A Lewis Acid Catalyzed Annulation to 2,1-Benzisoxazoles

[Image: see text] We report here a new, atom economical annulation to 2,1-benzisoxazole scaffolds via the BF(3)·Et(2)O-catalyzed reaction of glyoxylate esters and nitrosoarenes. The developed method represents a convergent route to this compound class from previously unexplored inputs and provides a range of 2,1-benzisoxazoles in moderate to high yields under convenient conditions. Along with exploration of substrate scope, initial mechanistic investigation through (18)O labeling and the synthesis of a reaction intermediate provides evidence for an unusual umpolung addition of glyoxylates to nitrosobenzenes with high O-selectivity, followed by a new type of Friedel–Crafts cyclization.