Halospirocyclization of <i>N</i> ‐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.