A cascade reaction of azolopyrimidines. Synthesis of unusual indole and azaindole derivatives

The reaction of bromo substituted pyrido[3',2':4,5]pyrrolo-[1,2-c]pyrimidine and pyrimido[1,6-a]indole methyl carboxylates with primary amines is described. The expected amide formation occurs but it is followed by an unexpected cascade process involving attack of the amine to the pyrimidine ring, opening of the pyrimidine ring, loss of the bromine substituent and competitive cyclizations to afford unusual imidazolidene substituted indoles and azaindoles.     

Azacarbazoles

Alkylation of 5H-pyridazino [4, 5-b] indole with halogen compounds or dimethyl sulfate in the presence of alkaline reagents gives 2-alkyl-2H-pyridazino [4, 5-b] indoles. Reduction of the methiodide or chlorobenzylate of 5H-pyridazino [4, 5-b] indole also gives 2-alkyl derivatives. LiAlH₄ reduction of 3-alkyl-3H-pyridazino [4, 5-b] indolones-4 gives 3-alkyl-3H-pyridazino [4, 5-b] indoles.For Part I see [1]. The main results of the research were reported at the Conference on Heterocyclic Rings in Organic Synthesis, Kiev, June 1964.     

Reaction of the N-mesylates of 1,3a,4,8b-tetrahydrocyclopenta[b]indoles and 3,4,4a,9a-tetrahydrocarbazoles with dimethyldioxirane and bromine

In reaction with dimethyldioxirane N-mesyl-1,3a,4,8b-tetrahydrocyclopenta[b]indoles and N-mesyl-3,3,4a,9a-tetrahydrocarbazoles mostly form the trans-epoxide. The reaction with molecular bromine leads to the product from halogenation in the aromatic ring, i.e., the corresponding N-mesyl-7-bromo-1,3a,4,8b-tetrahydrocyclopenta[b]indole or N-mesyl-6-bromo-3,4,4a,9a-tetrahydrocarbazole. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1306–1313, September, 2006.     

Synthesis and properties of 1,2-dihydropyridazino[4,5-b]indole II

The possibility of the synthesis of substituted 1,2-dihydropyridazino[4,5-b]indoles by the reaction of 1-methyl-2-carbomethoxy-3-(α-halobenzyl)indole or 1-methyl-2-carbomethoxy-3-(α-acetoxybenzyl)indole with hydrazines was demonstrated. The oxidation, reduction, and acylation reactions of the resulting 1,2-dihydropyridazino[4,5-b]indoles were studied.     

Thiol-mediated radical cyclization: regioselective formation of indole-annulated sulfur heterocycles by tandem cyclization

Indole-2-yl-prop-2-ynyl sulfides, under thiophenol-mediated alkenyl radical cyclization conditions, afforded exclusively 4-thiophenyl-2,3,4,9-tetrahydrothiopyrano[2,3-b]indoles or 3-thiophenylmethyl-2,3,8-trihydrothieno[2,3-b]indoles depending on the substituent at the indole nitrogen.     

A convenient access to 1,3-disubstituted furo[3,4-b]indoles by acid ion-exchange resin-catalyzed furan formation

Efficient synthesis of furo[3,4-b]indoles starting from the corresponding indole is reported. The first route involves derivatization, protection, and deprotection steps, which stretch the syntheses. The second method provides a shorter and more efficient strategy to accessing the furoindole. The innovation starts with alkylation at C-2 of the indole presenting at the C-3 position a ketone-acetal, followed by the cycloaromatization catalyzed by polymeric ion-exchange resins. The second route represents a significant improvement over other methods previously described.     

Synthesis of diversely functionalized hexahydropyrrolo[2,3-b]indoles using domino reactions, olefination, isomerization and Claisen rearrangement followed by reductive cyclization

Hexahydropyrrolo[2,3-b]indoles 6 were synthesized in five steps from indolin-3-one 8 by a general and efficient method, in which elements of molecular diversity were readily added onto the 3a-position of the pyrrolo[2,3-b]indole ring system. Horner-Wadsworth-Emmons reaction of 2-allyloxyindolin-3-ones 7, derived from indolin-3-one 8 and a variety of allylic alcohols, smoothly proceeded with successive Claisen rearrangement to give the corresponding 3-allyl-3-cyanomethylindolin-2-ones 15. Indolin-2-ones 15 were converted into pyrrolo[2,3-b]indoles 6 using partial hydrolysis followed by reductive cyclization with LiAlH(4). Synthesis of N-methylated pyrrolo[2,3-b]indole derivatives 23 and 26 is also described.     

Investigation of the products of the reaction of epichlorohydrin with aromatic amines

The action of hydrogen halides on 7a,8-dihydro-7H-azirino[1,2-]benz[g]indole gives 2-halomethyl-2,3-dihydro-1H-benz[g]indoles and 3-halo-1,2,3,4-tetrahydrobenzo[h]quinolines, which were converted to the corresponding N-nitroso derivatives and then to the isonitroso derivatives. 2-(Benzoxymethyl)-2,3-dihydro-1H-benz[g]indole hydrohalides were obtained by heating 1-benzoyl-2-halomethyl-2,3-dihydro-1H-benz[g]indoles. The reaction of 3-halo-1,2,3,4-tetrahydrobenzo[h]quinolines with thionyl chloride at room temperature gives 3-halo-6-chloro-1,2,3,4-tetrahydrobenzo[h]quinolines, while refluxing with thionyl chloride gives 6-chlorobenzo[h]quinoline.See [1] for communication XVI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 342–346, March, 1973.     

Regioselective 1,3-Dipolar Cycloaddition Reactions of Unsymmetrical Münchnones (1,3-Oxazolium-5-olates) with 2- and 3-Nitroindoles. A New Synthesis of Pyrrolo[3,4-b]indoles

The unsymmetrical mesoionic münchnones 13 (3-benzyl-2-methyl-4-phenyl-1,3-oxazolium-5-olate) and 14 (3-benzyl-4-methyl-2-phenyl-1,3-oxazolium-5-olate) react with the N-protected 2- and 3-nitroindoles 1 (ethyl 2-nitroindole-1-carboxylate), 6 (3-nitro-1-(phenylsulfonyl)indole), and 17 (ethyl 3-nitroindole-1-carboxylate) in refluxing THF to afford in good to excellent yields the pyrrolo[3,4-b]indoles 15 (2-benzyl-1-methyl-3-phenyl-4-carboethoxy-2,4-dihydropyrrolo[3,4-b]indole), 16 (2-benzyl-3-methyl-1-phenyl-4-carboethoxy-2,4-dihydropyrrolo[3,4-b]indole), 18 (2-benzyl-1-methyl-3-phenyl-4-(phenylsulfonyl)-2,4-dihydropyrrolo[3,4-b]indole), and 19 (2-benzyl-3-methyl-1-phenyl-4-(phenylsulfonyl)-2,4-dihydropyrrolo[3,4-b]indole). In several cases the regiochemistry, which is opposite to that predicted by FMO theory, is very high and leads essentially to a single pyrrolo[3,4-b]indole; e.g., 6+13→19 in 74% yield.     

Furan ring opening–indole ring closure: recyclization of 2-(2-aminophenyl)furans into 2-(2-oxoalkyl)indoles

The acid-catalyzed rearrangement of 5-alkyl-2-[2-(sulfonylamino)phenyl]furans into 2-(2-oxoalkyl)indoles is described. When the N-sulfonyl group in the starting compounds was displaced by an N-acyl group, the corresponding indoles were not formed under the same reaction conditions due to the in situ indole deacylation and decomposition. The presence of an alkyl group at the C5 position of the furan ring is also crucial for the efficiency of the process. The discussed rearrangement provides a simple and efficient approach to 2-(2-oxoalkyl)indoles.     

Synthesis of 6-bromo-2-arylindoles using 2-iodobenzoic acid as precursor

The synthesis of 6-bromo-2-arylindoles starting from readily available 2-iodobenzoic acid is presented. Regioselective bromination of the latter was followed by Curtius rearrangement and trapping of the isocyanate with benzyl alcohol led to the benzyl carbamate of 2-iodo-5-bromoaniline. Chemoselective Sonogashira coupling of this compound with arylacetylenes followed by TBAF induced 5-endo-dig cyclization gave the desired bromo indoles. The method allows selective introduction of a bromine atom at the indole C-6 position.     

Synthesis of substituted indolizino[8,7-<Emphasis Type="Italic">b</Emphasis>]indoles from harmine and their biological activity

The reaction of harmine with phenacyl bromides or ethyl bromoacetate gives quaternized harmine derivatives. The cyclization of the phenacylharminium salts yields the corresponding 2-aryl-11H-indolizino[8,7-b]indoles. Vilsmaier-Haack formylation of 11H-indolizino[8,7-b]indoles leads to the corresponding 3,10-bisformyl derivatives. The acylation proceeds selectively at C(3) to give 3-acetyl-2-aryl-11H-indolizino[8,7-b]indole.     

Synthesis of cyclopent[bindoles by formal [3+2]-addition of indolylmethyl cations to alkenes

Treatment of indole-2- or 3-methanols with tin(IV) chloride as Lewis acid in the presence of styrenes results informal [3+2]-addition of the indole stabilised cation to the alkene to give cyclopent[b]indoles with a high degree of stereoselectivity; use of methylcyclohexene as the alkene component gave the cis-fused cyclopent[b]indole 17, which was independently synthesised in enantiomerically pure form from the diketone 18.     

Halocyclization of 3-{[2-methyl(bromo)prop-2-en-1-yl]-sulfanyl}-5<Emphasis Type="Italic">H</Emphasis>-[1,2,4]triazino[5,6-<Emphasis Type="Italic">b</Emphasis>]indoles

Reactions of 3-[(2-bromoprop-2-en-1-yl)sulfanyl]-5H-[1,2,4]triazino[5,6-b]indole with bromine and of 3-[(2-methylprop-2-en-1-yl)sulfanyl]-5H-[1,2,4]triazino[5,6-b]indole with iodine and bromine afforded 3-halomethyl-10H-[1,3]thiazolo[3′,2′: 2,3][1,2,4]triazino[5,6-b]indol-4-ium halides whose structures were determined by ¹H NMR and X-ray analysis.     

1,2,3,9a-Tetrahydro-9H-imidazo[1,2-a]indoles

When derivatives of 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-one or 1-carbamoylmethyl-2-methylene-2,3-dihydroindole are reacted with lithium aluminum hydride, derivatives of 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indole are formed. Under the same conditions 1-(N-phenylcarbamoylmethyl)-2-methylene-2,3-dihydroindole is not cyclized to an imidazo[1,2-a]indole. WHen treated with proton acids imidazo[1,2-a]indoles are converted to 3H-indolium salts. Opening of the imidazolidine ring is also found when imidazo[1,2-a]indole is acylated with benzoyl chloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 227–230, February, 1987.     

Scope and mechanism of the Pd(II)-catalyzed arylation/carboalkoxylation of unactivated olefins with indoles

Treatment of 1-methyl-2-(4-pentenyl)indole (5) with a catalytic amount of [PdCl2(MeCN)2] (2; 5 mol %) and a stoichiometric amount of CuCl2 (3 equiv) in methanol under CO (1 atm) at room temperature for 30 min gives methyl (9-methyl-2,3,4,9-tetrahydro-4-carbazolyl)acetate (6), which was isolated in 83% yield. A number of 2- and 3-alkenyl indoles undergo a similar palladium-catalyzed cyclization/carboalkoxylation to give the corresponding polycyclic indole derivatives in moderate to excellent yields with excellent regio- and diastereoselectivity. Under similar conditions, vinyl arenes undergo intermolecular arylation/carboalkoxylation with indoles to give 3-(1-aryl-2-carbomethoxyethyl) indoles in moderate yield with high regioselectivity. Stereochemical analyses of the palladium-catalyzed cyclization/carboalkoxylation of both 2- and 3-alkenyl indoles are in agreement with mechanisms involving outer-sphere attack of the indole on a palladium-olefin complex followed by alpha-migratory insertion of CO and methanolysis of the resulting acyl palladium intermediate. CuCl2 functions as the terminal oxidant in this palladium-catalyzed cyclization/carboalkoxylation of alkenyl indoles and also significantly increases the rate of reaction of 2 with the alkenyl indole to form the corresponding acyl palladium complex. Spectroscopic studies are in agreement with the intermediacy of a heterobimetallic Pd/Cu complex as the active catalyst in this reaction.     

Synthesis of 1H-[1,2]diazepino[4,5-b]indole derivatives

A synthesis of four 1H-[1,2]diazepino[4,5-b]indole derivatives and some preliminary information about their biological activity are presented. The starting materials were 2-ethoxycarbonylindoles and 2-ethoxy-carbonyl-3-formylindoles, la, b and 2a, b, respectively. 2-Ethoxycarbonyls la, b reacted with 1-dimethylamino-2-nitroethylene and -2-ethoxycarbonyl-3-formylindoles 2a, b in the presence of nitroalkanes (nitromethane or nitroethane) giving 3-(2-nitrovinyl)indoles 3a, b. Reduction of 3a, b yielded β-(2-oxoalkyl)indoles 4. On reaction with an excess of hydrazine hydrate, compounds 4 gave satisfactory yields of 5-oxo-1H-[1,2]diazepino[4,5-b]indoles 5.     

Triethylbenzylammonium Chloride as a Useful and Efficient Catalyst for the Alkylation of Indole/substituted Indoles in Water: A Comparative Study between Conventional and Microwave Irradiation

A green and facile method for the alkylation of indole/substituted indole in water using a phase Transfer catalyst (Triethylbenzylammonium Chloride, TEBA) to synthesise bis‐indolyl methanes (BIMs) and Michael addition of indole to α,β‐unsaturated carbonyl compounds is reported. The substitution of indoles occurred exclusively at the 3‐position and products of N‐alkylation has not been observed. However, for 3‐substituted indoles, reactions were found to occur at the 2‐position. A comparative study between conventional heating and microwave irradiation has also been reported.     

Tandem hydroformylation/Fischer indole synthesis: a novel and convenient approach to indoles from olefins

[reaction: see text] A novel one-pot synthesis of indole systems via tandem hydroformylation/Fischer indole synthesis starting from olefins and arylhydrazines is described. This tandem procedure leads directly to 3-substituted indoles if unsubstituted phenylhydrazine is used and to 3,5- respectively 3,7-disubstituted indoles if para- or ortho-substituted arylhydrazines are used.     

Sterically Controlled Regiospecific Cyclization of Aldose-5-ethyl-1,2,4-triazino[5,6- b ]indol-3-ylhydrazones to Linearly Annelated 3-Polyhydroxyalkyl-10-ethyl-1,2,4-triazolo-[4′,3′:2,3]-1,2,4-triazino[5,6- b ]indoles

 Condensation of aldoses with 5-ethyl-3-hydrazino-1,2,4-triazino[5,6-b ]indole gave the corresponding aldose-5-ethyl-1,2,4-triazino[5,6-b ]indol-3-ylhydrazones which were acetylated to their poly-O-acetyl derivatives. The latter underwent sterically controlled regiospecific oxidative cyclization with bromine in acetic acid and sodium acetate to sterically favourable linearly annelated 3-polyacetoxyalkyl-10-ethyl-1,2,4-triazole[4′,3′:2,3]-1,2,4-triazino[5,6-b ]indoles rather than to their sterically unfavourable angularly annelated regioisomers. The regiospecific outcome of this heterocyclization is discussed in terms of electronic as well as steric factors, and the assigned structures have been corroborated on the basis of chemical as well as spectroscopic evidence. De-O-acetylation of the acetoxyindoles with ammonium hydroxide in methanol gave the title compounds. Representative members of the prepared compounds were tested for antimicrobial activity.