B(C6F5)3 catalyzed synthesis of dihydropyrano[3,2-b]chromenediones under solvent-free conditions

Abstract

A simple, efficient, solventless, and one step, B(C₆F₅)₃ catalyzed, synthesis of dihydropyrano[3,2-b]chromenediones from dimedone, aldehyde and kojic acid is described. This protocol proceeds smoothly, accommodates aromatic as well as heteroaromatic aldehydes and gives dihydropyrano[3,2-b]chromenediones in excellent yield.     

Microwave-assisted novel synthesis of amino-thieno[3,2-b]pyridines under solvent-free conditions

In the presence of a catalytic amount of ytterbium(III) triflate and under microwave irradiation, mixtures of 2-amino-3-thiophenecarbonitriles, ketones, and silica gel afforded smoothly the corresponding amino-thieno[2,3-b]pyridine derivatives in one step. A wide variety of ketones were tested under these conditions. The reactions proceeded rapidly and afforded the desired products in good to excellent yields.     

Domino Knoevenagel hetero-Diels-Alder reactions: a stereoselective synthesis of sugar fused furo[3,2-b]pyrano[4,3-d]pyran derivatives

The O-prenyl derivative of a sugar aldehyde derived from d-glucose undergoes smooth intramolecular domino Knoevenagel hetero-Diels-Alder reactions with 1,3-diones to afford a novel class of carbohydrate analogues, cis-fused furopyranopyrans in good yields with a high degree of chemoselectivity. The stereochemistry of the products was assigned by NMR.     

A novel heterotricyclic assembly through intramolecular imino Diels-Alder reaction: synthesis of pyrrolo[3,4-b]quinolines

The synthesis of a series of hexahydropyrrolo[3,4-b]quinolines has been achieved in excellent yields by the reaction of aldimines derived from aromatic amines and N-prenylated aliphatic aldehydes in acetonitrile with InCl₃ as a catalyst in a short duration of time.     

Domino Knoevenagel-hetero-Diels-Alder reactions: a stereoselective synthesis of sugar-annulated furo[3,2-b] pyrano[4,3-d]pyran derivatives

The O-propargyl derivative of a sugar aldehyde derived from d-glucose undergoes smooth intramolecular domino Knoevenagel-hetero-Diels-Alder reactions with 1,3-diketones in the presence of CuI/Et₃N system in refluxing methanol to afford a novel class of carbohydrate analogues, furopyranopyrans in good yields. 1-Aryl-pyrazol-5-ones also undergo smooth coupling with O-propargyl tethered sugar aldehyde under similar conditions to furnish pyrazole-annulated furopyranopyrans. The stereochemistry of the products was assigned by various NMR experiments.     

Synthesis of some novel functionalized dihydropyrido[2,3-d]pyrimidines via an one-pot three-component reaction catalysed by InCl3

Some novel functionalized dihydropyrido[2,3-d]pyrimidine derivatives 4 were synthesized using a one-pot three-component reaction of 6-aminouracils 1, aryl aldehydes 2 and 3-cyanoacetyl indole 3 using InCl₃ as catalyst.     

Unprecedented InCl3-catalyzed formation of cis-fused perhydrofuro[2,3-b]oxepines

2-Methylindole and its N-substituted derivatives react smoothly with 2,3-dihydrofuran (DHF) in the presence of a catalytic amount of InCl₃ under mild conditions to afford the corresponding 2-methyl-3-perhydrofuro[2,3-b]oxepin-4-yl-1H-indole derivatives in fairly good yields with high diastereoselectivity, while 3,4-dihydro-2H-pyran (DHP) affords exclusively 5,5-di(1H-3-indolyl)-1-pentanol derivatives in high yields under similar reaction conditions.     

InBr3-catalyzed three-component, one-pot synthesis of imidazo[1,2-a]pyridines

Indium(III) bromide has been used for the first time for the synthesis of imidazo[1,2-a]pyridines in a one-pot operation from 2-aminopyridine, aldehydes, and alkynes. InBr₃ was found to be more effective for the activation of both alkyne and imine derived from aryl aldehyde and 2-aminopyridine.     

BF3·OEt2-catalyzed tandem Prins Friedel-Crafts reaction: a novel synthesis of sugar fused diarylhexahydro-2H-furo[3,2-b]pyrans

d-Glucose based homoallylic alcohol reacts smoothly with various aldehydes in the presence of arenes and a catalytic amount of BF₃·OEt₂ under mild conditions to afford a novel series of 5,7-diaryl-hexahydro-2H-furo[3,2-b]pyrans in good yields with high cis-selectivity.     

FeCl3-catalyzed three-component reaction: a novel synthesis of tetrahydro-2,6-dioxopyrimidin-4-yl-2,3-dihydrophthalazine-1,4-dione derivatives under solvent-free conditions

Three-component coupling of phthalhydrazide, aldehydes, and barbituric acid has been accomplished in the presence of 15 mol % FeCl₃ under solvent-free conditions to afford the corresponding tetrahydro-2,6-dioxopyrimidin-4-yl)-2,3-dihydrophthalazine-1,4-dione derivatives in excellent yields. This method provides high yields, shorter reaction time, and mild reaction conditions. This is the first example of the condensation of phthalhydrazide, aldehydes, and barbituric acid to provide a novel series of phthalhydrazide derivatives.     

Microwave promoted diastereoselective synthesis of dihydroindeno[1,2-b]furans via one-pot three-component reaction in solvent-free conditions

An efficient method was developed for the synthesis of fused dihydroindeno[1,2-b]furans. One-pot three-component reaction of 1,3-indanedione, aromatic aldehyde and pyridinium ylide in the presence of triethylamine under microwave-irradiation in solvent-free conditions afforded dihydroindeno[1,2-b]furans in a diastereoselective manner in excellent yields.     

InCl3-catalyzed four-component reaction: a novel synthesis of N-carbazolyl dihydropyridines

We have developed a simple, efficient, and environmentally benign microwave-assisted InCl₃-catalyzed synthesis of N-carbazolyldihydropyridines via a four-component reaction of 3-amino-9-ethylcarbazole, malononitrile, aromatic aldehydes, and acetylenic esters. The use of microwave heating allowed for reduced reaction times and resulted in higher yields. This four-component reaction is atom-efficient, high-yielding, and applicable to a wide variety of four-component reactions.     

Regioselective synthesis of fused benzopyrazolo[3,4-b]quinolines under solvent-free conditions

New 6,8-dihydro-5H-benzo[f]pyrazolo[3,4-b]quinolines 6 have been obtained in a novel solvent-free three-component reaction involving β-tetralone along with 5-aminopyrazoles 1 and benzaldehydes 2. The isomeric 6,10-dihydro-5H-benzo[h]pyrazolo[3,4-b]quinolines 9 could not be prepared in a similar fashion directly from α-tetralone, but were obtained by the reaction of amines 1 with benzylidene-derivative 10 of α-tetralone in similar conditions. The yields of quinolines obtained via this novel protocol were good and the reaction times varied from few minutes to just few seconds.     

Ugi-type four-component reaction for a novel synthesis of 5-oxo-perhydrofuro[3,2-b]pyran carboxylate derivatives

The four-component coupling (4CC) of sugar hydroxyaldehyde, Meldrum’s acid, isocyanide, and a secondary alcohol in dichloromethane has been accomplished at room temperature in a highly stereoselective manner to produce a novel class of carbohydrate derivatives, 5-oxo-perhydrofuro[3,2-b]pyrans in good yields with trans-selectivity. The stereochemistry of the products was assigned by various NMR experiments.     

An efficient diastereoselective synthesis of spiro pyrido[2,1-b][1,3]oxazines via a novel pyridine-based three-component reaction

The zwitterions generated from pyridine and dialkyl acetylenedicarboxylate (DAAD) reacted with benzofuran-2,3-diones to form highly substituted spiro pyrido[2,1-b][1,3]oxazines in good to high yields without using a catalyst.     

Studies with enaminones and enaminonitriles: synthesis of 3-aroyl and 3-heteroaroyl-pyrazolo-[1,5-a]pyrimidines

The reaction of electron rich aromatics with cyanoacetic acid and acetic anhydride afforded 3-oxoalkanenitriles. Indium trichloride was used as a Lewis acid catalyst when the aromatic ring was not sufficiently reactive. The synthesized 3-oxoalkanenitriles were subsequently condensed with dimethylformamide dimethylacetal (DMFDMA) to yield enaminones that reacted readily with hydrazine hydrate to yield 4-aroylpyrazole-3-amines. The 4-aroylpyrazole-3-amines were condensed with enaminones to yield 3-aroylpyrazolo[1,5-a]pyrimidines.     

Photochemical synthesis of benzoxazolo[3,2-b]isoquinolin-11-one and isoquinolino[3,2-b][1,3]benzoxazin-11-one under basic conditions

Irradiation of N-phenyl substituted isoquinolines in acetonitrile containing 1 M NaOH in a multilamp reactor (MLR) furnished benzoxazolo[3,2-b]isoquinolin-11-ones. In contrast, irradiation of the N-benzyl substituted isoquinoline derivative under the same conditions afforded the hydrolysed N-benzylbenzamide derivative. The isoquinolinobenzoxazine was obtained by irradiating the N-benzyl substituted isoquinoline derivative at higher basic conditions. The required isoquinolines were synthesized under solvent-free, solid supported microwave conditions.     

Al(OTf)3-catalyzed one-pot synthesis of pyrrolo[3,2-d]pyrimidinedione derivatives

A series of polysubstituted pyrrolo[3,2-d]pyrimidinedione derivatives have been synthesized in excellent yields. This prominent scaffold is obtained via an Al(OTf)₃-catalyzed tandem addition-annulation sequence between propargylic alcohols and aminopyrimidines. The process is simple, facile, inexpensive, and provides a diverse range of substituted pyrrolo [3,2-d]pyrimidinedione derivatives with short reaction times from readily obtainable starting materials.     

InBr3-catalyzed annulations of cyclic 1,3-diketones with aryl propargyl alcohols: a novel synthesis of 2,4-diaryldihydropyrans

The cyclic 1,3-dicarbonyl compounds undergo smooth cyclization with aryl propargyl alcohols in the presence of 10 mol % indium tribromide in refluxing dichloroethane to produce 2,4-diarylpyran derivatives in good yields with high selectivity.     

Sc(OTf)3-catalyzed sugar based tandem ene-Prins cyclization: a novel synthesis of hexahydro-2H-furo[3,2-b]pyranopyran scaffolds

Ttandem ene-Prins cyclization between an aldehyde and an olefin tethered sugar aldehyde has been achieved using a catalytic amount of scandium triflate (10 mol %) at ambient temperature to give a novel series of sugar annulated pyranopyran derivatives in good yields with high selectivity. This is the first report on sugar based ene-Prins cyclization between an aldehyde and O-prenyl derivative of a sugar aldehyde.