Anthracene 9-carboxylic acid dimerization

These systems also provided the possibility of achieving stereochemical control of the dimerization. The effect of the preorientation of the two anthracene moieties was examined in detail in the four regioisomers of bis(anthracene-l-carbonyl)-y-CD (Scheme 10). The reaction proceeds stereospecifically. Alkaline hydrolysis of the ester linkage afforded the photodimers of 1-anthracene carboxylic acid (Scheme 29 X = H, Y = COOH, Z = H). The syn head-to-head dimer was exclusively formed starting from the A,B and A,C regioisomers, whereas the anti analogs were formed from the A,D and A,E regioisomers. Asymmetric induction was observed in the D3 dimer. When (S)-borneol was present, the specificity was... 

Similar experiments performed at higher CTAB concentrations near the phase transition from isotropic solution to lyotropic liquid crystals show that the phase transition temperature is affected by the presence of rheologically active compounds (155,161). Figure 13 demonstrates that the phase transition temperature increases when small amounts of 9-anthracene carboxylic acid are solubilized. Irradiation at X = 366 nm, i.e. photodimerization, removes the effect, and reirradiation at X = 254 nm (splitting of the dimers) causes a reincrease of the phase transition temperature. 

Fig. 14.9 Anthracene-9- and -1-carboxylic acids (12 and 13), showing the square self-assembled dimer of 12 leading to columnar...

In the case of double salts of anthracene-9-carboxylic acid (9-AC), which usually cyrstallized with included water and/or solvent, the 9-AC" component in the crystal underwent decarboxylation and reduction along with dimerization (Scheme 45) [77]. Although the head-to-tail dimer and a mixed dimer were obtained, the head-to-head one was not produced. The reactivity was influenced by the amount of the included solvenL e.g., (9-AC )2(c-chxiiH2 )(EtbH)xi was photostable, while (9-AC )2(c-chxnH2 )(EtOH)o,5 gave six photoproducts. Incidentally, the elusive head-to-head dimer was selectively obtained by solid-state irradiation of the 9-AC homocrystal as a thermally unstable product [78]. 

Ito and coworkers, for example, have demonstrated that 1,2-diamines (e.g., cyclohexane-1,2-diamine) can be reacted with anthracene-9-propionic acid (9-ap) in a double salt formation to afford a solid that reacts to give a head-to-head photodimer in 55% yield. Dunels and coworkers have also demonstrated that the salt formed from 9- N,N-dimethylamino)anthracene (dmaa) and furan-2-carboxylic acid reacts to give the head-to-tail dimer in near quantitative yield. An unsymmetrical [4+4] cycloaddition has also been reported via salt formation involving dmaa and the diacid muco. The salt assembled with anthracene pairs arranged in a head-to-tail fashion with C=C bonds separated by 3.58 and 3.65 A (Figure 22). On UV irradiation, the head-to-tail photoadduct formed in quantitative yield. 

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