General Preparation Strategies

Similar pentaerythritol cryptands have been prepared by a slight modification of the above approach. Although the general strategy is as illustrated in Eq. (8.11), atfetal formation is accomplished by reaction of pentaerythritol with paraformaldehyde. This reaction leads to diacetal 12 which is hydrolyzed in dilute H2SO4 to yield the monoacetal, 13. The latter is then used in a fashion similar to that described in Eq. 8.10, above. 

To perform Diels-Alder reactions on solid phase, the 2(lH)-pyrazinone scaffold is linked to a suitable support via its amide nitrogen atom. While N-l-substituted pyrazinones are readily accessible by the choice of an appropriate amine, it is not possible to prepare N-l-unsubstituted pyrazinones using the general strategy as previously outlined in the introduction. How-... 

Axial addition to oxocarbenium ions derived from 1,3-dioxanes provides protected a f/-l,3-diols. Our group has developed 4-acetoxy-1,3-dioxanes as oxocarbenium ion precursors. This general strategy for the convergent preparation of anfz-l,3-diols complements cyanohydrin acetonide methodology, which gives access to sy -l,3-diol synthons (Sect. 2). 

A general strategy developed for the synthesis of supramolecular block copolymers involves the preparation of macromolecular chains end-capped with a 2,2 6/,2//-terpyridine ligand which can be selectively complexed with RUCI3. Under these conditions only the mono-complex between the ter-pyridine group and Ru(III) is formed. Subsequent reaction with another 2,2 6/,2"-terpyridine terminated polymer under reductive conditions for the transformation of Ru(III) to Ru(II) leads to the formation of supramolecular block copolymers. Using this methodology the copolymer with PEO and PS blocks was prepared (Scheme 42) [ 107]. 

A variety of functionalized [3]radialenes have been prepared starting from the appropriately substituted cyclopropanes or cyclopropenes. West and Zecher have pioneered the chemistry of [3]radialenes with quinoid substituents. The general strategy of this synthesis is outlined in Scheme 513. A tris(4-hydroxyphenyl)cyclopropenylium... 

With the synthesis of epothilones A and B secured, subsequent studies concentrated on the preparation of analogs of the natural molecules. In addition to providing structure-activity relationships, it was anticipated that these studies would provide a further test for the generality of the RCM process. In this context, a general strategy was developed by Nicolaou et al. [20] to investigate the... 

The requirements for glycoside syntheses, high chemical and stereochemical yield, and applicability to large-scale preparations were not effectively met by any of the methods just described. However, it seems that the general strategy for glycoside synthesis is reasonable ... 

The general strategy for the synthesis of (-)-swainsonine [5] is to prepare an acyclic key intermediate with the required stereochemistry and proceed then to a double intramolecular cyclisation. 

Fig.l. General strategy of the Chemically Induced Phase Separation (CIPS) technique to prepare macroporous thermosets having a closed cell morphology... 

Finally, an entirely different approach to milnacipran (2) was recently reported in the literature (Scheme 14.6). In this case, the general strategy is based on position-selective deprotonation of cyclopropane carboxamides. Thus, cyclopropane amide 27, which was easily prepared from commercially available cyclopropane carboxylic acid, underwent... 

The reduction can be stopped at the benzylamino alcohol stage using an appropriate reducing agent. For example, in their general strategy to prepare pseudodistomins, Naito and co-workers reduced the bicyclic oxazohne 390 to the... 

Few solid-phase syntheses of oxazoles have been reported (Table 15.17). The most general strategy is the dehydration of a-(acylamino) ketones (Entry 2, Table 15.17) or 2-(acylamino)phenols (Entry 1, Table 15.17). Oxazolidin-2-ones have been prepared by intramolecular nucleophilic cleavage of carbamates from insoluble supports (Entries 5 and 6, Table 15.17). Resin-bound 2-aminoethanols, which are accessible by nucleophilic ring-opening of oxiranes with amines, undergo cyclocondensation with aldehydes to yield oxazolidines [220,221]. These compounds are unstable towards acids, and can be released from the support only under neutral or basic reaction conditions. 

In the following paragraphs the general strategies used in organometallic transformations of imidazoles to prepared histaminergic ligands will be reviewed. 

The preparation of fused nitrogen heterocycles such as pyrrolizidines, indolizidines, quinolizidines, pyrrolidinoazocines and piperidinoazocines by the RCM of appropriate dienes (equation 38), is another case where presence of a ring assists the RCM reaction. However, when n = 7 (with x = 1), the C=C bonds, separated by 11 single bonds, are too far apart for RCM to occur. Applications of this general strategy are in prospect for the formation of fused nitrogen heterocyclic systems in problems of alkaloid synthesis240. 

Surface science has been one of the first beneficiaries of self-assembled nanostructures (in the form of SAMs). Self-assembly is a very general strategy for forming molecularly tailored interfaces, and, other than the few systems that have formed the basis for the majority of work in SAMs, almost none of the obvious opportunities to use self-assembly to build ordered, nanostructured interfaces have been examined. The preparation of more sophisticated structures based on molecules with complex stmctures, on self-assembled colloids, on multilayered polymers formed by electrostatic interactions between charged groups166,167, or on biologically derived structures is just beginning168-171. 

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