Olefinsare important functional groups in organic synthesis. Not only they have highprevalence in natural products, they can also be modified into many functionalgroups via many well-known procedures. Traditionally Olefination strategiesrely on nucleophilic attack of a carbon nucleophile on a carbonyl group(Wittig, Julia, Horner-Wadsworth-Emmons), or palladium catalyzed couplingreactions (Stille, Suzuki, Heck). These reactions are well studied anddependable, but there are still many challenges when accessing olefins in asensitive environment or in an already complex structure. These methodsgenerally need activation of functional groups, and somewhat harsh conditions,making them not compatible with many functional groups. Mandatory protectionand deprotection of those functional groups make syntheses lengthier and withlower yield.
Sinceits discovery in the 1950s, and because of its broad functional grouptolerance, and straightforward implantations, olefin metathesis, afundamentally different olefination method, has gained acceptance as a powerfultool for construction of carbon-carbon double bonds. In recent years detailed,experimental and computational mechanistic studies have resulted in synthesesof well-defined ruthenium, tungsten, and molybdenum complexes, capable ofselectively generating either Z, or E alkenes. Because of its value, to haveone catalyst to generate both E and Z-olefins via one method, stereoretentiveolefin metathesis has recently gained a lot of attention. Early studies usingnot very well defines catalysts showed evidence of retention of stereochemistryat low conversion. But, thermodynamic E to Z ratios were observed after reactionreached equilibrium.
Various olefinswere examined, and it showed that the stereochemistry of reactant olefinsometimes influences the stereochemistry of product, when using the samecatalyst. Because of their high air and moisture tolerance and high functionalgroup compatibility, Ruthenium-based metathesis catalysts have become some ofthe most useful complexes in total synthesis of natural products and complexmaterials. Different Z-selective ruthenium-based olefin metathesis catalystshave been developed. One of these systems uses a ruthenium catalyst bearingcathecothiolate ligands, going through stereoretention to provide z-olefins.
Furtherstudies revealed that this catalyst also Kinetically generates E-olefins