Cyclic carbodiimides nucleophilic

Cyclic carbodiimides. Bis(iminophosphoranes) behave as nucleophiles toward BocjO. After an isocyanate is formed, a Wittig reaction follows. Either an intramolecular or intermolecular process predominates according to the influence of ring strain. 

Williams, A., and Ibrahim, I. A. (1981) A mechanism involving cyclic tautomers for the reaction with nucleophiles of the water-soluble peptide coupling reagent l-ethyl-3-(3-dimethyla-minopropyl) carbodiimide (EDC). J. Am. Chem. Soc. 103, 7090—7095. 

The palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a [42] and aziridine 20b [39] with the activated olefin 4a for the formation of five membered cyclic ether 21a and pyrrolidine derivative 21b has also been reported in our laboratories. The mechanistic issue is very much similar to that discussed in Scheme 9. Pd(0) catalyst added oxidatively to 20 to produce the 7r-allylpalladium complex 22. The Michael addition of a hetero nucleophile in 22 to the activated olefin 4a gives 23 which undergoes intramolecular nucleophilic attack on the inner 7r-allylic carbon atom to give the cy-clized products 21 and Pd(0) species is generated (Scheme 10). Similarly, the palladium-catalyzed [3 + 2] cycloaddition of vinylic oxirane 20a with the N-losylimincs 24 is also known (Scheme 11) [43]. Intermolecular cycloaddition of vinyl epoxides and aziridines with the heterocumulenes such as isocyanates, carbodiimides and isothiocyanates is also known [44,45]. Alper et al. reported the regio- and enatioselective formation of the thiaolidine, oxathiolane, and dithiolane derivatives by the palladium-catalyzed cyclization reaction of 2-vinylthiirane with heterocumulenes [46]. 

The nucleophilic reactions of N-sulfurcarbodiimides are similar to the nucleophilic reactions of other carbodiimides. However, oligomerization reactions are less pronounced. The cyclic dimer of N-p-toluenesulfonyl-N -phenylcarbodiimide 31 is obtained on dissociation of the cycloadduct 30 obtained in the outlined reaction. " ... 

The original Pfittner-Moffatt procedure for alcohol oxidation by activated dimethyl sulfoxide utilized dicyclohexylcarbodiimide (DCC) and a source of protons such as polyphosphoric acid or pyridinium tri-fluoroacetate. The use of strong acids such as the common mineral acids must be avoided since, although acidic conditions are initially required, the reaction must readily become basic in the later stages of the process. Mechanistically it is reasonable to suggest that the activation follows the pattern whereby initial attack of the nucleophilic sulfinyl oxygen of dimethyl sulfoxide, with the protonated carbodiimide, forms a sulfonium isourea. This is followed by displacement of dicyclohexylurea by the alcohol to form an alkoxysulfonium salt. Base treatment of this salt forms an ylide, which collapses via the proven cyclic mechanism to the carbonyl compound and dimethyl sulfide (Scheme 4). 

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