Efficient direct aromatic amination by parent nitrenium ion. Photolyses of 1-aminopyridinium and 1-aminoquinolinium salts and effect of crown ethers
Photolyses of 1-aminopyridinium salts 1a–f, 2-aminoisoquinolinium salt 2 and 1-aminoquinolinium salts 3a–f gave aniline 4 or a mixture of 2-, 3- and 4-toluidines 5a–7a in benzene–trifluoroacetic acid (TFA) or in toluene–TFA, respectively. The use of 1-aminoquinolinium perchlorate 3a showed the highest yield in these photolyses. Irradiation of 3a in the presence of ethylbenzene, p-xylene, mesitylene, anisole and chlorobenzene similarly yielded arylamines. The yields of arylamines were generally increased in the presence of a small amount of crown ether. The aromatic amination is discussed in terms of the intermediacy of a parent nitrenium ion.