Indoles and Related Compounds

Indoles are commonly found in alkaloid natural products and pharmaceutical agents. Thus, tremendous efforts in the catalytic C-H functionalization reaction 

Transition Metal-Catalyzed Heterocycle Synthesis via C—H Activation, First Edition. Edited by Xiao-Feng Wu. 2016 Wiley-VCH Verlag GmbH Co. KGaA. Published 2016 by Wiley-VCH Verlag GmbH Co. KGaA. 

3- dihydroindole, 2-methylindole (eq. 12.7), 2-methyl-2,3-dihydroindole, 3-ethylindole, and 3-ethyl-2,3-dihydroindole were all completely hydrogenated to the corresponding octahydroindoles over Raney Ni in dioxane at 220-250°C and 25-30 MPa H2. With 

3- dimethylindole, however, an unidentified product was obtained under these conditions. 

With Raney Ni in ethanol the hydrogenation of indole to 2,3-dihydroindole occurs quantitatively at 100-110°C and a maximum pressure of 9-10 MPa H2, and further hydrogenation at 150-160°C gives 1-ethyloctahydroindole quantitatively. Similarly, 

Teuber and Schmitt hydrogenated 5-methoxyindole over ruthenium dioxide in 90% ethanol at elevated temperature and pressure and obtained the corresponding octahy-droindole in a 79% yield (eq. 12.9).11 The hydrogenation was difficult to complete with platinum or rhodium-platinum as catalyst in acetic acid. 

Carbazole is hydrogenated to give dodecahydrocarbazole as the sole isolable product with Raney Ni in dioxane in 7 h at 230°C or in 1 h at 260°C under 25-30 MPa H2 in 83 and 87% yields, respectively.9 Similarly, 9-methyl- and 9-ethyldodecahydrocar-bazoles were obtained in 85 and 80% yields from the corresponding carbazoles in hydrogenation at 230°C and 200°C, respectively. Carbazole was also hydrogenated to dodecahydrocarbazole in 82% yield over copper-chromium oxide in dioxane at 230°C and 25-30 MPa H2 in 15 h. 

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Because the nucleophiles can be introduced at the orr/io-posidon of the nitro group, various heterocycles can be prepared via VNS and related reacdons. Indoles and related compounds are prepared via the VNS reacdon and subsequent cyclizadon. The VNS reaction of nitroarenes followed by cyclizadon v/ithEt- N-Me SiCl gives 1-hydroxyindoles fEq. 9.53. Cyclizadon is Mso catrilyzed on treatment v/ith bases, in which nitroso intermediates are postidated. 

Molecular orbital calculations" and nuclear magnetic resonance studies " revealed that C-2 in indole and related compounds," the phenyl... 

The reduction of the indolinones 209 with NBH in methanol leads readily to the indoles 210 in 56-96% yield. Intermediacy of the corresponding alcohols has been proposed." The reduction of indoles and related compounds has been the subject of a previous review." Oxindoles (211) are reduced with LAH to indoles (212) but in low yields. Small amounts of the indolines 213 are also obtained. Dimerization on hydride reduction has also been recorded." ... 

Rearrangement reactions of indoles and related compounds 04YZ481. 

Suzuki. H., Iwata, C., Sakurai, K., Tokumoto. K.. Takahashi, H., Hanada, M., Yokoyama. Y. and Murakami, Y, Synthetic studies on indoles and related compounds. Part 41. A general synthetic route for 1-substituted 4-oxygenated P-carbolines, Tetrahedron, 53, 1593, 1997. 

Fluorinated Indolizines, Indolizidines, Indoles, and Related Compounds... 

Osanai, K., Yokoyama, Y, Kondo, K. andMurakami, Y. (1999) Total s3mthesis of optically active costaclavine (s5mthetic studies of indoles and related compounds part 48). Chem. Pharm. Bull., 47, 1587-90. 

Thiophen Analogues of Indole and Related Compounds.—5/f-Thieno[2,3-c]-pyrroles (528) have been prepared by dehydration of iV-oxides, autooxidation of the dihydrothieno[2,3-c]pyrroles, and by dehydrogenation of... 

Planar Chiral xf-Arene-Cr(CO) Complexes Al-Aryl indoles and related compounds having a chiral C—N bond have received recent attention as novel atropisomeric intermediates for asymmetric synthesis [10, 48]. Al-Aryl indoles 59,60 can be prepared by stereoselective... 

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