Structure determination of photoproducts of anthracenes with (arylmethoxymethyl) sidechains

Irradiation of 9-(arylmethoxymethyl)anthracenes 3 leads either to a cyclomer and cyclodimer mixture (3a -> 4a,5a), to selectively formed dimers (3b -> 5b), or a selectively formed cyclomer (3c -> 4c). The [4 pi+4 pi]cyclodimerization is under the conditions used a regioselective head-to-tail process. In the crystals of the dimers 5a,b, the sidechains are attached in an antiperiplanar position related to the CC bonds generated in the dimerization. In solutions, however, the structures consist of three rotamers the equilibration of which was studied by temperature-dependent NMR spectra. ((c) Wiley-VCH Verlag GmbH & Co.