Conversion of Mannich Phenol Bases; III. Synthesis and Transformations of 3,4-Dihydro-2H-1, 3-Benzoxazin-2-one Derivatives

Abstract

At present the only direct method for the preparation of 3,4-dihydro-2H-1,3-benzoxazin-2-one derivatives (I) involved the treatment of o-hydroxybenzyl halides with alkali metal cyanates¹. Alternatively, a catalytic reduction¹ of not easily accessible^1,2 heterocyclic ring substituted 3,4-dihydro-2H-1, 3-benzoxazin-2-ones has been used. Recently we have described a method for the preparation of 2-thioxo-2H-3,4-dihydro-1, 3-benzoxazine derivatives³ from o-hydroxybenzyltrimethylammonium salts (II) and potassium thiocyanate. The salts (II) can be much easier obtained than the corresponding o-hydroxybenzyl halides. They are prepared with very high yields by quaternization of mannich phenol bases obtained from phenol derivatives, paraformaldehyde and dimethlamine⁴. Our further studies on the transformation of Mannich phenol bases have shown that o-hydroxybenzyltrimethy-ammonium salts (II) react with potassium cyante to give derivatives of 3,4-dihydro-2H-1,3-benzoxazin-one (I) (Scheme 1).