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Normal, Abnormal, and Cascade Wittig Olefinations of alpha-Oxoketenes


Description : α-Oxoketenes generated in situ by a thermal Wolff rearrangement have been found to participate as 1,2- and 1,4-ambident C-electrophilic/O-nucleophilic reagents to- wards donor/acceptor carbonyl-stabilized Wittig ylides. This resulted in the very direct and practical syntheses of func- tionalized allenes by a normal Wittig olefination, 4H-pyran-4- ones by an abnormal Wittig olefination, or 4H-pyranylidenes following a Wittig/abnormal Wittig cascade sequence as a function of the substrates combination employed. Mechanis- tic experimental and computational studies provided a full rational for these reactivity switches. Some unusual mecha- nistic features for Lewis acid-free Wittig olefinations were identified in this series such as the involvement of betaine intermediates and some degree of reversibility in the normal Wittig olefination. The abnormal Wittig olefination was fully uncovered.
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Contributeur : Gaelle Chouraqui <>
Soumis le : lundi 14 janvier 2019 - 15:47:29
Dernière modification le : jeudi 23 janvier 2020 - 18:22:05