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T1 - Ring closing enyne metathesis

H.; Kluger, C., Combining ring-opening metathesis polymerization (ROMP) with Sharpless-type "click" reactions: An easy method for the preparation of side chain functionalized poly(oxynorbornenes).

In conclusion, we have demonstrated that W-based MAP complexes promote more efficient and endo-selective enyne RCM than the corresponding Mo-based variants; the most notable distinction is fewer side reactions with W-based system. The observations described above, along with the findings concerning Z-selective homo-coupling of terminal olefins, underline the importance of examining W-based catalysts along with Mo-based catalysts in the context of various applications. The strategies outlined above, involving Mo- as well as W-based catalysts for olefin metathesis, will constitute a critical and unique attribute of the future studies in these laboratories.

KW - Ring-closing alkyne metathesis

Organic Chemistry II - Ring Closing Metathesis - YouTube

H., Connecting supramolecular receptors onto diblock-co-polymers: combining ring opening metathesis polymerization with 1,3-dipolar cycloadditions.

We carried out further structural optimization of the W-based MAP catalysts for enyne metathesis of 12. Initial efforts focused on screening of various imido groups (). Out of four aryl imido groups investigated, the original 2,6-di-iso-propylphenylimido complexes (as in 21) emerged as optimal, especially in terms of enantioselectivity. The effect of different chiral phenoxides derived from mono-protected BINOL or octahydro-BINOLs were examined next (). Whereas incorporation of different substitution at the 3,3’ positions of the chiral diols (different halides in entries 1, 2, 4 and 5, as well as Me in entry 3 in ) resulted in less enantioselective reactions, catalyst 22 with a methyl ether unit on the chiral aryloxide was more reactive and promoted more selective reactions; cyclic diene 13 was formed in 60% isolated yield and 81% ee (entry 6, ). Further solvent screening () identified diethyl ether as the optimal solvent in terms of endo-selectivity and enantioselectivity (91% ee), although the yield of the isolated product was only 35% as a consequence of significant competitive oligomerization.

We have previously reported examples of enantioselective enyne metathesis desymmetrization reactions performed under ethylene. Such processes likely involve cross-metathesis with ethylene, followed by enantioselective RCM of the tetraene intermediate. We report here that W-based catalysts provide enhanced endo-as well as enantioselectivity for desymmetrization of aniline dienyne 12. As summarized in , under otherwise identical conditions, while Mo-based catalyst 20 provided a 2.5:1 mixture of 13 and 19, with only 21% ee for the major isomer 13, the corresponding W-catalyst 21 yielded a higher ratio (8:1 favoring 13) with an ee of 70%. Both catalysts can be generated in situ from alcoholysis of the corresponding bis-pyrrolide complexes. We note that, unlike the reaction performed in the presence of W-F6, which cleanly yielded the desired product, the reaction catalyzed by 20 and 21 led to a significant amount of oligomerization (20-30%). When the same transformations were carried out in the presence of ethylene, the endo- and enantioselectivities of the products remained the same, which implies that such reactions proceed through a true enyne metathesis pathway.

Ring-closing metathesis - Revolvy

At least in certain cases, W-based catalysts are more endo-selective than Mo-based alkylidenes. As shown in , enyne metathesis of internal alkyne substrates 16 with Mo-F6 yielded a mixture of endo- and exo-products in a ratio of 5:1. It is plausible that the sterically less accessible internal alkyne discourages Mo-alkylidene alkyne association as depicted in ii in , pathway 1, leading to partial reaction through pathway 3 and initiation at the alkene site. An indiscriminative α- and β-addition of the alkylidene to the internal alkyne may also play a role for the low selectivity. The use of W-F6 resulted in a much-improved endo-selectivity of 10:1, albeit with a lower reaction efficiency; a 10 mol % loading was necessary to achieve full conversion to the desired product.

Ring Closing Alkyne Metathesis

There has been rapid progress and growing interest in alkyne metathesis within the past decade. The availability of highly active catalysts as well as their applications in both organic synthesis and polymer chemistry has served to motivate the advancement of this field. In this article, the development of several different metathesis catalysts, including two heterogeneous ones, are reviewed with an emphasis on comparing strengths and weaknesses. In Section 4, the applications of alkyne metathesis to synthesis of natural products, conjugated polymers as well as shape-persistent macrocycles are discussed. In the last section, a comparison of alkyne metathesis to the well established alkene metathesis is given. Developing an alkyne metathesis catalyst with both high reactivity and robustness to air and moisture remains an unsolved problem of this important and useful reaction. 1 Introduction 2 Mechanistic Overview 3 Catalyst Synthesis 3.1 Homogeneous Systems 3.2 Heterogeneous Systems 4 Synthetic Applications of Alkyne Metathesis 4.1 Ring-Closing Alkyne Metathesis (RCAM) 4.2 Natural Product Synthesis 4.3 Polymer Synthesis 4.4 Cyclooligomerization 5 Alkyne Metathesis vs. Alkene Metathesis 5.1 Catalysts 5.2 Cross-Metathesis 5.3 Ring-Opening Metathesis 5.4 Ring-Closing Metathesis 5.5 Cyclooligomerization 5.6 Acyclic Diene/Diyne Metathesis 6 Conclusion and Outlook

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Ring-closing metathesis , or RCM , ..


Topic: Ring Closing Alkyne Metathesis – 717157 | …

Ring closing enyne metathesis to form 10-15-membered rings was achieved by using a tartrate-derived linker to attach ene and yne subunits. The exo/endo selectivity of the ring closure reaction of these substrates was found to be a function of ring size, whereby larger rings (12-15) give endo-products selectively, while smaller rings (5-11) give exo-products. The E/Z selectivity of the resultant macrocyclic 1,3-dienes was not predictable except for 10- and 11 -membered rings. However, both the exo/endo-mode selectivity of the ring closure and the E/Z selectivity of the 1,3-dienes were improved by performing these reactions under ethylene atmosphere. The presence of ethylene induces a selective cross metathesis between the alkyne moiety and ethylene to generate an acyclic 1,3-diene which can undergo ring closing diene metathesis between the isolated olefin and the distal monosubstituted double bond of the 1,3-diene to generate exclusively the endo-product with high E-selectivity.

RCAM - ring closing alkyne metathesis in Medical & …

N2 - There has been rapid progress and growing interest in alkyne metathesis within the past decade. The availability of highly active catalysts as well as their applications in both organic synthesis and polymer chemistry has served to motivate the advancement of this field. In this article, the development of several different metathesis catalysts, including two heterogeneous ones, are reviewed with an emphasis on comparing strengths and weaknesses. In Section 4, the applications of alkyne metathesis to synthesis of natural products, conjugated polymers as well as shape-persistent macrocycles are discussed. In the last section, a comparison of alkyne metathesis to the well established alkene metathesis is given. Developing an alkyne metathesis catalyst with both high reactivity and robustness to air and moisture remains an unsolved problem of this important and useful reaction. 1 Introduction 2 Mechanistic Overview 3 Catalyst Synthesis 3.1 Homogeneous Systems 3.2 Heterogeneous Systems 4 Synthetic Applications of Alkyne Metathesis 4.1 Ring-Closing Alkyne Metathesis (RCAM) 4.2 Natural Product Synthesis 4.3 Polymer Synthesis 4.4 Cyclooligomerization 5 Alkyne Metathesis vs. Alkene Metathesis 5.1 Catalysts 5.2 Cross-Metathesis 5.3 Ring-Opening Metathesis 5.4 Ring-Closing Metathesis 5.5 Cyclooligomerization 5.6 Acyclic Diene/Diyne Metathesis 6 Conclusion and Outlook

Ring closing enyne metathesis: Control over mode selectivity and ..

AB - There has been rapid progress and growing interest in alkyne metathesis within the past decade. The availability of highly active catalysts as well as their applications in both organic synthesis and polymer chemistry has served to motivate the advancement of this field. In this article, the development of several different metathesis catalysts, including two heterogeneous ones, are reviewed with an emphasis on comparing strengths and weaknesses. In Section 4, the applications of alkyne metathesis to synthesis of natural products, conjugated polymers as well as shape-persistent macrocycles are discussed. In the last section, a comparison of alkyne metathesis to the well established alkene metathesis is given. Developing an alkyne metathesis catalyst with both high reactivity and robustness to air and moisture remains an unsolved problem of this important and useful reaction. 1 Introduction 2 Mechanistic Overview 3 Catalyst Synthesis 3.1 Homogeneous Systems 3.2 Heterogeneous Systems 4 Synthetic Applications of Alkyne Metathesis 4.1 Ring-Closing Alkyne Metathesis (RCAM) 4.2 Natural Product Synthesis 4.3 Polymer Synthesis 4.4 Cyclooligomerization 5 Alkyne Metathesis vs. Alkene Metathesis 5.1 Catalysts 5.2 Cross-Metathesis 5.3 Ring-Opening Metathesis 5.4 Ring-Closing Metathesis 5.5 Cyclooligomerization 5.6 Acyclic Diene/Diyne Metathesis 6 Conclusion and Outlook

Ring closing enyne metathesis to form 10 ..

N2 - Ring closing enyne metathesis to form 10-15-membered rings was achieved by using a tartrate-derived linker to attach ene and yne subunits. The exo/endo selectivity of the ring closure reaction of these substrates was found to be a function of ring size, whereby larger rings (12-15) give endo-products selectively, while smaller rings (5-11) give exo-products. The E/Z selectivity of the resultant macrocyclic 1,3-dienes was not predictable except for 10- and 11 -membered rings. However, both the exo/endo-mode selectivity of the ring closure and the E/Z selectivity of the 1,3-dienes were improved by performing these reactions under ethylene atmosphere. The presence of ethylene induces a selective cross metathesis between the alkyne moiety and ethylene to generate an acyclic 1,3-diene which can undergo ring closing diene metathesis between the isolated olefin and the distal monosubstituted double bond of the 1,3-diene to generate exclusively the endo-product with high E-selectivity.

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