A Lewis Acid Catalyzed annulation to 2,1-benzisoxazoles.

We report here a new, atom economical annulation to 2,1-benzisoxazole scaffolds via the BF3·Et2O-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.