Mechanism and stereospecificity of Z-enamide synthesis from salicylaldehydes with isoxazoles using DFT calculations

Publication date: Available online 17 October 2019Source: Journal of Organometallic ChemistryAuthor(s): Baoping Ling, Yuan-Ye Jiang, Yuxia Liu, Peng Liu, Rutao Liu, Siwei BiAbstractA mechanistic study on Rh-catalyzed synthesis of stereospecific Z-enamide from salicyladehydes and isoxazoles has been performed with DFT calculations. The aldehydic C–H bond activation was found directed by anionic phenolic group rather than neutral phenolic hydroxyl, which reasonably rationalizes the reversibility of the C–H bond activation. Direct ring-opening rather than N–O oxidative addition of isoxazole, and subsequent C–C reductive elimination generate the stable tripodal intermediate that has been demonstrated by LC-MS analysis. Finally, sequential amino and phenolic protonations of the tripodal species produce the product Z-enamide. Stereospecificity of Z-enamide can be attributed to the rigid carbon-carbon double bond formed by direct ringopening of isoxazole. The rate-determining process is found to include the directing ring-opening and C–N reductive elimination with an overall barrier of 26.7 kcal/mol.Graphical abstract

Source: Journal of Organometallic Chemistry - October 19, 2019 Category: Chemistry Source Type: research