Carbazoles and Related Compounds

1 Clausine P and Glycozolidine (Synthesis of Carbazoles by Intramolecular Ar-H/Ar-X Arylation) 

The target structures of these elegant and short total syntheses are shown in 

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SYNTHESIS OF CARBAZOLES AND RELATED COMPOUNDS VIA C-E BOND-FORMING COUPLING REACTIONS... 

Some of the enzymes involved in the known pathways for the degradation of quinoline have been isolated and purified. However, not all enzymes have been identified, or characterized. In this section, we will consider the enzymes associated with the degradation of quinoline (and related compounds), carbazole and indole. To examine the enzymatic work, the reader is referred to the previous section, in which the metabolic pathways were detailed. 

Five-membered rings are also readily synthesized using this coupling methodology, enabling the production of dibenzo[M]fused heterocycles such as dibenzo-furans [2, 7], carbazoles [7, 8] (Scheme 1, G = O, NR respectively), and related compounds [8, 9]. Carbazoles are important structural motifs found in pharmaceuti-... 

Compared to the number of halogenated pyrroles and indoles, the number of known halogenated carbazoles, carbolines, indolocarbazoles, and related compounds is much smaller <96MI1>, and the number of recently discovered examples of these types is fewer still. 

Phenyl azide can yield benzotriazole on irradiation , but more generally products of self-insertion or of attack on the solvent are found to lead to azepines and related compounds " - . Photolysis of o-azidobiphenyls formed carbazoles by intramolecular cyclization similar to that found in thermolysis and an analogous intramolecular cyclization involving, e.g. a nitro group could occur (reaction 74) in direct photolysis but not apparently in photosensitized reactions when only azobiphenyl was formed in appreciable yield The... 

Deactivation of 2-naphthylamine singlet state by pyridines in enhanced by dipole moment and the ability to form hydrogen bonds. Picosecond laser spectroscopy shows charge transfer from the excited amine. The fluorescence of 2-iV,A -dimethylaminopyridine induced by p-nitroaniline is also caused by exciplex formation. The latter enhances triplet population of p-nitroaniline. The quenching of the fluoresence of carbazole and some derivatives by trichloroacetic acid and related compounds in fluid solutions has been studied by Johnson.A charge-transfer interaction is involved and the basicity of carbazole and derivatives determined. Charge transfer is also involved by quenching of carbazole by halocarbons. The A -isopropylcarbazole-dimethylterephthalate exciplex has been observed in PMMA films.Photoinduced electron-transfer in the p-phenylenediamine-paraquat complex yields the paraquat cation. ... 

The Wittig-type reactions of iminophosphoranes with isocyanates and related compounds have also been extensively used in heterocyclic synthesis. Examples include the preparations of the mesoionic [l,3,4]thiadiazolo[2,3-c][l,2,4]triazines (210) from (209), 0 bicyclic guanidines, e.g. (212), from (211), naphthypyridines (215), (216), and (217) from (213) and (214), 2 pyrido[l,2-f]pyrimido-[4,5-d)pyrimidines (218), 7H-pyrido-[4,3-c]- (219) and 10H-pyrido[3,4-b]- (220) carbazoles, tricyclic fused 2,4-diimino-l,3-diazetidines (222) from the bisiminophosphorane (221), benzotriazepines (225) from (223) and (224), 6 and mesoionic thiazolo-[2,3-b]-1,3,4-thiadiazoles (227) and N,N-bisheteroarylamines from the iminophosphorane (226), derived from 3-amino-4-phenylthiazole-2(3H)-thione. The carbodiimides (229), prepared from the iminophosphorane (228), can be converted into quinolines or a-carboline derivatives depending on the nature of the isocyanate used in the reaction with (228) and the reactions of iminophosphoranes (230) and (231) with aryl and styryl isocyanates provide one-pot syntheses of quinoline, a-carboline, and quinindoline derivatives. 9... 

The Cadogan reaction refers to the deoxygenation of o-nitrostyrenes 1 or o-nitrostilbenes with trialkyl phosphite or trialkylphosphine and subsequent cyclization of the resulting intermediate nitrene 2 to form indoles 3. The reductive cyclization protocol has also been exploited to prepare a variety of A -containing heterocyclic compounds including carbazoles, indazoles, benzimidazole, benzotriazoles, anthranils, phenazines, phenothiazines, quinolines, and related compounds. 

Cadogan himself further extended the scope of the Cadogan reaction. As early as in 1965, he already prepared carbazoles, indoles, indazoles, thiazoles and related compounds. In 1966, he synthesized phenothiazine (21) and anthranil 23, respectively, employing the reductive cyclization of nitrocompounds by triethyl phosphite. ... 

Jackson, G.D.F., and W.H.F. Sasse Synthetical Applications of Activated Metal Catalysts. XXI. The Formation of Carbazole from Aniline and Related Compounds in Presence of Degassed Raney Nickel. Austr. J. Chem. 17, 347 (1964). 

Electrochemical and spectroscopic techniques have been used to study the oxidation of carbazole and 71 of its derivatives.207,208 Positions 3, 6, and 9 of the carbazole nucleus are the most reactive sites, as expected from Hiickel theory. The products isolated are symmetric carbon-carbon (3,3 ) and nitrogen-nitrogen (9,9 ) dimers. Substitution of carbazoles in the 3-, 6-, and 9-positions prevents anodic dimerization at these positions the electrochemical formation of a stable radical-cation is possible.209 The electrochemical oxidation of iminobibenzyl and several related compounds have been investigated in CH3CN-Bu4NC104 and their electrochemistry was compared with that of related carbazoles.210... 

This section highlights the most significant applications of pyrroles, indoles, and carbazoles in the areas covered in CHEC-II(1996) <1996CHEC-II(2)207> and in related fields where substantial advances have been made since 1995. While sections on polymers, dyes, drugs, and medicinal compounds deal with novel applications of both old and new compounds, the survey of natural products has been restricted to those new structures that have been discovered during the past decade. 

The behaviour of poly(N-vinyl carbazole) is certainly complex, and an attanpt has been made recently to gain an insight into the photophysical properties of this polymer by studying the related compounds below. Monomer fluorescence is observed in these compounds... 

Many aromatic systems have been oxidized by Fremy s salt, including phenols, naphthols, anilines, quinolines, indoles, carbazoles, and polyaromatic systems. The review articles by Zimmer and Parker can be consulted for specific examples. Slight modifications of the mechanism presented in Scheme 20 explain the oxidation of most of these classes of compounds [63], Oxidations by Fremy s salt and related nitroxides have been used in the total synthesis of several biologically active compounds [64], Recent examples can be found in the syntheses of the antitumor antibiotic streptonigrone (34), the antitumor agent EO-9 (35), the anti-rheumatic agent epoxyquinomicin B (36), and the antineoplastic agent makaluvamine C (37) (Scheme 21) [65]. 

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