Synthetic Approaches to Carbapenem Skeleton

In the synthesis of 183 and C-5/C-6 cis-carbapenems, the acid 178 was obtained by the TBS protection of the azetidinone nitrogen in 176 followed by hydrogenolysis of the product 177 C-5 benzyl ester [118]. Arndt-Eistert homologation was employed for the introduction of methylene fragment and preserved the cis stereochemistry. 

Reaction of the azetidinone carboxylic acid 178 with diazomethane followed by the Wolff rearrangement of the resulting product furnished homologated acid 180. 

A propargylic group was introduced onto the C-3 of the 4-acetoxy-2-azetidinone 184 by a zinc-mediated Barbier-type reaction of the latter with propargyl 

PhCHsCHs, CpCHs, C-prop, f-Bu, Ph, Et02C, BnOCHj, AcOCHj 

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