Stereoselective route to oxetanocin carbocyclic analogues based on a [2+2] photocycloaddition to a chiral 2(5H)-furanone

The synthesis of the trisubstituted cyclobutane 7, which is a suitable precursor for the preparation of oxetanocin carbocyclic analogues, is described. The key step involves a regio- and diastereoselective [2 + 2] photochemical reaction of ketene diethyl acetal with (S)-5-pivaloyloxymethyl-2(5H)-furanone, 3. As an application of this methodology, (-)-cyclobut-A has been prepared from the intermediate 7.