Hydrogen bonding template synthesis

Scheme 10 Leigh has reported the hydrogen-bonding templated synthesis of catenane 15...

Scheme 14 [3]Rotaxane 23 can be prepared by hydrogen-bonding templated synthesis employing the threading-followed-by-capping methodology...

Scheme 16 Synthesis of [3]rotaxane 27 by hydrogen-bonding templated synthesis... 

The functionalisation also allows extending the complexity of intertwined molecular assemblies involving molecular catenanes, rotaxanes and knots. Elaborate interlocked assemblies constructed by means of metal-templation techniques and ji-ji-stacking preorganisation were reviewed [3, 11], Our last survey was devoted to the hydrogen bond templated synthesis of amide-based catenanes and rotaxanes [32], Since then a considerable advancement in elucidation of mechanisms of templation and derivatisation of the amide-based interlocked structures has been reached. Moreover, in 2000 we reported a one pot synthesis of amide-based knots such as 8 [21], which is so far the easiest preparation of molecular knots. In the following, specific possibilities of functionalisation of amide-based catenanes, rotaxanes and knots will be discussed. 

In the following sections, examples of hydrogen-bonding templates for the synthesis of macrocycles, cages, interlocked species, helicates and for the photochemical reaction of olefins will be discussed. The use of hydrogen-bonding templates in dynamic combinatorial libraries will also be presented. 

Figure 28. The hydrogen-bonding template-directed synthesis of the [2]catenane 87.

Figure 4. Hydrogen bond templated threading of a tetraamide ring in synthesis of amide-based catenanes and...

Apart from the successful imprinting discussed above, the recognition for many templates is far from that is required for the particular application, even after careful optimization of the other factors affecting the molecular recognition properties. Often, a large excess of MAA in the synthesis step is required for recognition to be observed and then only in solvents of low to medium polarity and hydrogen bond... 

Crego-Calama M, Reinhoudt DN, ten Cate MGJ (2005) Templation in Noncovalent Synthesis of Hydrogen-Bonded Rosettes. 249 in press Crepy KVL, Imamoto T (2003) New P-Chirogenic Phosphine Ligands and Their Use in Catalytic Asymmetric Reactions. 229 1-40 Cristau H-J, see Taillefer M (2003) 229 41-73... 

Schalley CA, WeUandt T, Briiggemann J,V6gtle F (2004) Hydrogen-Bond-Mediated Template Synthesis of Rotaxanes, Catenanes, and Knotanes. 248 141-200 Scheer M,see Balazs G (2003) 232 1-23... 

Condensation of the carbonyl function with an amine from a second 1,2-diaminoethane molecule coupled with a repeat of the initial reaction sequence will lead to the cyclic product. It is of interest that this is one case in which the synthesis will also proceed in the absence of a metal ion. Starting from a mono-protonated salt of 1,2-diaminoethane in acetone, the metal-free condensation may proceed via a reaction such as [2.7], Once again, a hydrogen-bonding network may act as a template for the reaction and also serve to stabilize the product once it is formed. A revised synthesis of the metal-free ligand (61) has been published (Hay,... 

Since Pedersen s original work on the use of cations to template the formation of crown ethers [18-20], a large number of different templating agents for macro-cyclization reactions have been reported. While the initial work concentrated on the use of metal cations, further developments demonstrated that species with hydrogen bonding donor or acceptor properties could be equally useful to template the synthesis of macrocyclic molecules. 

With this separation of the hydrogen bond-acceptor template and the sites for the stopper attachment, the steric effects due to shielding by the wheel are avoided making the synthesis of the rotaxane 48 more efficient (in some of the systems the yields of rotaxane formation increase from 5 to 30% when the functionalised centre-piece is added). 

This elegant synthesis has demonstrated the possibility of using a hydrogen bond-acceptor template to prepare template-free interlocked species (in a similar fashion to Sauvage s catenanes syntheses which make use of transition metals as templates). 

Hydrogen Bonding vs ti-tc Stacking in Templated Synthesis of Interlocked Species... 

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