The crystal and molecular structures of five 2,5-bis(aryl-2-vinyl)-l,4-dimethoxybenzene derivatives la-le were determined by X-ray diffraction with respect to topochemical aspects. We found three types of packing arrangements: (1) a-type packing with 7 A. stacking axes, (2) /3-type packing with 4 A, stacking axes and (3) a third intermediate packing type. The intermolecular distances between the vinylic double bonds of all derivatives exceed the limits of 4 A. in the crystals. Therefore photochemical [2 +2]cycloadditions were not observed in the crystals of these compounds. A correlation between the inclination angle of the molecular plane to the stacking axis and the separation between potentially reactive double bonds was detected.

The 2,5‐bisacrylate‐substituted 1,4‐benzoquinone bisketal 7a was synthesized by electrochemical oxidation of the corresponding dimethoxybenzene 6. The methyl ester 7a was transesterified to the corresponding ethyl, n‐propyl and isopropyl esters 7b−7d by Ti(OEt)4 catalysis and to the corresponding n‐butyl and benzyl esters 7e−7f by the Li alkoxides. The bisketals 7a−7f were hydrolyzed to the corresponding 2,5‐bisacrylate‐substituted 1,4‐benzoquinones 1a−1f. The crystal structure of the ethyl ester 1b was determined by X‐ray diffraction, which revealed short intermolecular contacts of 3.463 and 4.051 Å between vinyl groups and quinone double bonds, respectively, related by twofold symmetry. Because of the shorter distance and the smaller shift in projection (vinyl: 1.002; quinone: 2.107 Å), only the vinyl group is photoactive in the crystal. In the solid state, topochemically controlled [2+2] photocycloadditions take place at the vinylic groups of the bisvinyl quinones 1a−1f, to afford dimers and oligomers (nmax = 7), under topochemical control. The cyclobutane units generated from 1b and from 1c−1f have twofold and centric symmetry, respectively, as determined by 1H‐NMR spectroscopy and simulation thereof. The twofold symmetry in the cycloaddition products of 1b is in agreement with the crystal structure of the monomers.

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1995 structure structure (organic substances) K 9000 15 -050 Molecular Structures and Packing Arrangements of Five 2,5-Bis(aryl-2-vinyl)-1,4-dimethoxybenzene Derivatives -(I). -(IRNGARTINGER, H.; LICHTENTHAELER, J.; HERPICH, R.; Struct.