Indoles amino-, tautomerism

Indole, 1-amino-reactivity, 4, 297 synthesis, 4, 361 Indole, 2-amino-oxidation, 4, 299 tautomerism, 4, 38, 74, 200 Indole, 3-amino-... 

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... 

Finally, indole ring formation is via condensation of the amino and keto functions. This is analogous to imine formation, as seen in part (a), but dehydration produces the aromatic pyrrole ring rather than an imine. Alternatively, one could write imine formation followed by tautomerism to the aromatic enamine. 

C-Aminoindoles autoxidize extremely rapidly. Consequently, comparatively few chemical reactions have been examined. The 2-amino derivative exists in the 3H-indole tautomeric form (473) and is protonated and alkylated on the annular nitrogen atom (72HC(25-2)179). The 1-methyl derivative (474) exits predominantly as such and not as the alternative 2-imino-3//-indole tautomer and is protonated at the 3-position to give a cation having the same electronic structure as that of the protonated (473). Acylation of (473) yields l-acetyl-2-acetylaminoindole, via the initial acylation of the annular nitrogen atom. Confirmation of this route has been established by the observation that 2-acetylaminoindole, obtained by hydrolysis of the diacetylated compound, is acetylated under identical conditions... 

Enamines derived from thiopyran-3-one, although tautomeric, tend to exist predominantly in conjugation with the sulfur atom the Fischer indole reaction, when applied to that ketone, affords solely the systems fused 2,3 on to the thiopyran (Scheme 10) (76CL5). 4-Amino-3,4-dihydro-2Ff-thiopyrans readily eliminate ammonia or amines on heating or treatment with acid, with formation of 2H- thiopyrans <78CR(C)(286)553). 

The substitution reaction may occur on a prototropic nonaromatic form. Both types of tautomerism, i.e., that prevailing in the parent heterocycles (pyrrole-pyrrolenine, indole-indolenine) and that typical of the hydroxy and amino derivatives, must be considered. 

Replacement of the amino group in the Mannich base is also applied to alkaloid synthesis. Thus, ellipticinc alkaloids are prepared by deamination of the intermediate indole Mannich base 457 (Fig. 174), which allows ring closure to the hcxa-atomic cycle evolving. subsequently toward the phenolic moiety (458) through the occurrence of tautomeric equilibria. 

The secondary amino group of the indole ring in tryptophan has a low field shift (293 ppm), probably because of rapid tautomerism with the C = N indolenine form, in which the nitrogen has a 7i-bonded structure. However, the equilibrium favours the indole form, the deshielding contribution from the ru-electrons in the indolenine form is, therefore, small, moving the chemical shift of the indole nitrogen atom in tryptophan to much higher field than in imidazole, but to lower field than in the saturated counterpart, proline. 

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