Novel 1,4,5,8-Phenanthrenediquinones and Unusual Deoxygenation using Trimethylsilyl Iodide

Attempt for aryl methyl ether cleavage of 5,8-dimethoxy-1,4-phenanthrenequinone (4) with boron trichloride or tribromide resulted in the halogenation of the quinone double bond to form 5a,b. Surprisingly, reaction of dimethyl ether 4 with trimethylsilyl iodide afforded the phenanthrenediquinone 6, whereas deoxygenation to 8 and 9 occurred by reaction of trimethylsilyl iodide with derivative 7. The phenanthrenediquinones 6 and 10 were obtained nearly quantitatively from 4 and 7 by using ceric ammonium nitrate as the oxidant. The cyclic voltammograms of the phenanthrenediquinones 6 and 10 were studied and rationalized by Hückel Molecular Orbital calculations.