CH606013

1456767 7-α-Methoxycephalosporins and 6-α- methoxypenicillins MERCK & CO Inc 19 Aug 1974 [27 Aug 1973 31 May 1974] 36398/74 Heading C2C Compounds I and II in which X is H or a blocked OH, NH 2 or COOH radical, R is phenyl, tetrazolyl or 5-membered heterocyclic having 1 or 2 hetero atoms selected from N, O and S, A is H, optionally substituted tetrazolylthio, C 1-6 alkanoyloxy or optionally mono- or di-C 1-6 alkylated carbamoyloxy or thiocarbamoyloxy and M is H, Na, K benzyl optionally substituted by p-NO 2 , p-Br or p-MeO, benzhydryl, Me 3 Si, trichloroethyl, MeSCH 2 CH 2 , but-3-enyl, phenacyl p-bromophenacyl and in addition A is pyridinium optionally substituted by alkyl, halo or amino when COOM is a carboxyl anion; and their unblocked derivatives are prepared by reacting a Compound III or IV in which M1 is as defined for M other than H, Na or K, with methanol in the presence of a Th(III), Bi(V) or Pb(IV) salt followed, if necessary by hydrolysis or salification.