Synthesis of pyrroles via ruthenium-catalyzed nitrogen-transfer [2

Pyrrole is a privileged five-membered aromatic nitrogen heterocycle, which is ubiquitous in natural products, drug molecules, and functional materials. Therefore, numerous synthetic routes to substituted pyrroles have been extensively developed. Nevertheless, the efficient and short-step synthesis of highly substituted and/or fused pyrroles has remained a significant challenge in organic chemistry. Here we report a ruthenium-catalyzed nitrogentransfer [2 + 2 + 1] cycloaddition of alpha,omega-diynes involving cyclic biscarbenoid intermediates. To achieve the key nitrogen transfer to carbenoid carbons, sulfoximines are employed as nitrene surrogates. Consequently, diverse fused pyrroles are successfully synthesized in good yields with wide functional group compatibility. Moreover, this method allows the synthesis of N-alkyl, N-aryl, and even N-H pyrroles, which are difficult to obtain using previous [2 + 2 + 1]-type reactions. Nitrogen transfer from sulfoximines to cyclic biscarbenoid intermediates is supported by density functional theory calculations and control experiments.