Palladium-catalyzed Coupling Process Research Articles

Selective palladium-catalyzed functionalization of α-methylene butanolides

We describe an efficient and selective functionalization of α-methylene-γ-butyrolactone. The two-step sequence involves the preparation of bromomethylene butyrolactone 2 in good yield prior to a palladium-catalyzed coupling process. The latter allowed the installation of aryl, alkenyl, and alkynyl groups under Suzuki-Miyaura, Heck, and Sonogashira cross-coupling conditions. The reaction sequences involving Pd(dppf)Cl2-CsF, Pd(OAc)2-PPh3-Ag2CO3, Pd(PPh4)4-CuI-Et3N as the corresponding catalytic systems allow the preparation of an unprecedented panel of α-unsaturated substituted butyrolactones 4–16 ranging from moderate to excellent yields. In all cases, the E-configuration of the exo-double bond is retained from the starting materials to the targets, regardless of the nature of the substituent introduced.

Solution-phase synthesis of a diverse library of benzisoxazoles utilizing the [3 + 2] cycloaddition of in situ-generated nitrile oxides and arynes.

A library of benzisoxazoles has been synthesized by the [3 + 2] cycloaddition of nitrile oxides with arynes and further diversified by acylation/sulfonylation and palladium-catalyzed coupling processes. The eight key intermediate benzisoxazoles have been prepared by the reaction of o-(trimethylsilyl)aryl triflates and chlorooximes in the presence of CsF in good to excellent yields under mild reaction conditions. These building blocks have been used as the key components of a diverse set of 3,5,6-trisubstituted benzisoxazoles.

Solution-Phase Synthesis of a Highly Substituted Furan Library

A library of furans has been synthesized by iodocyclization and further diversified by palladium-catalyzed coupling processes. The key intermediate 3-iodofurans have been prepared by the electrophilic iodocyclization of 2-iodo-2-alken-1-ones in the presence of various nucleophiles in good to excellent yields under mild reaction conditions. These 3-iodofurans are the key components for library generation through subsequent elaboration by palladium-catalyzed processes, such as Suzuki-Miyaura, Sonagashira, Heck, aminocarbonylation, and carboalkoxylation chemistry to afford a diverse set of 2,3,4,5-tetrasubstituted furans.

Palladium-Catalyzed Four-Membered Ring Annelation Reactions at Dibenzobarrelene

A palladium-catalyzed coupling process of dibenzobarrelene withannelated aryl halides leads to special benzocyclobutenes, resemblingDiels-Alder adducts of antiaromatic benzocyclobutadieneswith anthracene. Moderate steric pressure in intermediary five-memberedpalladacycles seems to be decisive for this type of transformation.

Efficient Synthesis of Phenanthridinone Derivatives via a Palladium-Catalyzed Coupling Process

A palladium-mediated domino reaction was developed to conveniently synthesize phenanthridinone derivatives. Phosphine ligand 1 strongly promotes the domino process, which includes aryl-aryl coupling and C-N bond formations concomitant with a deamidation reaction. The versatility and applicability to a broad range of substrates make this reaction useful for the development of bioactive derivatives. [reaction: see text].

Novel N‐Aryl and N‐Heteroaryl Sulfamide Synthesis via Palladium Cross‐Coupling.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Elucidating reactivity differences in palladium-catalyzed coupling processes: the chemistry of palladium hydrides.

This communication describes a series of studies directed at obtaining a better understanding of the Heck reaction. For the first time, the postulated palladium-hydride intermediate (L2PdHX) in the catalytic cycle of the Heck arylation has been identified. In addition, this study establishes that the base-mediated Pd(0)-regeneration step (L2PdHX --> PdL2) of the cycle can be kinetically slow and thermodynamically unfavorable and that the process is remarkably sensitive to the structure of L (PCy3 vs P(t-Bu)3). Finally, this investigation demonstrates that, for certain catalyst systems, slow rates of Heck arylation can be correlated with reluctant reductive elimination of L2PdHX, furnishing a possible rationalization for Brønsted-base (Cs2CO3 vs Cy2NMe) and ligand (PCy3 vs P(t-Bu)3) effects that have been observed.

Novel N-aryl and N-heteroaryl sulfamide synthesis via palladium cross coupling.

A novel and efficient synthesis of N-aryl and N-heteroaryl sulfamides via an intermolecular palladium-catalyzed coupling process has been developed. The reactions proceeded with good to excellent yields and were tolerant of a wide range of functional groups. [reaction: see text]

Palladium‐Catalyzed Coupling Reactions of Aryl Chlorides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Palladium-catalyzed coupling reactions of aryl chlorides.

Collectively, palladium-catalyzed coupling reactions represent some of the most powerful and versatile tools available to synthetic organic chemists. Their widespread popularity stems in part from the fact that they are generally tolerant to a large number of functional groups, which allows them to be employed in a wide range of applications. However, for many years a major limitation of palladium-catalyzed coupling processes has been the poor reactivity of aryl chlorides, which from the standpoints of cost and availability are more attractive substrates than the corresponding bromides, iodides, and triflates. Traditional palladium/triarylphosphane catalysts are only effective for the coupling of certain activated aryl chlorides (for example, heteroaryl chlorides and substrates that bear electron-withdrawing groups), but not for aryl chlorides in general. Since 1998, major advances have been described by a number of research groups addressing this challenge; catalysts based on bulky, electron-rich phosphanes and carbenes have proved to be particularly mild and versatile. This review summarizes both the seminal early work and the exciting recent developments in the area of palladium-catalyzed couplings of aryl chlorides.

Annulated ring-systems by domino-heck-aldol-condensation and domino-Heck-Michael-addition processes

A palladium catalyzed coupling process of functionalized aryl bromides with allylic alcohols results in 5-membered ring annulation, whereas with homoallylic alcohols 6-membered rings are formed.

Kinetic resolution of epoxides by chiral organoaluminum catalyst short synthesis of (-)-C 16 juvenile hormone

The use of chiral organoaluminum reagent as a catalyst to resolve simple ketoepoxides is explored. The optically pure ketoepoxide 10 was recovered after 80% conversion. The recovered pure epoxide is a useful chiral building block in the synthesis of chiral terpenes. The method applies for the short asymmetric synthesis of the juvenile hormone by the synthetic route which depends on the palladium-catalyzed coupling process.