-centered radicals from air-sensitive organoboron compounds via nucleohomolytic substitution at boron is one of the most general methods to generate non-functionalized and functionalized radicals. Due to their reduced Lewis acidity, the very popular, air-stable, and readily available alkylboronic pinacol esters are not suitable substrates for this process. Herein, is reported their <i>in situ</i> conversion to alkylboronic catechol esters by boron-transesterification
... sesterification with a substoichiometric amount of catechol methyl borate (MeO–Bcat) telescoped onto a wide array of radical chain processes. This simple one-pot, radical-chain, deboronative protocol allows for the conversion of pinacol boronic esters into iodides, bromides, chlorides, and thioethers. The process is also suitable the formation of nitriles and allylated compounds via C–C bond formation using sulfonyl radical traps. Finally, a particularly mild protocol for the protodeboronation of pinacol boronic esters is given. The power of combining radical and classical boron chemistry, is illustrated with a highly modular 5-membered ring formation using a combination of a three-component coupling reaction and a protodeboronative cyclization.