Benign catalysis with zinc: atom-economical and divergent synthesis of nitrogen heterocycles by formal [3 + 2] annulation of isoxazoles with ynol ethers

Abstract

Herein, we disclose an efficient zinc-catalyzed formal [3 + 2] annulation of isoxazoles with ynol ethers under exceptionally mild reaction conditions, leading to the atom-economical and divergent synthesis of 2-alkoxyl 1H-pyrroles and 3H-pyrroles, respectively. Importantly, this zinc-catalyzed protocol demonstrates the dramatically divergent reactivity from the relevant platinum catalysis, where the formal [4 + 2] annulation of isoxazoles with ynol ethers was involved. In addition, theoretical calculations provide further evidence for the feasibility of the proposed reaction mechanism, especially the distinct selectivity.