Palladium/Copper‐Cocatalyzed Oxidative Amidobrominations of Alkenes

In the presence of LiBr, a palladium/copper combination catalyzes dehydrogenative amidobrominations of acrylates with NH‐sulfoximines, leading to N‐vinylated products by dual NH/CH coupling, followed by oxidative enamide bromination. Mechanistically, the domino process is proposed to involve palladium(II) species as key intermediates. First synthetic applications of the products have been demonstrated.     

Synthesis of Strained γ‐Lactams by Palladium(0)‐Catalyzed C(sp3)−H Alkenylation and Application to Alkaloid Synthesis

A variety of strained α‐alkylidene‐γ‐lactams were synthesized by palladium(0)‐catalyzed intramolecular C(sp³)?H alkenylation from easily accessible acyclic and monocyclic bromoalkene precursors. These lactams are valuable intermediates for accessing various classes of mono‐ and bicylic alkaloids containing a pyrrolidine ring, as illustrated with the synthesis of an advanced model of the marine natural product plakoridine A and of the indolizidine alkaloid δ‐coniceine.     

O‐Alkyl S‐3,3‐Dimethyl‐2‐oxobutyl Dithiocarbonates as Versatile Sulfur‐Transfer Agents in Radical C(sp3)?H Functionalization

Boiling of the title compounds in ethereal solvents or cycloalkanes in the presence of a radical initiator leads to radical C(sp³)? H functionalization, by which a sulfur atom is introduced into the ethereal solvents at the oxygenated carbon atom or into the cycloalkanes. Both acyclic and cyclic ethers, such as [18]crown‐6 and [D₈]THF, undergo the sulfur transfer. The reaction is useful for the synthesis of monothioacetals, thiols, and sulfides from simple starting materials.     

A Heterogeneous‐Catalyst‐Based,Microwave‐Assisted Protocol for the Synthesis of 2,2′‐Bipyridines

A new method of preparing 2,2′‐bipyridines with short reaction times by using microwave assistance and heterogeneous catalysts has been developed. With a Negishi‐like protocol, it was found that Ni/Al₂O₃–SiO₂ afforded 2,2′‐bipyridine products in up to 86 % yield in 1 h. Palladium supported on alumina also provided yields of 2,2′‐bipyridines comparable to those seen for homogeneous PEPPSI^TM (1,3‐diisopropylimidazol‐2‐ylidene)(3‐chloropyridyl)palladium(II)dichloride) and tetrakis(triphenylphosphanyl)palladium complexes.     

Palladium‐Catalyzed Intramolecular Reductive Cross‐Coupling of Csp2Csp3 Bond Formation

A Pd‐catalyzed efficient reductive cross‐coupling reaction without metallic reductant to construct a Csp²?Csp³ bond has been reported. A Pd^IV complex was proposed to be a key intermediate, which subsequently went through double oxidative addition and double reductive elimination to produce the cross‐coupling products by involving Pd^0/II/IV in one transformation. The oxidative addition from Pd^II to Pd^IV was partially demonstrated to be a radical process by self‐oxidation of substrate without additional oxidants. Furthermore, the solvent was proved to be the reductant for this transformation through XPS analysis.     

Transition‐Metal‐Mediated and ‐Catalyzed C−F Bond Activation by Fluorine Elimination

The activation of carbon–fluorine (C?F) bonds is an important topic in synthetic organic chemistry. Metal‐mediated and ‐catalyzed elimination of β‐ or α‐fluorine proceeds under milder conditions than oxidative addition to C?F bonds. The β‐ or α‐fluorine elimination is initiated from organometallic intermediates having fluorine substituents on carbon atoms β or α to metal centers, respectively. Transformations through these elimination processes (C?F bond cleavage), which are typically preceded by carbon–carbon (or carbon–heteroatom) bond formation, have been increasingly developed in the past five years as C?F bond activation methods. In this Minireview, we summarize the applications of transition‐metal‐mediated and ‐catalyzed fluorine elimination to synthetic organic chemistry from a historical perspective with early studies and from a systematic perspective with recent studies.     

Microwave‐Assisted Palladium‐Catalyzed Direct Arylation of 1,4‐Disubstituted 1,2,3‐Triazoles with Aryl Chlorides

Treatment of 1,4‐disubstituted 1,2,3‐triazoles with aryl chlorides in the presence of potassium carbonate under palladium catalysis and microwave irradiation at 250 °C for 15 min leads to arylation of the triazole at the 5‐position. A variety of functional groups, including ester and hydroxy groups, are compatible. The procedure is suitable for the regioselective preparation of trisubstituted triazoles. Microwave irradiation accelerates the reaction, thus allowing the rapid synthesis of trisubstituted triazoles, which are difficult to synthesize selectively.     

Nickel‐Catalyzed Umpolung Arylation of Ambiphilic α‐Bromoalkyl Boronic Esters

A nickel‐catalyzed reductive arylation of ambiphilic α‐bromoalkyl boronic esters with aryl halides is described. This platform provides an unrecognized opportunity to promote the catalytic umpolung reactivity of ambiphilic reagents with aryl halides, thus unlocking a new cross‐coupling strategy that complements existing methods for the preparation of densely functionalized alkyl‐substituted organometallic reagents from simple and readily accessible precursors.     

Palladium‐catalyzed cyclization of β‐bromo‐α,β‐unsaturated ketones with arylhydrazines leading to 3‐substituted 1‐aryl‐1 H‐pyrazoles

β‐Bromo‐α,β‐unsaturated ketones are condensed with arylhydrazines to form hydrazones, which are in situ intramolecularly cyclized into 3‐substituted 1‐aryl‐1 H‐pyrazoles under a catalytic system of Pd(OAc)₂/1,3‐bis(diphenylhosphino)propane (dppp)/NaO^tBu. Copyright © 2012 John Wiley & Sons, Ltd.     

Iridium‐Catalyzed Intramolecular Methoxy C−H Addition to Carbon–Carbon Triple Bonds: Direct Synthesis of 3‐Substituted Benzofurans from o‐Methoxyphenylalkynes

Catalytic hydroalkylation of an alkyne with methyl ether was accomplished. Intramolecular addition of the C?H bond of a methoxy group in 1‐methoxy‐2‐(arylethynyl)benzenes across a carbon–carbon triple bond took place efficiently either in toluene at 110 °C or in p‐xylene at 135 °C in the presence of an iridium catalyst. The initial 5‐exo cyclization products underwent double‐bond migration during the reaction to give 3‐(arylmethyl)benzofurans in high yields.     

Syntheses of α‐Amino Acids by Using CO2 as a C1 Source

The incorporation of CO₂ into organic compounds is currently one of the most active research topics in organic chemistry, because CO₂ is an abundant, inexpensive, nontoxic, and renewable C1 source. However, CO₂ is also a thermodynamically stable and kinetically inert gaseous compound, and as such, special strategies are required to activate CO₂ and incorporate it into organic compounds. In particular, because the carbon atom adjacent to the nitrogen atom of amine derivatives is positively charged, umpolung carboxylation, which is a difficult chemical process, should be considered for the production of α‐amino acids by using CO₂. In this Minireview, we summarize recent synthetic methods for α‐amino acids that use CO₂ as a carboxylic acid unit.