With cyclic carbodiimides

Methyloxalyl chloride reacts with cyclic carbodiimides (n = 6) to form the spirobi(oxazoli-dine) derivative 59. ... 

Behringer and Meier found that treatment of thiourea 105 with yellow mercury(Il) oxide gave traces of N, AT-pentamethylenecarbodiimide (107), the smallest known cyclic carbodiimide. Compound 107 was reported as unstable and able to polymerize readily (larger ring homologs were, ex-... 

Cyclic carbodiimide 48 theoretically exists as two conformational isomers. Comparison of the coupling constant values, calculated using AMI Hamiltonian and Karplus relationship, with the experimental vicinal coupling constants of 8.33 and 1.05 Hz, undoubtedly prove its methyl-out structure 48 <1996JOC4289>. 

Bis(iminophosphorane) 225 was reacted with carbon dioxide in dry benzene at 70°C in a sealed tube to afford the nine-membered cyclic carbodiimide 48 in 98% yield (Equation 24) < 1996JOC4289>. 

Cyclic carbodiimides react with HFA to form six- and four-membered rings 123 and 124, which have been investigated spectroscopically. Isolation was successful only in the case of the 10-membered ring 123b the other two compounds are in equilibrium with their precursors (225). 

Carbodiimides have chiral structures similar to allenes, i.e., they can exist in optically active forms. Schloegl and Mechtler were the first to report a partial optical separation of N,N"-diferrocenylcarbodiimide into enantiomers by chromatography on acetylated cellulose, but other authors doubt the validity of these results. According to theoretical calculations a separation of carbodiimide enantiomers is not possible. N,N -diferrocenylcarbodiimide was also obtained in optically active form by kinetic resolution in the reaction with (-)-S-6,6"-dinitrodiphenic acid. Cervinka and coworkers isolated both enantiomers of (R,S)-N,N"-bis(o -phenylethyl)carbodiimide, and they found that they undergo racemization at room temperature. A recent study on the racemization mechanism of macrocyclic carbodiimides indicates that the open chain as well as the large ring carbodiimides racemize by nitrogen inversion or tra 5-rotation, while medium size cyclic carbodiimides racemize by cw-rotation. ... 

The cyclic thiourea 19, upon reaction with HgO affords the cyclic carbodiimide 20, but the compound has not been isolated in pure form. ... 

The reaction of bisaryliminophosphoranes with di-t-butylcarbonate(Boc)20 in the presence of 4-dimethylaminopyridine, or carbon dioxide results in the formation of an intermediate isocyanate, which reacts with the second -N=PPh3 group to form a cyclic carbodiimide or a cyclic dicarbodiimide. Reaction of the bisaryliminophosphorane with carbon disulfide generates a bis-isothiocyanate which undergoes reaction with the bisaryliminophosphorane to give the corresponding cyclic dicarbodiimide in high yield. Examples of these reactions are listed in Tables 11.1 and 11.2. 

Cyclic carbodiimides also undergo a facile [2+2] cycloaddition reaction with alkyl- and aryl isocyanates to give the cycloadducts 44. With aryl isocyanates the reaction is exothermic and is completed within several minutes. 

The reaction of cyclic carbodiimides 47 (n = 4,5), generated in situ, with carbon disulfide, results in the formation of the diisothiocyanates 48 in 23-28 % yield. ... 

Cyclic carbodiimides 49 (n = 5,6,11) react with phenyl-, phenethyl- and diphenylketene to give the [2-1-2] cycloadducts 50 in yields of > 90... 

Cyclic carbodiimides also undergo a rapid reaction with phosgene in methylenechloride to form the expected adducts 55, which on hydrolysis give cyclic allophanoyl chlorides 56.22... 

The reaction of cyclic carbodiimides with oxalyl chloride affords bicyclic para-banic acid derivatives 57 (when n = 11) or spiro(oxazolisine) derivatives 58 (when... 

I became involved in carbodiimide chemistry in my research work on isocyanates at the former Donald S. Gilmore Research Laboratories of the Upjohn Company in North Haven, CT. Carbodiimides are readily synthesized from isocyanates using a phospholene oxide catalyst. This reaction can be conducted without a solvent, and the byproduct is carbon dioxide. We used this reaction in the manufacture of a liquid version of MDI (4,4 -diisocyanatodiphenylmethane), which today is sold in huge quantities worldwide. By reacting MDI with dicarboxylic acids in a vented extruder we manufactured a family of thermoplastic polyamide elastomers, which are sold today by the Dow Chemical Company. Also, N-sulfonylcarbodiimides were synthesized for the first time in our laboratories. They are the precursors of the antidiabetic sulfonamides, such as Upjohn s Tolbutamide (Orinase). Because of the close relationship of isocyanates with carbodiimides we studied many linear and cyclic carbodiimide reactions, especially their cycloaddition reactions. 

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. 

The synthesis of larger rings has also been accomplished including the fully unsaturated azolo-fused 1,3-diazepines (222) from bis(iminophosphoranes) (221) and novel cyclic carbodiimides (e.g. 223). Iminophosphoranes are also intermediates in the synthesis of macrolactams (e.g. 225) from the reaction of co-azido acid anhydrides (e.g. 224) with tributylphosphine. The synthesis of iminophosphorane-containing cryptands and a spherand-type structure have been reported. 

Additives can also be used to improve the hydrolytic stability of polyester polyurethanes. Glycol-cured materials are reported to be stabilized with cyclic imines. Substituted ureas or thioureas ethylene-diaminetetraacetic acid-derived chelating agents oxycarbonyl isocyanates epoxies carbodiimides, alone " or in combination with silica silanes " substituted phthalimides and an undisclosed combination of additives have all been cited as stabilizers for polyester polyurethanes. 

Cyclic carbodiimides 38 react with carbon disulfide to give aliphatic diisothiocyanates 39. This reaction involves an initial [2-1-2] cycloaddition across one of the C=N groups of the carbodiimide . 

Mixed dimers derived from macrocyclic carbodiimides and diphenylcarbodiimide are also reported. For example, the unstable 1,3-diazahepta-l,2-diene 15 (n = 4) was trapped with diphenylcarbodiimide to give the [2-1-2] cycloadduct 16 (n = 4). The larger ring cyclic carbodiimides also afford the [2-1-2] cycloadducts 16. These reactions proceed in quantitative yield... 

A full development of the rate law for the bimolecular reaction of MDI to yield carbodiimide and CO indicates that the reaction should truly be 2nd-order in MDI. This would be observed experimentally under conditions in which MDI is at limiting concentrations. This is not the case for these experimements MDI is present in considerable excess (usually 5.5-6 g of MDI (4.7-5.1 ml) are used in an 8.8 ml vessel). So at least at the early stages of reaction, the carbon dioxide evolution would be expected to display pseudo-zero order kinetics. As the amount of MDI is depleted, then 2nd-order kinetics should be observed. In fact, the asymptotic portion of the 225 C Isotherm can be fitted to a 2nd-order rate law. This kinetic analysis is consistent with a more detailed mechanism for the decomposition, in which 2 molecules of MDI form a cyclic intermediate through a thermally allowed [2+2] cycloaddition, which is formed at steady state concentrations and may then decompose to carbodiimide and carbon dioxide. Isocyanates and other related compounds have been reported to participate in [2 + 2] and [4 + 2] cycloaddition reactions (8.91. 

Amidines and cyclic amidines are also converted into 1,2,4-thiadiazoles by reaction with isothiocyanates, imino-sulfenyl chlorides, di- and trichloromethyl sulfenyl chlorides, and carbon disulfide in the presence of sulfur. Ureas, thioureas, guanidines, carbodiimides, and cyanimides react with chlorocarbonylsulfenyl chloride to produce 1,2,4-thiadiazol-5-one derivatives in another example of a type B synthesis <1996CHEC-II(4)307>. 

---