DFT Investigation of the Diastereoselectivity of the MX and MX Lewis-Acid-Catalyzed Mukaiyama Aldol Reaction between C,O,O-Tris(trimethylsilyl)ketene Acetal and Aldehydes.

The kinetics and diastereoselectivity of the Mukaiyama aldol reaction between C,O,O-tris(trimethylsilyl)ketene acetal and aldehydes bearing alkyl, vinyl, and aromatic substituents is influenced by the nature of Lewis acid catalysts. A density functional theory investigation using the M06-2X exchange-correlation functional and the PCM scheme to account for solvent effects has been carried out to characterize the structure and energetics of the transition state when the Lewis acid is ZnBr (MX) or GaCl (MX) in comparison to the uncatalyzed reaction. The main observations are that (i) the pro-syn transition states are always more stable than the pro-anti ones; (ii) for MX, the transition state presents a cyclic structure, whereas it is open for MX, owing to steric interactions; (iii) the difference of activation free enthalpy between the pro-anti and pro-syn transition states decreases when the reaction is catalyzed, by either MX or MX, demonstrating a reduction of the diastereoselectivity with respect to the uncatalyzed reaction; (iv) this decrease of diastereoselectivity is larger for MX- than for MX-catalyzed reactions; and (v) the MX-catalyzed reactions are kinetically favored by 1-2 kcal mol with respect to the MX ones.

Unraveling the Concerted Reaction Mechanism of the Noncatalyzed Mukaiyama Reaction between C,O,O-Tris(trimethylsilyl)ketene Acetal and Aldehydes Using Density Functional Theory.

The uncatalyzed Mukaiyama aldol reaction between C,O,O-tris(trimethylsilyl)ketene acetal and aldehydes bearing alkyl, vinyl, and aromatic substituents has been studied theoretically using density functional theory with the M06-2X exchange-correlation functional. These DFT calculations mostly demonstrate that (i) the syn product is both kinetically and thermodynamically favored, (ii) the diastereoselectivity of the uncatalyzed reaction is larger than observed for the reaction catalyzed by HgI2 and it is inverted with respect to the latter, (iii) solvents with larger dielectric constants increase the activation barrier but reduce the diastereoselectivity, (iv) the concerted reaction is preferred over the stepwise reaction, and (v) the OSiMe3 group in geminal lowers the activation barrier and increases the energy of reaction. Analyzing the concerted mechanism unravels four types of cyclic transition states, two pro-anti and two pro-syn.

Ultrasonic-assisted synthesis of flavones by oxidative cyclization of 2'-hydroxychalcones using iodine monochloride.

This paper presents an efficient methodology for the synthesis of flavones via the oxidative cyclization of 2'-hydroxychalcones in the presence of iodine monochloride with DMSO under ultrasound irradiation. Ultrasonic irradiation enhances the cyclization reaction and leads to reduced reaction time at lower reaction temperatures while generating flavones with high yields.

Green condensation reaction of aromatic aldehydes with active methylene compounds catalyzed by anion-exchange resin under ultrasound irradiation.

To realize a practical and green chemistry, two important challenges need to be addressed, namely the effective process for the activation of reaction and efficient, eco-friendly and robust chemical methods for the reaction conversion to target products via highly selective catalytic and reactions. Ultrasonic energy promotes the conversion process through its special cavitational effects. Combined with anion-exchange resin as a heterogeneous, reusable and efficient catalyst, Ultrasonic energy enhances the Knoevenagel condensation and leads to reduced reaction time at lower reaction temperature with less amounts of solvent and catalyst.

Amberlyst-15 and Amberlite-200C: efficient catalysts for aldol and cross-aldol condensation under ultrasound irradiation.

This paper presents an improved synthesis of trans-chalcones and α,α'-bis(arylmethylidene) cycloalkanones under ultrasound irradiation in the presence of commercial acid-resins as catalysts in solvent free conditions. Several trans-chalcones and α,α'-bis(arylmethylidene) cycloalkanones were synthesized in good yields and excellent selectivity in a short reaction time.

Esterification of fatty acid over Tunisian acid activated clay: kinetic study.

Tunisian acid activated clay was investigated as catalyst in the esterification of stearic acid with ethyl alcohol, carried out in a semi-continuous reactor. Kinetic study shows that the reaction is first order with respect to acid concentration. The activation energy found was 21 kJ/mol.

Solvent free synthesis of 1,3-diaryl-2-propenones catalyzed by commercial acid-clays under ultrasound irradiation.

This paper presents a novel solvent free method of synthesis of trans-chalcones. The method was based on ultrasound irradiation of the reagents (aryl methyl ketones and aryl aldehydes) in presence of commercial acid-montmorillonites as catalysts. The trans-chalcones were synthesized in high yields (85-95%) and excellent selectivity in a short reaction time.

Influence of the neutralization step on the oxidative and thermal stability of acid olive oil.

This study elucidate the modification on oxidative and thermal stability of acid olive oils during the neutralization step. The neutralization of an acidified olive oil, chosen as model, was carried out by substituting lime (calcium hydroxide) for soda (sodium hydroxide) as the neutralizing agent. Resulting olive oil preserved almost 95% of their alpha-tocopherol content and had higher temperatures of thermal decomposition than oils neutralized with soda.

Investigation of the configuration of alkyl phenyl ketone phenylhydrazones from ab initio 1H NMR chemical shifts.

Using ab initio GIAO calculations the experimental 1H NMR spectra of the E and Z isomers of alkyl phenyl ketone phenylhydrazones R1-C(Ph) = N-NH-Ph (R1 = Me, Et, iPr, and tBu) have been re-interpreted and deviations from Karabatsos' rule or from the assignment of Bellamy and Hunter have been discussed in the light of the optimized geometrical structures.