Stilbene cross-metathesis

As expected, there was no formation of stilbenes or a dinitrile product and, more surprisingly, in all of the reactions reported only 5-7% of the allyltrimeth-ylsilane self-metathesis product was observed. It was proposed that this lack of allylsilane self-metathesis was due to the steric bulk of the TMS group reducing the reactivity of the Me3SiCH2 substituted alkylidene. In a more recent report by Blechert and co-workers it was noted that allyltrimethylsilane and its hydrocarbon equivalent (4,4-dimethylpent-l-ene) had comparable reactivities in the cross-metathesis reaction [28], further suggesting that the selectivity arises from steric rather than electronic effects. 

The Mo-catalysed cross-metathesis of acrylonitrile (59) [17,18] and allylsilane (60) [19] with alkenes 61 and 62 produced cross-products 63 and 64 with high selectivity. Reaction of 1-octene with 2 equivalents of styrene (65) afforded 66 in 89% yield. Only small amounts of stilbene (68) and 67 as the homoproducts were formed [23]. 

Synthetic approach to hydroxy ( )-stilbene via solid-phase cross metathesis... 

Cross-metathesis of stilbene with symmetrical olefins is only possible at 100°C with the Rc207/Al203 catalyst when it is activated with Bu Sn. With equimolar amounts of the reactants an equilibrium mixture (50% conversion) is obtained (Warwel 1985). 

These examples illustrate the occurrence of metal contamination during mech-anochemical treatment of organic molecules without affecting the reactivity and yields, however wear in organic mechanosynthesis can also lead to incompatibility in a chemical sense, which especially holds for metal-catalyzed reactions. In a recently pubhshed demonstration of olefin cross-metathesis reaction conducted under ball-milhng conditions [33], the authors reported on an observation that the model metathesis reaction of styrene to produce stilbene proceeded with diminished... 

Treatment of 1,2-diamino substrates with 1,2-dicarbonyls for the formation of the pyrazine core was a commonly used approach in 2013. Schmidt and his group developed a one-pot synthesis of quinoxahnes, involving a ruthenium-catalyzed cross-metathesis reaction of the starting styrene, forming the respective stilbene, followed by a ruthenium-catalyzed oxidation to the 1,2-diketone, and a subsequent condensation with phenyl-ene diamine, yielding the respective diarylquinoxalines 128 in moderate yields (Scheme 55) (13JOC5427). 

Velder, J., Ritter, S., Lex, J., Schmalz, H.-G., A simple access to biologically important trans-stilbenes via Ru-catalyzed cross metathesis. Synthesis 2006, 273-278. 

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