Visible-light-promoted cc bond cleavage: photocatalytic generation of iminium ions and amino radicals

Photoscissors: Structurally variable and synthetically robust iminium ions and amino radicals species could be simultaneously generated by visible-light-promoted photoredox cleavage of the C?C bonds in simple vicinal diamine precursors under very mild reaction conditions.     

Palladium-catalyzed cross-coupling reactions of electron-deficient alkenes with N-tosylhydrazones: functional-group-controlled cc bond construction

In the zone: A palladium-catalyzed cross-coupling reaction of electron-deficient alkenes with N-tosylhydrazones, which affords diverse C?C bonds resulting from the functional-group-controlled effect, is reported. These cascade transformations present remarkable stereoselectivity and a high synthetic potential. The presence of water substantially promotes both reaction routes.     

Titanium-catalyzed vinylic and allylic cf bond activation-scope, limitations and mechanistic insight

The hydrodefluorination (HDF) of fluoroalkenes in the presence of a variety of titanium catalysts was studied with respect to scope, selectivity, and mechanism. Optimization revealed that the catalyst requires low steric bulk and high electron density; secondary silanes serve as the preferred hydride source. A broad range of substrates yield partially fluorinated alkenes, such as previously unknown (Z)-1,2-(difluorovinyl)ferrocene. Mechanistic studies indicate a titanium(III) hydride as the active species, which forms a titanium(III) fluoride by H/F exchange with the substrate. The HDF step can follow both an insertion/elimination and a σ-bond metathesis mechanism; the E/Z selectivity is controlled by the substrate. The catalysts' ineffieciency towards fluoroallenes was rationalized by studying their reactivity towards Group?6 hydride complexes.     

Cobalt-catalyzed direct arylation and benzylation by ch/co cleavage with sulfamates, carbamates, and phosphates

Inexpensive cobalt catalysts enable the first direct arylation and benzylation of (hetero)arenes with aryl carbamates, sulfamates, and phosphates with ample scope. The non-radical C?H/C?O arylation reaction even proved viable at ambient temperature.     

Magnesium-mediated benzothiazole activation: a room-temperature cascade of ch deprotonation, cc coupling, ring-opening, and nucleophilic addition reactions

Ligand domin(o)ated: In contrast to the straightforward deprotonation of benzothiazole using Grignard reagents, treatment of benzothiazole with 1 leads to a novel type of activation. The initial magnesiation initiates an unstoppable domino reaction of C?C coupling, ring opening, nucleophilic addition, and deprotonation to give 2. THF=tetrahydrofuran.     

Enantioselective intramolecular benzylic ch bond amination: efficient synthesis of optically active benzosultams

'Salen' along: The iridium(III)-salen complex 1 efficiently catalyzes the title reaction of 2-ethylbenzenesulfonyl azides to give five-membered sultams with high enantioselectivity. Other 2-alkyl-substitued substrates lead to five- and six-membered sultams with high enantioselectivity; the regioselectivity depends upon the substrate and the catalyst used. EDG=electron-donating group.     

Application of copper(i) iodide/diorganoyl dichalcogenides to the synthesis of 4-organochalcogen isoquinolines by regioselective cn and cchalcogen bond formation

A copper-catalyzed cyclization of (ortho-alkynyl)benzaldimines with diorganoyl dichalcogenides allowed the synthesis of 4-organochalcogen isoquinolines, whereas the presence of base in the reaction medium inhibited the product formation producing the undesirable isoquinoline without the organochalcogen atom at the 4-position. The cyclization reaction was carried out by using CuI (20?%) as a catalyst with diorganoyl dichalcogenides (1.5?equiv) in the presence of DMF at 100?°C. Furthermore, the reaction did not require an argon atmosphere and was carried out in an open flask. The cyclization reaction tolerated a variety of functional groups both in ortho-alkynylbenzaldimines and diorganoyl dichalcogenides, such as trifluoromethyl, chloro, fluorine, and methoxyl, to give the six-membered heterocyclic ring exclusively through a 6-endo-dig cyclization process. The organochalcogen group present at the 4-position of the isoquinoline ring was further subjected to a selective chalcogen-lithium exchange reaction followed by the addition of aldehydes to afford the desired secondary alcohols in good yields. The obtained isoquinolines also proved to be suitable substrates for the Suzuki and Sonogashira coupling conditions affording the corresponding products through C?C bond formation.     

Gold catalysis: non-spirocyclic intermediates in the conversion of furanynes by the formal insertion of an alkyne into an aryl-alkyl cc single bond

It takes al-kynes: The formation of furyl-substituted heterocycles from furanynes with donor groups on the furan-alkyne tether and mechanistic control experiments indicate the involvement of open-chained carbenium ions in the overall insertion of an alkyne into a C?C bond, rather than the usual spirocyclic intermediates.     

A visible-light-mediated oxidative cn bond formation/aromatization cascade: photocatalytic preparation of N-arylindoles

Just add light and air: Structurally diverse N-arylindoles can be prepared from readily prepared o-styryl anilines through visible-light photocatalysis. The reaction, which is conducted open to air, is mediated by [Ru(bpz)(3) ](PF(6) )(2) (bpz=2,2'-bipyrazine) and involves both C?N bond formation and aromatization. Using suitably substituted substrates, a 1,2-carbon shift can be also incorporated into this cascade reaction.     

Synthesis of phenanthridinones from N-methoxybenzamides and arenes by multiple palladium-catalyzed ch activation steps at room temperature

Many steps make light work: Substituted phenanthridinones can be obtained with high regioselectivity and in very good yields by palladium-catalyzed cyclization reactions of N-methoxybenzamides with arenes. The reaction proceeds through multiple oxidative C?H activation and C?C/C?N formation steps in one pot at room temperature, and thus provides a simple method for generating bioactive phenanthridinones.     

CC or co bond cleavage in a phenolic lignin model compound: selectivity depends on vanadium catalyst

The aerobic oxidation of a phenolic lignin model compound with a vanadium catalyst results in the oxidative cleavage of the C?C bond between the aryl ring and the adjacent hydroxy-substituted carbon atom. Labeling experiments indicate key mechanistic differences to a previously reported related C?O bond cleavage reaction. The selectivity in C?C versus C?O bond cleavage depends on the choice of the vanadium catalyst.     

Copper(I) promoted CC bond forming reactions: direct activation of allyl alcohols

Allylic alcohols, acetates, carbonates and chlorides can be activated by copper(I) salts towards nucleophilic substitution by carbon nucleophiles under relatively mild conditions.     

Copper-catalyzed formation of C-O bonds by direct α-C-H bond activation of ethers using stoichiometric amounts of peroxide in batch and continuous-flow formats

Peroxides and ethers in flow: 2-Carbonyl-substituted phenols and β-ketoesters react safely with ethers in a microreactor environment using a copper catalyst and an organic peroxide (TBHP). This protocol results in unsymmetrical acetal scaffolds not easily available otherwise (see scheme).     

Iridium pentahydride complex catalyzed formation of CC bond by CH bond activation followed by olefin insertion

The formation of carbon-carbon bond was found to occur by first carbon-hydrogen bond activation followed by olefin insertion under the catalysis of an iridium pentahydride complex.     

An α-Cyclopropanation of Carbonyl Derivatives by Oxidative Umpolung

The reactivity of iodine(III) reagents towards nucleophiles is often associated with umpolung and cationic mechanisms. Herein, we report a general process converting a range of ketone derivatives into α-cyclopropanated ketones by oxidative umpolung. Mechanistic investigation and careful characterization of side products revealed that the reaction follows an unexpected pathway and suggests the intermediacy of non-classical carbocations.     

Allyldialkyl complexes of ruthenium(IV): Preparation and reductive CC bond formation followed by CH bond activation

New η³-allyldimethyl complexes Ru(η⁵-C₅R₅)(η³-C₃H₅)(CH₃)₂, where R = H or CH₃, are prepared from Ru(η⁵-C₅R₅)(η³-C₃H₅)Br₂ by alkylation with trimethyl-aluminium. The Ru^IV dimethyl complex is thermally converted to the Ru^II 1-methylallyl compound, Ru(η⁵-C₅R₅)(η³-CH₂CHCHCH₃)L, where L = CO or t-C₄H₉NC, with evolution of methane. Kinetic and deuteration studies on the reductive process are also discussed.     

Umpolung of α-Allenic Ketones and Esters by Phosphorus Groups

Abstract

Change in the regioselectivity of the addition of nucleophilic compounds YH (ROH, RSH, RNH₂) on α -allenic ketones and esters can be achieved by using the triphenylphosphonio group as an umpolung agent¹⁾. In this way α, β-unsaturated ketones and esters 4 are obtained with heteroatomic substituents in the γ position. The Umpolung scheme of the activated allene 1 is charaterized by a functional vinylphosphonium salt 2 as a synthetic equivalent of the a⁴-synthon 3.     

Brønsted-acid-catalyzed activation of nitroalkanes: a direct enantioselective aza-Henry reaction

A direct asymmetric organocatalytic aza-Henry reaction has been developed in which a new bifunctional Br?nsted-acid-catalyzed activation of nitroalkanes provides an efficient access to alpha,beta-diamino acids with high dia- and enantioselectivities under mild and base-free reaction conditions.     

Nickel-catalyzed reductive cross-coupling of polyfluoroarenes with alkyl electrophiles by site-selective C–F bond activation

A nickel-catalyzed reductive cross-coupling reactions between polyfluoroarenes and alkyl electrophiles is reported to access substituted fluoroarenes through chelation-assisted C–F activation. Diverse primary and secondary alkyl (pseudo)halides can be employed to couple with polyfluoroarenes, showing excellent regioselectivity. Furthermore, the nickel-catalyzed asymmetric cross-coupling of polyfluoroarenes with racemic alkyl halides is preliminarily explored. In addition, the practicability of the title transformation is also demonstrated by total synthesis of losmapimod and an analog as key steps. The developed method exhibits many advantages, including economic catalytic systems, commercially available alkyl electrophiles, and lack of sensitive organometallic reagents.     

Catalytic generation of zinc carbenes from alkynes: zinc-catalyzed cyclopropanation and sih bond insertion reactions

Think zinc: Synthetically relevant zinc(II) carbenes are catalytically generated from alkynes. This new approach allows zinc-catalyzed cyclopropanation and Si?H bond insertion reactions to generate the corresponding cyclopropylfurans or silane derivatives. The structure of the key carbene intermediate was studied using theoretical methods.