Collect. Czech. Chem. Commun. 1993, 58, 1631-1635

Novel Dehydrogenation of 2,5-Diaryl Substituted ∆2-Oxazolines to Oxazoles

Robert F. X. Klein, Václav Horák and Godfrey A. S. Baker

Department of Chemistry, Georgetown University, Washington, DC 20057-0001, U.S.A.


The dehydrogenation of various 2,5-diaryl substituted ∆2-oxazolines with either Br2/LiBr/CaCO3 (molar ratio 1.05 : 2 : 3) or CuBr2/LiBr/CaCO3 (molar ratio 2 : 1 : 3) in refluxing o-dichlorobenzene gives the corresponding oxazole up to 87% yield. Free radical benzylic bromination followed by dehydrobromination is the expected dehydrogenation mechanism. The successful application of the reagent combination for this transformation is in contrast to standard dehydrogenation reagents, including N-bromosuccinimide, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, chloranil, NiO2 and active γ-MnO2.