The copper-promoted reaction of o-halogenodiarylazo-compounds with nucleophiles. Part 1. The copper-promoted reaction of o-bromodiarylazo-compounds with trialkyl phosphites. A novel method for the preparation of dialkyl arylphosphonates

Abstract

o-Bromodiarylazo-compounds react with triethyl phosphite in the presence of copper(II) acetate in dry ethanol to give the corresponding o-diethylphosphonatodiarylazo-compounds in good yield. Reaction is facilitated by the presence of an o′-donor substituent in the o-bromodiarylazo-compound. In 10% aqueous ethanol reductive replacement competes with nucleophilic substitution in o-bromodiarylazo-compounds having an o′-donor suestituent but not in those devoid of such a substituent. Under these conditions reduction of the copper(II) acetate to a copper(I) species occurs with liberation of acetic acid. The former o-bromodiarylazo-compounds readily undergo reductive substitution in the presence of acetic acid or, better, trifluoroacetic acid and copper(I) acetate or copper–bronze in ethanol, whereas the latter do not. In the presence of acetic acid biaryl coupling competes with reductive substitution and becomes the principal reaction when no acid is present. Neither reductive substitution nor biaryl coupling occur when the copper(I) acetate or copper–bronze are replaced by copper(II) acetate.