A highly stereoselective synthesis of the 1β-methylcarbapenem key intermediate from (R)-3-hydroxybutyric acid

(3R,4R)-4-Acetoxy-3-[(R)-1-(formyloxy)ethyl]-2-azetidinone 6 could be prepared highly stereoselectivity from (R)-3-hydroxybutyric acid by employing the [2+2]-cycloaddition reaction of chlorosulfonyl isocyanate with the 2H,4H-1,3-dioxin derivative and the Baeyer-Villiger reaction accompanying novel cleavage of the acetal moiety. The Reformatsky reaction of 6 with sterically crowded 3-(2-bromopropionyl)-2-oxazolidone derivatives readily afforded the title key intermediate after sequential chemical manipulations.