Regio- and stereochemically controlled formation of hydroxamic acid containing anti- or syn-1,4-cycloalkenols from acylnitroso-derived Diels-Alder adducts

Treatment of acylnitroso hetero Diels-Alder cycloadducts 2 with iron(III) o r copper(II) in an alcohol solvent induces ring opening to afford predomina ntly monocyclic anti-1,4-hydroxamic acids 3. However, treatment of cycloadd ucts 2 with copper(II) in toluene reverses the stereoselectivity of the rin g opening to afford syn-1,4-hydroxamic acids 4. These regio- and stereosele ctive processes separately provide anti-1,4- and syn-1,4-disubstituted cycl opentenes while regenerating a hydroxamic acid moiety, thus enhancing the c hemical versatility of the Diels-Alder cycloadducts.