Halospirocyclization of N ‐Benzylpropiolamides With NXS to Halogenated Azaspiro[5.5]undecanones

A facile and efficient approach for the halospirocyclization of N ‐benzylpropiolamides has been developed. Employing N ‐halosuccinimides (NXS) as halogenating reagents, this reaction proceeds smoothly at room temperature without the need for photochemistry, electrochemistry, or metal reagents. A diverse array of halogenated azaspiro[5.5]undecanones was obtained in moderate to excellent yields, displaying excellent functional group tolerance. The gram‐scale reaction and the synthesis of brominated 2‐oxaspiro[5.5]undecanone further underscore the scalability and practicality of this method.