An expedient microwave-assisted, solvent-free, solid-supported synthesis of pyrrolo[2,3-d]pyrimidine-pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives by intramolecular hetero Diels-Alder reaction

A rapid synthesis of pyrrolo[2,3-d]pyrimidine annulated pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives has been accomplished in good yields via an intramolecular domino hetero Diels-Alder reaction using microwave irradiation under solvent-free, solid-supported conditions.     

A rapid access to indolo[2,1-a]pyrrolo[4′,3′:4,5]pyrano[5,6-c]coumarin/[6,5-c]chromone derivatives by domino Knoevenagal intramolecular hetero Diels-Alder reactions

Knoevenagal condensation of indole-2-carbaldehyde containing an internal dienophile with coumarins, followed by domino intramolecular hetero Diels-Alder reaction, provides polycyclic heterocycles. Different approaches for stereo- and chemoselective synthesis of indolo[2,1-a]pyrrolo[4′,3′:4,5]pyrano[5,6-c]coumarin and indolo[2,1-a]pyrrolo[4′,3′:4,5]pyrano[6,5-c]chromone derivatives are described.     

Convenient synthesis of fused pyrano[3,2-h]- and furo[3,2-h]benzo[f]coumarins from naphthalene-2,3-diol

The treatment of 8-propargyloxy-benzo[f]coumarin with boron trifluoride diethyl etherate in N,N-dimethylformamide under reflux or MW irradiation resulted in pyrano[3,2-h]benzo[f]coumarin, while the furo[3,2-h]benzo[f]coumarin is received from the treatment with N-methylformamide under MW irradiation.     

Synthesis of some novel spiro substituted pyrido[2,3-c]coumarins by exploring ‘tertiary amino effect’ reaction strategy

Some novel spiro substituted pyrido[2,3-c]coumarin derivatives were synthesized from 4-hydroxycoumarin by exploring ‘tertiary amino effect’ reaction strategy.     

Photochemistry of 3H-furo[3,4-c]pyrazoles and 3H-thieno[3,4-c]pyrazoles

The first examples of 3H-furo[3,4-c]pyrazoles and 3H-thieno[3,4-c]pyrazoles were prepared in an attempt to isolate examples of cyclopropane-fused thiophenes and furans. Adducts of acetylenic ketones and 2-diazopropane were reacted with 10-camphorsulfonic acid or phosphorus pentasulfide to produce the title compounds. Photolysis of these compounds did not give the cyclopropane-fused products rather an unreported photochemical fragmentation was observed.     

A convenient approach to the design and synthesis of indolo[3,2-c]coumarins via the microwave-assisted Cadogan reaction

3-(4,5-Dimethoxy-2-nitrophenyl)coumarins bearing various substituents on the benzene ring of the coumarin system have been prepared from salicylaldehydes and 2-(4,5-dimethoxy-2-nitrophenyl)acetonitrile by means of the Perkin condensation. Further cyclization of these 3-aryl coumarins through the microwave-assisted Cadogan reaction afforded the corresponding indolo[3,2-c]coumarins in good to excellent yields.     

Novel 6-substituted benzothiazol-2-yl indolo[1,2-c]quinazolines and benzimidazo[1,2-c]quinazolines

The synthetic route to and a preliminary biological evaluation of novel indolo[1,2-c]quinazolines (8) and benzimidazo[1,2-c]quinazolines (9) are described. The products were obtained by condensation of the appropriate diamines (e.g. 2-(2-aminophenyl)indole or 2-(2-aminophenyl)benzimidazole) with 2-cyanobenzothiazoles. This work further demonstrates the general applicability of microwaves for a facile and rapid access to original heterocycles with potential pharmaceutical value.     

Synthesis of novel fluorescent benzo[a]pyrano[2,3-c]phenazine and benzo[a]chromeno[2,3-c]phenazine derivatives via facile four-component domino protocol

An efficient and practical route to novel fluorescent benzo[a]pyrano[2,3-c]phenazine framework has been developed by one-pot, four-component reaction of 2-hydroxynaphthalene-1,4-dione, 1,2-phenylenediamines, aromatic aldehydes, and Meldrum’s acid in glacial acetic acid at 70 °C. Photophysical studies of these compounds have been reported. Reactions involving cyclohexane-1,3-dione/5-methylcyclohexane-1,3-dione/dimedone in the place of Meldrum’s acid yielded corresponding benzo[a]chromeno[2,3-c]phenazine derivatives. Crystal structure of 3k established the regioisomer formed. Mild reaction conditions, good yields, short reaction time, and easy separation are some of the salient features of the present protocol.     

A new route to pyrazolo[3,4-c] and [4,3-c]pyridinones via heterocyclization of vic-substituted hydroxamic acids of acetylenylpyrazoles

We report in this paper the synthesis of 6-substituted pyrazolo[4,3-c]pyridin-4-ones, 6-substituted 5-hydroxypyrazolo[4,3-c]pyridin-6-ones, 5-substituted pyrazolo[3,4-c]pyridin-7-ones and 5-substituted 6-hydroxypyrazolo[3,4-c]pyridin-7-ones by heterocyclization of vic-acetylenylpyrazol-hydroxamic acids under the influence of copper(I) salt in dimethylformamide or with organic bases in butanol or methanol.     

A new strategy for the synthesis of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines and pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines

A series of pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines were prepared via oxidative cyclization of aldehyde N-(1,3-diphenylpyrazolo[3,4-d]pyrimidin-4-yl)hydrazones. Dimroth rearrangement of such a series yielded pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidines.     

Synthesis of original thiazoloindolo[3,2-c]quinoline and novel 8-N-substituted-11H-indolo[3,2-c]quinoline derivatives from benzotriazoles. Part I

Synthesis of novel thiazoloindolo[3,2-c]quinoline and 8-substituted-11H-indolo[3,2-c]quinolines was performed via Graebe-Ullmann thermal cyclization from appropriated N-arylated benzotriazoles. 7H-4,7-Diaza-benzo[de]anthracene, a by-product reaction structurally closed to pyridoacridine skeleton was also identified.     

Rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones to furo[3,4-c]quinoline-3,4(1H,5H)-diones

Thermally assisted base-catalyzed rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones 1 to the corresponding furo[3,4-c]quinoline-3,4(1H,5H)-diones 2 is reported, and a mechanism of the transformation is proposed.     

Substituted chromones in [3+2] cycloadditions with nonstabilized azomethine ylides: synthesis of 1-benzopyrano[2,3-c]pyrrolidines and 1-benzopyrano[2,3-c:3,4-c′]dipyrrolidines

Chromones bearing electron-withdrawing substituents at the 2- or 3-position react with nonstabilized azomethine ylides to produce 1-benzopyrano[2,3-c]pyrrolidines in good yields. Reactions of 3-cyanochromones proceed diastereoselectively to give 1-benzopyrano[2,3-c]pyrrolidines and tetrahydro-1H-spiro[chromeno[2,3-c]pyrrol-9,5′-oxazolidine]-9a-carbonitriles, depending on the reactant ratio, as a result of a 1,3-dipolar cycloaddition of the azomethine ylide at the double bond and carbonyl group of the chromone system. The latter undergoes demethylenation and recyclization into a novel hexahydrochromeno[2,3-c:3,4-c′]dipyrrole tetracyclic system on heating with hydrochloric acid.     

Short and efficient access to imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives

Access to N-protected or N-free imidazo[1,2-a]pyrrolo[3,2-c]pyridine derivatives as potential antiviral compounds was achieved in good yields from N-protected 7-amino-8-halo-2-methylimidazo[1,2-a]pyridines by catalytic coupling of terminal acetylenes under mild conditions using [PdCl₂(PPh₃)₂] or [Cu(Phen)(PPh₃)₂]NO₃.     

CuCl-catalyzed one-pot synthesis of 5,6-dihydropyrazolo[1,5-c]quinazolines

A simple and efficient procedure for the preparation of 5,6-dihydropyrazolo[1,5-c]quinazolines via CuCl-catalyzed tandem reaction of 5-(2-bromoaryl)-1H-pyrazoles with aldehydes and aqueous ammonia under nitrogen atmosphere has been developed. The usefulness of this novel methodology was showcased by its successful application in the preparation of a potential Eg5 inhibitor.     

Synthesis of some tetrazole fused pyrido[2,3-c]coumarin derivatives from a one-pot three-component reaction via intramolecular 1,3-dipolar cycloaddition reaction of azide to nitriles

Some novel tetrazole fused pyrido[2,3-c]coumarin derivatives 5/7/9 were synthesized from a one-pot three-component reaction of 4-chloro-3-formylcoumarins 2, sodium azide 3, and alkyl/aryl acetonitriles 4/6/8.     

Novel methods to functionalize thiazolo[4,5-c]pyridines

Novel substituted thiazole[4,5-c]pyridines have been synthesized in good yields from unsubstituted thiazole[4,5-c]pyridine using direct C-H coupling reactions and N-oxide rearrangement chemistry.     

An efficient synthesis of novel estrieno[2.3-b] and [3.4-c]pyrroles

An efficient protocol for the preparation of novel estrieno[2.3-b] and [3.4-c]pyrroles 1 and 2 using Pd(0)-catalyzed amination and Bischler indole synthesis is described.     

Structural studies of 4-aryloctahydro-pyrido[1,2-c]pyrimidine derivatives

¹³C cross-polarisation magic angle spinning NMR data have been reported for four derivatives of 4-aryl-octahydro-pyrido[1,2-c]pyrimidine-1,3-dione and the X-ray diffraction data for two (with 2′-Me and 2′-OMe). The crystal structures show the presence of centrosymmetric cyclic dimers with intermolecular C1O?H-N or C3O?H-N hydrogen bonds, the configuration at the chiral centres (C4 and C4_a) was determined as RR (SS). The twisting of aromatic ring at C4 with respect to the pyrido[1,2-c]pyrimidine skeleton is about 68-109°.     

A convenient synthesis of benzofuro[3,2-c]isoquinolines and naphtho[1′,2′:4,5]furo[3,2-c]isoquinolines

A convenient method for the preparation of benzofuro[3,2-c]isoquinoline derivatives is described. The condensation reaction of methyl 2-(chloromethyl)-benzoate with substituted salicylonitriles 7a-c and intramolecular cyclization of the resulting substituted methyl 2-[(2-cyanobenzyl)oxy]benzoates 10a-c using potassium tert-butoxide results in the substituted benzofuro[3,2-c]isoquinolin-5(6H)-ones 1a-c. The same sequence of reactions starting from 2-(chloromethyl)benzonitrile and compounds 7a-c gave substituted 5-aminobenzofuro[3,2-c]isoquinolines 13a-c. In addition, this method is useful for the synthesis of other heterocycles. For example, using 1-cyano-2-naphthol 16, instead of the salicylonitriles 7a-c, gives naphtho[1′,2′:4,5]furo[3,2-c]isoquinolines.