Selective Synthesis of Pyrazolonyl Spirodihydroquinolines or Pyrazolonyl Spiroindolines under Aerobic or Anaerobic Conditions

α-Carbonyl Rh-Carbenoid Initiated Cascade Assembly of Diazobarbiturates with Alkylidene Pyrazolones for Synthesis of Spirofuropyrimidines

Catalyzed by Rh2(esp)2 (10 mol%) and (±)-BINAP (20 mol%) in DCE at 80 °C, the cascade assembly between diazobarbiturates and alkylidene pyrazolones proceeded readily and produced spiro-furopyrimidines in 38-96% chemical yields. The chemical structure of the prepared spirofuro-pyrimidines was firmly confirmed by X-ray diffraction analysis.

One-Pot Synthesis of Indolin-3-ones Mediated by LiN(SiMe3)2/CsF

Indolin-3-ones are essential heterocycles with wide-ranging biological activities and medicinal values, and therefore, efficient approaches to their synthesis remain in demand. Herein, a novel and operationally simple method to generate indolin-3-ones is reported by using a tandem reaction of N-methylbenzylamines and methyl 2-fluorobenzoates mediated by the LiN(SiMe3)2 and CsF system (34 examples, 30-85% yields). The synthesis of C2-quaternary indolin-3-one further demonstrated the potential practicability of these tandem reactions.

Divergent synthesis of pyrrolizine derivatives through C-H bond functionalization of pyrroles

Presented herein is the synthesis of diversely functionalized pyrrolizines from the reaction of N-alkoxycarbamoyl pyrroles with CF3-ynones. The formation of the product is based on a C-H bond activation-initiated cascade process including N-alkoxycarbamoyl group-directed alkenylation of the pyrrole scaffold followed by simultaneous intramolecular nucleophilic addition along with cleavage and transfer of the directing group. By taking advantage of the rich chemistry of the transferred alkoxycarbamoyl moiety, the products could be transformed into a series of structurally and biologically interesting pyrrolizine derivatives. To our knowledge, this is the first example in which the N-alkoxycarbamoyl unit acted as a transferable and transformable directing group for the divergent synthesis of pyrrolizines.

Synthesis of CF3-Substituted N-Heterocyclic Compounds Based on C-H Activation-Initiated Formal [2 + 3] Annulation Featuring with a Latent Nucleophilic Site

Presented herein is a novel synthesis of CF3-substituted pyrrolo[1,2-a]indole derivatives based on the cascade reactions of N-alkoxycarbamoyl indoles with CF3-ynones. Mechanistically, the formation of a product involves a tandem process initiated by Rh(III)-catalyzed and N-alkoxycarbamoyl group-directed regioselective C2-H alkenylation of the indole scaffold followed by in situ removal of the directing group and intramolecular N-nucleophilic addition/annulation under one set of reaction conditions. To our knowledge, this is the first example in which a N-alkoxycarbamoyl unit initially acts as a directing group for C2-H functionalization of the indole scaffold and is then removed to provide the required reactive NH-moiety for subsequent intramolecular condensation. Moreover, the products thus obtained could be conveniently transformed into structurally and biologically attractive cycloheptenone fused indole derivatives through an acid-promoted cascade transformation. In addition, studies on the activity of selected products against human cancer cell lines demonstrated their potential as lead compounds for the development of novel anticancer drugs.

EMM-Promoted Pd-Catalyzed Solid State Intramolecular Heck-Type Cyclization/Boronation and Suzuki Couplings: Access to Functionalized Indolines

EMM (electromagnetic mill)-promoted Pd-catalyzed solid state intramolecular Heck-type cyclization/boronation and Suzuki couplings are reported. Compared to previous mechanochemistry that constructed one chemical bond through a cross-coupling reaction, this strategy realizes cascade transformation along with multiple chemical bond formation. This conversion does not require organic solvents or additional heating, and it shows a good substrate scope and high functional group tolerance.

Free Amine-Directed Redox Neutral Ruthenium(II) Catalysis toward Regioselective Synthesis of Heterobiaryls

A regioselective coupling of ortho-heteroaryl anilines and 7-oxabenzonorbornadienes has been developed by leveraging free amine-directed redox-neutral Ru(II) catalysis. This protocol facilitates formal C-2 arylation of the indole moiety under mild conditions to offer valuable heterobiaryls in high yields. The reaction displays a broad substrate generality and scalability and retains efficacy in the presence of diverse pharmacophore scaffolds. Moreover, products bearing a free amine group were successfully employed in Mg(NTf2)2-catalyzed double Michael addition cascade, which led to the synthesis of intricate indole- and pyrrole-fused azaheterocycles.

C-H activation-initiated spiroannulation reactions and their applications in the synthesis of spirocyclic compounds

Spirocyclic skeletons are prevalent in natural products, pharmaceuticals and organic functional materials. Meanwhile, transition-metal-catalyzed C-H activation reactions have demonstrated unparalleled advantages such as high efficiency, excellent atom-economy, good chemoselectivity and regioselectivity for the formation of target organic molecules. In recent years, C-H activation reactions have been creatively utilized in the synthesis of spirocyclic compounds. This review summarizes the most recent progress made in C-H activation-initiated spiroannulation reactions and their applications in the construction of structurally diverse and biologically valuable spirocyclic scaffolds by using alkynes, diazo compounds, maleimides, alkenes, quinones and cyclopropenones as the coupling partners.

A highly diastereoselective (5+1) annulation of allenoates and pyrazolones catalyzed by CH3OK

The first (5+1) annulation of allenoates and pyrazolones catalyzed by CH3OK has been reported. A series of spiro-pyrazolone derivatives were obtained as single diastereomers in high yields (≤95%) under mild conditions. The synthetic utility was demonstrated by a scale-up reaction and various transformations of the products. The proposed mechanism suggests that the allenoate works as a 1,5-biselectrophilic 5C synthon for the first time and controlled experiments disclose that K+ plays an important role in the diastereoselectivity-determining step through an eight-membered ring transition state. Also, this 1,5-biselectrophilic allenoate will be able to act as a 5C synthon for (5+n) annulation.

Synthesis of Naphtho[1',2':4,5]furo[3,2-b]pyridinones via Ir(III)-Catalyzed C6/C5 Dual C-H Functionalization of N-Pyridyl-2-pyridones with Diazonaphthalen-2(1H)-ones

Presented herein is an unprecedented synthesis of naphtho[1',2':4,5]furo[3,2-b]pyridinones via Ir(III)-catalyzed C6/C5 dual C-H functionalization of N-pyridyl-2-pyridones with diazonaphthalen-2(1H)-ones. This protocol forms C-C and C-O bonds in one pot in which diazonaphthalen-2(1H)-ones serve as bifunctional reagents, providing both alkyl and aryloxy sources. To the best of our knowledge, this is the first example of an Ir(III)-catalyzed synthesis of the title compounds by using diazonaphthalen-2(1H)-ones as bifunctional substrates. Notably, this method features operational simplicity, good functional group tolerance, high efficiency, and high atom economy.