4-Azafluorene

A wide range of azaarenes including acridines and benzacridines, 4-azafluorene, and 10-azabenzo[fl]pyrene (Figure 1.32) has been identified in particulate samples of urban air, and some of them have been recovered from contaminated sediments (Yamauchi and Handa 1987). 

Azulen aus 4-Azafluoren dunkelblaue, feste Masse (159) breites Maximum bei 570... 

This also may be looked upon as a substituent reaction (see Chapter 2.06) but a few examples are given here. A suitably substituted pyridine will undergo Pschorr cyclization to give 2- and 4-azafluorene and two other products (equation 181) (65CJC940). With a 2-substituted pyridine (287), cyclization on to the pyridine nitrogen is heavily favoured (equation 182) (54JCS4263). Decomposition of 3-(o-azidophenyl)pyridine results in a nitrene... 

Pyrolysis of pyrazolo[3,4-b]pyridine247 and the 1-phenyl derivative248 proceed by loss of nitrogen gas. The 1-phenyl derivative, at 770°C, underwent 49% conversion to 4-azafluorene. The formation of a carbene (272) from the 3-H tautomer was proposed because the alternative carbene (273) is known to lead to mixtures of 1- and 3-azafluorenes. 

Onychine (135) was first described as a natural product in 1976, when its isolation from Onychopetalum amazonicum (Annonaceae) was reported (83), and its structure was given as 4-methyl-l-azafluoren-9-one (158) on the basis of elemental analysis and high-resolution MS, as well as UV, IR, and H-NMR spectra. As in all the azafluorenone alkaloids discovered to date, the complex UV spectrum is reminiscent of that of fluoren-9-one, and the H-NMR spectrum clearly indicates the presence of a 2,3-disubstituted 4-methylpyridine moiety. The immediate conclusion, therefore, is that onychine is either l-methyl-4-azafluoren-9-one (135) or 4-methyl-l-azafluoren-9-one (158), which is supported by the spectral properties of the secondary alcohol obtained by reduction of the ketone group and of the acetylation and hydrogenolysis products of this... 

In analogy to fluorene the more acidic 5H-indeno(l,2-b)pyridine (= 4-azafluorene) (133) smoothly condenses with (7i) to (134) which cyclize uniformly to 6-phenyl-acenaphtho(l,2-b)pyridine (= 2-phenyl-7-azafluoranthene) (75J)44 ... 

Varlamov, A.V. Levov, A.N. Toze, F Chernyshev, A.I. Davydov, V.V. Ryabov, M.A. Egorova, O.A. Amination of 4-azafluorene under chichibabin reaction conditions. Some chemical transformations of l-amino-4-azafluorene. Chem. Heterocycl. Compd. 2002, 3S(12),1484-1490. 

A number of azaarenes have also been detected in cigarette smoke (/7, 28, 56). These have included quinoline, methyl- and dimethylquinolines, isoquinoline, and alkylisoquinolines, benzo[/i]quinoline, acridine, phenan-thridine, benzo[/]quinoline, 4-azafluorenes, 1-azafluoranthenes, 4-azapyrenes, 9-methylcarbazoles, indole, alkylindoles, alkylcarbazoles, benzo[Z>]carbazole, dibenzo[c,g]carbazole, and benz[c]acridine. 

The Baltz-Schiemann reaction can also be used for the synthesis of 4-fluoropyridine derivatives [21, 22, 26-29]. For example, it was successfully apphed to the synthesis of 4-fluoroazafluorene [79]. First, l-amino-4-azafluorene (92) was synthesized... 

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