Oxazines, Thiazines, and their Fused Derivatives

Oxazines, Thiazines, and their Fused Derivatives 359 Oxazines 359... 

In the first edition of Comprehensive Heterocyclic Chemistry (CHEC-I) 1,3-thiazines and 1,3-oxazines were reviewed together indeed, much of their chemistry is similar, providing justification for this arrangement. However, there are areas in which this is not so, and in this edition the two types of heterocycle are treated separately. This allows a more focused approach, but as Quiniou and Guilloton <90AHC(50)85> have already pointed out, one feature which complicates any survey of 1,3-thiazines is the interrelationship of these compounds to cephalosporins. The literature dealing with cephems and related systems is vast and requires individual treatment, so here the emphasis is on the synthesis and reactions of simple 1,3-thiazines and their benzo derivatives. Other fused systems are not included unless their chemistry illustrates some important property of the 1,3-thiazine heterocycle itself. 

Oxazines and thiazines were considered together in CHEC(1984) and this meant that the review was restricted. In CHEC-II(1996) <1996CHEC-II(6)383>, the individual heterocycles and their derivatives were reviewed separately, which allowed for a thorough coverage. This trend is continued in this edition where the 1,3-thiazines and their derivatives are discussed, and this includes a review of the chemistry, syntheses, and applications. It does not include the vast literature dealing with cephems and related systems and other fused systems are not included unless their chemistry illustrates some significant property of the 1,3-thiazine heterocycle itself. 

The continuing interest in the chemistry of the 1,3-oxazines and the related thiazines and pyrimidines may arise in part from their versatile synthetic applicability and their pharmacological usefulness. Although six-membered saturated or partially saturated 1,3-heterocycles and their derivatives fused with a benzene ring have been thoroughly studied since the beginning of the twentieth century, much less attention has been paid to their saturated counterparts, the related cycloalkane-fused bicyclic 1,3-heterocycles. 

This group of compounds covers N-bridgehead oxazino-oxazines, thiazino-oxazines, and thia-zino-thiazines, and also their benzo-fused derivatives. Of the theoretically possible 10 oxazino-oxazines, three have ring file numbers, but no reference has been found for [l,4]oxazino[4,3-c][l,3]oxazines. The number of known benzo-fused systems is four. Of the theoretically possible 16 thiazino-oxazines, three are known and one benzo-fused system. Finally, of the 10 theoretically possible thiazino-thiazines two are known and one benzo-fused system (see Table 7). None of the groups of compounds was considered in CHEC-I, nor in previous reviews, therefore the whole of the literature has been surveyed. 

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