Unexpected copper-catalyzed aerobic oxidative cleavage of C(sp3)-C(sp3) bond of glycol ethers

Ultrasound-promoted synthesis of a copper-iron-based catalyst for the microwave-assisted acyloxylation of 1,4-dioxane and cyclohexene

A copper-iron-based catalyst has been prepared by a low-temperature co-precipitation and sonication method. The use of high-energy ultrasound reduces the time required for the preparation process from one workweek to one day with respect to the catalysts obtained by conventional coprecipitation and thermal treatment methods. The resulting material has been characterized at compositional, textural, structural, and chemical levels by ICP-AES, BET, SEM-EDS, XRD, TEM, and FTIR among other techniques. The material shows catalytic activity in the acyloxylation reaction of 1,4-dioxane and cyclohexene under microwave irradiation. In parallel with the optimized catalyst synthesis, the use of microwaves allowed for a substantial improvement in the outcome of the reaction in terms of cleanliness, yield, and time.

Hydroxyl-Directed Ru(II)-Catalyzed Synthesis of Fused Dihydrofurans Using 1,4-Dioxane and Sulfoxonium Ylides as Annulating Agents

An unprecedented annulation reaction is developed for the synthesis of dihydrofuran-fused compounds. In this Ru-catalyzed hydroxyl-group-directed reaction, easily affordable sulfoxonium ylides and 1,4-dioxane were used as the annulating partners. This is the first example of the use of 1,4-dioxane as a methylene source to construct a heterocyclic scaffold. A wide range of dihydrofuran0fused coumarins and naphthalenes were synthesized using this three-component reaction.

A novel quinoline-based NNN-pincer Cu(II) complex as a superior catalyst for oxidative esterification of allylic C(sp3)-H bonds

We report for the first time that the quinoline-based NNN-pincer Cu(II) complex acts as an air stable superior catalyst for the oxidative cross-coupling of the allyl sp³ C-H bond with an acid for the synthesis of allyl esters in a homogeneous system at ambient temperature. The synthesized catalyst, 1, has been well characterized by various analytical techniques (HRMS, single crystal X-ray diffraction, CV, EPR, UV-vis spectroscopy) and showed excellent catalytic activity for the oxidative esterification of allylic C(sp³)-H bonds at 40 °C within a very short period of time (1 h) using only 1 mol% of the catalyst. A wide variety of aromatic allylic esters were synthesized in moderate to good yields, which could be extended to aliphatic allyl esters as well.

Scalable Total Synthesis of (-)-Triptonide: Serendipitous Discovery of a Visible-Light-Promoted Olefin Coupling Initiated by Metal-Catalyzed Hydrogen Atom Transfer (MHAT)

An efficient and scalable total synthesis of (-)-triptonide is accomplished based on a metal-catalyzed hydrogen atom transfer (MHAT)-initiated radical cyclization. During the optimization of the key step, we discovered that blue LEDs significantly promoted the efficiency of reaction initiated by Co(TPP)-catalyzed MHAT. Further exploration and optimization of this catalytic system led to development of a dehydrogenative MHAT-initiated Giese reaction.

Ammonium iodide-catalyzed radical-mediated tandem cyclization of aromatic aldehydes, arylamines and 1,4-dioxane

We have developed a novel approach for the construction of 2-((2-arylquinolin-4-yl)oxy)ethan-1-ol derivatives involving a radical-mediated tandem cyclization reaction.

Hypervalent-iodine promoted selective cleavage of C(sp3)–C(sp3) bonds in ethers

A visible-light-promoted and radical-mediated strategy for the site-specific cleavage of C(sp3)–C(sp3) bonds in ethers is reported.

Site-Specific Oxidation of (sp3)C-C(sp3)/H Bonds by NaNO2/HCl

A site-specific oxidation of (sp³)C-C(sp³) and (sp³)C-H bonds in aryl alkanes by the use of NaNO₂/HCl was explored. The method is chemical-oxidant-free, transition-metal-free, uses water as the solvent, and proceeds under mild conditions, making it valuable and attractive to synthetic organic chemistry.

Microwave-Enhanced Coupling of Carboxylic Acids with Liquid Ketones and Cyclic Ethers Using Tetrabutylammonium Iodide/t-Butyl Hydroperoxide

The oxidative coupling of carboxylic acids with liquid ketones and cyclic ethers has been accomplished in minutes using t-butyl hydroperoxide in the presence of tetrabutylammonium iodide under microwave irradiation in the absence of a solvent. In addition to drastically shortening the reaction times, the use of microwaves resulted, in general, in yields equal to or higher than those obtained by conventional heating.

Copper Promoted Aerobic Oxidative C(sp3)-C(sp3) Bond Cleavage of N-(2-(Pyridin-2-yl)-ethyl)anilines

A strategy of aerobic oxidative C(sp³)-C(sp³) bond cleavage of N-ethylaniline derivatives bearing azaarenes for the synthesis of N-aryl formamides has been developed. This approach was carried out smoothly with the CuI/TEMPO/air system to give N-aryl formamides in yields of 50-90%. With this methodology, a mutagenically active compound was constructed in 90% yield. Moreover, the reaction also provided a one-pot synthetic tool for accessing a promoter of hematopoietic stem cells by difunctionalization in 61% yield.

Alkylarylation of N-allylbenzamides and N-allylanilines with simple ethers for the direct construction of ether substituted dihydroisoquinolinones and indolines

A radical-initiated cascade addition and cyclization of N-allylbenzamides with simple ethers to construct ether-substituted dihydroisoquinolinones was performed in the presence of CuI. The cleavage of the sp³ C-H bond in ether and the sp² C-H bond in phenyl was involved in this reaction. Moreover, the arylalkylation of N-allylanilines was also realized under similar reaction conditions, providing ether-functionalized indolines in good to moderate yields.

Tuneable access to isoquinolines via a transition-metal-free C(sp3)–C(sp3) bond cleavage rearrangement reaction

A novel divergent synthesis of multi-substituted isoquinolines via C(sp³)–C(sp³) bond cleavage rearrangement reactions was realized.

A metal-free and mild approach to 1,3,4-oxadiazol-2(3H)-ones via oxidative C–C bond cleavage using molecular oxygen

A metal-free aerobic oxidative C–C bond cleavage reaction for the synthesis of 1,3,4-oxadiazol-2(3H)-ones is described.

Copper porphyrin catalyzed esterification of C(sp3)–H via a cross-dehydrogenative coupling reaction

Copper porphyrin was an efficient catalyst for the direct esterification of C(sp³)–H bonds using DTBP as an oxidant.

Chemoselective C(α)–C(β) bond cleavage of saturated aryl ketones with amines leading to α-ketoamides: a copper-catalyzed aerobic oxidation process with air

An unprecedented chemoselective C(α)–C(β) bond cleavage of simple saturated aryl ketones with amines leading to α-ketoamidesvia a copper-catalyzed aerobic oxidation process with air has been disclosed.

Synthesis of esters via sp3 C–H functionalisation

This review describes various methods for the synthesis of eleven classes of esters involving sp³ C–H functionalisation.

A radical addition/cyclization of diverse ethers to 2-isocyanobiaryls under mildly basic aqueous conditions

Addition of ethers and acetals to 2-isocyanobiaryls: a radical cascade promoted under mildly basic aqueous conditions.

A NCS mediated oxidative C-H bond functionalization: direct esterification between a C(sp(3))-H bond and carboxylic acids

A transition metal free oxidative C-H bond functionalization/esterification of α-alkoxy alkanes with acids is described in this report. This method is effectively mediated by NCS instead of traditional oxidants, like TBHP or its derivatives, and directly generates the esterification products in moderate to high yield under mild conditions. This tranformation constitutes a practical and general approach toward various α-acyloxy ethers with broad substrate generality; alkyl-, aryl-, alkenyl- and alkynyl-carboxylic acids are all well tolerated.

Revealing the halide effect on the kinetics of the aerobic oxidation of Cu(i) to Cu(ii)

Different halide ligands lead to distinct kinetic features in the aerobic oxidation of Cu(i) to Cu(ii) due to the formation of different Cu–O₂ transition states.

Copper-catalyzed oxidative esterification of unactivated C(sp3)–H bonds with carboxylic acids via cross dehydrogenative coupling

An effective copper-catalyzed esterification of unactivated (non-benzylic and allylic) C(sp³)–H bonds of hydrocarbons with Selectfluor as an oxidant has been developed.

Palladium catalyzed Csp2–H activation for direct aryl hydroxylation: the unprecedented role of 1,4-dioxane as a source of hydroxyl radicals

Direct aryl hydroxylation has been achieved via palladium-catalysed C_sp2–H activation using versatile directing groups through unprecedented hydroxyl transfer from 1,4-dioxane.

Selective nickel- and manganese-catalyzed decarboxylative cross coupling of some α,β-unsaturated carboxylic acids with cyclic ethers

A nickel- and manganese-catalyzed decarboxylative cross coupling of α, β-unsaturated carboxylic acids with cyclic ethers such as tetrahydrofuran and 1, 4-dioxane was developed. Oxyalkylation was achieved when nickel acetate was used as catalyst, while manganese acetate promoted the reaction of alkenylation.

Palladium Catalyzed Aryl C-H Amination with O2 via In Situ Formation of Peroxide-Based Oxidant(s) from Dioxane

(DAF)Pd(OAc)2 (DAF = 4,5-diazafluorenone) catalyzes aerobic intramolecular aryl C-H amination with N-benzenesulfonyl-2-aminobiphenyl in dioxane to afford the corresponding carbazole product. Mechanistic studies show that the reaction involves in situ generation of peroxide species from 1,4-dioxane and O2, and the reaction further benefits from the presence of glycolic acid, an oxidative decomposition product of dioxane. An induction period observed for the formation of the carbazole product correlates with the formation of 1,4-dioxan-2-hydroperoxide via autoxidation of 1,4-dioxane, and the in situ-generated peroxide is proposed to serve as the reactive oxidant in the reaction. These findings have important implications for the palladium-catalyzed aerobic oxidation reactions conducted in ethereal solvents.