This invention provides a process for preparing azetidinones useful as {HEAD ~ intermediates} in the synthesis of penems and as {TAIL ~ hypocholesterolemic agents}, particularly for azetidinones substituted in the C 3 and C 4 positions and optionally substituted at the ring nitrogen, comprising reacting a β amide, a β acid ester, or a β thiolcarbonic acid ester with a silylating agent and a cyclizing agent 
This invention provides a process for preparing azetidinones useful as { HEAD ~ intermediates } in the synthesis of penems and as { TAIL ~ hypocholesterolemic agents } , particularly for azetidinones substituted in the C 3 and C 4 positions and optionally substituted at the ring nitrogen , comprising reacting a β amide , a β acid ester , or a β thiolcarbonic acid ester with a silylating agent and a cyclizing agent
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