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Deprotonation of Benzoxazole and Oxazole Using Lithium Magnesates

Omar Bayh 1 Hacan Awad 2 Florence Mongin 3 Christophe Hoarau 4 Laurent Bischoff 4 Francois Trécourt 5 Guy Quéguiner 5 Francis Marsais 4 Fernando Blanco 5 Belén Abarca 6 Rafaël Ballesteros 6
1 IRCOF - Institut de Chimie Organique Fine
2 LU - Lebanese University [Beirut]
3 ISCR - Institut des Sciences Chimiques de Rennes
4 COBRA - Chimie Organique et Bioorganique : Réactivité et Analyse
5 UNIROUEN - Université de Rouen Normandie
6 UV - Universitat de València
Abstract : The first deprotonations of oxazole and benzoxazole using lithium magnesates are described. The reactions occurred in tetrahydrofuran at room temperature using 1/3 equiv of lithium tributylmagnesate. As 2-lithiooxazole and 2-lithiobenzoxazole, lithium tri(2-oxazolyl)magnesate and lithium tri(2-benzoxazolyl)magnesate very rapidly and completely isomerized to the more stable 2-(isocyano)enolate and 2-(isocyano)phenolate type structures, respectively, a result shown by NMR analysis. The isolation of 2-substituted oxazoles and benzoxazoles in medium to good yields after electrophilic trapping was interpreted in two ways:  (1) the equilibration between the open and closed structures is faster than the trapping of the open isomers, and the closed isomers are more reactive than the open ones, or (2) the open isomers react with electrophiles in a intramolecular Passerini type reaction. The nonreactivity of the 2-(isocyano)enolate type structure toward anisaldehyde in the absence of lithium bromide makes the intramolecular Passerini type reaction more plausible.
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https://hal-normandie-univ.archives-ouvertes.fr/hal-02385053
Contributor : Laurent Bischoff Connect in order to contact the contributor
Submitted on : Thursday, November 28, 2019 - 4:09:24 PM
Last modification on : Friday, December 10, 2021 - 3:52:15 PM

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COMUE-NORMANDIE | UNIV-RENNES1 | INC-CNRS | INSA-ROUEN | ISCR | UNIV-RENNES | UNIROUEN | COBRA | INSA-GROUPE | CNRS | UR1-UFR-SPM | ISCR-CORINT | ENSICAEN | UNILEHAVRE | UNICAEN | INSA-RENNES | UR1-MMS

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Omar Bayh, Hacan Awad, Florence Mongin, Christophe Hoarau, Laurent Bischoff, et al.. Deprotonation of Benzoxazole and Oxazole Using Lithium Magnesates. Journal of Organic Chemistry, American Chemical Society, 2005, 70 (13), pp.5190-5196. ⟨10.1021/jo050493w⟩. ⟨hal-02385053⟩

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