Lanthanide triflate catalyzed 1,3-dipolar cycloaddition reactions: stereoselective synthesis of indenoisoxazolidines

Substituted indenones reacted smoothly with a variety of in situ generated nitrones in the presence of lanthanide triflates to give exclusive exo 1,3-dipolar cycloaddition products in high yield. Judicious choice of the nitrone substituents allowed for further modification of the indenoisoxazolidine core to the corresponding indenoisoxazoline and indenoisoxazole analogs in high yield.