An expedient route to highly functionalized 2H-chromene-2-thiones via ring annulation of β-oxodithioesters catalyzed by InCl3 under solvent-free conditions

A convenient and one-pot synthesis of 3-aroyl/heteroaroyl-2H-chromene-2-thiones and benzo[f]2H-chromene-2-thiones has been developed by the condensation of β-oxodithioesters and salicylaldehydes/α-hydroxynaphthaldehydes in the presence of indium trichloride under solvent-free conditions. The reaction is operationally facile, readily scalable, and offers rapid entry into differentially substituted chromene-2-thione scaffolds.     

Electrochemically induced chain transformation of salicylaldehydes and alkyl cyanoacetates into substituted 4H-chromenes

Electrolysis of salicylaldehydes and alkyl cyanoacetates in ethanol in an undivided cell in the presence of sodium bromide results in the formation of substituted alkyl 2-amino-4-(1-cyano-2-alkoxy-2-oxoethyl)-4H-chromene-3-carboxylates in 85-95% yields.     

l-Proline-accelerated,eco-friendly synthesis of 9-substituted-2,3,4,9-tetrahydro-1H-xanthen-1-ones under mild conditions

An efficient l-proline-accelerated synthesis of 9-substituted-2,3,4,9-tetrahydro-1H-xanthen-1-one derivatives has been accomplished via one-pot condensation of dimedone or 1,3-cyclohexanedione with substituted salicylaldehydes under mild reaction conditions. This protocol demonstrates several notable advantages, including operational simplicity, short reaction times, environmentally friendly conditions, no necessity of extraction and chromatographic purification steps, and high yields of the target products.     

Environment-friendly organic synthesis using bismuth compounds. Bismuth triflate catalyzed synthesis of substituted 3,4-dihydro-2H-1-benzopyrans

A highly catalytic method for the synthesis of dihydrobenzopyrans from salicylaldehydes has been developed. An extension of this method to the synthesis of a pyrano[2,3,b]benzopyran has also been achieved. Bi(OTf)₃·xH₂O (1 < x < 4) (0.1 mol%) smoothly catalyzes the condensation of substituted salicylaldehydes with 2,2-dimethoxypropane to give the corresponding substituted 3,4-dihydro-2H-1-benzopyrans as a mixture of diastereomers (9:1) in moderate yields. The relative configuration of the methoxy groups in the two diastereomers was established by NOE experiments. The advantages of this method include the use of an easy to handle, inexpensive and relatively non-toxic catalyst.     

Potassium exchanged layered zirconium phosphate as catalyst in the preparation of 4H-chromenes

Substituted 4H-chromenes were easily prepared by reaction of salicylaldehydes and ethylcyanoacetate in solvent free conditions using potassium exchanged layered zirconium phosphate as catalyst.     

A novel carbanion-olefin intramolecular cyclization: synthesis of substituted 2-aroyl-3,4-dihydro-2H-benzopyrans from salicylaldehydes

Utilization of a novel carbanion-olefin intramolecular 6-endo-trig cyclization reaction to provide 2-aroyl-3,4-dihydro-2H-benzopyrans is described. Through a sequence of a Wittig reaction, O-alkylation, and carbanion-olefin intramolecular cyclization, salicylaldehydes were converted into a series of new 2-aroyl-3,4-dihydro-2H-benzopyrans in two steps or in one-pot reaction.     

A simple and convenient synthesis of 2-(perfluoroalkyl)-4H-chromenes from salicyl N-tosylimines or salicylaldehydes and methyl 2-perfluoroalkynoates

Et₃N-catalyzed reactions of salicyl N-tosylimines or salicylaldehydes with methyl 2-perfluoroalkynoates proceed smoothly at room temperature in dichloromethane (DCM) or dimethyl sulfoxide (DMSO) to give the corresponding fluorinated chromenes in good to excellent yields with high regioselectivity.     

New HA 14-1 analogues: synthesis of 2-amino-4-cyano-4H-chromenes

The synthesis of 2-amino-4-cyano-4H-chromene derivatives as new HA 14-1 analogues by a simple and efficient method is reported. In addition, the reaction of 2-amino-2H-chromene-3-carbonitriles, salicylaldehydes and amines results in the formation of new chromeno[2,3-d]pyrimidine derivatives.     

Pseudo four-component reaction of salicylaldehydes and cyclic ketones with two molecules of malononitrile: A facile and efficient way to synthesize 4-[2-(dicyanomethylene)cyclic or heterocyclic]-2-amino-4H-chromenes

A new type of catalytic cascade pseudo four-component reaction has been found. The simple and facile pseudo four-component reaction of salicylaldehydes and cyclic or heterocyclic ketones with two molecules of malononitrile catalyzed by sodium acetate at ambient temperature results in the formation of 4-substituted 2-amino-4H-chromenes in 70–90% yields. Thus, a new simple and efficient ‘one-pot’ method to synthesize substituted 2-amino-4H-chromenes was found directly from such reasonable starting compounds as salicylaldehydes, cyclic or heterocyclic ketones and malononitrile.     

One-pot synthesis of ortho-hydroxycinnamate esters

Phenols are converted to salicylaldehydes with paraformaldehyde, MgCl₂-Et₃N in THF, and subsequent treatment with methyl (triphenylphosphoranylidene)acetate gave the corresponding methyl ortho-hydroxycinnamate derivatives. The sequence is conveniently carried out as a one-pot procedure.     

A solvent-free protocol for the synthesis of 3-formyl-2H-chromenes via domino oxa Michael/aldol reaction

A new solvent-free, TBD-catalyzed protocol for the synthesis of 3-formyl-2H-chromenes is presented. Substituted salicylaldehydes 1 and 3-methyl-2-butenal 2 in the presence of 10 mol % of TBD underwent a domino oxa Michael/aldol reaction to effectively yield the corresponding 2H-chromene derivatives 3. The methodology represents an improvement either in terms of efficiency and sustainability as a small amount of catalyst is required and the work-up procedure is simple and straightforward.     

Reactions of salicyl N-tosylimines or salicylaldehydes with diethyl acetylenedicarboxylate for the synthesis of highly functionalized chromenes

Reactions of diethyl acetylenedicarboxylate with salicyl N-tosylimines or salicylaldehydes proceeded smoothly in the presence of DABCO or dimethylphenylphosphine under mild conditions to give the corresponding chromenes in excellent yields.     

In situ intramolecular difluorocarbene-triggered synthesis of 2-gem-difluoro-2,3-dihydrobenzofuran-3-ols

Herein we report an unprecedented reaction between substituted salicylaldehydes and SCDA to furnish 2,2-difluoro-2,3-dihydrobenzofuran-3-ols. The reaction is highly effective for a range of diverse salicylaldehydes bearing meta-electron-withdrawing substituents. Of particular interest was the discovery that the requirement for a base in the occurred reaction directly correlated with the pKa of the substrates used.     

Morita-Baylis-Hillman route to 4H-pyrrolo[1,2-a][1]benzazepine derivatives

A simple method for synthesizing substituted 4H-pyrrolo[1,2-a][1]benzazepines using acid-assisted cyclization of the Morita-Baylis-Hillman adducts of 2-(1H-pyrrol-1-yl)benzaldehydes with methyl acrylate or methyl vinyl ketone as a key step has been developed.     

Microwave-assisted synthesis of substituted 2-amino-1H-imidazoles from imidazo[1,2-a]pyrimidines

An efficient method for the synthesis of mono- and disubstituted 2-amino-1H-imidazoles via microwave-assisted hydrazinolysis of substituted imidazo[1,2-a]pyrimidines is reported. This protocol avoids strong acidic conditions and is superior to the classical cyclocondensation of α-haloketones with N-acetylguanidine.     

New domino approach for the synthesis of 2,3-disubstituted benzo[b]furans via copper-catalyzed multi-component coupling reactions followed by cyclization

An efficient domino process for the construction of 2,3-disubstituted benzo[b]furans has been developed via copper-catalyzed three-component coupling reactions of salicylaldehydes, amines, and alkynes followed by base-assisted O-annulation reaction.     

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.     

Transition-metal-free synthesis of (Z)-3-ylidenephthalides from 2-acyl-benzoic acids

We report a highly efficient method for the synthesis of (Z)-3-ylidenephthalides via intramolecular cyclization of readily available 2-acyl-benzoic acids mediated by TSTU at room temperature. Using this method, diversely substituted (Z)-3-ylidenephthalides have been generated in good to excellent yields. The application of the method is highlighted by gram-scale preparation of the antiplatelet drug n-butylphthalide.     

One-pot approach to the synthesis of novel 12H-chromeno[2′,3′:4,5]imidazo[1,2-a]pyridines in aqueous media

The chromeno-imidazo[1,2-a]pyridine scaffold was generated in an one pot condensation/cyclization reaction involving a salicylaldehyde and 1-(cyanomethyl)pyridinium chloride, in aqueous sodium carbonate solution. These novel compounds were isolated in 47-71% yield. The reaction pathway was followed by ¹H NMR spectroscopy allowing a clear understanding of the side reactions involved in the process.Different mono-substituted pyridinium chlorides were synthesized and reacted with mono-substituted salicylaldehydes and a detailed discussion of the scope of the synthetic method is also presented.     

KF/Al2O3催化下取代水杨醛与达米酮的反应

取代水杨醛与5,5-二甲基-1,3-环己二酮(达米酮)在KF/Al2O3催化下反应生成一系列苯并吡喃的衍生物.产物的结构通过红外光谱、核磁共振氢谱和元素分析进行表征,并通过X单晶衍射分析进一步证实产物的结构.