Styrene-alkyne cross ene-yne metathesis: Catalyst screening and optimization for unbranched terminal alkyne substrates

Cross metathesis between styrenes and unbranched terminal alkynes is reported. Styrene cross metathesis with terminal alkynes that lack branching at the propargylic position are unknown. In general, unbranched terminal alkynes have been problematic in cross metathesis due to competing alkyne oligomerization. A catalyst screen was performed for a variety of Grubbs catalysts to optimize the yield of the desired 1,3‑diene product. This catalyst screen identified two ruthenium carbene complexes that have been rarely used for cross metathesis applications. Additionally, a side product arising from a competing alkene metathesis was minimized by choice of catalyst and through reaction optimization.