CARBODIIMIDE, POLYMERIC DERIV

In the above-mentioned patents post-polymerization modification is performed in a single step. An alternative is the performance of two sequential modification steps. In the first step the polymer is reacted with tin or germanium derivatives (triphenyl tin, tributyl tin, diphenyl tin dichloride, dioctyl tin dichloride, phenyl tin trichlorde etc.). In the subsequent modification step heterocumulene compounds (ketenes, thioketenes, isocyanates, thioiso-cyanates and carbodiimides) are applied [437,438]. Specific interaction with silica is obtained by end group functionalization with vinyl monomers which contain hydroxyl or epoxy groups. The effects are observed if the PDI is below 5 [439,440]. 

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. ... 

Transition metal carbodiimides, such as MnNCN and CuNCN, and carbodiimides derived from zinc, mercury,silver and thallium are also known. A preceramic polymeric titanium carbodiimide is obtained in the reaction of TiCU with bis(trimethyl-silyl)carbodiimide. Liganded carbodiimidotitanium complexes are obtained in the reaction of CpaTiCla with Me3SnN=C=NSi(i-Pr)3. ° Also, dicyclopentadienyl titanium (IV) diisocyanates are converted into carbodiimides with LiN(SrMe3)2. ... 

Linear carbodiimides with pendant carbodiimide groups are obtained by reacting polymeric azides derived from vinyl azide 33 with triphenylphosphine to form poly(phosphine imines) 34, which are subsequently converted to polycarbodiimides 35." ... 

Cellular poly(carbodiimides) derived from polymeric isocyanate (PMDI) can be continuously produced using a phospholene oxide catalyst. As the component temperature is increased from 25 °C to 80 °C at a constant catalyst level, foam densities decrease with increasing component temperatures, with an expected corresponding decrease in compressive strength. The foam friability also decreases with increasing component temperature. 

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.

The interaction of germyl carbodiimides with weak protic acids, for example, CH3OH and HjE (E = O, Se), provides useful synthetic routes to the production of a variety of germyl derivatives, namely, GeHaOCHa and (GeHa)2E. The advantage of this type of reaction is that the only other product is a nonvolatile white solid that has been described as a polymerized cyanamide of the form (H2NCN) . >3... 

The titanium catalysts have been widely used in the catalysis of polymerization of olefins [335], the details of their applications will not be discussed here. Chiral titanium complexes have also been employed as the catalysts for asymmetric polymerization of a variety of carbodiimides by Novak [336]. As shown in Scheme 14.149, the polymerization of achiral carbodiimides in the presence of a chiral titanium complex derived from 3,3 -Br2BINOL and Ti(O Bu)4, gave the well-defined regio- and stereoregular helical polyguanidines with a relatively... 

Peptide synthesis requires the use of selective protecting groups. An N-protected amino acid with a free carboxyl group is coupled to an 0-pro-tected amino acid with a free amino group in the presence of dicyclohexyl-carbodiimide (DCC). Amide formation occurs, the protecting groups are removed, and the sequence is repeated. Amines are often protected as their ferf-butyloxycarbonyl (Boc) derivatives, and acids are protected as esters. This synthetic sequence is often carried out by the Merrifield solid-phase method, in which the peptide is esterified to an insoluble polymeric support. 

Another potential problem with DCC is that at the completion of the reaction some DCU remains in solution with the product, necessitating additional purification. Water-soluble carbodiimide derivatives such as l-Cyclohexyl-3-(2-morpholinoethyl)carbodiimide Metho-p-toluenesulffonate and l-Ethyl-3-(3 -dimethylaminopropyl)carbodiimide Hydrochloride (EDCI) obviate this problem, as they are removed by a simple extraction. Many newer coupling agents have been developed for peptide synthesis and other acylation reactions. These include Benzotriazol-l-yloxytris(dimethylamino)phosphonium Hexafluorophosphate (BOP)," 0-Benzotriazol-l-yl-N,N,N, N -tetramethyluronium Hexafluorophosphate (HBTU)," Bis(2-oxo-3-oxazolidinyl)phosphinic Chloride (BOP-Cl), and (1 //-1,2,3-benzotriazol-1 -yloxy)tris(pyrTolidino)phosphonium hexafluorophosphate (PyBOP). In addition to linear and polymeric amides, lactams of various ring sizes have been synthesized using these methods (eq 1)."... 

---