Endo-templates

The mold represents an endo-template, i.e., it is filled with molten metal (usually bronze) which solidifies upon cooling. After removal of the mold the final bell is obtained. 

Bell-manufacturing is a consecutive templating procedure where the casts are again used as templates in a subsequent templating step. It makes use of exo- and endo-templates. The concepts of exo- and endo-templates were first discussed in [1]. Endo-templates are filled,whereas exo-templates are covered to produce the desired form (see Table 1). In the case of bicontinuous templates this distinction is not possible. Between consecutive templating steps there is usually a soHdifi-... 

Fig. 11. Endo-templating scheme for the preparation of nanoparticles within block copolymer...

The preparation methods for mesoporous support materials can be classified by the nature of the (endo-) template, which can either be ionic (e.g. alkyl trimethylammonium halides leading to MCM materials i or neutral (e.g. hydrophilic block copolymers leading to SB A materials ). Avoiding these conventional templates, Wei reported the preparation of mesoporous silica using glucose and Polarz succeeded in using cyclodextrins . 

The interior cavity of coordination cages has also been exploited as endo-template for the synthesis of highly monodispersed nanoparticles. 

Yamauchi Y, Fujita M (2010) Self-assembled cage as an endo-template for cyclophane synthesis. Chem Commun 46 5897-5899... 

If the template effect of Endo and Kroto[9] does indeed exist and the growth of the tubule occurs outwards, a knowledge of the characteristics of the innermost tube is then of paramount importance in any attempt at modelizing the structure of a symmetric nanotube[ll]. By reversing eqn (17), possible values for Px and Qx can be obtained from... 

A new form of template polymerization based on ring-opening polymerization of 4-methylcncdioxalane has been reported by Endo and coworkers (Scheme 8.15).220,221 For this system, the monomer is covalently bound and the daughter polymer is released from the template as a consequence of the polymerization process. 

The polymerization of several different protected monomers was executed with the molybdenum initiator. Two types of norbornene templates were generated as mixtures of diastereomers one class possessed a single saccharide substituent attached through either an endo or exo ester group, and the other was equipped with two carbohydrate residues appended to the bicyclic scaffold... 

In order to test this proposal, several theozymes were constructed.1101 Antibody 26D9 was originally elicited in response to a piperidine-N-oxide hapten (4, Figure 2), in which the polarized N-0 bond was meant to mimic the breaking C-0 bond of the epoxide in the cyclization transition state, and the 6-membered piperidine ring was used to represent the size and shape of the 6-endo transition state Hapten 4 was used as a template to create several... 

In the case of the template 204, the endo/exo selectivity was only 1.8 1, but the material yield was high with a facial selectivity of 10 1. The ylides were also trapped with methyl acrylate, generating the expected cycloadducts with reasonable regio and diastereocontrol. Although the endo/exo selectivity was relatively poor, the facial selectivity and material yield were both reasonable and the removal of the template is nondestructive. 

The use of a doubly stabilized ylide derived from condensation of the template with ethyl glyoxylate trimer followed by condensation with suitable dipolarophiles, led to the expected mixture of exo and endo products under thermal conditions (60). While material yields could be improved by the addition of Lewis acid, the exo/ endo ratios were reduced due an increase in the formation of exo products. Subsequent destructive removal of the template furnished a range of amino acids, exemphfied in Scheme 3.66. 

Regiocontrol was also high with unsymmetrical dipolarophiles, as was the endo/exo selectivity. Simple destructive template removal followed by Boc protection gave a range of enantiomerically pure polycychc proline derivatives, as exemplified in... 

Harwood and co-workers (105) utihzed a phenyloxazine-3-one as a chiral derived template for cycloaddition (Scheme 4.50). An oxazinone template can be formed from phenylglycinol as the template precursor. The diazoamide needed for cycloaddition was generated by addition of diazomalonyl chloride, trimethyl-dioxane-4-one, or succinimidyl diazoacetate, providing the ester, acetyl, or hydrogen R group of the diazoamide 198. After addition of rhodium acetate, A-methylmaleimide was used as the dipolarophile to provide a product that predominantly adds from the less hindered a-face of the template in an endo fashion. The cycloaddition also provided some of the adduct that approaches from the p-face as well. p-Face addition also occurred with complete exo-selectivity. Mono- and disubstituted acetylenic compounds were added as well, providing similar cycloadducts. 

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