Cucurbituril derivatives

A large range of rotaxanes are based on the inclusion complexes of a pyridinium guest in a flexible host containing electron-rich Jt-systerns. In the case of the cucurbituril derivatives, the complex 76 can be capped to give the rotaxane 94 <2004OL2665>. 

Although cucurbit[5]uril (CB[5J) became available only recently, along with other CB homologues. its derivative decamethylcucurbit[5]uril (Me-CB[5]) " was known since 1992, and its chemistry was studied (see Cucurbituril Derivatives). Because CB[5] and Me-CB[5] have essentially identical cavity structures, their chemistry is also expected to be the same. 

The first cucurbituril derivative decamethylcucurbit[5]uril (Me-CB[5]) (Chart I) was synthesized from dimethylgly-coluril and formaldehyde in 1992. " The X-ray structural analysis shows a cavity of 4 A in diameter and two identical portals of 2.5 A in diameter. Bradshaw and coworkers studied complexation of Me-CB[5] with metal ions in 50% formic acid/water solution by calorimetric and potentiometric methods.Me-CB[5] binds most metal ions in a 1 1 stoichiometry in the acidic solution. Interestingly, Me-CB[5] shows exceptionally high affinity for Pb ion (log K > 9). which is mainly due to the size match between Pb and Me-CB[5] portals. The p a value (9.56) for protonation of Me-CB[5] indicates that Me-CB [5] behaves as a base in an aqueous solution. 

Bernal I, Mukhopadhyay U, Vivrovets AV, Fedin VP, Clegg W. A previously unrecognised hydronium di-cation in the crystal structure of a cucurbituril derivative. Chem Commun 2005 3791-2. 

Affinity of cucurbituril to cationic species is understandable because its cavity is formed from electron-rich carbonyl portals. This can be exemplified by a cationic species such as ferrocenylam-monium derivatives depicted in Scheme 2.45. 

The slow addition of diamines to refluxing solutions of glycoluril derivatives and formaldehyde in methanol yielded novel heterocycles (85)-(91) related to cucurbituril (Equation (20)) <85JOC60>. 

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). 

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

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