Rhodium-Catalyzed Decarbonylative C–H Arylation of 2‑Aryloxybenzoic Acids Leading to Dibenzofuran Derivatives

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

RuHCl(CO)(PPh₃)₃‑Catalyzed α‑Alkylation of Ketones with Primary Alcohols

The α-alkylation reaction of ketones with primary alcohols to give α-alkylated ketones was achieved using RuHCl(CO)(PPh₃)₃ as a catalyst in the presence of Cs₂CO₃ as a base. This reaction proceeds via an aldol condensation of ketones with aldehydes, formed via transfer dehydrogenation of alcohols, to give α,β-unsaturated ketones, which then undergo transfer hydrogenation with primary alcohols to give α-alkylated ketones and aldehydes, the latter of which participate in the next catalytic cycle. While the reaction of aliphatic primary alcohols was sluggish compared with that of benzylic alcohols, a catalytic amount of 1,10-phenanthroline was found to promote the alkylation dramatically

Flow Update for the Carbonylation of 1‑Silyl-Substituted Organolithiums under CO Pressure

The generation of, and subsequent reactions with, 1-silyl-substituted organolithiums with CO was carried out using serially connected flow microreactors. The flow system proved to be quite useful for the carbonylation of silyl-substituted organolithiums under slightly pressurized conditions of CO, which was created conveniently by the use of a back-pressure regulator. This flow system, coupled with heating, accelerated the carbonylation reaction of 1-silyl-substituted organolithiums and allowed the stable silyl-substituted alkyllithium, 1,3-disilylallyllithium, which was not effective in a batch-flask reaction under a CO atmosphere, to participate in an efficient carbonylation reaction

Radical Addition of Alkyl Halides to Formaldehyde in the Presence of Cyanoborohydride as a Radical Mediator. A New Protocol for Hydroxymethylation Reaction

Hydroxymethylation of alkyl halides was achieved using paraformaldehyde as a radical C1 synthon in the presence of tetrabutylammonium cyanoborohydride as a hydrogen source. The reaction proceeds via a radical chain mechanism involving an alkyl radical addition to formaldehyde to form an alkoxy radical, which abstracts hydrogen from a hydroborate anion

Synthesis of Fluorenones through Rhodium-Catalyzed Intramolecular Acylation of Biarylcarboxylic Acids

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

Modernized Low Pressure Carbonylation Methods in Batch and Flow Employing Common Acids as a CO Source

Carbonylation reactions, such as Heck, Sonogashira, and radical carbonylations, were successfully carried out in a “two-chamber reactor” where carbon monoxide was produced <i>ex situ</i> 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

Carbonylative Mizoroki–Heck Reaction of Alkyl Iodides with Arylalkenes Using a Pd/Photoirradiation System

A carbonylative Mizoroki–Heck reaction using alkyl iodides was achieved with a Pd/photoirradiation system using DBU as a base. In this reaction, alkyl radicals were formed from alkyl iodides via single-electron transfer (SET) and then underwent a sequential addition to CO and alkenes to give β-keto radicals. It is proposed that DBU would abstract a proton α to carbonyl to form radical anions, giving α,β-unsaturated ketones via SET

Bromoallylation of Alkenes Leading to 4‑Alkenyl Bromides Based on Trapping of β‑Bromoalkyl Radicals

A radical-chain addition of allyl bromides to aryl alkenes, vinyl ester, and vinyl phthalimide was studied in which elusive β-bromoalkyl radicals were trapped efficiently to give 5-bromo-1-pentenes in good to high yields (16 examples). A subsequent carbonylative radical cyclization with AIBN/Bu₃SnH/CO was successful in giving the corresponding 3,5-disubstituted cyclohexanone derivatives in moderate yields. Synthesis of a piperidine ring was also successful by subsequent reaction with primary amine

Borohydride-Mediated Radical Addition Reactions of Organic Iodides to Electron-Deficient Alkenes

Cyanoborohydrides are efficient reagents in the reductive addition reactions of alkyl iodides and electron-deficient olefins. In contrast to using tin reagents, the reaction took place chemoselectively at the carbon–iodine bond but not at the carbon–bromine or carbon–chlorine bond. The reaction system was successfully applied to three-component reactions, including radical carbonylation. The rate constant for the hydrogen abstraction of a primary alkyl radical from tetrabutylammonium cyanoborohydride was estimated to be <1 × 10⁴ M^–1 s^–1 at 25 °C by a kinetic competition method. This value is 3 orders of magnitude smaller than that of tributyltin hydride

Photocatalytic One-Pot Synthesis of Homoallyl Ketones via a Norrish Type I Reaction of Cyclopentanones

A photocatalytic synthesis of homoallyl ketones was achieved via a one-pot procedure starting from a Norrish Type I reaction of cyclopentanones, followed by a decatungstate-catalyzed hydroacylation of electron-deficient olefins by the resulting 4-pentenals. The site-selective formyl H-abstraction in the second step can be explained by radical polar effects in the transition state