Template mediation

A small number of template mediated reactions which afford thioether macrocycles are also known, e.g. the small trithia [9]aneS3 is also obtained in good yield using Mo(CO)3 as a template.73,74 The crown trithioether is readily demetallated by addition of a further equivalent of [NMe4]2[S(CH2)2S(CH2)2S]. Also, dibenzo-[18]aneS6 and dibenzo-[15]aneS5 have been prepared via an iron dicarbonyl template.75,76 Metal-induced cyclo-oligomerization reactions of... 

Scheme 11. Hexa(dodecyloxy)hexaphenylbenzene 41 is used as a precursor in a template-mediated synthesis of PAHs.

Templating by oligopeptides is a more complicated proposition than the essentially linear solution available for nucleotide systems. Regular structures can be designed, but conformations typically depend on pH, and template aggregation is potentially more of a problem. Two groups have achieved success in the sort of template-mediated ligation reactions we have discussed for nucleotide systems, and their results illustrate the problems.160,611... 

Scheme 10.7 Template mediated synthesis of hexakisadducts of Qq involving an octahedral addition pattern using DMA as equilibrating addend.

Using the template mediation technique, mixed hexakisadducts with different types of addends are also easily available [26]. Here the precursor is not but a adduct with an incomplete octahedral addition pattern. The possible structures of mixed hexakisadducts with two different addends in octahedral positions are depicted in Figure 10.12. 

Scheme 10.11 Template-mediated fourfold cyclopropanation of e-bis-adduct4, leading to hexakisadduct 55. (i) DMA, second generation (G2) bromomalonate CHBr(COOG2)2, DBU, toluene-CH2Cl2, 3d, room temp.

Klein JU, Whitcombe MJ, MuUiolland F, Vulfson EN. Template-mediated synthesis of a polymeric receptor specific to amino acid sequences. Angew Chem Int Ed 1999 38 2057-2060. 

I would like to thank my students who have played a crucial part in the rapid progress that we have made on the role of template-mediated synthesis of hemozoin. I would also like to thank Professor D. Scott Bohle for providing a preprint of the most recent powder diffraction model of hemozoin and for reading sections of this manuscript prior to submission. Without his assistance and cooperation, this review would have been instantly out of date. I would also like to thank the Research Corporation, the Hunkele Charitable Trust of Pittsburgh, the National Foundation of Infectious Diseases, and Duquesne University for financial support of this work. 

Ryoo, R., Joo, S.H., and Jun, S. Synthesis of highly ordered carbon molecular sieves via template-mediated structural transformation. J. Phys. Chem. B 103, 1999 7743-7746. 

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

Metal ion template mediation in macrocyclic synthesis has been a part of the field since its inception, its importance having been realized early in the development of this area. Two specific roles for the metal ion in template reactions have been proposed. These are, in turn, kinetic and thermodynamic in origin." In the kinetic template effect, the arrangement of ligands already coordinated to the metal ion provides control in a subsequent condensation during which the macrocycle is formed. The thermodynamic effect serves to promote stabilization of a structure which would not be favored in the absence of a metal ion. Schiff base condensations tend to be dependent on this latter type of template effect. Some of the more routine and general synthetic procedures will be described here. A more in-depth treatment can be found in a review by Curtis, with particular emphasis on general methods as well as modifications of preformed macrocycles." ... 

Fig. 10.1. Preparation of molecularly imprinted proteins by template mediated freeze drying.

Fig. 10.5. Preparation of molecular receptors by template mediated cross-linking of polysaccharides.

Dhal PK, Arnold FH (1991) Template-mediated synthesis of metal-complexing polymers for molecular recognition. J Am Chem Soc 113 7417... 

Novel bis-/3-diketones of formula (2), where Y is CFI2OCH2CH2OCFI2 or CFI20-1,2-C6H4-OCH2, have recently been reported as convenient agents for the template-mediated self-assembly of... 

The 34 ( 8), 44 (19), and 47 (19) types are all now known to be structures with the chabazite framework topology (as determined by single-crystal methods) but prepared with different templates, TEAOH, cyclohexyl ami ne, or N,N-di ethyl-ethanol ami ne, respectively. As initially prepared, there was sufficient variation in the x-ray powder patterns of the as-synthesized forms for different framework topologies to be considered. Once calcined, the three species exhibit essentially identical powder patterns, consistent with the framework topology. Other properties vary substantially among the three species. There still remains the possibility of unique, template mediated, framework siting for the metal in these and other tempiated forms of the chabazite topology. 

R. Ryoo, S.H. Joo, and S. Jun, Synthesis of Highly Ordered Carbon Molecular Sieves via Template-mediated Structural Transformation. J. Phys. Chem. B, 1999, 103, 7743-7746. 

L.E. Iton, F. Trouw, T.O. Brun, J.E. Epperson, J.W. White, and S J. Henderson, Small-Angle Neutron-Scattering Studies of the Template-Mediated Crystallization of ZSM-5-Type Zeolite. Langmuir, 1992, 8. 1045-1048. 

S.I. Zones and R.A. Vannordstrand, Novel Zeolite Transformations - the Template-mediated Conversion of Cubic-P Zeolite to SSZ-13. Zeolites, 1988, 8, 166-174. 

SFB 624 in Bonn proposed a definition for template-assisted reactions [265] which states that a template steers a reaction through spatial pre-organization of the reactants via a suitably defined pattern of non-covalent, covalent, or coordinative-reversible bonds. It acts as an entropic sink such that thermochemical criteria can be used to characterize the template-mediated process. Template-mediated reactions may revolve several times but high turn over numbers are not necessarily required. Also, the template does not necessarily need to be recovered once the reaction took place. In this work, we elaborate on this non-formal description, which aims to embrace as many chemical processes involving templates and host-guest interactions as possible. Our aim is to arrive at a more formal basis utilizing well-established thermochemical concepts. The classical thermochemical approach of physical chemistry to chemical reactions may provide an option to define transferable concepts for the plethora of template-assisted processes. 

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