Ruthenium Carbene-Mediated Construction of Strained Allenes via the Enyne Cross-Metathesis/Cyclopropanation of 1,6-Enynes.

Herein, we report on the unprecedented dimerization of 1,6-enynes using a commercially available ruthenium complex RuCl2(PPh3)3, which results in a series of bicyclo[3.1.0]hexyl allene derivatives in moderate to excellent yields. Mechanistic investigation indicates that the in-situ-generated ruthenium vinylidene undergoes a site-selective metathesis process to provide allenyl ruthenium carbene, which can be intramolecularly trapped by the pendent C=C bond of enyne through a [2 + 2] cycloaddition/metal elimination process.