The reaction of some 4‐pyrones with activated isocyanates

Abstract The pyrones, 2,6‐diphenyl‐4H‐pyran‐4‐one, flavone, and 2‐phenyl‐4H‐naphtho[2,1‐b]pyran‐4‐one reacted with activated isocyanates, such as trichloroacetyl isocyanate, giving 4‐trichloroacetylimino derivatives. These acylimino compounds underwent a slow reaction with a second mole of isocyanate to give a bisiminopyran. It is shown that carbonyl groups that are conjugated with electron‐releasing groups will react with activated isocyanates.