Halogenated ketenes. 39. A new synthesis for substituted coumarins

A new general synthesis of substituted coumarins is described. The in situ cycloaddition of chloroketenes with α-methoxymethylenecyclohexanones yields (4 + 2) cycloaddition products, 3,4-dihydro-2-pyranones. The chlorine atom is reductively removed and methanol is spontaneously eliminated to yield the 5,6,7,8-tetra-hydrocoumarins. Dehydrogenation of these compounds results in good yields of the substituted coumarins.     

Synthesis of C3-dihydrofuran substituted coumarins via multicomponent approach

An efficient method was developed for the synthesis of dihydrofuran substituted coumarin from a one-pot, four-component reaction of 2-hydroxy aromatic aldehydes, 6-methyl, 4-hydroxy pyranone, aromatic aldehyde, and pyridinium ylide in the presence of tri-ethylamine under microwave irradiation. The reaction proceeds under solvent-free conditions to afford C3-dihydrofuran substituted coumarin in a diastereoselective manner in good yields (71–89%).     

A facile transformation of amino acids to functionalized coumarins

The synthesis of novel chiral coumarins functionalized with proteinogenic amino acid side chains via N-protected γ-amino-β-keto esters and their incorporation into the cell permeable HIV-1 TAT peptide through the modified solid phase peptide synthesis are described.     

Temperature effect study upon the fluorescence emission of substituted coumarins

The interpretation of temperature effect on fluorescence emission is rather complicated and not well understood. Several established temperature influences are not the most likely contributors to the non-radiative decay process. In order to understand the effect of temperature in the excited state, the fluorescence emission spectra of 4-methyl-7-methoxy (I), 4-methyl-5,7-diethoxy (II), 4-methyl-5-ethoxy-7-methoxy (III) and 4-methyl-7,8-diethoxy (IV) coumarins in aqueous solution as well as in benzene solution have been studied at different temperatures. It is observed that the fluorescence intensity decreases with increase in temperature for the first three coumarins but remains constant in the case of 4-methyl-7,8-diethoxy coumarin (IV). The radiative life-time and the activation energy for the deactivation process have been estimated. It seems that intramolecular quenching by the substituent group plays an important role in the deactivation process. The possible physical interpretation of the quenching mechanism is discussed in terms of the position and the nature of the substituent groups which could twist about the connecting bonds leading to a non-planar non-fluorescent state of the molecule.     

A facile synthesis of substituted benzyl selenocyanates

Benzyl selenocyanates can be made from the corresponding benzylic bromides or chlorides in 30-60 minutes using acetonitrile as a solvent. The products may be obtained pure in satisfactory yields without recourse to chromatography.     

Synthesis of substituted 2H[1]benzopyrans from coumarins and chromones

A convenient route to substituted 2H[1]benzopyrans is described in which trialkylaluminium compounds are added to coumarins or chromones and the resultant Z-2-(3-hydroxy-1-propenyl)phenols are converted by thermal cyclization in the presence of silica gel to 2H[l]benzopyrans.     

A facile preparation of imidazolinium chlorides

A process for the preparation of symmetric and unsymmetric imidazolinium chlorides that involves reaction of a formamidine with dichloroethane and a base (a) is described. This method makes it possible to obtain numerous imidazolinium chlorides under solvent-free reaction conditions and in excellent yields with purification by simple filtration. Alternatively, symmetric imidazolinium chlorides can be prepared directly in moderate yields from substituted anilines by utilizing half of the formamidine intermediate as sacrificial base (b).     

A facile preparation of vinyl sulfides

Vinyl sulfides are formed in high yield by the alkylation of trimethylsiloxy mercaptides.     

A facile preparation of 2,6-diarylpyrazines

2,6-Diarylpyrazines were prepared in good yields by a novel method of condensing methoxycarbonylhydrazine with N,N-bis(arylcarbonylmethyl)-p-toluenesulfonamides, unsymmetrical derivatives of which were synthesized by a new (or different) procedure. The structures of these 2,6-diarylpyrazines were established by spectral data and X-ray diffraction analysis. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:341–345, 1998     

A facile synthesis of some substituted furopyrimidine derivatives

Some substituted furopyrimidine derivatives are prepared in high yield in 4 steps, starting from the reaction of furoin (1,2‐di(furan‐2‐yl)‐2‐hydroxyethanone) and malonitrile.     

A facile preparation of backbone-substituted, functionalized and chiral imidazolinium salts

A versatile and modular method for the preparation of various backbone-substituted, functionalized and chiral imidazolinium salts from the reaction of formamidines with alkene oxides has been described, providing a more straightforward access to substituted imidazolinium salts than the previously reported methods.     

A facile preparation of differentiated 1,2-divinylcycloalkanols

A method is described which permits one-step conversion of 2-chlorocycloalkanones to differentiated 1,2-divinylcycloalkanols, 2-vinylcycloalkanones, or 2-vinylcycloalkanols.     

A facile preparation of selenohydantoins using isoselenocyanate

Reactions of isoselenocyanate with methyl aminoacetate hydrochlorides in the presence of triethylamine afforded selenohydantoins, 2‐selenoxoimidazolidin‐4‐ones, in high yields.     

A facile one-step preparation of chlorofluoromethylene olefins

The “insitu” reaction of triphenylphosphine, fluorotrichloromethane, zinc dust, and an aldehyde or ketone in dimethylformamide at 60°C provides a facile one-step synthesis of chlorofluoromethylene olefins. A study of representative examples of carbonyl compounds demonstrates that this approach gives yields of olefinic products comparable to other more elaborate or expensive synthetic routes. It should prove to be synthetically useful for the preparation of chlorofluoromethylene olefins from aldehydes and reactive ketones.