Annulation Of Alkynes Research Articles

Iron‐Carbonyl‐Catalyzed Redox‐Neutral [4+2] Annulation of N−H Imines and Internal Alkynes by C−H Bond Activation

AbstractStoichiometric C−H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C−H transformations have not been developed. Herein, an iron‐catalyzed annulation of N−H imines and internal alkynes to furnish cis‐3,4‐dihydroisoquinolines is described, and represents the first iron‐carbonyl‐catalyzed C−H activation reaction of arenes. Remarkablely, this is also the first redox‐neutral [4+2] annulation of imines and alkynes proceeding by C−H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C−H bond activation to afford a dinuclear ferracycle and a synergetic diiron‐promoted H‐transfer to the alkyne as the turnover‐determining step.

Iron-Carbonyl-Catalyzed Redox-Neutral [4+2] Annulation of N-H Imines and Internal Alkynes by C-H Bond Activation.

Stoichiometric C-H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C-H transformations have not been developed. Herein, an iron-catalyzed annulation of N-H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C-H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C-H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C-H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step.

ChemInform Abstract: Carboxylate‐Assisted Ruthenium‐Catalyzed Alkyne Annulations by C—H/HET—H Bond Functionalizations

AbstractReview: [82 refs.

Cobalt-Catalyzed Annulation of Salicylaldehydes and Alkynes to Form Chromones and 4-Chromanones.

A unique cobalt(I)-diphosphine catalytic system has been identified for the coupling of salicylaldehyde (SA) and an internal alkyne affording a dehydrogenative annulation product (chromone) or a reductive annulation product (4-chromanone) depending on the alkyne substituents. Distinct from related rhodium(I)- and rhodium(III)-catalyzed reactions of SA and alkynes, these annulation reactions feature aldehyde C-H oxidative addition of SA and subsequent hydrometalation of the C=O bond of another SA molecule as common key steps. The reductive annulation to 4-chromanones also involves the action of Zn as a stoichiometric reductant. In addition to these mechanistic features, the Co(I) catalysis described herein is complementary to the Rh(I) - and Rh(III) -catalyzed reactions of SA and internal alkynes, particularly in the context of chromone synthesis.

Cobalt‐Catalyzed Annulation of Salicylaldehydes and Alkynes to Form Chromones and 4‐Chromanones

AbstractA unique cobalt(I)–diphosphine catalytic system has been identified for the coupling of salicylaldehyde (SA) and an internal alkyne affording a dehydrogenative annulation product (chromone) or a reductive annulation product (4‐chromanone) depending on the alkyne substituents. Distinct from related rhodium(I)‐ and rhodium(III)‐catalyzed reactions of SA and alkynes, these annulation reactions feature aldehyde C−H oxidative addition of SA and subsequent hydrometalation of the C=O bond of another SA molecule as common key steps. The reductive annulation to 4‐chromanones also involves the action of Zn as a stoichiometric reductant. In addition to these mechanistic features, the CoI catalysis described herein is complementary to the RhI‐ and RhIII‐catalyzed reactions of SA and internal alkynes, particularly in the context of chromone synthesis.

Cobalt-catalyzed synthesis of quinolines from the redox-neutral annulation of anilides and alkynes

A new method of cobalt-catalyzed annulation of anilides and internal alkynes for the efficient synthesis of quinoline scaffolds was developed.

Cobalt(iii)-catalyzed annulation of esters and alkynes: a facile route to indenones.

An efficient protocol for the synthesis of indenones has been developed via the annulation of benzoic esters and internal alkynes by exploiting the cobalt catalyst.

Cp*Co(iii)-catalyzed vinylic C–H bond activation under mild conditions: expedient pyrrole synthesis via (3 + 2) annulation of enamides and alkynes

Cobalt(iii)-catalyzed (3 + 2) oxidative annulation of enamides and alkynes for the synthesis of pyrroles has been developed under mild conditions and simple tuning of reaction temperature lead to the formation of bothN-Ac andN-H pyrroles under an exactly identical catalytic system.

ChemInform Abstract: Rhodium(III)‐Catalyzed Redox‐Neutral C—H Annulation of Arylnitrones and Alkynes for the Synthesis of Indole Derivatives.

ChemInform Abstract: Rhodium(III)‐Catalyzed Redox‐Neutral C—H Annulation of Arylnitrones and Alkynes for the Synthesis of Indole Derivatives.

Palladium(II)-Catalyzed Annulation of Alkynes with 2-(Cyanomethyl)phenylboronates Leading to 3,4-Disubstituted 2-Naphthalenamines.

1,2-Bis(diphenylphosphino)ethane (dppe)-ligated palladium(II) complexes catalyze the annulation of internal alkynes with 2-(cyanomethyl)phenylboronates to provide 3,4-disubstituted-2-naphthalenamines in good yields. The annulation reaction proceeds under mild and neutral conditions and requires methanol as an essential solvent. In addition to symmetrical alkynes, unsymmetrical alkynes substituted by aryl, alkyl, and alkynyl groups participate in the annulation to afford the corresponding 2-naphthalenamines with electron-withdrawing sp(2)- and sp-carbons preferentially located at the C-3 position. Substituents including an alkyl or alkoxy group on the cyanomethyl moiety and a halogen atom on the benzene ring in the boronates are compatible with the reaction conditions. The annulation proceeds through the transmetalation of the palladium(II) complexes with the boronates and alkyne insertion followed by nucleophilic addition of the generated alkenylpalladium(II) species to the intramolecular cyano group. Stoichiometric reactions revealed that the methanol solvent was effective for both transmetalation and catalyst regeneration.

Regioselective Access to Sultam Motifs through Cobalt‐Catalyzed Annulation of Aryl Sulfonamides and Alkynes using an 8‐Aminoquinoline Directing Group

AbstractThe use of cobalt as catalyst in direct CH activation protocols as a replacement for more expensive second row transition metals is currently attracting significant attention. Herein we disclose a facile cobalt‐catalyzed CH functionalization route towards sultam motifs through annulation of easily prepared aryl sulfonamides and alkynes using 8‐aminoquinoline as a directing group. The reaction shows broad substrate scope with products obtained in a highly regioselective manner in good to excellent isolated yields. Mechanistic insights suggest the formation of a Co(III)‐aryl key species via a rate‐determining arene CH activation during the annulation reaction.magnified image

Ruthenium(II)-Catalyzed Alkene C-H Bond Functionalization on Cinnamic Acids: A Facile Synthesis of Versatile α-Pyrones.

An inexpensive ruthenium(II) complex enabled oxidative annulation of alkynes by using cinnamic acid derivatives to provide diversely decorated multisubstituted α-pyrones.

Rhodium(III)-Catalyzed C-H Activation/Alkyne Annulation by Weak Coordination of Peresters with O-O Bond as an Internal Oxidant.

A redox-economic strategy has been developed, involved in an efficient Rh(III)-catalyzed oxidative C-H activation and alkyne annulation with perester as the oxidizing directing group. In this process, the cleavage of an oxidizing O-O bond as an internal oxidant is described for the first time. This reaction could be carried out under mild conditions and exhibits excellent regioselectivity and wide functional groups tolerance.

Rhodium(III)‐Catalyzed Redox‐Neutral CH Annulation of Arylnitrones and Alkynes for the Synthesis of Indole Derivatives

AbstractBy using a nitrone as the oxidizing directing group, a mild, practical and efficient rhodium(III)‐catalyzed CH functionalization for the synthesis of indole derivatives has been developed. This reaction obviates the need for an external oxidant and shows good functional group tolerance. The employment of a sterically hindered Mes group on the carbon center of the nitrone is crucial to produce indoles in high yield.magnified image

Stereodivergent Synthesis of N-Heterocycles by Catalyst-Controlled, Activity-Directed Tandem Annulation of Diazo Compounds with Amino Alkynes

A stereodivergent synthesis of five-membered N-heterocycles, such as 2,3-dihydropyrroles, and 2-methylene and 3-methylene pyrrolidines, has been developed through a tandem annulation of amino alkynes with diazo compounds and involves the trapping of in situ formed intermediates. Mechanistic investigations indicate that the copper-catalyzed tandem annulations proceed by allenoate formation and subsequent intramolecular hydroamination. In contrast, the rhodium-catalyzed protocol features a carbenoid insertion into the NH bond and subsequent Conia-ene cyclization.

Stereodivergent Synthesis of N-Heterocycles by Catalyst-Controlled, Activity-Directed Tandem Annulation of Diazo Compounds with Amino Alkynes.

A stereodivergent synthesis of five-membered N-heterocycles, such as 2,3-dihydropyrroles, and 2-methylene and 3-methylene pyrrolidines, has been developed through a tandem annulation of amino alkynes with diazo compounds and involves the trapping of in situ formed intermediates. Mechanistic investigations indicate that the copper-catalyzed tandem annulations proceed by allenoate formation and subsequent intramolecular hydroamination. In contrast, the rhodium-catalyzed protocol features a carbenoid insertion into the NH bond and subsequent Conia-ene cyclization.

ChemInform Abstract: Metal‐Free [2 + 2 + 1] Annulation of Alkynes, Nitriles and Nitrogen Atoms from Iminoiodanes for Synthesis of Highly Substituted Imidazoles.

AbstractThe title reaction is promoted by BF3 nitrile complexes and proceeds in moderate to good yields with high regioselectivities.

ChemInform Abstract: Ruthenium(II)‐Catalyzed C—H Activation/Alkyne Annulation by Weak Coordination with O2 as the Sole Oxidant.

AbstractThis is the first example of a ruthenium‐catalyzed alkyne annulation via C—H functionalization using oxygen as the oxidant giving isocoumarins and other pyran‐fused ring systems.

Rhodium(III)-Catalyzed Oxidative Annulation of 7-Azaindoles and Alkynes via Double C-H Activation.

Rhodium(III)-catalyzed double C-H activation involving N-directed ortho C-H activation and subsequent roll-over C-H activation of the heterocycle ring has been developed to form complex 7-azaindole derivatives in moderate to excellent yields. A broad scope of 7-azaindoles and internal alkynes has been demonstrated in this oxidative annulation reaction.

Efficient Approach to Mesoionic Triazolo[5,1-a]isoquinolium through Rhodium-Catalyzed Annulation of Triazoles and Internal Alkynes.

Rhodium-catalyzed annulation reactions between triazoles and internal alkynes, leading to various mesoionic isoquinoliums, are described. The reaction involves sequential triazole-directed C-H activation and C-C, C-N, and C-O bond formation processes in a one-pot manner. The starting materials and catalysts are easily available. The reaction offers a facile and practical approach to mesoionic isoquinolium derivatives.