Due to the high electrophilic nature of azo-dienophiles, azo-Diels–Alder proceeds rapidly even without the need of a catalyst and is therefore regarded as the “click reaction”. This spontaneity causes strong background reaction and poses a daunting challenge to chemists for developing the catalytic asymmetric version. Reported herein is the first catalytic asymmetric dearomative azo-Diels–Alder reaction between2-vinylindoles and triazoledione. This protocol makes use of the high energy barrier of dearomatization to avert the strong background reaction of azo-Diels–Alder reaction, allowing the implementation of the projected reaction at ambient temperature. Density functional theory calculations have been performed to gain insights into the reaction mechanism and the origins of the enantioselectivity. By using this method,a variety of tetracyclic indole derivatives have been readily prepared in good to excellent yields and with excellent diastereo-and enantio–selectivities(33 examples, up to 97% yield and >99% ee, >20:1 dr).
Yu-Hang MiaoZheng-Xu ZhangXu-Yi HuangYuan-Zhao HuaShi-Kun JiaXiao XiaoMin-Can WangLi-Ping XuGuang-Jian Mei
Extensive experimental studies have been performed on the Diels-Alder(DA)reactions in ionic liquids(ILs),which demonstrate that the IL environment can significantly influence the reaction rates and selectivity.However,the underlying microscopic mechanism remains ambiguous.In this work,the multiscale reaction density functional theory is applied to explore the effect of 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM][PF_(6)])solvent on the reaction of cyclopentadiene(CP)with acrolein,methyl acrylate,or acrylonitrile.By analyzing the free energy landscape during the reaction,it is found that the polarization effect has a relatively small influence,while the solvation effect makes both the activation free energy and reaction free energy decrease.In addition,the rearrangement of local solvent structure shows that the cation spatial distribution responds more evidently to the reaction than the anion,and this indicates that the cation plays a dominant role in the solvation effect and so as to affect the reaction rates and selectivity of the DA reactions.
Mesoporous aluminosilica hollow nanospheres were prepared easily,which possess very strong acid site.The heterogeneous catalyst can be utilized in both intramolecular aza-Michael addition cyclization and intermolecular Diels-Alder reaction.The catalyst could be easily recovered and reused.Furthermore,the catalyst could be used in continuous flow chemistry for the uninterrupted synthesis of 2,3-dihydroquinolin-4(1H)-ones,which disclosed the potential application of the present solid catalyst in both academic and industrial syntheses.In addition,the catalyst could be recovered and reused at least 7 times without obvious loss of activity.
LI BaoyanMENG JingjingLI YingdingJIANG LingxiaCHENG TanyuLIU Guohua
