Carbodiimides polymeric

Macromolecules with carbodiimide linkages in their repeat units are obtained from aliphatic and aromatic diisocyanates using a phospholene oxide catalyst. However, instead of linear polymers, only crossUnked thermosets are obtained in this manner. In contrast, linear polymers with pendant carbodiimide units are obtained from poly(vinyl azide) by subsequent reaction with triphenylphosphine to formpoly(phosphine imines) followed by reaction with monoisocyanates to generate the Unear poly(carbodiimides). 

The homopolymerization of carbodiimides affords polyguanidines, which are nylon-1 imides. Because of their thermal instability, the homopolymers have found no utiUty as industrial polymers. Polyguanidines are also obtained in the reaction of hexamethylene-bis(t-butylcarbodiimide) with diamines. The polyaddition reactions of bis-carbodiimides with dialcohols and dithiols also produce the corresponding addition polymers. In the reaction of hexamethylene-bis(t-butylcarbodiimide) the polyaddition reactions proceed across the less sterically hindered C=N bond. Masked bis-carbodiimides, which are thermally unblocked, are also used in crosslinking reactions. 

Polymeric substrates with carbodiimide end groups are often used in solid phase amidation reactions in peptide synthesis. 

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POLYMERIC CARBODIIMIDE. II. MOFFAT OXIDATION 4-tert-BUTYLCYCLOHEXANONE... 

Also, oligomeric and polymeric carbodiimides are used extensively in solid state chemistry as shown in Chapter 12. 

Polymeric carbodiimides are also used in peptide synthesis. For example, a polymeric carbodiimide with a N-cyclohexyl-N -phenyl endgroup is used in the synthesis of a metalloproteinase inhibitor. ... 

In the reaction of acylhydrazines with isothiocyanates, N-substituted thiourea derivatives 14 are formed, which react with a polystyrene based polymeric carbodiimide (PCD) to generate the nitrogen substituted carbodiimide 15, which cyclizes to form 2-amino-1,3,4-oxazoles 16. ... 

The remaining chapters are carbodiimides with unsaturated substituents, halogenated carbodiimides, acyl-, thioacyl- and imidoylcarbodiimides, silicon substituted carbodiimides, nitrogen substituted carbodiimides, phosphorous substituted carbodiimides, sulfur substituted carbodiimides, metal substituted carbodiimides, cyclic carbodiimides, polymeric carbodiimides and application of carbodiimides. 

Two syntheses of racemic betalamic acid have been carried out so far. In Dreiding s approach (Scheme 1) (11,90,91), chelidamic acid (62) was used as the starting material. Hydrogenation of 62 with a rhodium catalyst yielded an all-cw piperidine derivative, which was converted to the dimethyl ester 63. The conditions used for the hydrogenation step kept the concomitant removal of the hydroxyl group to a minimum. The oxidation of alcohol 63 to the corresponding piperidone derivative 64 required careful control of the reaction conditions to avoid overoxidation to pyridine derivatives. This was accomplished by use of a polymeric carbodiimide in the Pfitzer-Moffat oxidation, which afforded the desired product 64 in 90% yield. For the introduction of the side chain, a new... 

Scheme 1. Synthesis of betalamic acid derivative 66. i, H2, Rh-AlzOs MeOH-HCl ii, DMSO-polymeric carbodiimide-Py-CF3C02H iii, (EtO)20PCH2CH=NN(Me)CONMc2-NaH iv, t-BuOCl.

Weinshenker, N. M., Shen, C. M. Polymeric reagents. I. Synthesis of an insoluble polymeric carbodiimide. Tetrahedron Lett. 1972, 3281-3284. 

The resin-supported carbodiimide 2 (R = Cy), related to the popular solution phase reagent dicyclohexylcarbodiimide (DCC), has been the most successfully employed polymeric carbodiimide of this series, especially in the presence of additives to accelerate the coupling reaction and avoid the acylisourea-unreactive acylurea rearrangement [2]. This carbodiimide has been used for esterification reactions, as exemplified in the reaction of dithiane-containing alcohol 3 with Fmoc-protected valine in the presence of a catalytic amount of N,N-dimethylami-nopyridine (DMAP) to give ester 4 [10] (Scheme 7.1). This polymer-supported reagent 2 (R = Cy) has also been used without any additive in the amidation reaction of 3,4-diaminocyclopentanol scaffolds with 2-(methylsulfanyl)acehc acid [11]. 

Scheme 7.2 Macrolactonization reaction using polymeric carbodiimide 5.

Scheme 7.5 Amidation reactions using the polymeric carbodiimide PS-EDC (11).

It also has been shown that azelate esters can also be used in place of adipate polyesters in thermoplastic polyurethanes, which also indicated improved hydrolytic stability as well as somewhat improved low-temperature properties as compared to those of the corresponding adipate polyester based urethanes (90). The tendency of polyester-based urethanes to hydrolyze, particularly at high humidities and elevated temperatures, can partly be reduced by incorporation of small amounts of polymeric carbodiimides (91). Alternately, the use of diisocyanate-containing carbodiimide groups helps to confer greater hydrolytic stability to polyester urethanes (92). 

Polymeric carbodiimide reagent for peptide synthesis. Japanese chemists have prepared a carbodiimide reagent attached to a styrene-divinylbenzene polymer as formulated and have used it successfully for synthesis of dipeptides. 

Various ureas upon treatment with tosyl or benzenesulfonyl chloride in the presence of a phase transfer catalyst, benzyltri-ethylammonium chloride, results in moderate to excellent yields of carbodiimides (eq 40). The polymeric carbodiimide in eq 41 offers the advantages of cleaner workup and recyclability if used to prepare aldehydes under Moffatt oxidation conditions. ... 

At the Hebrew University of Jerusalem, M. Frankel, Y. Wolman, Y.S. Klausner, C. Gilon and M. Chorev were engaged in the development of synthetic methods, such as the design and preparation of polymeric carbodiimides and water-soluble active esters. 

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