Carbazole-5,7 -dione

Folyphosphoric acid trimethylsilyl ester (PPSE)[1] can be used in sulfolane, CH,Cl2 or nitromethane. It is similar to polyphosphoric acid but the overall conditions arc milder and the work-up more convenient. PPSE has been used in the cydization of ris-arylhydrazones of cyclohexane-l,2-diones to give indolo[2,3-a]carbazole analogues[2],... 

The parent indolo[2,3-fl]carbazole (1) has also been the subject of a study probing its reactivity toward oxidizing agents. One of the substrates involved, namely 85 (prepared from 1 and 2,5-dimethoxytetrahydrofuran in the presence of acid), was subjected to treatment with m-chloroperbenzoic acid, to give the dione 86 as the major product and a sensitive compound assigned the hydroxy structure 87. A cleaner reaction took place when 85 underwent oxidation with tert-butyl hydroperoxide assisted by VO(acac)2, to produce 86 exclusively in 86% yield. Likewise, A,N -dimethylindolo[2,3-fl]carbazole furnished the dione 88 on treatment with this combination of reagents (96J(X 413). 

Bouaziz Z., Nebois P., Poumaroux A., Pillion H. Carbazole-l,4-Diones Syntheses and Properties Heterocycles 2000 52 977-1000... 

The UV spectrum [7max 238, 256 (sh), 293 (sh), 314, 362 (sh), and 390 (sh) nm] of rebeccamycin (337) indicated the presence of an indolo[2,3-fl]pyrrolo[3,4-c]carbazole-5,7(6H)-dione framework. This was also discernible from its IR spectrum. The H-NMR spectrum indicated the presence of an amide NH at 8 11.37 and an indole NH at 6 10.30, in addition to signals for aromatic protons and a sugar moiety. Unlike (+)-staurosporine (295) (see Scheme 2.74), where the lactam function deshielded only the ortho C-4 proton, the C-4 and C-8 aromatic protons in rebeccamycin are both deshielded due to the anisotropic deshielding effect of the phthalimide function. 

Combes synthesis with pentan-2,4-dione that led to 157, was ascribed to unfavorable steric hindrance in the alternative orientation in the Combes synthesis. 2-Amino-l,4-dimethylcarbazole underwent the Skraup reaction in the only orientation available to it. Finally, the carbazol-1-yIhydrazone of ethyl pyruvate underwent normal Fischer indolization giving 158 its 3-isomer gave an indole by cyclization at C-4 producing 159. ... 

Pyrrole and hexane-2,5-dione in acetic acid in the presence of zinc acetate produced some 1,4,5,9-tetramethyl carbazole, although the main product was 371. ... 

The result was confirmed by a second synthesis. The dimethylated C ring was built onto indole by condensation of hexane-2,5-dione with the reactive indolic 2,3 positions. Formylation of the resulting 1,4-dimethyl-carbazole (CCLXXXVIII) with X-methylformanilide proceeded preferentially in the 3-position to give the aldehyde CCLXXXIX whose... 

Scheme 15.16 Palladium(ll)-catalyzed oxidative cyclization to 4-methoxy-2-methyl-5H-benzo[fo]carbazole-6,l 1-dione.

Recovered starting material (N-[2-methoxy-4-methylphenyl]-2-amino-l,4-naphthoquinone). Isolated yield of 4-methoxy-2-methyl-5H-benzo[l)]carbazole-6,ll-dione. 

R = H R = OMe) were obtained from the corresponding hydrazones in the former case the main product of the reaction was 1,2,3,4-tetrahydro-carbazol-l-one. Better yields were reported for the cyclization of 32 (R = Me R = H) and for the cyclohexane-1,2-dione mononaphthylhydra-zones, " the products from the last two being dehydrogenated to the fully aromatic naphtho[c] cinnolines. 

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