In the course of topochemical investigations of substituted quinones the 2-monovinyl-substituted 1,4-benzoquinones 1 were synthesized by electrochemical oxidation of the corresponding 1,4-dimethoxybenzene derivatives 3 to the quinone bisketals 4 and subsequent hydrolysis. In solution, the aryl-substituted vinylquinones 1a-1t underwent unexpected Diels-Alder additions. The stereochemically unique course of the reaction was proved spectroscopically and by X-ray structure analysis of the dimer 8k. As a basic requirement for the topochemical studies, the crystal structures of eight quinones 1 were determined by X-ray diffraction. In the crystals of 1a, 1c, 1e, 1f, 1i and 1n with an alpha-type packing arrangement, the vinylic double bonds have short contacts (< 4.4 Angstrom) across a centre of symmetry. The quinone 1k crystallizes in a beta arrangement with short distances (< 4.0 Angstrom) between molecules related by translation and in a gamma arrangement without suitable contacts. The crystals of all quinones 1 were irradiated with UV light to perform [2+2] cycloadditions. The photoreactive quinones dimerized exclusively at the vinylic double bonds, resulting in the corresponding cyclobutanes 9. Topochemically controlled the dimers 9a-9c, 9e, 9l-9n, 9q, 9r and 9u with molecular C-i symmetry were formed whereas the dimers 9k and 9t have C-s symmetry. The structures of the cyclobutanes were determined by spectroscopical investigations and in the case of 9b, 9e and 9r additionally by X-ray analysis. Despite short contacts, crystals of 1f and 1i were photostable. This is probably because of insufficient lattice flexibility indicated by relatively high densities.

2,5-Bisvinyl-1,4-benzoquinones 1 and 2-vinyl-1,4-benzoquinones 2 substituted with aryl or ester end groups have been synthesized. The 2,5-bisstyryl-1,4-benzoquinones 1 (R=phenyl, p-tolyl, o-tolyl) crystallize with a 7 Angstrom-stacking axis. But only for the o-tolyl derivative the contacts between the vinyl groups are close enough to allow a four-center type photopolymerization. The ester derivative 1 (R=COOEt) has a layer structure and can be photooligomerized in the crystal. The generated cyclobutane subgroups have twofold symmetry. The vinylquinones 2 (R=aryl) may be dimerized photochemically in the crystal at the vinyl groups to centrosymmetric cyclobutanes. Crystals with 4 Angstrom stacking axis are also photoreactive.