Macrocyclic carbodiimides

Title Macrocyclic Carbodiimides (MC-CDI) and Their Derivatives, Syntheses, and Applications of the Same... 

Observations Polypropylene oxide macrocyclic carbodiimides were prepared by... 

The step 1 product was diluted with 1500 ml toluene to a final concentration of 0.013 mol/L. The mixture was then treated with 1,3-dimethyl-3-phospholene oxide and heated to 90°C while the cyclization reaction was monitored by Fouier transform infrared (FTIR). When the characteristic—NCO peak was eliminated in the macrocyclic carbodiimide (2134 cm-1), the reaction was stopped, concentrated, dried, and the crude product isolated. The crude product was purified by liquid column chromatography on silica gel using either ethyl acetate or ethyl acetate/ -hexane, 9 1, respectively, and the product isolated. 

Physical properties for step 2 macrocyclic carbodiimides are provided in Table 2. 

TABLE 2. Physical Properties of Step 2 Macrocyclic Carbodiimides Prepared by Ring Closure of Step 1 Product Using l,3-Dimethyl-3-phospholene Oxide... 

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. ... 

Cycloadducts derived from macrocyclic carbodiimides and diphenylcarbodiimide are also known (see Section 11.3.3). 

The reaction of carbon disulfide with iminophosphoranes is quite general. In addition to trialkyl- and triaryliminophosphoranes also bisalkoxyalkyliminophosphoranes, trialkoxyiminophosphoranes , dimeric trichlorophosphazenes and phosphoramidate anions react similarly. Bisiminophosphoranes react with carbon disulfide to give diisothiocyanates which are used in the construction of macrocyclic carbodiimides". ... 

This transformation, now known as the aza-Wittig reaction, is exceedingly useful in the formation of heterocyclic systems and macrocyclic carbodiimides. ... 

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 useful method to synthesize ten and fourteen-membered ring imides 346 involved an initial condensation of macrocyclic -ketoestes 343 with alkyl or aryl isocyanates and carbodiimides, respectively, in the presence of a base [68]. After a nucleophilic attack of the enolate on the isocyanate C, the resultant amide N anion 344 induced a ring closure by addition to the keto group. Then, the intermediately formed four-membered ring 345 underwent a fragmentation... 

A reactive macrocyclic ether-urethane carbodiimide (MC-CDI), which is the key intermediate for synthesizing poly(amide-urethane) and poly(amide-imide-urethane), was prepared by the sequential self-repetitive reaction. A se-... 

Another carbodiimide, l-cyclohexyl-3-(2-morpholinoethyl)carbodiimide methyl /t-toluenesulfonate, has been used for macrocyclization in the synthesis of milbemycin /J3 [52]. 

Stable macrocycles with one or two carbodiimide groups in the ring have been synthesized by Molina and his coworkers (see Section 11.2.3). 

Macrocyclic bis-thioureas 17, on treatment with PhsP and CCU/EtsN, afford cyclic bis-carbodiimides 18. °... 

Review. New synthetic reactions based on the onium salts of aza-arenes have been reviewed (75 references). The reactions discussed involve activation of carboxylic acids or alcohols with 2-haIopyridinium, benzoxazolium, benzothiazolium, and pyridinium salts to afford 2-acyloxy or 2-alkoxy intermediates, which can be transformed into esters, amides, thiol esters, (macrocyclic) lactones, acid fluorides, olefins, allenes, carbodiimides, isocyanates, isothiocyanates, and nitriles under appropriate conditions. 

Less common than the previously described macrocyclizations, Pd-catalyzed reactions of unsaturated substrates (X =Y =Z) with vinyloxiranes yield cycloadducts. Hetero-cu-mulenes have been used (Scheme 19) isocyanates (RN=C=0) and carbodiimides (RN=C=NR ) give oxazolidinone derivatives, whereas carbon dioxide (0=C=0) yields cyclic carbonates. ... 

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