Photochemical oxidative dimerisation of 4-phenylazo-1-naphthol in organic solvents

The photo-oxygenation of 4-phenylazo-1-naphthol (1) gives the dimer 4,4′-bis(phenylazo)-2,2′-binaphthyl-1,1′-diol (2) in organic solvents, with a particularly good yield (28%) in chloroform.