Cucurbituril syntheses

Template effects have been used in rotaxane synthesis to direct threading of the axle through the wheel. Since macrocycHc compounds such as cyclodextrins, crown ethers, cyclophanes, and cucurbiturils form stable complexes with specific guest molecules, they have been widely used in the templated synthesis of rotax-anes as ring (wheel) components. Here, we briefly discuss macrocycles used in the synthesis of rotaxane dendrimers and their important features. 

Instead of conventional organic polymers, Kim and coworkers addressed coordination polymers in polyrotaxane synthesis [134,135]. The cyclic, cucurbituril... 

Cucurbit [6] uril and increasingly its higher homologues have been used extensively in a variety of host-guest chemistry and nanostructure assemblies. Of particular appeal are rotaxanes and molecular necklaces, mechanically interlocked assemblies of molecules based on CB [6]. Efficient synthesis of ID, 2D and 3D polyrotaxanes and molecular necklaces (cucurbituril beads linked by a macrocyclic molecule string ) has been achieved by a combination of self-assembly and coordination chemistry. We discuss rotaxanes and molecular necklaces in Section 10.7, and cucurbil-based systems are summarised in a recent review.23... 

Scheme 4. The acid-catalyzed synthesis of cucurbituril 20 [55,56] displays all of the hallmarks of a product-directed self-assembly. The product is obtained from urea, glyoxal, and formaldehyde through the intermediacy of the glycoluril 19...

Cucurbituril (cucrbit[6]uril or CB[6]), a hexameric macrocycle 141 (R = H, = 6) with a 1,3,5,6-tetraazocane core unit, is self-assembled from an acid-catalyzed condensation reaction of glycouril and formaldehyde (see Section 14.09.9.1.1 and 1996CHEC-II(9)705). Although its synthesis first appeared in 1905, its chemical nature and structure remained unknown until 1981, when full characterization was reported by Mock and co-workers <1981JA7367>. 

The above-mentioned directed synthesis always requires a certain strong interaction between the wheel and the axle before making the interlocked bond in any method. As for the example of the wheels depicted in Scheme 3, hydrophobic interaction is the major attractive interaction in the cases of cucurbituril and cyclodextrin (A, B), thereby resulting in limitation as the wheel-axle complex formation should be done in water. In particular, it is an additional difficulty to employ the complexation in strongly acidic conditions owing to the extremely low solubility of cucurbituril. 

In this review, I describe our efforts to construct interlocked structures such as rotaxanes, polyrotaxanes and molecular necklaces incorporating cucurbituril as a molecular bead by utilizing the principles of self-assembly and coordination chemistry. A key to the success of this synthesis is the high affinity of cucurbituril toward alkyl diammonium ions, which allows formation of a stable pseudorotaxane... 

Cucurbituril (269) is a nonadecacyclic cage compound consisting of six tetrazocane units fusing six glycoluril moieties. It is readily synthesized from urea, glyoxal, and formaldehyde (see Section 9.26.9.1.1 for details on the synthesis of cucurbituril and derivatives, and Section 9.26.3.3 for details on structure). 

Cucurbituril (cucurbit[6]uril, or CB[6]) is a hexameric macrocyclic compoxmd self-assembled from an acid-catalyzed condensation reaction of glycoluril and formaldehyde (Scheme 1). Although its synthesis was first reported by Behrend and coworkers in 1905j its chemical nature and stmcture were unknown until they were revealed by Mock and coworkers in 198iP CB[6] has a cavity of 5.5 A diameter, accessible from the exterior by two carbonyl-laced portals of 4 A diameter. Although the size of the cavity is similar to that of a-cyclodextrin ( < highly symmetrical structure... 

Calixarenes Synthesis and Historical Perspectives, p. 153 Cucurbituril, Its Homologues, and Derivatives, p. 390... 

Cucurbituril, Its Homologues, and Derivatives, p. 390 The Diphenylmethane Moiety, p. 452 Interpenetration, p. 735 Macrocycle Synthesis, p. 830 Rotaxanes and Pseudorotaxanes. p. 1194 Self-Assembly Definition and Kinetic and Thermodynamic Considerations, p. 1248 Self-Assembly Terminology, p. 1263 Strict Self-Assembly and Self-Assembly with Covalent Modifications, p. 1372 The Template Effect, p. 1493... 

Krasia and Steinke [28] first reported the polymer synthesis using diazide and dialkyne under catalysis of cucurbituril. 

Fig. 1.35 Mock s synthesis of a [2]rotaxane via a 1,3-dipolar cycloadditions catalyzed by cucurbituril.

Our interest in cucurbituril as a macrocyclic component ( bead ) in polyrotaxane synthesis originates from our interest in the synthesis of well-defined poly-... 

Fig. 1.39 Synthesis of poly(hexamethylene amine) and post-threading of its protonated form, 3, with cucurbituril. (i) BH3-DMS, THF, 48 h, 66%, (ii) 20 wt% HCl.

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