Bifunctional components

Several synthetic routes to oxepanes involving the formation of two C—C bonds from bifunctional components (equation 42) have been reported <72HC(26)1>. Thus oxepanes (156 X = CH2Br, Y = CH(C02Et)2) and (157 X = CH(C02Et)2, Y = CH2Br) have been synthesized by a double nucleophilic displacement of bromide ion using appropriately substituted... 

In the literature there is also an example of an intramolecular Ugi reaction with dipeptides used as bifunctional components, via their amino and carboxy groups [78] (Scheme 1.29). The postulated mechanism for this reaction, leading to N-substituted 2,5-diketopiperazines, is a U-4C-3CR characterized by the formation of a nine-membered cyclic intermediate that evolves to diketopiperazines 86 via ring contraction. Despite the ring size, the configurations of the two Ca of the dipeptide have some influence on the newly generated stereocenter, and diastereomeric ratios up to 6 1 can be obtained. 

Substituted morpholin-2-one-5-carboxamide derivatives have been efficiently synthesized from commercially available glycolaldehyde dimer as the bifunctional component with various a-amino acids and isocyanides [80]. 

Polycondensation reactions involving two types of bifunctional components AA and BB (A and B are antagonist functions) are unimportant for our purpose. If the components are reacted stoichiometrically to high conversion, the polycondensate molecules carry A and B functions at their chain end in equal amounts which are... 

If one introduces a component into a polycondensation with a functionality of 3 or more the situation dramatically changes. Branches, branched branches, and crosslinks between polymer chains will cause a more rapid increase in molecular weight as the polymerization proceeds, and ultimately to higher final values than possible from linear polycondensations (see Section 20.2). The extent to which branches and crosslinks will occur will be proportional to the ratio of the polyfunctional to the bifunctional components present, and to the number of functionalities on the polyfunctional component. Usually 3, but up to 8, functionalities per monomer may be used for this component of polyfunctional polycondensations. 

Both the sol fraction and the cross-link density are thus highly sensitive to the value of r, the former increasing and the latter decreasing rapidly with the increase in the proportion of the bifunctional component. 

Some of the components shown in the examples above have two electrophilic centres and some have a nucleophilic and an electrophilic centre in other situations components with two nucleophilic centres are required. In general, components in which the two reacting centres are either 1,2- or 1,3-related are utilised most often in heterocyclic synthesis, but 1,4- (e.g. HX-C-C-YH) (X and Y are heteroatoms) and 1,5-related (e.g. 0=C-(C)3-C=0) bifunctional components, and reactants that provide one-carbon units (formate, or a synthon for carbonic acid - phosgene, Cl2C=0, or a safer equivalent) are also important. 

We now consider a more general case of stepwise reaction between Aj and By-, where i, j = 2,3, . Addition of bifunctional components increases the chain lengths between the branch points. Consider such a mixture of Aa,- moles of A and Afiy moles of By. Assuming that A groups react only with B groups, this... 

The determination of bifunctional compounds was reviewed by Poole and Zlatkis [267]. Only a few reagents capable of forming cyclic derivatives with bifunctional compounds have been described in the literature. Boronic acids are applicable to a wide range of bifunctional compounds. All of these reactions are highly selective, and some reagents have been developed that also have a high detection selectivity. These are of particular interest for the analysis of a few bifunctional components in a complex matrix without the need for a tedious sample clean-up [267]. 

Polyesterification and polyamidation (77) have also been effected with perchloroaromatic bifunctional components (Ballester, 1979). (Acylating components tetrachloroterephthaloyl dichloride, 4,4 -dichloroformyl-octachlorobiphenyl. Substrates tetrachlorohydroquinone, tetrachloresorci-... 

Generally, the bifunctional components ate used for creating the block-copolymers of (-AB-) type. The necessary oligomers could be obtained by means of either condensation reactions or usual polymerization. The end groups of monomer taken in excess ate responsible for the chemical nature of process in case of condensation. 

Cu(II) state mostly existed on the catalyst surface. However, after the reaction, the relative areal intensity ratio between Cu(l) and Cu(ll) states remaikably increases up to more than 1 1. Note that the Cu(ll) state after the chemical reaction might be formed by air oxidation during the sample preparation of the XPS measurement. Consequently, it is believed that the present cycloaddition reactions were proceeded by the Cu(l) species formed in situ during the reaction. The excess amount of phenylacetylene could behave as a reductant to convert Cu(l) from the activated Cu(ll) surface, via the formation of Cu(II)-acetylide. Apparently, such a well-defined hybrid system with bifunctional components provides a new way to design high-performance catalysts with high activity and reusability for gas- and solution-phase reactions. 

The employment of a protecting group is not necessarily required, and in this particular case the reaction of non-stoi-chiometric amounts of bifunctional components, Diol-1 and MDI, under suitable reaction conditions can even be advantageous ... 

In order to form block copolymers in blends of polycondensates, it is possible to use bisepoxides that react with the end groups of the blend components. A combination of peroxide and unsaturated bifunctional components (MA, triallylisocya-nurate, low-molecular-weight unsaturated rubber) was reported to induce copolymer formation in PS/PE and polyolefins blends [157-159]. 

The use of bifunctional components (i.e., AA -i- BB, or AB-type monomers) in a Passerini-3CR either leads to ring or polymer formation [31]. Directed synthesis is mainly determined by the concentration of the reaction mixture, as typical for step-growth processes. Ring formation is more likely to take place in high dilution, whereas polymer formation only occurs at high concentrations or in bulk. For... 

Scheme 4 Possible combinations of two bifunctional components (AA + BB) and one monofunctional component in a Passerini-3CR, resulting in different repeat units (a) alpha-amide substituted polyesters, (b) alternating poly(ester-amide)s and (c) polyamides with ester side chains...

Furthermore, a dialdehyde, a diisocyanide, and a carboxylic acid were applied in the Passerini one-pot polymerization (Scheme 4c). For this combination of reactants, Li et al. used adipaldehyde, 1,6-diisocyanohexane, and undecanoic acid, resulting in polyamides with functional side groups [35]. Optimization of the reaction conditions revealed that a IM chloroform solution of bifunctional components and a 2.2-fold excess of the carboxylic acid at 40°C gave the best results, yielding polymers with of up to 16.6 kDa in a yield of 90%. Here, m-alkene- or a)-alk5me-functionalized carboxylic acids were used as monomers in order to allow post-polymerization modifications via thiol-ene addition or copper-catalyzed azide-alkyne click chemistry (CuAAC). 

A similar strategy was followed when using the Ugi-5CC for the direct polymerization of two bifunctional components [72]. The application of 1,12-diaminododecane, 1,6-diisoyanohexane, isobutyraldehyde, methanol, and carbon dioxide resulted in the respective polyamide bearing methyl carbamate side chains. 

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