UV light mediated photocatalyst-free generation of ketyl radicals with concurrent 1,2-boron shift and one-pot synthesis of benzoxaboroles under continuous-flow conditions

Ketyl radicals are highly invaluable intermediates in organic synthesis and their functionalization like coupling with alkene alkyne, CO2 and cyano compounds have been reported in literature. The photocatalyzed reactions using metal and organo-photocatalysts generate ketyl radicals by single electron transfer (SET), proton-coupled electron transfer (PCET), halogen atom abstraction (XAT) and hydrogen atom transfer (HAT) mechanism. A photocatalyst free UV light mediated generation of ketyl radicals in presence of bis(pinacoloto)diboron (B2pin2) is developed. The addition of Bpin radical to a carbonyl group, and followed by 1,2-boron shift generated a thermodynamically favourable ketyl radical. This method was applied for one-pot synthesis of benzoxaboroles from ortho halo benzaldehydes. B2pin2 played dual role, as a facilitator of ketyl radical formation, as well as a borylation agent.