Metal-Free C-N or C-C Bond Cleavages of α-Azido Ketones: An Oxidative-Amidation Strategy for the Synthesis of α-Ketothioamides and Amides

Easy Access to α-Ketothioamides via Oxidative Amidation of Bunte Salts Using Electrolysis or Hypervalent Iodine

Two new protocols leveraging electrochemical and hypervalent iodine-mediated synthesis of α-ketothioamides have been developed by using easily accessible and cost-effective Bunte salts and secondary amines. The methods are efficient, simple, and straightforward, and showcase the formation of C-N bonds across diverse substrates under ambient conditions.

Metal-free oxidative coupling of aryl acetylene with elemental sulphur and amines: facile access to α-ketothioamides

A simple and efficient oxidative coupling of aromatic alkynes with elemental sulphur and secondary amines has been reported. The iodine/DMSO system easily promoted the transformations, affording thioglyoxamides via C-S, C-O, and C-N bond formations. In this context, acetylenic C-H bond oxidation has occurred through iodination, leading to the desired products. Moreover, this metal-free, one-pot protocol is accomplished by using readily available starting materials, without external oxidants, and under aerobic conditions, providing a variety of α-ketothioamide compounds in moderate to good yields.

Direct Synthesis of α-Ketothioamide Derivatives through a One-Pot Reaction of Sulfur Ylides, Nitrosobenzenes, and Thioacetic Acid

A one-pot approach has been developed for the synthesis of α-ketothioamide derivatives from sulfur ylides, nitrosobenzenes, and thioacetic acid. This protocol is carried out under mild reaction conditions in generally moderate to excellent yields without any precious catalysts, affording the derivatives with structural diversity. Additionally, a possible mechanism for this chemical transformation is proposed.

C-C Bond Cleavage-Induced C- to N-Acyl Transfer for Synthesis of Amides

A new approach for the preparation of amides was developed using C-C bond cleavage that initiates C- to N-acyl transfer, employing activated ketones as acylation reagents and amine nucleophiles. The reaction was operational under the coupling reagent system that is commonly utilized for peptide bond formations. The method enables practical preparation of amides using linear and cyclic ketone substrates under mild conditions.

Nucleophilic sulfur controlled efficient ketothioamide synthesis from tribromomethyl carbinols

A mild, catalyst and oxidant-free efficient protocol for synthesizing α-ketothioamides is reported with a broad substrate scope. The presented protocol demonstrates the confined reactivity of amines. The polysulfide derived from elemental sulfur and amines in an aqueous medium drives the pathway toward diverse α-ketothioamides over thioamides. Substrates with different substituent groups were compatible with the presented protocol, and the respective ketothioamides were separated in good to excellent yields. The ketothioamides, known to exhibit anti-cancer properties, were synthesized by the proposed protocol. Furthermore, the synthetic utility was explored with the typical synthesis of ketoamides.

Towards More Practical Methods for the Chemical Synthesis of Thioamides Using Sulfuration Agents: A Decade Update

Compounds possessing a thioamide function play a crucial role in organic synthesis, serving as key building blocks. They are also important in the pharmaceutical chemistry and drug design, owing to their ability to mimic the amide function in biomolecules while retaining or developing biological activity. From the synthetic viewpoint, several methods have been developed for preparing thioamides using sulfuration agents. The purpose of this review is to give an update of the last decade of contributions focusing on the formation of thioamides employing different sulfur sources. When appropriate, the cleanness and practicality of the new methods are highlighted.

Metal-Free Syntheses of α-Ketothioamide and α-Ketoamide Derivatives from Sulfoxonium Ylides

An efficient base, additive and metal-free synthetic methods for α-ketothioamide and α-ketoamide derivatives from readily available sulfoxonium ylides have been described. Sulfoxonium ylides with primary or secondary amines afforded α-ketothioamides in the presence of elemental sulfur, whereas α-ketoamides were produced when I2 and TBHP were present. The reaction proceeded well at room temperature and generated the corresponding molecules in good to excellent yields. The reaction can be scaled-up and tolerated by a range of functional groups with simple operational procedures.

Electrochemical Oxidative C-C Bond Cleavage of Ketones for C-N Bond Formation: A Route to Amides

Herein, we report an efficient electrochemical activation of the C-C bond of aryl ketones for the preparation of amides under catalyst- and external-oxidant-free conditions using aliphatic amines as the N source. Under environmentally benign electrolysis conditions, a series of amides were synthesized in good yield. Our control experiments revealed that electricity plays an important role in this transformation.

Tandem oxidative amidation of benzylic alcohols by copper(II) supported on metformin-graphitic carbon nitride nanosheets as an efficient catalyst

In this research, an efficient heterogeneous catalyst based on graphitic carbon nitride nanosheets (CN) has been reported. The CN was functionalized by 1,3-dibromopropane as a linker (CN-Pr-Br) and subsequently modified with metformin (CN-Pr-Met). Furthermore, the copper(II) was coordinated on modified CN (CN-Pr-Met-Cu(II)) and during this process, 7.94% copper(II) was loaded into the catalyst structure. The synthesized catalyst was evaluated by various techniques including fourier-transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and inductively coupled plasma atomic emission spectroscopy (ICP-OES). CN-Pr-Met-Cu(II) was used as a catalyst in the synthesis of amides via the oxidation of benzyl alcohols. The conditions of this reaction were optimized in terms of temperature, time, amount of catalyst, type of base, oxidant, and solvent. Moreover, a variety of amides with an efficiency of 75-95% were synthesized. The reaction was carried out in the presence of benzyl alcohols, amine hydrochloride salts, tert-butyl hydroperoxide (TBHP), CaCO3, and CN-Pr-Met-Cu(II) at 80 °C of acetonitrile solvent. The synthesized catalyst can be easily separated from the reaction medium and reused for 7 consecutive runs without a significant reduction in reaction efficiency.

Visible-Light-Mediated Photocatalytic Oxidative C–C Bond Cleavage of Geminal Diazides: An Approach to Oxamates

Photoredox catalysis has received great attention in both academia and industry and remarkable progress has been made over the past decade. Now, it has been shown that a visible-light-mediated oxidative C–C bond cleavage of geminal diazides can be induced by organic dye catalysis for the synthesis of oxamates. A mechanistic study, confirmed by control experiments, indicates that this proceeds through single-electron transfer (SET). This methodology can be applied to convert a wide array of geminal diazides into oxamates.

Chromatography-Free Multicomponent Synthesis of Thioureas Enabled by Aqueous Solution of Elemental Sulfur

The development of a new three-component chromatography-free reaction of isocyanides, amines and elemental sulfur allowed us the straightforward synthesis of thioureas in water. Considering a large pool of organic and inorganic bases, we first optimized the preparation of aqueous polysulfide solution from elemental sulfur. Using polysulfide solution, we were able to omit the otherwise mandatory chromatography, and to isolate the crystalline products directly from the reaction mixture by a simple filtration, retaining the sulfur in the solution phase. A wide range of thioureas synthesized in this way confirmed the reasonable substrate and functional group tolerance of our protocol.

Synthesis of primary N-arylthioglyoxamides from anilines, elemental sulfur and primary C-H bonds in acetophenones

A simple method for coupling of anilines, acetophenones, and elemental sulfur to afford N-arylthioglyoxamides has been developed. Reactions proceeded in the presence of Na₂SO₃ and DMSO, thus eliminating the need for transition metals and external oxidants. Functionalities such as halogen, ester, methylthio, and heterocycle groups were compatible with the conditions. Electron-poor acetophenones sometimes gave isosteric glyoxamides.

Sulfurative coupling of acetophenones and aniline in the presence of Na₂SO₃ and DMSO solvent to afford N-arylthioglyoxamides was developed.