In contrast to 3a, needles of 3b were suitable for structural characterization (Figure and Supporting Information). In the solid state, 3b is essentially flat (largest distances from leastsquares plane defined by the C-atoms: O2, 0.0385(9) Å and C3, 0.0183(10) Å). It crystallizes with one molecule of 1,4-dioxane in the space group P1̅ . The asymmetric unit contains half of a formula unit (Z'=1/2), whereby 3b and 1,4-dioxane are located each on a center of inversion. No significant π-π stacking is observed. In addition to these results, we were also able to determine the crystal structure of the precursor 1,8-dibromo-4,5dimethoxyanthracene, which has not yet been reported (in contrast to the crystal structure of the direct precursor 2b) and is provided in the Supporting Information. -7-