Stereoselective Direct Copper-Catalyzed Alkenylation of Oxazoles with Bromoalkenes
作者:François Besselièvre、Sandrine Piguel、Florence Mahuteau-Betzer、David S. Grierson
DOI:10.1021/ol801512q
日期:2008.9.18
A copper-catalyzeddirectalkenylation of oxazoles with bromoalkenes has been developed. The method is both regio- and stereoselective and tolerates a variety of functional groups. A wide range of 2-E-vinyl-substituted oxazoles were obtained in high yields including the highly fluorescent alkaloid annuloline.
Deuteration experiments on 2-lithiated oxazoles show a pKa dependent regioselectivity suggesting that the ring cleaved tautomer dominates the equilibrium. Transmetallation to the zinc derivative gives a species which behaves as a C2 ring closed nucleophile as judged by deuteration and palladium catalysed coupling experiments. These conclusions are supported by nmr spectroscopy studies of the metallated species.
C-H Bond Activation: A Versatile Protocol for the Direct Arylation and Alkenylation of Oxazoles
The versatile palladium complex Pd(PPh3)4 catalyses both direct arylation and alkenylation of oxazoles efficiently. The method is regioselective and stereospecific with respect to bromoalkenes and tolerates a wide range of functional groups.