Corinne Gosmini

Reductive Cross‐Coupling Reactions between Two Electrophiles

Reductive cross-electrophile coupling reactions have recently been developed to a versatile and sustainable synthetic tool for selective C-C bond formation. The employment of cheap and abundant electrophiles avoids the pre-formation and handling of organometallic reagents. In situ reductive coupling is effected in the presence of a transition-metal catalyst (Ni, Co, Pd, Fe) and a suitable metallic reductant (Mn, Zn, Mg). This Concept article assesses the current state of the art and summarizes recent protocols with various combinations of alkyl, alkenyl, allyl, and aryl reagents and highlights key mechanistic studies.

Cobalt‐Catalyzed Formation of Symmetrical Biaryls and Its Mechanism

Effective devotion: An efficient cobalt-catalyzed method devoted to the formation of symmetrical biaryls is described avoiding the preparation of organometallic reagents. Various aromatic halides functionalized by a variety of reactive group reagents are employed. Preliminary DFT calculations have shown that the involvement of a Co(I)/Co(III) couple is realistic at least in the case of 1,3-diazadienes as ligands (FG = functional group).

Cobalt-Catalyzed Electrophilic Amination of Arylzincs with N-Chloroamines

Roles reversed: An efficient cobalt-catalyzed electrophilic amination of arylzinc reagents has been achieved. A variety of functionalized arylzincs and N-chloroamines were coupled under mild conditions (see scheme). Both secondary and tertiary arylamines were obtained in moderate to excellent yields.

Cobalt-catalysed synthesis of highly substituted styrene derivatives via arylzincation of alkynes.

A new two-step procedure was developed by carbozincation of internal and terminal alkynes to synthesise highly functionalised vinylzinc bromides. Various tri and tetrasubstituted alkenes were prepared in moderate to good yields under mild reaction conditions in a stereo-selective manner. This methodology represents an interesting alternative to previously known methods.

Room-Temperature Palladium-Catalyzed Negishi-Type Coupling: A Combined Experimental and Theoretical Study

An air-stable, bulky electron-accepting phosphine ligand (phosphabarrelene) allows the easy reduction of a Pd(II) precursor to a Pd(0) complex, highly active in room-temperature Negishi-type cross-coupling. DFT calculations show that the use of the electron-accepting ligand favors both transmetalation (TM) and reductive-elimination (RE) processes (see scheme; OA = oxidative addition).

Cobalt-Catalyzed Enantio- and Diastereoselective Intramolecular Hydroacylation of Trisubstituted Alkenes

Enantio- and diastereoselective synthesis of trans-2,3-disubstituted indanones is achieved by intramolecular hydroacylation of 2-alkenylbenzaldehydes bearing trisubstituted alkenyl groups under cobalt-chiral diphosphine catalysis. Notably, a high level of enantioselectivity is induced regardless of the stereochemistry (E/Z ratio) of the alkenyl group of the starting material. Deuterium-labeling experiments shed light on the productive reaction pathways of the E- and Z-isomers.

Cobalt-Catalyzed Esterification of Amides

The first cobalt-catalyzed amide activation of N-Boc-amides, and their conversion into esters, is reported here. This new methodology presents a very practical process that does not require an inert atmosphere, uses an inexpensive cobalt catalyst, and proceeds under mild reaction conditions. This catalytic system has a broad substrate scope and has been shown to be highly efficient, with catalyst loadings as low as 1 mol %.

Cobalt‐Catalyzed Reductive Cross‐Coupling Between Styryl and Benzyl Halides

A simple and efficient protocol for the direct reductive cross-coupling between alkenyl and benzyl halides using a Co/Mn system has been developed. This reaction proceeds smoothly in the presence of [CoBr2 (PPh3 )2 ] as the catalyst, with NaI as an additive in acetonitrile with a broad scope of functionalized alkenyl and benzyl halides. Different functional groups are tolerated on both coupling partners, thus, significantly extending the general scope of transition-metal-catalyzed benzylation of alkenyl halides. Moderate to excellent yields were also obtained. From a mechanistic point of view, a radical chain mechanism was proposed. This reaction is stereospecific and some studies suggest the retention of the double-bond configuration.

Characterization of the ultraviolet-visible photoproducts of thiophanate-methyl using high performance liquid chromatography coupled with high resolution tandem mass spectrometry-Detection in grapes and tomatoes.

UV-visible irradiation of thiophanate-methyl (TM) led to the formation of nine photoproducts that were characterized by high performance liquid chromatography coupled with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Although carbendazime has been reported in the literature to be the major metabolite and photoproduct of thiophanate-methyl, it was not detected in this study. However, an isomer of carbendazime referred as PP2, which was unambiguously characterized owing to CID experiments, was found in great abundance. Grape berries and cherry tomatoes treated with aqueous solutions of thiophanate-methyl were submitted to irradiation under laboratory conditions. TM and PP2 were detected in both peel and flesh of berries. The ability of TM and PP2 to pass through the fruit skin has been shown to be highly compound and matrix dependent. In vitro bioassays on Vibrio fischeri bacteria showed that the global ecotoxicity of the TM solution increases significantly with the irradiation time. PP2 should likely contribute to this ecotoxicity enhancement since in silico estimations for Daphnia magna provide a LC50 value seven times lower for PP2 than for the parent molecule.

N-Boc-amides in cross-coupling reactions

Since 2015, the use of amides as electrophilic partners in cross-coupling reactions has experienced exponential growth. Diverse amide derivatives have been studied and among them N-Boc-amides have shown good activities towards various cross-coupling reactions and presents, in our view, an important synthetic usefulness. This review describes the recent developments of these chemical transformations involving N-Boc-amides.