Mechanochemical Defluorinative Arylation of Trifluoroacetamides: An Entry to Aromatic Amides.

The amide bond is prominent in natural and synthetic organic molecules endowed with activity in various fields. Among a wide array of amide synthetic methods, substitution on a pre-existing (O)C-N moiety is an underexplored strategy for the synthesis of amides. In this work, we disclose a new protocol for the defluorinative arylation of aliphatic and aromatic trifluoroacetamides yielding aromatic amides. The mechanochemically induced reaction of either arylboronic acids, trimethoxyphenylsilanes, diaryliodonium salts, or dimethyl(phenyl)sulfonium salts with trifluoroacetamides affords substituted aromatic amides in good to excellent yields. These nickel-catalyzed reactions are enabled by C-CF3 bond activation using Dy2O3 as an additive. The current protocol provides versatile and scalable routes for accessing a wide variety of substituted aromatic amides. Moreover, the protocol described in this work overcomes the drawbacks and limitations in the previously reported methods.

Mechanochemical arylative detrifluoromethylation of trifluoromethylarenes.

The stoichiometric defluorinative functionalization of ArCF3 is a conceptually appealing research target. It enables the challenging late-stage functionalization of CF3-containing aromatic molecules and contributes to the remedy of environmental risks resulting from the accumulation of relatively inert ArCF3-containing molecules. Similarly, Ar-CN bond features limit their utilization in cross-coupling reactions. Thus, the employment of benzonitriles in decyanative Suzuki-Miyaura type coupling remains in high demand in the field of C-C bond formation. Herein, we report mechanochemically induced and ytterbium oxide (Yb2O3)-mediated defluorinative cyanation of trifluoromethylarenes. In addition, we describe a facile mechanochemically facilitated and nickel-catalyzed decyanative arylation of benzonitriles to access biphenyls. Combining both processes in a one-pot multicomponent protocol to achieve a concise direct arylative detrifluoromethylation of ArCF3 is described herein. This work is the first hitherto realization of C-C coupling with CF3 as a formal leaving group.

Mechanochemical Conversion of Aromatic Amines to Aryl Trifluoromethyl Ethers.

Increased interest in the trifluoromethoxy group in organic synthesis and medicinal chemistry has induced a demand for new, selective, general, and faster methods applicable to natural products and highly functionalized compounds at a later stage of hit-to-lead campaigns. Applying pyrylium tetrafluoroborate, we have developed a mechanochemical protocol to selectively substitute the aromatic amino group with the OCF3 functionality. The scope of our method includes 31 examples of ring-substituted anilines, including amides and sulfonamides. Expected SNAr products were obtained in excellent yields. The presented concise method opens a pathway to new chemical spaces for the pharmaceutical industry.

Arylation of ortho-Hydroxyarylenaminones by Sulfonium Salts and Arenesulfonyl Chlorides: An Access to Isoflavones.

Herein we disclose three new methods for the straightforward and efficient synthesis of 3-arylchromones following the arylation of ortho-hydroxyarylenaminones by vast diversities of bench-stable and easy-to-use sulfonium salts and arenesulfonyl chlorides. Both developed methods, namely the light-mediated photoredox and electrophilic arylation, showed good efficiency, and are feasible for the preparation of 3-arylchromones in good-to-excellent yields. This work showcases the first described attempt where the sulfonium salts and arenesulfonyl chlorides were successfully utilized for the construction of the chromone heterocycle system.

Cu-Catalyzed Arylation of Bromo-Difluoro-Acetamides by Aryl Boronic Acids, Aryl Trialkoxysilanes and Dimethyl-Aryl-Sulfonium Salts: New Entries to Aromatic Amides.

We describe a mechanism-guided discovery of a synthetic methodology that enables the preparation of aromatic amides from 2-bromo-2,2-difluoroacetamides utilizing a copper-catalyzed direct arylation. Readily available and structurally simple aryl precursors such as aryl boronic acids, aryl trialkoxysilanes and dimethyl-aryl-sulfonium salts were used as the source for the aryl substituents. The scope of the reactions was tested, and the reactions were insensitive to the electronic nature of the aryl groups, as both electron-rich and electron-deficient aryls were successfully introduced. A wide range of 2-bromo-2,2-difluoroacetamides as either aliphatic or aromatic secondary or tertiary amides were also reactive under the developed conditions. The described synthetic protocols displayed excellent efficiency and were successfully utilized for the expeditious preparation of diverse aromatic amides in good-to-excellent yields. The reactions were scaled up to gram quantities.

Photoredox Functionalization of 3-Halogenchromones, 3-Formylchromones, and Chromone-3-carboxylic Acids: Routes to 3-Acylchromones.

This work describes a set of new and efficient synthetic routes toward 3-acyl-substituted chromones ranging from readily available chromone precursors, namely 3-halogenchromones, 3-formylchromones, and chromone-3-carboxylic acids by means of visible-light photoredox catalysis. The operationally simple protocols transform a wide variety of chromone derivatives into challenging 3-acyl-substituted chromones in excellent yield. This research also aimed at comparing the developed methodologies by using as the key evaluation criteria the efficiency of the reaction and general availability of the starting materials. The application of all developed methods for the gram-scale preparation of the title chromones was also demonstrated.

Transition-metal-catalyzed arylation of nitroimidazoles and further transformations of manipulable nitro group.

Pd- or Ni-catalyzed C-H arylation of 4-nitroimidazole derivatives directed by a manipulable nitro group was developed. The reaction tolerates a wide range of substituted aryl halides and 4-nitroimidazoles. The experiments indicated that the nitro group has influence on regioselectivity of the reaction. In addition, we have shown that the efficiency of the Suzuki-Miyaura cross-coupling reaction of nitroimidazoles is slightly lower in comparison to the direct C-H arylation. The exploration of the chemical potential of the nitro group and a putative reaction mechanism are discussed.

Mechanochemical synthesis of aromatic ketones: pyrylium tetrafluoroborate mediated deaminative arylation of amides.

A new method has been introduced that is able to tackle the complexities of N-C(O) activation in amide moieties through utilization of pyrylium tetrafluoroborate in a mechanochemical setting, where amide bonds undergo activation and subsequent conversion to biaryl ketones. Due to the employment of a mechanochemical setting, the reaction conforms to green chemistry principles, offering an environmentally friendly approach to traditional amide derivatization techniques that rely on transition metals to achieve further functionalization.

Increasing obsidian diversity during the Chalcolithic Period at Yeghegis-1 Rockshelter (Armenia) reveals shifts in land use and social networks.

The newly excavated rockshelter of Yeghegis-1 in Armenia reflects an occupation of five centuries, as attested by radiocarbon dates from ∼ 4100 to 4000 cal BCE in the lowest layer to ∼ 3600-3500 cal BCE at the top. It is a partially collapsed cave in which pastoralists, we hypothesize, wintered with their herds. The stone tool assemblage is predominantly obsidian (92.1%), despite the shelter being > 60 km on foot from the nearest sources. We use obsidian sourcing to investigate two purported trends in the Southern Caucasus during the Chalcolithic Period: (1) occupation of more varied high-altitude environments and (2) more expansive social networks. Our data show both trends were dynamic phenomena. There was a greater balance in use of the nearest pasturelands over time, perhaps linked to risk management and/or resource sustainability. During later occupations, artifacts from distant sources reveal more extensive connections. This increase in connectivity likely played a central role in the shifts in societal complexity that gave rise to widely shared material culture throughout the Armenian Highlands around the start of the Early Bronze Age. In such a model, greater social connectivity becomes a key mechanism for, rather than a product of, the spread of cultural and/or technological innovations.

Tandem dinucleophilic cyclization of cyclohexane-1,3-diones with pyridinium salts.

The cyclization of cyclohexane-1,3-diones with various substituted pyridinium salts afforded functionalized 8-oxa-10-aza-tricyclo[7.3.1.0(2,7)]trideca-2(7),11-dienes. The reaction proceeds by regioselective attack of the central carbon atom of the 1,3-dicarbonyl unit to 4-position of the pyridinium salt and subsequent cyclization by base-assisted proton migration and nucleophilic addition of the oxygen atom to the 2-position, as was elucidated by DFT computations. Fairly extensive screening of bases and additives revealed that the presence of potassium cations is essential for formation of the product.

2,3-unsubstituted chromones and their enaminone precursors as versatile reagents for the synthesis of fused pyridines.

A divergent and regioselective approach to fused pyridines was developed through formal [3 + 3] cyclocondensations from simple 2,3-unsubstituted chromones or their enaminone precursors.

Synthesis of fluorinated purine and 1-deazapurine glycosides as potential inhibitors of adenosine deaminase.

The synthesis of 2- and 6-trifluoromethylated purines and 1-deazapurines was performed by formal [3 + 3]-cyclization reactions of 5-aminoimidazoles with a set of trifluoromethyl-substituted 1,3-CCC- and 1,3-CNC-dielectrophiles. The corresponding fluorinated nucleosides were synthesized by glycosylation of 9-unsubstituted purines and 1-deazapurines with peracetylated ß-ribose, ß-glucose, and rhamnose and subsequent deprotection. These scaffolds can be considered as potential inhibitors of adenosine deaminase (ADA) and inosine monophosphate dehydrogenase (IMPDH) enzymes.

Mechanochemical synthesis of aromatic sulfonamides.

A three-component Pd-catalysed aminosulfonylation reaction of K2S2O5 and amine with aryl bromides or aromatic carboxylic acids was developed. This strategy was developed to utilise mechanical energy and accommodate primary as well as secondary aliphatic and aromatic amines to provide a new shortcut to a wide range of sulfonamides. Studies on the scope and limitations of the reaction indicated its tolerance of a vast range of functional groups and many structural patterns. The reactions were scaled up to gram quantities.

Chelation control in the [3 + 3] annulation reaction of alkoxy-substituted 1,1-diacylcyclopropanes with 1,3-bis(trimethylsilyloxy)-1,3-butadienes. diversity-oriented synthesis of isochromanes.

Functionalized arenes were prepared by chelation-controlled [3 + 3] cyclization/cyclopropane opening reactions of 1-trimethylsilyloxy-1,3-butadienes with benzyloxy- or methoxy-substituted 1,1-diacylcyclopropanes. A number of benzyloxy-substituted derivatives were transformed into isochromanes by deprotection and subsequent cyclization. Mixed chromanes-isochromanes were prepared starting with 1,3-bis(silyloxy)-1,3-butadienes containing a remote chloride group.

3-Methoxalylchromone--a novel versatile reagent for the regioselective purine isostere synthesis.

The first synthesis of 3-methoxalylchromone was described. The reaction of the latter with electron-rich aminoheterocycles afforded a set of heteroannelated pyridines bearing a CO(2)Me substituent located at the α-position of the pyridine core.

Visible-light-mediated arylation of ortho-hydroxyarylenaminones: direct access to isoflavones.

In this work we highlight two new methods for the synthesis of isoflavones through consecutive domino arylation of ortho-hydroxyarylenaminones with in situ photogenerated aryl radicals. As precursors for aryl radicals we used aryl onium reagents such as diazonium and diaryliodonium salts. Notably, the photo-Meerwein arylation by aryl diazonium tetrafluoroborates demonstrated high efficiency in terms of yields and can be considered as a method of choice for the straightforward assembly of 3-aryl-substituted chromones. Ultimately, 26 compounds were prepared in good to excellent yields using the developed synthetic protocols.

Copper-catalyzed direct C-H arylselenation of 4-nitro-pyrazoles and other heterocycles with selenium powder and aryl iodides. Access to unsymmetrical heteroaryl selenides.

A one-pot, Cu-catalyzed direct C-H arylselenation protocol using elemental Se and aryl iodides was developed for nitro-substituted, N-alkylated pyrazoles, imidazoles and other heterocycles including 4H-chromen-4-one. This general and concise method allows one to obtain a large number of unsymmetrical heteroaryl selenides bearing a variety of substituents. The presence of the nitro group was confirmed to be essential for the C-H activation and can also be used for further functionalisation and manipulation. Several examples of heteroannulated benzoselenazines were also synthesized using the developed synthetic protocol.

Synthesis of 3,4-benzo-7-hydroxy-2,9-diazabicyclo[3.3.1]non-7-enes by cyclization of 1,3-bis(silyl enol ethers) with quinazolines.

A variety of functionalized 3,4-benzo-7-hydroxy-2,9-diazabicyclo[3.3.1]non-7-enes were prepared by one-pot cyclizations of 1,3-bis(silyl enol ethers) with quinazolines. The mechanism of the cyclization was studied by B3LYP/6-31G(d) density functional theory computations. The products could be functionalized by Suzuki cross-coupling reactions. The reaction of 1,3-bis(silyl enol ethers) with phthalazine afforded open-chain rather than cyclization products.

Application of Silicon-Initiated Water Splitting for the Reduction of Organic Substrates.

The use of water as a donor for hydrogen suitable for the reduction of several important classes of organic compounds is described. It is found that the reductive water splitting can be promoted by several metalloids among which silicon shows the best efficiency. The developed methodologies were applied for the reduction of nitro compounds, N-oxides, sulfoxides, alkenes, alkynes, hydrodehalogenation as well as for the gram-scale synthesis of several substrates of industrial importance.