Borylation–Reduction–Borylation for the Formation of 1,4-Azaborines

Given the current interest in materials containing 1,4-azaborine units, the development of new routes to these structures is important. Carbonyl directed electrophilic borylation using BBr3 is a facile method for the ortho-borylation of N,N-diaryl-amide derivatives. Subsequent addition of Et3SiH results in carbonyl reduction and then formation of 1,4-azaborines that can be protected in situ using a Grignard reagent. Overall, borylation–reduction–borylation is a one-pot methodology to access 1,4-azaborines from simple precursors.