Synthesis of 4-Amino-1,3-oxazine-2-ones and 4-Amino-1,3-oxazine-2-thiones via Electrocyclic Ring Closure

Article abstract of DOI:10.1007/BF00816869

The title compounds 3 and 4 are easily obtainable by reaction of 2-acyl-1-chloro-enamines 2 with trimethylsilyl-isocyanate, trimethylsilyl-isothiocyanate or sodium rhodanide, respectively.Primarily formed acylvinyl-iso(thio)cyanates D, G spontaneously undergo electrocyclization.A one-pot operation leads directly to 4-amino-1,3-oxazine-2-thiones 4 starting from acylketenedichlorides 1 via 2 by successive addition of secondary amine and sodium rhodanide.Reaction of 2 with ammonium dithiocarbamate results in an unexpected formation of 4.Treatment of 4 with mercuric acetate offers a further access to 4-amino-1,3-oxazine-2-ones 3.Finally, 3 are obtained from 2 on the sequence of ammonolysis to acylketeneaminals 5 and phosgenation.Characteristic scopes and limitations as well as mechanistic features of these transformations are discussed. - Keywords: 1,3-Oxazine-2-ones; 1,3-Oxazine-2-thiones; Acylketenedichlorides; Acylketeneaminals; 2-Acyl-1-chloro-enamines; Electrocyclic reactions; Acylmigration