Chemodivergent [4 + 1] and [3 + 2 + 1] Annulations of Dioxazolones with Allenoates: Access to Two Distinct Functionalized Heterocycles

Dioxazolones have emerged as a privileged class of building blocks via rearrangement reactions. Nevertheless, their participation in interrupted rearrangement reactions remains underexplored because of the generation of highly reactive and unstable intermediates. Herein, we report two distinct strategies to realize the interrupted Lossen rearrangement of dioxazolones. Simple modulation of the catalyst and reaction conditions enables two divergent annulation pathways to access two types of valuable heterocycles. Employing DABCO as the catalyst and water as the additive, a formal [4 + 1] annulation affords five-membered heterocycles. By contrast, when PPh2Cy and primary amines are applied, followed by NaOH treatment, a formal [3 + 2 + 1] annulation occurs, furnishing six-membered heterocycles.