3- Amino alkylated indoles

Keywords Indoles, aldehydes, secondary amines, L-Proline, solvent-free, room temperature, one-pot multicomponent reaction, Mannich-type reaction, 3-amino alkylated indoles... 

In 1960, Mold et al. (2592) reported the isolation and identification of the tricyclic A-heterocyclic 5H, QH-dipyrrolo[l,2-fl r,2 -(i]pyrazine-5,10-dione (pyrocoll) V (Figure XVlI.E-3) from CSC and demonstrated its relationship to its precursor in tobacco, the amino acid proline. Obviously, pyrocoll is not an aza-arene but an amide. Rodgman and Cook (3279) reported the identification of indole, carbazole, and several alkylated indoles and car-bazoles in CSC and confirmed the presence of 5H, QH-dipyrrolo[l,2-fl r,2 -(i]pyrazine-5,10-dione (pyrocoll) V described previously by Mold et al. (2592). Rodgman and Cook also assessed previously reported biological studies on indole, 3-methylindole (skatole), and carbazole None was reported to be tumorigenic in laboratory animals [Hartwell (1544), Shubik and Hartwell (3664)]. 

Indoles react with epoxides and aziridines in the presence of Lewis acids (see section 17.5 for reaction of indolyl anions with such reactants) with opening of the three-membered ring and consequent 3-(2-hydroxyalkylation) and 3-(2-amino-alkylation) of the heterocycle. Both ytterbium triflate and phenylboronic acid are good catalysts for reaction with epoxides under high pressure " silica gel is also an effective catalyst, but slow at normal pressure and temperature." Lewis acid-mediated reaction with aziridines can be catalysed by zinc triflate or boron trifluoride.More reactive alkylating electrophiles react at lower temperatures, at room temperature with dimethylallyl bromide for example. ... 

The preparation of indoles by the benzyne route is illustrated by the base-induced cyclization of the amino-alcohols (171 R = H or Me) to indole and 3-methylin-dole, respectively/ The photochemical reaction of o-bromo- or o-iodo-aniline with the enolates (172 R = H, Me, or PrO leads to indoles (173)/ The salt (174), generated by the action of lithium di-isopropylamide on o-tolyl isocyanide, serves as a source of diverse indole derivatives (i) it cyclizes spontaneously to 1-lithioindole, which forms 3-alkyl-indoles on treatment with alkyl halides in the presence of magnesium iodide, (ii) it reacts with allyl esters RC02CH2CH=CH2 (R = alkyl or aryl) to give the ketones (175), which cyclize... 

The Butin indole ring synthesis is a new variation of several amino-carbonyl indole-forming reactions related most closely to the Reissert reaction (Chapter 40). The fundamental reaction is illustrated in Scheme 1 [1, 2], Alkylation of suitable furans 2 with the benzyUc alcohols 1 afforded the o-tosylaminobenzylfurans 3 in good yield. A conventional acid hydrolysis of the furan ring, which serves as a 1,4-dicarbonyl unit, led to indoles 5 via enol tautomer 4. 

The nonpolar amino acids (Figure 4.3a) include all those with alkyl chain R groups (alanine, valine, leucine, and isoleucine), as well as proline (with its unusual cyclic structure), methionine (one of the two sulfur-containing amino acids), and two aromatic amino acids, phenylalanine and tryptophan. Tryptophan is sometimes considered a borderline member of this group because it can interact favorably with water via the N-H moiety of the indole ring. Proline, strictly speaking, is not an amino acid but rather an a-imino acid. 

Grigg et al. also reported the alkylation of indole at the C3-position with alcohols, catalyzed by the 1/KOH system (Scheme 5.32) [69]. A variety of indole derivatives having an alkyl substituent at the C3-position were synthesized by this methodology. The same group also developed a Cp lr-catalyzed process for successive carbon-nitrogen and carbon-carbon bond formation, starting with 2-amino-phenethyl alcohol (also see Scheme 5.22). 

Reduced indole derivatives can be synthesized by using the phenolic oxidation approach. Thus, A-alkyl-A-benzoyltyramines 120, on treatment with IBTA in trifluoroethanol (TFE), followed by aqueous workup, afford the hexahydroindol-6-ones 122. The formation of 122 is rationalized by intramolecular Michael-type addition of amino group to the double bond of the intermediate dienone 121 (91JOC435) (Scheme 33). 

Dodd and co-workers (5) reported the first known synthesis of 11//-indolizino[8,7-h]indoles by the cycloaddition reaction of a nonstabilized ylide 21 and diethylacetylene dicarboxylate (DEAD). The azomethine ylide, formed by the alkylation of the 3,4-dihydro-p-carboline (22) with trimethylsilyl methyl triflate to the triflate salt, followed by in situ desilyation with cesium fluoride, underwent cycloaddition with DEAD at low temperature. The expected major cycloadduct 23 was isolated, along with quantities of a minor product 24, presumed to have been formed by initial reaction of the ylide with 1 equiv of DEAD and the intermediate undergoing reaction with a further equivalent of DEAD before cyclization. Dodd offers no explanation for the unexpected position of the double bond in the newly generated five-membered ring, although it is most likely due to post-reaction isomerization to the thermodynamically more stable p-amino acrylate system (Scheme 3.5). 

Amino-l,2,4-triazole was alkylated with 4-nitrobenzyl bromide by simply refluxing the mixture in isopropanol to give SO in excellent yield. The aminotriazole SO was deaminated with NaNOa in aqueous HCI and the nitro group was reduced with ammonium formate catalyzed by 10% Pd/C to deliver 47 in an improved yield over the route shown in Scheme 17. Diazotization of 47, reduction of the diazonium salt with sodium sulphite and Fischer indolization of the resulting hydrazine with 4-( /, /-dimethylamino)butanol dimethyl acetal was performed in a single step to afford rizatriptan (4) in 45% yield. 

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... 

Support-bound C-nucleophiles have also been successfully added to imines. Poly-styrene-bound thiol esters can be converted into ketene acetals by O-silylation, and then alkylated with imines in the presence of Lewis acids. Further examples include Mannich reactions of support-bound alkynes and indoles (Table 10.10). Some Man-nich-type products (e.g. 3-(aminomethyl)indoles, 2-(aminomethyl)phenols, (3-amino ketones) are unstable and can decompose upon treatment with acids. 3-(Amino-... 

The heterocyclization of peri-aminonaphthoyl compounds allows the preparation of three main types of benzo[crf]indole series, namely, bases 113, benzo[crf]indolium salts 114, and benzo[crf)indole-2-ones 115. Because closure to the nitrogen heterocycle is so facile, peri-amino-substituted naphthaldehydes and naphthyl ketones, even under conditions of their formation, are converted into benzo[crf]indoles 113. Those unsubstituted in position 2, as well as 2-alkyl-substituted benzo[cd]indoles 113 (R = H, Aik), have not been isolated because of their easy oxidation by air. 

Indoles can be used as radical acceptors instead of 63 [120, 121]. Simple and twofold reactions giving either 3-alkylindoles [120] or l,l-bis(3-indolyl)alkanes [121] were observed in 16-72% and 54-90% yield, respectively. In both methods the indole is subject to radical addition in 3-position. The resulting a-amino radical undergoes a further oxidation and deprotonation to the 3-substituted indole. In the case of twofold additions, the second indole unit is introduced by a subsequent polar Friedel-Crafts-type alkylation. 

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