Cephalosporins thiazine ring

Moreover, there are several patents and reports on cephalosporins and 7-alkoxy derivatives thereof, which are characterized by a pyridazine-derived substituent attached to the thiazine ring. Some typical examples are given in formulae (126) [347-356], (127) [357], (128) [358], (129) [359, 360] and (130) [355, 361-363] in which R1 represents a variable acyl group. 

Penicillins and cephalosporins are the most important compounds which possess a four-membered / -lactam ring. In the penicillins this ring is fused with a thiazol-idine ring. In the cephalosporins it is anellated with the six-membered dihydro-thiazine ring (Fig. 336). The penicillins are amides of 6-aminopenicillanic acid (Table 58). 

Nitrogen- and Sulphur-containing Rings.- The preparation of 1,3-thiazines as intermediates in the synthesis of cephalosporins has been published utilising a [4+2] cycloaddition of the l-thia-3-azadienes (81) with a,3-unsaturated aldehydes and ketones. The reaction proceeds thermally, except where R = CC Et when a Lewis-acid catalyst is required, and yields are generally high. 

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