Chemoselective, Catalytic Olefin Isomerization
Fogg.* Organometallics, 2016, 35, 691-698.
"Olefin Isomerization-Metathesis: Ensuring Process Orthogonality in the One-Pot Transformation of Essential-Oil Phenylpropenoids into High-Value Antioxidants." C.S.
Olefin isomerization promoted by olefin metathesis catalysts
Transition-metal-catalyzed olefin isomerization has played a crucial role in the synthesis of organic compounds, commodity chemicals, natural products, and petroleum feedstocks. Although noble metals such as Ru, Rh and Ir as catalysts for the conversions have made dramatic achievements, the disadvantages of the rare resource, high cost, and poisoning products have limited its wide application in the synthesis. Due to the abundant supply, low cost and easy removal from the final products, the first-row transition metals have attracted much attention from the chemists and have proven to be very promising with respect to the development of more sustainable catalytic system in olefin isomerizaton. This review summaried the advances in olefin isomerization catalyzed by iron, cobalt, nickel in the past years and illustrates the differences among different catalytic systems in catalytic activity, regio- and stereo-selectivity, and substrate scope. Recent developments in the olefin isomerization catalyzed by the first-row metals have proven to be very promising and effective. The reaction mechanism was discussed to have deep insight into the isomerization. The mechanism of olefin isomerization was illustrated clearly in the reported articles through intermolecular or intramolecular hydrogen shift, and the stereoselectivity and regioselectivity in different catalytic system was still worthy of further investigations. Further studies in the field to solve the challenges in high catalytic activity, stereoselectivity, and wide substrate scopes would bring the isomerization into better prospect.
The formation of these secondary compounds is expected to be minimal when one of the two catalytic processes dominates, while it should be important when the rates of metathesis and isomerization are comparable. Moreover, since secondary products are formed from the primary products 7 and 8, their importance will grow with the progress of the reaction. In the majority of the experiments of , the conversion of the substrate was below 50%, and the amount of secondary isomerization products was low. The only exceptions are entry 6, where the rates of isomerization and metathesis are comparable, and entry 8, where the conversion is high.
Isomerization During Olefin Metathesis: An Assessment …
A novel ruthenium-catalyzed tandem ring-closing metathesis (RCM) double-bond isomerization reaction is described in this paper. The utility of this method for the efficient syntheses of five-, six-, and seven-membered cyclic enol ethers is demonstrated. It relies on the conversion of a metathesis-active ruthenium carbene species to an isomerization-active ruthenium−hydride species in situ. This conversion is achieved by using various additives. Scope and limitations of the different protocols are discussed, and some mechanistic considerations based on 31P and 1H NMR spectroscopic studies are presented.
Olefin metathesis and isomerization: From ..
Bottom line: to minimize side products arising from isomerization, minimize decomposition of the metathesis catalyst. This includes removing impurities that inhibit a catalyst or promote its decomposition. Catalyst screening and conducting the metathesis at a lower temperature may also be helpful.
(2003) Olefin isomerization promoted by olefin metathesis catalysts.
Catalytic amounts of Co(SalBu,Bu)Cl and organosilane irreversibly isomerize terminal alkenes by one position. The same catalysts effect cycloisomerization of dienes and retrocycloisomerization of strained rings. Strong Lewis bases like amines and imidazoles, and labile functionalities like epoxides, are tolerated.
Reactions of Olefins in Water: Olefin Metathesis and Isomerization
(1992) The organometallic chemistry of aqueous ruthenium(II) with functionalized olefins: complex formation, isomerization, and metathesis chain transfer. Dissertation (Ph.D.), California Institute of Technology.