A multistep process is disclosed for preparing azetidinone intermediates used in the making penems and carbapenems wherein intermediates containing ##STR1## R' is independently hydrogen or 1, 2 or 3 of lower alkyl or lower alkoxy, preferably hydrogen, wherein R" is methyl, ethyl, a phenyl or alkyl, preferably ethyl, as a readily removable nitrogen protecting group are made.
                            披露了一种用于制备在制造青霉烯和碳青霉烯时使用的氮杂
环丁烷中间体的多步骤过程,其中间体包含##STR1## R'独立地是氢或1个、2个或3个低级烷基或低级烷氧基,最好是氢,其中R"是甲基、乙基、苯基或烷基,最好是乙基,作为一种易于移除的氮保护基团。