Revealing carbocations in highly asynchronous concerted reactions: The ene-type reaction between dithiocarboxylic acids and alkenes |
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Authors: | Maria-Assunta Chiacchio Laura Legnani Pierluigi Caramella Tomás Tejero Pedro Merino |
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Affiliation: | 1. Dipartimento di Chimica, Università di Pavia, Via Taramelli, 12, 27100 Pavia, Italy;2. Dipartimento di Scienze del Farmaco, University of Catania, V.le A. Doria 6, 95125 Catania, Italy;3. Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Universidad de Zaragoza-CSIC, 50009 Zaragoza, Spain;4. Instituto de Biocomputación y Física de Sistemas Complejos (BIFI), Universidad de Zaragoza, 50009 Zaragoza, Spain |
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Abstract: | The ene-type reaction between (dithio)carboxylic acids and alkenes has been studied computationally by DFT and topological (analysis of the electron localization function, ELF) methods. The reaction proceeds under kinetic control and the observed differences in regioselectivity are well-explained by the relative stability of the different transition structures. In agreement with experimental observations, electron-rich alkenes lead to Markownikoff adducts while electron-poor alkenes lead to Michael adducts. In all cases the reaction proceeds through an only transition structure (one kinetic step) although a different synchronicity was observed depending on the alkene electronics. The ELF analysis of the reactions corroborates the existence of a transient carbocation (hidden intermediate) in the reactions with electron-rich alkenes. On the other hand, electron-poor alkenes proceed through a more synchronous concerted mechanism. It can be predicted that with electron-rich alkenes bearing highly donating the transient carbocations might be captured by a nucleophile. |
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Keywords: | Ene-reaction Hidden intermediates Dithiocarboxylic acids Carbocations ELF analysis |
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