Novel syntheses of the carbapenem key intermediates, (3R,4R)-4-acetoxy-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-2-azetidinone and (3S,4R)-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-carboxymethyl-2-azetidinone, from (S)-ethyl lactate-Science-Chemical Encyclopedia-lookchem

Novel syntheses of the carbapenem key intermediates, (3R,4R)-4-acetoxy-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-2-azetidinone and (3S,4R)-3-[(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-carboxymethyl-2-azetidinone, from (S)-ethyl lactate
Add time:07/13/2019 Source:sciencedirect.com

Two types of the carbapenem key intermediates (4 and 6) have been efficiently synthesized from inexpensive (S)-ethyl lactate (7). Thus, (S)-2-benzyloxypropanal readily obtainable from 7 was condensed with di-p-anisylmethylamine to give the chiral imine. The [2+2]-cycloaddition reaction of diketene with the imine underwent in a highly stereoselective manner, yielding the desired 3,4-trans-3-acetyl-β-lactam (13a) as a major product (diastereoselectivity 7∼10:1). This was elaborated to 4 and 6 in 9 and 6 steps, respectively.

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