Macrocyclic syntheses ring closing reactions

Clipping. The clipping method relies on the synthesis of the rotaxane by formation of the macrocycle (host) in the presence of a dumbbell shaped molecule. The partial macrocycle undergoes a ring closing reaction around the dumbbell shaped molecule, thereby forming the rotaxane. 

Grasillas, A. Perez-Castells, J. Macrocyclization by ring-closing metathesis in the total synthesis of natural products Reaction conditions and limitations. Angew. Chem. Int. Ed. 2006,45, 6086-6101. 

Gradihas A, CasteUs JP. Macrocyclization by Ring-Closing Metathesis in the Total Synthesis of Natural Products Reaction Conditions and Limitations. Angew Chem Int Ed. 2006 45(37) 6086-6101. 

With a-monosubstituted ylides the oxidation results in the formation of alkenes (by subsequent Wittig reaction on the intermediate aldehyde). A recent example of such synthesis is found in the preparation of all-(Z)-cyclododecate-traene by oxidation of the appropriate bis-ylide [33]. It must be pointed out that an approach of the same macrocycle based on ring closing metathesis was found ineffective. 

Examples of template procedures in which the ring-closing condensation involves reaction at a centre other than a donor atom have been documented. In an early synthesis of this type, the reaction of bis-(dimethylglyoximato)nickel(n) (62) with boron trifluoride was demonstrated to yield the corresponding complex of the N4-donor macrocycle (63) (Schrauzer, 1962 Umland Thierig, 1962). In this reaction the proton of each bridging oxime linkage is replaced by a BF2+ moiety. X-ray... 

Metathesis is the most useful reaction in recent synthetic organic chemistry.In this reaction, bond fission of two double bonds occurs and two new double bonds are simultaneously formed after exchange (Equation (1)). Ring-closing olefin metathesis is now used for the synthesis of five-membered to macrocyclic ring compounds. 

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. 

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