Process for the preparation of 3-substituted-2-azetidinones

Provided is a process for diastereoselectively preparing compounds of the formula ##STR1## which includes the step of subjecting a compound of the formula ##STR2## to a salt whose anion is a nucleophilic base whose conjugate acid has a pKa in the range of between about -7 to about 14, or a silylated derivative of the salt; wherein R.sub.1 is said nucleophile; R is hydrogen, or protected amino, R.sub.2 is R.sub.4 as defined herein below; R.sub.3 is a leaving group; and R.sub.4 is hydrogen, C.sub.1 -C.sub.6 alkyl, or a group of the formula wherein R.sub.6 is 2-furyl, naphthyl, phenyl, phenyl substituted with 1, 2 or 3 substituents selected from C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, nitro, halo, carboxy and amido; or R.sub.6 is a group of the formula in which R.sub.7 is selected from C.sub.1 -C.sub.6 alkyl, C.sub.2 -C.sub.6 alkenyl, benzyl, phenyl, or benzyl or phenyl substituted with 1, 2 or 3 substituents selected from C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, nitro, halo, carboxy and amido; or R.sub.4 is a group of the formula ##STR3## wherein L is --OR.sub.7 where R.sub.7 is as defined; or R.sub.4 is a group of the formula ##STR4## wherein: G is trimethylsilylmethyl, hydrogen, C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 substituted alkyl, phenyl, or phenyl substituted with 1, 2 or 3 substituents selected from C.sub.1 -C.sub.6 alkyl, C.sub.1 -C.sub.6 alkoxy, C.sub.1 -C.sub.6 alkylthio, nitro, halo, carboxy and amido.