Ring closing methathesis reaction

Ring-closing methathesis reactions were also performed using the step 1 Catalyst as illustrated in Eq. (1). 

The ring-closing methathesis catalysts (10mol% catalyst in refluxing toluene) are also effective for this transposition.40,41 Both ester and ether functionalities appear compatible with these reaction conditions (Scheme 17). 

A remarkable ring-closing methathesis (RCM) reaction was highly effective in the syntheses of a number of cyclic sulfones, in high to good yields, from sulfonates (Equations 29-31) <2004S1696>. 

Scheme 4. Ru-catalyzed ring-closing methathesis processes, in conjunction with Zr-vatalyzed enantioselective alkylation reactions provide a convenient protocol for efficient synthesis of optically pure materials...

DOrner and Westermann [149] reported the preparation of the pseudodisaccharide 143 with a triazole tether (Scheme 37) as a prototype for the synthesis of carbohydrate-containing macrocycles, through a Huisgen-catalysed reaction and ring-closing methathesis as the key steps. Standard conditions were used, Cu(OAc)2 and sodium ascorbate as the Cu(I) source and a mixture of water and f-BuOH as solvent, for the conversion of protected glucopyra-nosyl azide 141 into pseudo-disaccharide 143 by using dialkyne 142 in a 77% yield. 

Nevertheless, self-assembling processes by nature rely on weak interactions and the isolation of chemically stable knots and links requires a final knotting step in which covalent bonds are formed. While irreversible reactions such as Williamson ether reactions" and ring closing methathesis are employed successfully to form knots and links, their template-directed syntheses have recently been enriched by the concept of dynamic covalent chemistry (DCC). DCC employs reversible covalent bond formation that allows equilibration of a system toward the most thermodynamically stable structures dictated by the sum of the non-covalent bonding interactions. 

Applications of the water-soluble catalysts to initiate methathesis of less strained alkenes are limited by the instability of some of the alkylidenes in water. For example, diethyldiallylmalonate, a standard metathesis substrate in organic solvents, does not ring close in either methanol or water/methanol mixtures. In this case the chain carrying species is the ruthenium methylene complex. As seen above, this complex is unstable in water. However, when the reaction is redesigned to use substrate 17 so that the methylene is not the chain carrying intermediate, ring closing can be carried out under aqueous conditions (Eq. 12). 

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