Transition-Metal-Free, Reductive Csp2-Csp3 Bond Constructions via Electrochemically Induced Alkyl Radicals.

Construction of the Csp2-Csp3 bond without the aid of transition metal catalysts has been achieved by coupling the electrogenerated alkyl radicals with electron deficient (hetero)arenes in an undivided cell. Simultaneous cathodic reduction of both unactivated alkyl halides and cyanobenzenes under high potential enables radical-radical cross-coupling to deliver alkylarenes in the absence of transition metals. Depending on the coupling partner, the electrogenerated alkyl radicals can also proceed the Minisci-type reaction with N-heteroarenes without redox agents.

Triflic Acid/Silane Promoted Deoxygenative Transformation of Ketones via Carbocations.

Deoxygenative transformation of ketones into value-added products often suffers from precious-metal-based catalysts or complicated operational conditions. Triflic acid and silane serve as a cooperative reductant to transform ketones via carbocations that undergo ß-H elimination much faster than hydride transfer from silane to produce alkenes with high selectivity. Alternatively, the presence of indoles would incept the protonated ketones to generate carbocations, allowing access to Csp2-Csp3 bond formation with high reactivity and selectivity in "one pot".

Electrochemically enhanced deoxygenative cross-coupling of aryl ketones with heteroarenes through in situ generated benzyl carbocations.

Triflic acids/silanes as cooperative reductants enable the convenient transformation of CO bonds through a multistep reaction pathway in one pot. Electrolysis of the acidic reaction mixture significantly improved carbonyl reduction and thus facilitated the generation of benzyl carbocations, which show high reactivity towards electron-rich heteroarenes for C-C bond formation.

Electrochemical reduction of functionalized carbonyl compounds: enhanced reactivity over tailored nanoporous gold.

The effect of the pore size of nanoporous gold on electrochemical reduction of functionalized carbonyl compounds was investigated. NPG with a pore size of ∼30 nm significantly enhanced the reactivity with high chemo-selectivity at a low-potential. Typically, p-nitrobenzaldehyde reduction demonstrates a high turnover frequency (TOF) up to 232 000 h-1.

Anodically Triggered Aldehyde Cation Autocatalysis for Alkylation of Heteroarenes.

Alkylation of heteroarenes by using aldehydes is a direct approach to increase molecular complexity, which however often involves the use of stochiometric oxidant, strong acid, and high temperature. This study concerns an energy-efficient electrochemical alkylation of heteroarenes by using aldehydes under mild conditions without mediators. Interestingly, the graphite anode can trigger aldehyde cationic species, which act as the effective autocatalysts to react with a range of heteroarenes to produce the corresponding products with excellent regioselectivity and in high yields. Compared to the traditional electro-synthesis approaches, this electro-triggered reaction provides an electricity-saving and eco-friendly route to high-value chemicals.

The direct trifluoromethylsilylation and cyanosilylation of aldehydes via an electrochemically induced intramolecular pathway.

The initiator-free electrochemical trifluoromethylsilylation and cyanosilylation of aldehydes were developed in an undivided cell. A DFT study reveals that the direct cathodic activation of trimethylsilyl reagents significantly released the congestion around the 'Si' atom, allowing the Si-O bond affinity to form concerted anion intermediates with aldehydes. Thus, intramolecular -CF3 and -CN migration make the reactions much easier to carry out without initiators.

Arylation of gem-difluoroalkenes using a Pd/Cu Co-catalytic system that avoids ß-fluoride elimination.

PdII/CuI co-catalyze an arylation reaction of gem-difluoroalkenes using arylsulfonyl chlorides to deliver α,α-difluorobenzyl products. The reaction proceeds through a ß,ß-difluoroalkyl-Pd intermediate that typically undergoes unimolecular ß-F elimination to deliver monofluorinated alkene products in a net C-F functionalization reaction. However to avoid ß-F elimination, we offer the ß,ß-difluoroalkyl-Pd intermediate an alternate low-energy route involving ß-H elimination to ultimately deliver difluorinated products in a net arylation/isomerization sequence. Overall, this reaction enables exploration of new reactivities of unstable fluorinated alkyl-metal species, while also providing new opportunities for transforming readily available fluorinated alkenes into more elaborate substructures.

Non-directed copper-catalyzed regioselective C-H sulfonylation of phenothiazines.

We develop a simple and general method for sulfonylation of phenothiazines under Cu(i) catalysis. The broad scope of aryl/alkyl sulfonyl chlorides was applicable to produce C3 sulfonylation products of phenothiazines in moderate to good yields. The further transformation of the sulfonylation products was successful, which afforded valuable polyheterocycles.

Eco-friendly solvents for palladium-catalyzed desulfitative C-H bond arylation of heteroarenes.

Herein, we report the Pd-catalyzed regioselective direct arylation of heteroarenes in which benzenesulfonyl chlorides are used as coupling partners through a desulfitative cross-coupling that can be performed in diethyl carbonate (DEC) or cyclopentyl methyl ether (CPME) as green and renewable solvents or even in neat conditions instead of dioxane or dimethylacetamide (DMA). Under these solvent conditions, the reaction proceeds with a wide range of heteroarenes. C2- or C5-arylated products were obtained with furan and pyrrole derivatives. Benzofuran was also arylated regioselectively at the C2-position, whereas the reaction proceeds selectively at the C3- or C4-positions if thiophenes and benzothiophenes are used. Moreover, in some cases, especially with 1-methylindole, solvent-free conditions afforded better regioselectivities and/or yields than the reaction performed in the presence of solvents.

Regioselective Pd-catalyzed methoxycarbonylation of alkenes using both paraformaldehyde and methanol as CO surrogates.

In recent years, considerable effort has focused on the development of novel carbonylative transformations using CO surrogates. Consequently, toxic CO gas can be replaced by more convenient inorganic or organic carbonyl compounds. Herein, the first regioselective methoxycarbonylation of alkenes with paraformaldehyde and methanol as CO substitutes is reported. This new procedure is applicable to a series of alkenes in the presence of a palladium catalyst under relatively mild conditions and is highly atom efficient.

Benzothiophene or benzofuran bridges in diaryl ethenes: two-step access by pd-catalyzed C-H activation and theoretical/experimental studies on their photoreactivity.

A series of terarylenes incorporating benzothiophene (BT)/benzofuran (BF) as the central ethene unit was synthesised by using sequential Pd-catalysed C-H activation reactions. This new methodology allows the easy modification of the nature of the pendant heteroarene groups. Diaryl ethene (DAE) derivatives with thiophene, thiazole, pyrrole, isoxazole and pyrazole rings were prepared. A large number of asymmetrical DAEs are easily accessible by this new method in both the BT and BF series. The study of their photochromic properties in solution revealed that the nature of the heteroarene and of the central unit drastically modify their photochromic behaviour. TD-DFT calculations were performed to assess the nature of the relevant excited states.

Perfluorocyclohexene bridges in inverse DiArylEthenes: synthesis through Pd-catalysed C-H bond activation, experimental and theoretical studies on their photoreactivity.

The palladium-catalysed direct di-heteroarylation of 1,2-dichloroperfluorocyclohexene with a variety of heteroarenes gives rise in to a new family of 1,2-di(heteroaryl)perfluorocyclohexenes. These derivatives do not exhibit photoreactivity and this unexpected outcome is explained by calculations demonstrating the lack of reactive isomers.

Ruthenium-containing phosphinesulfonate chelate for the hydrogenation of aryl ketones.

Various ruthenium(II) complexes that contain phosphinesulfonate chelate have been synthesized. Arene-free complexes were found to be efficient in the base-free hydrogenation of various aryl ketones, whereas the arene-containing precatalysts required the presence of an amine as an additive. The seminal asymmetric hydrogenation reaction by using the new Sulfo-Binepine ligand was also investigated for the possible intervention of a dihydride species.