• Citer

A new and facile synthesis of ketene imines and their 2-iminoazetidine dimer from nitriles via their nitrilium salts

par Fuks, Robert ;Baudoux, Dominique ;Piccinni Leopardi, Carla ;Declercq, Jean-Paul;Van Meerssche, Maurice
Référence Journal of organic chemistry, 53, 1, page (18-22)
Publication Publié, 1988

Article révisé par les pairs

• Détails
• Contenu

Résumé :

A new one-pot synthesis of N-tert-butylketene imines 3 was accomplished on the basis of the reaction of N-tert-butylacetonitrilium tetrachloroferrate 2 with an organic base such as triethylamine or N-trisubstituted amidine 4. The α-hydrogen in 2 is particularly acidic, thus allowing very smooth experimental conditions to remove it with the organic base at -80°C. The usefulness of this synthesis was demonstrated by the facile preparation of alkyl or functionally substituted ketene imines and especially the as yet undescribed unsubstituted 3f on a preparative scale. The nitrilium salt 2 was easily formed "in situ" from the corresponding nitrile, tert-butyl chloride, and FeCl3, all commercially available starting materials. When the reaction was similarly carried out at -40°C instead of -80°C, the major compound isolated was a 2-iminoazetidine 5 a dimer of 3. Owing to its a priori unexpected structure, an X-ray analysis was carried out to confirm the formula 5a. The same dimer was isolated by adding 1 mol of HCl and 1 mol of FeCl3 to 2 mol of 3 and it was then left for several hours at room temperature. This easy dimerization is rationalized assuming the formation of a very reactive ketene iminium 8 by the protonation of the ketene imine 3, which, by a two-step polar cycloaddition with 3, leads to 5 (Scheme IV). A similar synthesis failed to give N-isopropylketene imines, except when two phenyl groups stabilized the ketene imine (e.g., 14). Only a s-triazine 15, a trimer of the parent ketene imine was isolated from N-isopropylisobutyronitrilium salt. Thus, the N-tert-butyl substituent appeared to be crucial to stabilize the ketene imines prepared from nitrilium tetrachloroferrates. © 1988 American Chemical Society.