Conspectus Numerous methods for transition metal catalyzed carbonylation reactions have been established. Examples that start from aryl, vinyl, allyl, and benzyl halides to give the corresponding ...carboxylic acid derivatives have all been well documented. In contrast, the corresponding alkyl halides often encounter difficulty. This is inherent to the relatively slow oxidative addition step onto the metal center and subsequent β-hydride elimination which causes isomerization of the alkyl metal species. Radical carbonylation reactions can override such problems of reactivity; however, carbonylation coupled to iodine atom transfer (atom transfer carbonylation), though useful, often suffers from a slow iodine atom transfer step that affects the outcome of the reaction. We found that atom transfer carbonylation of primary, secondary, and tertiary alkyl iodides was efficiently accelerated by the addition of a palladium catalyst under light irradiation. Stereochemical studies support a mechanistic pathway based on the synergic interplay of radical and Pd-catalyzed reaction steps which ultimately lead to an acylpalladium species. The radical/Pd-combined reaction system has a wide range of applications, including the synthesis of carboxylic acid esters, lactones, amides, lactams, and unsymmetrical ketones such as alkyl alkynyl and alkyl aryl ketones. The design of unique multicomponent carbonylation reactions involving vicinal C-functionalization of alkenes, double and triple carbonylation reactions, in tandem with radical cyclization reactions, has also been achieved. Thus, the radical/Pd-combined strategy provides a solution to a longstanding problem of reactivity involving the carbonylation of alkyl halides. This novel methodology expands the breadth and utility of carbonylation chemistry over either the original radical carbonylation reactions or metal-catalyzed carbonylation reactions.
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The synergistic control of the SH2 transition states of hydrogen abstraction by polar and steric effects provides a promising strategy in achieving site-selective C(sp3)–H functionalization under ...decatungstate anion photocatalysis. By using this photocatalytic approach, the C–H bonds of alkanes, alcohols, ethers, ketones, amides, esters, nitriles, and pyridylalkanes were functionalized site-selectively. In the remarkable case of a 2,4-disubstituted cyclohexanone bearing five methyl, five methylene, and three methine C–H bonds, one methine C–H bond in the isoamyl tether was selectively functionalized.
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Conspectus 1,4-Hydrogen transfer from the 1-hydroxyallyl radical to give the enoxyl (α-keto) radical is an exothermic process with a high activation energy based on DFT calculations. The lack of ...experimental examples of such 1,4-H shift reactions lies in the difficulty of generating the 1-hydroxyallyl radical. We have shown that radical carbonylation of alkenyl radicals with CO followed by nucleophilic trapping of the carbonyl portion of the resulting radical by amines gives rise to 1-amino-substituted 1-hydroxyallyl radicals in situ. At the outset of this chemistry, we examined intramolecular trapping reactions via radical carbonylation of alkynylamines mediated by tributyltin hydride. Consequently, α-methylene lactams were obtained, for which the initially formed 1-amino-substituted 1-hydroxyallyl radical underwent a 1,4-H shift followed by subsequent β-scission, which led to the expulsion of a tributyltin radical. A competing pathway of the 1,4-H shift of 1-amino-substituted 1-hydroxyallyl radicals involving hydrogen abstraction was observed, which led to the formation of α-stannylmethylene lactams as a major byproduct. However, in contrast, when intermolecular trapping of α-ketenyl radicals by amines was carried out, the 1,4-H shift from the 1-amino-substituted 1-hydroxyallyl radical became the major pathway, which gave good yields of α,β-unsaturated amides. Thus, we were able to develop three-component reactions comprising terminal alkynes, CO, and amines that led to α,β-unsaturated amides via the 1,4-H shift reaction. DFT calculations support the observation that the 1,4-H shift is more facile when 1-hydroxyallyl radicals have both 1-amino and 3-tin substituents. The choice of substituents on the amine nitrogen is also important, since N–C bond cleavage via an SH2-type reaction can become a competing pathway. Such an unusual SH2-type reaction at the amine nitrogen is favored when the leaving alkyl radicals are stable, such as PhC(•)H(CH3) and t-Bu•. Interestingly, even nucleophilic attack of tertiary amines onto α-ketenyl radicals causes cleavage of the C–N bond. For this reaction, DFT calculations predict an indirect homolytic substitution mechanism involving expulsion of alkyl radicals through the zwitterionic radical intermediate arising from nucleophilic amine addition onto the α-ketenyl radical. In contrast, the carbonylation of aryl radicals, generated from aryl iodides, in the presence of amines gave aromatic carboxylic amides in good yields. It is proposed that radical anions originating from acyl radicals and amines undergo electron transfer to aryl iodides to give aminocarbonylation products.
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Microreactors have brought significant improvements to chemical synthesis and production because of their advantageous characteristics over batch reactors, which include highly efficient mixing, ...efficient heat and mass transfer ability, precise control of the residence time, large surface area-to-volume ratio and high operational safety. Microreactor technology has been found to be beneficial for gas-liquid biphasic reactions, for which the large interfacial area between the two phases is ensured. Carbonylation reactions with carbon monoxide, by which a wide range of carbonyl compounds can be prepared, deal with a variety of reactive species, such as organo transition metals, radicals, cations and anions. These reactions have long been carried out using a glass batch flask or a stainless-steel made autoclave, however, carbonylation reactions using a flow microreactor are now rapidly increasing in popularity. This review focuses on a new greener wave of carbonylation reactions using a flow microreactor.
This review describes a new greener wave of carbonylation reactions using a flow microreactor.
A facile sunlight-induced derivatization of heteroaromatics via photocatalyzed C-H functionalization in amides, ethers, alkanes and aldehydes is described. Tetrabutylammonium decatungstate (TBADT) ...was used as the photocatalyst and allowed to carry out the process under mild conditions.
The TBADT‐catalyzed C(sp3)–H functionalization of perfluorophenyl‐ and perfluoroalkyl‐substituted alkanes was studied to determine how the fluorous substituents affect site‐selectivity. Alkylation of ...alkyl‐substituted perfluorobenzene avoids α‐C–H bonds, unlike their alkylbenzene counterparts, allowing site‐selective functionalization of C–H bonds remote to the aromatic ring. Alkylation of alkanes having a perfluoroalkyl group also avoided α‐C–H bonds. Radical polar effects in the SH2 transition states could explain this avoidance of α‐C–H functionalization.
The TBADT‐catalyzed C(sp3)–H functionalization of perfluorophenyl‐ and perfluoroalkyl‐substituted alkanes was investigated. Alkylation of alkanes having a perfluoroalkyl group and alkyl‐substituted perfluorobenzenes avoided α‐C–H bonds. Radical polar effects in the SH2 transition states could explain this avoidance of α‐C–H functionalization.
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Carbonylation reactions, such as Heck, Sonogashira, and radical carbonylations, were successfully carried out in a “two-chamber reactor” where carbon monoxide was produced ex situ by the Morgan ...reaction (dehydration of formic acid by sulfuric acid). By a subsequent application in a microflow system using a “tube-in-tube” reactor where gas-permeable Teflon AF2400 was used as the inner tube, it is demonstrated that formic acid/sulfuric acid can be employed concomitantly with an amine base such as triethylamine in the Heck aminocarbonylation of aryl iodide.
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In this article, we discuss how effective photo-induced organic reactions became when applied evolving photo flow technologies through our experiences over these two last decades. We started with the ...flow update of traditional 2 + 2 cycloaddition using Mikroglas Dwell device as a flow reactor and a compact light source, such as blacklight, instead of a high-pressure mercury lamp. Then we examined Barton nitrite reaction using a photo flow reactor consisting of stainless-steel channels and a quartz glass top provided by DNS. Again the use of blacklight was successful. However, the energy profile of these reactions was improved further by the use of LED lights. We used a photo-flow set-up, consisting of stainless steel engraved microchannels covered by a quartz top (MiChS L-1) and a sodium lamp, for the isomerization of a fulleroid to PCBM. Photo-redox-catalyzed alkene alkylation proceeded within a shortened reaction time when the same photo flow reactor and white LED were used instead of a batch reactor. Photo-induced reductive 5-exo-dig radical cyclization and reduction of alkenyl halides proceeded smoothly, thanks to the combination of a photo flow reactor and low-pressure Hg lamp. We also applied flow technologies for photo-bromination and chlorination of C-H bonds. Photocatalytic oxidation of benzyl alcohol by molecular oxygen became quick when high-power LED irradiation was employed.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
An efficient approach to the synthesis of fluorenones via the rhodium-catalyzed intramolecular acylation of biarylcarboxylic acids was developed. Using this procedure, fluorenones with various ...substituents can be synthesized in good to high yields. This work marks the first recorded use of catalytic intramolecular acylation to synthesize fluorenones.
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Rhodium-catalyzed intramolecular C–H arylation of 2-aryloxybenzoic acids proceeded accompanied by decarbonylation to give dibenzofuran derivatives in high yields. The present reaction is widely ...applicable to substrates bearing various functionalities.
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