[3+2] Cycloaddition of Methylenedihydrobenzofurandiones and Nitrilimines: Synthesis of Sipropyrazole Compounds

The [3＋2] cycloaddition of methylenedihydrobenzofurandiones and nitrilimines worked efficiently in CHCl 3 at room temperature in the presence of Et 3 N, producing biologically interesting spirocyclic pyrazole derivatives in high yield (78%～94%) with excellent diastereoselectivity.