Net Intermolecular Silyloxypyrone-Based (5+2) Cycloadditions Utilizing Amides as Enabling and Cleavable Tethers

Org Lett. 2023 Oct 6;25(39):7137-7141. doi: 10.1021/acs.orglett.3c02635. Epub 2023 Sep 26.

Abstract

Silyloxypyrone-based (5+2) cycloadditions were facilitated by amides that allowed for increased reactivity and a pathway for cleaving the tether to afford net intermolecular cycloadducts. Various amides underwent facile cycloaddition, and several experiments revealed steric and electronic factors that accelerate the reaction. tert-Butyl amides reacted faster than less hindered variants in multiple cases. In the case of dearomative oxidopyrylium-indole (5+2) cycloadditions, an amine-based tether was ineffective, whereas amides enabled this powerful transformation. Theoretical calculations evidenced a concerted asynchronous reaction in which the amide facilitates a conformational driving force enabling cycloaddition. Finally, a one-pot acylation/(5+2) cycloaddition/nucleophilic lactam opening and other examples of tosyl lactam opening of a modified cycloadduct were demonstrated.