Phosphine-Promoted Tandem Intermolecular Diels-Alder Reactions with Pentadienyl 4-Nitrobenzoate as a Diene Precursor.
Le ZhangYe LiuChao-Xu LiLei ZhuGuo-Yin XiongShi-Lu FanJian-Jun DaiHua XiaoPublished in: Organic letters (2023)
A phosphine-promoted tandem Diels-Alder reaction using pentadienyl 4-nitrobenzoate (α-vinyl MBH adduct) as a diene precursor with 3-olefinic oxindoles or CF 3 -activated ketones as dienophiles has been developed. The reaction proceeds through the formation of a pentadienyl phosphonium intermediate via S N 2'' addition, which acts as both a D-A diene and a precursor for the exomethylene moiety. This method offers a metal-free and step-efficient approach for synthesizing exomethylene-bearing spirooxindoles and dihydropyrans, which are privileged structures found in natural products.
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