Lewis Acid-Catalyzed Stereoselective Hetero Diels-Alder Reactions of (E)-1-Phenylsulfonyl-3-alken-2-ones with Vinyl Ethers : Synthetically Equivalent to Stereoselective Michael Type Conjugate Additions

This article summarizes the Lewis acid-catalyzed hetero Diels-Alder reactions of new 1-oxa-1,3-butadienes. (E)-1-Phenylsulfonyl-3-alken-2-ones undergo smooth hetero Diels-Alder reactions with vinyl ethers in the presence of Lewis acid. The reactions are absolutely endo-selective producing 2,4-cis-3,4-dihydro-2H-pyrans, the configuration at 3-position depending upon the stereochemistry of the starting vinyl ethers. This reaction can be successfully extended to the catalytic asymmetric version of hetero Diels-Alder reaction by using chiral titanium reagents. The resulting homochiral dihydropyran cycloadducts are transformed to 2-cyclohexen-1-ones which are useful as new chiral building blocks