Catalytic Reductive ortho-C-H Silylation of Phenols with Traceless, Versatile Acetal Directing Groups and Synthetic Applications of Dioxasilines

A new, highly selective, bond functionalization strategy, achieved via relay of two transition metal catalysts and the use of traceless acetal directing groups, has been employed to provide facile formation of C-Si bonds and concomitant functionalization of a silicon group in a single vessel. Specifically, this approach involves the relay of Ir-catalyzed hydrosilylation of inexpensive and readily available phenyl acetates, exploiting disubstituted silyl synthons to afford silyl acetals and Rh-catalyzed ortho-C-H silylation to provide dioxasilines. A subsequent nucleophilic addition to silicon removes the acetal directing groups and directly provides unmasked phenol products and, thus, useful functional groups at silicon achieved in a single vessel. This traceless acetal directing group strategy for catalytic ortho-C-H silylation of phenols was also successfully applied to preparation of multisubstituted arenes. Remarkably, a new formal α-chloroacetyl directing group has been developed that allows catalytic reductive C-H silylation of sterically hindered phenols. In particular, this new method permits access to highly versatile and nicely differentiated 1,2,3-trisubstituted arenes that are difficult to access by other catalytic routes. In addition, the resulting dioxasilines can serve as chromatographically stable halosilane equivalents, which allow not only removal of acetal directing groups but also introduce useful functional groups leading to silicon-bridged biaryls. We demonstrated that this catalytic C-H bond silylation strategy has powerful synthetic potential by creating direct applications of dioxasilines to other important transformations, examples of which include aryne chemistry, Au-catalyzed direct arylation, sequential orthogonal cross-couplings, and late-stage silylation of phenolic bioactive molecules and BINOL scaffolds.

The molecular mechanism of palladium-catalysed cyanoesterification of methyl cyanoformate onto norbornene

Potential energy surface mapping was completed for the entire catalytic cycle of palladium-catalysed cyanoesterification onto norbornene (NBE) using density functional theory calculations. We found that after the oxidative addition step of the reagent methyl cyanoformate, the reaction proceeds through an insertion of olefin into a Pd(II)-COOMe bond first. Subsequently, reductive elimination occurs by transferring the cyanide group from the Pd center to NBE. This rearrangement is triggered by the rotation of the ester group into a π-interaction with the Pd(II) centre. The regioselectivity of olefin insertion is controlled by ionic and covalent interactions in the precursor π-complex formation step. Importantly, all of the intermediates and transition states along the exo pathway were found to be more stable than the corresponding structures of the endo pathway without any sign of crossing over between the two surfaces via isomerization. The rate-determining step is the reductive elimination despite the fact that the corresponding activation barrier is reduced by conformational changes via the rotation of a MeOOC-C(NBE) bond.

Palladium-Catalyzed Carbamate-Directed Regioselective Halogenation: A Route to Halogenated Anilines

This study describes an efficient method for ortho-selective halogenation of N-arylcarbamates under mild conditions for the first time. Although being weakly coordinating, N-arylcarbamates act very well as a removable directing group for activation of C-H bonds. The developed procedure results in extremely valuable halogenated N-arylcarbmates that can further be hydrolyzed to halogenated anilines. The obtained reaction conditions showed broad scope and wide functional group tolerance. All the products were formed in good yields with extremely high selectivity.

Enantioselective oxidative boron Heck reactions

This review highlights the use of the oxidative boron Heck reaction in enantioselective Heck-type couplings.

Rhodium-catalyzed tunable oxidative cyclization toward the selective synthesis of α-pyrones and furans

The Rh^III-catalyzed tunable oxidative cyclization of readily availableN-tosylacrylamides and diazo compounds toward the selective synthesis of fully substituted furans and α-pyrones is presented.

Palladium-catalyzed direct C–H arylation of ferrocenecarboxamides with aryl halides

A simple and facile protocol for palladium-catalyzed ortho-arylation of ferrocenecarboxamides with aryl halides was developed with the assistance of the bidentate directing group.

Ruthenium-catalyzed direct arylations with aryl chlorides

Aryl chlorides are readily available at lower cost than the corresponding bromides and iodides, but are much more challenging as substrates in metal-catalyzed cross-couplings.

[RuCl2(η6-p-cymene)] complexes bearing phosphinous acid ligands: preparation, application in C–H bond functionalization and mechanistic investigations

A series of [RuCl₂(η⁶-p-cymene)] complexes bearing phosphinous acid (PA) ligands have been straightforwardly prepared from the dimer [RuCl₂(p-cymene)]₂ and secondary phosphine oxides (SPOs) and fully characterized.

Cu(ii)-catalyzed C6-selective C–H thiolation of 2-pyridones using air as the oxidant

Cu(II)-catalyzed C6-selective C–H thiolation of 2-pyridones with aryl and alkyl disulfides to provide functional thioethers has been achieved.

Amino acid-promoted C–H alkylation with alkylboronic acids using a removable directing group

Palladium-catalyzed C–H alkylation reaction with alkylboronic acids has been developed using a removable pyridyldiisopropylsilyl directing group.

Direct access to 2-(hetero)arylated pyridines from 6-substituted 2-bromopyridines via phosphine-free palladium-catalyzed C–H bond arylations: the importance of the C6 substituent

A Pd(OAc)₂ catalyst promotes the arylation of heteroarenes with 6-substituted 2-bromopyridines, via C–H bond activation, providing straightforward access to 2-(hetero)arylpyridines.

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.

Synthesis of esters via sp3 C–H functionalisation

This review describes various methods for the synthesis of eleven classes of esters involving sp³ C–H functionalisation.

Reactivity of (poly)fluorobenzamides in palladium-catalysed direct arylations

Under PdCl₂/PivOK as reaction conditions, fluoro substituents act as better directing groups than amides in the palladium-catalysed direct arylations.

Double C–H amination by consecutive SET oxidations

A new method for intramolecular C–H oxidative amination is based on a FeCl₃-mediated oxidative reaction of anilines with activated sp³ C–H bonds.

Palladium N-heterocyclic carbene catalyzed expected and unexpected C–C and C–N functionalization reactions of 1-aryl-3-methyl-1H-pyrazol-5(4H)-ones

A palladium N-heterocyclic carbene complex of vitamin B₁ developed earlier in our laboratory was successfully employed as an efficient catalyst for the regioselective C–C and C–N functionalization reactions of 1-aryl-3-methyl-1H-pyrazol-5(4H)-ones.

Palladium-catalyzed direct desulfitative C2 arylations of 3-halo-N-protected indoles using (hetero)arenesulfonyl chlorides

Halo-substituents at the indolyl C3 position act as temporary blocking groups allowing the regioselective formation of 2-arylindoles through a direct desulfitative arylation. This method allows one to prepare a wide variety of indole derivatives in a few steps.

Copper-catalyzed direct C–H fluoroalkenylation of heteroarenes

Efficient copper-catalyzed direct C–H fluoroalkenylation of heterocycles using various gem-bromofluoroalkenes as electrophiles is reported for the first time.

Rh(III)-catalyzed direct C-H/C-H cross-coupling of quinones with arenes assisted by a directing group: identification of carbazole quinones as GSKβ inhibitors

Rh-catalyzed direct C-H/C-H cross-coupling reaction of various (hetero)arenes with quinones is developed. This protocol is effective for a broad range of both quinone and arene substrates and a wide range of directing groups for this reaction, affording structurally diverse aryl-substituted quinones with high synthetic utility. Moreover, the present synthetic route allowed for the rapid construction of the carbazole quinone moiety that was identified as a new inhibitor scaffold for GSKβ.