Theoretical study of the Wittig, aza-Wittig and arsa-Wittig reactions of Me3P=XH ylide (X=CH, N and As) with cyclic ketones in the gas phase and solution phase

Publication date: 15 August 2017 Source:Computational and Theoretical Chemistry, Volume 1114 Author(s): Nisha Jarwal, Pompozhi Protasis Thankachan A computational study of the comparative reactivity of the Wittig, aza-Wittig and arsa-Wittig reactions of cyclopentanone and cyclobutanone with Me3P=XH ylide (X=CH, N and As) in the gas phase has been performed at B3LYP/6-31G∗∗ level of theory. Calculations have also been performed using integral equation formalism polarizable continuum model (IEFPCM), with THF solvent at B3LYP/6-31G∗∗ level of theory. In the gas phase as well as in solvent, these reactions were predicted to be two step processes with two complexes R and P (reactant complex and product complex), two transition states, one for addition (TS1) and the other for elimination (TS2) and two four-membered cyclic intermediates (INT1 and INT2), except that INT2 was not found in the aza-Wittig reaction. In our calculations, the Wittig reaction is found to be more favorable both thermodynamically and kinetically than aza- and arsa-Wittig reactions. The Wittig reaction is found to be more exothermic and to involve a lower activation barrier to formation of INT1 than the aza and arsa-Wittig reactions. The activation barriers in the reactions of cyclopentanone are higher as compared to the reaction of cyclobutanone in gas phase and solution phase. The addition activation barriers for each reaction are overestimated in the solvent model as compared to gas phase reacti...

Source: Computational and Theoretical Chemistry - May 26, 2017 Category: Chemistry Source Type: research