A process for preparing penem esters by reacting ##STR1## wherein R.sub.1 is a hydroxy protecting group and X is a C.sub.1 -C.sub.10 alkyl or aryl group, with ##STR2## wherein R.sub.2 is hydrogen or a C.sub.1 -C.sub.6 alkyl group in the presence of an anhydrous organic solvent, condensing the product with ##STR3## wherein X is a halogen atom or a --OCOOR.sub.3 group and then cyclizing.
                            一种制备青霉烷酯的方法,包括将式子##STR1##中R.sub.1是羟基保护基,X是C.sub.1-C.sub.10烷基或芳基基团,与式子##STR2##中R.sub.2是氢或C.sub.1-C.sub.6烷基在无
水有机溶剂存在下反应,将产物与式子##STR3##中X是卤素原子或--OCOOR.sub.3基团进行缩合反应,然后环化。