TfOH-Catalyzed Reactions of Aryl Methyl Ketones with Ynamides: Synthesis of 1-Amino-1H-indenes and 2,4-Dienamides

The efficient synthesis of 1-amino-1H-indenes and 2,4-dienamides was realized via TfOH-catalyzed reactions of aryl methyl ketones with terminal ynamides in two distinct pathways. Aromatic ketones with high electrophilicity underwent [3 + 2] annulation with ynamides to produce 1-amino-1H-indenes, while aromatic ketones with low electrophilicity proceeded under the same conditions to afford 2,4-dienamides. Furthermore, the obtained 1-amino-1H-indenes could be converted into the corresponding 1H-indenes and dihydro-1H-indenes in excellent yields.

Bis-benzofulvenes: Synthesis and Studies on Their Optoelectronic Properties

We report the synthesis of bis-benzofulvenes and the studies on their optical and redox properties. Bis-benzofulvenes were achieved through the Pd-catalyzed intramolecular Heck coupling followed by Ni⁰-mediated C(sp²)-Br dimerization. Low optical and electrochemical energy gaps of 2.05 and 1.68 eV were achieved by tuning the substituent on the exomethylene unit and the aromatic ring. The observed trends in the energy gaps were compared, and the frontier molecular orbitals were visualized using the density functional theory.

Regioselective cobalt(II)-catalyzed [2 + 3] cycloaddition reaction of fluoroalkylated alkynes with 2-formylphenylboronic acids: easy access to 2-fluoroalkylated indenols

[2 + 3] cycloaddition reactions of fluorinated alkynes with 2-formylphenylboronic acids under the influence of Co(acac)₂·2H₂O in two-component solvents of acetonitrile/2-propanol at reflux temperature for 18 h took place smoothly, affording the corresponding fluoroalkylated indenol derivatives in good yields. This reaction shows excellent regioselectivity, giving 2-fluoroalkylated indenols, together with a very small amount of 3-fluoroalkylated indanones as side products.

Rhodium-Catalyzed Successive C-H Bond Functionalizations To Synthesize Complex Indenols Bearing a Benzofuran Unit

An efficient rhodium-catalyzed redox-neutral annulations of N-phenoxyacetamides and ynones via successive double C-H bond activations has been developed. A series of novel and complex indenols bearing a benzofuran unit were generated with moderate to excellent regioselecetivities under mild conditions. Adding N-ethylcyclohexanamine (CyNHEt) could restrict the formation of the mono C-H bond activation byproduct, which is not the intermediate of the reaction demonstrated via the mechanistic investigations.

Synthesis of Benzofulvenes via Cp*Co(III)-Catalyzed C-H Activation and Carbocyclization of Aromatic Ketones with Internal Alkynes

A highly efficient and practical synthesis of benzofulvenes was developed via ketone-directed Cp*Co(III)-catalyzed sequential C-H activation, addition, cyclization, and dehydration cascade processes between simple aromatic ketones and alkynes. The reaction tolerates a variety of functional groups, and various benzofulvenes were efficiently synthesized in 42-92% yields.

Recent Advances in C–H Bond Functionalization with Ruthenium-Based Catalysts

The past decades have witnessed rapid development in organic synthesis via catalysis, particularly the reactions through C–H bond functionalization. Transition metals such as Pd, Rh and Ru constitute a crucial catalyst in these C–H bond functionalization reactions. This process is highly attractive not only because it saves reaction time and reduces waste,but also, more importantly, it allows the reaction to be performed in a highly region specific manner. Indeed, several organic compounds could be readily accessed via C–H bond functionalization with transition metals. In the recent past, tremendous progress has been made on C–H bond functionalization via ruthenium catalysis, including less expensive but more stable ruthenium(II) catalysts. The ruthenium-catalysed C–H bond functionalization, viz. arylation, alkenylation, annulation, oxygenation, and halogenation involving C–C, C–O, C–N, and C–X bond forming reactions, has been described and presented in numerous reviews. This review discusses the recent development of C–H bond functionalization with various ruthenium-based catalysts. The first section of the review presents arylation reactions covering arylation directed by N–Heteroaryl groups, oxidative arylation, dehydrative arylation and arylation involving decarboxylative and sp3-C–H bond functionalization. Subsequently, the ruthenium-catalysed alkenylation, alkylation, allylation including oxidative alkenylation and meta-selective C–H bond alkylation has been presented. Finally, the oxidative annulation of various arenes with alkynes involving C–H/O–H or C–H/N–H bond cleavage reactions has been discussed.

Nickel-catalyzed, ligand-free, diastereoselective synthesis of 3-methyleneindan-1-ols

Nickel-catalyzed, highly diastereoselective annulations between activated allenes and 2-acetylarylboronic acid or 2-formylarylboronic acids to give 3-methyleneindan-1-ols are reported.

Rh(iii)-Catalyzed regioselective C–H [4 + 2] C-annulation of vinyl enaminones with alkynes to form polysubstituted salicylaldehydes

Sterically congested polysubstituted salicylaldehydes are accessed through a Rh(iii)-catalyzed regioselective vinylic C–H [4 + 2] C-annulation reaction of vinyl enaminones with alkynes.

Transition-Metal-Catalyzed C-H Bond Addition to Carbonyls, Imines, and Related Polarized π Bonds

The transition-metal-catalyzed addition of C-H bonds to carbonyls, imines, and related polarized π bonds has emerged as a particularly efficient and powerful approach for the construction of an incredibly diverse array of heteroatom-substituted products. Readily available and stable inputs are typically employed, and reactions often proceed with very high functional group compatibility and without the production of waste byproducts. Additionally, many transition-metal-catalyzed C-H bond additions to polarized π bonds occur within cascade reaction sequences to provide rapid access to a diverse array of different heterocyclic as well as carbocyclic products. This review highlights the diversity of transformations that have been achieved, catalysts that have been used, and types of products that have been prepared through the transition-metal-catalyzed addition of C-H bonds to carbonyls, imines, and related polarized π bonds.

Cobalt-Catalyzed Cyclization of N-Methoxy Benzamides with Alkynes using an Internal Oxidant through C-H/N-O Bond Activation

The cyclization of substituted N-methoxy benzamides with alkynes in the presence of an easily affordable cobalt complex and NaOAc provides isoquinolone derivatives in good to excellent yields. The cyclization reaction is compatible with a range of functional group-substituted benzamides, as well as ester- and alcohol-substituted alkynes. The cobalt complex [Co(III) Cp*(OR)2 ] (R=Me or Ac) serves as an efficient catalyst for the cyclization reaction. Later, isoquinolone derivatives were converted into 1-chloro and 1-bromo substituted isoquinoline derivatives in excellent yields in the presence of POCl3 or PBr3 .

Rh(III)-Catalyzed Diastereoselective C-H Bond Addition/Cyclization Cascade of Enone Tethered Aldehydes

The Rh(III)-catalyzed cascade addition of a C-H bond across alkene and carbonyl π-bonds is reported. The reaction proceeds under mild reaction conditions with low catalyst loading. A range of directing groups were shown to be effective as was the functionalization of alkenyl in addition to aromatic C(sp2)-H bonds. When the enone and aldehyde electrophile were tethered together, cyclic β-hydroxy ketones with three contiguous stereocenters were obtained with high diastereoselectivity. The intermolecular three-component cascade reaction was demonstrated for both aldehyde and imine electrophiles. Moreover, the first x-ray structure of a cationic Cp*Rh(III) enolate with interatomic distances consistent with an η3-bound enolate is reported.

Transition metal-catalyzed ketone-directed or mediated C-H functionalization

Transition metal-catalyzed C-H functionalization has evolved into a prominent and indispensable tool in organic synthesis. While nitrogen, phosphorus and sulfur-based functional groups (FGs) are widely employed as effective directing groups (DGs) to control the site-selectivity of C-H activation, the use of common FGs (e.g. ketone, alcohol and amine) as DGs has been continuously pursued. Ketones are an especially attractive choice of DGs and substrates due to their prevalence in various molecules and versatile reactivity as synthetic intermediates. Over the last two decades, transition metal-catalyzed C-H functionalization that is directed or mediated by ketones has experienced vigorous growth. This review summarizes these advancements into three major categories: use of ketone carbonyls as DGs, direct β-functionalization, and α-alkylation/alkenylation with unactivated olefins and alkynes. Each of these subsections is discussed from the perspective of strategic design and reaction discovery.

Iridium-catalyzed asymmetric [3+2] annulation of aromatic ketimines with alkynes via C–H activation: unexpected inversion of the enantioselectivity induced by protic acids

The enantiodivergent synthesis of annulation products was achieved in the Ir-catalyzed asymmetric [3+2] annulation of cyclic N-acyl ketimines with internal alkynes via C–H activation.

Rhodium-catalyzed annulation of arenes with alkynes through weak chelation-assisted C–H activation

This feature article reviews the recent achievements of rhodium-catalyzed annulation of arenes with alkynes through weak chelation-assisted C–H activation, which sets a stage for the synthesis of diverse appealing polycyclic compounds.

An air-stable half-sandwich RuIIcomplex as an efficient catalyst for [3+2] annulation of 2-arylcyclo-2-enones with alkynes

An air-stable half-sandwich Ru^IIcomplex, [Ru(p-cymene)(MeCN)₃](SbF6)₂, catalyzed a [3+2] annulation reaction of 2-arylcyclo-2-enones with alkynesviaC(sp²)–H/alkene functionalization to construct synthetically challenging spiro carbocyclic indenes bearing a quaternary carbon.

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.

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.

Direct Synthesis of Protoberberine Alkaloids by Rh-Catalyzed C-H Bond Activation as the Key Step

A one-pot reaction of substituted benzaldehydes with alkyne-amines by a Rh-catalyzed C-H activation and annulation to afford various natural and unnatural protoberberine alkaloids is reported. This reaction provides a convenient route for the generation of a compound library of protoberberine salts, which recently have attracted great attention because of their diverse biological activities. In addition, pyridinium salt derivatives can also be formed in good yields from α,β-unsaturated aldehydes and amino-alkynes. This reaction proceeds with excellent regioselectivity and good functional group compatibility under mild reaction conditions by using O2 as the oxidant.

Ruthenium-catalyzed direct C3 alkylation of indoles with α,β-unsaturated ketones

In this paper, a simple and highly efficient ruthenium-catalyzed direct C3 alkylation of indoles with various α,β-unsaturated ketones without chelation assistance has been developed.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.