Palladium-Catalyzed Aminocarbonylation of Allylic Alcohols

Palladium/Lewis Acid Co-catalyzed Cyclocarbonylation of (2-Aminoaryl)(aryl)methanols: An Access to 3-Aryl-indolin-2-ones

A benign approach to valuable 3-aryl-indolin-2-ones was developed based on palladium(II)/Lewis acid-cocatalyzed cyclocarbonylation of readily available (2-aminoaryl)(aryl)methanols. The protocol features producing water as the only byproduct, mild reaction conditions, and good efficiency, constituting an array of 3-arylindolin-2-ones in yields of 35 to 90%. The reaction can be easily scaled up to the gram scale in good yields.

Regioselective C-H Active Carbonylation via 1,4-Palladium Migration

We report a highly regioselective three-component coupling reaction of styrene, CO gas, and an amine compound to synthesize multisubstituted α,β-unsaturated amides, which involves a palladium-catalyzed sequential 1,4-palladium migration, C(sp²)-H activation, carbonylation, and amination. Salient features of this strategy include the use of 1 atm of CO, excellent stereochemistry, and good functional group tolerance. Further, a series of control experiments and density functional theory calculations were performed to afford some insights for the transfer mechanism.

Palladium-catalyzed dearomative cyclocarbonylation of allyl alcohol for the synthesis of quinolizinones

An approach for the synthesis of quinolizinone with potential bioactivity has been developed via palladium-catalytic dearomative cyclocarbonylation of allyl alcohol. Diverse quinolizinone compounds could be attained with good efficiencies. A feasible reaction pathway could be a successive procedure of allylation, dearomatization, CO insertion and the Heck reaction.

Cobalt-Catalyzed Cross-Couplings between Alkyl Halides and Grignard Reagents

Metal-catalyzed cross-couplings have emerged as essential tools for the construction of C-C bonds. The identification of efficient catalytic systems as well as large substrate scope made these cross-couplings key reactions to access valuable molecules ranging from materials, agrochemicals to active pharmaceutical ingredients. They have been increasingly integrated in retrosynthetic plans, allowing shorter and original route development. Palladium-catalyzed cross-couplings still largely rule the field, with the most popular reactions in industrial processes being the Suzuki and Sonogashira couplings. However, the extensive use of palladium complexes raises several problems such as limited resources, high cost, environmental impact, and frequent need for sophisticated ligands. As a consequence, the use of nonprecious and cheap metal catalysts has appeared as a new horizon in cross-coupling development. Over the last three decades, a growing interest has thus been devoted to Fe-, Co-, Cu-, or Ni-catalyzed cross-couplings. Their natural abundance makes them cost-effective, allowing the conception of more sustainable and less expensive chemical processes, especially for large-scale production of active molecules. In addition to these economical and environmental considerations, the 3d metal catalysts also exhibit complementary reactivity with palladium complexes, facilitating the use of alkyl halide partners due to the decrease of β-elimination side reactions. In particular, by using cobalt catalysts, numerous cross-couplings between alkyl halides and organometallics have been described. However, cobalt catalysis still stays far behind palladium catalysis in terms of popularity and applications, and the expansion of the substrate scope as well as the development of simple and robust catalytic systems remains an important challenge.In 2012, our group entered the cobalt catalysis field by developing a cobalt-catalyzed cross-coupling between C-bromo glycosides and Grignard reagents. The generality of the coupling allowed the preparation of a range of valuable C-aryl and C-vinyl glycoside building blocks. We then focused on the functionalization of saturated N-heterocycles, and a variety of halo-azetidines, -pyrrolidines, and -piperidines were successfully reacted with aryl and alkenyl Grignard reagents under cobalt catalysis. With the objective of preparing valuable α-aryl amides, a cobalt-catalyzed cross-coupling applied to α-bromo amides was studied and then extended to α-bromo lactams. Recently, we also reported an efficient and general cross-coupling involving cyclopropyl- and cyclobutyl-magnesium bromides. This method allows the alkylation of functionalized small strained rings by a range of primary and secondary alkyl halides.

Palladium-Catalyzed Hydride Addition/C-H Bond Activation Cascade: Cycloisomerization of 1,6-Diynes

The use of ammonium halide salts as metal hydride precursors in a new Pd-catalyzed cycloisomerization of 1,6-diynes, which affords unexplored silylated 2-azafluorenes, is reported. This cascade process includes the addition of a Pd-hydride species to a π-system, intramolecular carbopalladation, and C(sp²)-H bond activation. A variety of functional groups are tolerated, and the synthetic utility of the resulting products has been demonstrated by a series of derivatizations.

Featuring Xantphos

This review highlights the use of the bisphosphine ligand group in homogeneous catalysis.

Cobalt-Catalyzed Cross-Coupling of α-Bromo Amides with Grignard Reagents

A cobalt-catalyzed cross-coupling between α-bromo amides and Grignard reagents is disclosed. The reaction is general and allows access to a large variety of α-aryl and β,γ-unsaturated amides. Some mechanistic investigations have been undertaken to determine the nature of the intermediate species.

Direct Palladium-Catalyzed Carbonylative Transformation of Allylic Alcohols and Related Derivatives

A direct, palladium-catalyzed, carbonylative transformation of allylic alcohols for the synthesis of β,γ-unsaturated carboxylic acids has been developed. With formic acid as the CO source, various allylic alcohols were conveniently transformed into the corresponding β,γ-unsaturated carboxylic acids with excellent linear and (E)-selectivity. The reaction was performed under mild conditions; toxic CO gas manipulation and high-pressure equipment were avoided in this procedure.

Efficient Pd-Catalyzed Regio- and Stereoselective Carboxylation of Allylic Alcohols with Formic Acid

Formic acid is efficiently used as a C1 source to directly carboxylate allylic alcohols in the presence of a low loading of palladium catalyst and acetic anhydride as additive to afford β,γ-unsaturated carboxylic acids with excellent chemo-, regio-, and stereoselectivity. The reaction proceeds through a carbonylation process with in situ-generated carbon monoxide under mild conditions, avoiding the use of high-pressure gaseous CO. A bisphosphine ligand with a large bite angle (4,5-bis{diphenylphosphino}-9,9-dimethylxanthene, Xantphos) was found to be uniquely effective for this transformation. The regio- and stereoconvergence of this reaction is ascribed to the thermodynamically favored isomerization of the allylic electrophile in the presence of the palladium catalyst.

The dearomative annulation between N-2-pyridylamidine and CO2 toward pyrido[1,2-a]-1,3,5-triazin-4-ones

A base-promoted dearomative annulation between N-2-pyridylamidine and an atmospheric pressure of CO₂ was developed, affording a series of pyrido[1,2-a]-1,3,5-triazin-4-ones in moderate to excellent yields.

Palladium-catalyzed highly regioselective hydroaminocarbonylation of aromatic alkenes to branched amides

Pd(t-Bu₃P)₂ has been successfully identified as an efficient catalyst for the hydroaminocarbonylation of aromatic alkenes to branched amides under relatively mild reaction conditions.