Base‐Promoted [3+2]‐Annulation of Oxime Esters and Aldehydes for Rapid Isoxazoline Formation

A base‐promoted [3+2]‐annulation of ketoxime esters and aldehydes is disclosed for the facile and rapid synthesis of 3,5‐disubstituted and 3,4,5‐trisubstituted isoxazolines. The key to our success is the pivalate leaving group of the oxime substrates, combined with cesium carbonate as promoter. This chemistry allows the assembly of a vast array of isoxazoline derivatives under simple base conditions in a method complementary to the classic isoxazoline formation via [3+2]‐dipolar cycloaddition of nitrile oxides and olefins. It also represents a new reaction pattern involving electrophilic amination/N–O bond substitution.

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