An Enantiomerically Pure Adamantylimido Molybdenum Alkylidene Complex. An Effective New Catalyst for Enantioselective Olefin Metathesis

Tsang, W. C. Peter; Jernelius, Jesper A.; Cortez, G. A.; Schrock, Richard R.; Hoveyda, Amir H.

doi:10.1021/ja021204d

Cited by 80 publications

(39 citation statements)

References 23 publications

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“…However, the high reactivity of 1 and 2 in metathesis reactions involving electron-rich alkenes and their low reactivity for disubstituted and electronpoor alkenes offers in principle access to selective metathesis reactions with molecules containing both types of alkene. Finally, both catalysts showed significant reactivity for electron-poor substrates such as styrene, n-butyl acrylate, and ethyl acrylate (Table 5, entries [23][24][25][26][27][28]. Disappointingly, no reaction was observed with acrylic acid and acrylonitrile (Table 5, entries 29-32).…”

Section: Resultsmentioning

confidence: 99%

Novel Metathesis Catalysts Based on Ruthenium 1,3‐Dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidenes: Synthesis, Structure, Immobilization, and Catalytic Activity

Yang

Mayr

Wurst

et al. 2004

Chemistry A European J

177

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The synthesis of novel ruthenium-based metathesis catalysts containing the saturated 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene ligand, that is, [RuCl2(NHC)[=CH-2-(2-PrO)-5-NO(2)-C6H3]] (1) and [Ru(CF3COO)2(NHC)[=CH-2-(2-PrO)-5-NO2-C6H3]] (2) (NHC=1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) is described. Both catalysts are highly active in ring-closing metathesis (RCM) and ring-opening cross-metathesis (ROCM). Compound 1 shows moderate activity in enyne metathesis. Compound 2 is not applicable to enyne metathesis since it shows high activity in the cyclopolymerization of diethyl dipropargylmalonate (DEDPM). Poly(DEDPM) prepared by the action of 2 consists of 95% five-membered rings, that is, poly(cyclopent-1-enevinylene)s, and 5 % of six-membered rings, that is, poly(cyclohex-1-ene-3-methylidene)s. The polymerization proceeds in a nonliving manner and results in polyenes with broad polydispersities (1.9< or =PDI< or =2.3). Supported analogues of 2 were prepared by immobilization on hydroxymethyl-Merrifield resin and a monolithic support derived from ring-opening-metathesis polymerization (ROMP). Catalyst loadings of 1 and 2.5%, respectively, were obtained. Both supported versions of 2 showed excellent reactivity. With 0.24-2% of the supported catalysts, yields in RCM and ROCM were in the range of 76-100%. Leaching of ruthenium was low and resulted in Ru contaminations of the products of less than 0.000014% (0.14 ppm).

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Section: Resultsmentioning

confidence: 99%

Novel Metathesis Catalysts Based on Ruthenium 1,3‐Dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidenes: Synthesis, Structure, Immobilization, and Catalytic Activity

Yang

Mayr

Wurst

et al. 2004

Chemistry A European J

177

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“…Common precursor for the metathesis substrates is protected D-glucal (127). Synthesis of 130 from 128 and 131 from 129, respectively, illustrates the principle [100].…”

Section: [Ru-ii] [Ru-iv]mentioning

confidence: 99%

"Ring Closing Metathesis of Substrates Containing more than two C-Cdouble Bonds: Rapid Access to Functionalized Heterocycles"

Schmidt¹,

Hermanns

2006

COC

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In most cases where ring closing metathesis is applied to the synthesis of heterocycles, α,ω-dienes are used as precursors. If substrates containing more than two double bonds are subjected to a metathesis reaction, carba-or heterocycles bearing additional exocyclic alkene functionality result, or multiple ring closing processes occur. This offers interesting and potentially very useful synthetic perspectives. On the other hand, selectivity problems need to be addressed as the cyclization of substrates with more than two double bonds available for olefin metathesis may result in constitutional isomers or stereoisomers. This review highlights problems and opportunities evolving from ring closing metathesis of tri-, tetra-, and polyenes as a strategy for the selective synthesis of functionalized heterocycles. The chapter on RCM of trienes is subdivided according to the symmetry of the metathesis precursor. The following two chapters deal with the double or multiple RCM of tetra-or polyenes. These processes are further classified according to the preferred cyclization mode. Finally, the application of cascade or domino metathesis reactions to the synthesis of heterocycles will be discussed. These processes can be classified into those where exclusively C-C-double bonds take part in the metathesis reaction, and those where one or more C-C-triple bonds are involved.

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“…Considering the paucity of effective methods for the preparation of nonracemic tertiary alcohols and ethers (22), the present protocol offers a convenient and enantioselective approach to a difficult problem in organic synthesis. As also depicted in Scheme 3 (12 3 13), meso trienes can be converted to structurally complex polycycles in 80% yield and excellent levels of enantioselectivity (96% to Ͼ98% ee) (23).…”

mentioning

confidence: 93%

Mo-catalyzed asymmetric olefin metathesis in target-oriented synthesis: Enantioselective synthesis of (+)-africanol

Cortez¹,

Schrock²,

Hoveyda³

2004

Proc. Natl. Acad. Sci. U.S.A.

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Catalytic asymmetric ring-opening metathesis (AROM) provides an efficient method for the synthesis of a variety of optically enriched small organic molecules that cannot be easily prepared by alternative methods. The development of Mo-catalyzed AROM transformations that occur in tandem with ring-closing metathesis are described. The utility of the Mo-catalyzed AROM͞ring-closing metathesis is demonstrated through an enantioselective approach to the synthesis of (؉)-africanol. O ne program of research in these laboratories during the past several years has focused on the design and development of chiral catalysts for efficient enantioselective olefin metathesis (1). As part of this initiative, we have synthesized, characterized, and examined the catalytic activity of high-oxidation-state Mobased chiral complexes such as 1-4 (Scheme 1) (1). These investigations have led to the development of a range of methods for catalytic asymmetric ring-closing metathesis (2-6) and asymmetric ring-opening metathesis (AROM) (7-10). Through such protocols, optically enriched organic molecules can be prepared that cannot be easily accessed by alternative approaches.With the availability of various chiral catalysts and the enantioselective transformations that can be promoted by such complexes, we have recently begun to explore the utility of catalytic asymmetric metathesis in target-oriented synthesis. Through application of catalytic asymmetric metathesis to multistep synthesis, we aim to demonstrate the unique features of asymmetric olefin metathesis, as well as identify and address any related shortcomings. We report herein key findings in connection with Mo-catalyzed AROM͞RCM (11). Furthermore, we disclose an enantioselective synthesis of sesquiterpenoid (ϩ)-africanol (12-17), where a Mo-catalyzed AROM͞RCM is used to establish the stereochemical identity of an early intermediate (Fig. 1). In addition to the crucial catalytic asymmetric metathesis step, the total synthesis addresses the utility of other metal-catalyzed transformations as a means to differentiate alkenes formed through metal-catalyzed enantioselective desymmetrizations.Catalytic ROM can be induced to occur in tandem with RCM to yield synthetically versatile bicyclic structures (18). Representative examples of catalytic AROM͞RCM, which may also be considered rearrangement processes, are illustrated in Schemes 2 and 3. It should be mentioned that it is not always clear whether cleavage of the more strained cyclic olefin occurs in an intramolecular fashion, where RCM (by means of alkylidene ii) gives rise to rupture of the ring, or ring-opening occurs first (19) (by means of iii formed by reaction of i with the substrate) followed by RCM. The different levels of asymmetric induction observed in the formation of 6 versus 8 (69% and 92% ee) may be partly the result of such mechanistic intricacies. The terminal olefin in 5 may be converted to ii (R ϭ H) more readily than would be the case with the more substituted alkene of substrate 7, which might prefer to proceed th...

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An Enantiomerically Pure Adamantylimido Molybdenum Alkylidene Complex. An Effective New Catalyst for Enantioselective Olefin Metathesis

Cited by 80 publications

References 23 publications

Novel Metathesis Catalysts Based on Ruthenium 1,3‐Dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidenes: Synthesis, Structure, Immobilization, and Catalytic Activity

Novel Metathesis Catalysts Based on Ruthenium 1,3‐Dimesityl‐3,4,5,6‐tetrahydropyrimidin‐2‐ylidenes: Synthesis, Structure, Immobilization, and Catalytic Activity

"Ring Closing Metathesis of Substrates Containing more than two C-Cdouble Bonds: Rapid Access to Functionalized Heterocycles"

Mo-catalyzed asymmetric olefin metathesis in target-oriented synthesis: Enantioselective synthesis of (+)-africanol

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