Synthesis of a Carbapenem and Penem Precursor

As mentioned above, in describing the synthesis of sanfetrinem (see section 3.1.1.1), enantiomerically pure 4-acetoxy-substituted azetidin-2-one 1 is the key starting material for the preparation of a variety of p-lactam antibiotics of the carbapenem and penem families. About 30 different syntheses of this compound have been reported in the literature [46,66], but only a few are industrially viable. 

Among these is theTakasago process outlined in Fig. 21, which exploits an enantioselec-tive catalytic reduction of a C-O double bond [67], 

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