Useful synthesis of benzotriazole photostabilizers by reductive carbonylation of ortho-nitrophenylazo compounds, catalyzed by Ru3(CO)12 in the presence of NEt3

Ru3(CO)12 catalyzes the reductive carbonylation of ortho-nitrophenylazo compounds to give the corresponding benzotriazoles, in ortho-dichlorobenzene or ortho-xylene, at 180-200 °C and 70-80 atm, although with rather low conversion and selectivity. Both conversion and selectivity are markedly increased by addition of a base such as Et3N, which acts, under our conditions, as a deoxygenating agent of the nitro group. The mechanism of the reaction has been investigated by studying the possible intermediates.