STEREOCONTROLLED SYNTHESIS OF 1-OXABICYCLIC BETA-LACTAM ANTIBIOTICS VIA [2+2]CYCLOADDITION OF ISOCYANATES TO SUGAR VINYL ETHERS

[2 + 2]Cycloaddition of chlorosulfonyl and trichloroacetyl isocyanates to sugar vinyl ethers affords the corresponding azetidin-2-ones in mo derate to good yields, Diastereofacial differentiation in these reacti ons is sterically dependent and usually provides excellent configurati on control at C-4 of the azetidin-2-one ring, Deprotection of the amid e nitrogen in those adducts, followed by suitable transformations of t he sugar part, enables construction of a variety of beta-lactam struct ures.