3-Formyl-7-hydroxycarbazole

In 1992, Furukawa et al. reported the isolation of 3-formyl-7-hydroxycarbazole (99) from the root bark of M. euchrestifolia (104). The UV spectrum [2max 233,245 (sh), 273, 288, and 326 nm] and the IR spectrum (v ax 1673 and 3336 cm ) of 3-formyl-7-hydroxycarbazole were very similar to those of clauszoline-K (98), indicating a 3-formylcarbazole framework. The H-NMR spectrum confirmed the structural similarity to clauszoline-K, and showed the presence of a hydroxy group instead of the methoxy group. All of the spectroscopic data supported the structure of 3-formyl-7-hydroxycarbazole (99) (Scheme 2.19). 

The relay compound 1025 required for the synthesis of all of these 7-oxygenated carbazole alkaloids was obtained starting from commercially available 4-bromo-toluene (1023) and m-anisidine (840) in two steps and 72% overall yield. Buchwald-Hartwig amination of 4-bromotoluene (1023) with m-anisidine (840) furnished quantitatively the corresponding diarylamine 1024. Oxidative cyclization of 1024 using catalytic amounts of palladium(ll) acetate afforded 3-methyl-7-methoxycarbazole (1025). Oxidation of 1025 with DDQ led to clauszoline-K (98), which, on cleavage of the methyl ether using boron tribromide, afforded 3-formyl-7-hydroxycarbazole (99) (546) (Scheme 5.149). 

A series of 7-oxygenated carbazole alkaloids has been synthesized by us for the first time, including clauszoline-K (117), 3-formyl-7-hydroxycarbazole (119), clau-sine M (120), clausine N (121), and siamenol (124) [148]. Clauszoline-K (117) and clauszoline-L (118) have been isolated by Ito et al. from the stem bark of C. excavata [115]. Wu and co-workers had isolated the same compound 118 one year earlier from the same source and named it clausine C (118) [158]. 3-Formyl-7-hydroxycarbazole (119) was obtained from the root bark of Murraya euchrestifolia [159]. Clausine M (120) and clausine N (121) were isolated from the root bark of C. excavata by Wu et al. [116]. Siamenol (124) was isolated from an extract of M. siamensis and proved to have anti-HIV activity [160]. 

The UV spectrum (7max 225,242,253,276,289, and 351 nm) of clausine D (29) was similar to that of O-demethylmurrayanine (24), which also represents a 3-formyl-l-hydroxycarbazole framework. The presence of a hydroxy group and a conjugated aldehyde group was further supported by strong absorptions at 3380 and 1655 cm in the IR spectrum. The H-NMR spectrum was very similar to that of O-demethylmurrayanine, except for the presence of a prenyl group ( 1.65,... 

Carbazole can be efficiently tetra-ferf-butylated with tcrt-butylchloride and aluminium chloride at room temperature giving 141 K. 4i,85. traces of 3,6-di- and 1,3,6-tri-tert-butylcarbazoles are also produced. 3-Formyl-2-hydroxycarbazole is alkylated at C-1 with dimethylallyl chloride in the presence of 30% aqueous potassium hydroxide. ... 

The products of the base-catalyzed Stobbe condensation of 3-formylindole and of 2-formylpyrroles undergo acid-catalyzed cyclization to yield l-hydroxycarbazole-3-carboxylic esters and 4-hydroxyindole-6-carboxylic esters, respectively (73JPR295, 74JPR386, 76JPR816). The analogous condensation of dimethyl homophthalate with 2-formyl-1-methylpyrrole and with 3-formylindole produces (443 Hetero = l-methyl-2-pyrrolyl, 3-indolyl), (444) and (445) under acidic conditions (76JHC83). 

Heptaphylline (1) has been synthesised by sequential C(3)-formylation and C(l)-isopentenylation of 2-hydroxycarbazole. l-Formyl-2-hydroxy-3-methyl-carbazole reacts with the Wittig reagent from 2-methylprop-l-en-3-yltriphenyl-phosphonium chloride-sodium hydroxide to generate girinimbine (2a) 2-hydroxy-3-methylcarbazole reacts with citral to give ( )-mahanimbine (3a). 

Formyl-2-hydroxycarbazole, see H-20108 9-Formyl-7-hydroxy-3,8-dimethyl-1 -oxo-5a,6-(2,2-dimethylpropano)-8,9-methano-5 3f,6,7,8,9-pentahydro-2,5-dioxaanthracene, see H-20057... 

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