Synthesis and X-ray structure of 1,2,2,2-tetrakis(3-methoxyphenyl)ethanone

Photochemical reductive dimerization of 3,3'-dimethoxybenzophenone (1b) gav e the symmetrical benzopinacol 1,1,2,2-tetrakis(3-methoxyphenyl)ethane-1,2- diol (2b), which was rearranged to the benzopinacolone 1,2,2,2-tetrakis(3-m ethoxyphenyl)ethanone (3b) by means of I-2 in boiling glacial HOAc. The str ucture of 3b was indicated by H-1 NMR and determined definitively by X-ray crystallography. The crystals are monoclinic, space group P2(1)/c, a = 12.2 50(2), b = 9.6997(12), c = 20.866(2) Angstrom, beta = 95.319(11)degrees, Z = 4, R = 0.053 for 4523 independent reflections. The structure establishes that the migrating 3-methoxyphenyl group retains bonding through its number 1' carbon atom to the parent C-2-unit during the rearrangement process.