It's complex: Ruthenium-catalyzed [3+2] cycloaddition of ethynylcyclopropanes with aldehydes and aldimines has been found to give the corresponding 2-ethynyltetrahydrofurans or -pyrrolidines in high to excellent yields. In both cases, the formation of a ruthenium allenylidene complex as a key reactive intermediate is supported by density functional theory calculations. Cp*=η5-C5Me5.
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