Cycloadducts carbodiimides

A successful method for preparing 1,3-thiazetidines is the cycloaddition of carbodiimides with isocyanates. The cycloadduct 151 was derived by the interaction of carbodiimide 152 and tosyl isothiocyanate . Reaction of 152 with methyl or phenyl isothiocyanate preferentially leads to iminotriazine-thiones. Cycloaddition between aryl isothiocyanates and dicyclohexylcar-bodiimide produced 153. ... 

Carbodiimides undergo a [4-1-2] cycloaddition reaction to form pyrrolo[3,4-f]pyridine derivatives <1998J(P1)3065>. Dehydrogenation of the cycloadduct in the presence of manganese dioxide gives improved yields (Scheme 8). 

Loss of sulfur from these species would give the carbodiimide, whereas addition of alkenes would give the cycloadducts. The authors infer that this intermediate cannot add conceitedly to alkenes in the supra-supra fashion because it would involve a four-electron transition state, but that a stepwise addition would hardly rationalize the stereospecificity observed this suggests that the thiaziridine (or the 1,3-dipole) participates in an antara facial reaction.63 However, according to recent discussions antarafacial addition is seldom observed68 and stereospecificity need not be lost in a stepwise process.69... 

Electron-poor multiple bonds in acetylene dicarboxylates42 137 149), ketenes 150 152> isocyanates, isothiocyanates, carbodiimides 138-153) and arynes42) add metallated ynamines to give adducts that still carry the ynamine moiety. This behaviour contrast with that of other ynamines which mostly undergo various cycloadditions but it must be stressed that even here cycloadducts may be formed as by-products. 

The cycloaddition of chiral (-)menthylcarbodiimide with prochiral ketenes affords chi-rally selective cycloadducts In the reaction of an optically active alcohol with dicy-clohexylcarbodiimide complete inversion of the configuration occurs after hydrolysis. " Treatment of arenesulfenic acids with alcohols, thiols or secondary amines in the presence of optically active carbodiimides affords the corresponding optically active arenesulfenic acid derivatives. DCC is used to convert an optically active selenoxide into the corresponding optically active selenimide with TsNHa. ... 

In a similar manner [2+4] cycloadducts are formed in the generation of N-trifluoromethyl-N -(2-pyridyl)carbodiimide. 

The reaction of hexamethylene diisocyanate with a phospholene oxide catalyst affords low molecular weight trifunctional oUgomers, in which the isocyanate and the carbodiimide groups are cotrimerized with the generated carbon dioxide to give six-membered ring cycloadducts. A diisocyanate byproduct is used as a masked isocyanate. ... 

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

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... 

In Table 2.1 the [2+2] cycloadducts derived from carbodiimides and isocyanates are listed. 

Table 2.1 l2+2j Cycloadducts derived from Carbodiimides and Isocyanates... 

The reaction of DCC with chlorosulfonyl isocyanate affords two products depending on the mode of addition of the reagents. When the isocyanate is added to the carbodiimide the [2+2] cycloadduct 211 is obtained, while addition of the carbodiimide to the isocyanate affords the six membered ring [2+2+2] adducts 212. " ... 

There is considerable discrepancy in the literature regarding the structures of the cycloadducts derived from carbonyl isocyanates and carbodiimides. For example, Arbuzov and Zobova " claim that a cycloadduct, mp 132-138 °C (dec.), derived from diphenylcar-bodiimide and phenylcarbonyl isocyanate at 0 °C has a diazetidinedione structure. Based on our findings an oxazetidine structure is indicated. 

Tsuge and Sakai obtain [2+4] cycloadducts 216 when the reaction of arylcarbonyl isocyanates with carbodiimides is conducted in refluxing benzene. Fom phenylcarbonyl isocyanate andN-phenyl-N -2-methylphenylcarbodiimide mixtures of [2+4] cycloadducts... 

Phenylthiocarbonyl isocyanate reacts similarly with carbodiimides to give [2+4] cycloadducts 217. From N-phenyl-N -cyclohexylcarbodiimide and phenyl-thiocarbonyl isocyanate two isomeric [2+4] cycloadducts are obtained. Aliphatic thiocarbonyl isocyanates react similarly to give [2+4] cycloadducts. " ... 

The cycloadducts derived from isothiocyanales and carbodiimides are listed in Table 2.2. 

Table 2.2 Cycloadducts derived from Isothiocyanates and Carbodiimides...

Heating of the cycloadduct derived from 4-nitrophenyl isothiocyanate and dicyclohexyl-carbodiimide causes cycloreversion to give the starting materials In the reaction of phenylcarbonyl isothiocyanate and substituted phenylcarbonyl isothiocyanates, respectively, with carbodiimides, [2-1-4] cycloadducts 221 are usually obtained, but the [2 + 2] cycloadduct 220 is also formed when the reaction of DCC with phenylth-iocarbonyl isothiocyanate is stopped at shorter reaction times. ... 

Dialkylaminothiocarbamoyl isothiocyanates react with carbodiimides to give [2+4] cycloadducts. [2 + 2 + 2] Cycloadducts 225 are obtained in the reaction of the shown carbodiimide 224 with methyl- or benzyl isothiocyanate. " The structure of the [2+ 2+2] cycloadducts were determined by X-ray crystallography. 

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. 

Cycloadducts 249 are also obtained in the reaction of bis(trifluoromethyl)thioketene 248 with carbodiimides. ... 

An exchange reaction occurs on treatment of the [2+2] cycloadduct obtained from a zirconocene imide and bis(trimethylsilyl)carbodiimide 260 and diphenylacetylene to form a new metalacycle 261. The latter reacts with diisopropylcarbodiimide to form the [2+2+2] cycloadduct 262.2 ... 

The reaction of carbodiimides with carbon disulfide gives rise to the formation of isothiocyanates 269. The initially formed cycloadduct 268 undergoes a cycloreversion reaction to give the reaction products. ... 

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. ... 

Carbodiimides also add to the B=N bond in (CF3)2B=NMc2 to give the unstable cycloadduct 276, which rearranges at 20 °C to give the metalacycle 111 ... 

Likewise, reaction of the cyclic dimer of Cl3P=N-2-FPh with diisopropylcarbodiimide affords a 50 % yield of the cycloadduct 279 (R = 2-FPh). The iminophosphoranes catalytically metathesise C=N bonds of carbodiimides via an addition/elimination process. 

Carbodiimides also add to metal carbon bonds in metalorganic compounds. For example, cyclopentadienyl iron dicarbonyl 286 affords [2-f2] cycloadducts 287 with diphenyl- and... 

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