Pt(IV)-catalyzed cyclization of arene-alkyne substrates via C-H bond functionalization

We herein report that PtCl₄ has proven to be a hydroarylation catalyst with an efficiency and substrate scope superior to previously known methods. This catalyst demonstrated consistent performance with arene-yne substrates of diverse structural features, including propargyl ethers, propargylamines, and alkynoate esters, providing good to excellent yields of the 6-endo products (chromenes, dihydroquinolines, and coumarins). In contrast, Pt(II), Pd(II), and Ga(III) salts were shown to be sensitive to the substitution on the alkyne moiety. PtCl₄ is compatible with both terminal and disubstituted alkynes, as well as with various functionalities on the arene ring, including methyl, methoxyl, hydroxyl, protected amine, and halide.     

Transition metal-catalyzed olefin arylation via C–H bond activation of arenes

In this article, two kinds of our transition metal-catalyzed olefin arylations are summarized and discussed. The first one is Ir-catalyzed novel anti-Markovnikov hydroarylation of olefins with benzene. Using this reaction catalyzed by [Ir(μ-acac-O,O′,C₃)(acac-O,O′)(acac-C₃)]₂ (acac = acetylacetonato), 1, straight-chain alkylarenes, which were not obtainable by the conventional Friedel-Crafts aromatic alkylation with olefins, were able to be successfully synthesized directly from arenes and olefins with the higher selectivity than that of branched alkylarenes. This is the first efficient catalyst which shows the desirable high regioselectivity. The reaction of benzene with propylene gave n-propylbenzene and cumene in 61% and 39% selectivities, respectively, and the reaction of benzene and styrene afforded 1,2-diphenylethane in 98% selectivity. The reaction of alkylarene and olefin showed meta and para orientations. A wide range of olefins and arenes can be employed for the synthesis of alkylarenes. The mechanism of the reaction involves C–H bond activation of benzene by Ir center to form Ir–phenyl species. The second reaction is Rh-catalyzed oxidative arylation of ethylene with benzene to directly produce styrene, namely one-step synthesis of styrene. The reaction of benzene with ethylene catalyzed by Rh(ppy)₂(OAc) (ppyH = 2-phenylpyridine, OAc = acetate), 3 with Cu oxidizing agent gave styrene and vinyl acetate in 77% and 23% selectivities, respectively, in contrast to those by Pd(OAc)₂, 47% of styrene and 53% of vinyl acetate. The mechanism of the reaction involves Rh-mediated C–H bond activation of benzene, which appears to be a rate-determining step. Furthermore, Rh complexes in a Rh(I) oxidation state at the beginning of the reaction work as catalysts for the reaction by addition of acacH and O₂ without any oxidizing agent, like Cu salt.     

Modification of polyhedral oligomeric silsesquioxane derivatives with heck reaction as possible new bio-hybrid materials

Abstract

The regioselective synthesis of Polyhedral oligomeric silsesquioxane (POSS)-based norbornyl imide derivatives through palladium catalyzed Heck coupling reaction was reported on an effective synthetic method to organic–inorganic bio-hybrids serving as advanced materials. The reaction of POSS-based imide derivatives with various aryl iodides catalyzed by palladium acetate in the presence of triethyl amine, as the base, in DMF afforded the products in moderate yields. All new POSS derivatives were structurally characterized by FTIR, ¹H, ¹³C NMR, HRMS and GC/MS analyses.     

Hydroarylation of arenes with styrenes using Montmorillonite K-10 as an efficient,selective, and recyclable catalyst

Abstract

Hydroarylation of styrene and its derivatives with arenes and heteroarenes was studied using Montmorillonite K-10 as an efficient, environmentally benign, economical, greener, and recyclable catalyst. The reaction gives 1,1-diarylalkanes with a very high selectivity and excellent yields in short time with greater substrate compatibility.     

Enantioselective Synthesis of Functionalized Arenes by Nickel-Catalyzed Site-Selective Hydroarylation of 1,3-Dienes with Aryl Boronates

A catalytic method for the site-selective and enantioselective synthesis of functionalized arenes by the intermolecular hydroarylation of terminal and internal 1,3-dienes with aryl pinacolato boronates is reported. The reactions are promoted by 5.0 mol % of a readily available monodentate phosphoramidite-Ni complex in ethanol, affording a variety of enantioenriched products in up to 96 % yield and 99:1 er. Mechanistic studies indicate that Ni–allyl formation is irreversible and related to the nature of the arylboronate.     

Enantioselective Preparation of Arenes with β‐Stereogenic Centers: Confronting the 1,1‐Disubstituted Olefin Problem Using CuH/Pd Cooperative Catalysis

Arenes with β‐stereogenic centers are important substructures in pharmaceuticals and natural products. We have developed an asymmetric anti‐Markovnikov hydroarylation of 1,1‐disubstituted olefins by dual palladium and copper hydride catalysis as a convenient and general approach to access these substructures. This efficient one‐step process addresses several limitations of the traditional stepwise approaches. The use of cesium benzoate as a base and a common phosphine ligand for both the Cu‐ and Pd‐catalyzed processes were important discoveries that allow these challenging olefin substrates to be efficiently transformed. A variety of aryl bromide coupling partners, including numerous heterocycles, were coupled with 1,1‐disubstituted alkenes to generate arenes with β‐stereogenic centers.     

Ni-Catalyzed Regioselective Hydroarylation of 1-Aryl-1,3-Butadienes with Aryl Halides

An efficient nickel-catalyzed regioselective hydroarylation of 1,3-dienes with aryl halides and a silane has been developed, affording a range of allylic arenes in good to excellent yields under mild conditions. This method exhibits broad substrate scope, and excellent functional group tolerance. Late-stage modification of complex architectures was demonstrated.     

Mechanistic Insights into the Post‐Cyclization Isomerization in Gold‐Catalyzed 7‐exo‐dig‐Hydroarylations

The subsequent double‐bond isomerization in the synthesis of dibenzocycloheptenes and their heteroaromatic analogues was investigated. In the case of biphenyls, a basic additive completely prevented an isomerization to the thermodynamic product. With electron‐rich intramolecular heteroaromatic nucleophiles, the isomerization was still observed, but the kinetic product can be obtained by careful control of the reaction times in most cases. Mechanistic studies demonstrated that a slow isomerization is also possible with the gold catalyst at elevated temperatures, but much faster isomerization rates were observed with acidic additives. An observed initiation period for the gold‐catalyzed isomerization indicates that not the homogenous catalyst, but a decomposition product of it may be the catalytically active species.     

Protecting group free syntheses of (±)-columbianetin and (±)-angelmarin

A five-step and protecting group free synthesis of (±)-columbianetin from cyclohexane-1,3-dione is reported. The former compound was converted into its p-hydroxycinnamate derivative, (±)-angelmarin, using Coster’s esterification procedure. Efforts to modify the synthesis so as to prepare angelmarin and columbianetin in an enantioselective manner are described.