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

Abstract

Photochemical reductive dimerization of 3,3'-dimethoxybenzophenone (1b) gave 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-methoxyphenyl)ethanone (3b) by means of I2 in boiling glacial HOAc. The structure of 3b was indicated by 1H NMR and determined definitively by X-ray crystallography. The crystals are monoclinic, space group P21/c, a = 12.250(2), b = 9.6997(12), c = 20.866(2) Å, β = 95.319(11)°, 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 C2-unit during the rearrangement process.Key words: X-ray structure, pinacol-pinacolone rearrangement, chemical bonding.