Quantification of Ion‐Pairing Effects on the Nucleophilic Reactivities of Benzoyl‐ and Phenyl‐Substituted Carbanions in Dimethylsulfoxide

Second‐order rate constants for the reactions of acceptor‐substituted phenacyl (PhCO?CH^??Acc) and benzyl anions (Ph?CH^??Acc) with diarylcarbenium ions and quinone methides (reference electrophiles) have been determined in dimethylsulfoxide (DMSO) solution at 20 °C. By studying the kinetics in the presence of variable concentrations of potassium, sodium and lithium salts (up to 10^?2 mol L^?1), the influence of ion‐pairing on the reaction rates was examined. As the concentration of K⁺ did not have any influence on the rate constants at carbanion concentrations in the range of 10^?4–10^?3 mol L^?1, the acquired rate constants could be assigned to the reactivities of the free carbanions. The counter ion effects increase, however, in the series K⁺<Na⁺<Li⁺, and the sensitivity of the carbanion reactivities toward variation of the counter ion strongly depends on the structure of the carbanions. The reactivity parameters N and s_N of the free carbanions were derived from the linear plots of log k₂ against the electrophilicity parameters E of the reference electrophiles, according to the linear‐free energy relationship log k₂(20 °C)=s_N(N+E). These reactivity parameters can be used to predict absolute rate constants for the reactions of these carbanions with other electrophiles of known E parameters.     

Steric shielding vs. σ–π orbital interactions in triplet–triplet energy transfer

The influence of non-covalent σ–π orbital interactions on triplet–triplet energy transfer (TTET) through tuning of the donor excitation energy remains basically unexplored. In the present work, we have investigated intermolecular TTET using donor moieties covalently linked to a rigid cholesterol (Ch) scaffold. For this purpose, diaryl ketones of π,π* electronic configuration tethered to α- or β-Ch were prepared from tiaprofenic acid (TPA) and suprofen (SUP). The obtained systems TPA-α-Ch, TPA-β-Ch, SUP-α-Ch and SUP-β-Ch were submitted to photophysical studies (laser flash photolysis and phosphorescence), in order to delineate the influence of steric shielding and σ–π orbital interactions on the rate of TTET to a series of energy acceptors. As a matter of fact, fine tuning of the donor triplet energy significantly modifies the rate constants of TTET in the absence of diffusion control. The experimental results are rationalized by means of theoretical calculations using first principles methods based on DFT as well as molecular dynamics.     

Knoevenagel Condensation Catalyzed by a Mexican Bentonite Using Infrared Irradiation

Diethyl malonate undergoes condensation with aromatic aldehydes without solvents. in the presence of a Mexican bentonite using infrared irradiation as the energy source, to give the benzylidenemalonate compounds in fair yield.     

Preparation of Benzylidene Barbituric Acids Promoted by Infrared Irradiation in Absence of Solvent

Several benzaldehydes were condensed with barbituric acid under infrared irradiation, in absence of solvent, affording the corresponding 5-benzylidene barbituric acids.     

A New High Yield Preparation of Benzyl Phenethyl Ethers by Phase Transfer Catalysis

A phase transfer method to prepare benzyl phenethyl ethers from electron-rich benzyl halides and 2-phenylethanols supporting electron-withdrawing groups is described. The yields are excellent, in contrast to the very low ones previously reported for the same kind of compounds prepared by other ways.     

Pseudoesters and Derivatives XXXV. Reactions of 4-Substituted-5-(Ethylthio)Furan-2(5H)-Ones Anions with Alkylating Agents

Alkylation of anions derived from 5-ethylthio-4-substituted furanones (1–3) is described. The regioselectivity depends on the alkylating agent but mainly on the nature of the substituent. The alkylation of 4-methoxyfuranone 3 proceeds regioselectively to afford the 5-alkylated derivative as sole product.