Unsymmetrical photodimerization of a 9-aminomethylanthracene in the crystalline salt

By the salt formation with particular nonaromatic dicarboxylic acids, rapid and selective photodimerization of 9-(N,N-dimethylaminomethyl)anthracene (1) was accomplished in the solid state. For instance, the salt with trans,trans-muconic acid or acetylenedicarboxylic acid was led quantitatively to the 9,10:4', 1' photodimer usy-ht-2, the first example of the unsymmetrical [4+4] photodimerization of anthracene in the solid state. The reactions were rationalized by the relevant C center dot center dot center dot C distances between the reacting carbons.