Abstract
( E)-1-Phenylsulfonyl-3-alken-2-ones as new hetero 1,3-dienes undergo smooth hereto Diels-Alder reactions with vinyl ethers in the presence of a catalytic amount of Lewis acid such as ZnI 2, Eu(fod) 3, and TiCl 2( i-PrO) 2. The reactions are absolutely endo-selective producing 2,4- cis-3,4-dihydro-2 H- pyrans in excellent yields, the configuration at 3-position depending upon the stereochemistry of the starting vinyl ethers. Reductive ring opening reactions of the 3,4-dihydro-2 H-pyran cycloadducts with Et 3SiH/TiCl 4 lead to 6-alkoxy-l-phenylsulfonyl-2-hexanones, and the sulfonyl-stabilized carbanions derived from the 3,4-dthydro-2 H-pyran cycloadducts are alkylated followed by reductive desulfonylation to give 2,4,6-trisubstituted 3,4-dihydro-2 H-pyran derivatives.
Published Version
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