Photoisomerization of perfluoroaryltetrahedranes to perfluoroarylcyclobutadienes.

Two perfluoroaryl-substituted cyclobutadiene derivatives, 6 and 7, were prepared as air- and moisture-sensitive red solids by the photochemical isomerization of the corresponding tetrahedranes (4 and 5, respectively). Remarkably, the 9,10-dicyanoanthracene-sensitized photochemical reaction of 4 also proceeded, giving 6, and the mechanism of this reaction is also discussed. The first aryl-substituted cyclobutadienes were characterized by spectroscopic data as well as by X-ray crystallography for 6, showing a distorted rectangular structure with extremely long C-C single bonds.