Ring azaindoles

AHCS1, p. 528). Ab initio (STO-3G) calculations of the geometry, eharge distribution, and gas-phase basieity of azaindoles eoneluded that the strueture of five-membered ring is almost unaffeeted by the position of the aza-N atom (83T2851). 

In agreement with the previous data on the protonation site in azaindoles (76AHCS1, p. 529), an example of monoprotonation of 3-aryl substituted 6-azaindoles at the pyridine ring has been demonstrated by UV speetroseopy [88JCS(P2)1839]. 

CARBAZOLES AND AZAINDOLES 5.2.7.1 Carbazole Ring Synthesis and Annulation... 

Palladium-catalyzed reactions of arylboronic acids have been utilized to craft precursors for constructing indole rings. Suzuki found that tris(2-ethoxyethenyl)borane (149) and catechol-derived boranes 150 readily couple with o-iodoanilines to yield 151, which easily cyclize to indoles 152 with acid [158]. Kumar and co-workers used this method to prepare 5-(4-pyridinyl)-7-azaindoles from 6-amino-5-iodo-2-methyl-3,4 -bipyridyl [159], A similar scheme with catechol-vinyl sulfide boranes also leads to indoles [160]. A Suzuki protocol has been employed by Sun and co-workers to synthesize a series of 6-aryloxindoles [161]. 

The conversion of 3-amino-4-oxo-l,jc-naphthyridines (117) into the corresponding 3-diazo-4-oxo compounds (118) followed by photolysis results in the formation of azaindoles (119) via nitrogen evolution and ring contraction (56LA(599)233, 60JCS1794). 

The pyrrolopyridine isomers, shown in Figure 1, represent the most widely studied compounds within the bicyclic 5-6 systems discussed here. Azaindole, a common name for these compounds, is found less frequently in the literature. Each ring of the pyrrolopyridines contains a nitrogen heteroatom. The most comprehensively studied isomers are compounds 1-6. There have been scarce, if any, references to isomers 7-12 in the period under investigation. 

As would be expected, the majority of the compounds described in this chapter can be considered as indoles with one or more nitrogens as heteroatoms in the six-membered ring. The four pyrrolopyridines are commonly referred to as azaindoles, terms more elegant than the IUPAC nomenclature. These compounds are also occasionally called diazaindenes. The following synonyms are frequently met ... 

Related NACAN-coordinated complexes containing benzothiazoles 50 or azaindoles 51 in place of the pyridyl rings have also been investigated [140,141]. Complex 50 is luminescent in solution at room temperature, with tt-tt spectral properties resembling monomeric [Pt(dpyb)Cl], whilst the azaindole complexes are emissive only in the solid state or in glasses at 77 K. 

The ring-closure of isopropyl methyl ketone 3-pyridylhydrazone (181) is said to give exclusively 2,3,3-trimethyl-4-azaindole (182),413 whereas acetone 2-chloro-5-pyridylhydrazone gives 5-chloro-2-methyl 4-azaindole.418 No product of attack at the y-position was reported. 

The pyrrolopyridines contain one nitrogen heteroatom in the five-membered pyrrole ring and one nitrogen atom in the six-membered pyridine ring. A more common name is azaindoles, with 7-azaindole (l//-pyrrolo[2,3-6]pyridine (1)) being the most widely studied isomer of the series. Twelve isomers of pyrrolopyridines are listed in the Chemical Abstracts Ring Formula Index. Table 1 lists the pyrrolopyridines with their Chemical Abstracts Registry Numbers. The 1//-pyrrolopyridines (l)-(6) are the most frequently prepared, but some work has also been carried out on the isomers (7), (8), and (10). Isomers (8), (9), (11), and (12) are tautomeric structures which are considered later (see Section 7.06.4.4). 

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