A Brønsted acid-promoted exo-cyclization of bicyclo1.1.0butyl ketones with hydrazines has been established. This approach enables efficient ring expansion, leading to a diverse range of 2,3-diazabicyclo3.1.1heptenes. Mechanistic studies reveal that the carbonyl group is pivotal, fulfilling a dual role as both the reactive center and a latent activating group. Moreover, the unique dual nucleophilic character of hydrazines, featuring two nitrogen-based nucleophilic sites, is crucial to the success of this transformation.
Cao et al. (Thu,) studied this question.