Palladium-Catalyzed Formal (3 + 2) Cycloaddition Reactions of 2‑Nitro-1,3-enynes with Vinylaziridines, -epoxides, and -cyclopropanes

A two-step Pd-catalyzed (3 + 2) cycloaddition/HNO2 elimination reaction sequence has been developed to give novel cyclic 1,3-dien-5-yne systems from Pd-stabilized zwitterionic 1,3-dipoles and 2-nitro-1,3-enyne substrates. The process is highly atom-efficient and tolerates the reaction of 2-vinyloxirane, 1-tosyl-2-vinylaziridine, and diethyl 2-vinylcyclopropane-1,1-dicarboxylate derived 1,3-dipoles with a variety of 2-nitro-1,3-enyne substrates. The stereochemistry of the intermediate (3 + 2) cycloadducts was determined by single crystal X-ray analysis. Furthermore, a selective kinetic elimination of the cycloadduct with an antiperiplanar relationship between the NO2 group and the participating hydrogen was demonstrated, allowing for efficient isolation of a single diastereoisomer of the cycloadduct.

本研究开发了一种两步钯催化(3+2)环加成/亚硝酸消除串联反应，可由钯稳定的两性离子1,3-偶极体与2-硝基-1,3-烯炔底物制备新型环状1,3-二烯-5-炔体系。该过程具有优异的原子经济性，可兼容2-乙烯基环氧乙烷、1-对甲苯磺酰基-2-乙烯基氮丙啶以及2-乙烯基环丙烷-1,1-二羧酸二乙酯衍生的1,3-偶极体与多种2-硝基-1,3-烯炔底物的反应。中间体(3+2)环加成产物的立体化学通过单晶X射线衍射分析得以确定。此外，当硝基与参与氢处于反叠构象时，环加成产物可发生选择性动力学消除，从而能够高效分离得到单一非对映异构体的环加成产物。