Olefins group compatibility, Ruthenium-based metathesis catalysts have become

 

Olefins
are important functional groups in organic synthesis. Not only they have high
prevalence in natural products, they can also be modified into many functional
groups via many well-known procedures. Traditionally Olefination strategies
rely on nucleophilic attack of a carbon nucleophile on a carbonyl group
(Wittig, Julia, Horner-Wadsworth-Emmons), or palladium catalyzed coupling
reactions (Stille, Suzuki, Heck). These reactions are well studied and
dependable, but there are still many challenges when accessing olefins in a
sensitive environment or in an already complex structure. These methods
generally need activation of functional groups, and somewhat harsh conditions,
making them not compatible with many functional groups. Mandatory protection
and deprotection of those functional groups make syntheses lengthier and with
lower yield.

 

Since
its discovery in the 1950s, and because of its broad functional group
tolerance, and straightforward implantations, olefin metathesis, a
fundamentally different olefination method, has gained acceptance as a powerful
tool for construction of carbon-carbon double bonds. In recent years detailed,
experimental and computational mechanistic studies have resulted in syntheses
of well-defined ruthenium, tungsten, and molybdenum complexes, capable of
selectively generating either Z, or E alkenes. Because of its value, to have
one catalyst to generate both E and Z-olefins via one method, stereoretentive
olefin metathesis has recently gained a lot of attention. Early studies using
not very well defines catalysts showed evidence of retention of stereochemistry
at low conversion. But, thermodynamic E to Z ratios were observed after reaction
reached equilibrium.  Various olefins
were examined, and it showed that the stereochemistry of reactant olefin
sometimes influences the stereochemistry of product, when using the same
catalyst. Because of their high air and moisture tolerance and high functional
group compatibility, Ruthenium-based metathesis catalysts have become some of
the most useful complexes in total synthesis of natural products and complex
materials. Different Z-selective ruthenium-based olefin metathesis catalysts
have been developed. One of these systems uses a ruthenium catalyst bearing
cathecothiolate ligands, going through stereoretention to provide z-olefins. Further
studies revealed that this catalyst also Kinetically generates E-olefins

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