Palladium-Catalyzed Bicycloaromatization of -(Alkynyl)styrenes with Alkynes: Economical Access to Chrysene Derivatives.

Herein, a palladium-catalyzed bicycloaromatization of -(alkynyl)styrenes with alkynes is reported. In this protocol, the 6-- cyclization of -(alkynyl)styrenes is followed by deprotonation to complete the first cycloaromatization, and then, a regioselective alkyne insertion/C-H activation occurs to achieve the second cycloaromatization, resulting in atom- and step-economical syntheses of polysubstituted chrysenes. Notably, the products can be further used to construct π-extended arenes using the Scholl reaction.

A Cascade C(sp)-H Annulation Involving C(alkyl),C(alkyl)-Palladacycle Intermediates.

C-H bond functionalization involving C,C-palladacycle intermediates provides a unique platform for developing novel reactions. However, the vast majority of studies have been limited to the transformations of C(aryl),C-palladacycles. In sharp contrast, catalytic reactions involving C(alkyl),C(alkyl)-palladacycles have rarely been reported.

Norbornene Derivatives-Controlled Palladium-Catalyzed Divergent Synthesis of Dibenzo[,]cycloheptenones and Fluorenones from Aryl Iodides and α-Oxocarboxylic Acids.

A palladium-catalyzed divergent cascade decarboxylative annulation of aryl iodides and α-oxocarboxylic acids using norbornene (NBE) derivatives as a controlled switch is reported. When NBE is used as a mediator, fluorenones are synthesized with moderate to excellent yields via a Catellani reaction that involves sequential -C-H arylation and -decarboxylative acylation of aryl iodides. Employing oxanorbornadiene (ONBD) instead of NBE enables the assembly of dibenzo[,]cycloheptenones by a retro-Diels-Alder reaction rather than the release of an ONBD.

Versatile Tetrasilane for Time-Controlled Palladium-Catalyzed Divergent Synthesis of Silacycles via C-H Activation.

Transition-metal-catalyzed intermolecular annulation of silicon reagents with organic molecules is still underdeveloped due to the scarcity of silicon reagent types and their diverse reactivity. Herein, a readily accessible silicon reagent (octamethyl-1,4-dioxacyclohexasilane) has been developed for divergent synthesis of silacycles via time-controlled palladium-catalyzed cascade C-H silacyclization. This protocol enables the rapid and selective transformation of acrylamides into spirosilacycles with different ring sizes, including benzodioxatetrasilecines, benzooxadisilepines, and benzosiloles, in moderate to good yields through a time switch.

Pd(II)-Catalyzed Synthesis of Polycyclic Heteroarenes via an Aminopalladation/C-H Activation/Dealkylation/Decarboxylative Cyclization Cascade.

Until now, cascade reactions involving five-membered ,-palladacycles rely heavily on Pd(0)-catalyzed C-H functionalization of aryl halides initiated by carbopalladation. Herein, we report a novel Pd(II)-catalyzed cascade decarboxylative cyclization of -alkynylanilines initiated by aminopalladation. In this protocol, -alkynylanilines undergo sequential aminopalladation, C-H activation, and dealkylation to form ,-palladacycles, which are then trapped by -bromobenzoic acids or 8-bromo-1-naphthoic acid to produce diverse polycyclic heteroarenes, such as dibenzo[,]carbazoles and multiple arene-fused cyclohepta[1,2-]indoles.

Research advances in palladium-catalysed intermolecular C-H annulation of aryl halides with various aromatic ring precursors.

Transition-metal-catalysed C-H functionalization has emerged as a powerful approach for the transformation of organic molecules due to its high atom and step economy. Palladium-catalysed intermolecular C-H annulation of aryl halides, especially those involving annulation of a five-membered ,-palladacycle with coupling reagents, have attracted considerable attention in the past decades. This review summarizes the progress on palladium-catalysed intermolecular C-H annulation of aryl halides with various aromatic ring precursors.

Chemoselective Transformations of Cyclic β-Bromoacrylic Acids with Palladacycles Formed by Aryl Iodides to Access Fused or Spiro Polycycles.

A palladium-catalyzed chemoselective decarboxylative annulation of different aryl iodides with cyclic β-bromoacrylic acids for the construction of interesting fused and spiro polycycles is disclosed. Notably, cyclic β-bromoacrylic acids can chemoselectively act as C1 or C2 insertion units by the use of different aryl iodides. 2-Iodo--methacryloylbenzamides can undergo a Heck/[4+2] annulation to afford hexahydrodibenzoisoquinoline-4,6(5)-diones.

Double C-S bond formation multiple Csp-H bond cleavage: synthesis of 4-hydroxythiazoles from amides and elemental sulfur under metal-free conditions.

A novel and efficient approach for the synthesis of 4-hydroxythiazoles from amides and elemental sulfur has been developed. In the presence of PO, DMSO and HMPA, this metal-free protocol proceeds smoothly and tolerates a spectrum of functional groups. Furthermore, this strategy involves the process of double Csp-S bond formation through the cleavage of multiple Csp-H bonds for the first time.

MeSiSiMe(O Bu): a disilane reagent for the synthesis of diverse silacycles Brook- and retro-Brook-type rearrangement.

Herein, a readily available disilane MeSiSiMe(O Bu) has been developed for the synthesis of diverse silacycles Brook- and retro-Brook-type rearrangement. This protocol enables the incorporation of a silylene into different starting materials, including acrylamides, alkene-tethered 2-(2-iodophenyl)-1-indoles, and 2-iodobiaryls, the cleavage of Si-Si, Si-C, and Si-O bonds, leading to the formation of spirobenzosiloles, fused benzosiloles, and π-conjugated dibenzosiloles in moderate to good yields. Preliminary mechanistic studies indicate that this transformation is realized by successive palladium-catalyzed bis-silylation and Brook- and retro-Brook-type rearrangement of silane-tethered silanols.

Atmosphere-Controlled Palladium-Catalyzed Divergent Decarboxylative Cyclization of 2-Iodobiphenyls and α-Oxocarboxylic Acids.

A novel palladium-catalyzed divergent decarboxylative cyclization of 2-iodobiphenyls and α-oxocarboxylic acids utilizing the atmosphere as a controlled switch is reported. Under the protection of a nitrogen atmosphere, tribenzotropones are synthesized by a [4 + 3] decarboxylative cyclization. Employing a palladium/O system enables a [4 + 2] decarboxylative cyclization to assemble triphenylenes.

Assembly of Furazan-Fused Quinolines via an Expeditious Metal-Free [2+2+1] Radical Tandem Cyclization Process.

A [2+2+1]-NO-segment-incorporating heteroannulative cascade is described. This versatile method, particularly using modular cyanoarylated ketimine substrates, allows efficient access to structurally diversified quinolines embedded with an oxadiazole core. This metal-free protocol proceeds smoothly at 30 °C, offers easy manipulation of substituents on the quinoline moiety, and tolerates a spectrum of functional groups.

α-Bromoacrylic Acids as C1 Insertion Units for Palladium-Catalyzed Decarboxylative Synthesis of Diverse Dibenzofulvenes.

Herein α-bromoacrylic acids have been employed as C1 insertion units to achieve the palladium-catalyzed [4 + 1] annulation of 2-iodobiphenyls, which provides an efficient platform for the construction of diverse dibenzofulvenes. This protocol enables the formation of double C(aryl)-C(vinyl) bonds via a C(vinyl)-Br bond cleavage and decarboxylation. It is particularly noteworthy that the method features a broad substrate scope, and various interesting frameworks, such as bridged ring, fused (hetero)aromatic ring, and divinylbenzene, can be successfully incorporated into the products.

α-Oxocarboxylic Acids as Three-Carbon Insertion Units for Palladium-Catalyzed Decarboxylative Cascade Synthesis of Diverse Fused Heteropolycycles.

A novel palladium-catalyzed decarboxylative cascade cyclization for the assembly of diverse fused heteropolycycles by employing α-oxocarboxylic acids as three-carbon insertion units is reported. This protocol enables the synthesis of isoquinolinedione- and indolo[2,1-]isoquinolinone-fused benzocycloheptanones in moderate to good yields by the use of different aryl iodides, including alkene-tethered 2-iodobenzamides and 2-(2-iodophenyl)-1-indoles. Notably, the approach achieves simultaneous construction of both six- and seven-membered rings via sequential intramolecular carbopalladation, C-H activation, and decarboxylation.

Palladium-Catalyzed [4 + 3] or [2 + 2 + 3] Annulation via C-H Activation and Subsequent Decarboxylation: Access to Heptagon-Embedded Polycyclic Aromatic Hydrocarbons.

The construction of a seven-membered ring in the polycyclic aromatic hydrocarbon skeleton remains a notoriously difficult but attractive challenge. Herein a novel palladium-catalyzed [4 + 3] decarboxylative annulation of 2-iodobiphenyls with 2-(2-halophenyl)acrylic acids is reported, which provides an efficient approach for assembling various tribenzo[7]annulenes via a C-H activation and decarboxylation process. Moreover, tribenzo[7]annulenes can be also synthesized via a [2 + 2 + 3] decarboxylative annulation strategy by employing readily available 1,2-halobenzenes, phenylboronic acids, and 2-(2-halophenyl)acrylic acids.

Catalyst- and Additive-Free Method for the Synthesis of 2-Substituted Benzothiazoles from Aromatic Amines, Aliphatic Amines, and Elemental Sulfur.

Under catalyst- and additive-free conditions, a novel, convenient, environmentally friendly method was developed for the synthesis of 2-substituted benzothiazoles via the three-component one pot reaction from aromatic amines, aliphatic amines, and elemental sulfur. The reaction achieves double C-S and one C-N bond formations via cleavage of two C-N bonds and multiple C-H bonds. Furthermore, the mechanism research shows that DMSO acts as an oxidant in the cyclization reaction.

KS as Sulfur Source and DMSO as Carbon Source for the Synthesis of 2-Unsubstituted Benzothiazoles.

We describe a three-component reaction of -iodoanilines with KS and DMSO that provides 2-unsubstituted benzothiazoles in moderate to good isolated yields with good functional group tolerance. Electron-rich aromatic amines and -phenylenediamines instead of -iodoanilines provided 2-unsubstituted benzothiazoles and 2-unsubstituted benzimidazoles with and without KS under similar conditions. Notably, DMSO plays three vital roles: carbon source, solvent, and oxidant.

Iodine-Catalyzed Three-Component Cascade Reaction for the Synthesis of Substituted 2-Phenylnaphtho[1,3]selenazoles under Transition-Metal-Free Conditions.

An efficient molecular iodine-catalyzed three-component cascade reaction for the construction of 2-phenylnaphtho[2,1-]selenazoles from naphthalen-2-amine, aldehydes, and selenium powder has been developed. The present approach has the advantages of metal-free conditions, simple operation, and available raw materials. Moreover, the mechanism of the study proved that the reaction underwent a radical process.

Palladium-Catalyzed Domino Heck/C-H Activation/Decarboxylation: A Rapid Entry to Fused Isoquinolinediones and Isoquinolinones.

A new palladium-catalyzed tandem cyclization of various alkene-tethered aryl iodides has been presented. In this protocol, -bromobenzoic acids are employed as coupling parters to achieve the insertion of aromatic rings by the cleavage of C(sp)-Br and decarboxylation, thus assembling various dibenzoisoquinolinediones and dibenzoisoquinolinones. In addition, a seven-membered ring can be constructed by the use of 8-bromo-1-naphthoic acid.

Palladium-Catalyzed Cascade Cyclization of Alkene-Tethered Aryl Halides with -Bromobenzoic Acids: Access to Diverse Fused Indolo[2,1-]isoquinolines.

A novel palladium-catalyzed cascade cyclization of alkene-tethered aryl halides with -bromobenzoic acids is described, which provides an efficient avenue for building various fused hexacyclic scaffolds containing indolo[2,1-]isoquinoline in moderate to excellent yield. The method enables the construction of three C-C bonds through an intramolecular carbopalladation, C-H activation, and a decarboxylation sequence. Furthermore, dihydrocyclohepta[]naphthalene-fused indolo[2,1-]isoquinolines can be synthesized in moderate yield by constructing a seven-membered ring.

NBE-Controlled Palladium-Catalyzed Interannular Selective C-H Silylation: Access to Divergent Silicon-Containing 1,1'-Biaryl-2-Acetamides.

A novel palladium-catalyzed interannular selective C-H silylation of 1,1'-biaryl-2-acetamides is described. The combination of palladium catalyst with copper oxidant enables meta- or ortho-selective C-H silylation by employing hexamethyldisilane as a trimethylsilyl source, which relies on the control of NBE derivatives as a switch, thus providing straightforward access to divergent silicon-containing 1,1'-biaryl-2-acetamides.

Transition-Metal-Free Sulfuration/Annulation of Alkenes: Economical Access to Thiophenes Enabled by the Cleavage of Multiple C-H Bonds.

A novel, atom economical, and transition-metal-free strategy for the synthesis of thiophenes from substituted buta-1-enes with potassium sulfide has been presented. The reaction achieves double C-S bond formations via cleavage of multiple C-H bonds and provides an efficient approach to access various functionalized thiophenes. Moreover, the strategy can also be used for the synthesis of thiophenes from 1,4-diaryl-1,3-dienes.

Palladium/Norbornene Chemistry: Synthesis of Norbornene-Containing Arylsilanes Involving Double C-Si Bond Formation.

A novel palladium-catalyzed three-component cascade reaction of aryl halides with norbornene and hexamethyldisilane has been described, which allows the simultaneous construction of two C-Si bonds and one C-C bond. The method achieves ortho C-H functionalization of aryl halides through the formation of the five-membered palladacycle, leading to norbornene-containing arylsilanes.

A radical cyclization cascade of 2-alkynylbenzonitriles with sodium arylsulfinates.

A convenient radical cyclization cascade procedure for the construction of sulfonated indenones from 2-alkynylbenzonitriles and sodium arylsulfinates has been explored under mild reaction conditions. The present methodology offers a low-cost and operationally straightforward approach to synthesizing various sulfonated indenones in moderate to good yields by simple use of cheap sodium persulfate as an oxidant and environmentally benign water as a co-solvent.

Palladium-Catalyzed Synthesis of Triphenylenes via Sequential C-H Activation and Decarboxylation.

A novel tandem intermolecular decarboxylative coupling reaction of o-bromobenzoic acids and aryl iodides has been developed. The method affords a range of unsymmetrically triphenylenes and displays unique regioselectivity and broad substrate scope. Mechanistically, palladium/norbornene-catalyzed C-H activation and subsequent double decarboxylative coupling reactions were involved.

Palladium-Catalyzed Tandem Reaction of Three Aryl Iodides Involving Triple C-H Activation.

A novel palladium-catalyzed tandem reaction of N-(2-iodoaryl)acrylamides with two aryl iodides for the synthesis of spirooxindole has been achieved. The reaction underwent the process of triple C-H activation and four C-C bond formations based on the double trapping of transient spirocyclic palladacycles which are obtained through remote C-H activation.