1,2-Oxazines, 1,2-benzoxazines and related compounds

This chapter reviews the literature for 1,2-oxazines, 1,2 benzoxazines, and related compounds, which can be synthesized by the dehydration of 5,6-dihydro-6-hydroxy-4H-1,2-oxazines. The latter are obtained from the cyclization of 3-acyl-1-nitrosopent-1-en-4-ones (or their oximino tautomers) by heating them with urea in boiling methanol, or ethanol. The method of preparation of 6H-1,2-oxazines is discussed. Examples are provided to emphasize the importance of the oxazinium salts as electrophiles; this is supported with schematic structure diagrams. The descriptions of synthesis of oxazines, their use as chiral synthons, and general reactions are also presented. The reduction of 1, 2-oxazines derivative is explained with examples. In certain reactions, the corresponding 1,2-oxazanes seem to be implicated as intermediates in certain reaction types and this is illustrated with an example.