Combined Oxypalladation/CH Functionalization: Palladium(II)-Catalyzed Intramolecular Oxidative Oxyarylation of Hydroxyalkenes

Wacker Oxidation of Methylenecyclobutanes: Scope and Selectivity in an Unusual Setting

Methylenecyclobutanes are found to undergo Wacker oxidation via a semi-pinacol-type rearrangement. Key to a successful process is the use of tert-butyl nitrite as oxidant, which not only enables efficient catalyst turn-over but also ensures high Markovnikov-selectivity under mild conditions. Thus, cyclopentanones (26 examples) can be accessed in an overall good yield and excellent selectivity (up to 97 % yield, generally >99 : 1 ketone:aldehyde ratio). Stereochemical analysis of the reaction sequence reveals migration aptitudes in line with related 1,2-shifts. By introducing a pyox ligand to palladium, prochiral methylenecyclobutanes can be desymmetrized, thus realizing the first enantioselective Wacker oxidation.

Room Temperature C-H Arylation of Benzofurans by Aryl Iodides

A robust method of room temperature direct arylation for benzofuran is reported. This discovery allows for mild arylation by commercially available aryl iodides with complete C-2 regioselectivity and tolerates a range of functional groups, including heat sensitive groups. Mechanistically, a Heck-type oxyarylation product from a direct arylation process is reported as a key piece of evidence for a carbopalladation intermediate.

Selective Palladium-Catalyzed Allenic C-H Bond Oxidation for the Synthesis of [3]Dendralenes

A highly selective palladium-catalyzed allenic C-H bond oxidation was developed, and it provides a novel and straightforward synthesis of [3]dendralene derivatives. A variety of [3]dendralenes with diverse substitution patterns are accessible with good efficiency and high stereoselectivity. The reaction tolerates a broad substrate scope containing various functional groups on the allene moiety, including ketone, aldehyde, ester, and phenyl groups. Also, a wide range of olefins with both electron-donating and electron-withdrawing aryls, acrylate, sulfone, and phosphonate groups are tolerated.

The Application of Copper/Iron Cocatalysis in Cross-Coupling Reactions

For conventional cross-couplings in organic chemistry, precious metal (such as Pd or Rh) complexes have been the preferable choices as catalysts. However, their high cost, toxicity, and potential contamination of products limit their massive applications on some occasions, particularly in the pharmaceutical industry, where close monitoring of the metal contamination of products is required. Therefore, the use of metals that are less expensive and less toxic than Pd or Rh can be greatly advantageous and earth abundant metal (such Fe or Cu) catalysts have shown promise for replacing the precious metals. Interestingly, a certain copper catalyst combined with an iron catalyst displays higher catalytic efficiency than itself in various coupling reactions. Notably, ligand-free conditions make such protocols more useful and practical in many cases. In this account, we summarize the recent progress made in this increasingly attractive topic by describing successful examples, including our own work in the literature, regarding effective copper/iron cocatalysis. In addition, a few examples involving a magnetic and readily recyclable CuFe2 O4 nanoparticle cocatalyst are also included.

Palladium-catalyzed oxidative arylating carbocyclization of allenynes: control of selectivity and role of H₂O

Highly selective protocols for the carbocyclization/arylation of allenynes using arylboronic acids are reported. Arylated vinylallenes are obtained with the use of BF3⋅Et2O as an additive, whereas addition of water leads to arylated trienes. These conditions provide the respective products with excellent selectivities (generally >97:3) for a range of boronic acids and different allenynes. It has been revealed that water plays a crucial role for the product distribution.