Electron spin resonance studies of radicals derived from 1,3,2-benzodioxaboroles

Abstract

The reactions of photochemically generated ethoxyl and t-butoxyl radicals with a number of 1,3,2-benzodioxaboroles and with 2-butyl-4,5-dimethyl-1,3,2-dioxaborole have been studied in solution using e.s.r. spectroscopy. With each borole, alkoxyl addition takes place at boron to give a perboryl radical adduct in which the unpaired electron occupies a π orbital delocalised over the borole residue. The perboryl adducts derived from 1,3,2-benzodioxaboroles which have a B-alkyl substituent (catechol boronates) break down by loss of the alkyl radical and the ease of this α-scission increases as the strength of the B–C bond decreases. The addition/fragmentation sequence corresponds to stepwise S_H2 alkoxydealkylation at boron.