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Deprotonation of Benzoxazole and Oxazole Using Lithium Magnesates

Deprotonation of Benzoxazole and Oxazole Using Lithium Magnesates

Omar Bayh, Haçan Awad, Florence Mongin, Christophe Hoarau, Laurent Bischoff, François Trécourt, Guy Quéguiner, Francis Marsais, Fernando Blanco, Belén Abarca, Rafael Ballesteros

J Org Chem. 2005 Jun 24;70(13):5190-6.

PMID: 15960523

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.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP20910207	Tri-n-butyllithium magnesate		20910-20-7	Price

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