CONTRIBUTION TO THE DEVELOPMENT OF NEW SUBSTITUTION PATTERNS OF OPTICALLY-ACTIVE BETA-LACTAMS - SYNTHESIS OF HOMOCHIRAL 4-(1-AMINOALKYL)AZETIDIN-2-ONES FROM N-(TERT-BUTYLOXYCARBONYL) ALPHA-AMINO ALDEHYDE-DERIVED IMINES VIA ASYMMETRIC STAUDINGER REACTION

Imines derived from N-(tert-butyloxycarbonyl) (N-Boc) alpha-amino aldehydes react with alkoxyketenes, generated from their corresponding acid chlorides and triethylamine, to produce homochiral cis-3-alkoxy-4-(1-aminoalkyl) beta-lactams with virtually complete control of diastereoselectivity. In a similar manner, the reaction of phthalimidoacetyl chloride with these imines in the presence of triethylamine afforded the corresponding 3-phthalimido beta-lactams as single diastereomers. The same reaction employing the Dane salt of glycine as the aminoketene synthon, activated with phenyl phosphorodichloridate, produced 3-amino beta-lactams in better chemical yields. Some aspects related to the degree of asymmetric induction of the above imines with respect to the known Evans-Sjogren ketenes, as well as their mechanistic implications within the context of the general model proposed by Hegedus for the stereochemical outcome of the Staudinger reaction, are also discussed.