An efficient route for the synthesis of 2-arylthiazino[5,6-b]indole derivatives

Substituted 2-thiobenzamidomethylindole derivatives (14a-e) were prepared by the reaction of 2-aminomethylindole (9) with substituted benzoyl chlorides, followed by sulfurization using Lawesson's reagent. Alternatively, these thioamides were obtained from the amine in one step in an efficient manner by using substituted benzaldehydes in the presence of sulfur, or at room temperature with the aid of substituted methyl dithiobenzoates. The Hugerschoff reactions of thiobenzamides (14a-e) with phenyltrimethylammonium tribromide provided the rare title 2-arylthiazino[5,6-b]indoles (15a-e) in good yields. A convenient one-pot approach for the synthesis of 2-phenyl-1,3-thiazino[5,6-b]indole (15a) from 2-aminomethylindole (9) is also described.     

A facile synthesis of pyrrolo[1,2-a]benzimidazoles and pyrazolo[3,4:4′,3′]pyrrolo[1,2-a]benzimidazole derivatives

Reaction of 2-cyanomethylbenzimidazole 1 with hydrazonoyl halides 2 led to formation of pyrrolo[1,2-a]benzimidazole derivatives 7. Similar reaction of 1 with halides 3 afforded 5-amino-4-(benzimidazol-2-yl)pyrazole derivatives 11 or 1-amino-2-arylpyrazolo[3,4:4′,3′]pyrrolo[1,2-a]benzimidazol-4-one 14 depending on the reaction conditions. The mechanisms of the studied reactions are discussed.     

Synthesis of tetrahydropyrido- and pyrido-[1′,2′:1,2]imidazo[4,5-b]pyrazine derivatives

Reactions of tetrafluoropyridazine with iminopiperidine and 2-aminopiccoline gave novel tetrahydropyrido- and pyrido-[1′,2′:1,2]imidazo[4,5-b]pyrazine heterocyclic frameworks respectively in high yields.     

2-Amidinylindole-3-carbaldehydes: synthesis of new tetracyclic compounds containing the pyrrolo[1,2-c]1,4-diazepine ring

2-Amidinylindol-3-carbaldehydes bearing an α-alkoxycarbonyl substituent on the cyclic-tertiary amine moiety were prepared. Pyrolysis of these amidines in diethylenglycol-monoethyl ether produced mainly a pyrrolo[1′,2′-1,2]-1,4-diazepino[5,6-b]indol-7,11-dione. A similar result was obtained starting from 2-amidinylbenzofuran-3-carbaldehyde.     

Synthesis of pyrido[2′,1′:2,3]imidazo[4,5-b]quinoline and pyrido[1′,2′:1,2]imidazo[4,5-b]quinoline and their benzo and aza analogs via tandem catalysis

In this paper we report regioselective tandem metal-catalyzed aminations on dihaloquinolines (2-chloro-3-iodoquinoline and 2,3-dibromoquinoline) with amino(benzo)(di)azines. Eight new heterocyclic scaffolds of the dipyridoimidazole type could be synthesized. By controlling the reaction temperature selective C-2 intermolecular Pd-catalyzed amination on 2,3-dibromoquinoline with amino(benzo)(di)azines can be achieved.     

Synthesis of pyrrolo[3,4-b]pyrroles and perhydrothiazolo[3′,4′-2,3]pyrrolo[4,5-c]pyrroles

The 1,3-dipolar cycloaddition reactions of various N-tethered alkenyl aldehydes with some cyclic and acyclic amino acids have been studied. Some key sulfonamides having strategically positioned aldehyde and olefinic tether have been synthesized and effectively subjected to intramolecular azomethine ylide cycloaddition reaction resulting in a series of pyrrolo[3,4-b]pyrrole and its N-1-C-2 derivatives, and a series of novel heterotricyclic compounds, perhydrothiazolo[3′,4′-2,3]pyrrolo[4,5-c]pyrroles, in good yields. The intramolecular cycloaddition reaction was found to be highly stereoselective to form only cis-fused cycloadducts in all cases.     

Synthesis and conformational analysis of naphth[1′,2′:5,6][1,3]oxazino[3,2-c][1,3]benzoxazine and naphth[1′,2′:5,6][1,3]oxazino[3,4-c][1,3]benzoxazine derivatives

A new functional group, the hydroxy group, was inserted into a Betti base by reaction with salicylaldehyde, and the naphthoxazine derivatives thus obtained were converted by ring-closure reactions with formaldehyde, acetaldehyde, propionaldehyde or phosgene to the corresponding naphth[1′2′:5,6][1,3]oxazino[3,2-c][1,3]benzoxazine derivatives. Further, the conformational analysis of these polycyclic compounds by NMR spectroscopy and an accompanying molecular modelling are reported; especially, both quantitative anisotropic ring current effects of the aromatic moieties in these compounds and steric substituent effects were employed to determine the stereochemistry of the naphthoxazinobenzoxazine derivatives.     

A facile,catalyst-free synthesis of new polycyclic pyrrolo[1,2-b]pyrazolone derivatives

A convenient and efficient procedure has been developed for the synthesis of a new ring system, pyrrolo[1,2-b]pyrazolone, via two-component coupling reaction followed by base mediated intramolecular cyclization. Single-pot synthesis replacing the two step process has also been successfully carried out. A series of polycyclic pyrrolo[1,2-b]pyrazolone derivatives have been obtained by employing the procedure along with some fused pyrrol-1-ylamine system. The products were formed very rapidly in catalyst free condition in a good yield (up to 75%) and also it had tolerance to a wide scope of substrates.     

Efficient synthesis of novel dipyridoimidazoles and pyrido[1′,2′;1,2]imidazo[4,5-d]pyridazine derivatives

Novel dipyrido[1,2-a;3′,4′-d]imidazoles 7a-d, dipyrido[1,2-a;4′,3′-d]imidazoles 8a,c and pyrido[1′,2′;1,2]imidazo[4,5-d]pyridazine derivatives 9a-d were synthesized by two pathways: thermal electrocyclic reaction of 3-alkenylimidazopyridine-2-oximes 10 and direct condensation of ethyl glycinate (or hydrazine) with 2,3-dicarbonylimidazo[1,2-a]pyridines 11.     

Improved synthesis of N-alkyl substituted dithieno[3,2-b:2′,3′-d]pyrroles

A new, convergent and improved synthetic method to prepare N-alkyl substituted dithienopyrroles is described. The procedure consists of a Pd-catalyzed amination of 3,3′-dibromo-2,2′-bithiophene. The reaction conditions were optimized, which makes this method applicable to prepare these molecules easily in high yields and on a large scale.     

Pyrazolo[2′,3′:3,4][1,3]oxazino[5,6-b]quinoxaline, a novel tetracyclic ring system

Reaction of 2-chloro-3-(3-chloro-1H-pyrazol-5-yl)quinoxaline and aldehydes does not afford the corresponding N-(α-hydroxyalkylated) derivatives but results in a cyclisation reaction to give a derivative bearing the hitherto undescribed pyrazolo[2′,3′:3,4][1,3]oxazino[5,6-b]quinoxaline system.     

Synthesis of pyridino[3′,2′:4,5]pyrrolo[3,2-g]pyrrolo[3,4-e]indolizin-1,3-dione and pyrrolo[3,2-c]pyrazole skeletons

A three step synthesis of an isogranulatimide analogue, in which the imidazole moiety is replaced by a pyrrole unit and the indole heterocycle is replaced by a 7-azaindole moiety is described. Moreover, a novel synthetic pathway to the pyrrolo[3,2-c]pyrazole skeleton is reported.     

First synthesis of 4-aminopyrido[2′,3′:4,5]furo[3,2-d]pyrimidines

This Letter describes for the first time the synthesis of pyrido[2′,3′:4,5]furo[3,2-d]pyrimidines substituted by a primary or secondary amino group on position 4 of the pyrimidine ring. Application of microwave irradiation technology allowed fast and convenient procedures.     

An efficient entry to pyrrolo[1,2-b]isoquinolines and related systems through Parham cyclisation

Aryllithiums generated by lithium-iodine exchange undergo intramolecular cyclisation to give pyrrolo[1,2-b]isoquinolines, in high yields. The best results were obtained when Weinreb or morpholine amides were used as internal electrophiles. The procedure has been extended to the preparation of seven and eight membered rings, opening a route to benzazepine and benzazocine skeletons.     

Synthesis of substituted dipyrido[3,2-a:2′,3′-c]phenazines and a new heterocyclic dipyrido[3,2-f:2′,3′-h]quinoxalino[2,3-b]quinoxaline

Three new α,α′-diimine ligands were synthesized based on condensation of 1,10-phenanthroline-5,6-dione with 1,2-phenylenediamine derivatives using different approaches. All compounds were fully characterized by IR, ¹H and ¹³C NMR, UV-visible, and MS spectroscopies. We report the first example of a dipyrido[3,2-f:2′,3′-h]quinoxalino[2,3-b]quinoxaline, which exhibits a strong absorption at 430 nm and an interesting electrochemical behavior. These new molecules may have biological potential and are of synthetic and technological importance.     

From N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine to propeller-shaped N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)-amine: syntheses and structures

Three unique propeller-shaped helicenyl amines compounds: N,N-diphenyl-N-naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl-amine (1), N-phenyl-N,N-di(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (2), and N,N,N-tri(naphtho[2,1-b]thieno[2,3-b:3′,2′-d]dithiophene-5-yl)amine (3) were efficiently synthesized by Wittig reaction and oxidative photocyclization. The crystal structures of 1, 2 and molecular configuration optimization (DFT-B3LYP/6-31+G(d)) of 3 reveal that the steric hindrance from the moiety of trithia[5]helicene effectively forces the nitrogen atom and the three bonded carbon atoms to coplanar and the interplanar angles of the facing terminal thiophene ring and benzene ring becoming larger when the helical arm increased from 1 to 3. Electrochemical properties and UV–vis absorption behaviors of 1, 2, 3 were primarily determined by the moiety of trithia[5]helicene.     

Pd-Mediated synthesis of 7H-benzo[3,4]azepino[1,2-a]indole-6-carboxylic acid derivatives from indole-containing Baylis-Hillman adducts

We synthesized novel tetracyclic fused indole derivatives via the intramolecular Heck reaction of indole-containing Baylis-Hillman adducts in good to moderate yields.     

Photo-induced aromatic assembly of benzocycloalka[1,2-b] furan and spiro[furan-2(3H),1′-benzocycloalkane] derivatives

The photo-induced benzannulation of benzocycloalka[1,2-b]furans produced hydrohelicene-type compounds in good yields. A similar photoreaction of the spiro[furan-2(3H),1′-benzocycloalkane]s afforded dihydrophenalene derivatives in moderate yields. Benzo[kl]xanthene was also formed by a similar photoreaction of spiro[furan-2(3H),9′-xanthene]. The reaction pathway was elucidated by the ¹H NMR spectrum of the reaction mixture and the alternative synthesis of the intermediate.     

A novel and efficient one-pot synthesis of furo[3′,4′:5,6]pyrido[2,3-c]pyrazole derivatives using organocatalysts

A novel approach to one-pot synthesis of dihydrofuro[3′,4′:5,6]pyrido[2,3-c]pyrazole and indeno[2′,1′:5,6]pyrido[2,3-c]pyrazole derivatives have been investigated using organocatalysts that are recyclable. This new protocol has the advantages of environmental friendliness, higher yield, low cost, as well as convenient operation. The catalytic efficiency of various small organocatalysts such as l-proline, trans-4-hydroxy-l-proline, l-thiaproline, cinchonidine, (+)-cinchonine, and dl-2-phenylglycine has also been studied.     

Cyclisation of 3-alkenylpyrido[1,2-a]pyrimidines to furo[2,3-d]pyrido[1,2-a]pyrimidines

3-Alkenylpyrido[1,2-a]pyrimidines react under mild conditions to give novel tricyclic furo[2,3-d]pyrido[1,2-a]pyrimidines in high yields. The cyclisation takes place in the presence of an acid catalyst. The product yield is affected by the type and the strength of the acid used. Exceptionally high yields were obtained when an organic acid like trifluoromethanesulfonic acid and trifluoroacetic acid were used. On the other hand, sulfuric acid gave the best results of the inorganic acids examined.