Deprotonation of benzoxazole and oxazole using lithium magnesates.
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.
Bayh
Omar
O
Laboratoire de Chimie Organique Fine et Hétérocyclique, UMR 6014, IRCOF, CNRS, Université et INSA de Rouen, Place E. Blondel BP 08, 76131 Mont-Saint-Aignan Cedex, France.
Awad
Haçan
H
Mongin
Florence
F
Hoarau
Christophe
C
Bischoff
Laurent
L
Trécourt
François
F
Quéguiner
Guy
G
Marsais
Francis
F
Blanco
Fernando
F
Abarca
Belén
B
Ballesteros
Rafael
R