Oxygen acidity of ring methoxylated 1,1-diarylalkanol radical cations bearing alpha-cyclopropyl groups. The competition between O-neophyl shift and C-cyclopropyl beta-scission in the intermediate 1,1-diarylalkoxyl radicals

A product and time-resolved kinetic study on the reactivity of the radical cations generated from cyclopropyl(4-methoxyphenyl)phenylmethanol (1) and cyclopropyl [bis(4-methoxyphenyl)] methanol (2) has been carried out in aqueous solution. In acidic solution, 1(center dot+) and 2(center dot+) display very low reactivities toward fragmentation, consistent with the presence of groups at Ce, (aryl and cyclopropyl) that after C-alpha-C-ss bond cleavage would produce relatively unstable carbon-centered radicals. In basic solution, 1(center dot+) and 2(center dot+) display oxygen acidity, undergoing -OH-induced deprotonation from the alpha-OH group, leading to the corresponding 1,1-diarylalkoxyl radicals 1r(center dot) and 2r(center dot), respectively, as directly observed by time resolved spectroscopy. The product distributions observed in the reactions of 1(center dot+) and 2(center dot+) under these conditions (cyclopropyl phenyl ketone, cyclopropyl(4-methoxyphenyl) ketone, and 4-methoxybenzophenone from 1(center dot+); cyclopropyl(4-methoxyphenyl) ketone and 4,4 '-dimethoxybenzophenone from 2(center dot+)) have been rationalized in terms of a water-induced competition between 0-neophyl shift and C-cyclopropyl ss-scission in the intermediate 1,1-diarylalkoxyl radicals 1r(center dot) and 2r(center dot).