Dialkyl carbodiimide

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. 

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 mechanism of the P-M oxidation consists of three distinct steps 1) activation of the DMSO by a protonated dialkyl carbodiimide 2) activation of the alcohol substrate and the formation of the key alkoxysulfonium ylide intermediate and 3) the intramolecular decomposition of the alkoxysulfonium ylide to afford the product ketone or aldehyde and the dialkyl urea by-product (established by isotopic labeling studies). The alkoxysulfonium ylide is a common intermediate in all other oxidations using activated DMSO. 

Another case, in which the capture of a dipolar intermediate is reported, is the cycloaddition of an arene-sulfonyl isocyanate to a dialkyl-carbodiimide. One of the ultimate products is a 2 1 adduct, and it is suggested that an open dipolar species, the product of the first addition, adds a second molecule of isocyanate in a subsequent step. Formation of 2 1 adducts is regarded as strong evidence of cycloadditions with polar intermediates . 

An extension of these methods that employs hydrazoic acid as an azide donating agent was developed by Tsuge and co-workers. They used TMSA (146) and allowed it to react with synunetrical M,hf -diphenylcarbodiimide or Nd f -dialkyl carbodiimides 239 in dry benzene at 50-60 °C for 48 hours. The products of these conversions were l-phenyl-5-[N-(trimethylsilyl)-anilino]-... 

The conversion of carbodiimides to allophanyl chlorides as illustrated in Scheme 68 appears to be a general synthesis of uretidinediones and the method of choice for dialkyl derivatives (78JOC4530). 

In summary, among the carbodiimide-based methods only the carbodiimide/dialkyl-aminopyridine technique has been widely used in the synthesis of depsipeptides. It usually affords the desired products in moderate or high yield and has good potential for routine use in the esterification of urethane-protected amino acids or peptide fragments even in the case... 

N -Alkyl-N2-[dialkyl(bzw. DiaryI)phosphoryl]-thioharnstoffe konnen nach zwei Metho-den in die entsprechenden Phosphoryl-carbodiimide umgewandelt werden828 ... 

The synthesis of carbodiimides by desulfurization of 1,3-disnbstitnted thioureas is the most general method of synthesis because dialkyl-, alkylaryl- anddiarylcarbodiimides with the same or different substituents are obtained. The desnlfurization of N,N -disubstituted thioureas 1 with yellow mercuric oxide is the classical method of synthesis of carbodiimides 2 used by Weith in 1873. ... 

In addition to dialkyl-, alkylaryl- and diarylcarbodiimides, heterocyclic carbodiimides, such as l,4-dioxan-2-ylcarbodiimides 6 are obtained by desulfurization of the corresponding thiourea 5. ... 

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. ... 

A 16 membered ring carbodiimide is obtained in the reaction of Me2SiCl2 with cyanamide." In addition to the tetramer, oligomers with n = 2 to 7 are detected. Also, higher oligomeric carbodiimides are formed in the reaction of alkyl- and dialkyl silicon chlorides with cyanamide in the presence of pyridine." Also, from bis(trimethylsilyl)carbodiimide and silicon tetrachloride in the presence of pyridine, the silicon polycarbodiimide 34 is obtained." ... 

The cycloaddition of isothiocyanates to imines gives 2-imino-l,3-thiazetid-ines, some of which are unstable.Cycloaddition of carbodiimines to bis(trifluoromethyl) ketene and isothiocyanates " gives 2,4-bis-imino-l,3-thiazetidines. The reaction of carbodiimides with 0,0-dimethyldithiooxalate to give 1,3-dialkyl-5,5-dimethoxy-2,4-imidazolidinedithiones... 

Carbodiimides. Selcni oxidation completes the synth Dialkyl selenides. Wli methanol at room temperaiur RSeR are obtained (6 exampii or foul-smelling RSeH. 

Eq. (5.11)) [18]. This method has also been applied to aldehydes [16, 18]. A variation of the electrophile gave a cyclic compound (Eq. (5.12)). Similarly, the acyllithium, which is generated in situ, can be trapped by dialkyl disulfides (Eq. (5.13)) [19] and also by heterocumulenes such as carbon disulfide [20], isocyanates [21], isothiocyanate [21], and carbodiimides [22]. 

In the case of jV,jV-dialkyl-5-phenyl-6f/-l, 3,4-thiadiazin-2-amines, the reaction stops at the stage of 1 as ring opening and formation of a carbodiimide moiety are not possible wnth the 2-(Ar,A -dialkylamino) compounds. 

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