Annulation of phosphole sulfides via [3+2] cycloaddition with nitrones

Owing to the unique electronic structure of phospholes, it is difficult to realize the annulation of phospholes with the endocyclic C=C bond. Herein we report the [3 + 2] cycloaddition reaction between phosphole sulfides and nitrones, affording the phospholene fused isoxazolidine skeleton with high yields and excellent regioselectivity. The oxygen atom is attached to the beta carbon atom of the phosphole exclusively. The C=C bond in the product cannot react with the nitrone. This work demonstrates that slightly antiaromatic phosphole sulfides are capable of acting as 2 pi-electron components in cycloaddition reactions.