Diastereoselective Synthesis of Dispiropyrrolidinyloxindoles via DBU-Promoted [3+2]-Cycloaddition of Cyclic Pyridinium Ylides and α,β-Unsaturated Ketones

A novel [3+2]-cycloaddition reaction of cyclic pyridinium ylides and alpha,beta-unsaturated ketones derived from indanones for the synthesis of dispiropyrrolidinyloxindoles is described herein. Various types of dispiropyrrolidinyloxindoles can be conveniently accessed with moderate to good yields and up to > 99 : 1 dr from easily available pyridinium salts which bear an electron-withdrawing group on the pyridine ring under mild conditions for short reaction time.