Effects of the Hydrophobicity of the Reactants on Diels−Alder Reactions in Water

On water: silver-catalyzed domino approach for the synthesis of benzoxazine/oxazine-fused isoquinolines and naphthyridines from o-alkynyl aldehydes

An operationally simple domino approach for the silver-catalyzed synthesis of oxazine/benzoxazine-fused isoquinolines 5a-q and naphthyridines 6a-v by the reaction of o-alkynyl aldehydes 3a-aa with amines having embedded nucleophiles 4a-d under mild reaction condition in water is described. The reaction shows selective C-N bond formation on the more electrophilic alkynyl carbon resulting in the formation of 6-endo-dig cyclized product. The competitive experiments show the viability of an intramolecular nucleophilic attack over an intermolecular attack of the external nucleophile. This methodology accommodates wide functional group variation, which proves to be useful for structural and biological assessment.

Synthesis of 5,5′-(arylmethylene)bis(pyrimidinone) derivatives in aqueous media

The condensation and addition reactions of aromatic aldehydes and 4,6-dihydroxypyrimidine or 2,4-dihydroxy-6-aminopyrimidine in water in the presence of triethylbenzylammonium chloride (TEBAC) afford a one-pot synthesis of 5,5′-(arylmethylene)bis[6-hydroxypyrimidine-4(3H)-one]s and 5,5′-(arylmethylene)bis[6-aminopyrimidine-2,4 (1H,3H)-dione]s. These compounds were characterised by elemental analysis and IR and 1H NMR spectra and further confirmed by a single crystal X-ray diffraction analysis.

Hydrophobicity and mixing effects on select heterogeneous, water-accelerated synthetic reactions

The influence of aqueous reaction media on organic reactions is a topic of long-standing interest, particularly as it affects the rate or selectivity of synthetic reactions. Sometimes such reactions appear homogeneous, typically in dilute solution, whereas others are obviously heterogeneous, typically in concentrated solution that is more characteristic of a preparative synthetic reaction. The latter situation has been termed "on water." Here, it is demonstrated that the rates of heterogeneous ene reactions, Passerini reactions, and Ugi reactions in pure water and in aqueous solutions are dependent on the mixing method and reactant polarity, consistent with the involvement of hydrophobic interactions in their acceleration.

Three-Component One-Pot Synthesis of Unsymmetrical 1,4-dihydropyridine Derivatives in Aqueous Media

A series of methyl ethyl 2,6-dimethyl-4-substituted-1,4-dihydropyridine-3,5-dicarboxylates were synthesised by the three-component reaction of aldehydes, ethyl acetoacetate and methyl β-aminocrotonate in the presence of triethylbenzylammonium chloride (TEBAC) in aqueous medium. This method has the advantage of good yields.

An efficient synthesis of 3,3′-arylmethylenebis(4-hydroxy-6-methyl-2H-pyran-2-one)s in aqueous media

The condensation reactions of aromatic aldehydes and 4-hydroxy-6-methyl-2H-pyran-2-one in water in the presence of sodium 1-dodecanesulfonate affords a one-pot synthesis of 3,3′-arylmethylene bis(4-hydroxy-6-methyl-2H-pyran-2-one)s.

Hydrogen bonding catalysis operates by charge stabilization in highly polar Diels-Alder reactions

[reaction: see text] The alcohol-catalyzed Diels-Alder reactions of acrolein and benzaldehyde with Rawal's diene were evaluated with density functional theory (B3LYP/6-31G(d)). Several potential modes of catalysis with two methanol molecules were used to model catalysis by TADDOLs. In agreement with crystallographic data, cooperative catalysis with TADDOLs is predicted to be favorable.

Novel and versatile methodology for synthesis of cyclic imides and evaluation of their cytotoxic, DNA binding, apoptotic inducing activities and molecular modeling study

Versatile method has been developed for synthesis of N-substituted imides. Thus, acid anhydrides, imides and dicarboxylic acids were successfully subjected to dehydrative cyclization with substituted amines using DPPOx and Et(3)N to afford N-substituted imides under mild conditions. The DNA binding and apoptosis induction were investigated with regard to their potential utility as cytotoxic agents. Molecular modeling methods are used to study the cytotoxic activity of the active compounds by means of molecular and quantum mechanics.

Origins of stereoselectivity in Diels-Alder cycloadditions catalyzed by chiral imidazolidinones

B3LYP/6-31G(d) density functional theory has been used to study Diels-Alder reactions of cyclopentadiene with alpha,beta-unsaturated aldehydes and ketones organocatalyzed by MacMillan's chiral imidazolidinones. Preferred conformations of transition structures and reaction intermediates have been located. The dramatically different reactivities and enantioselectivities exhibited by two similar chiral imidazolidinones are rationalized.

Water in Oil Microemulsions as Reaction Media for a Diels−Alder Reaction between N-Ethylmaleimide and Cyclopentadiene

The Diels-Alder reaction between N-ethylmaleimide and cyclopentadiene in water/AOT/isooctane microemulsions, where AOT denotes sodium bis(2-ethylhexyl)sulfosuccinate, was studied. The rate of the reaction was found to be higher than that obtained in pure isooctane, irrespective of the particular microemulsion composition used. The efficiency of this catalytic action ranged from a factor of 3 at low water contents (viz., W = [H2O]/[AOT] = 2) to 15 at W = 35. On the basis of these results, the reaction takes place simultaneously in the continuous medium and at the microemulsion interface. The favorable arrangement of the reactants at the interface results in more than 95% of the reaction occurring in this microenvironment. The kinetic analysis revealed the rate constant at the microemulsion interface to change with the water content. For small W values a bimolecular rate constant at the interface close to that observed in hexane was obtained. This value increases with W and for W > 20, a value close to that obtained in ethanol was found. This can be ascribed to the absence of hydrogen bonding at the microemulsion interface as well as the accelerating effects due to enforced hydrophobic interactions.

Synthesis of 3-Amino-1-Aryl-9-Methoxy-5,6-Dihydro-1H- Benzo[f] Chromene-2-Carbonitriles in Aqueous Media

3-Amino-1-aryl-9-methoxy-5,6-dihydro-1 H-benzo[ f]chromene-2-carbonitriles were synthesised by the reaction of substituted cinnamonitriles with 7-methoxy-2-tetralone using triethylbenzylammonium chloride (TEBA) as catalyst in aqueous media. The synthetic method has the advantages of good yields, less pollution, simple operation and being environment friendly. The structures of the products were identified by IR, 1H NMR and elemental analysis and confirmed by X-ray analysis.