Search

A palladium‐catalyzed denitrogenative transannulation strategy to access various 3‐substituted isocoumarin‐1‐imine frameworks using 1,2,3‐benzotriazin‐4(3H)‐ones and terminal alkynes is described. The reaction is highly regioselective and tolerates a wide range of functional groups. The reaction is believed to proceed via a five‐membered palladacycle intermediate extruding environmentally benign molecular nitrogen as a by‐product. The utility of this method was showcased through the one‐pot synthesis of biologically relevant 3‐substituted isocoumarin scaffolds. [ABSTRACT FROM AUTHOR]

An efficient palladium-catalyzed denitrogenative Suzuki–Miyaura type cross-coupling of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acid is described. The reaction is compatible with various aryl and alkenyl boronic acids affording ortho-arylated and alkenylated benzamides in good to high yields. Heteroaromatic boronic acids were also successfully employed. Along with this, a coupling reaction was established by using phenyl boronate ester as the coupling partner. The reaction is believed to proceed via a five-membered aza-palladacyclic intermediate. DFT calculations were studied comparing the reactivity of palladium and nickel complexes in the five-membered aza-metallacycle formation from 1,2,3-benzotriazin-4(3H)-ones. The application of the reaction was successfully demonstrated by converting ortho-alkenylated products to ortho-alkylated products in high yields via a reduction reaction. [ABSTRACT FROM AUTHOR]

An efficient zinc‐catalyzed N‐alkylation reaction of aromatic amines was achieved using aliphatic, aromatic, and heteroaromatic alcohols as the alkylating reagent. A variety of aniline derivatives, including heteroaromatic amines, underwent the N‐alkylation reaction and furnished the corresponding monoalkylated products in good to excellent yields. The application of the reaction is also further demonstrated by the synthesis of a 2‐phenylquinoline derivative from acetophenone and 2‐aminobenzyl alcohol. Deuterium labeling experiments show that the reaction proceeds via a borrowing hydrogen process. [ABSTRACT FROM AUTHOR]

A new and efficient metal‐free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g‐C3N4 catalyst has been described. The functionalized quaternary ammonium hydroxide (g‐C3N4‐OH) has been prepared from graphitic carbon nitride (g‐C3N4) scaffold by converting the residual –NH2 and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion‐exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH‐ form) by post‐synthetic modification. The resultant g‐C3N4‐OH was characterized by XRD, FTIR, field‐emission scanning electron microscope (FESEM), high‐resolution transmission electron microscope (HRTEM), N2 adsorption/desorption isotherms, and acid–base titration. Tested as solid‐base catalysts, the g‐C3N4‐OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g‐C3N4‐OH solid‐base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%). [ABSTRACT FROM AUTHOR]

The first example of potassium tert-butoxide mediated aerobic hydroxylation of arylboronic acids is described. A variety of arylboronic acids bearing both electron donating and withdrawing substituents successfully participated in the reaction and furnished phenols in good yields. This strategy also provides access to one pot synthesis of (E)-3-phenoxy acrylates from arylboronic acids and propiolates. The solvent plays an important role and a binary solvent system comprising CH3CN/THF is found to be the best. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis and application of a Zn-Bp-BTC MOF (Bp – 4,4′-bipyridine; BTC – 1,3,5-benzene tricarboxylic acid; MOF – metal organic framework) as a heterogeneous catalyst for mediating organic reactions. Initially, conditions were optimized for the Knoevenagel condensation reaction using Zn-Bp-BTC as a heterogeneous catalyst by varying the solvent, temperature and catalyst loading. Although the reaction proceeded at room temperature using methanol as the solvent, 60 °C offered the best yield in a shorter duration. Under optimized reaction conditions, a wide range of α,β-unsaturated dicyano compounds were prepared from the corresponding carbonyl precursor and malononitrile, the active methylene counterpart. Systematic investigation was also carried out to assess the role of the ligand and metal salt in the Knoevenagel condensation reaction. It was found that the Zn-Bp-BTC MOF catalyzed the reaction efficiently in comparison to its analogue Zn-BTC MOF and precursor Zn(NO3)2·6H2O. Finally, catalytic recycling and stability studies showed that the catalyst is able to mediate the reaction for up to five consecutive cycles without undergoing any significant chemical or morphological changes. Further, the catalyst was tested for its efficacy in a multi-component reaction (MCR). A MCR with the Zn-Bp-BTC MOF as the catalyst afforded good yields and there was no reaction in the absence of the catalyst. Similarly, the catalyst was tested for its efficiency in benzimidazole synthesis. [ABSTRACT FROM AUTHOR]

Abstract: The role of the reductant in the palladium N‐heterocyclic carbene (NHC) catalyzed reductive Heck reaction and its effect on the mechanism of the reaction is reported. For the first time in this type of transformation, the palladium‐NHC‐catalyzed reductive Heck reaction was shown to proceed in the presence of LiOMe and iPrOH even at 10 °C to give the products very efficiently in excellent yields and with exceptional chemoselectivities. This study shows that the reaction proceeds through two distinct mechanisms that depend on the nature of the reducing agent. In the presence of a protic solvent or acidic medium the reaction undergoes protonation to yield the reduced product, whereas in the absence of proton source, it proceeds through the insertion of the reductant followed by reductive elimination. The kinetic data reveal that the oxidative addition is the rate‐determining step in the reaction. The reaction profiles show first‐order kinetics in aryl iodide and Pd and zero‐order kinetics in LiOMe, benzylideneacetone, and the excess amount of NHC ligand. In addition, the reaction progress kinetic analysis shows that neither catalyst decomposition nor product inhibition occurs during the reaction. DFT calculations of the key steps confirm that the oxidative addition step is the rate‐determining step in the reaction. Deuterium‐labeling experiments indicate that the product is formed by the protonation of the Pd−Calkyl bond of the intermediate formed after enone insertion into the Pd−CAr bond. Application of chiral NHC ligands in the asymmetric reductive Heck reaction only results in poor enantioselectivities (enantiomeric excess up to 20 %) and is also substrate specific. DFT calculations suggest that the migration of the aryl group to the alkene of the substrate is the enantioselectivity‐determining step of the reaction. It is further shown that if the steric bulk at the enone is small (a methyl group), the two transition state barriers from [PdII(L2)(ArI)(enone)] species Cre and Csi, which have the re and si face of the enone substrate coordinated to Pd, are very similar, in line with the experimental results. With a slightly larger group (an isopropyl substituent) a significant difference in energy barriers is calculated (2.6 kcal mol−1), and in the experiment this product is formed with a modest enantiomeric excess (up to 20 %). [ABSTRACT FROM AUTHOR]

A palladium-catalyzed enantioselective reductive Heck reaction of enones using monodentate phosphoramidite ligands is described. α,α,α',α'-tetraaryl-1,3-dioxolane-4,5-dimethanol (TADDOL)-based phosphoramidites with palladium(II) acetate, and N-methyl dicyclohexylamine as reducing agent gives the reductive Heck product in high yields and enantioselectivities of up to 90 %. The solvent plays an important role and in diethyl carbonate, the chemo- and enantioselectivity appeared to be the highest. [ABSTRACT FROM AUTHOR]

We describe a highly step and atom economical cobalt-catalyzed cyclization of 1,6-enynes with aldehydes to synthesize functionalized pyrrolidines and dihydrofurans with high chemo- and stereoselectivity. The catalytic reaction plausibly proceeds via the cobaltacycle intermediate generated from the reaction of enyne substrate with cobalt catalyst, followed by switchable C–H functionalization of weakly coordinating aldehydes depending on the electronic nature of the ligand. [ABSTRACT FROM AUTHOR]

We have studied the mechanism of the palladiumcatalyzed reductive Heck reaction of para-substituted enones with 4-iodoanisole by using N,N-diisopropylethylamine (DIPEA) as the reductant. Kinetic studies and in situ spectroscopic analysis have provided a detailed insight into the reaction. Progress kinetic analysis demonstrated that neither catalyst decomposition nor product inhibition occurred during the catalysis. The reaction is first order in the palladium and aryl iodide, and zero order in the activated alkene, N-heterocyclic carbene (NHC) ligand, and DIPEA. The experiments with deuterated solvent ([D7]DMF) and deuterated base ([D15]Et3N) supported the role of the amine as a reductant in the reaction. The palladium complex [Pd0(NHC)(1)] has been identified as the resting state. The kinetic experiments by stopped-flow UV/Vis also revealed that the presence of the second substrate, benzylideneacetone 1, slows down the oxidative addition of 4-iodoanisole through its competing coordination to the palladium center. The kinetic and mechanistic studies indicated that the oxidative addition of the aryl iodide is the rate-determining step. Various scenarios for the oxidative addition step have been analyzed by using DFT calculations (bp86/def2-TZVP) that supported the inhibiting effect of substrate 1 by formation of resting state [Pd0(NHC)(1)] species at the cost of further increase in the energy barrier of the oxidative addition step. [ABSTRACT FROM AUTHOR]

A surprisingly practical Pd(OAc)2 or Pd(TFA)2-catalyzed reductive Heck reaction between aryl iodides α and,β-unsaturated ketones is described using N,N-diisopropylethylamine (DIPEA, Hünigs base) as the reductant. In general, 1 mol% of Pd(OAc)2 is sufficient to afford good yields using electron-rich or halogen-substituted aryl iodides. Electron-deficient aryl iodides preferentially give homocoupling. Enones containing aryl or bulky substituents on the β-carbon react smoothly, producing mainly reductive Heck product, whereas enones with alkyl substituents on the β-carbon afford a mixture of reductive Heck and Heck product. Deuterium labeling experiments show that the reaction is a bona fide reductive Heck reaction and exclude a Heck reaction-conjugate reduction cascade. [ABSTRACT FROM AUTHOR]

A highlychemo- and stereoselective cobalt-catalyzed hydroarylativecyclization of 1,6-enynes with aromatic ketones and esters to synthesizefunctionalized pyrrolidines and dihydrofurans is described. A mechanisminvolving cobaltacycle triggered C–H activation of aromaticketones and esters was proposed. [ABSTRACT FROM AUTHOR]

A nickel-catalyzed regio- and stereoselective reductive coupling of oxa- and azabicyclic alkenes with activated alkenes and electron-rich alkynes is described. Thus, 7-oxabenzonorbornadienes underwent reductive coupling with various vinyl ketones such as ethyl, methyl, propyl and α-methyl-substituted vinyl ketones, in the presence of a nickel(II) iodide (NiI2), zinc (Zn), and water catalyst system in acetonitrile at 50 °C for 14 h to afford 2-alkylnaphthalenes in good to excellent yields. Under similar reaction conditions, 7-azabenzonorbornadiene derivatives provided cis-2-alkyl-1,2-dihydronaphthalene derivatives in high yields. On the other hand, the nickel(II) iodide, tris(4-fluorophenyl)phoshine [P(4-FC6H4)3] and zinc catalyst system successfully catalyzed the reductive coupling reaction of electron-rich alkynes, with 7-aza- and 7-oxabenzonorbornadienes to give cis-2-alkenyl-1,2-dihydronaphthalene derivatives in good to excellent yields. In the reaction, a mild reducing agent (zinc) and simple hydrogen source (water) were used. [ABSTRACT FROM AUTHOR]

An efficient method for the synthesis of three classes of heterocyclic derivatives such as 3,3-disubstituted phthalides, 3-hydroxyisoindolin-1-ones and 3-hydroxyoxindoles, is reported. In the presence of the simple reductive system, zinc (Zn)/ammonia (NH3) [or zinc-copper (Zn-Cu)/ammonia], a wide range of alkenes including acrylates, acrylonitrile, acrylamide and vinyl sulfoxide underwent reductive coupling with methyl 2-acylbenzoates and subsequent lactonization to provide 3,3-disubstituted phthalides in good to high yields at ambient temperature. In a similar manner, 3-hydroxyisoindolin-1-one and 3-hydroxyoxindole derivatives could also be easily prepared by direct reductive coupling of phthalimides and N-substituted isatins with activated alkenes, respectively. Application of this methodology towards the synthesis of 1-naphthol derivatives on a gram scale is also depicted. Furthermore, the intramolecular phthalimides-ene reductive coupling afforded the respective cyclization products with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

Metal-catalyzed annulation reactions to synthesize carbo- and heterocycles have been an attractive field of research for many years. The development of new cyclization reactions utilizing readily available less expensive metal catalyst is one of the important tasks. In this regard, this review summerizes and discusses about nickel- and cobalt-catalyzed [4+2] and [3+2] annulation reactions of ortho-halo substituted imines and alkynes. Nickel complexes under suitable reaction conditions underwent [4+2] annulation to form six-membered isoquinoline (salts) derivatives. However, cobalt complexes afforded aminoindenes via [3+2] annulation reactions. Both reactions proceed through a five membered metallacycle. The regioselective insertion of alkyne containing keto or ester groups into the metallacycle further demonstrates the difference in selectivity of these metal complexes. [ABSTRACT FROM AUTHOR]

Discover nickel! A nickel‐catalyzed alkenylative cyclization of 1,6‐enynes and alkenyl boronic acids affording substituted pyrrolidines and dihydrofurans is described (see scheme; cod=1,5‐cyclooctadiene, Ts = p‐toluene sulfonate). The reaction is highly chemo‐ and stereoselective. A possible reaction mechanism involving a nickelacyclopentene intermediate is proposed. [ABSTRACT FROM AUTHOR]

A cobalt-catalyzed reductive coupling of terminal alkynes, RCCH, with activated alkenes, R′CHCH2, in the presence of zinc and water to give functionalized trans-disubstituted alkenes, RCHCHCH2CH2R′, is described. A variety of aromatic terminal alkynes underwent reductive coupling with activated alkenes including enones, acrylates, acrylonitrile, and vinyl sulfones in the presence of a CoCl2/P(OMe)3/Zn catalyst system to afford 1,2- trans-disubstituted alkenes with high regio- and stereoselectivity. Similarly, aliphatic terminal alkynes also efficiently participated in the coupling reaction with acrylates, enones, and vinyl sulfone, in the presence of the CoCl2/P(OPh)3/Zn system providing a mixture of 1,2- trans- and 1,1-disubstituted functionalized terminal alkene products in high yields. The scope of the reaction was also extended by the coupling of 1,3-enynes and acetylene gas with alkenes. Furthermore, a phosphine-free cobalt-catalyzed reductive coupling of terminal alkynes with enones, affording 1,2- trans-disubstituted alkenes as the major products in a high regioisomeric ratio, is demonstrated. In the reactions, less expensive and air-stable cobalt complexes, a mild reducing agent (Zn) and a simple hydrogen source (water) were used. A possible reaction mechanism involving a cobaltacyclopentene as the key intermediate is proposed. [ABSTRACT FROM AUTHOR]

Reaction of oxabicyclic alkenes with alkynes and organoboronic acids in the presence of Ni(cod)2, P(t-Bu)3, and CsF in a binary solvent toluene–methanol (1 : 3) at 75 to 85 °C provided exo-5,6-disubstituted 7-oxanorbornene derivatives in good to excellent yields. [ABSTRACT FROM AUTHOR]

A CoI2/(R)-BINAP, Zn, ZnI2, H2O system efficiently catalyzes the intermolecular asymmetric reductive coupling of alkynes with cyclic enones to afford highly regio- and enantioselective β-alkenyl cydic ketones. A possible mechanism that involves the formation of a cobaltacyclo-pentene intermediate from the alkyne and cyclic enone is proposed. [ABSTRACT FROM AUTHOR]

A correction to the article "Palladium(II) Acetate Catalyzed Reductive Heck Reaction of Enones; A Practical Approach" that was published in the 2015 issue.

The cobalt-catalyzed reaction of 1,6-enynes (I) with benzaldehyde leads either to aldehydes [cf. [ABSTRACT FROM AUTHOR]

An abstract of the article "Palladium(II) Acetate Catalyzed Reductive Heck Reaction of Enones; a Practical Approach" by S. Mannathan and colleagues is presented.

The highly chemo- and stereoselective title reaction furnishes functionalized pyrrolidines and dihydrofurans via cobalt-triggered C-H activation. [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "Nickel-Catalyzed Regio- and Stereoselective Reductive Coupling of Oxa- and Azabicyclic Alkenes with Enones and Electron-Rich Alkynes" by C.-H. Cheng and others, published in the "Advanced Synthesis & Catalysis" in 2014.

The front cover picture, provided by Chien ‐ Hong Cheng, illustrates a highly regio ‐ and stereoselective nickel ‐ catalyzed reductive coupling reaction of oxa ‐ and azabicyclic alkenes with enones and electron ‐ rich alkynes. The reaction is highly atom economical affording cis ‐ 2 ‐ alkyl ‐ and alkenyl ‐ 1,2 ‐ dihydronaphthalenes in good to excellent yields. Besides, 2 ‐ alkyl naphthalene derivatives also can be prepared under similar reaction conditions. The picture at the center is Department of Chemistry, National Tsing Hua University, in Hsinchu, Taiwan. Details can be found in the full paper on pages 2239 – 2246 (S. Mannathan and C. ‐ H. Cheng, Adv. Synth. Catal. 2014, 356, 2239 – 2246 DOI: 10.1002/adsc.201300910). [ABSTRACT FROM AUTHOR]

Review: [17 refs. [ABSTRACT FROM AUTHOR]

The article focuses on the research "Nickel-Catalyzed Chemo- and Stereoselective Alkenylative Cyclization of 1,6-Enynes with Alkenyl Boronic Acids" by S. Mannathan published in a 2013 issue of "Chemistry: A European Journal."

A highly regio- and diastereoselective three-component reductive coupling reaction affording exo-5,6-disubstituted 7-oxanorbornene derivatives in good to excellent yields is reported. [ABSTRACT FROM AUTHOR]

The bridged alcohol systems are synthesized by reductive [3 + 2] cycloaddition of cyclic enones with alkynes in the presence of Co salts. [ABSTRACT FROM AUTHOR]

In the presence of suitable ligands the reaction allows a mild, convenient, and highly selective access to a number of trans-disubstituted alkenes. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed denitrogenative transannulation strategy to access various 3-substituted isocoumarin-1-imine frameworks using 1,2,3-benzotriazin-4(3H)-ones and terminal alkynes is described. The reaction is highly regioselective and tolerates a wide range of functional groups. The reaction is believed to proceed via a five-membered palladacycle intermediate extruding environmentally benign molecular nitrogen as a by-product. The utility of this method was showcased through the one-pot synthesis of biologically relevant 3-substituted isocoumarin scaffolds., (© 2023 Wiley-VCH GmbH.)

An efficient and straightforward approach to synthesize salicylanilide aryl and alkyl sulfonates from 1,2,3-benzotriazin-4(3 H )-ones and organosulfonic acids is described. This protocol is operationally simple and scalable, exhibits a broad substrate scope with high functional group tolerance, and affords the desired products in good to high yield. Application of the reaction is also demonstrated by converting the desired product to synthetically useful salicylamides in high yields., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

An efficient trifluoroacetic acid-mediated denitrogenative hydroxylation of 1,2,3-benzotriazin-4(3 H )-ones is described. This metal-free approach is compatible with a wide range of 1,2,3-benzotriazin-4(3 H )-ones, affording ortho -hydroxylated benzamides in good to high yields with a short reaction time. The reaction is believed to proceed via a benzene diazonium intermediate. The synthetic utility of the reaction was successfully demonstrated by the preparation of an antimicrobial drug, Riparin C, and benzoxazine-2,4(3 H )-diones in good yields.

An efficient palladium-catalyzed approach to access various functionalized ( Z )-3-benzylidene-isoindoline-1-ones and ( Z )-3-benzylidene(imino)isobenzofuranones via a denitrogenative tandem alkynylation/cyclization reaction of 1,2,3-benzotriazin-4(3 H )-ones with aromatic terminal alkynes is described. Furthermore, a denitrogenative ortho -alkynylation reaction of 1,2,3-benzotriazinones with aliphatic terminal alkynes is also developed. The reaction proceeds through a five-membered azapalladacyclic intermediate with the extrusion of a nitrogen molecule. The significance of the reaction is also demonstrated by a one-pot synthesis of ( Z )-3-benzylideneisobenzofuran-1(3 H )-one derivatives in good to high yields.

A novel nickel-catalyzed approach to synthesize ortho-arylated and alkenylated benzamides in good to high yields via a denitrogenative cross-coupling reaction of 1,2,3-benzotriazin-4(3 H)-ones with organoboronic acids is described. The reaction proceeds through a five-membered azanickelacyclic intermediate with the extrusion of a nitrogen molecule. Moreover, the resulting ortho-arylated benzamides were successfully converted into synthetically useful substituted fluorenones and ortho-arylated benzylamine derivatives in high yields.

A nickel-catalyzed highly regioselective 1,4-addition reaction of boronic acids to dienones to form products with an all-carbon quaternary center is described. The 3-alkenyl group of dienones is the key for the reaction to proceed smoothly. A mechanism involving the coordination of the dienyl group to the nickel center is proposed.

A CoI(2)/(R)-BINAP, Zn, ZnI(2), H(2)O system efficiently catalyzes the intermolecular asymmetric reductive coupling of alkynes with cyclic enones to afford highly regio- and enantioselective β-alkenyl cyclic ketones. A possible mechanism that involves the formation of a cobaltacyclopentene intermediate from the alkyne and cyclic enone is proposed., (© 2011 American Chemical Society)