Pericyclic Ring Closure of Ketenimines to Quinolinones

Significance

2-Carbonyl-substituted arylketenimines are shown to undergo sequential [1,5] migration followed by electrocyclization to form quinolin-4(3H)-ones in yields up to 97%. The starting ketenimines were prepared in three steps from 2-azido-benzoyl chloride. The sulfur-substituted derivatives (X = S) give much higher yields than the selenium, oxygen and nitrogen analogues. Model ab initio and DFT calculations predict that 1,3-oxazines are the kinetically controlled while the quinolinones are the thermodynamically controlled products. These predictions were not experimentally verified. Different substituents X were tested, but little variation for the R¹ and R² substituents was achieved.