Copper-Catalyzed <i>trans</i>-Carbohalogenation of Terminal Alkynes with Functionalized Tertiary Alkyl Halides

A highly <i>trans</i>-selective Cu-catalyzed carbohalogenation including carbobromination, carboiodination, and carbochlorination of terminal alkynes with activated tertiary alkyl halides has been realized, providing quaternary-carbon-containing alkenyl halides in good yields with excellent regio- and stereoselectivity. Meanwhile, an unprecedented alkyne <i>trans</i>-carboalkynylation process has been achieved via the tandem <i>trans</i>-carbohalogenation/Sonogashira coupling reaction, which furnishes highly functionalized 1,3-enynes in a single chemical transformation

Copper-Catalyzed <i>trans</i>-Carbohalogenation of Terminal Alkynes with Functionalized Tertiary Alkyl Halides

A highly <i>trans</i>-selective Cu-catalyzed carbohalogenation including carbobromination, carboiodination, and carbochlorination of terminal alkynes with activated tertiary alkyl halides has been realized, providing quaternary-carbon-containing alkenyl halides in good yields with excellent regio- and stereoselectivity. Meanwhile, an unprecedented alkyne <i>trans</i>-carboalkynylation process has been achieved via the tandem <i>trans</i>-carbohalogenation/Sonogashira coupling reaction, which furnishes highly functionalized 1,3-enynes in a single chemical transformation

Catalyst-Substrate Helical Character Matching Determines the Enantioselectivity in the Ishihara-Type Iodoarenes Catalyzed Asymmetric Kita-Dearomative Spirolactonization

Catalyst design has traditionally focused on rigid structural elements to prevent conformational flexibility. Ishihara’s elegant design of conformationally flexible C2-symmetric iodoarenes, a new class of privileged organocatalysts, for the catalytic asymmetric dearomatization (CADA) of naphthols is a notable exception. Despite the widespread use of the Ishihara catalysts for CADAs, the reaction mechanism remains the subject of debate, and the mode of asymmetric induction has not been well established. Here, we report an in-depth computational investigation of three possible mechanisms in the literature. Our results, however, reveal that this reaction is best rationalized by a fourth mechanism called “proton-transfer-coupled-dearomatization (PTCD)”, which is predicted to be strongly favored over other competing pathways. The PTCD mechanism is consistent with a control experiment and further validated by applying it to rationalize the enantioselectivities. Oxidation of the flexible I(I) catalyst to catalytic active I(III) species induces a defined C2-symmetric helical chiral environment with a delicate balance between flexibility and rigidity. A match/mismatch effect between the active catalyst and the substrate’s helical shape in the dearomatization transition states was observed. The helical shape match allows the active catalyst to adapt its conformation to maximize attractive noncovalent interactions, including I(III)···O halogen bond, N–H···O hydrogen bond, and π···π stacking, to stabilize the favored transition state. A stereochemical model capable of rationalizing the effect of catalyst structural variation on the enantioselectivities is developed. The present study enriches our understanding of how flexible catalysts achieve high stereoinduction and may serve as an inspiration for the future exploration of conformational flexibility for new catalyst designs

Rhodium-Catalyzed 2‑Arylphenol-Derived Six-Membered Silacyclization: Straightforward Access toward Dibenzooxasilines and Silicon-Containing Planar Chiral Metallocenes

The C/Si switch strategy has been regarded as a useful and efficient strategy for the discovery of drugs and materials. Thus, development of a methodology to access diverse silacycles is of great significance and in great demand. Among these, C–H bond silylation provides a powerful and straightforward synthetic method to form diverse silacycles in an atom- and step-economical fashion. However, C–H bond silylation has not been used to access any six-membered silicon-bridged π-conjugated scaffolds and enantioselective six-membered C–H silylation has never been presented. Herein, we successfully accessed diverse six-membered π-conjugated dibenzooxasilines via C–H bond silylation and investigated their photophysical properties. Furthermore, we realized enantioselective six-membered C–H siylation to directly afford planar chiral metallocene oxasilolanes with high ee (up to 95% ee). We also demonstrated the synthetic usefulness of dibenzooxasilines and planar chiral metallocene-fused benzooxasilolines as valuable synthetic intermediates via diverse additional transformations. Moreover, six-membered silicon-bridged ladder π-conjugated systems were designed and rapidly constructed by using our methods. The “isomerization” and “silicon” effects on molecular geometries and photophysical properties were also evaluated in detail