C−C Bond Formation via C−H Bond Activation Under Protic Conditions: On the Role of Phosphane Ligand and Cosolvent

In Situ Generation of Ruthenium Carbonyl Phosphine Complexes as a Versatile Method for the Development of Enantioselective C-O Bond Arylation

We report here a method for in situ generation of various ruthenium carbonyl phosphine catalysts for arylation via cleavage of inert aromatic carbon-oxygen bonds. The use of catalyst systems consisting of [RuCl₂ (CO)(p-cymene)], CsF, styrene, and phosphines enabled facile screening of phosphine ligands. Asymmetric C-O arylation was also achieved for atropo-enantioselective biaryl synthesis using a chiral monodentate phosphine ligand.

Rh(ii)-catalyzed branch-selective C-H alkylation of aryl sulfonamides with vinylsilanes

Rhodium(ii)-catalyzed unusual branch-selective ortho-C-H alkylation of aryl sulfonamides with vinylsilanes was achieved using an 8-aminoquinoline directing group. Notably, the para-substituted aryl sulfonamides gave mono-(branched)alkylated products exclusively without the formation of any double C-H alkylated byproducts. The results of deuterium labeling experiments suggest that both hydrometalation and carbometalation pathways are involved in this conversion.

Non-Selective Dimerization of Vinyl Silanes by the Putative (Phenanthroline)PdMe Cation to 1,4-Bis(trialkoxysilyl)butenes

Activation of the dialkylpalladium complex (phen)Pd(CH3)2 (phen = 1,10-phenanthroline) with B(C6F5)3 affords a competent catalyst for the dimerization of vinyl silanes. All organic products of the catalytic dimerization of trialkoxyvinylsilanes were characterized by in situ NMR spectroscopy and GC–MS. The putative palladium cation was characterized by NMR spectroscopy. Upon activation, the palladium complex generated products in moderate yield (60–70%) and selectivity (~60:40, dimer:disproportionation products).

Electronic Control on Linear versus Branched Alkylation of 2-/3-Aroylbenzofurans with Acrylates: Combined DFT and Synthetic Studies

Investigations on the factors that govern unusual branched alkylation of 2-aroylbenzofurans with acrylates by Ru-catalyzed carbonyl-directed C-H activation has been carried out by calculating the kinetics associated with the two key steps-the coordination of the acrylate with the intermediate ruthenacycle and the subsequent migratory insertion reaction-studied with the help of DFT calculations. Eight possible orientations for each mode of alkylation have been considered for the calculations. From these calculations, it has been understood that there is a synergistic operation of the steric and electronic effects favoring the branched alkylation. Further DFT investigations on the alkylation of the isomeric 3-aroylbenzofurans indicated a preference for the linear alkylation and this has been verified experimentally. Overall, the observed/calculated complementary selectivity in the alkylation of 2-/3-aroylbenzofurans with acrylates reveals that the substrate-dependent charge distribution of the Ru-C bond in the intermediate ruthenacycle is an important determining factor and thus the current work opens up a new domain of substrate design for controlling regioselectivity.

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.

Ruthenium(0)-catalyzed hydroarylation of alkynes via ketone-directed C–H functionalization using in situ-generated ruthenium complexes

Ketone-directed Ru(0)-catalyzed hydroarylation of alkynes enabled byin situgeneration of a Ru(0) catalyst from an air-stable, inexpensive and user-friendly Ru(ii) precatalyst is reported.

Carboxylate-assisted ruthenium(ii)-catalyzed C–H activations of monodentate amides with conjugated alkenes

Carboxylate assistance enabled efficient and chemoselective ruthenium(ii)-catalyzed hydroarylations of α,β-unsaturated ketones via C–H activation on monodentate benzamides.

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.

Ru-catalyzed branched versus linear selective C3-alkylation of 2-aroylbenzofurans with acrylates via C-H activation

The carbonyl-directed C3-H activation and alkylation of 2-aroylbenzo[b]furans with acrylates occurs selectively either in a linear or branched fashion, depending on the catalyst employed; [Ru(p-cymene)Cl2]2 or Ru(PPh3)3Cl2, respectively. Two alternate pathways--funded upon the differences in steric and electronic preferences of these two complexes--is proposed for the selectivity of linear versus branched products.

Room-temperature regioselective C-H/olefin coupling of aromatic ketones using an activated ruthenium catalyst with a carbonyl ligand and structural elucidation of key intermediates

Mechanistic studies of the ruthenium-catalyzed reaction of aromatic ketones with olefins are presented. Treatment of the original catalyst, RuH(2)(CO)(PPh(3))(3), with trimethylvinylsilane at 90 °C for 1-1.5 h afforded an activated ruthenium catalyst, Ru(o-C(6)H(4)PPh(2))(H)(CO)(PPh(3))(2), as a mixture of four geometric isomers. The activated complex showed high catalytic activity for C-H/olefin coupling, and the reaction of 2'-methylacetophenone with trimethylvinylsilane at room temperature for 48 h gave the corresponding ortho-alkylation product in 99% isolated yield. The activated catalyst was thermally robust and showed excellent catalytic activity under refluxing toluene conditions. (1)H and (31)P NMR studies of the C-H/olefin coupling at room temperature suggested that an ortho-ruthenated complex, P,P'-cis-C,H-cis-Ru(2'-(6'-MeC(6)H(4)C(O)Me))(H)(CO)(PPh(3))(2), participated in the reaction as a key intermediate. Isotope labeling studies using acetophenone-d(5) indicated that the rate-limiting step was the C-C bond formation, not the C-H bond cleavage, and that each step prior to the reductive elimination was reversible. The rate of C-H/olefin coupling was found to exhibit pseudo first-order kinetics and to show first-order dependence on the ruthenium complex concentration.