Synthesis of Substituted Quinolines and Coumarins through a Sequential Vinylic Substitution/Annulation Process

The mechanism of the Pd-catalyzed formation of coumarins: a theoretical study

The mechanism of the formation of coumarins via the Pd-catalyzed intramolecular hydroarylation of the C-C triple bond is elucidated computationally, in corroboration with experimental data. It is shown that the reaction follows the concerted metalation-deprotonation (CMD) mechanism. The typically suspected mechanisms of ambiphilic metal ligand activation (AMLA), electrophilic aromatic substitution (EAS), and oxidative addition (OA) are suggested to be non-competitive, based on predicted conformations and energetics. Two forms of the Pd catalysts are used: Pd(OAc)2, and Pd(TFA)2. The predicted activation free energy barrier for the TFA-based catalyst is lower, both in the gas phase and in the CH2Cl2 solvent, in agreement with the experimental observations. Adding electron-withdrawing groups to the catalyst assists the first and rate-limiting step of the reaction, the deprotonation of the aromatic ring, as understood through charge analysis.

Practical and convenient synthesis of coumarins from phenols and propiolic acid esters

This protocol describes the synthesis of 6,7-methylenedioxy-4-phenylcoumarin from sesamol and ethyl phenylpropiolate using a Pd(OAc)2 catalyst to illustrate coumarin synthesis. This procedure is simple and easy and can be applied to the synthesis of other coumarins that have electron-rich phenol groups. The reaction is conducted by stirring a solution of Pd(OAc)2, sesamol and ethyl phenylpropiolate in trifluoroacetic acid at room temperature (15-20 degrees C) under atmospheric conditions. This protocol can be completed in 3 d.

An efficient palladium-catalyzed synthesis of cinnamaldehydes from acrolein diethyl acetal and aryl iodides and bromides

The reaction of aryl iodides and bromides with acrolein diethyl acetal in the presence of Pd(OAc)(2), (n)()Bu(4)NOAc, K(2)CO(3), KCl, and DMF, at 90 degrees C until the disappearance of the acetal followed by the addition of 2 N HCl to the crude reaction mixture, affords cinnamaldehydes in good to high yields. A variety of functional groups are tolerated in the aryl halides, including ether, aldehyde, ketone, ester, dialkylamino, nitrile, and nitro groups. The presence of substituents close to the oxidative addition site does not hamper the reaction.

Synthesis of Substituted 2-Pyridyl-4-phenylquinolines

The acid-catalyzed condensation of o-aminobenzophenones with aromatic acetyl derivatives, in a basic methanol/tetrahydrofuran medium, has been used to prepare a series of substituted 2-pyridyl-4-phenylquinolines. Derivatives having two aza binding sites can act as asymmetric bidendate ligands to complex transition metals such as ruthenium, osmium or iridium. All the compounds were characterized by elemental analysis, Ei or FAB (+) MS, ¹H- and ¹³C-NMR spectroscopies. Complete assignments of the ¹H spectra were accomplished by using a combination of one- and two-dimensional NMR techniques.

New method for preparation of coumarins and quinolinones via Pd-catalyzed intramolecular hydroarylation of C-C triple bonds

A new and general method has been developed for preparation of coumarins and quinolinones by intramolecular hydroarylation of alkynes. Various aryl alkynoates and alkynanilides undergo fast intramolecular reaction at room temperature in the presence of a catalytic amount of Pd(OAc)(2) in a mixed solvent containing trifluoroacetic acid (TFA), affording coumarins and quinolinones in moderate to excellent yields with more than 1000 turnover numbers (TON) to Pd. The methodology proved to tolerate a number of functional groups such as Br and CHO. On the basis of isotope experiments, a possible mechanism involving ethynyl chelation-assisted electrophilic metalation of aromatic C-H bonds by in-situ generated cationic Pd(II) species has been discussed. Also the involvement of vinylcationic species has been suggested.

Palladium-catalyzed synthesis of [E]-6-(2-acylvinyl)uracils and [E]-6-(2-acylvinyl)-1-[(2-hydroxyethoxy)methyl]uracils--their antiviral and cytotoxic activities

[E]-6-(2-Acylvinyl)uracils and their corresponding 1-(2-hydroxyethoxy)methyl derivatives were synthesized through palladium-catalyzed reactions which involved an interesting rearrangement. Some of the acylvinyl uracils (3, 4, and 5) and the acyclonucleosides (8 and 10) showed pronounced activity against human T-lymphocyte Molt 4/C8 and CEM cells. However, they were less toxic to murine L1210 and FM3A cells. The compounds did not have any marked antiviral activity.