Efficient synthesis of functionalized furans via ruthenium-catalyzed cyclization of epoxyalkyne derivatives

Ruthenium catalyst TpRuPPh(3)(CH3CN)(2)Cl is found to effect the cyclization of epoxyalkynes to furans in the presence of Et3N. The reactions worked well for various epoxyalkynes with suitable oxygen and nitrogen functionalities with low loading of catalyst. It failed with disubstituted epoxyalkynes. The mechanism was elucidated by a deuterium labeling experiment that suggested that the mechanism involved a ruthenium-vinylidenium intermediate.