Solvent-free and room temperature synthesis of thiochromans in the presence of a catalytic amount of tungstophosphoric acid

Tungstophosphoric acid catalyzed rapid and good yielding reactions of α,β-unsaturated aldehydes with arenethiols to give the corresponding 4-thioaryl-1,2,3,4-tetrahydro-1-benzothiopyrans (thiochromans) under solvent-free and room temperature conditions.     

Use of cheaper metal than Rh, CHCl3-free Pd catalyst, in 1,2-addition of aromatic aldehydes with arylboronic acids

Pd(OAc)₂-(±)-tol-BINAP-catalyzed arylation reaction of aromatic aldehydes with arylboronic acids in the absence of CHCl₃ is described.     

Synthesis of glyoxylyl peptides using a phosphine labile α,α′-diaminoacetic acid derivative

We describe in this letter the preparation of a novel protected α,α′-diaminoacetic acid derivative that acts as a masked glyoxylic acid equivalent. The reagent could easily be introduced on a peptide chain using standard Fmoc/tert-butyl solid-phase methods and resisted to the TFA treatment allowing the deprotection and cleavage of the peptide. Unmasking of the glyoxylyl group was performed in solution in the presence of a phosphine.     

Synthesis of tetrachloroisophthalic and-terephthalic aldehydes and stable bis(nitrile oxides) based on them

A new route for the synthesis of 2,4,5,6-tetrachloroisophthalic and 2,3,5,6-tetrachloroterephthalic aldehydes from the corresponding tetrachlorobenzenes was developed. The method involves dichloromethylation of the initial compounds with chloroform in the presence of aluminum chloride and subsequent hydrolysis of the resulting 1,3-bis(dichloromethyl)-2,4,5,6-tetrachlorobenzene and 1,4-bis(dichloromethyl)-2,3,5,6-tetrachlorobenzene. Stable 2,4,5,6-tetrachlorobenzene-1,3-dicarbonitrile oxide and 2,3,5,6-tetrachlorobenzene-1,4-dicarbonitrile oxide were obtained for the first time from the above aldehydesvia the corresponding oximes. The products were characterized by IR and¹³C NMR spectra, and were converted into substituted 1,3- and 1,4-phenylenebis(isoxazolines) using 1,3-dipolar cycloaddition with styrene. Translated fromIzvestiya Akademit Nauk. Seriya Khimicheskaya, No. 1, pp. 106–109, January. 1997.     

A novel sodium carbonate-catalyzed regioselective synthesis of pyrano[2,3-h]coumarins using a three-component reaction

In this work, a novel, convenient, and efficient approach to the synthesis of pyrano[2,3-h]coumarins has been reported based on the multicomponent reaction. The one-pot reaction between 5,7-dihydroxy-4-methylcoumarin, dialkyl acetylenedicarboxylate and aromatic aldehydes catalyzed by sodium carbonate lead to the formation of a novel class of pyrano[2,3-h]coumarin derivatives. High atom-economy, excellent yields, simple procedure, and mild reaction conditions are the important features of this protocol. This method allows access to a variety of pyrano[2,3-h]coumarins via using a broad substrate scope.     

KF/clinoptilolite nanoparticles as a novel catalyst for the green synthesis of chromens using three component reactions of 4‐hydroxycoumarins: Study of antioxidant activity

In this research, the green synthesis of chromen derivatives in good yields is described via three‐component reactions of 4‐hydroxycumarine, aldehydes or ketones, and methyl ketones in the presence of KF/clinoptilolite nanoparticles (KF/CP‐NPs) under solvent‐free conditions at 50°C in low time. The present methodology suggests some advantages such as low reaction time, easy and simple procedure, green method, inexpensive catalyst, high yield of product, and existence of different substrates for performing these reactions. In addition, it should be mentioned that antioxidant activity was studied for some prepared compounds, such as 4a–4d, by DPPH radical trapping and reducing potential tests of ferric ion and then comparing results with TBHQ and BHT as synthetic antioxidants. In this study, compounds 4c was shown to have moderate DPPH radical trapping, and compounds 4b and 4d displayed good reducing power of ferric ion.     

Palladium-Catalyzed Direct C2-and Further C7-Acylation of Indoles with Aldehydes

The palladium‐catalyzed direct C2‐ and further C7‐acylation of indoles with aldehydes have been developed. This method provides a convenient pathway toward a variety of mono‐ and diacylated indoles.     

Reactions of a Silylyne Complex with Aldehydes: Formation of W−Si−O−C Four-Membered Metallacycles and Their Metathesis-Like Fragmentation

A tungsten silylyne complex having a W≡Si triple bond reacted with two molecules of aldehydes at room temperature to give W−Si−O−C four-membered metallacycles by [2+2] cycloaddition and subsequent formyl hydrogen transfer from one aldehyde molecule to another. Upon heating to 70 °C, the four-membered metallacycles underwent metathesis-like fragmentation cleanly to afford carbyne complexes and “silanoic esters,” in a manner similar to that of metallacyclobutadiene, an intermediate of alkyne metathesis reactions, and dimerization of the latter products gave 1,3-cyclodisiloxanes. The “silanoic ester” was also trapped by pivalaldehyde to give a [2+2] cycloaddition product in high yield.     

Palladium on activated carbon catalyzed reductive amination of aldehydes and ketones by triethylsilane

Various aldehydes and ketones were efficiently transformed into the corresponding amines using amine derivatives in the presence of triethylsilane and a catalytic amount of palladium on activated carbon in ethanol. The proposed method provides a one‐pot synthesis of various amines in excellent yields after short reaction times. Copyright © 2013 John Wiley & Sons, Ltd.