Abstract: An azetidinone derivative having the general formula (I): ##STR1## wherein R.sup.1 and R.sup.2 are hydrogen atom or a protective group and R.sup.3 is an alkyl group or hydrogen atom, a process for preparing the same, and a process for preparing an azetidinone derivative having the general formula (II): ##STR2## wherein R.sup.1, R.sup.2 and R.sup.3 are as above. The azetidinone derivative (I) of the present invention can be converted into an important intermediate of 1.beta.-methylcarbapenem antibiotics of a selective reduction of the double bond.

Abstract: .beta.-Aminothiol ester having the general formula (I): ##STR1## which is useful as an intermediate in the preparation of carbapenen beta-lactam antiobiotics, wherein R.sup.1 is alkyl or aryl and R.sup.2 and R.sup.3 are protective groups. The .beta.-Aminothiol ester of formula (I) is prepared by reacting a .beta.-hydroxythiol ester having the general formula (III): ##STR2## wherein R.sup.1 is as above, with a boron compound having the general formula (IV): ##STR3## wherein each of R and R' is alkyl or cycloalkyl, or R and R' taken together, form a ring including the boron atom in the presence of a tertiary amine, the obtained reaction mixture being reacted with an imine having the general formula (V): ##STR4## Wherein R.sup.2 and R.sup.3 are protective groups, followed by treating the resultant product with hydrogen peroxide.

Abstract: .beta.-N-substituted aminothiol ester represented by the general formual (I): ##STR1## wherein R.sup.1 is an alkyl group or an aryl group and R.sup.2 is an aralkyl group, a process for preparing the same, and an azetidinone derivative represented by the general formula (VI): ##STR2## wherein R.sup.2 is as above. The .beta.-N-substituted aminothiol ester (I) of the present invention can be an excellent intermediate for preparing the .beta.-lactam (II).