Process for preparing beta-lactam antibiotic substances

A process for preparing a compound having the formula ##STR18## wherein R.sup.8 represents a group selected from the group consisting of straight or branched lower alkyl, lower alkoxymethyl, benzyloxymethyl, lower alkanoyloxy lower alkyl, benzoyloxymethyl, cyanomethyl, 2,2,2-trichloroethyl, phthalimidomethyl, benzyl, p-methoxybenzyl, p-nitrobenzyl, benzhydryl, phenacyl, p-bromophenacyl, p-methoxyphenacyl, p-nitrophenacyl, and tri lower alkylsilyl, R.sup.9 to R.sup.12 may be the same or different and each represents hydrogen or a group selected from the group consisting of straight or branched lower alkyl, lower alkoxy, halogen, cyano, lower alkoxycarbonyl, or R.sup.9 and R.sup.10 together and R.sup.11 and R.sup.12 together may be linked to form a ring fused with the benzene ring to which they are attached,

• n is 1 or 2 and R represents a straight or branched alkyl having from 1 to 6 carbon atoms which comprises contacting a penam compound having the formula ##STR19## wherein R.sup.8 to R.sup.12 and n have the same meanings as defined above, with a metal oxide in an inert solvent or with a quinone compound substituted with an electron attractive group thereby oxidizing said panam compound to its quinoid form, and contacting the resulting oxidation product with a lower alkanol having the formula R--OH wherein R has the same meaning as defined above, said metal oxide and said quinone compound being one which oxidizes phenol to a quinoid form without destruction of the penam nucleus.