(E)-2-Oxo-1-sulfonyl-3-alkenes as new hetero 1,3-dienes undergo smooth hetero Diels-Alder reactions with vinyl ethers in the presence of Eu(fod)3 or TiCl2(i-PrO)2. The reactions are absolutely endo-selective producing 2,4-cis-3,4-dihydro-2H-pyrans in excellent yields, sufficient catalytic cycles being attained. The sulfonyl-stabilized carbanions derived from the cycloadducts are alkylated followed by reductive desulfonylation.
在 Eu(fod)3 或 TiCl2(i-PrO)2 存在下,(E)-2-氧代-1-磺酰基-3-烯作为新的杂 1,3-二烯与
乙烯基醚发生平稳的杂 Diels-Alder 反应。这些反应具有绝对的内选择性,能以极好的产率生成 2,4-顺式-
3,4-二氢-2H-吡喃,并能达到足够的催化循环。环加成物产生的磺酰基稳定的碳阴离子先进行烷基化反应,然后再进行还原脱磺反应。