Palladium/Norbornene-Catalyzed Decarbonylative Difunctionalization of Thioesters

Enabling Aryl Chloride-Mediated Palladium/Norbornene Cooperative Catalysis

While the palladium/norbornene (Pd/NBE) cooperative catalysis has become increasingly useful for arene functionalization, its substrate scope has been mainly restricted to reactive aryl iodides and bromides. Despite being a more available and attractive feedstock, common aryl chlorides have not been used as substrates for the Pd/NBE catalysis. Herein, we report the first general Pd/NBE-catalyzed vicinal difunctionalization of aryl chlorides. Enabled by the combination of secondary-amide-substituted NBEs and XPhos ligand, diverse aryl chlorides can now undergo successful ortho alkylation, amination, and acylation with different ipso terminations, including olefination, hydrogenation, and alkynylation. To show the utility of this method, late-stage derivatizations of complex bioactive compounds and sequential functionalizations of polyhaloarenes have been achieved.

Site-Selective Ortho/Ipso C-H Difunctionalizations of Arenes using Thianthrene as a Leaving Group

Site-selective ortho/ipso C-H difunctionalizations of aromatic compounds were designed to afford polyfunctionalized arenes including challenging 1,2,3,4-tetrasubstituted ones (62 examples, up to 97 % yields). To ensure the excellent regioselectivity of the process while keeping high efficiency, an original strategy based on a "C-H thianthenation/Catellani-type reaction" sequence was developed starting from simple arenes. Non-prefunctionalized arenes were first regioselectively converted into the corresponding thianthrenium salts. Then, a palladium-catalyzed, norbornene (NBE)-mediated process allowed the synthesis of ipso-olefinated/ortho-alkylated polyfunctionalized arenes using a thianthrene as a leaving group (revisited Catellani reaction). Pleasingly, using a commercially available norbornene (NBE) and a unique catalytic system, synthetic challenges known for the Catellani reaction with aryl iodides were smoothly and successfully tackled with the "thianthrenium" approach. The protocol was robust (gram-scale reaction) and was widely applied to the two-fold functionalization of various arenes including bio-active compounds. Moreover, a panel of olefins and alkyl halides as coupling partners was suitable. Pleasingly, the "thianthrenium" strategy was successfully further applied to the incorporation of other groups at the ipso (CN/alkyl/H, aryl) and ortho (alkyl, aryl, amine, thiol) positions, showcasing the generality of the process.

Palladium/norbornene-catalyzed diversified trifunctionalization of aryl-thianthreniums

A novel Catellani-type conversion is reported using aryl-thianthreniums (aryl-TTs) instead of aryl halides. Three classes of ortho-dual C-H functionalization involving alkylation, amination, and deuterated methylation and five types of ipso-operation including alkenylation, cyanation, methylation, hydrogenation, and alkynylation all proceed well in this procedure. In this conversion, aryl-TTs exhibit satisfactory reactivity and feature the advantage that the leaving TT unit can be recovered. More strikingly, this finding represents a new chemistry conversion of aryl-TTs, wherein contiguous tri-functionalization in a single chemical manipulation is realized.

Synthesis of Biaryl Carboxylic Acids through a Cascade Suzuki-Miyaura Coupling/Friedel-Crafts Alkylation/Lewis-Acid-Catalyzed Rearrangement/Aromatization Process

In this study, we present a series of 1,3-dicarbonyls that can undergo a cascade Suzuki coupling, followed by a Friedel-Crafts reaction to produce molecules containing polycyclic alcohols. These polycyclic alcohols can then be converted into biaryl carboxylic acids through ring-opening rearrangement reactions catalyzed by a Lewis acid. The Friedel-Crafts reaction exhibits selective para-positioning of the hydroxyl group and demonstrates good compatibility with functional groups with a yield of up to 82%. Substrates with substituted hydroxyl groups can also be converted into biaryl carboxylic acids through a Lewis-acid-catalyzed ring-opening rearrangement.

A Practical and Regioselective Strategy for Aromatic C-H Difunctionalization via Site-Selective C-H Thianthrenation

Herein, we present a novel Catellani-type reaction that employed aryl-thianthrenium salts as aryl substrates to trigger the subsequent palladium/norbornene cooperatively catalyzed progress. This strategy can achieve site-selective C-H difunctionalization of aryl compounds without directing groups or a known initiating reagent. A series of functionalized syntheses of bioactive molecules further demonstrated the potential of this strategy.

Construction of Indole-Fused Seven- and Eight-Membered Azaheterocycles via a Tandem Pd/NBE-Catalyzed Decarbonylation and Dual C-H Activation Sequence

Herein, we report the transformation of aromatic acids to indole-fused seven- and eight-membered azaheterocycles. Two C-C bonds are formed via the cleavage of one C-C bond and two C-H bonds. The incorporation of indole moieties into bioactive pharmaceuticals and natural products to construct a medium-sized polyfused heterocycle demonstrates the synthetic utility of the protocol.

Construction of Chalcogenated Methylene Chroman-3-ones via Palladium-Catalyzed Carbocyclization

We report herein the synthesis of exo-chalcogenated methylene chroman-3-ones via palladium-catalyzed intramolecular acyl-chalcogenation of alkyne with thio- and selenoesters. Chalcogen containing tetrasubstituted alkenes are obtained stereoselectively. This protocol tolerates various functional groups and heterocycles, affording the chroman-3-one products in moderate-to-good yields.

Divergent Acyl and Decarbonylative Liebeskind-Srogl Cross-Coupling of Thioesters by Cu-Cofactor and Pd-NHC (NHC = N-Heterocyclic Carbene) Catalysis

Transition-metal-catalyzed cross-coupling reactions of thioesters by selective acyl C(O)-S cleavage have emerged as a powerful platform for the preparation of complex molecules. Herein, we report divergent Liebeskind-Srogl cross-coupling of thioesters by Pd-NHC (NHC = N-heterocyclic carbene) catalysis. The reaction provides straightforward access to functionalized ketones by highly selective C(acyl)-S cleavage under mild conditions. Most crucially, the conditions enable direct functionalization of a range of complex pharmaceuticals decorated with a palette of sensitive functional groups, providing attractive products for medicinal chemistry programs. Furthermore, decarbonylative Liebeskind-Srogl cross-coupling by C(acyl)-S/C(aryl)-C(O) cleavage is reported. Cu metal cofactor directs the reaction pathway to acyl or decarbonylative pathway. This reactivity is applicable to complex pharmaceuticals. The reaction represents the mildest decarbonylative Suzuki cross-coupling discovered to date. The Cu-directed divergent acyl and decarbonylative cross-coupling of thioesters opens up chemical space in complex molecule synthesis.

Siloxane-containing derivatives of benzoic acid: chemical transformation of the carboxyl group

This research presents a scalable method for chemical transformation of Si-containing derivatives of benzoic acid to a wide range of corresponding esters, thioesters, amides, etc. Some of them form HOF-like structures in the crystalline state.