A highly efficient synthesis of the key intermediate 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. ... )-ethyl lactate was found to proceed with a high stereoselectivity similar to that observed for 4i. The formed optically ...