Merging C–H Vinylation with Switchable 6π-Electrocyclizations for Divergent Heterocycle Synthesis

Abstract

Pyridinium-containing polyheterocycles exhibit distinctive biological properties and interesting electrochemical and optical properties and thus are widely used as drugs, functional materials, and photocatalysts. Here, we describe a unified two-step strategy by merging Rh-catalyzed C–H vinylation with two switchable electrocyclizations, including aza-6π-electrocyclization and all-carbon-6π-electrocyclization, for rapid and divergent access to dihydropyridoisoquinoliniums and dihydrobenzoquinolines. Through computation, the high selectivity of aza-electrocyclization in the presence of an appropriate “HCl” source under either thermal conditions or photochemical conditions is shown to result from the favorable kinetics and symmetries of frontier orbitals. We further demonstrated the value of this protocol by the synthesis of several complex pyridinium-containing polyheterocycles, including the two alkaloids berberine and chelerythrine.

Rhodium‐Catalyzed Oxidative Coupling of Potassium Vinyltrifluoroborate with Arenes: A Direct Access to Functionalized Styrene Derivatives

“…Among the screening of different oxidants, Cu(OAc) 2 was found to be the best choice, and other copper, silver or manganese salts gave relatively lower yield or did not promote the reaction at all (entries 9-17). It was of note that silver additives such as AgOTf, AgBF 4 and AgNTf 2 which exerted a positive influence on the most rhodium and ruthenium-catalyzed CÀ H functionalization, however, slightly suppressed the catalytic activity of this alkenylation reaction and resulted in the desired products in relative lower yields (entries [18][19][20]. Therefore, the best yield of 82% was achieved without any additives (entry 21).…”

“…Subsequently, Yu group developed an efficient Cu‐catalyzed C−H alkenylation with acyclic and cyclic vinyl boronates assisted by oxazoline‐aniline bidentate directing group under mild conditions, which provided a reliable access to multisubstituted alkenes and dienes [19] . More recently, Zhang reported Rh‐catalyzed C−H activation/oxidative Suzuki coupling with two switchable electrocyclizations with high monovinylation selectivity, for rapid and divergent access to dihydropyridoisoquinoliniums and dihydro‐benzoquinolines [20] . Inspired by these pioneering works and in continuation of our interest in the research of C−H alkenylations, [21] we herein describe an unprecedented Rh(III)‐catalyzed highly selective mono‐alkenylation of aromatic C−H bonds with a nontoxic, commercially available potassium vinyltrifluoroborate as vinyl reagent.…”

Research Progress on the Synthesis of Protoberberine Skeleton and Its Anti-inflammatory Activity

“…首 先以水为溶剂, [Cp*Rh(OAc) 2 ]催化底物与氧化鎓叶立 德 31 发生 C-H 键活化/环化反应, 得到芳基异喹啉 33, 含有不同取代基的底物在此步收率约为 40%～80%, 第 二步 C-H 键活化反应 [24] 可采用多聚甲醛亲电取代得到 [23] 或铑催化的乙烯基三氟硼酸钾 38 [25] 亲电 取代活化 C-H 键(Scheme 4d), 四步即可以 23%的总收 率合成巴马汀. 类似的, 胡天惠等 [26] 在 2020 年用频哪 醇乙烯基硼酸酯 43 以 72%收率完成了定向的 C-H 乙 烯基化(Scheme 4e), 以五步 8%的收率合成了小檗碱.…”

Cascade 8π Electrocyclization/Benzannulation to Access Highly Substituted Phenylpyridines

“…To demonstrate the practical utility of this developed method, we carried out the gram-scale reaction, delivering the corresponding product 1d in 77% yield (Scheme a). Additionally, the product 20d could further undergo an intramolecular 6π electrocyclization to afford the structurally more complex tricyclic product e under 254 nm UV-light irradiation (Scheme b). Ligands bearing nitrogen and phosphine are widely used in catalyzing organic reactions, here we designed and synthesized a new ligand through the modification of the product 1d .…”