Selective photochemical synthesis of 3,3′-dimethoxy-4,2′-dihydroxybiphenyl

3,3′-Dimethoxy-4,2′-dihydroxybiphenyl (4,2′-DHBP) can be synthesized with high selectivity from 2-methoxyphenol (guaiacol) by photochemical excitation. Alternate methods to synthesize guaiacol dimers, e.g. peroxidase-catalyzed or electrochemically initiated dimerizations, generate a very low yield of 4,2′-DHBP in comparison. Product yield of the photochemical synthesis of 4,2′-DHBP can be enhanced by the addition of benzophenone as an activator without measurable loss in selectivity. Analytical GC-MS as well as a preparative HPLC method for the isolation of 4,2′-DHBP are described. The enzymatic and photochemical approach reveal similar selectivities of about 90%, however the peroxidase reaction leads to 3,3′-dimethoxy-4,4′-dihydroxybiphenyl (4,4′-DHBP) whereas the photochemical reaction affords 3,3′-dimethoxy-4,2′-dihydroxybiphenyl (4,2′-DHBP).