Acylating agents, polymeric

Polymerization of /3-lactams, involving cleavage of the amide bond, can be induced by treatment with strongly basic catalysts or by acylating agents (75S547 p. 581). 

Various classes of cationic initiators have been used to polymerize lactones protic acids, Lewis acids, acylating agents, and alkylating agents. These initiators are often difficult to handle experimentally... 

In lipase-catalyzed transesterifications, frequent use of enol esters as acyl agents has been seen [1, 5], since the leaving unsaturated alcohol irreversibly tautomerizes to an aldehyde or a ketone, leading to the desired product in high yields. The polymerization of divinyl adipate and 1,4-butanediol proceeded in the presence of lipase PF at 45 °C [39]. Under similar reaction conditions, adipic acid and diethyl adipate did not afford the polymeric materials, indicating the high polymerizability of bis(enol ester) toward lipase catalyst. 

Species XL and XLI correspond to species XXXV and XXXVI for polymerization in the absence of an acylating agent. The acylating agent achieves facile polymerization of many... 

What are the roles of an acylating agent and activated monomer in the anionic polymerization of lactams ... 

Resin-bound 1-hydroxybenzotriazole (HOBt) has also been prepared [312-314], and yields, upon O-acylation, highly reactive esters [312,315,316], These are even cleaved by weak nucleophiles, such as anilines or even N-hydroxysuccinimide (Entry 7, Table 3.14). The reactivity of resin-bound HOBt esters is greater than that of resin-bound 4-acyl-2-nitrophenyl esters [296], Similarly, resin-bound /V-hydroxysuccinimide has also been used for the preparation of polymeric acylating agents (Entry 6, Table 3.14 [317-319]). 

Covalent compounds, which are strong alkylating or acylating agents may initiate the cationic polymerization of heterocycles. Again, as in the case of acids, classification of these agents is relative for example, alkyl bromide will efficiently alkylate strongly nucleophilic monomers like cyclic amines or oxazolines and thus initiate their polymerization whereas it will be uneffective in the polymerization of cyclic ethers. 

The polymeric phenols 3 proved to be recyclable. A sample was reactivated for three reaction cycles using benzoyl chloride 2 as acylating agent. Coupling with benzylamine was used to determine the loading, which was found to be virtually identical for all three cycles [13]. 

Polymerizations in the presence of an acylating agent are often referred to as assisted (or activated) polymerizations. The rate of lactam polymerization depends on the concentrations of the activated monomer and propagating chains, which, for an assisted lactam polymerization, are determined by the concentrations of base and iV-acyllactam (or acylatig agent), respectively. The degree of... 

C (R = OH, Ri = H) by hydriodic acid. Benzylation of this product and conversion to the acid chloride provided an acylating agent for CII, which was prepared from 0-benzyl isovanillin (Cl). The amide (CIII R, R2 = CH2C6H5, Ri = 0) was reduced by lithium aluminum hydride and palladium-on-charcoal to the desired phenol (CIII R, Ri, R2 = H), the structure of which was verified by conversion to belladine (CIII R, R2 = CH3 Ri = H) by diazomethane. Manganese dioxide, lead dioxide, silver oxide, and potassium ferricyanide were effective in the oxidation of cm (R,Ri,R2 = H)to( + )-narwedine. A maximum yield of 1.4% was obtained. Polymerization products predominated in all cases 103). 

Cationic polymerization takes place in the presence of any of the following catalyst (a) protic acid such as HBr, HCl, triflicacid, etc., (b) lewis acid such as ZnClj, AICI3, etc., and (c) alkilating or acylating agents such as EtjO BF, etc., as shown in Figure 7.4 [12]. 

The use of transfer polymeric reagents (PRs) as excellent acylating agents for high yield and high purity peptide synthesis is described. 

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