Cyclic carbodiimides synthesis

The synthesis of larger rings has also been accomplished including the fully unsaturated azolo-fused 1,3-diazepines (222) from bis(iminophosphoranes) (221) and novel cyclic carbodiimides (e.g. 223). Iminophosphoranes are also intermediates in the synthesis of macrolactams (e.g. 225) from the reaction of co-azido acid anhydrides (e.g. 224) with tributylphosphine. The synthesis of iminophosphorane-containing cryptands and a spherand-type structure have been reported. 

Amidines and cyclic amidines are also converted into 1,2,4-thiadiazoles by reaction with isothiocyanates, imino-sulfenyl chlorides, di- and trichloromethyl sulfenyl chlorides, and carbon disulfide in the presence of sulfur. Ureas, thioureas, guanidines, carbodiimides, and cyanimides react with chlorocarbonylsulfenyl chloride to produce 1,2,4-thiadiazol-5-one derivatives in another example of a type B synthesis <1996CHEC-II(4)307>. 

Ethylenimines or aziridines [lb] can be considered cyclic imines and are only briefly covered in Section 5. The preparation of heterocyclic imine systems, semicarbazones, hydrazones, azines, and oximes, is omitted from this chapter. The synthesis of carbodiimides is presented in Chapter 9. 

In 1959 Shchukina et a I. 56 showed that the addition of pyridine to DCC increases the yield (65-85%) of depsipeptides constructed from Z-protected amino acids and serine, threonine, or salicylic acid derivatives. The ferf-butyl ester of Af-(benzyloxycarbonyl)-leucylleucic acid (Table 2) was prepared in 60% yield under the same conditions of addition using a 2 molar excess of pyridine to carbodiimide. 57 The DCC/pyridine technique was successfully utilized in the ring closure between ()-alanine and leucic acid residues during the synthesis of the cyclic hexadepsipeptide destruxin B.[58 Under this modified approach the... 

Since the most common group of 1,3-diazocines is related to cyclic urea 104 (called, for example, perhydro-l,3-diazocine-2-one or N,N -pentamethyleneurea), a separate section is devoted to the synthesis, chemistry, and applications of 104, substituted 104, and related molecules such as thiourea 105, guanidines 106, and carbodiimide 107. 

Carbodiimides serve well in the 1,1-enediamine synthesis due to the 1,3-diazo arrangement in its structure. An earlier report on the preparation of 1,1-enediamines from carbodiimides appeared in 1965 by Gompper and Kunz98. In the presence of base, carbon acids add to carbodiimides 79 to give enediamines 80 in moderate to excellent yields (equation 26)98,99. Due to the structural feature of carbodiimides, only acyclic 1,1-enediamines can be expected. However, cyclic structures at the jS-carbon atom (80a) were also obtained. 

The [2+4] diastereoselective annulation of vinyl carbodiimides 48 to cyclic N-alkylimines 49 affords the S,S-diastereomer of the bicyclic dihydropyrimidine 50. This reaction is used in the synthesis of batzelladin alkaloids. 

Peptide synthesis. In the synthesis of a cyclic hexapeptide, this water-soluble carbodiimide was used for the dehydrative coupling of two tripeptides and also for the cyclization step. 

The only recent report on the synthesis of the benzoselenazole ring is an extension of an oxidative cyclization method developed earlier. In this case Treppendahl has oxidized phenylselenoureas (43 R = Ph, Me) with H2O2 and obtained benzoselenazolylguanidines (44) and cyclic dimers and trimers of the corresponding carbodiimides [Eq. (13)]. Phenylselenourea (43 R = H) gave only an open-chain dimer of phenylcarbodiimide. 

The chemical synthesis of cyclic nucleotides may be undertaken in a fashion analogous to their biosynthesis cyclization of an adenosine anhydride adduct. As the cyclic phosphate product is high energy, use of an anhydride intermediate, as may be obtained by reaction of a carbodiimide, will insure that cyclization is a thermodynamically allowable process. Hence, under conditions of high dilution and in the presence of DCC, adenosine... 

N-acoxydicarboxylic acid imides, polymeric carbodiimides, --, dual-function -, synthesis of peptides, cyclic, on - 20, 629 suppl. 26... 

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