Palladium-catalyzed intramolecular carbopalladation/cyclization cascade: access to polycyclic N-fused heterocycles

An efficient palladium-catalyzed intramolecular carbopalladation/cyclization cascade toward tetra- and pentacyclic N-fused heterocycles has been developed. This transformation proceeds via the palladium-catalyzed coupling of aryl halides with internal propargylic esters or ethers followed by the 5-endo-dig cyclization leading to polycyclic pyrroloheterocycles in moderate to excellent yields.     

Palladium-catalyzed arylation of alpha-methylene-gamma-butyrolactone: 3-benzylfuran-2(5H)-ones vs (Z)-benzylidene-gamma-butyrolactones and their reduction to 3-benzyl-gamma-butyrolactones

[reaction: see text] The palladium-catalyzed arylation of the alpha-methylene-gamma-butyrolactone proceeds in good yields and may be directed toward the synthesis of 3-benzylfuran-2(5H)-ones when the starting aryl iodides contain strongly electron-withdrawing groups. The combined palladium-catalyzed arylation/hydrogenation of the alpha-methylene-gamma-butyrolactone represents a new simple entry into functionalized alpha-benzyl-gamma-butyrolactones.     

Tandem Pd-catalyzed carbonylation and intramolecular vinyl allene Diels-Alder reaction toward galiellalactone analogues

A novel route toward new galiellalactone analogues via a tandem palladium-catalyzed carbonylation and intramolecular Diels-Alder reaction of a dienyne carbonate is presented.     

Approaches toward the total synthesis of the nine-membered thio-lactone core of griseoviridin

Three different approaches toward the synthesis of the macrocyclic thiolactone core of griseoviridin have been studied. Intramolecular palladium-catalyzed thiol coupling and esterification (carboxylate activation) have led to the formation of unexpected rearranged products. An intermolecular palladium-catalyzed thiol/vinyl iodide coupling followed by an esterification (alcohol activation) ultimately led to the nine-membered core of griseoviridin.     

CO2 as Both a Selective Agent and Reaction Media in Palla-dium-Catalyzed Reductive Ullmann-Type Coupling Reaction

Carbon dioxide as both a selective agent and reaction media in the palladium-catalyzed Ullmann-type coupling has been described. The results showed that aryl chlorides could be easily activated in the presence of carbon dioxide and the chemoselectivity shifted toward the palladium-catalyzed Ullmann-type coupling reaction. In liquid carbon dioxide, homocoupling reactions of aryl halides, including less reactive aryl chlorides, were carried out smoothly in moderate to good yields using Pd/C, zinc, and H2O as the catalytic system at room temperature.     

Selectively substituted thiophenes and indoles by a tandem palladium-catalyzed multicomponent reaction

A variety of di- and trisubstituted thiophenes were synthesized by a one-pot palladium-catalyzed ortho-alkylation sequence terminated by either Heck or C-H coupling. Initial results toward the functionalization of indoles are also presented.     

Palladium-catalyzed oxidative carbocyclization/arylation of enallenes

A stereoselective palladium-catalyzed oxidative carbocyclization/arylation of enallenes is described. The reaction shows wide tolerance toward highly functionalized arylboronic acids and results in a cis addition of two carbon moieties to an olefin in good to excellent yields.     

Parallel approach to selective catalysts for palladium-catalyzed desymmetrization of 2,4-cyclopentenediol

[reaction: see text] Work toward the development of a bis-phosphine ligand system for the palladium-catalyzed desymmetrization of meso-diols is reported. A parallel approach using phosphine-containing amino acids and a "representational search" was taken to find a polymer-supported catalyst system. The selectivities reported are comparable to many other polymer-bound asymmetric catalysts.     

Palladium-catalyzed Ullmann-type reductive homocoupling of iodoaryl glycosides

A catalytic synthesis of novel biaryl-linked divalent glycosides was achieved using an electroreductive palladium-catalyzed iodoaryl-iodoaryl coupling reaction. This new method was optimized for the synthesis of divalent biaryl-linked mannopyranosides that was subsequently generalized toward several carbohydrate substrates with yields up to 96%.     

Novel synthetic approach toward (+/-)-beta-cuparenone via palladium-catalyzed tandem Heck cyclization of 1-bromo-5-methyl-1-aryl-hexa-1,5-dien-3-ol derivatives

A novel and convenient synthetic route toward (+/-)-beta-cuparenone and many other sesquiterpene natural product precursors has been developed via palladium-catalyzed tandem Heck cyclization of 1-bromo-5-methyl-1-aryl-hexa-1,5-dien-3-ols. [reaction: see text].     

Second-generation synthesis of salvinorin A

Functionalization toward total synthesis of the hallucinogenic neoclerodane diterpenoid salvinorin A was accomplished via three double sequences: bis-enol triflate synthesis, palladium-catalyzed double carbonylation to the bis-enol triflate, and samarium diiodide-mediated double conjugate reduction. The configuration at C-12 was controlled by chelation-controlled diastereoselective reduction.     

Rhodium-catalyzed multicomponent-coupling reactions involving a carborhodation-cross-coupling sequence

[reaction: see text] A rhodium-catalyzed multicomponent-coupling reaction has been developed that involves a cross-coupling with organohalides as part of the reaction sequence. Through several experiments toward mechanistic investigations, it has also been demonstrated that the reaction most likely proceeds via a carborhodation-oxidative addition-reductive elimination pathway, which clearly contrasts to the corresponding palladium-catalyzed processes.     

A new approach to the bicyclo[3.3.1]nonane framework of huperzine A-like molecules via palladium-catalyzed intramolecular γ-arylation

In our synthetic studies toward huperzine A, a diastereoselective α′-alkylation of the α-amido-γ-methyl hexenone 4 was realized through a dianion intermediate which significantly enhanced the reactivity. Under the attempted Heck reaction conditions, an unexpected and unprecedented palladium-catalyzed intramolecular γ-arylation of 3 was observed, which generated 18 with bicyclo[3.3.1]nonane framework in satisfactory yield.     

Synthesis of 5-arylthiazoles. Comparative study between Suzuki cross-coupling reaction and direct arylation

A facile synthetic route to the new thiazol-5-ylboronic acid pinacol ester was described herein. Its reactivity toward Suzuki cross-coupling reaction was studied to provide various 5-arylthiazoles. A comparative study between Suzuki cross-coupling reactions and palladium-catalyzed C5–H direct arylation on thiazole ring was achieved.     

Addressing challenges in palladium-catalyzed cross-coupling reactions through ligand design

The development of palladium-catalyzed cross-coupling reactions has revolutionized the synthesis of organic molecules on both bench-top and industrial scales. While significant research effort has been directed toward evaluating how modifying various reaction parameters can influence the outcome of a given cross-coupling reaction, the design and implementation of novel ancillary ligand frameworks has played a particularly important role in advancing the state-of-the-art. This Review seeks to highlight notable examples from the recent chemical literature, in which newly developed ancillary ligands have enabled more challenging substrate transformations to be addressed with greater selectivity and/or under increasingly mild conditions. Throughout, the importance and subtlety of ligand effects in palladium-catalyzed cross-coupling reactions are described, in an effort to inspire further development and understanding within the field of ancillary ligand design.     

Palladium-catalyzed oxidative Heck coupling reaction for direct synthesis of 4-arylcoumarins using coumarins and arylboronic acids

An efficient protocol for the direct synthesis of 4-arylcoumarins via palladium-catalyzed oxidative Heck coupling reaction of coumarins and arylboronic acids was developed. 4-Arylcoumarins were obtained in moderate to excellent yields, and the reaction also showed tolerance toward functional groups such as hydro, methoxy, diethylamino, nitro, and chloro groups.     

Predictable and site-selective functionalization of poly(hetero)arene compounds by palladium catalysis

The challenge of achieving selective and predictable functionalizations at C-H bonds with complex poly(hetero)aromatic substrates was addressed by two different approaches. Site-selectivity can be obtained by applying various reaction conditions that are (hetero)arene specific to substrates that contain indoles, pyridine N-oxide, and polyfluorinated benzenes. An experimental classification of electron-rich heteroarenes based on their reactivity toward palladium-catalyzed C-H functionalization was established, the result of which correlated well with the order of reactivity predicted by the DFT-calculated concerted metalation-deprotonation (CMD) pathway. Model substrates containing two reactive heteroarenes were then reacted under general reaction conditions to demonstrate the applicability this reactivity chart in predicting the regioselectivity of the palladium-catalyzed direct arylation and benzylation reactions.     

A highly efficient palladium-catalyzed desulfitative arylation of azoles with sodium arylsulfinates

A highly efficient palladium-catalyzed direct desulfitative arylation of azoles at C2-position has been developed using sodium arylsulfinates as aryl sources. Azoles including benzoxazoles, benzothiazoles, oxazoles, thiazoles, and 1,3,4-oxadiazoles reacted with sodium arylsulfinates smoothly to generate the corresponding products in good to excellent yields, and various substitution patterns were tolerated toward the reaction.     

Palladium-catalyzed direct (hetero)arylation of ethyl oxazole-4-carboxylate: an efficient access to (hetero)aryloxazoles

A straightforward route toward 2-(hetero)arylated and 2,5-di(hetero)arylated oxazoles through regiocontrolled palladium-catalyzed direct (hetero)arylation of ethyl oxazole-4-carboxylate with iodo-, bromo-, and chloro(hetero)aromatics followed by a two-step hydrolysis/decarboxylation sequence was described. The method was applied here to a neat synthesis of two 2,5-di(hetero)aryloxazole natural products, balsoxin and texaline.     

Sequential Pd(II)-Pd(0) catalysis for the rapid synthesis of coumarins

Electrophilic palladium-catalyzed cycloisomerization of brominated aryl propiolates produces brominated coumarins. The brominated coumarins can be diversified by reduction of the Pd(II) catalyst to Pd(0) followed by Suzuki, Sonogashira, Heck, or Hartwig-Buchwald coupling. Thus, a single loading of precatalyst can be used to conduct sequential reactions, allowing the synthesis of functionalized coumarins. Extension of this methodology toward the synthesis of coumarin libraries is discussed.