Ring-substituted azetidinones structures

Z = C02iBu, C02C6Hi3,C02(CH2)3C02IBu, C02(CH2)3C02H, or OCH3 FIGURE 11.14 Structure of ring-substituted azetidinones 26. 

The p-amino-a-hydroxy esters have been converted to diamino acids [88, 89] and related compounds like the nitrogen-substituted azetidinone shown in Scheme 13, a key structure in the synthesis of the commercially available antibiotic loracarbef [90] by substitution of the alcohol moiety with an azide. Several approaches have been used to achieve this transformation. Mesylation of the alcohol followed by substitution with sodium or trimethylsilyl azide provided cis-diamino acids [88,89]. trans-Diamino acids were obtained by ring opening of the aziridine [88] or by inversion of the alcohol bearing carbon followed by substitution under Mitsunobo conditions [90]. 

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