Carbodiimides cycloadducts derived from

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

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... 

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. 

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. ... 

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. 

Table 2.1 [2+4] Cycloadducts derived from Carbodiimides and Cyclic Diketones...

Heating of the cycloadducts derived from arenesulfonyl isocyanates with dialkyl-carbodiimides in refluxing o-dichlorobenzene gives rise to the formation of N-sulfonylcarbodiimides and the lower boiling alkyl isocyanate. For example, reaction of p-toluenesulfonyl isocyanate 13 with di-n-butylcarbodiimide affords N-p-toluenesulfonyl-N -n-butylcarbodiimide 14 in 42 % yield. Reactions with DCC and diisopropylcarbodiimide proceed similarly. 

The [2-1-2] cycloadducts derived from two different linear carbodiimides (mixed dimers) were first synthesized by Ulrich and coworkers in 1987 . For example, lV-(4-dimethyl-aminophenyl)-lV -methylcarbodiimide, acting as a nucleophile, reacts with A-(4-nitro-phenyl)-lV -isopropylcarbodiimide, acting as the electrophile, to form the cycloadduct 14 in 69 % yield. The reaction proceeds across the aliphatic substituted C=N bonds, most likely involving a linear dipolar intermediate. 

The CO insertion product is obtained in low yield. A similar reaction is observed with diphenylbutadiyne and diphenylcarbodiimide When the [2+2] cycloadduct derived from bis(trimethylsilyl)carbodiimide and a zir-conocene imide 32 is treated with diphenylacetylene a new metallacycle 33 is produced. Reaction of 33 with diisopropylcarbodiimide affords the six-membered ring metallacycle... 

Table 3. 15 Some cycloadducts derived from ketenes and carbodiimides...

Table 3.16 [2- -2] Cycloadducts derived from carbodiimides and isocyanates...

In the reaction of allenes with C=N heterocumulenes, such as isocyanates, isothiocyanates and carbodiimides, [2+2] cycloadducts or switter ionic linear 1 1 adducts are also formed. For example, from tetramethoxyallene and phenyl isocyanate the [2+2] cycloadduct is obtained Also, from tetrathiethylallene and p-toluenesulfonyl isothiocyanate the four-membered ring cycloadduct is formed In contrast, the same allene reacts with p-toluenesulfonyl isocyanate to give a [2+2] cycloadduct, which is in equilibrium with the linear switter ionic adduct. Using chlorosulfonyl isocyanate as the reagent, only a switter ionic product is formed Some [2+2] cycloadducts derived from allenes and isocyanates are listed in Chapter 3, Section 3.3.1. 

In the reaction of the titanium vinylmethyl derivative 290 with carbodiimides the [2-1-2] cycloadducts 291, derived from addition of the carbodiimide across the Ti—C bond of the... 

Cycloaddition Reactions. In [2+2] cycloaddition reactions with car-bodiimides sometimes [2+4] cycloadducts are produced as coproducts. Examples include the reaction of phenylcarbonyl isocyanate, phenylcarbonyl isothiocyanate and thiocarbamoyl isothiocyanate with carbodiimides to give [2+4] cycloadducts, discussed in Section 5.3.1. In the current section, mainly [2+4] cycloaddition of carbodiimides as dienophile with dienes derived from oxoketenes, generated in situ or masked oxoketenes, especially 2,3-diones investigated by Kollenz and his coworkers are discussed. 

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... 

In the reaction of the titanium vinylmethyl derivative 107 with carbodiimides, the [2+2] cycloadduct 108, derived from addition across the Ti=C bond, is obtained in high yields. ... 

The reaction of a variety of liganded metal derivatives with carbodiimides give [1+2] or [2+2] cycloadducts or more complicated products resulting from rearrangement or reductive coupling reactions. Also, amidinate complexes, which are sometimes obtained in the reaction of metal complexes with carbodiimides, are included. 

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