3- Amino indoles, formation

How anthranilic acid is converted to indole is poorly understood. The amino group of anthranilic acid has been shown to form the nitrogen of the indole ring. Further, the available data suggest that the carboxyl group of anthranilic acid is lost on indole formation. ... 

The mixture of ethynylaniline li (0.19 mmol), paraformaldehyde 2d (2 equiv.), and amino ester 3 (1.2 equiv.) in dioxane was stirred with CuX (5 mol%) under microwave irradiation (300 W). After indole formation was complete on TLC, the reaction mixture was treated with MsOH at 80 °C for 30 min... 

Scheme 1 Synthesis of 1-amino indoles via Palladium-catalyzed intramolecular C-N bond formation...

Heterocyclization by catalytic formation of N—Car bond to give indoles, amino-pyridines, and N-aryl-substituted saturated heterocycles 98ACR805. 

Ethyl 3-azido-l-methyl-177-indole-2-carboxylate 361 is prepared in 70% yield by diazotization of amine 360 followed by substitution of the created diazonium group with sodium azide. In cycloadditions with nitrile anions, azide 361 forms triazole intermediates 362. However, under the reaction conditions, cyclocondensation of the amino and ethoxycarbonyl groups in 362 results in formation of an additional ring. This domino process provides efficiently 4/7-indolo[2,3-i ]l,2,3-triazolo[l,5- ]pyrimidines 363 in 70-80% yield (Scheme 57) <2006TL2187>. 

The reaction of aromatic amino acids, dipeptides, or protected amino acids with [Ru(Cp )(CH3CN)3]PF6 in THF (THF = tetrahydro-furan) leads to the formation of robust Ru(Cp ) sandwich complexes in which side-chain phenyl (e.g., Phe, Tyr) or indole groups (Trp) are bound 7]6 to a Ru(Cp ) center (cf. 31 AA = Phe) (75, 76). The similar... 

A similar formation of indoles has been achieved starting from o-nitro-styrenes. Under hydroformylation conditions, the nitro group is reduced to the amino group, which condenses with the in situ generated aldehyde [48].This approach is comparable with the indole syntheses of Reis-sert [49], Batcho and Leimgruber [50], and Sugasawa [51]. 

Alkali metal borohydrides are frequently used for the reduction of rc-electron-deficient heteroaromatic systems, but reduction of jt-electron-excessive arenes is generally possible only after protonation of the systems [e.g. 35-37]. The use of tetra-n-butylammonium borohydride under neutral conditions for the conversion of alkylindoles into indolines [38] is therefore somewhat unusual. Reduction of indoles by diborane under strongly alkaline conditions involves the initial interaction of the indolyl anion with the diborane to form an amino-borane which, under the basic conditions, reacts with a second molecule of diborane to produce the indoline [39]. The reaction of tetra-n-butylammonium borohydride with indoles could also proceed via the intermediate formation of diborane. 

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