[3 + 2] Cycloaddition of Azaoxyallyl Cations with Cyclic Ketones: Access to Spiro-4-oxazolidinones.

The first formal [3 + 2] cycloaddition reaction of in situ generated azaoxyallyl cation with cyclic ketones has been developed using mild reaction conditions. A variety of spiro-4-oxazolidinones was obtained in excellent yields (up to 99%). The high efficiency of this process, coupled with the operational simplicity, makes it an attractive method for the synthesis of spiro-4-oxazolidinones.