Sequential Formal (4 + 1)-Spirocycloaddition/Oxidative Cleavage between Indoles and β‑Nitrostyrenes: One-Pot Route to Benzamide-Containing (3),4,5-Substituted Isoxazoles

An effective protocol for the synthesis of benzamide-containing
(3),4,5-substituted isoxazoles was developed. This one-pot procedure
involved a formal (4 + 1)-spirocycloaddition between indoles and β-nitrostyrenes,
followed by an oxidative cleavage with a mixture of acetic anhydride
and hydrogen peroxide, which led to the formation of a highly functionalized
isoxazole moiety. A total of 33 such compounds were synthesized in
yields ranging from 44% to 91%, demonstrating good tolerance for various
functional groups.