Synthesis and Topochemistry of 2,5‐Bisacrylate‐Substituted 1,4‐Benzoquinones

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 ( n max = 7), under topochemical control. The cyclobutane units generated from 1b and from 1c − 1f have twofold and centric symmetry, respectively, as determined by 1 H‐NMR spectroscopy and simulation thereof. The twofold symmetry in the cycloaddition products of 1b is in agreement with the crystal structure of the monomers.