Indole conversion

In our previous indole oxidation experiments, H202 has been added continuously with a flow rate of 10 pmol min 1 to a buffered indole solution in a batch reactor. In this case a constant maximum conversion at pH values between 3.0 and 8.0 was observed, whereas the indole conversion of the tandem system is limited by the H202 formation rate. At pH... 

Indene, 6,7-dimethoxy-3-methyl-2-CARBETHOXY-, 40, 43 Indene, 44, 63 hydroxylation of, 41, 53 Indole, conversion to indole-3-acetic acid, 44, 64... 

These compounds can be malodorous as in the case of quinoline, or they can have a plecisant odor as does indole. They decompose on heating to give organic bases or ammonia that reduce the acidity of refining catalysts in conversion units such as reformers or crackers, and initiate gum formation in distillates (kerosene, gas oil). 

Dimethylaminomethylindole (gramine). Cool 42 5 ml. of aqueous methylamine solution (5 2N ca. 25 per cent, w/v) contained in an 100 ml. flask in an ice bath, add 30 g. of cold acetic acid, followed by 17 -2 g. of cold, 37 per cent, aqueous formaldehyde solution. Pour the solution on to 23 -4 g. of indole use 10 ml. of water to rinse out the flask. Allow the mixture to warm up to room temperature, with occasional shaking as the indole dissolves. Keep the solution at 30-40° overnight and then pour it, with vigorous stirring, into a solution of 40 g. of potassium hydroxide in 300 ml. of water crystals separate. Cool in an ice bath for 2 hours, collect the crystalline solid by suction flltration, wash with three 50 ml. portions of cold water, and dry to constant weight at 50°. The yield of gramine is 34 g. this is quite suitable for conversion into 3-indoleacetic acid. The pure compound may be obtained by recrystaUisation from acetone-hexane m.p. 133-134°. 

The mechanism of the Fischer cyclization outlined in equation 7.1 has been supported by spectroscopic observation of various intermediates[4] and by isolation of examples of intermediates in specialized structures[5]. In particular, it has been possible to isolate enehydrazines under neutral conditions and to demonstrate their conversion to indoles under the influence of acid cata-lysts[6]. 

Similar halogenations have been done on 2-lithio-l-phenylsulfonylindole[2], 2-Lithio-l-phenylsulfonylindole is readily converted to the 2-(trimethylsilyl) derivative[2,3]. 2-Trialkylstannylindoles can also be prepared via 2-lithio-indoles[4,5], 2-Sulfonamido groups can be introduced by reaction of a 2-lithioindole with sulfur dioxide, followed by conversion of the sulfinic acid group to the sulfonyl chloride with A-chlorosuccinimide[6]. 

An important method for construction of functionalized 3-alkyl substituents involves introduction of a nucleophilic carbon synthon by displacement of an a-substituent. This corresponds to formation of a benzylic bond but the ability of the indole ring to act as an electron donor strongly influences the reaction pattern. Under many conditions displacement takes place by an elimination-addition sequence[l]. Substituents that are normally poor leaving groups, e.g. alkoxy or dialkylamino, exhibit a convenient level of reactivity. Conversely, the 3-(halomethyl)indoles are too reactive to be synthetically useful unless stabilized by a ring EW substituent. 3-(Dimethylaminomethyl)indoles (gramine derivatives) prepared by Mannich reactions or the derived quaternary salts are often the preferred starting material for the nucleophilic substitution reactions. 

The conversion of indoles to oxindoles can be achieved in several ways. Reaction of indoles with a halogenaling agent such as NCS, NBS or pyridin-ium bromide perbromide in hydroxylic solvents leads to oxindoles[l]. The reaction proceeds by nucleophilic addition to a 3-haloindolenium intermediate. 

As foretold in the introduction, ring formation via attack on a double bond in the endo-trig mode is not well exemplified. The palladium(II) catalyzed oxidative cyclization of o-aminostyrenes to indoles has been described (78JA5800). The treatment of o-methyl-selenocinnamates with bromine in pyridine gives excellent yields of benzoselenophene-2-carboxylates (Scheme 10a) (77BSF157). The base promoted conversion of dienoic thioamides to 2-aminothiophenes is another synthetically useful example of this type (Scheme 10b) (73RTC1331). 

The Piloty-Robinson pyrrole synthesis (74JOC2575,18JCS639) may be viewed as a monocyclic equivalent of the Fischer indole synthesis. The conversion of ketazines into pyrroles under strongly acidic conditions apparently proceeds through a [3,3] sigmatropic rearrange-... 

The course of the photochemically mediated isomerization of vinylazirines is dependent on the stereochemistry of the vinyl group, as is illustrated in Scheme 94a (75JA4682). Under thermal conditions the isomerization proceeds through formation of the butadienylnitrene and subsequent pyrrole formation. Analogous conversions of azirines to indoles have also been effected (Scheme 94b). It is possible that some of the vinyl azide cyclizations discussed in Section 3.03.2.1 proceed via the azirine indeed, such an intermediate has been observed... 

Treatment of 1-azirine (292) with eatalytie quantities of diehlorobis(benzonitrile)pal-ladium(II) gave a quantitative yield of the indole (293) (77CC664). This transformation proeeeds through the intermediaey of a 2 1 azirine-palladium ehloride eomplex. Conversion of the 1-azirine ring to indoles under uneatalyzed thermolytie eonditions provides a meehanistieally interesting eomparison with the Pd(II)-eatalyzed eonversions. The C—N bond eleavage in the latter is apparently aeeelerated as a result of the eoordination of the azirine to palladium. 

The Madelung indole synthesis has been employed in the preparation of some complex indole systems. Uhle et al. reported the conversion of N-formyl-5,6,7,8-tetrahydronaphthylamine 28 into 1,3,4,5-tetrahydrobenz[c,ti]indole 29 with t-BuOK in 11% yield in regard to synthesis of ergot alkaloids. ... 

A synthesis of an indolo[3,2-fl]carbazole (2) was reported in 1951—the first preparation of a compound belonging to this class (Scheme 13). This was accomplished commencing with cyclohexanone, via conversion to the bishydrazone 108, which underwent Fischer indolization in glacial acetic acid to furnish the octahy-dro derivative 109. After a final dehydrogenation step, the desired product 2 was obtained (51JCS809). 

The structure of ( )-169 is determined to have a ( )-3a,3a -bispyrrolo[2,3-(j] indole skeleton by carrying out X-ray single crystallographic analysis of its derivative 252 (99H1237). Compound 252 is obtained from ( )-169 by the following sequence of reactions (1) alkaline hydrolysis of ( )-169 to 249 (88%), (2) conversion of 249 to 251 (71%) by treatment with NaH and chloroacetyl chloride, (3) substitution of chlorine on the chloroacetyl group for acetate 252 (93%) by the reaction with NaOAc. 

Allen et al mainly on the evaluation of data reported by previous workers, advanced structure (5) for 2-methylpyrrole dimer. These data were (a) the monobasic nature of the dimer and (b) the conversion by aqueous acid into an indole which they showed by elimination (i.e., by the synthesis of 2,5-, 2,6-, and 2,7-dimethylindoIes) to be 2,4-dimethyIindole (this compound has since been synthesized by Marion and Oldfield ). Structure (5) for the dimer was confirmed by Edwards and Smith by conversion, by way of the methiodide (6), into the pyrrolidinopyrrole (7), the structure of which was proved by synthesis l,5-dimethylpyrrolid-2-one was condensed with 2-methyI-pyrrole by means of POCI3 to give the cation (8), isomeric with the... 

The Batcho indole synthesis involves the conversion of an o-nitrotolnene to a fi-dialkyl-amino-o-nitrostyrene v/ith dimethylformairude acetM, followed by redncdve cychzadon to indoles. This provides a nsefid strategy for synthesis of snbsdtuted indoles fEq. 10.49. ... 

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