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

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 1,3oxazepino3,2-aindole 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.