Synthesis of 3-[1-(t-Butyldimethylsilyloxy)ethyl]-4-carboxymethyl-2-azetidinone Derivatives

Isoxazolidine derivatives 7 and 8 were synthesized from N-benzyl-C-(2-benzyloxyethyl)nitrones by 1,3-dipolar cycloaddition with ethyl crotonate. The isoxazolidine derivatives were converted to β-amino acid esters 9a and 9b by reduction with zinc in acetic acid. The β-amino acid esters were reacted with methylmagnesium bromide to give the 2-azetidinones (13a, 13b). The benzyl group of 2-azetidinones were removed by Birch reduction. The products were oxidized with PDC to give 3-[1-(t-butyldimethylsilyloxy)ethyl]-4-carboxymethyl-2-azetidinone derivatives (2a, 2c).

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