Nucleophile-Dependent Z/E- and Regioselectivity in the Palladium-Catalyzed Asymmetric Allylic C–H Alkylation of 1,4-Dienes
2019
Lin, Hua-Chen | Xie, Pei-Pei | Dai, Zhen-Yao | Zhang, Shuo-Qing | Wang, Pu-Sheng | Chen, Yu-Gen | Wang, Tian-Ci | Hong, Xin | Gong, Liu-Zhu
The asymmetric allylic alkylation (AAA), which features employing active allylic substrates, has historical significance in organic synthesis. The allylic C–H alkylation is principally more atom- and step-economic than the classical allylic functionalizations and thus can be considered a transformative variant. However, asymmetric allylic C–H alkylation reactions are still scarce and yet underdeveloped. Herein, we have found that Z/E- and regioselectivities in the Pd-catalyzed asymmetric allylic C–H alkylation of 1,4-dienes are highly dependent on the type of nucleophiles. A highly stereoselective allylic C–H alkylation of 1,4-dienes with azlactones has been established by palladium-chiral phosphoramidite catalysis. The protocol proceeds under mild conditions and can accommodate a wide scope of substrates, delivering structurally divergent α,α-disubstituted α-amino acid surrogates in high yields and excellent levels of diastereo-, Z/E-, regio-, and enantioselectivities. Notably, this method provides key chiral intermediates for an efficient synthesis of lepadiformine marine alkaloids. Experimental and computational studies on the reaction mechanism suggest a novel concerted proton and two-electron transfer process for the allylic C–H cleavage and reveal that the Z/E- and regioselectivities are governed by the geometry and coordination pattern of nucleophiles.
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