Indoles nitrosation

The nitrosation of pyrroles and indoles is not a simple process. The 3-nitroso derivatives (84) obtained from indoles exist largely in oximino forms (85) (80IJC(B)767). Nitrosation of pyrrole or alkylpyrroles may result in ring opening or oxidation of the ring and removal of the alkyl groups. This is illustrated by the formation of the maleimide (86) from 2,3,4 -trime thylpyrrole. 

Jap-KIingermarm reactions, 4, 301 oxidation, 4, 299 reactions, 4, 299 synthesis, 4, 362 tautomerism, 4, 38, 200 Indole, 5-amino-synthesis, 4, 341 Indole, C-amino-oxidation, 4, 299 tautomerism, 4, 298 Indole, 3-(2-aminobutyl)-as antidepressant, 4, 371 Indole, (2-aminoethyl)-synthesis, 4, 278 Indole, 3-(2-aminoethyl)-synthesis, 4, 337 Indole, aminomethyl-reactions, 4, 71 Indole, 4-aminomethyl-synthesis, 4, 150 Indole, (aminovinyl)-synthesis, 4, 286 Indole, 1-aroyl-oxidation, 4, 57 oxidative dimerization catalysis by Pd(II) salts, 4, 252 Indole, 1-aroyloxy-rearrangement, 4, 244 Indole, 2-aryl-nitration, 4, 211 nitrosation, 4, 210 synthesis, 4, 324 Indole, 3-(arylazo)-rearrangement, 4, 301 Indole, 3-(arylthio)-synthesis, 4, 368 Indole, 3-azophenyl-nitration, 4, 49 Indole, 1-benzenesulfonyl-by lithiation, 4, 238 Indole, 1-benzoyl photosensitized reactions with methyl acrylate, 4, 268 Indole, 3-benzoyl-l,2-dimethyl-reactions... 

Nitroso derivatives (120) are obtained from indoles they exist largely in oximino forms (121) (80IJC(B)767). The N-nitrosation of 5-chloroindole is followed by a migration of the nitroso group from N to C-3, to give an indolenine-3-oxime (122) hydrolysis and recyclization leads to a indazole carbaldehyde (123) (86JA4115). 

Owing to the susceptibility of indole, isoindole and pyrrole rings to oxidation (see Section 3.05.1.4) and acid-catalyzed dimerization and polymerization (see Section 3.05.1.2.2), the products of the reactions with nitrating and nitrosating agents are subject to the reaction conditions. 

Upon reaction with nitrous acid, indole produces a complex mixture of products. In addition to 3-oximino-3H -indole (16), which is the stable tautomeric form of 3-nitrosoindole (17), dimeric products of the type (18) and (19) are also formed. In contrast, (16) appears to be the sole product of the nitrosation of indole with amyl nitrite and sodium ethoxide (72HC(25-2)537). Studies of the nitrosation of pyrrole are somewhat indecisive. The mononitrosopyrrole, obtained from the reaction of pyrrole with nitrous acid, has not been fully characterized, but there is some evidence that nitrosation of pyrrole with amyl nitrite and sodium ethoxide leads to the sodium salt of the 3-nitroso derivative. However, upon the addition of acid, the product rearranges to give the oxime of 3-formylisoxazole (20) (B-77MI30502). 

The hydrazine 89 is made from the amine by nitrosation and reduction and the keto-acid 90 is available as levulinic acid. Now comes the big question when the Fischer indole synthesis is carried out on the hydrazone 91 which enamine is formed, the one we want 92, or the one we don t want 93 Since the Fischer indole is an acid- (or Lewis acid-) catalysed reaction we expect the more substituted enamine 92 to be favoured. 

The mechanism of melatonin s interaction with reactive species probably involves donation of an electron to form the melatoninyl cation radical or through a radical addition at the site C3. Other possibilities include hydrogen donation from the nitrogen atom or substitution at position C2, C4, and C7 and nitrosation [169]. The mechanisms by which melatonin protects against LP most likely involve direct or indirect antioxidant and free-radical scavenging activities of this indoleamine [169,171]. 2-Phenyl indole derivatives have redox properties because of the presence of an electron-rich aromatic ring system that allows the indoleamine to easily function as an electron donor. For these derivatives, the possible antioxidant mechanism might be most probably toward carbon-centered radicals described by Antosiewicz et al. [172]. 

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