Addition of pyrroles onto terminal alkynes catalyzed by a dinuclear ruthenium (II) complex

The addition of pyrroles onto alkynes has been catalyzed by a dinuclear ruthenium complex, Ru2(CO)4(PPh3)2Br4, resulting in the formation of geminal 2-vinylpyrroles in high yields under mild conditions. Further functionalization with pyrroles or alkynes to afford dipyrrolmethanes or 2,5-bis(vinyl)pyrroles via the vinyl functional group can readily be achieved. A mechanism involving cationic ruthenium complexes was proposed based on the product regioselectivity, deuteration and infrared spectroscopic studies carried out on the catalytic process.

Graphical abstractIn this work, we report the ability of Ru(CO)4L2Br4 (where L = CO or PPh3) to catalyze the hydroarylation reaction of pyrroles and terminal alkynes. The unprecedented bis(vinyl)pyrroles and mixed pyrrole double addition product was formed in the process..Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Pyrrole addition onto alkynes has been catalyzed by Ru2(CO)4(PPh3)2Br4. ► Formation of exclusively geminal 2-vinylpyrrole product in high yields. ► Further addition to give dipyrrolmethanes or 2,5-bis(vinyl)pyrroles is possible. ► A mechanism involving cationic ruthenium complexes was proposed.