Containing Peripheral N-Heteroaromatic Substituents

From a retrosynfhetic viewpoint, N-aryl-l,2-diimine Ni precatalysts are synthesized by (i) reaction of 1,2 diimines with nickel halides from (ii) 1,2-diimine ligands which in turn are obtained by (iii) condensing 1,2-dicarbonyl substrates with two equivalents of primary aromatic amines, usually under acidic conditions [11]. In analogy, the synthesis of N-hetaryl 1,2 diimine catalysts starts from the corresponding substituted N-heterocyclic primary amines as the amine building blocks. The synthesis of three types of such heterocycles, N-amino-pyrroles, -indoles and -carbazoles, and their corresponding diimine derivatives is presented in the following sections. 

Paal-Knorr condensation of these 1,4-diketones with protected hydrazines gives access to the corresponding N-protected N-aminopyrroles 1-8 in a simple proce- 

The N-aminopyrroles 9-16 were obtained from these amides in 80-95% yield by alkahne hydrolysis (1-36 h) with a KOH saturated refluxing ethylene glycol solution. This convenient but rather drastic deprotection protocol shows that N-ami -nopyrroles are quite stable compounds. The high stabihty of aminopyrroles 9-16 presumably results from fhe fact fhat both a-positions are blocked in fhese 2,5-di-substituted pyrroles. The parent member of this family of compounds, unsubstituted N-aminopyrrole, is fhe only commercially available N-amino-azole. Ironically, it is also fhe least stable compound in the series. 

In summary, N-amino-2,5-disubstituted pyrroles wifh a range of substituents can be conveniently prepared on a large scale. The only hmitation of the method is fhe commercial availability of fhe starting 1,4-diketones. They in turn are most easily prepared from fhe Stetter condensation. 

To further extend fhe substitution pattern of fhese building blocks, benzarmelated N-amino-N-heterocycles were prepared Electrophilic amination of indole, 2-mefhylindole, or carbazole using hydroxylamine-O-sulfonic acid [25] yielded fhe corresponding N-amino-indole 17, -2-methyhndole 18, and -carbazole 19, respectively. However, attempting the same reaction with 2,7-dimethyhndole or dibenza-zepine (iminostilbene) failed, most likely due to steric hindrance. 

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N,O] Salicylimine Nickel Complexes Containing Peripheral N-Heteroaromatic Substituents... 

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