This invention provides a process for preparing azetidinones useful as intermediates in the synthesis of penems and as hypocholesterolemic agents, particularly for {TAIL ~ azetidinones} substituted in the C 3 and C 4 positions and optionally substituted at {HEAD ~ 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 intermediates in the synthesis of penems and as hypocholesterolemic agents , particularly for { TAIL ~ azetidinones } substituted in the C 3 and C 4 positions and optionally substituted at { HEAD ~ 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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