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124. 5-Unsubstituted Pyrido[3,2,1-jk]carbazol-6-ones: Syntheses, Substitution and Cyclization Reactions
Stadlbauer W., Dang V.H., Guttenberger, N.,
in J. Heterocyclic Chem. 52 (2015), 114-123

The synthesis of the 5-unsubstituted pyrido[3,2,1-jk]carbazol-6-one 4 can be achieved by the reaction of carbazole (1) and malonate derivatives, either in a 3-step synthesis via 5-acetyl-pyridocarbazolone 3 or in a 1-step reaction from 1 and malonic acid/phosphoryl chloride. The 5-acetyl derivative 5 can be transformed via a tosylate intermediate to 4-azido-pyridocarbazolone 11, which cyclizes by thermal decomposition to the isoxazolo-pyrido[3,2,1-jk]carbazolone . The thermolysis conditions were investigated by differential scanning calorimetry (DSC). Nitration of pyridocarbazolone 4 and subsequent introduction of azide leads to azido derivative 23, which cyclizes on thermolysis to furazan-oxide derivative 24. Again the thermolysis conditions were investigated by DSC. 5-Chloro-5-nitro-pyrido[3,2,1-jk]carbazole-4,6-dione, obtained from 4 by subsequent nitration and chlorination, forms by exchange of both 5-substituents 5,5-dihydroxy-pyridocarbazoledione 17, which acylates phenol to give 5-hydroxy-5-(p-hydroxyphenyl)-pyridocarbazoledione 20. Acid catalyzed cyclodehydratation of 20 forms a highly fused benzofuro-pyridocarbazole 21. Another C-C-coupling at position 5 starts from 4-chloro-5-nitro-pyridocarbazolone 22 and diethyl malonate 2a, which forms the diethyl (nitrocarbazolyl)malonate 25. With dimethyl malonate 2c, the intermediate dimethyl (nitrocarbazolyl)malonate gives on thermolysis the (nitrocarbazolyl)acetate 27 by loss of one ester group.

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