Thiol-Michael addition in polar aprotic solvents: nucleophilic initiation or base catalysis?

摘要: The thiol-Michael addition of ethanethiol to ethyl acrylate, methyl vinylsulfone and maleimide initiated by ethyl-, diethyl-, triethylamine triethylphosphine in tetrahydrofuran (THF) is investigated at room temperature for concentrations ranging from 0.5 2 mol L−1 the reactants 0.03 0.3 initiators. Rate coefficients all elementary steps a reaction scheme consisting both base catalyzed nucleophile mechanism are calculated using CBS-QB3 corrected solvation with COSMO-RS. Diffusional limitations taken into account coupled encounter pair model. ab initio apparent kinetic parameters used microkinetic model simulated conversions agree well experimental data. Competition aza-Michael shown be insignificant. Regardless choice ene or catalyst, conversion governed an anionic cycle which first thiolate occurs, followed rate-controlling proton transfer obtained Michael adduct anion another thiol. For acrylates vinylsulfones, quasi-equilibrated, while maleimides this has positive affinity, explaining their large reactivity. catalyst strongly affects initiation mechanism. Using tertiary phosphines only nucleophilic takes place amines, catalysis occurs. primary secondary amines mechanisms contribute. presented insights on diffusional critical further optimization additions polymer conjugation.