Abstract
a-Methyl-2,3,3,4a-tetrahydro-1 H-carbazoles 3, obtained from arylhydrazines 1 and 2-methylcy- clohexanone 2, react with diethyl malonate 5a by cyclocondensation to 7-hydroxy-13b-methyl- tetrahydro-pyrano(2',3':4,5)pyrido(3,2,1- jk )carbazolediones 6. With methanetricarboxylates 5b,c , cyclocondensation forms a mixture of pyrano-pyrido-carbazole-carboxylates 7 and pyrido-carbazole- carboxylates 8. Degradation of pyrano-pyrido-carbazolediones 6 by alkaline ring-opening and decarboxylation leads to 5-acetyl derivatives 10 . Deacetylation with sulfuric acid reveals the 5-un sub- stituted 4-hydroxy-11b-methyl-1,2,3,11b-tetrahydro- 6 H-pyrido(3,2,1-jk)carbazol-6-one (9). Pyrido- carbazolone 9 was also obtained in a single step reaction from t etrahydrocarbazole 3a and malonic acid 5d with phosphoryl chloride as catalyst in low yields . Electrophilic halogenation of 9 takes place at position 5 and gives 5-bromo compou nd 15 or 5,5-dihalogenated products 14 , 16 or 17 , depending on the reaction conditions. Nitration t akes also place in an electrophilic reaction to give 4-hydrox y-5-nitro-pyrido-carbazolone 20 . Nucleophilic exchange of the 4-hydroxy group in pyridocarbazolones 9 and 20 by reaction with phosphoryl chloride gives reactive 4-chloro intermediates 18 and 21 , which react with sodium azide to 4-azido derivati ves 19 and 22 . 4-Azido-5-nitro-pyrido-carbazolone 22 with the reactive ortho-nitro group in the neighborship of the azido group cyclizes thermolyti cally to furoxane 23 . This reaction was studied by differential scanning calorimetry (DSC).
Highlights
4a-Methyl-2,3,3,4a-tetrahydro-1H-carbazoles 3, obtained from arylhydrazines 1 and 2-methylcyclohexanone 2, react with diethyl malonate 5a by cyclocondensation to 7-hydroxy-13b-methyltetrahydro-pyrano[2',3':4,5]pyrido[3,2,1-jk]carbazolediones 6
Nucleophilic exchange of the 4-hydroxy group in pyridocarbazolones 9 and 20 by reaction with phosphoryl chloride gives reactive 4-chloro intermediates and 21, which react with sodium azide to 4-azido derivatives and 22. 4-Azido-5-nitro-pyrido-carbazolone with the reactive ortho-nitro group in the neighborship of the azido group cyclizes thermolytically to furoxane
The synthesis of the tetrahydro-pyridocarbazole system started from 2,3,4,4a-tetrahydro-1H-carbazoles 3, obtained from phenylhydrazines 1 and 2-methylcyclohexanone (2) via a Fischer indole synthesis, 1a and 2 give a mixture of two isomers, 4a-methyl-2,3,4,4a-tetrahydro-1H-carbazole (3a) and 1-methyl-2,3,4,9-tetrahydro-1H-carbazole (4a) [12] which are easy to separate according to their chemical properties [13]
Summary
Tetrahydropyrido[3,2,1-jk]carbazol-6-one (colored partial structure in A) is R part of the heterocyclic skeleton of many natural products, e. g. The formation of tetrahydropyrido[3,2,1-jk]carbazol-6-ones 9 was investigated by building up the 4-hydroxy-2-pyridone part from tetrahydrocarbazoles 3 as enamine part, and malonate 5a as C-3 source, via a 3-step reaction sequence which has attracted our attention in similar ring systems for many years [10, 11]. In this reaction way, the formation of a pyrono-pyridocarbazole ring system takes place, followed by the stepwise degradation to the pyrido-carbazole ring system
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