Penicillinates stereoselective reduction

In addition to these deacylation or transacylation methods, much effort has been directed towards the introduction of a 7a-methoxy substituent into the cephalosporin nucleus. Such methods have also usually been applicable to penicillins. One of the first methods developed made use of the diazo intermediate (211) derived from 7-aminocephalosporanic acid (183). Treatment with bromo-azide yielded a mixture of isomers (212), which with silver tetrafluoroborate and methanol formed (213). Reduction and acylation readily followed. The stereoselective addition of methoxide to... 

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