Competing kinetic pathways in the bromine addition to allylic ethers in 1,2‐dichloroethane: Opposite temperature effects |
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| Authors: | Alessandro Cecchi Giuditta Bartalucci Cinzia Chiappe Roberto Bianchini |
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| Affiliation: | 1. Dipartimento Chimica Organica, Università di Firenze, Polo Scientifico, via della Lastruccia 13, Sesto Fiorentino (FI), Italy;2. Dipartimento Chimica Bioorganica e Biofarmacia, Università di Pisa, via Bonanno 33, Pisa 56126, Italy;3. Dipartimento Chimica Organica, Università di Firenze, Polo Scientifico, via della Lastruccia 13, Sesto Fiorentino (FI), ItalyDipartimento Chimica Organica, Università di Firenze, Polo Scientifico, via della Lastruccia 13, Sesto Fiorentino (FI), Italy |
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| Abstract: | The kinetics of the electrophilic bromination of three allylic ethers in a nonprotic solvent, 1,2‐dichloroethane, has been investigated. Two of them followed a prevalent second‐order pathway, while the third one exhibited a classical, clean third order. The second‐order pathway in the first two olefins is attributed to electrophilic assistance of the ethereal oxygen to the attacking bromine molecule. In the molecular bromination of 2,4‐cis‐dimethyl‐8‐oxabicyclo[3.2.1]‐6‐octen‐3‐cis‐ol, opposite temperature dependences were found for the two different kinetic pathways. An exoergonic process for the second‐order reaction was explained by the lesser stability of the bromiranium–bromide ionic intermediate, compared to the bromiranium–tribromide in the third‐order profile. © 2007 Wiley Periodicals, Inc. 39: 197–203, 2007 |
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