Unusual oxidative cleavage of the aryl-ethynyl bonds in (arylethynyl)polymethylbenzenes with iodine in dimethyl sulfoxide

While heating 1,2,4,5-tetramethyl-3,6-bis(phenylethynyl)benzene, 1,3,5-trim ethyl-2,4-bis(phenylethynyl)benzene, and 1,2,4,5-tetramethyl-3-(phenylethyn yl)benzene with iodine in DMSO in the absence of oxygen, the triple bonds a re oxidized to give the corresponding 1,2-diketones. In the presence of oxy gen, the previously unknown competitive oxidative process causes the cleava ge of the aryl-ethynyl bonds so that duroquinone and the corresponding 4-hy droxybenzils are formed. This cleavage is produced by oxygen only in the pr esence of iodine and DMSO. It was shown that the key stage of the process i s the formation of intermediate charge-transfer complexes between polymethy lbenzene rings and iodine.