A highly efficient synthesis of the keyintermediate 2 of 1β-methylcarbapenems was accomplished in 10 steps and 30% overall yield starting from commercially available ()-methyl 3-hydroxy-2-methylpropionate. The explored synthetic scheme features the addition reaction of diketene with a chiral imine as a key diastereoselective step.
A novel and efficient synthesis of the key intermediate of 1β-methylcarbapenem antibiotics employing [ 2+2 ]-cycloaddition reaction of diketene with a chiral imine
steps and 30 % overall yield. Thus, (S)-3-benzyloxy-2-methylpropanal readily obtainable from (S)-5, was condensed with di-p-anisylmethylamine to afford the chiral imine. The [2+2]-cycloaddition reaction of diketene with the imine was found to proceed in a highly diastereoselective manner, giving the desired 3,4-trans-3-acetyl-β-lactam (max. diastereoselectivity 11-15:1). This was readily elaborated to