A new synthesis has been developed for the hitherto unreported 2-substituted-3-oxo-4H-1,4-oxazines 3b-3j via the cyclodehydrohalogenation of N-aryl-N-dichloroacetyl-2-amino-4′-nitroacetophenones in dimethyl sulfoxide with potassium t-butoxide. The structures of all the oxazine derivatives have been verified by IR and NMR spectroscopy and correlations between the structures and spectrographic characteristics have been made. In every case the only tautomer present was the one in which the carbonyl group in position 3 of the oxazine ring existed in the “keto” form. Attempts to extend these cyclic elimination reactions to the synthesis of oxazepines have failed
A New Synthesis of 2,3-Dihydrobenzo[1,4]dioxine and 3,4-Dihydro-2H-benzo[1,4]oxazine Derivatives by Tandem Palladium-Catalyzed Oxidative Aminocarbonylation—Cyclization of 2-Prop-2-ynyloxyphenols and 2-Prop-2-ynyloxyanilines.