P(NMe2)3-Mediated Reductive (1+4) Annulation Reaction of α-Keto Esters with Nitroalkenes: A Facile Synthesis of Polysubstituted Isoxazoline N-Oxides.

A P(NMe₂)₃-mediated reductive (1+4) annulation reaction of αketo esters with substituted nitroalkenes has been developed, providing a feasible protocol to construct polysubstituted isoxazoline N-oxides in moderate to excellent yields from readily available starting materials. This reaction originates from the characteristic reactivity of in situ generated KukhtinRamirez adducts and presumably proceeds through a tandem Michael addition-intramolecular S_N2 sequence. To further expand the utility of this annulation reaction, isoxazolines have been efficiently prepared from corresponding annulation products upon treatment with trimethyl phosphite. [ABSTRACT FROM AUTHOR]