Palladium(0)-catalyzed asymmetric C(sp3)-H arylation using a chiral binol-derived phosphate and an achiral ligand

High enantioselectivities can be achieved using an appropriate chiral base/achiral ligand combination in Pd⁰-catalyzed C(sp³)–H activation.

The first efficient palladium(0)-catalyzed enantioselective C(sp³)–H activation reaction using a catalytic chiral base and an achiral phosphine ligand is reported. Fine-tuning the binol-derived phosphoric acid pre-catalyst and the reaction conditions was found to be crucial to achieve high levels of enantioselectivity for a variety of indoline products containing both tri- and tetrasubstituted stereocenters.

C-H Activation in Primary 3-Phenylpropylamines: Synthesis of Seven-Membered Palladacycles through Orthometalation. Stoichiometric Preparation of Benzazepinones and Catalytic Synthesis of Ureas

The dimeric cyclometalated complexes [Pd2{κ(2)C,N-C6H4CH2CH2C(R)(Me)NH2-2}2(μ-Cl)2] (R = Me (1a), H (1b)) are prepared by reacting 1,1-dimethyl-3-phenylpropylammonium or 1-methyl-3-phenylpropylammonium triflate with Pd(OAc)2 in a 1:1 molar ratio and subsequent treatment with excess NaCl. The mononuclear derivatives [Pd{κ(2)C,N-C6H4CH2CH2C(R)(Me)NH2-2}Cl(L)] (L = PPh3, R = Me (3a), H (3b); L = 4-picoline (4-pic), R = Me (4a), H (4b)) were prepared from 1a,b by splitting the chloro bridges with the neutral ligands L. A conformational analysis of the mononuclear palladacycles in solution has been carried out. Insertion of CO takes place into the Pd-C bond of complexes 1a,b, affording Pd(0) and the tetrahydro-benzazepinone 5a or 5b, which possesses potential pharmacological interest. Additionally, the triflate salt A or B undergoes catalytic carbonylation with CO to afford the corresponding N,N'-dialkylurea, using Pd(OAc)2/Cu(OAc)2, in boiling acetonitrile. The crystal structures of 3a·(1)/2H2O, 3b, 4b·CHCl3, and 5a were determined by X-ray diffraction studies.

Pd-Catalyzed C(sp(3))-H Functionalization/Carbenoid Insertion: All-Carbon Quaternary Centers via Multiple C-C Bond Formation

A Pd-catalyzed C(sp(3))-H functionalization/carbenoid insertion is described. The method allows for the rapid synthesis of bicyclic frameworks, generating all-carbon quaternary centers via multiple C-C bond formations in a straightforward manner.

Synthesis and Application of Tetrahydro-2H-fluorenes by a Pd(0)-Catalyzed Benzylic C(sp(3) )-H Functionalization

A new method has been developed for the synthesis of tetrahydro-2H-fluorenes based on a Pd(0)-catalyzed benzylic C(sp(3) )-H functionalization. Importantly, the success of the cyclization step was dependent on there being substituents at the two positions ortho to the benzylic group to avoid an undesired C(sp(2) )-H functionalization. This method was subsequently used to prepare the right-hand fragment of the hexacyclic triterpenoid benzohopanes, and therefore represents a powerful tool for the construction of the related compounds.

TADDOL-based phosphorus(III)-ligands in enantioselective Pd(0)-catalysed C-H functionalisations

Monodentate TADDOL-derived phosphoramidites and phosphonites are versatile chiral ligands for enantioselective Pd(0)-catalysed C-H functionalisations. They enable highly selective cyclisations to access a wide range of chiral carbo- and heterocycles. The high attractiveness of this ligand class consists in their modular structure, allowing for a quick assembly of a library with variable steric properties. Asymmetric C-H functionalisation methods utilising catalytic systems based on Pd(0) complexes and TADDOL-type ligands are presented and aspects of selectivity are discussed.

2-(Trifluoromethyl)indoles via Pd(0)-Catalyzed C(sp(3))-H Functionalization of Trifluoroacetimidoyl Chlorides

Perfluoroalkylated indoles are valuable compounds in drug discovery. A Pd(0)-catalyzed C(sp(3))-H functionalization enables access to 2-(trifluoromethyl)indoles from trifluoroacetimidoyl chlorides. These are stable compounds, easily obtained from anilines. The cyclization operates with catalyst loadings as low as 1 mol % and accommodates a variety of substituents.

Synthesis of Strained γ-Lactams by Palladium(0)-Catalyzed C(sp(3) )-H Alkenylation and Application to Alkaloid Synthesis

A variety of strained α-alkylidene-γ-lactams were synthesized by palladium(0)-catalyzed intramolecular C(sp(3) )-H alkenylation from easily accessible acyclic and monocyclic bromoalkene precursors. These lactams are valuable intermediates for accessing various classes of mono- and bicylic alkaloids containing a pyrrolidine ring, as illustrated with the synthesis of an advanced model of the marine natural product plakoridine A and of the indolizidine alkaloid δ-coniceine.

Chemoselective reductive alkynylation of tertiary amides by Ir and Cu(i) bis-metal sequential catalysis

We report a versatile method for the direct, catalytic reductive alkynylation of tertiary amides to give propargylic amines.

Transition metal-free oxidative ortho-acylation of phenols with N-heteroarylmethanes via double C–H activation

The direct oxidative acylation of phenols with N-heteroarylmethanes via sp³C–H and sp²C–H double activation was achieved under metal-free conditions. The reaction proceeds in a facile I₂/DMSO/O₂ system regio-selectively to produce valuable (2-hydroxyphenyl)arylmethanones. A plausible mechanism was proposed.

Copper-catalysed aerobic oxidative esterification of N-heteroaryl methanes with alcohols

Efficient copper-catalysed aerobic oxidative esterification of N-heteroaryl methanes with alcohols has been developed. A variety of N-heteroaryl esters including those with functional groups are produced in good to excellent yields under the present reaction conditions.

Modular synthesis of dihydro-isoquinolines: palladium-catalyzed sequential C(sp2)-H and C(sp3)-H bond activation

An efficient synthesis of dihydro-isoquinolines via a Pd-catalyzed double C-H bond [a C(sp2)-H and a C(sp3)-H bond] activation/annulation (CHAA) reaction is presented. This methodology features a short reaction time, high atom economy (loss of H2O only) and the formation of a sterically less favoured tertiary C-N bond. This fast (30 min) and environmentally benign radical C-H activation approach has demonstrated the potential direction for the future design/development of fast and efficient C-H direct functionalization processes.

Enantioselective palladium(0)-catalyzed intramolecular cyclopropane functionalization: access to dihydroquinolones, dihydroisoquinolones and the BMS-791325 ring system

Taddol-based phosphoramidite ligands enable enantioselective palladium(0)-catalyzed C-H arylation of cyclopropanes. The cyclized products are obtained in high yields and enantioselectivities. The reported method provides efficient access to a broad range of synthetically attractive cyclopropyl containing dihydroquinolones and dihydroisoquinolones as well as allows for an efficient enantioselective construction of the 7-membered ring of the cyclopropyl indolobenzazepine core of BMS-791325.

Oxalyl amide assisted palladium-catalyzed synthesis of pyrrolidones via carbonylation of γ-C(sp3)-H bonds of aliphatic amine substrates

The first Pd-catalyzed regioselective γ-carbonylation of oxalyl amide protected aliphatic amines with carbon monoxide leading to synthesis of pyrrolidones has been developed. Both γ-methyl and cyclopropyl methylene C-H bonds are well activated to obtain the corresponding pyrrolidones in moderate to excellent yields. The role of 3-(trifluoromethyl)benzoic acid as an additive is critical as it helps in stabilizing the palladium intermediate formed during the catalytic cycle. The reaction scope is extended to benzylamine and allyl amine derivatives, thereby affording the corresponding products in good to excellent yields.

Transition metal-catalyzed direct remote C–H functionalization of alkyl groups via C(sp3)–H bond activation

This review is focused on the recent advances in the transition metal-catalyzed direct remote C–H-functionalization of alkyl groups via C(sp³)–H bond activation. In general, carboxamide/ester-chelated β-functionalization reactions are summarized.

NIS/CHP-mediated reaction of isocyanides with hydrazones: access to aminopyrazoles

A NIS/CHP-mediated reaction of isocyanides with hydrazones to construct aminopyrazoles has been developed.

Metal-free methylation of a pyridine N-oxide C–H bond by using peroxides

Metal-free methylation of a pyridine N-oxide C–H bond was developed using peroxide as a methyl reagent under neat conditions. Pyridine N-oxide derivatives with various groups (e.g., Cl, NO₂, and OCH₃) were all suitable substrates.

The catalytic aerobic synthesis of quaternary α-hydroxy phosphonates via direct hydroxylation of phosphonate compounds

A highly efficient Cu-catalyzed direct hydroxylation of phosphonate compounds has been developed. This transformation provides a powerful method for the synthesis of quaternary α-hydroxy phosphonates in good yields.

Experimental and computational studies on the mechanism of the Pd-catalyzed C(sp3)–H γ-arylation of amino acid derivatives assisted by the 2-pyridylsulfonyl group

Experimental and computational studies on the mechanism of the Pd(OAc)₂-catalyzed C(sp³)–H γ-arylation of amino acid derivatives are reported.