Chiral Lewis Acid-Catalyzed Asymmetric Hetero Diels-Alder Reaction of (<i>E</i>)-2-Oxo-1-phenylsulfonyl-3-alkenes with Vinyl Ethers

Abstract

Abstract (E)-2-Oxo-1-phenylsulfonyl-3-alkenes are effectively activated with the aid of a catalytic amount of chiral titanium reagents in hetero Diels-Alder reactions with vinyl ethers to produce (2R,4R) or (2R,4S)-2,4-cis-2-alkoxy-4-substituted-3,4-dihydro-2H-pyrans in highly endo- and enantioselective manners. The resulting cycloadducts are transformed to 5-substituted (5R)-2-phenylsulfonyl-2-cyclohexen-1-ones which are useful as new chiral building blocks.