Highly enantioselective direct Mannich reaction of seven-membered cyclic imines dibenzo[b,f][1,4]oxazepines with acetone via organocatalysis

Various substituted dibenzo[b,f][ 1 and 4]oxazepines as seven-membered cyclic imines underwent a highly enantioselective direct Mannich reaction with acetone when catalyzed by proline. These reactions gave a range of optically active β-carbonyl seven-membered N-heterocycles with excellent enantioselectivity (93%–98% ee). With 2-butanone as a Mannich donor, the single regioselective product was obtained with 96%–97% ee. The absolute configuration of the product was assigned to be R by X-ray single crystal analysis of its derivative.

Graphical AbstractWith (S)-proline as an organocatalyst, a direct Mannich reaction between dibenzo[b,f][ 1 and 4]oxazepines and acetone or 2-butanone afforded the optically active β-carbonyl seven-membered N-heterocycles with excellent enantioselectivity.Figure optionsDownload as PowerPoint slide