Copper(II)-mediated oxidative coupling of 2-aminonaphthalene homologues. Competition between the straight dimerization and the formation of carbazoles

Whereas the Cu(II)-mediated oxidative coupling of 2-aminonaphthalenes 7a an d 7b results in the clean formation of l,l'-binaphthyls 13a and 13b, respec tively, their higher homologues and congeners 8-12 have been found to exhib it a different reaction pattern. Thus, 2-aminoanthracene (8) gave a similar to1:1 mixture of the expected bianthryl derivative 15 and the carbazole 16 , whereas the 9-aminophenanthrene (10), 3-phenyl-1-aminonaphthalene (11), a nd 2-aminochrysene (12) produced almost exclusively the corresponding carba zoles 19, 20, and 21, respectively. By contrast, the isomeric 3-aminophenan threne (9) gave rise to the azo compound 17 as a result of the preferential oxidation on the nitrogen. The carbazoles have been shown to arise directl y from the coupling reactions rather than from the primarily formed binapht hyls. Alternatively, carbazole 19 can also be prepared from Ib on reaction with hydrazine. On the other hand, treatment of 3a with hydrazine resulted in the formation of a similar to2:7 mixture of amine 11 and arylhydrazine 2 2. 2,2'-Diamino-1,1'-bianthryl (15) has been resolved into enantiomers via cocrystallization with (-)-N-benzylcinchonidinium chloride and shown to hav e (R)-(-)-15 configuration by X-ray crystallography.