1, 3-Oxazines and Related Compounds. IX. Alkylation, Acylation, and Cleavage Reaction of 6-Methyl-4-oxo-2-thioxo-3, 4-dihydro-2H-1, 3-oxazine

Abstract

Alkylation of the title compound (2) with alkyl halides in the presence of Et₃N proceeded exclusively on the sulfur atom to give the S-alkyl-1, 3-oxazine derivatives. Acylation with acylchlorides took place regioselectively on the nitrogen atom, giving the N-acyl derivatives. 1, 3-Oxazine 2 was found to undergo cleavage of the ring into acetylketene and thiocyanic acid. Hence, treatment of 2 with alkyl halides in the presence of K₂CO₃gave alkyl thiocyanates ; treatment with active methylene compounds afforded γ-pyrone derivatives. N-Acyl derivatives of 2 also underwent thermal cleavage of the ring, leading to the corresponding acyl isothiocyanates.