Reaction, intramolecular polymerization

The synthesis of five-, six-, and seven-membered cyclic esters or timides uses intramolecular condensations under the same reaction condifions as described for intermolecular reactions. Yields are generally excellent. An example from the colchicine synthesis of E.E. van Ta-melen (1961) is given below. The synthesis of macrocyclic lactones (macrolides) and lactams (n > 8), however, which are of considerable biochemical and pharmacological interest, poses additional problems because of competing intermolecular polymerization reactions (see p. 246ff.). Inconveniently high dilution, which would be necessary to circumvent this side-... 

The cyclization reactions discussed here either involve the intramolecular reaction of a donor group D with an acceptor group A or a cyclizing dimerization of two molecules with two terminal acceptors and two donors. A polymerization reaction will always compete with cyclization. For macrolides see p. 146 and p. 319 — 329. 

Polymeranalogous reactions considered above may be referred to as intramolecular condensation transformations since they are accompanied by elimination of low-molecular products. On the other hand, PCSs can be obtained via polymeranalogous transformations, principally intramolecular polymerization reactions . Thermal and chemical cyclization of poly(acrilonitrile) (PAN) is an example of processes of this type. It was demonstrated by a number of researchers216-225 that thermal transformations of PAN follow the scheme ... 

The core of reversed micelles can be transformed to a highly viscous domain (nanogel) by entrapping appropriate species, such as viscous solvents and hydrophilic macromolecules, or by performing in situ appropriate polymerization reactions or intramolecular cross-linking of water-soluble polymer chains [232-234]. 

The ruthenium catalyst system, 14, shown in Fig. 3, also carries out ADMET condensation chemistry, albeit with higher concentrations being required to achieve reasonable reaction rates [32]. The possibility of intramolecular compl-exation with this catalyst influences the polymerization reaction, but nonetheless, ruthenium catalysis has proved to be a valuable contributor to overall condensation metathesis chemistry. Equally significant, these catalysts are tolerant to the presence of alcohol functionality [33] and are relatively easy to synthesize. For these reasons, ruthenium catalysis continues to be important in both ADMET and ring closing metathesis chemistry. 

In an approach to a dihydrooritidine analogue, the intermolecular [2 + 2]-photo-cycloaddition of 2, 3 -0-isopropylideneuridine to chiral and achiral acrylates was found to be unsatisfactory both with respect to regio- and diastereoselectivity. The intramolecular approach was more successful, and uridine 143 produced selectively the single diastereomerically pure product 144. Due to concurrent photodimerization and polymerization reactions, however, the yield was only moderate (Scheme 6.50) [136]. 

Usually polymer has its own configuration in die complex formation. The fact that the polymer complex gives a unique polymer radical is shown (164-169). Nylon oligomer gives a polymer radical in carbon tetrachloride and it polymerizes vinyl compounds. This initiation reaction of the polymerization reaction was considered as an intramolecular cooperative reaction. The following scheme was presented... 

It is a well-established characteristic of polymerization reactions that a monomer changes to a polymer via an activated intermediate.3 Chemical activation of a monomer requires (1) a redistribution of electron densities in the bonds of the monomeric molecule (the intramolecular effect) and/or (2) a change of properties of existing (loose) intermolecular bonds between the reacting sites (intermolecular effect an alteration of mutual orientation may suffice). For practical purposes,... 

The principal advantage of the Mannich reaction is that it enables two different molecules to be bonded together in one step, as depicted in Eq. 1 (Fig. 3), whereas Eq. 2 stresses the alternatives connected with regioselectivity in polyfunctional substrates, which, on the other hand, also allow interesting cyclization or polymerization reactions to be performed. When the amino group is present in the substrate (Eq. 3), intramolecular Mannich reactions leading to cyclic products or to polymeric derivatives may occur. 

In the process of heating, polyorganosiloxane rubbers undergo a series of chemical transformations where, along with destruction and depolymerization reactions, intramolecular conversions, polymerization-type, exchange, and crosslinking reactions proceed. 

A novel intra-ion-pair electron(i) transfer cleavage of the —C-B— bond is reported by Chatterjee et al. [98] from the photoreaction of triphenyl alkyl borate salts of cyanine dye (110) to generate a carbon-centered radical (113) whose utility for initiating a free radical polymerization reaction has been demonstrated (Scheme 26). An intramolecular concerted bond cleavage/coupling process is described [99] from phenyl anthracene sulphoniiun salt derivatives as a part of designing a novel Photoacid system. 

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