Metathesis molybdenum-catalyzed olefin

Enantioselective cyclic ether is synthesized by molybdenum-catalyzed olefin metathesis. Cyclopentene derivative 85a is reacted with 5 mol% of chiral molybdenum catalyst 76 to give pyran derivative 86a in high yield and high ee... 

Since the discovery of ruthenium and molybdenum carbene complexes that efficiently catalyze olefin metathesis under mild reaction conditions and that are compatible with a broad range of functional groups, olefin metathesis has increasingly been used for the preparation of alkenes on insoluble supports. In particular, the ruthenium complexes Cl2(PCy3)2Ru=CHR, developed by Grubbs, show sufficient catalytic activity even in the presence of air and water [781] and are well suited for solid-phase synthesis. 

Olefin metathesis is a unique reaction and is only possible by transition metal catalysis. In fact only complexes of Mo, W, Re, and Ru are known to catalyze olefin metathesis. Once it was known that metallocarbenes were the actual catalytic species, a variety of metal carbene complexes were prepared and evaluated as catalysts. Two types of catalysts have emerged as the most useful overall. The molybdenum-based catalysts developed by Schrock and ruthenium-based catalysts developed by Grubbs. 

The proposed idea that metal alkyhdene complexes are be able to catalyze olefin metathesis was confirmed in 1980 [8] and consolidated in 1986 by Schrock with the development of the first well-characterized, highly active, neutral tungsten (Cl, Fig. 3) [9] and molybdenum (C2) [10] alkylidene complexes. These complexes were able to catalyze both the metathesis of different olefins and the ROMP of functionalized norbomene to polynorbomene with low polydispersities [11]. Moreover, these catalysts were used by Wagener and coworkers to perform the first quantitative ADMET polymerization [12] and copolymerization [13] of 1,5-hexadiene and 1,9-decadiene. However, the low stability of these catalysts in... 

With the experimental tools of Grubbs group, SonBinh Nguyen discovered in a short period of time that 81 did not only catalyze the metathesis of acyclic olefins but was also competitive with Schrock s molybdenum carbenes in ringclosing metathesis (RCM) [171]. Compared with Schrock s compounds, the ruthenium carbenes had the advantage that they were only moderately sensitive... 

Molybdenum-catalyzed enantioselective olefin metathesis reactions of P-stereogenic phosphinates (597) which led to formation of five-, six-, and seven-membered P-heterocycles (698) in up to 98% ee has been reported by Hoveyda and co-workers (Scheme 148). ° ... 

The molybdenum(VI) complex with BIPHEN (Schrock-Hoveyda catalyst) has been widely used as an enantioselective olefin metathesis catalyst for a variety of substrates (145). Recently, the synthesis of a tetrahydrocannabiol derivative in molybdenum-catalyzed asymmetric allylic alkylation by using Trost-ligands is carried out. Enhanced regio-, enantio-, and diastereoselectivities relative to the palladium ones have been observed (146). 

Olefin metathesis is the transition-metal-catalyzed inter- or intramolecular exchange of alkylidene units of alkenes. The metathesis of propene is the most simple example in the presence of a suitable catalyst, an equilibrium mixture of ethene, 2-butene, and unreacted propene is obtained (Eq. 1). This example illustrates one of the most important features of olefin metathesis its reversibility. The metathesis of propene was the first technical process exploiting the olefin metathesis reaction. It is known as the Phillips triolefin process and was run from 1966 till 1972 for the production of 2-butene (feedstock propene) and from 1985 for the production of propene (feedstock ethene and 2-butene, which is nowadays obtained by dimerization of ethene). Typical catalysts are oxides of tungsten, molybdenum or rhenium supported on silica or alumina [ 1 ]. 

Along with better efficacy in cross metathesis, one of the areas of olefin metathesis that was awaited eagerly is the area of asymmetric olefin metathesis. As of 2000, only a few reports for evidence of asymmetric induction, all of which were catalyzed by molybdenum complexes, had been published. ... 

The metathesis or transalkylidenation reaction is catalyzed by complexes of tungsten, molybdenum or rhenium, in a heterogeneous or homogeneous phase, and consists in the. scission of the double bond with the formation of two new olefins. 

More recently, the pincer iridium catalysts for alkane dehydrogenation, in combination with Schrock s molybdenum catalyst for olefin metathesis (Chapter 21), has been shown to catalyze alkane metathesis (Equation 18.47). This combination of catalysts provides... 

For over two decades, the development of olefin metathesis by many research groups has yielded more stable catalysts with higher turnover frequencies and greater substrate range. Modern olefin metathesis reactions are catalyzed by well-defined complexes of transition metals, such as ruthenium, tungsten, and molybdenum. In these complexes, the metal atom is naturally surrounded by carefully chosen ligands, which provide the desired electronic and steric environment to the metal. 

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