Catalytic Asymmetric [8+3] Annulation Reactions of Tropones or Azaheptafulvenes with meso‐Aziridines

Abstract

Highly enantioselective [8+3] high-order cycloaddition reactions of tropones or azaheptafulvenes with meso-aziridines were achieved by a desymmetrization/annulation process in the presence of chiral N,N'-dioxide/Mg(OTf) complex. The corresponding tetrahydrocyclohepta[b][1,4]oxazines and tetrahydro-1H-cyclohepta- [b]-pyrazines were obtained in good yields (66-98 %) with excellent diastereo- and enantioselectivities (>19:1 d.r., 90-96 % ee). A possible transition state model was proposed to elucidate the origin of chiral induction based on the control experiments and X-ray crystal structure of the catalyst.

Asymmetric Catalytic Concise Synthesis of Hetero-3,3′-Bisoxindoles for the Construction of Bispyrroloindoline Alkaloids

“…The stereocontrol of this coupling reaction was considered based on the previous studies on the catalyst structures 47,48 and the outcome of this reaction process. A diastereo-and enantioselective nucleophilic attack model (Figure 1) for generating major isomers was suggested.…”

Synthesis of Substituted Tropones and Advancement for the Construction of Structurally Significant Skeletons

“…In the year 2018, Xiaohua Liu, Xiaoming Feng, and co‐researchers developed the [8+3] cycloaddition involving meso ‐aziridine and tropone or azaheptafulvenes (Scheme 21) (Table 3). [88] This catalytic asymmetric cycloaddition reaction occurred via desymmetrization/annulation process. N,N’‐dioxide/Mg(OTf) 2 complex was used as a catalyst to produce good yields (66–98 %) of the corresponding cycloadducts, tetrahydrocyclohepta[ b ][1,4]oxazines and tetrahydro‐1 H ‐cyclohepta‐[ b ]‐pyrazines with excellent enantioselectivity of 90–99 % ee and diastereoselectivity of >19 : 1.…”

Magnesium Catalysis in Asymmetric Synthesis

“…43,44 Very recently, the Feng group also reported elegant asymmetric [8 + 3] cycloadditions of tropones or azaheptafulvenes (14-9) by using dioxide/Mg(II) as the catalyst, and as expected, obtained the corresponding polycyclic adducts with good results. 45 In recent studies, Feng and coworkers used a dioxide/Mg(II) system to activate alkylidene malonates, leading to the a-addition of isocyanides to activated olefins. The authors reacted a-isocyanoacetamides with alkylidene malonates, which delivered a series of enantioenriched oxazole derivatives with high enantioselectivities.…”