This invention provides {HEAD ~ a process} for preparing {TAIL ~ azetidinones} useful as intermediates in the synthesis of penems and as 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 
for preparing
This invention provides { HEAD ~ a process } for preparing { TAIL ~ azetidinones } useful as intermediates in the synthesis of penems and as 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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