Absence of the Thorpe–Ingold effect by gem-diphenyl groups in ring-closing enyne metathesis

In tandem ring-closing metathesis of alkynyl silaketals containing two different tethered olefins, the gem-dimethyl group showed the expected Thorpe–Ingold effect, thereby giving good level of group selectivity. Unexpectedly, however, the corresponding gem-diphenyl group did not show any Thorpe–Ingold effect for the ring-closure reaction.