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.