Isomerization of pyridazino [4,5-b] indoles to pyrrolo [3,4-b] indoles

The dihydropyridazine ring undergoes contraction to a dihydropyrrole ring to give 1-phenyl-2-benzylideneaminodihydropyrrolo[3,4-b]indol-3-ones when 1-phenyldihydropyridazino[4,5-b]indol-4-ones are treated with aromatic aldehydes under acid catalysis conditions. The reaction mechanism consists in the formation of a (3-indolyl)phenylmethyl cation, which leads to opening of the pyridazine ring and subsequent development of a bond between the carbonium center and the amide nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1406–1408, October, 1976.     

Synthesis of pyrido[3,4-b]pyrano[3,4-b]indoles

The synthesis of some pyrido[3,4-b]pyrano[3,4-b]indoles ( 3 ) from 3-hydroxy-4-(3-indolyl)piperidines ( 6 ) is reported.     

Dihydropyrrolo[3,4-b]- and dihydropyrimido[4,5-b]indoles

Aromatic aldehydes react with indole-2-carboxylic acid azides under acid catalysis conditions to give the corresponding 3-(-halobenzyl)indoles, which react with aliphatic and aromatic amines to give the corresponding aminobenzylindoles. The latter undergo intramolecular cyclization to dihydropyrrolo[3,4-b]indoles at room temperature and are converted to dihydropyrimido[4,5-b]indoles through the Curtius rearrangement when they are heated to 80-110°C. Acetylation of the latter products gives N- and O-acetyl derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 935–939, July, 1982.     

Synthesis of hexahydroazonino[5,6-b]indoles from hexahydroazepino[4,3-b]-and-[3,4-b]indoles and activated alkynes

A reaction of substituted hexahydroazepino[4,3-b]-and-[3,4-b]indoles with activated alkynes was studied. A one-step method for the synthesis of isomeric hexahydroazonino[5,6-b]indoles different by positions of the double bond in the azonine ring was developed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2244–2250, November, 2007.     

The synthesis of substituted 2,3-dihydrothieno[2,3-b]-thiophenes via intramolecular michael addition

The first regiospecific synthesis of the 2,3-dihydrothieno[2,3-b]thiophene ring system was achieved using an intramolecular Michael addition in the key cyclization step. This strategy represents a novel and potentially general method for dihydrothiophene and dihydrothiophene S,S-dioxide annellation.     

New method of synthesis of δ-carbolines from 3-indolinone via pyrano[3,2-b]indoles

2-Arylidene-1-acetylindolin-3-ones were obtained from 1-acetylindolin-3-ones and p-substituted benzaldehydes or 4-pyridinecarboxaldehyde, by the action of malonodinitrile, andwere converted into 2-amino-4-aryl-5-acetyl-3-cyanopyrano[3,2-b]indoles. When heated with an aqueous-alcoholic solution of KOH, the latter compounds transform into 2-alkoxy-4-aryl-3-cyano--carbolines. The possible paths of formation of -carbolines and pyrano[3,2-b]indoles are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 230–235, February, 1985.     

The synthesis of 11H-1,2,4-triazolo[4,3-b]pyridazino[4,5-b]indoles,11H-tetrazolo[4,5-b]pyridazino[4,5-b]indoles and 1,2,4-triazolo[3,4-f]-1,2,4-triazino[4,5-a]indoles

This paper describes the synthesis of the previously unknown 11H-1,2,4-triazolo[4,3-b]pyridazino[4,5-b]indoles (2) and 11H-tetrazolo[4,5-b]pyridazino[4,5-b]indoles (3) from 4-hydrazino-5H-pyridazino[4,5-b]indoles (1) , as well as the synthesis of 1,2,4-triazolo[3,4-f]-1,2,4-triazino-[4,5-a]indoles (10) from 2-indolecarbohydrazide (4) . Compounds 2 were obtained by acylation of compounds 1 , followed of thermal cyclization and compounds 3 by treating compounds 1 with nitrous acid. The reactions of compound 4 with formic acid or ethyl orthoformiate gave 1,2-dihydro-1-oxo-1,2,4-triazino[4,5-a]indole (6) . Treating this last compound with phosphorus oxychloride or phosphorus pentasulfide, followed by hydrazine, gave 1-hydrazino-1,2,4-triazino-[4,5-a]indole (9) . Acylation of this last compound, followed of cyclization gave compounds 10 . All the compounds were characterized by elemental analysis and ir and ¹H-nmr spectra.     

A reinvestigation of the synthesis of 3H-[1,2]diazepino[5,6-b]indoles. The synthesis of pyrido[4,3-b]indoles

Recently reported [1] syntheses of 6-methyl-1,2,4,5-tetrahydro-1,4-dioxo-3H[1,2]diazepino[5,6-b]indole ( 5 ) and 4-hydroxy-6-methyl-3H[1,2]diazepino[5,6-b]indole ( 12 ) were reinvestigated and shown to be in error. The correct assignments for these respective structures are 3-amino-1,9-dihydro-9-methyl-2H-pyrido[4,3-b]indol-2,4(3H)-dione ( 6 ) and 3-amino-3,9-dihydro-9-methyl-2H-pyrido[4,3-b]indol-2-one ( 13 ). Condensation of 6 and 13 with p-nitrobenzaldehyde produced benzylidene derivatives, which confirmed the presence of the amino groups.     

Acid-catalyzed highly diastereoselective and effective synthesis of 1,3-disubstituted tetrahydropyrano[3,4-b]indoles

We successfully explored for the first time that trifluoroacetic acid (TFA) can effectively catalyze the oxa-Pictet-Spengler reaction of secondary tryptophols and acetals to synthesize 1,3-disubstituted 1,3,4,9-tetrahydropyrano[3,4-b]indoles in high yield (up to >99%) and diastereoselectivity (>20:1). The secondary tryptophols were synthesized from indole-3-acetic acid. The one-pot synthesis of tetrahydropyrano[3,4-b]indoles was successfully developed from secondary tryptophols and in situ prepared acetals from aldehydes and trimethylorthoformate and thus the cost-efficiency of the protocol was effectively enhanced. Finally, the catalytic asymmetric synthesis of the 1,3-disubstituted tetrahydropyrano[3,4-b]indole was also demonstrated after enantioselective achievement of highly enantiopure secondary tryptophols.     

“On-water” synthesis of 3-substituted indoles via Knoevenagel/Michael addition sequence catalyzed by Cu doped ZnS NPs

Cu doped ZnS NPs represent a green catalyst for an ‘on-water’ one-pot rapid synthesis of 3-substituted indole derivatives via Knoevenagel/Michael addition reaction of indane-1,3-dione, aromatic aldehydes, and indole. The catalytic activity of Cu doped ZnS NPs was about sevenfold higher as compared to the ZnS NPs. The Cu doped ZnS NPs catalyst could be recovered and reused for five reaction cycles, giving a total TOF = 201 h⁻¹.     

Reaction of indoles with aldehydes. Synthesis of dihydropyrrolo[3,4-b]indoles

Aromatic aldehydes react with amides of 1-methylindole-2-carboxylic acid under acid catalysis conditions to give 1-aryl-4-methyldihydropyrrolo[3,4-b]indol-3-ones. The intermediate 1-methyl-2-CONHR-3(-X-benzyl)indoles, which are subsequently converted to the indicated cyclic compounds, were isolated. o-Acetyl derivatives were obtained by the action of acetic anhydride on derivatives of unsubstituted amides. Dihydropyrrolo[3,4-b] indol-3-ones were reduced by LiAlH₄ to the corresponding dihydropyrrolo[3,4-b] indoles. A mechanism for the formation of dihydropyrrolo[3,4-b] indoles is proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1516–1523, November, 1976.     

A cycloisomerization/Friedel-Crafts alkylation strategy for the synthesis of pyrano[3,4-b]indoles

The synthesis of pyrano[3,4-b]indoles is described. The reaction sequence involves Sonogashira coupling of dihydropyran propargyl ether scaffolds with iodoanilines to afford intermediate indoles. Lewis acid-catalyzed ionization of the dihydropyrans, followed by intramolecular C3 alkylation of the indole, provides the title compounds.     

Synthesis of isoxazolobenzoxepanes via Michael addition of indoles to nitroalkenes and sequential intramolecular nitrile oxide cycloaddition

Nitroalkenes derived from O-propargyl salicylaldehyde undergo facile Michael addition with indoles leading to indole-derived Michael adducts. Intramolecular nitrile oxide cycloaddition (INOC) of the Michael adducts results in isoxazolobenzoxepanes in good to excellent yields.     

New multicomponent domino reaction on water: highly diastereoselective synthesis of spiro[indoline-3,4′-pyrazolo[3,4-b]pyridines] catalyzed by NaCl

A direct and efficient approach for the preparation of medicinally promising pyrazolopyridinyl spirooxindoles has been developed through a sequential one-pot, three-component reaction of easily available isatin, α-cyanoacetic ester or malononitrile, and 5-amino-3-methylpyrazole catalyzed by sodium chloride in water. Desired products were obtained in high to excellent yields using a simple workup procedure. The product synthesized using α-cyanoacetic ester showed high diastereoselectivity in which the stereochemistry of major diastereomer was confirmed by X-ray diffraction analysis. The present green synthesis shows attractive characteristics such as the use of water as the reaction medium, one pot conditions, short reaction period, easy workup/purification, and reduced waste production, without use of any acid or metal promoters.     

InBr3-catalyzed Friedel-Crafts addition of indoles to chiral aromatic epoxides: a facile route to enantiopure indolyl derivatives

Aromatic optically active epoxides can be opened in a regioselective and clean way with indoles in the presence of catalytic amount of InBr3 (1 mol %). The reaction takes place with a SN2 pathway affording the 2-aryl-2-(3'-indolyl)ethan-1-ols with excellent enantioselectivity (ee up to 99%).     

Total synthesis of (-)-kainic acid via intramolecular Michael addition: a second-generation route

A total synthesis of (-)-kainic acid starting from the commercially available 2-azetidinone is described. The key delta-lactone intermediate was concisely prepared from the commercially available azetidinone through the Reformatsky-type reaction and an introduction of a glycine moiety. The construction of the functionalized pyrrolidine ring was executed by a one-pot sequential elimination-Michael addition protocol of a beta-amino-delta-lactone intermediate with high diastereoselectivity.     

Pyrrolo- and pyrido[1,2-a]indoles via an intramolecular wittig reaction

Several pyrrolo- and pyrido[1,2-a]indoles were prepared via an intramolecular Wittig reaction in good yields. This reaction sequence represents a facile entry into the mitosene ring system.     

Benzoazabicyclo[4.3.1] derivatives by intramolecular Michael addition of piperidinone enolates to enoates

Piperidinones with a 2-bromobenzyl substituent in the 5-position were subjected to a Heck coupling reaction with ethyl acrylate resulting in the highly functionalized cinnamates 9a-d. A subsequent deprotonation of the piperidinones using NaN(SiM₃)₂ in THF induced an intramolecular Michael addition of the enolate to the cinnamate part. In this way, a range of novel 2,6-methano-4H-4-benzazonines 10-13 were obtained. In each case, a separable mixture of endo/exo-diastereomers was obtained.