Aliphatic carbodiimides

The reaction of alcohols with diarylcarbodiimides [16, 35, 36] is catalyzed by sodium alkoxides but not by triethylamine. Recently Schmidt and Moos-miiller [37, 38] found that cuprous chloride (0.075 mole/100 mmole dialkyl-carbodiimide) catalyzes the reaction of primary, secondary, and tertiary alcohols with aliphatic carbodiimides to give O Af -trialkylpseudoureas. Several examples of the use of these methods are described in Tables I and II. 

Carbodiimides are used in the laboratory as stabilizing agents, coupling agents and as condensation agents and a potential for exposure exists during these operations. The aliphatic carbodiimides are reported to be irritating to the skin, eyes and the respiratory tract. Contact dermatitis caused by DCC was reported. ... 

In many of the carbodiimide reactions N,N -dicyclohexylcarbodiimide (DCC) is used. However, N,N -diisopropylcarbodiimide (DIPCD) is also often used. Aliphatic carbodiimides, having secondary alkyl groups as substituents, are more stable than carbodiimides... 

Heating of N-isopropyl-N phenylcarbodiimide at atmospheric pressure affords a mixture of N,N -diisopropyl-, N,N diphenyl- and the starting carbodiimide. " Apparently, a thermal metathesis reaction occurs. Vanadium 0x0 [V(0)(0-i-Pr)3] andimido vanadium complexes [V(NPhMe)Cl3] are found to be catalysts for this metathesis reaction. Likewise, mixtures of aromatic and aliphatic carbodiimides undergo the carbodiimide metathesis reaction. Vanadium 0x0 complexes V(0)(0-i-Pr)3 are precatalysts which are converted into the reactive imido complexes V(NR)(0-i-Pr)3 during the reaction. 

The metathesis of symmetrical aliphatic carbodiimides is also catalyzed by tungsten imido complexes above 140 Other carbodiimide metathesis catalysts include Cr(ll)/Si02/ iminophosphoranes, imido circonocenes, guanidine supported titanium complexes and group 14 amide complexes. ... 

Carbodiimides undergo cyclooligomerization reactions. In this regard they are similar to isocyanates, the mono imides of carbon dioxide. For example, aliphatic carbodiimides undergo rapid dimerization catalyzed by tetrafluoroboric acid at room temperature to give salts of the cyclodimers 183. Neutralization with dilute sodium hydroxide, or better filtration through basic AI2O3, afford l,3-dialkyl-2,4-bisalkylimino-l,3-diazetidines 184. ... 

Salts of aliphatic carbodiimide dimers are also obtained in the reaction of carbodiimides with dimethyl sulfate. The cyclic dimer of dibenzylcarbodiimide, mp 102-103 °C, was isolated in low yield from the distillation residue of the monomer. The crystal structure of l,3-dicyclohexyl-2,4-bis(cyclohexylimino)-l,3-diazetidine, the cyclodimer of DCC, is... 

The homopolymerization of aliphatic carbodiimides, using n-butyl lithium as catalyst in hydrocarbon solvents at room temperature, affords nylon-1 imides 199 (R=Me, n-Bu, allyl, Ph), which have no commercial interest because unzipping occurs on heating. In the unzipping process the monomer is regenerated. The polymerization failed with DDC, diisopropylcarbodiimide and methyl-t-butylcarbodiimide. 

Aliphatic carbodiimides often react with heterocumulenes to form six-membered ring 1 2 cycloadducts. For example, DCC reacts with N-p-toluenesulfonyl-N -cyclohexylcarbodiimide to give the 1 2 cycloadduct 207, mp 123-124 °C in 93 % yield. The initially formed polar intermediate 206 reacts with a second sulfonylcarbodiimide molecule to give the final product. ... 

Similar [2+2+2] cycloadducts 208 are obtained in the reaction of arenesulfonyl isocyanates with aliphatic carbodiimides... 

Similar six-membered ring 1 2 cycloaddncts are obtained from aliphatic carbodiimides and aliphatic isocyanates, arenesulfonyl isocyanates and chlorosulfonyl isocyanates. 

Cycloaddition Reactions Across C—C Multiple Bonds. Cycloadducts derived from carbodiimides and olefins or allenes are not known. However, the [2+2] cycloaddition of ketenes, R2C=C=0, to carbodiimides affords 4-imino-2-azetidinones (/3-lactames) 239 in high yield. Aliphatic carbodiimides show higher reactivity in comparison to aromatic carbodiimides, and the reaction proceeds across the aliphatic C=N bond in N-alkyl-N -arylcarbodiimides. The cycloadducts obtained in this reaction are listed in Table 2.3. 

In the reaction of Me2N+=SO BF4 272 with aliphatic carbodiimides the initial [2-1-2] cycloadduct 273 is rearranged to give 1,2,4-thiadiazetidinium salts 274. ... 

Aluminium amidinate complexes 392 are synthesized by addition of aluminum alkyls to aliphatic carbodiimides. Also, alkylation of carbodiimides with MeLi, followed by reaction with AICI3 affords aluminum amidinate complexes... 

In the reaction of aromatic or heterocyclic carboxylic acids with adjacent reactive groups with two equivalents of carbodiimides also heterocycles are readily obtained. For example, salicylic acid 608 reacts with aliphatic carbodiimides to give benzoxazine derivatives 609, together with the corresponding urea. ... 

In addition to DCC and EDC many other aliphatic carbodiimides are used in peptide synthesis. Examples include N-t-butyl-N -methylcarbodiimide (BMC), N-t-butyl-N -ethylcarbodiimide (BEC), N,N -dicyclopentylcarbodiimide andN-cyclohexyl-N -isopropylcarbodiimide (CIC). DCC, diisopropylcarbodiimide, BMC and BEC perform similarly in peptide synthesis. " N-cyclohexyl-N -isopropylcarbodiimide (CIC) is comparable or even better than DCC for mediation of peptide bond formation in sohd phase synthesis. Also, the solubility of the derived urea in dichloromethane is useful in the standard procedure. " ... 

Reaction of aliphatic carbodiimides with 98 % H2O2 produces peroxycarboximidic acid 712, which can be used to oxidize arenes to arene oxides. ... 

The homopolymerization of aliphatic carbodiimides affords nylon-1 imides 19. The thus obtained poly(guanidines) are of no interest as industrial polymers because unzipping occurs on heating. ... 

Fluoro group containing aliphatic carbodiimides are used to impart oil and water repellent finishes to nylon and polyester fabrics and to leather materials. " ... 

An efficient method for preparation of aromatic and aliphatic carbodiimides involves the reaction of an Isocyanate with 3-methyl-1-phenyl-S-phospholene-1-oxide, the most readily prepared catalyst of Us type. ... 

Dimerization of carbodiimides.4 Aliphatic carbodiimides (1) when mixed with 0.5... 

Carbonyl diisocyanate (46) was shown to undergo a Diels-Alder type of cycloaddition with azomethines to give 2,3,6,7-tetrahydro-4/7,8/7-[l,3,5]triazino[2,l-Z>][l,3,5]oxadiazin-4,8-diones (16) (Scheme 5). A large variety of the triazino[2,l-ft][l,3,5]oxadiazines were realized by the suitable selection of dienophiles. Thus, l,3,5-triazino[2,l-Z>][l,3,5]oxadiazines (17), (18 R = NMe), and (19) and were synthesized by the reaction of carbonyl diisocyanate with alkyl or aryl isocyanates, dimethyl cyanamide, or aliphatic carbodiimides, respectively <86CB1133>. Due to the high reactivity of the cumulated double bonds, carbonyl diisocyanate (46) was also found to undergo [4 + 2] cycloadditions with cyclohexanone to yield cyclohexan-l-spiro-9 -[l,3,5]-oxadiazino-[3,4-e][l,3,5j-dioxazin-5 -spiro-l"-cyclohexane-2, 7 -dione (47) (Scheme 6) <76LA1634>. 

An interesting new method of synthesis of carbonimidoyl dichlorides involves the addition of dichlorocarbene to aliphatic carbodiimides. Thus, reaction of phenyl(bromodichloromethyl)mercury (LXV) (the dichlorocarbene precursor) with diisopropylcarbodiimide produces isopropyl-carbonimidoyl dichloride (LXVI) in 63% yield... 

While uncatalyzed reaction of sulfonamides and carbodiimides is limited to aliphatic carbodiimides, the CuCl-catalyzed coupling is more general reaction (Scheme 3.73). CuCl-catalyzed coupling of arylsulfonamides 274 with carbodiimides 275 readily proceeded with DCC, DIC, and DPTC obtaining the corresponding guanidines 276 (Table 3.36), but not with sterically hindered carbodiimides... 

The stability of aliphatic carbodiimides in which primary alkyl groups are attached to the nitrogen is limited in contrast, diisopropyl-, dicyclohexyl and di-t-butylcarbodiimides are indefinitely stable. Also, Af-methyl-Af -t-butylcarbodiimide is a stable compound. 

Salts of aliphatic carbodiimide dimers are also obtained in the reaction of carbodiimides with dimethyl sulfate. 

Pentacoordinated phosphoranes, such as 129, react with aliphatic carbodiimides to give hexacoordinated phosphorus amidinates 130. ... 

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