[4 + 3] Annulation of diazoenals and 3-substituted 2-oxindoles: rapid access to indolo-oxazepines and a 5-HT4 receptor antagonist core

Abstract

Herein, we report a new catalytic strategy for the efficient construction of indolo-oxazepine heterocycles. The transformation features a dirhodium carboxylate/Brønsted acid co-catalyzed [4 + 3] annulation between diazoenals and 3-substituted 2-oxindoles, providing direct access to valuable [1,3]oxazepino[3,2-a]indole derivatives. The synthetic utility of the methodology was demonstrated by a short synthesis of the indolo-oxazepane framework of a 5-HT₄ receptor antagonist, highlighting its potential utility in medicinal chemistry.