Solid-Phase [2+2] Cycloadditions between Chlorosulfonyl Isocyanate and Chiral Vinyl Ethers

Abstract

Vinyl ethers 10, 23, and 33 were attached to Wang resin through the p-oxyphenylsulfonyl linker. The [2+2] cycloadditions between chlorosulfonyl isocyanate and the polymer-bound vinyl ethers 12, 24, and 34, followed by intramolecular alkylation of the β-lactam nitrogen atom, gave mixtures of the corresponding diastereomeric clavams 8/9 and 21/22 or the oxacephams 31/32, accompanied by the oxirane 7 or the oxetane 30, respectively. This cyclization/cleavage step was performed in the presence of the strong organic bases BEMP and DBU. The corresponding reaction sequences performed in solution provided the oxabicyclic β-lactams without the accompanying anhydrosugars. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)