Metal-Catalyzed Cycloisomerization and Tandem Oxycyclization/Hydroxylation of Alkynols: Synthesis of Nonfused, Spiranic and Fused Oxabicyclic β-Lactams

2-Azetidinone-tethered alkynols, readily prepared from the corresponding aldehydes or ketones, were used as starting materials for the oxycyclization reaction catalyzed by precious metals. AgOAc exclusively affords dihydrofurans, methylenetetrahydrofurans, or methylenetetrahydro-2H-pyrans through specific 5-endo, 5-exo, or 6-exo pathways, respectively. Interestingly, in the presence of a catalytic amount of Pt-II or Au-III salts, cyclization reactions occurred preferentially through a tandem oxycyclization/hydroxylation of alkynols to afford a variety of nonfused, spiranic and fused oxabicyclic beta-lactams in moderate to high yields. Besides, it has been observed that the tandem gold-catalyzed cycloetherification/hydroxylation of a methoxymethyl alkynyl ether can be accomplished.