Merging Grubbs second-generation catalyst with photocatalysis enables Z -selective metathesis of olefins: scope, limitations, and mechanism.

Olefin cross-metathesis is a cornerstone reaction in organic synthesis where stereoselectivity is typically governed by the structure of the catalyst. In this work, we show that merging Grubbs second generation catalyst, a classical E -selective catalyst, with a readily available photocatalyst, enables the exclusive formation of the contra-thermodynamic Z -isomer. The scope and limitations of this unprecedented approach are discussed based on both computational and experimental mechanistic data.