Synthesis of novel 4-(1-ethoxycarbonyl-methylidene)-azetidin-2-ones via a Lewis acid-catalyzed reaction of ethyl diazoacetate

Treatment of (3R,4R,1'R)-3-[1-(t-butyldimethylsilyloxy)ethyl]-4-acetoxy-azetidin-2-one with Et diazoacetate in the presence of a Lewis acid such as TiCl4, TiF4, AlCl3 or SnCl4 affords the novel (3S,1'R)-3-[1-(t-butyldimethylsilyloxy)ethyl]-4-(1-ethoxycarbonyl-methylidene)-azetidin-2-one as an E and/or Z isomer.