Selectivities in the reaction of vicinal diimines and acyl chlorides

The reaction of vicinal diimines and acyl chlorides in the presence of triethylamine produces 3-imino-β-lactams and/or bis-β-lactams chemo-, regio-, and stereoselectively, which are important intermediates in pharmaceutical and organic synthesis. The selectivities in the reaction have been investigated. The results indicate that all diimines react with various ketenes generated from acyl chlorides in the presence of triethylamine to give rise to cis-4-imino-β-lactams (mono-cis-β-lactams) diastereoselectively due to the electron-withdrawing property of the imino group in the vicinal diimines. Bis-β-lactams were obtained from diimines via the mono-cis-β-lactams as intermediates. Only ketenes with strong electron-donating substituents can react with the mono-cis-β-lactams to yield bis-β-lactams, affording a pair of C2-symmetric cis-bis-β-lactams with symmetric diimines, two or four pairs of diastereomeric bis-β-lactams with ketoaldehyde-derived unsymmetric diimines depending on the steric hindrance of their N-substituents. The current investigation provides very important information for the selective preparation of mono- and bis-β-lactams from vicinal diimines.