Oxidation indole carbinols

Scheme 7 Oxidation of indole carbinols using the Fe(N03)3-9H20/TEMP0 catalytic system. ...

Indole derivatives with carbonyl units (Scheme 7) have been found in natural products, possess versatile bioactivity and are important intermediates in many organic syntheses. The introduction of the carbonyl moieties to indoles significantly enhances their reactivity and can be achieved by oxidation of indole carbinols with Fe(N03)3-9H20/TEMP0/NaCl at room temperature and atmospheric pressure of dioxygen, using toluene as a solvent. NaCl is an important accelerator for the oxidation, reducing the reaction time from 15 to 2 h however, the role of Cl is not quite clear. 

Indenopyrene, see Indeno[l,2,3-crf pyrene l//-Indole, see Indole Indolene, see Indoline Inexit, see Lindane Inhibisol, see 1,1,1-Trichloroethane Insecticide 497, see Dieldrin Insecticide 4049, see Malathion Insectophene, see a-Endosulfan, p-Endosulfan Intox 8, see Chlordane Inverton 245, see 2,4,5-T lodomethane, see Methyl iodide IP, see Indeno[l,2,3-crf pyrene IP3, see Isoamyl alcohol Ipaner, see 2,4-D IPE, see Isopropyl ether IPH, see Phenol Ipersan, see Trifluralin Iphanon, see Camphor Isceon 11, see Trichlorofluoromethane Isceon 122, see Dichlorodifluoromethane Iscobrome, see Methyl bromide Iscobrome D, see Ethylene dibromide Isoacetophorone, see Isophorone a-Isoamylene, see 3-Methyl-l-butene Isoamyl ethanoate, see Isoamyl acetate Isoamylhydride, see 2-Methylbutane Isoamylol, see Isoamyl alcohol Isobac, see 2,4-Dichlorophenol Isobenzofuran-l,3-dione, see Phthalic anhydride 1,3-Isobenzofurandione, see Phthalic anhydride IsoBuAc, see Isobutyl acetate IsoBuBz, see Isobutylbenzene Isobutane, see 2-Methylpropane Isobutanol, see Isobutyl alcohol Isobutene, see 2-Methylpropene Isobutenyl methyl ketone, see Mesityl oxide Isobutyl carbinol, see Isoamyl alcohol Isobutylene, see 2-Methylpropene Isobutylethylene, see 4-Methyl-l-pentene Isobutyl ketone, see Diisobutyl ketone Isobutyl methyl ketone, see 4-Methyl-2-pentanone Isobutyltrimethylmethane, see 2,2,4-Trimethylpentane Isocumene, see Propylbenzene Isocyanatomethane, see Methyl isocyanate Isocyanic acid, methyl ester, see Methyl isocyanate Isocyanic acid, methylphenylene ester, see 2,4-Toluene-diisocyanate... 

The lithium derivatives of 1-substituted pyrroles and indoles provide another general route of access to 2-acyl pyrroles and indoles. The ketones can be obtained directly by reaction with aryl nitriles or acid halides but, at least for 1-benzenesulfonylindole, a two-step procedure involving reaction with an aldehyde followed by oxidation of the carbinol to the ketone is frequently more convenient (equation 179) (73JOC3324, 75JOC2613). This method is probably the most general route to 2-acylindoles, although many have also been prepared by direct Fischer cyclization (see Section 3.06.3.4.2). 

Bader and Oroshnik (142) hydrogenated a-(3-indolyl)-2-pyridine-methanol in the presence of platinum oxide in alcohol solution containing a considerable excess of acetic acid. They obtained 3.5% of the piperidine carbinol and 51% of 2-skatylpiperidine [2-(3-indolylmethyl)-piperidine] showing that the indole ring remained intact. The same authors (143) showed that 4-skatylpyridine was converted to 4-skatylpiperidine. 

Fused indole 232 resulted from the reaction of a donor-acceptor cyclopropane with an indole bearing a Michael acceptor at C2.The products were obtained in good yield with high diastereoselectivity (16 examples, 64-90% yield) (140L3954). Tetracyclic-fused indole 233 was prepared by a [3+3]-cycloaddition of an indol-2-yl carbinol with an azadiene (11 examples, 42-90% yield). This could be followed by an oxidative ring expansion promoted by (bis(trifluoroacetoxy)iodo)benzene to produce a series of indole azepinones (6 examples, 59-71% yield) (14CC11181). Fused indole 234 was synthesized by the first calcium(II)-promoted Nazarov cyclization (87% yield).The substituent a to the ester functionality could vary electron-rich arenes, heteroarenes, and secondary alkyl... 

The reduction of several indolo[2,3-a]quinolizidines by BY gave novel products resulting from reduction of the indole double bond, cleavage of the C-D ring junction, or reduction of a lactame to a carbinol amine [371]. The known reduction of aromatic nitro compounds has been used as a key step in the synthesis of 2-aryl-2/f-benzotriazoles. Thus, treatment of the o-nitrophenylazo dye 342 gave the 2-aryl-2/7-benzotriazole-l-oxides 343 in good yields [513]. 

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