Transfer Hydrogenative Coupling Research Articles

Dynamic Kinetic Resolution of 2‐(Quinolin‐8‐yl)Benzaldehydes: Atroposelective Iridium‐Catalyzed Transfer Hydrogenative Allylation

AbstractAn atroposelective Ir‐catalyzed dynamic kinetic resolution (DKR) of 2‐(quinolin‐8‐yl)benzaldehydes/1‐naphthaldehydes by transfer hydrogenative coupling of allyl acetate is disclosed. The allylation reaction takes place with simultaneous installation of central and axial chirality, reaching high diastereoselectivities and excellent enantiomeric excesses when ortho‐cyclometalated iridium‐DM‐BINAP is used as the catalyst. The racemization of the substrates occurs through a designed transient Lewis acid‐base interaction between the quinoline nitrogen atom and the aldehyde carbonyl group.

Dynamic Kinetic Resolution of 2-(Quinolin-8-yl)Benzaldehydes: Atroposelective Iridium-Catalyzed Transfer Hydrogenative Allylation.

An atroposelective Ir-catalyzed dynamic kinetic resolution (DKR) of 2-(quinolin-8-yl)benzaldehydes/1-naphthaldehydes by transfer hydrogenative coupling of allyl acetate is disclosed. The allylation reaction takes place with simultaneous installation of central and axial chirality, reaching high diastereoselectivities and excellent enantiomeric excesses when ortho-cyclometalated iridium-DM-BINAP is used as the catalyst. The racemization of the substrates occurs through a designed transient Lewis acid-base interaction between the quinoline nitrogen atom and the aldehyde carbonyl group.

Selective transfer hydrogenation coupling of nitroaromatics to azoxy/azo compounds by electron-enriched single Ni-N4 sites on mesoporous N-doped carbon

Developing an active and selective non-precious metal catalyst to boost transfer hydrogenation coupling (THC) of nitroaromatics to their corresponding aromatic azoxy/azo compounds is desirable, but remains a great challenge. Herein, for the first time, we report a facile microwave-assisted pyrolysis strategy to successfully prepare the unique Ni-N4 sites on open-mouth quasi-stellate mesoporous N-doped carbon (NC) with enlarged electronic density led by the shortening Ni-N coordination distance (h-Ni1N4 /NC) by microwave heating the 1,10-phenanthroline-Ni complex coated stellate mesoporous SiO2 followed by alkali-leaching, distinct from the single-atom Ni-N5 sites on NC (l-Ni1N5/NC) prepared by a conventional pyrolysis method, unambiguously confirmed by diverse characterization technologies and DFT calculations. More importantly, h-Ni1N4/NC efficiently boosts the selective THC of nitrobenzene to azoxy under mild conditions using isopropyl alcohol (IPA) as hydrogen donor, showing much higher turnover frequency (33.4 h−1) and selectivity (95.6%) than traditional l-Ni1N5/NC catalyst (13.5 h -1°/85.3%) and supported Ni nanoparticles on NC (10.1 h -1, no detectable azoxy). Kinetic experiments and theoretical calculations reveal that the enriched electron density of Ni atoms in single Ni-N 4 sites efficiently lowers activation barrier for IPA/nitrobenzene activation and azoxy formation over h-Ni1N4/NC, which contributes to the outstanding catalytic performance for azoxybenzene production. Moreover, the approach was extended to the transformation of diverse nitroaromatics to corresponding azoxy compounds with high yield. In addition, by varying reaction parameters, h-Ni1N4/NC catalyst enables highly active and selective production of azo compounds via THC reaction of nitroaromatics.

Catch It If You Can: Copper-Catalyzed (Transfer) Hydrogenation Reactions and Coupling Reactions by Intercepting Reactive Intermediates Thereof

The key reactive intermediate of copper(I)-catalyzed alkyne semihydrogenations is a vinylcopper(I) complex. This intermediate can be exploited as a starting point for a variety of trapping reactions. In this manner, an alkyne semihydrogenation can be turned into a dihydrogen­-mediated coupling reaction. Therefore, the development of copper-catalyzed (transfer) hydrogenation reactions is closely intertwined with the corresponding reductive trapping reactions. This short review highlights and conceptualizes the results in this area so far, with H2-mediated carbon–carbon and carbon–heteroatom bond-forming reactions emerging under both a transfer hydrogenation setting as well as with the direct use of H2. In all cases, highly selective catalysts are required that give rise to atom-economic multicomponent coupling reactions with rapidly rising molecular complexity. The coupling reactions are put into perspective by presenting the corresponding (transfer) hydrogenation processes first.1 Introduction: H2-Mediated C–C Bond-Forming Reactions2 Accessing Copper(I) Hydride Complexes as Key Reagents for Coupling Reactions; Requirements for Successful Trapping Reactions3 Homogeneous Copper-Catalyzed Transfer Hydrogenations4 Trapping of Reactive Intermediates of Alkyne Transfer Semi­hydrogenation Reactions: First Steps Towards Hydrogenative Alkyne Functionalizations5 Copper(I)-Catalyzed Alkyne Semihydrogenations6 Copper(I)-Catalyzed H2-Mediated Alkyne Functionalizations; Trapping of Reactive Intermediates from Catalytic Hydrogenations6.1 A Detour: Copper(I)-Catalyzed Allylic Reductions, Catalytic Generation of Hydride Nucleophiles from H26.2 Trapping with Allylic Electrophiles: A Copper(I)-Catalyzed Hydro­allylation Reaction of Alkynes6.3 Trapping with Aryl Iodides7 Conclusion

Application of a reusable Co-based nanocatalyst in alcohol dehydrogenative coupling strategy: Synthesis of quinoxaline and imine scaffolds

A nitrogen doped carbon supported cobalt catalyzed efficient synthesis of imines and quinoxaline motifs is reported. Co(OAc)2-Phen/Carbon-800 (Co-phen/C-800) showed the superior reactivity compared to other materials prepared at different temperature, in the synthesis of quinoxalines by the coupling between diamines and diols. Moreover, applying the transfer hydrogenation and acceptorless dehydrogenative coupling strategy, imines and quinoxaline derivatives were synthesized from the nitro compounds. The practical applicability of this protocol was demonstrated by the gram-scale synthesis and the reusability of the catalyst upto 8th cycle. Furthermore, several kinetic experiments were carried out to realize the probable mechanism.

Synthesis and Characterization of Pd(II) and Ru(II) Complexes of Tetradentate N,N,N,N-(Diphosphinomethyl)amine Ligands: Catalytic Properties in Transfer Hydrogenation and Heck Coupling Reactions

Synthesis and Characterization of Pd(II) and Ru(II) Complexes of Tetradentate N,N,N,N-(Diphosphinomethyl)amine Ligands: Catalytic Properties in Transfer Hydrogenation and Heck Coupling Reactions

Preparation and spectroscopic studies of Fe(II), Ru(II), Pd(II) and Zn(II) complexes of Schiff base containing terephthalaldehyde and their transfer hydrogenation and Suzuki-Miyaura coupling reaction

AbstractThis study describes synthesis, spectroscopic characterization and catalytic activities of Fe(II), Ru(II), Pd(II) and Zn(II) complexes with a novel Schiff base ligand (L) derived from methyl 2-amino-5,5,7,7-tetramethyl-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate and terephthalaldehyde. We used spectroscopic techniques including IR, UV-Vis, 1H-NMR, 13C-NMR, elemental analysis and also mass analysis and magnetic susceptibility measurements to identify the products. The Pd(II) complex was used as a potential catalyst for Suzuki-Miyaura coupling reaction of some aryl halides under optimized conditions. The effect of various bases such as NaOH, KOH, and KOBut was investigated in transfer hydrogenation (TH) of ketones by isopropyl alcohol as the hydrogen source. Ru(II) and Pd(II) complexes showed catalytic activity while Zn(II) and Fe(II) metal complexes failed to do that.

Rhodium-Catalyzed Aldehyde Arylation via Formate-Mediated Transfer Hydrogenation: Beyond Metallic Reductants in Grignard/Nozaki-Hiyami-Kishi-Type Addition.

The first intermolecular carbonyl arylations via transfer hydrogenative reductive coupling are described. Using rhodium catalysts modified by tBu2PMe, sodium formate-mediated reductive coupling of aryl iodides with aldehydes occurs in a chemoselective fashion in the presence of protic functional groups and lower halides. This work expands the emerging paradigm of transfer hydrogenative coupling as an alternative to pre-formed carbanions or metallic reductants in C═X addition.

Enantioselective Ruthenium-Catalyzed Benzocyclobutenone-Ketol Cycloaddition: Merging C-C Bond Activation and Transfer Hydrogenative Coupling for Type II Polyketide Construction.

The first enantioselective intermolecular metal-catalyzed cycloadditions of benzocyclobutenones via C-C bond oxidative addition are described. In the presence of a ruthenium(0) complex modified by ( R)-DM-SEGPHOS, tetralone-derived ketols and benzocyclobutenones combine to form cycloadducts with complete regio- and diastereoselectivity and high enantioselectivity. Using this method, the "bay region" substructure of the angucycline natural product arenimycin was prepared.

Straightforward synthesis of quinolines from enones and 2-aminobenzyl alcohols using an iridium-catalyzed transfer hydrogenative strategy.

A new protocol for the direct synthesis of quinolines from enones and 2-aminobenzyl alcohols via iridium-catalyzed transfer hydrogenative reactions has been demonstrated. This method employs easily available [IrCp*Cl2]2/t-BuOK as the efficient catalyst system, proceeding with the merits of high step- and atom efficiency, mild reaction conditions and operational simplicity. The experimental studies suggest that the reactions start with transfer hydrogenation, followed by the Friedländer reaction to give the final products.

Transition-metal-catalyst-free synthesis of anthranilic acid derivatives by transfer hydrogenative coupling of 2-nitroaryl methanols with alcohols/amines.

By using a transfer hydrogenative coupling strategy, we herein describe a new method for the efficient synthesis of anthranilic acid derivatives, a significantly important class of compounds with extensive applications in organic synthesis and the discovery of bioactive molecules, from 2-nitroaryl methanols and readily available alcohols/amines. The synthesis proceeds with the merits of no need for a transition metal catalyst, operational simplicity, broad substrate scope, good functional tolerance, and high step efficiency, which offers a useful alternative to access anthranilic acid derivatives.

Ruthenium-catalyzed insertion of adjacent diol carbon atoms into C-C bonds: Entry to type II polyketides.

Current catalytic processes involving carbon-carbon bond activation rely on π-unsaturated coupling partners. Exploiting the concept of transfer hydrogenative coupling, we report a ruthenium(0)-catalyzed cycloaddition of benzocyclobutenones that functionalizes two adjacent saturated diol carbon-hydrogen bonds. These regio- and diastereoselective processes enable convergent construction of type II polyketide substructures.

Regioselective Hydrohydroxyalkylation of Styrene with Primary Alcohols or Aldehydes via Ruthenium-Catalyzed C-C Bond Forming Transfer Hydrogenation.

Transfer hydrogenative coupling of styrene with primary alcohols using the precatalyst HClRu(CO)(PCy3 )2 modified by AgOTf or HBF4 delivers branched or linear adducts from benzylic or aliphatic alcohols, respectively. Related 2-propanol mediated reductive couplings also are described.

ChemInform Abstract: A Novel Iridium/Acid Co‐Catalyzed Transfer Hydrogenative C(sp3)—H Bond Alkylation to Access Functionalized N‐Heteroaromatics.

AbstractA novel transfer hydrogenative coupling strategy for sp3 C—H bonds is introduced.

Ruthenium-Catalyzed Transfer Hydrogenation for C-C Bond Formation: Hydrohydroxyalkylation and Hydroaminoalkylation via Reactant Redox Pairs.

Merging the chemistry of transfer hydrogenation and carbonyl or imine addition, a broad new family of redox-neutral or reductive hydrohydroxyalkylations and hydroaminomethylations have been developed. In these processes, hydrogen redistribution between alcohols and π-unsaturated reactants is accompanied by C-C bond formation, enabling direct conversion of lower alcohols to higher alcohols. Similarly, hydrogen redistribution between amines to π-unsaturated reactants results in direct conversion of lower amines to higher amines. Alternatively, equivalent products of hydrohydroxyalkylation and hydroaminomethylation may be generated through the reaction of carbonyl compounds or imines with π-unsaturated reactants under the conditions of 2-propanol-mediated reductive coupling. Finally, using vicinally dioxygenated reactants, that is, diol, ketols, or diones, successive transfer hydrogenative coupling occurs to generate 2 C-C bonds, resulting in products of formal [4+2] cycloaddition.

Cu–Pd/γ-Al2O3catalyzed the coupling of multi-step reactions: direct synthesis of benzimidazole derivatives

Catalyzed by the synergy effects of Cu–Pd bimetal and acidity of γ-Al2O3, the transfer hydrogenation and successive cyclization coupling reaction fromo-nitroaniline and alcohol to afford benzimidazole derivatives in high yield was realized.

A novel iridium/acid co-catalyzed transfer hydrogenative C(sp(3))-H bond alkylation to access functionalized N-heteroaromatics.

A novel iridium/acid co-catalysed transfer hydrogenative coupling strategy, enabling direct alkylation of C(sp(3))-H bonds and atom-economic access to alkyl chain-lengthened N-heteroaromatics from six-membered 2-alkyl cyclic amines and aldehydes, has been demonstrated. This work has built an important basis to convert cyclic amines, a class of bulk chemical raw materials, into functionalized products.

ChemInform Abstract: Enantioselective Carbonyl Propargylation by Iridium‐Catalyzed Transfer Hydrogenative Coupling of Alcohols and Propargyl Chlorides.

AbstractThe desired compounds are prepared from silyl‐substituted propargyl chlorides and benzyl alcohols or aromatic aldehydes.

Iridium-catalyzed allylation of chiral β-stereogenic alcohols: bypassing discrete formation of epimerizable aldehydes.

The cyclometalated π-allyliridium 3,4-dinitro-C,O-benzoate complex modified by (R)- or (S)-Cl,MeO-BIPHEP promotes the transfer hydrogenative coupling of allyl acetate to β-stereogenic alcohols with good to excellent levels of catalyst-directed diastereoselectivity to furnish homoallylic alcohols. Remote electronic effects of the C,O-benzoate of the catalyst play a critical role in suppressing epimerization of the transient α-stereogenic aldehyde.

Enantioselective Carbonyl Propargylation by Iridium‐Catalyzed Transfer Hydrogenative Coupling of Alcohols and Propargyl Chlorides

It takes alkynes! Exposure of propargyl chlorides to primary benzylic alcohols in the presence of [Ir(cod){(R)-segphos}]OTf (cod = 1,5-cyclooctadiene, segphos = 5,5'-bis(diphenylphosphino)-4,4'-bi-1,3-benzodioxole, Tf = trifluoromethanesulfonyl) results in hydrogen exchange to give allenyliridium-aldehyde pairs that combine to form products of propargylation with high ee value (see scheme). The reaction can also be conducted using aldehydes.