Ring opening 4-dimethylaminopyridine

In the case of the reactions with 4-dimethylaminopyridine, complete replacement of the halogens occurs before ring opening to a tetracation which cyclizes on heating to give 7. ° ... 

The regiospecific 5 2 ring-opening reactions of 2-substituted aziridinium and azeti-dinium ions at the least-substituted carbon by 4-dimethylaminopyridine in acetonitrile occurs 17000 times faster with the aziridinium ion than with the azetidinium ion. However, only a portion of the faster rate is due to the additional ring strain in the aziridinium ion. A/7 =46.5kJ mor and A5 = 165.4 J mor K" for the aziridinium ion reaction. 

The enol acetates of aldehydes (but not ketones) are obtained in high yield with acetic anhydride and triethylamine with 4-JV,JV-dimethylaminopyridine. Regiospecific enol acetates (95) are obtained by nucleophilic ring opening of cyclopropyl ketones [equation (60)]. ... 

The use of nucleophilic catalysts is promising. Indeed, ring-opening polymerisation of LA initiated by alcohols and catalysed by nucleophiles, such as tertiary amines (e.g., 4-dimethylaminopyridine, 4-pyrrolidinopyridine) (Nederberg et al, 2001) and N-imidazolium carbenes (Connor et al, 2002) is well controlled. A monomer activation mechanism (Fig. 4.11), similar to the one reported for biocatalysis, has been proposed. 

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