Indoles pyrolysis

A stepwise process, via hydrogen migration tautomers arriving at the same products, has been shown by density-functional theory to be responsible for the observed products of indole pyrolysis. 3-Phenyl-3-nitrosoindole, on activation with benzoyl chloride, has been found to react with indoles and indolizines (as nucleophiles) to afford products of 1,2-addition which can undergo a 1,3-nucleophilic migration in... 

Flash vacuum pyrolysis of 2-methoxycarbonylpyrrole (11) gives the ketene (12), characterized by IR absorption at 2110 cm. On warming to -100 to -90 °C the dimer (13) is formed (82CC360). Flash vacuum pyrolysis of indole-2-carboxylic acid (14) results in loss of water and the formation of a ketene (15) showing absorption at 2106 cm (82CC360). 

The 1-azirines obtained from the vapor phase pyrolysis of 4,5-disubstituted 1-phthalimido-1,2,3-triazoles (157) have been found to undergo further thermal reactions (71CC1S18). Those azirines which contain a methyl group in the 2-position of the ring are cleaved to nitriles and phthalimidocarbenes, whereas those azirines which possess a phenyl substituent in the 2-position rearrange to indoles. 

Beckmann rearrangement, 4, 292 pyrolysis, 4, 202 synthesis, 4, 223 Wittig reaction, 4, 294 Wolff-Kishner reduction, 4, 291 Indole, 1-acyl-2,3-disubstituted photoisomerization, 4, 204 photo-Fries rearrangement, 4, 204 photoisomerization, 4, 42 synthesis, 4, 82 Indole, 2-acyl acidity, 4, 297 synthesis, 4, 337, 360 Indole, 3-acyl-acidity, 4, 297 cleavage, 4, 289 reduction, 4, 289 synthesis, 4, 360 Indole, 7-acyl-synthesis, 4, 246... 

This structure rationalizes (a) the formation of mono- and, under more vigorous conditions, tetra-acetyl derivatives, (b) the methyla-tion to a dimethyl derivative still containing two active hydrogens, (c) the pyrolysis back to monomeric indole, (d) the formation of a benzylidene derivative containing the Ph CH=N— Ar ehromophore, (e) the failure to form a simple nitroso derivative, (f) the Zn/AcOH reduction of the dimethyl trimer to base C18H20N2, shown to be identical with the dihydro derivative of (26). 

Goodacre, R. Kell, D. B. Rapid and quantitative analysis of bioprocesses using pyrolysis mass spectrometry and neural networks—Application to indole production. Anal. Chim. Acta 1993, 279,17-26. 

The use of flash vacuum pyrolysis of 3-hydroxypyridine-2-carboxylic acid 348 to obtain the symmetrical dipyr-rolo[ 1, 2-a 1, 2 - ]pyrazinc-5,10-dione 352 is noteworthy <2002TL5285> and has been used to generate the corresponding indole-containing diketopiperazine <20030BC2168> (Scheme 26). 

Figure 11.11 Pyrogram of a paint sample collected from a decorative frame of the Universal Judgement by Bonamico Buffalmacco (fourteenth century, Monumental Cemetery of Pisa, Italy). Pyrolysis was performed with a microfurnace pyrolyser, at 600°C, in the presence of HMDS. 1, Benzene 2, ethyl acrylate 3, methyl methacrylate 4, acetic acid, trimethyl silyl ester 5, pyrrole 6, toluene 7, 2 methylpyrrole 8, 3 methylpyrrole 9, crotonic acid 10, ben zaldehyde 11, phenol 12, 2 methylphenol 13, 4 methylphenol 14, 2,4 dimethyl phenol 15, benzyl nitrile 16, 3 phenylpropionitrile 17, indole 18, phthalate 19, phthalate 20, ben zyl benzoate HMDS pyrolysis products [27]...

Internal nitrenes normally react at the adjacent position. Reduction of 2-(2-nitrophenyl)furan by ethyl phosphite yields furoindole derivatives in fair yield (34%) only, whereas much better results attend the pyrolysis of 2-(2-azidophenyl)furan.280 Furopyrazoles are obtained similarly.281 Azidofurans yield nitrenes that insert into adjacent CH links to form furo-pyrroles.282 Quite different results attend either the pyrolysis or the photolysis of azide 107a for the expected insertion into the side chain occurs giving the related indole but it is accompanied by the surprising replacement of furan oxygen by nitrogen producing 107b and similar products.283... 

Interestingly, the Fischer indole synthesis does not easily proceed from acetaldehyde to afford indole. Usually, indole-2-carboxylic acid is prepared from phenylhydrazine with a pyruvate ester followed by hydrolysis. Traditional methods for decarboxylation of indole-2-carboxylic acid to form indole are not environmentally benign. They include pyrolysis or heating with copper-bronze powder, copper(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. 

The next three procedures provide useful synthetic intermediates. A stereospecific synthesis of ETHYL (Z)-3-BROMO-2-PROPENOATE affords an alternative vinyl bromide partner for the coupling chemistry in the preceding procedure. A very simple but elegant illustration of the flash vacuum pyrolysis technique is used to prepare BENZOCYCLOBUTENONE from o-toluoyl chloride. Another member of the functionalized indole family of synthetic intermediates is presented in a four-step procedure for 5-METHOXYINDOLE-2-ACETIC ACID METHYL ESTER. 

In a subsequent study, Schnitzer and Spiteller [15] hydrolyzed each fraction with 2 M H2S04. After neutralization of the soluble materials, the latter were reduced with NaBH4 and then acetylated. The resulting acetates were analyzed by capillary gas chromatography/mass spectrometry, and identified by comparing their mass spectra with those of reference compounds of known structures and with literature data. Eighteen N-heterocyclics were identified. These compounds induded hydroxy-and oxy-indoles, quinolines, isoquinolines, aminobenzofurans, piperidines, pyrro-lines, and pyrrolidines. In addition, a number of benzylamines and nitriles were also identified. It is noteworthy that the N heterocyclics were isolated and identified without the use of pyrolysis. 

Schulten et al. [16] identified the following N-containing compounds in NH-N fractions separated from several soils by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) pyrrole (la), methyl pyrrole (lb), pyridine (IVa), methylpyridine (IVb), indole (Via), and benzothiazole (XI). The Roman numerals refer to the chem-... 

Vinylbenzotriazoles give indoles on flash pyrolysis at 600°C/10 2 Torr. However, depending on the vinyl substituents, side reactions leading to A-phenylketenimines or benzonitrile are also observed... 

Condensation of formyl-pyrroles and -indoles with a wide range of other activated methylene compounds has been reported. These include, for example, hydantoin, which provides a useful synthetic route to tryptophane and j8- (pyrrolyl)alanines, thiohydantoin, rhodanine and AT-substituted barbituric acids (B-77MI30505, 79HC(25-3)357). Flash pyrolysis of the condensation product derived from 3-formyl-2,5-dimethylpyrrole with Meldrum s acid produces 6-hydroxy-2-methylindole, (440) — (441) (74AJC2605), whilst the analogous... 

Benzo[6]thiophene is best stored in amber-colored bottles or tin cans in the presence of certain acid catalysts it polymerizes.397 On pyrolysis (see also Section V,C) it undergoes self-condensation less readily than indole.398 On exposure to daylight or mercury vapor lamp... 

Pyrolysis of CH4 and NH3 gives very low yields of amino acids. The pyrolysis conditions are from 800° to 1200°C with contact times of a second or less. However, the pyrolysis of CH4 and other hydrocarbons gives good yields of benzene, phenylacetylene, and many other hydrocarbons. It can be shown that phenylacetylene would be converted to phenylalanine and tyrosine in the primitive ocean.17 Pyrolysis of the hydrocarbons in the presence of NH3 gives substantial yields of indole, which can be converted to tryptophan in the primitive ocean. 

---