Pyrano carbazoles

Reviews have been published on Rhazyal and indoline Vinca alkaloids, and a book d has been devoted to the chemistry, botany, folklore, and biological activities associated with Vinca species. A table surveys all the Rutaceae species so far studied and lists the alkaloids obtained therefrom canthinone, euxylo-phorine, and pyrano-carbazoles of the murrayacine-mahanimbine series have been obtained from this family. 

Pyrano[3,4-b]indol-3-ones are the most useful equivalents of the indol-2,3-quinodimethane synthon which are currently available for synthetic application. These compounds can be synthesized readily from indole-3-acetic acids and carboxylic anhydrides[5,6]. On heating with electrophilic alkenes or alkynes, adducts are formed which undergo decarboxylation to 1,2-dihydro-carbazoles or carbazoles, respectively. 

Pyrano[3,2-g]benzoxazine, dihydrosynthesis, 3, 714 Pyranobenzoxazines synthesis, 6, 190 Pyranobenzoxazoles mass spectra, 3, 615 Pyrano[2,3-a]carbazoles synthesis, 4, 235 Pyrano[2,3- 6]carbazoles synthesis, 4, 235 Pyrano[3,2-a]carbazoles synthesis, 4, 235 Pyranochromones synthesis, 3, 821 Pyranochromones, dihydrosynthesis, 3, 81 817 Pyranocoumarins crystal data, 3, 623 mass spectra, 3, 610 Pyranodipyranones synthesis, 3, 794 Pyrano[3,2-6]indol-4-ones synthesis, 4, 302 Pyran-2-ol, dihydrodehydration, 3, 762 Pyran-2-ol, 3-methyltetrahydro-synthesis, 3, 775 Pyran-2-ol, tetrahydro-6-substituted synthesis, 3, 775 Pyran-4-ol, tetrahydro-IR spectra, 3, 594 Raman spectra, 3, 594 Pyranols, tetrahydro-bond lengths, 3, 621 synthesis, 3, 777... 

The molybdenum-mediated arylamine cyclization was also applied to the total synthesis of pyrano[3,2-a]carbazole alkaloids (Scheme 26). Reaction of the 5-aminochromene 71 with the complex salt 62 affords the complex 72, which on oxidative cyclization provides girinimbine 73, a key compound for the transformation into further pyrano[3,2-a] carbazole alkaloids. Oxidation of 73 with DDQ leads to murrayacine 74, while epoxidation of 73 using meta-chloro-perbenzoic acid (MCPBA) followed by hydrolysis provides dihydroxygirinim-bine75 [113]. 

In 1964, Chakraborty et al. isolated girinimbine (115) from the stem bark of M. koenigii (108). Girinimbine represented the first pyrano[3,2-a]carbazole alkaloid isolated from natural sources. Later, Joshi et al. isolated the same alkaloid from the roots of a different source, C. heptaphylla (91). Based on chemical degradation studies. 

In 1996, Ito et al. reported the isolation of clauszoline-A (167) and clauszoline-B (168) from the acetone extract of the stem bark of C. excavata collected in Singapore (74). These alkaloids represented the first, naturally occurring 2,8-dioxygenated-3-formylcarbazole alkaloids with a dimethylpyran ring fused to C-7 and C-8 of the carbazole nucleus. The extracts of the leaves and bark of this tree have been used in traditional medicine for the treatment of snakebites and abdominal pain (74). One year later, the same group isolated another pyrano[2,3-fl]carbazole alkaloid, clauszoline-H (169), from the roots of the same natural source in Japan (47) (Scheme 2.34). 

In 1991, Furukawa et al. reported the isolation of pyrayafoline B (170) from the stem bark of M. euchrestifolia collected in May in Taiwan (87). In the same year, the same group isolated a further pyrano[2,3- ]carbazole alkaloid, pyrayafoline E (171), from the stem bark of M. euchrestifolia. Pyrayafoline E was isolated from Nature in racemic form (70). These alkaloids are the first members of the naturally occurring 2,7-dioxygenated-3-methylcarbazole alkaloids having a dimethyl pyran ring fused to C-6 and C-7 of the carbazole nucleus (70,87) (Scheme 2.35). 

Recently, Tripathi et al. reported a new pyrano[3,2-a]carbazole alkaloid, 7-isovaleryl-oxy-8-methoxygirinimbine (1569) from the leaves of Murraya koenigii (896) (Scheme 6.2). 

HydroxycarbazoIes react with citral to form either pyrano[3,2-a]carbazoles (132) or pyrano[2,3]carbazoles (133), whilst 1-hydroxycarbazoles produce pyrano[2,3-a]-carbazoles (81SC823, 81H(16)1445). Other cyclization reactions involving substituted pyrroles or indoles and aldehydes or ketones in which the substituent becomes part of the new ring system are discussed under the relevant sections relating to the reactivity of the substituent. 

Cycloalka[o]carbazoles have been prepared by the IMDA reaction of l-(w-alkynyl)pyrano[3,4-h]indol-3-ones with subsequent cycloelimination of carbon dioxide30. 

In a similar manner, the TV -methylated pyrano[2,3-6]carbazoles 28 and the [3,2-6] analogues 29 exhibit photochromism at room temperature. The single absorption band shown by the [2,3-6] series is red shifted with respect to naphtho[2,l-6]pyran and the intensity is also greater. The colourability is particularly enhanced by the introduction of a 2-thienyl group at the 8-position. Again, faster fading characteristics are observed relative to the parent diphenyl substituted naphthopyrans <01HCA1163>. 

The alkaloid, acronycine, a pyrano[2,3-c]acridine (Table 12.1, ref.58), and the carbazole alkaloids (ref.81) contain cyclic systems derived from 2-hydroxy... 

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