Kinetic studies of conjugate addition of amines to allenic and acrylic esters and their correlation with antibacterial activities against Staphylococcus aureus

Reactivities of tertiary phosphines towards allenic, acetylenic, and vinylic Michael acceptors

The addition of phosphines (PR3) to Michael acceptors is a key step in many Lewis-base catalysed reactions. The kinetics of the reactions of ten phosphines with ethyl acrylate, ethyl allenoate, ethyl propiolate, ethenesulfonyl fluoride, and ethyl 2-butynoate in dichloromethane at 20 °C was followed by photometric and NMR spectroscopic methods. The experimentally determined second-order rate constants k 2 show that electronic effects in sterically unencumbered phosphines affect their nucleophilicity towards different classes of Michael acceptors in the same ordering. Michael acceptors with sp-hybridised electrophilic centres, however, are less susceptible to changes in the PR3 nucleophilicity than those with sp2-hybridised reactive sites. Linear correlations of lg k 2 from this work with published rate constants for SN2 and SN1 reactions as well as with Brønsted basicities and fugalities for PR3 demonstrate the generality of the detected reactivity trends. Computed reaction barriers (ΔG ‡ calc) as well as reaction energies (ΔG add) for Michael adduct formations show excellent correlations with experimentally obtained reaction barriers (ΔG ‡ exp) corroborating the interpretation of the kinetic data and revealing the philicity/fugality features of the reactants in phospha-Michael additions.

Direct Synthesis of Coumarin Derivatives from Alkynoic Esters via Dual-organocatalysis

An efficient synthetic method for coumarin derivatives was developed using a dual-organocatalytic reaction. A combination of p-toluenesulfonic acid monohydrate and piperidine was found to efficiently catalyze the cyclization between salicylaldehydes and alkynoic esters to give various coumarin derivatives in good yield and high selectivity. Mechanistic and kinetic data suggested that the conjugate addition between piperidine and alkynoic esters played a crucial role in the reaction mechanism.

Reactivities of allenic and olefinic Michael acceptors towards phosphines

The kinetics of the reactions of tributylphosphine with allenic and olefinic Michael acceptors in dichloromethane at 20 °C was followed by photometric and NMR spectroscopic methods. Combination with DFT-calculated methyl anion affinities revealed the relevance of retroaddition barriers in phosphine-catalysed reactions when mixtures of allenic and olefinic substrates are used.