Zhang-Jie Shi

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.

Pyridinyl Directed Alkenylation with Olefins via Rh(III)-Catalyzed C–C Bond Cleavage of Secondary Arylmethanols

Novel C-C bond cleavage of secondary alcohols through Rh(III)-catalyzed β-carbon elimination directed by a pyridinyl group is reported. A five-membered rhodacycle is proposed as a key intermediate, which undergoes further alkenylation with various olefins. This novel transformation shows high efficiency along with excellent selectivity in mild conditions. A wide range of functionalities are compatible. This study offers a new strategy to carry out C-C bond activation.

Intra/Intermolecular Direct Allylic Alkylation via Pd(II)-Catalyzed Allylic C−H Activation

The first catalytic direct alkylation of allylic C-H bonds via Pd(II)-catalysis is described in the absence of base. Polysubstituted cyclic compounds can also be constructed by the intramolecular direct allylic 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.

Transition metal-catalyzed direct nucleophilic addition of C–H bonds to carbon–heteroatom double bonds

Transition metal-catalyzed direct C–H functionalization has drawn great attention in the past several decades owing to its advantages compared to conventional organic transformations, including higher atom-, step- and cost-economy and the avoidance of tedious prefunctionalization and waste emission. At the current stage, to make the C–H functionalization more applicable, chemists have devoted themselves to expanding the substrate and reaction scope. In the past decade, we exerted ourselves to develop new transformations based on direct C–H functionalization. In this minireview we report on our recent achievements on the addition of C–H bonds to carbonyls and imines. The addition of organometallic reagents, such as Grignard reagents, toward carbon–heteroatom double bonds is one of the most powerful reactions in organic synthesis to produce secondary and tertiary alcohols and amines. This chemistry is broadly used in both laboratory and industry. However, this powerful transformation suffers from some drawbacks: (1) the preparation of initial organohalides from easily available fossil feedstocks is tedious and sluggish; (2) substantial amounts of metal halide salts are emitted as waste; (3) last but not least, the manipulation of organometallic reagents is complicated due to their sensitivity to air and moisture. In contrast, direct insertion of polar double bonds to C–H bonds via transition-metal catalysis is ideal from the viewpoint of atom-, step- and cost-economy and the avoidance of the waste emission, as well as of the complex manipulation of sensitive reagents. Starting from this point, we made a commitment to this project years ago and have made credible achievements in this field. We first carried out Ir-catalyzed addition of pyridinyl C–H bonds to aldehydes promoted by silane, showing an unusual C-3 selectivity. Later on, we developed Rh-catalyzed addition of aryl C–H bonds with aldimines in the absence of any additives with directing strategy with highest atom- and step-economy. The mechanism was investigated in depth by the isolation of key intermediates and systematic thermodynamic and kinetic studies. Such a concept was expanded to the coupling of aryl/alkenyl C–H bonds with aldehydes and imines. Notably, a tandem process of relayed C–H activation/alkyne insertion/cyclization between benzoates/benzimide and alkynes was developed, indicating the potential of the direct coupling of esters and amides with C–H bonds. Ideally, this strategy opens a new window to approach the ideal reactions to produce amines and alcohols from hydrocarbons.