Aziridinium cation

The first one regards the addition of a nitrogen atom of PTAD (177) to BCP (3), giving an aziridinium cation adduct, which is only postulated as intermedi-... 

In a second example, the Norton group has presented evidence that the reduction of phenyl substituted aziridinium cations to the corresponding amines by Cp Ru (dppf)H proceeds via a similar mechanism [34] that is shown in Scheme 13. 

A key issue of this reaction is that aziridinium cations are electrochemically much more readily reduced (by 0.6-0.9 V) than their alkyl substituted analogs. 

The amine product plays a critical role, as it deprotonates the H2 complex 18 to regenerate the catalytically active 17. This also prevents side reactions based on nucleophilic ring opening of the aziridinium cations by the amine products. Alkyl substituted aziridinium cations react via a classical SN2-mechanism. 

In aqueous solutions the 14N relaxation of symmetrical ammonium salts occurs due to the reorientation of water dipoles. (79) From relaxation studies on the highly strained A Af-dimethyl-aziridinium cation it is reported that the electronic distribution around the nitrogen nucleus is distorted from tetrahedral symmetry. (79)... 

Modification of the polystyryl anion was also necessary for the preparation of block copolymers with living cationic poly(l -/-butylaziridine). In the absence of modification only a mixture of homopolymers was obtained. Thus, the carbanion was first converted with propylene sulfide to the thiolate anion 126) which was then coupled with the living aziridinium cation ... 

It is known that alkyl amine is a stronger base than water therefore, NaOH or KOH cannot deprotonate the amino group. On the other hand, the amino group is a good nucleophile that attacks the /3-carbon to form an aziridinium cation and then quickly decomposes back to the starting material in the absence of a base. A representative mechanism is illustrated here using 2-bromoethylamine and KOH. 

Sometimes it is difficult to distinguish an H" transfer from a single-electron transfer folloived by an H transfer. There is clear evidence [i.e., broadening of the H NMR resonances of Cp Ru(dppf)H, in which dppf = l,l -bis(diphenylphosphino)ferrocene, by electron exchange with the corresponding radical cation] for electron transfer in the reaction of Cp Ru(dppf)H with the phenyl-substituted aziridinium cation in Equation 3.134. ... 

On the basis of ring opening reactions of 2 substituted aziridines described in the literature [17,18,19], the polymerization initiated with dimethylsulfate or boron trifluoride etherate was expected to propagate mainly by nucleophilic attack of the free aziridine on the methylene carbon of the aziridinium cation following the scheme ... 

Micouin et al. found that the nucleophilic substitution of bicycUc hydrazine-epoxide 7 using alkynylaluminum reagent led to the formation of hydroxy group-rearranged product 8 (Scheme 6) [20]. The plausible mechanism of this unique reaction involves (1) the initial formation of aziridinium cation intermediate catalyzed by aluminum Lewis acid and (2) the intramolecular nucleophilic migration of alkynyl group, as in transition state 9. 

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