Palladium-catalyzed Annulation Reaction Research Articles

Computational Insights into Palladium-Catalyzed Site-Selective Anilide and Benzamide-Type [3+2] Annulation via Double C-H Bond Activation.

The mechanism of palladium-catalyzed annulation reactions of benzamide- and anilide-type aromatic systems with maleimides is investigated using density functional theory. Double C-H bond activation is key to forming the desired annulation product. The first C-H bond activation for anilide- and amide-type ligands can occur at the ortho and benzylic C-H bonds, while the second C-H activation occurs at the meta carbon of the aromatic rings. For the anilide-type system, ortho and benzylic C-H bond activations occur via four- and five-membered palladacycles, respectively. In contrast, for the benzamide-type system, ortho and benzylic C-H bond activations occur via five- and six-membered palladacycles, respectively. The energy span model suggests that the initial C-H bond activation step at the benzylic position determines the turnover frequency for both anilide- and benzamide-type systems. Energy decomposition analysis and distortion-interaction/activation-strain analyses are employed to understand the electronic and steric factors controlling the turnover frequency-determining transition state.

Palladium-Catalyzed Synthesis of Indanone via C-H Annulation Reaction of Aldehydes with Norbornenes.

A novel methodology for the synthesis of indanone derivates has been developed. The palladium-catalyzed annulation reaction of o-bromobenzaldehydes with norbornene derivatives is achieved through extremely concise reaction processes. The indanone skeleton was established directly via C-H activation of the aldehyde group under a mild reaction condition. This method is simple and practical, which simplified the traditional synthesis method for the rapid construction of indanone.

Palladium-Catalyzed Stitching of 1,3-C(sp3)-H Bonds with Dihaloarenes: Short Synthesis of (±)-Echinolactone D.

Palladium-catalyzed C(sp3)-H functionalization presents an efficient strategy to construct a variety of carbon-carbon bonds. However, application of this approach toward the preparation of five-membered benzo-fused carbocycles via the most simplifying C-H activation logic has not been realized. In this Article, we report a palladium-catalyzed annulation reaction between gem-dimethyl-containing amides and 1-bromo-2-iodoarenes that effectively constructs two Calkyl-Caryl bonds and provides access to a variety of five-membered benzo-fused compounds. In this transformation, the dihaloarene is stitched to the gem-dimethyl moiety via two sequential β-C(sp3)-H arylations utilizing the differential reactivity of the 1,2-difunctionalized electrophile. This annulation reaction is enabled by a dual-ligand system comprising of an N-acyl glycine and a pyridine-3-sulfonic acid that synergistically promotes the palladium stitching and provides the bicyclic products. This method displays a broad substrate scope and shows excellent amide compatibility. We also demonstrate the synthetic potential of this annulation by synthesizing echinolactone D.

1,2-Palladasilacyclobutene: The Missing Link in the Pd-Catalyzed Annulation of Alkynes for the Silirene-to-Silole Transformation.

The palladium-catalyzed annulation reaction of alkynes enables an attractive approach to siloles. Their access from silirenes and terminal alkynes proved rather general, involving reactive intermediates that have remained elusive to date. Starting from 1,2-bis(3-thienyl)silirene as a source of photochromic siloles, the mechanism of the annulation reaction has been revisited, and palladasilacyclobutenes resulting from the activation of the silirene could be isolated and thoroughly characterized (NMR, X-ray, and DFT). Their role as reactive intermediates and their fate in the course of the reaction were also studied in situ. In combination with in-depth DFT calculations, a clearer picture of the mechanism and the reactive key species is disclosed.

Palladium-catalyzed (3 + 2) annulations of 1,3-bis-electrophilic motifs: straightforward synthesis of functionalized pyrrolidines

Here we have developed a new 1,3-bis-electrophilic motif, which was applied in palladium-catalyzed (3 + 2) annulation reactions for the construction of functionalized pyrrolidines in good yields.

Palladium-catalyzed oxidative annulation of N-(8-quinolinyl) aryl carboxamides with 1-aryl-2-tosyloxy ethanones

A novel and facile palladium-catalyzed annulation reaction between N-(8-quinolinyl) aryl carboxamides and 1-aryl-2-tosyloxy ethanones was herein demonstrated. The practical transformation took place readily in the presence of Pd(OAc)2 without any ligands, offering the desired 3-aryl-2-(8-quinolinyl) isoquinolin-1(2H)-ones with good functional groups tolerance (29 examples) and high efficiencies (up to 90% yields). The mechanism of the protocol was proposed to take place through a C-H/N-H activation pathway, which was verified by the control reactions.

Synthesis of Tribenzo[b,d,f]azepines via Palladium-Catalyzed Annulation Reaction of 2-Iodobiphenyls with 2-Halogenoanilines.

A palladium-catalyzed annulation reaction of 2-iodobiphenyls with 2-halogenoanilines has been developed. A variety of 2-iodobiphenyls and 2-halogenoanilines can undergo this transformation. Diversified tribenzo[b,d,f]azepine derivatives can be synthesized in moderate to excellent yields according to this method.

Dithienylethene-Based Photochromic Siloles: A Straightforward and Divergent Synthetic Strategy.

A straightforward synthetic methodology for the preparation of photochromic siloles based on the dithienylethene motif is developed. It relies upon an efficient palladium-catalyzed annulation reaction of a 2,3-bis(3-thienyl)-silirene with terminal alkynes in mild conditions. The reaction is functional group-tolerant and can be performed in high yields with a variety of functional terminal alkynes. It can even be extended to a polymeric polypropargylmethacrylamide (PPMA) substrate affording the corresponding photochromic polymer with different degree of photochromic unit incorporation by simply adjusting the polymer/ silirene stoichiometric ratio.

Recent advances in annulation reactions based on zwitterionic π-allyl palladium and propargyl palladium complexes

Carbocyclic and heterocyclic compounds could be constructed through the palladium-catalyzed annulation reactions of zwitterionic π-allyl palladium or propargyl palladium complexes with unsaturated electrophiles.

Palladium-Catalyzed [5 + 1] Annulation of Salicylic Acid Derivatives and Propargylic Carbonates

Abstract A palladium-catalyzed annulation reaction between salicylic acid derivatives and propargylic carbonates via the cleavage of a propargylic carbon–oxygen bond is described. This rare annulation reaction uses propargylic compounds as the C1 component for heterocyclic products and can be applied to the preparation of unique five- or six-membered cyclic compounds. The corresponding products contain a fully substituted allylic carbon and the reaction is characterized by high functional-group tolerance.

Tetrachlorinated Polycyclic Aromatic Dicarboximides: New Electron-Poor π-Scaffolds and NIR Emitters by Palladium-Catalyzed Annulation Reaction.

Herein we report a palladium-catalyzed annulation reaction consisting of a Suzuki-Miyaura cross-coupling and a C-H arylation cascade for the synthesis of tetrachlorinated polycyclic aromatic dicarboximides (PADIs). This convergent synthetic route afforded a broad series of hitherto unknown electron-deficient PADIs under optimized reaction conditions by coupling of a dibromo-tetrachloro-perylene dicarboximide with different polycyclic aromatic hydrocarbon (PAH) boronic acid pinacol esters in up to 89 % yields. The new PADI compounds show broad absorption in the visible range and some of them emit in the near-infrared (NIR) region. Cyclic and square wave voltammetric studies revealed that these tetrachlorinated PADIs are more electron-deficient than a non-chlorinated reference compound and they possess lower lying frontier orbitals. Thus, the newly synthesized electron-poor PADIs are potential n-type semiconductors. Moreover, these chlorinated PADIs are interesting building blocks for the construction of large π-extended arrays by metal-mediated coupling reactions.

A General Synthetic Route to Polycyclic Aromatic Dicarboximides by Palladium-Catalyzed Annulation Reaction.

Here we report a general method for the synthesis of polycyclic aromatic dicarboximides (PADIs) by palladium-catalyzed annulation of naphthalene dicarboximide to different types of aromatic substrates. Reaction conditions were optimized by systematic variation of ligand, solvent, and additive. It was shown that solvent has a decisive effect on the yield of the reaction products, and thus 1-chloronaphthalene as solvent afforded the highest yield. By applying the optimized reaction conditions, a broad series of planar carbo- and heterocycle containing PADIs were synthesized in up to 97% yield. Moreover, this approach could be applied to curved aromatic scaffold to achieve the respective bowl-shaped PADI. Two-fold annulation was accomplished by employing arene diboronic esters, affording polycyclic aromatic bis(dicarboximides). The optical and electrochemical properties of this broad series of PADIs were explored as well.

Synthesis of 9,10-Phenanthrenes via Palladium-Catalyzed Aryne Annulation by o-Halostyrenes and Formal Synthesis of (±)-Tylophorine.

A novel palladium-catalyzed annulation reaction of in situ generated arynes and o-halostyrenes has been developed. This methodology affords moderate to excellent yields of substituted phenanthrenes and is tolerant of a variety of functional groups such as nitrile, ester, amide, and ketone. This annulation chemistry has been successfully applied to the formal total synthesis of a biologically active alkaloid (±)-tylophorine.

Efficient synthesis of rigid ladder polymers via palladium catalyzed annulation.

We report a new method to synthesize rigid ladder polymers using efficient palladium catalyzed annulation reactions with low catalyst loading (1 mol %). Rigid ladder polymers with benzocyclobutene backbone linkages can be synthesized from copolymerization of readily accessible aryl dibromides and norbornadiene or polymerization of AB type monomers bearing norbornene and aryl bromide or triflate moieties. High molecular weight (10-40 kDa) rigid ladder polymers can be obtained with complete monomer conversions. Diverse monomers also gave different, fixed ladder polymer conformations. The ladder polymers exhibited excellent thermal stability, high carbonization yield, and large intrinsic porosity.

Synthesis of 1,2-Disubstituted Acenaphthylenes by Palladium-Catalyzed Annulation Reactions of Dibromoarenes with Internal Alkynes

A simple and versatile route to 1,2-disubstituted acenaphthylenes has been developed. The method involves palladium-catalyzed annulation of 1,8-dibromonaphthalene or 5,6-dibromoacenaphthylene with an internal alkyne, and does not require any organometallic reagent. A range of 1,2-disubstituted acenaphthylenes and 5,6-disubstituted 1,2-dihydrocyclopenta[f,g]acenaphthylenes were prepared in moderate to good yields. The method provides a rapid and simple route to dibenzo[j,l]fluoranthene through an ­Ullmann coupling.

ChemInform Abstract: Regioselective Construction of Indene Skeletons by Palladium‐Catalyzed Annulation of Alkynylborates with o‐Iodophenyl Ketones.

A palladium-catalyzed annulation reaction of alkynylborates with o-iodophenyl ketones to form indenes is described. Highly substituted indene skeletons are efficiently constructed with site-specific installation of the substituents.

A facile access to substituted indoles utilizing palladium catalyzed annulation under microwave enhanced conditions

A facile access to differently substituted indoles using palladium catalyzed annulation reactions under microwave enhanced conditions has been achieved. A highly active and efficient catalytic system PdCl2/(A-taphos) for the synthesis of indole via palladium catalyzed ring annulation of ortho iodo anilines and aldehydes has been developed.

Palladium-catalyzed annulation reactions of methyl o-halobenzoates with azabicyclic alkenes: a general protocol for the construction of benzo[c]phenanthridine derivatives

The annulation reaction of methyl o-halobenzoates with azabicyclic alkenes proceeds efficiently to give the corresponding benzo[c]phenanthridine derivatives in good to excellent yields using a developed base-free methodology based on our preliminary studies. Thirty-seven application examples validate the compatibility of the present strategy with different groups, particularly with the electron-deficient ones, that are difficult to access using other traditional methods. In addition, annulation reactions with non-symmetric azabicyclic alkenes are achieved in high regioselectivity.

Palladium-Catalyzed Annulation Reactions for Diastereoselective Cyclopentene Synthesis

Palladium-catalyzed annulation reactions of conjugate acceptors and allenyl boronic ester provide substituted cyclopentenes in high yields and, where applicable, diastereoselectivities. This method provides rapid assembly of building blocks for natural product synthesis, including polycyclic lactone and lactam products. Reactions are hypothesized to initiate by conjugate addition of a nucleophilic propargylpalladium complex.

ChemInform Abstract: Prop-2-ynylic Carbonates as a1,a2 Synthons in Palladium Catalyzed Annulation Reactions with Bifunctional Nucleophiles.

ChemInform Abstract: Prop-2-ynylic Carbonates as a1,a2 Synthons in Palladium Catalyzed Annulation Reactions with Bifunctional Nucleophiles.