Phosphane-catalyzed [4+1] annulation between nitroalkenes and Morita-Baylis-Hillman carbonates: facile synthesis of isoxazoline N-oxides by phosphorus ylides.

A phosphane-catalyzed [4+1] annulation between nitroalkenes and Morita-Baylis-Hillman carbonates has been realized; this provides facile and diastereoselective access to polysubstituted isoxazoline N-oxides in moderate to excellent yields. In the annulation, an in situ formed allylic phosphorus ylide presumably serves as a pivotal active intermediate. This reaction accordingly represents the first example of phosphorus ylide initiated [4+1] cyclization of nitroalkenes to give isoxazoline N-oxides.