Convenient Syntheses of Enantiopure 1,2-Oxazin-4-yl Nonaflates and Phosphates and Their Palladium-Catalyzed Cross-Couplings

Abstract

Efficient methods to prepare enantiopure 1,2-oxazin-4-yl nonaflates and phosphates were elaborated. The corresponding 1,2-oxazin-4-ones were transformed into their enolates and then quenched with nonafluorobutanesulfonyl fluoride or diphenyl chlorophosphate to provide the title compounds. Alternatively, the corresponding α-bromo ketones were subjected to Perkow reactions efficiently leading to the respective enol phosphates. A variety of palladium-catalyzed cross-couplings such as Kumada–Corriu, Sonogashira, Heck reactions or borylation reactions were studied, which delivered the expected new 4-substituted 1,2-oxazine derivatives generally in satisfactory yields. A few typical subsequent transformations were studied including a copper-catalyzed [3+2] cycloaddition with a galactose-derived azide. They demonstrate the synthetic potential of the newly prepared enantiopure 4-substituted 1,2-oxazines.