Group-Selective Ring-Closing Enyne Metathesis:  Concentration-Dependent Selectivity Profile of Alkynylsilyloxy-Tethered Dienynes

Highly group-selective ring-closing metathesis of alkynylsilyloxy-tethered dienynes was achieved by using Grubbs first- and second-generation catalyst. The remarkable selectivity increase at higher concentration for differentiating between two alkene moieties in nearly identical steric and stereoelectronic environments is believed to be the result of a higher ring-closure rate for smaller-sized ring formation under rapid pre-equilibration of the two alkylidene species generated from either alkene moiety.