Bi-Jie Li

An efficient organocatalytic method for constructing biaryls through aromatic C–H activation

The direct functionalization of C–H bonds has drawn the attention of chemists for almost a century. C–H activation has mainly been achieved through four metal-mediated pathways: oxidative addition, electrophilic substitution, σ-bond metathesis and metal-associated carbene/nitrene/oxo insertion. However, the identification of methods that do not require transition-metal catalysts is important because methods involving such catalysts are often expensive. Another advantage would be that the requirement to remove metallic impurities from products could be avoided, an important issue in the synthesis of pharmaceutical compounds. Here, we describe the identification of a cross-coupling between aryl iodides/bromides and the C–H bonds of arenes that is mediated solely by the presence of 1,10-phenanthroline as catalyst in the presence of KOt-Bu as a base. This apparently transition-metal-free process provides a new strategy with which to achieve direct C–H functionalization. C–H activation has usually been achieved by transition metal-mediated pathways. Here, a cross-coupling between aryl halides and common arenes mediated by 1,10-phenanthroline as catalyst, in the presence of potassium tert-butoxide as base is described. Such reactions open a new window for achieving C–H activation without the need for transition metal catalysts.

Activation of "Inert" Alkenyl/Aryl CO Bond and Its Application in Cross-Coupling Reactions

Enol and phenol functionalities are very common in organic molecules. Utilization of these materials is very appealing in organic synthesis because they are important alternatives to organohalides in cross-coupling reactions. In this review, we summarize the transition-metal-catalyzed cross-coupling of enol- and phenol-based electrophiles, including phosphates, sulfonates, ethers, carboxylates, and phenolates.

Challenge and progress: palladium-catalyzed sp3 C–H activation

Palladium-catalysis has been broadly applied to sp2 C–H activation. Recently, palladium-catalyzed sp3 C–H activation has also been considered as an important strategy to construct synthetically useful C–C/C–X bonds. Allylic sp3 C–H bonds can be successfully activated by Pd(II) species to produce η3-coordinated palladium species for further transformations, while activation of general sp3 C–H bonds mainly proceeds through directed pathways with the assistance of proper directing groups or initiated by oxidative addition. Various catalytic mechanisms were extensively investigated through either Pd(II)/Pd(0), Pd(II)/Pd(IV) or Pd(0)/Pd(II) catalytic cycles. The challenges faced in this area have also been addressed in this perspective article.

Biaryl Construction via Ni-Catalyzed C-O Activation of Phenolic Carboxylates

Biaryl scaffolds were constructed via Ni-catalyzed aryl C-O activation by avoiding cleavage of the more reactive acyl C-O bond of aryl carboxylates. Now aryl esters, in general, can be successfully employed in cross-coupling reactions for the first time. The substrate scope and synthetic utility of the chemistry were demonstrated by the syntheses of more than 40 biaryls and by constructing complex organic molecules. Water was observed to play an important role in facilitating this transformation.

Rhodium/Copper‐Catalyzed Annulation of Benzimides with Internal Alkynes: Indenone Synthesis through Sequential CH and CN Cleavage

Doubled up: a rhodium(III)/copper(II) system co-catalyzes the annulation of benzimides with internal alkynes for the synthesis of indenones (see scheme; Cp*=C(5) Me(5)). The reaction involves an uncommon nucleophilic addition of a transition-metal-carbon bond to an imide moiety. This novel reaction provides a facile route to synthesize indenones from readily available benzimides and internal alkynes.

Cross Dehydrogenative Arylation (CDA) of a Benzylic CH Bond with Arenes by Iron Catalysis

Hooking up: FeCl(2) catalyzes the efficient cross dehydrogenative arylation of substrates having benzylic C-H bonds (see scheme). High regioselectivity was observed during the cross-coupling between compounds containing aromatic C(sp(2))-H bonds and benzylic C(sp(3))-H bonds. This process is proposed to proceed by single-electron-transfer oxidation and Friedel-Crafts alkylation.

Palladium-Catalyzed Cross-Coupling of Polyfluoroarenes with Simple Arenes

The most efficient method to construct biaryls is the direct dehydrogenative cross-coupling of two different aromatic rings. Such an ideal cross arylation starting from distinct polyfluoroarenes and simple arenes was presented. The selectivity of the cross-coupling was controlled by both of the electronic property of fluoroarenes and steric hindrance of simple arenes. Diisopropyl sulfide was essential to promote the efficacy.

Cross-Coupling of Alkenyl/Aryl Carboxylates with Grignard Reagent via Fe-Catalyzed C−O Bond Activation

Iron-catalyzed cross-coupling of alkenyl/aryl carboxylates with primary alkyl Grignard reagent was described. This reaction brought a new family of electrophiles to iron catalysis. The combination of an inexpensive carboxylate electrophile and an iron catalyst would generate ample advantages.

Nickel-Catalyzed Efficient and Practical Suzuki−Miyaura Coupling of Alkenyl and Aryl Carbamates with Aryl Boroxines

Suzuki-Miyaura coupling of unactivated alkenyl carbamates is described to construct polysubstituted olefins. The developed process is also suitable for heteroaromatic and even electron-rich aromatic carbamates.

N-Directing group assisted rhodium-catalyzed aryl C-H addition to aryl aldehydes.

Direct aryl C-H addition to aryl aldehydes to produce biaryl methanols was reported via Rh catalysis with an N-containing directing group. The method is highly atom-, step-, and redox-economic. The procedure is robust, reliable, and compatible with water and air.