Transition-Metal-Catalyzed Aldehydic C−H Activation by Azodicarboxylates

Photoredox-Catalyzed Hydroacylation of Azobenzenes with Carboxylic Acids

Acyl hydrazides are widely found in bioactive compounds and have important applications as versatile synthetic intermediates. In the current report, a photoredox-catalyzed hydroacylation of azobenzenes was disclosed with carboxylic acids as the acylation reagent, affording a variety of N,N'-disubstituted hydrazides. The process possesses the advantages of mild reaction conditions, broad substrate scope, and high efficiency. Preliminary mechanistic investigation indicated that the addition of an acyl radical to the azo compound should be involved.

Light-accelerated "on-water" hydroacylation of dialkyl azodicarboxylates

The hydroacylation of dialkyl azodicarboxylates has received a lot of attention lately due to the great importance of acyl hydrazides in organic chemistry. Herein, we report an inexpensive and green photochemical approach, where light irradiation (390 nm) significantly accelerates the reaction between dialkyl azodicarboxylates and aldehydes, while water is employed as the solvent. A variety of aromatic and aliphatic aldehydes were converted into their corresponding acyl hydrazides in good to excellent yields in really short reaction times (15-210 min) and the reaction mechanism was also studied. Applications of this reaction in the syntheses of Vorinostat and Moclobemide were demonstrated.

Visible-Light-Mediated (sp 3)Cα-H Functionalization of Ethers Enabled by Electron Donor-Acceptor Complex

A synthetically beneficial visible-light-mediated protocol has been disclosed to achieve C-H amination of readily available feedstocks cyclic and acyclic ethers. A rarely identified N-bromosuccinamide-tetrahydrofuran electron donor-acceptor complex served as an initiator to functionalize both α-diazoketones and dialkyl azodicarboxylates. This developed methodology gives an alternative and milder way to construct the C-N bond and can be explored for the formation of C-C bond to perform arylation and allylation reactions.

Photochemical Activation of a Hydroxyquinone-Derived Phenyliodonium Ylide by Visible Light: Synthetic and Mechanistic Investigations

We have identified and extensively investigated the photochemical activation and reaction of a hydroxyquinone-derived phenyliodonium ylide in the presence of visible light using experiment and theory. These studies revealed that in its photoexcited state this iodonium is capable of facilitating a range of single-electron transfer (SET) processes, including hydrogen atom transfer (HAT), a Povarov-type reaction, and atom-transfer radical addition chemistry. Where possible, we have employed density functional theory (DFT) to develop a more complete understanding of these photoinduced synthetic transformations.

Phenylglyoxylic Acid: An Efficient Initiator for the Photochemical Hydrogen Atom Transfer C-H Functionalization of Heterocycles

C-H functionalization at the α-position of heterocycles has become a rapidly growing area of research. Herein, a cheap and efficient photochemical method was developed for the C-H functionalization of heterocycles. Phenylglyoxylic acid (PhCOCOOH) could behave as an alternative to metal-based catalysts and organic dyes and provided a very general and wide array of photochemical C-H alkylation, alkenylation, and alkynylation, as well as C-N bond forming reaction methodologies. This novel, mild, and metal-free protocol was successfully employed in the functionalization of a wide range of C-H bonds, utilizing not only O- or N-heterocycles, but also the less studied S-heterocycles.

Synthetic Approaches to Acyl Hydrazides and Their Use as Synthons in Organic Synthesis

Acyl hydrazides constitute very important moieties in organic chemistry and have been employed as starting materials for different transformations to many classes of organic compounds. In this review, at first the approaches towards the synthesis of acyl hydrazides are presented. Furthermore, in the second part, the uses of this skeleton as an important intermediate for the synthesis of useful organic compounds are analyzed.

1 Introduction

2 Approaches towards the Synthesis of Acyl Hydrazides

2.1 Synthesis of Acyl Hydrazides from Aldehydes

2.2 Synthesis of Acyl Hydrazides from Carboxylic Acid Derivatives

3 Acyl Hydrazides as Useful Synthons in Synthetic Organic Transfor mations­

3.1 Acyl Hydrazides as Synthetic Precursors for the Synthesis of Car bonyl Compounds

3.2 Acyl Hydrazides as Synthetic Precursors for the Synthesis of Het erocyclic Rings

4 Conclusion

Palladium catalyzed chemo- and site-selective C-H acetoxylation and hydroxylation of oxobenzoxazine derivatives

An efficient protocol for the introduction of acetoxy and hydroxy functionalities on unactivated aryl sp2 carbons of oxobenzoxazine derivatives via an ortho-C-H activation reaction using a palladium catalyst has been developed for the first time. Interestingly, this intermolecular C-H functionalization reaction takes place in a facile and simple manner with high chemo- and site selectivity.

Application of dialkyl azodicarboxylate frameworks featuring multi-functional properties

The application of dialkyl azodicarboxylates as versatile reagents in Mitsunobu, oxidation, electrophilic, amination and carbonylation reactions is reviewed.

Cross-dehydrogenative coupling and oxidative-amination reactions of ethers and alcohols with aromatics and heteroaromatics

This is a perspective on cross-dehydrogenative coupling reactions of aromatic and heteroaromatic systems with ethers and alcohols via metal or organic catalysis, and through uncatalyzed means, leading to C–C and C–N bond formation.

Cross-dehydrogenative coupling (CDC) is a process in which, typically, a C–C bond is formed at the expense of two C–H bonds, either catalyzed by metals or other organic compounds, or via uncatalyzed processes. In this perspective, we present various modes of C–H bond-activation at sp³ centers adjacent to ether oxygen atoms, followed by C–C bond formation with aromatic systems as well as with heteroaromatic systems. C–N bond-formation with NH-containing heteroaromatics, leading to hemiaminal ethers, is also an event that can occur analogously to C–C bond formation, but at the expense of C–H and N–H bonds. A large variety of hemiaminal ether-forming reactions have recently appeared in the literature and this perspective also includes this complementary chemistry. In addition, the participation of C–H bonds in alcohols in such processes is also described. Facile access to a wide range of compounds can be attained through these processes, rendering such reactions useful for synthetic applications via C_sp³ bond activations.

An overview of the synthesis of acyl hydrazides from aldehydes and reactions of the products thereof

An overview of the methods for the formation and reaction of acyl hydrazides.

Copper-catalyzed carbonylation of anilines by diisopropyl azodicarboxylate for the synthesis of carbamates

Herein, a simple Cu-catalyzed system for the synthesis of carbamates has been developed using anilines with diisopropyl azodicarboxylate as a carbonyl source under solvent-free conditions.

A facile, one-pot procedure for the conversion of aromatic aldehydes to esters, as well as thioesters and amides, via acyl hydrazide intermediates

A facile, one-pot procedure for the conversion of aromatic aldehydes to esters, as well as thioesters and amides, via acyl hydrazide intermediates.

Vanadyl species-catalyzed complementary β-oxidative carbonylation of styrene derivatives with aldehydes

By judicious choice of the counter anions in the vanadyl catalysts, we can achieve β-hydroxylated and t-butyl peroxylated carbonylation of styrenes by aromatic 1° and 2° alkyl aldehydes in a complementary manner.

Photoorganocatalytic hydroacylation of dialkyl azodicarboxylates by utilising activated ketones as photocatalysts

A fast and efficient visible-light metal-free hydroacylation of dialkyl azodicarboxylates is described. Among a variety of activated ketones, phenyl glyoxylic acid and its ethyl ester were identified as suitable photoorganocatalysts. A range of aliphatic and aromatic aldehydes were employed, thus leading to products in high to excellent yields.

Efficient imidation of C(sp3)–H bonds adjacent to oxygen atoms of aryl ethers under metal-free conditions

A metal-free intermolecular oxidative C–N formation reaction of aryl ethers with saccharins was realized for the first time.

Radicals in transition metal catalyzed reactions? transition metal catalyzed radical reactions? - a fruitful interplay anyway: part 2. Radical catalysis by group 8 and 9 elements

This review summarizes the current status of transition metal catalyzed reactions involving radical intermediates in organic chemistry. This part focuses on radical-based methods catalyzed by group 8 and group 9 metal complexes. Reductive and redox-neutral coupling methods catalyzed by low-valent metal complexes as well as catalytic oxidative C-C bond formations are reviewed.

1H, 13C and 15N NMR studies on adducts formation of rhodium(II) tetraacylates with some azoles in CDCl3 solution

Adduct formations of rhodium(II) tetraacetate and tetratrifluoroacetate with some 1H-imidazoles, oxazoles, thiazoles, 1H-pyrazoles and isoxazole have been investigated by the use of 1H, 13C, 15N NMR and electronic absorption spectroscopy (VIS) in the visible range. Azoles tend to form axial adducts containing rhodium(II) tetraacylates bonded via nitrogen atom. Bulky substituents close to the nitrogen atom prevent the Rh--N bond formation, and in several cases switch over the binding site to the oxygen or sulphur atoms. The (15)N adduct formation shift Deltadelta(15N) (Deltadelta = delta(adduct) - delta(ligand)) varied from ca - 40 to - 70 ppm for the nitrogen atom involved in complexation, and of a few parts per million only, from ca - 6 to 3 ppm, for the non-bonded nitrogen atom within the same molecule. The Deltadelta(1H) values do not exceed one ppm; Deltadelta(13C) ranges from - 1 to 6 ppm. Various complexation modes have been proved by electronic absorption spectroscopy in the visible region (VIS). For comparison purposes, some adducts of pyridine, thiophene and furan derivatives have been measured as well. The experimental findings were compared with calculated chemical shifts, obtained by means of DFT B3LYP method, using 6-311 + G(2d,p), 6-31(d)/LanL2DZ and 6-311G(d,p) basis set.

Use of N−N Bond Stereodynamics in Ring-Closing Metathesis to Form Medium-Sized Rings and Macrocycles

A unique strategy based on double ring-closing metathesis for the formation of a 14-membered macrocyclic enamide has been developed. This strategy hinges upon the well-known stereodynamic and conformational behavior of N-substituted diacylhydrazines, which promotes an effective ring-closing metathesis of hydrazine-derived dienes and enynes to form 8- to 14-membered rings.