Use Of Transition Metal Catalysis Research Articles

S-Arylation of Thioic S-Acid Using Thianthrenium Salts via Photoactivation of Electron Donor-Acceptor Complex.

Thioesters make up an important class of bioactive compounds. Due to their chemoselectivity, they have been widely used in the synthesis of a wide range of complex bioactive molecules and natural products. At present, chemists have developed a variety of methods for the preparation of thioester compounds. However, these methods usually require the use of transition metal catalysis or harsh reaction conditions. The strategy of synthesizing thioester compounds via visible light-induced electron donor-acceptor (EDA) complex reactions avoids the problems associated with conventional methods through the development of photocatalysis. Here we report a sustainable method for thiocarbonylating aryl sulfonium salts via a visible light-induced EDA complex process without transition metals.

Stereoselective Copper‐Catalyzed Olefination of Imines

AbstractAlkenes are an important class of organic molecules found among synthetic intermediates and bioactive compounds. They are commonly synthesized through stoichiometric Wittig‐type olefination of carbonyls and imines, using ylides or their equivalents. Despite the importance of Wittig‐type olefination reactions, their catalytic variants remain underdeveloped. We explored the use of transition metal catalysis to form ylide equivalents from readily available starting materials. Our investigation led to a new copper‐catalyzed olefination of imines with alkenyl boronate esters as coupling partners. We identified a heterobimetallic complex, obtained by hydrocupration of the alkenyl boronate esters, as the key catalytic intermediate that serves as an ylide equivalent. The high E‐selectivity observed in the reaction is due to the stereoselective addition of this intermediate to an imine, followed by stereospecific anti‐elimination.

Stereoselective Copper-Catalyzed Olefination of Imines.

Alkenes are an important class of organic molecules found among synthetic intermediates and bioactive compounds. They are commonly synthesized through stoichiometric Wittig-type olefination of carbonyls and imines, using ylides or their equivalents. Despite the importance of Wittig-type olefination reactions, their catalytic variants remain underdeveloped. We explored the use of transition metal catalysis to form ylide equivalents from readily available starting materials. Our investigation led to a new copper-catalyzed olefination of imines with alkenyl boronate esters as coupling partners. We identified a heterobimetallic complex, obtained by hydrocupration of the alkenyl boronate esters, as the key catalytic intermediate that serves as an ylide equivalent. The high E-selectivity observed in the reaction is due to the stereoselective addition of this intermediate to an imine, followed by stereospecific anti-elimination.

Cover Feature: Recent Advances in Catalytic Chemical Recycling of Polyolefins (ChemCatChem 13/2023)

The Cover Feature shows the desirable life-cycle for polyolefins, leading from the small building olefinic blocks to polymeric materials present everywhere in our daily life and the use of transition metal catalysis to cut and recycle the polymers back to smaller molecules or new building blocks. In their Review, M. Hapke and co-workers compiled the state-of-the-art for chemical recycling of polyethylenes and polypropylenes at rather low reaction temperatures up to 300 °C using homogeneous and heterogeneous catalysis. The cover image was made by Ella Maru Studio. More information can be found in the Review by M. Hapke and co-workers.

Ni-Catalyzed Synthesis of Thiocarboxylic Acid Derivatives.

A Ni-catalyzed cross-coupling of readily accessible O-alkyl xanthate esters or thiocarbonyl imidazolides and organozinc reagents for the synthesis of thiocarboxylic acid derivatives has been developed. This method benefits from a fast reaction time, mild reaction conditions, and ease of starting material synthesis. The use of transition-metal catalysis to access a diverse range of thiocarbonyl-containing compounds provides a useful complementary approach when compared with previously established methodologies.

Dialkylation of Indoles with Trichloroacetimidates to Access 3,3-Disubstituted Indolenines.

2-Substituted indoles may be directly transformed to 3,3-dialkyl indolenines with trichloroacetimidate electrophiles and the Lewis acid TMSOTf. These reactions provide rapid access to complex indolenines which are present in a variety of complex natural products and medicinally relevant small molecule structures. This method provides an alternative to the use of transition metal catalysis. The indolenines are readily transformed into spiroindoline systems which are privileged scaffolds in medicinal chemistry.

Remote C\u2212H functionalization using radical translocating arylating groups

Site selective chemical functionalization at unactivated C(sp3)−H bonds is highly challenging and recent successful studies mostly focus on the use of transition metal catalysis in combination with directing groups. Radical chemistry offers a complementary approach with the Barton and the Hofmann-Löffler-Freytag reactions being landmark contributions in the area of remote C−H functionalization at unactivated aliphatic sites. Herein we introduce the concept of radical translocation arylation at unactivated secondary and tertiary C(sp3)−H bonds in various alcohols. The straightforward two-step sequence comprises an ionic alcohol sulfonylation with especially designed ortho-iodoaryl sulfonyl chlorides followed by a radical cascade reaction including aryl radical generation, remote radical translocation, aryl migration, reduction, and SO2 extrusion to give the corresponding γ-arylated alcohols. Moderate to good yields are obtained, remote C−H arylation occurs with excellent regioselectivity and for secondary C(sp3)−H bonds good to excellent stereoselectivity is achieved.

A Nickel-Catalyzed Carbonyl-Heck Reaction.

The use of transition-metal catalysis to enable the coupling of readily available organic molecules has greatly enhanced the ability of chemists to access complex chemical structures. In this work, an intermolecular coupling reaction that unites organotriflates and aldehydes is presented. A unique catalyst system is identified to enable this reaction, featuring a Ni0 precatalyst, a tridentate Triphos ligand, and a bulky amine base. This transformation provides access to a variety of ketone-containing products without the selectivity- and reactivity-related challenges associated with more traditional Friedel-Crafts reactions. A Heck-type mechanism is postulated, wherein the π bond of the aldehyde takes the role of the olefin in the insertion/elimination steps.

Transfer of axial chirality through the nickel-catalysed hydrocyanation of chiral allenes.

The transfer of axial chirality of allenes is beginning to be exploited as a powerful method for creating central chirality, particularly through the use of transition metal catalysis. In this communication, the transfer of axial chirality of chiral allenes via nickel-catalysed hydrocyanation is achieved through both regio- and face-selective hydronickelation as well as regioselective reductive elimination. This protocol was applied to 12 substrates and gave chiral carbonitriles with up to 97% ee. Further application to hydrocyanative cyclization using a chiral allene-yne is also presented, along with a discussion of the corresponding mechanism of racemization.

ChemInform Abstract: (Hetero)aromatics from Dienynes, Enediynes and Enyne—Allenes

AbstractReview: 216 refs.

ChemInform Abstract: Allenyl‐β‐Lactams. Versatile Scaffolds for the Synthesis of Heterocycles.

The hybrid allenic β-lactam moiety represents an excellent building block for carbo- and heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under thermal and radical-induced conditions. More recently, the use of transition-metal catalysis has been introduced as an alternative that relies on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of bi- and tricyclic compounds in a regio- and stereoselective manner. This overview focuses on the most recently developed cyclizations on 2-azetidinone-tethered allenes along with remarkable early works accounting for the mechanism, as well as for the regio- and diastereoselectivities of the cyclizations.

ChemInform Abstract: Novel Cyclization Reactions of Aminoallenes

AbstractReview: 109 refs.

Allenyl‐β‐lactams: versatile scaffolds for the synthesis of heterocycles

The hybrid allenic β-lactam moiety represents an excellent building block for carbo- and heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under thermal and radical-induced conditions. More recently, the use of transition-metal catalysis has been introduced as an alternative that relies on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of bi- and tricyclic compounds in a regio- and stereoselective manner. This overview focuses on the most recently developed cyclizations on 2-azetidinone-tethered allenes along with remarkable early works accounting for the mechanism, as well as for the regio- and diastereoselectivities of the cyclizations.

Novel Cyclization Reactions of Aminoallenes

AbstractThe aminoallene moiety represents an excellent building block for heterocyclization reactions, affording a large number of cyclic structures containing different sized skeletons in a single step. This strategy has been studied under basic and electrophile‐induced conditions. More recently, the use of transition metal catalysis has been introduced as an alternative relying on the activation of the allenic component. This overview focuses on the most recently developed cyclizations of aminoallenes along with remarkable early works accounting for the mechanism, as well as for the regio‐ and stereoselectivity of the cyclizations.

Direct stereoselective α-arylation of unmodified enals using an organocatalytic cross-coupling-like reaction

Cross-coupling reactions typically rely on the use of transition metal catalysis. However, although achieving this process using metal-free organocatalysts is highly challenging, it could offer unique opportunities to discover novel bond-forming strategies in organic synthesis. Here we report a new amine catalysed direct stereoselective C-H α-arylation reaction of unmodified enals with bromoarenes. The power of this process, which involves an unprecedented iminium-Michael-alkylation-enamine-retro-Michael cascade sequence, has been demonstrated in the context of direct α-functionalization reactions of simple, unmodified enals with 4-bromophenols, 1-bromo-2-naphthol and 3-bromoindoles under mild reaction conditions. Notably, the process can be used for highly stereoselective syntheses of non-readily accessible E isomers, which normally require the use of transition metal-promoted cross-couplings and functionalized enals. The results of these studies significantly expand the scope of aminocatalysis.

Exploiting [2+2] cycloaddition chemistry: achievements with allenes

The allene moiety represents an excellent partner for the [2+2] cycloaddition with alkenes and alkynes, affording the cyclobutane and cyclobutene skeletons in a single step. This strategy has been widely studied under thermal, photochemical and microwave induced conditions. More recently, the use of transition metal catalysis has been introduced as an alternative relying on the activation of the allenic component. On the other hand, the intramolecular version has attracted much attention as a strategy for the synthesis of polycyclic compounds in a regio- and stereoselective fashion. This critical review focuses on the most recently developed [2+2] cycloadditions on allenes along with remarkable early works accounting for the mechanism, the regio- and diastereoselectivity of the cycloadducts formed (103 references).

Post‐Modification of meso–meso‐Linked Porphyrin Arrays by Iridium and Rhodium Catalyses for Tuning of Energy Gap

meso-meso-Linked diporphyrins fabricated with multiple unsaturated carboxylic acid groups are efficiently synthesized by the use of transition-metal catalysis. Iridium-catalyzed direct borylation of meso-meso-linked diporphyrins furnish multi-borylated diporphyrins with high regioselectivity. Then, the introduction of alpha,beta- or alpha,beta,gamma,delta-unsaturated ester functions to the diporphyrins is achieved through rhodium-catalyzed Heck-type addition of the borylated diporphyrins to acrylate or 2,4-pentadienoate esters. Saponification of the esters to the corresponding acids is accomplished in high yields. The post-modification of diporphyrin 6 smoothly provides a water-soluble multiporphyrin array 1 in 84% total yield in 3 steps. This functionalization significantly affects the electronic properties of the porphyrins, resulting in different energy levels of each porphyrin unit. The absorption and fluorescence spectra indicate efficient energy transfer in the porphyrin dimers.

有機リンおよびイオウ化合物の遷移金属触媒合成

Organoheteroatom compounds of phosphorous and sulfur are important in relation to the development of biologically active substances and materials. Conventional synthesis in general employed substitution reactions of organohalogen compounds with heteroatom reagents. It was considered that i) the addition reaction to unsaturated compounds; ii) the substitution reaction of C-H bond; iii) single bond metathesis would be more favorable, since the starting materials are readily available, and the reactions are atom-economical. Described here is the use of transition metal catalysis for such syntheses of organosulfur and organophosphorous compounds.