Synthesis of gamma-halogenated ketones via the Ce(IV)-mediated oxidative coupling of cyclobutanols and inorganic halides

Photoinduced Fe-Catalyzed Bromination and Iodination of Unstrained Cyclic Alcohols

We report a photoinduced iron catalysis for the efficient C─C bond cleavage and bromination or iodination of unstrained tertiary cycloalkanols with NBS/NIS. The reaction features good functional group tolerance and...

Electrophotochemical Ring-Opening Bromination of tert-Cycloalkanols

An electrophotochemical ring-opening bromination of unstrained tert-cycloalkanols has been developed. This electrophotochemical method enables the oxidative transformation of cycloalkanols with 5- to 7-membered rings into synthetically useful ω-bromoketones without the use of chemical oxidants or transition-metal catalysts. Alkoxy radical species would be key intermediates in the present transformation, which generate through homolysis of the O-Br bond in hypobromite intermediates under visible light irradiation.

Copper-catalyzed radical ring-opening halogenation with HX

An efficient copper-catalyzed radical ring-opening halogenation with HX (aq) is described. This protocol features redox-neutral conditions, green halogen sources, and a broad substrate scope, providing practical access to distally chlorinated, brominated and iodinated alkyl ketones and alkyl nitriles with moderate to good yields.

Rapid and scalable synthesis of fluoroketones via cerium-mediated C-C bond cleavage

Ketones with remote fluorination are an important motif in the synthesis of bioactive molecules. Here we demonstrate that ceric ammonium nitrate (CAN) is able to produce this functionality under incredibly mild conditions and short reaction times (30 min) while eliminating the need for precious metals in previous methods. Importantly, this method allows the efficient synthesis of a wide variety of γ-fluoroketones and is highly scalable. Preliminary mechanistic studies suggest this reaction proceeds through a radical pathway.

Nickel-Catalyzed Arylation/Alkenylation of tert-Cyclobutanols with Aryl/Alkenyl Triflates via a CC Bond Cleavage

Herein, we first present a nickel-catalyzed arylation and alkenylation of tert-cyclobutanols with aryl/alkenyl triflates via a C-C bond cleavage. An array of γ-substituted ketones was obtained in moderate-to-good yields, thus featuring earth-abundant nickel catalysis, broad substrate scope, and simple reaction conditions. Preliminary mechanistic experiments indicated that β-carbon elimination pathways might be involved in the catalytic cycle.

Pd-Catalyzed coupling reaction of cyclobutanols with propargylic carbonates

Pd-Catalyzed ring opening coupling reaction of cyclobutanols with propargylic carbonates afforded δ-allenyl ketones efficiently.

Visible light-promoted ring-opening functionalization of unstrained cycloalkanols via inert C-C bond scission

Described herein is a novel, useful, visible light-promoted ring-opening functionalization of unstrained cycloalkanols. Upon scission of an inert cyclic C-C σ-bond, a set of medium- and large-sized rings are readily brominated under mild reaction conditions to afford the corresponding distal bromo-substituted alkyl ketones that are hard to synthesize otherwise. The products are versatile building blocks, which are easily converted to other valuable molecules in one-step operation. This protocol is also applicable to the unprecedented ring-opening cyanation and alkynylation of unstrained cycloalkanols.

Enhanced Structural Variety of Nonplanar N-Oxyl Radical Catalysts and Their Application to the Aerobic Oxidation of Benzylic C-H Bonds

The design and synthesis of structurally variable, nonplanar N-oxyl radical catalysts and their application to the aerobic oxidation, etherification, and acetoamidation of benzylic C-H bonds are described. The catalytic oxidation of C-H bonds represents a powerful tool to synthesize oxygenated functional molecules from simple hydrocarbons in a straightforward way. Electron-deficient N-oxyl radical catalysts, such as phthalimidoyl N-oxyl (PINO) radical, generated from N-hydroxyphthalimide (1), have attracted much attention because of their applications in the oxidation of C-H bonds with high bond dissociation energy (BDE). However, a few sites in 1 are available for structural modifications and improvements of the catalytic performance. By replacing one carbonyl group in 1 with a trifluoromethyl (CF3)-substituted sp(3)-carbon, we generated an additional tunable site and a nonplanar backbone, while retaining the desirable electron-withdrawing properties and increasing the lipophilicity with respect to 1. We synthesized a variety of N-hydroxy precatalysts containing such a CF3 moiety, and investigated their utility in the aerobic oxidation of benzylic C-H bonds. Precatalysts with electron-withdrawing substituents, such as trifluoroethoxy and the acetophenone moieties, afforded higher yields than a corresponding methoxy-substituted analogue. The introduction of substituents at the aromatic ring was also effective, as evident from the performance of 7-CF3 and 4,5,6,7-tetrafluoro precatalysts. Especially the combination of trifluoroethoxy- and 4,5,6,7-tetrafluoro substitution afforded a superior performance. These catalyst systems exhibited high functional group tolerance during the aerobic oxidation of C-H bonds, and benzylic etherification and Ritter-type reactions could be carried out at room temperature when a selected precatalyst and N-bromosuccinimide (NBS) were used.

Ring-opening selenation of cyclobutanols: synthesis of γ-selenylated alkyl ketones through C–C bond cleavage

An efficient, practical, and operationally simple manganese-mediated ring-opening selenation of cyclobutanols is disclosed.

Manganese-Promoted Ring-Opening Hydrazination of Cyclobutanols: Synthesis of Alkyl Hydrazines

We herein disclose an efficient manganese-promoted hydrazination of cyclobutanols through cyclic C-C bond cleavage. The ring opening occurs under mild reaction conditions, readily affording a variety of alkyl hydrazines in synthetically useful yields and exclusive regioselectivities. The chain reaction mechanism involving the addition of alkyl carbon radical to azodicarboxylate is proposed.

Manganese-catalyzed regiospecific sp3C–S bond formation through C–C bond cleavage of cyclobutanols

A manganese-catalyzed regioselective sp³C–S bond formation through C–C bond cleavage of cyclobutanols is described.

Regiospecific synthesis of distally chlorinated ketones via C–C bond cleavage of cycloalkanols

A variety of distally Csp³-chlorinated ketones were efficiently synthesized via silver-catalyzed ring opening of cycloalkanols under mild reaction conditions.

Manganese-catalyzed ring-opening chlorination of cyclobutanols: regiospecific synthesis of γ-chloroketones

An efficient, mild, and practical ring-opening chlorination of cyclobutanols is developed by means of manganese catalysis.

Iron- or silver-catalyzed oxidative fluorination of cyclopropanols for the synthesis of β-fluoroketones

The Fe^III- or Ag^I-catalyzed oxidative fluorination of cyclopropanols via radical rearrangement is disclosed.

A facile and regioselective synthesis of 1-tetralones via silver-catalyzed ring expansion

A regioselective synthesis of 1-tetralones via silver-catalyzed ring expansion is described.

Mechanistic studies on the CAN-mediated intramolecular cyclization of δ-aryl-β-dicarbonyl compounds

The synthesis of 2-tetralones through the cyclization of δ-aryl-β-dicarbonyl substrates by using CAN is described. Appropriately functionalized aromatic substrates undergo intramolecular cyclizations generating 2-tetralone derivatives in moderate to good yields. DFT computational studies indicate that successful formation of 2-tetralones from δ-aryl-β-dicarbonyl radicals is dependent on the stability of the subsequent cyclohexadienyl radical intermediates. Furthermore, DFT computational studies were used to rationalize the observed site selectivity in the 2-tetralone products.

On the nature of the oxidative heterocoupling of lithium enolates

The coupling of enolates through single-electron oxidation is one of the most direct routes for generating 1,4-dicarbonyls. Recent work on the intermolecular heterocoupling of equimolar amounts of two different enolates through single-electron oxidation has shown that synthetically useful yields beyond those predicted by statistics can be obtained. To determine the underlying basis for the selective formation of heterocoupled products, kinetic, (7)Li NMR, and synthetic studies were performed. The collection of data obtained from these experiments shows that the selective formation of heterocoupled products is a consequence of heteroaggregation of lithium enolates.