Reactions of Aryldiazomethanes with Chloranil

Abstract The reactions of several aryldiazomethanes (1a: p-tolyl; 1b: phenyl; 1c: p-chlorophenyl) with chloranil gave stilbenes (3) and spiro-oxetanes (4) at 20 °C in tetrahydrofuran or 1,2-dichloroethane. The isomer ratios of 3 were ca. 2 to 3:1 in favor of cis, depending on the solvents and on the substituents of 1. In the case of 4, however, stable trans-isomers were selectively formed. On the other hand, the presence of added CH3OH suppressed the formations of 3 and 4 and, instead, induced redox reactions giving α,α-dimethoxyarylmethanes and tetrachlorohydroquinone (6). In these redox reactions, the acid decompositions of 1 with 6 were also found. However, the presence of CF3CH2OH allowed the formation of considerable amount of 3 and 4, along with the redox products. The mechanism of these reactions will be discussed.