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.

Copper-Catalyzed O-Difluoromethylation of Functionalized Aliphatic Alcohols: Access to Complex Organic Molecules with an OCF2H Group.

A two-step synthetic strategy toward difluoromethyl ethers via a CuI-catalyzed reaction of the alcohols, bearing additional protected functionalities, with FSO2CF2CO2H has been developed. The high potential of the developed protocol has been shown by preparing novel OCF2H-analogues of GABA and l-proline. The described transformation has good functional group compatibility and can serve as a powerful synthetic tool for late-stage preparation of complex OCF2H-containing organic compounds as well as building blocks for drug discovery.

Synthesis of 3,3'-carbonyl-bis(chromones) and their activity as mammalian alkaline phosphatase inhibitors.

Hitherto unknown 3,3'-carbonyl-bis(chromones) 8, dimeric chromones bridged by a carbonyl group, were prepared by reaction of chromone-3-carboxylic acid chloride with 3-(dimethylamino)-1- (2-hydroxyphenyl)-2-propen-1-ones 9. The method is generally applicable for the synthesis of novel symmetrical or non-symmetrical products which were found to inhibit mammalian alkaline phosphatases.

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.

Synthesis of functionalized 2-salicyloylfurans, furo[3,2-b]chromen-9-ones and 2-benzoyl-8H-thieno[2,3-b]indoles by one-pot cyclizations of 3-halochromones with ß-ketoamides and 1,3-dihydroindole-2-thiones.

Functionalized 2-salicyloylfurans and 2-benzoyl-8H-thieno[2,3-b]indoles were prepared under mild conditions by reaction of 3-halochromones with ß-ketoamides and 1,3-dihydroindole-2-thiones, correspondently. The subsequent oxidative cyclization of the products resulted in formation of the corresponding furo[3,2-b]chromen-9-ones. These molecules could also be directly prepared from 3-halochromones using a one-pot protocol. The cyclization reactions reported herein are mechanistically surprising as they proceed via the oxygen and not via the (more nucleophilic) nitrogen atom of the ß-ketoamide.

Endo-selective Pd-catalyzed silyl methyl Heck reaction.

A palladium (Pd)-catalyzed endo-selective Heck reaction of iodomethylsilyl ethers of phenols and aliphatic alkenols has been developed. Mechanistic studies reveal that this silyl methyl Heck reaction operates via a hybrid Pd-radical process and that the silicon atom is crucial for the observed endo selectivity. The obtained allylic silyloxycycles were further oxidized into (Z)-alkenyldiols.

Regioselective and guided C-H activation of 4-nitropyrazoles.

A divergent and regioselective approach to 5-aryl-4-nitro-1H-pyrazoles was developed by guided transition-metal-catalyzed arylation of 4-nitro-1H-pyrazoles. This method provides a convenient tool for the functionalization of the pharmacologically relevant pyrazole scaffold. The scope and limitations of the methodology were studied.

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.

Synthesis and reactivity of 5-polyfluoroalkyl-5-deazaalloxazines.

Reaction of 6-arylamino-1,3-dialkyluracils with anhydrides of polyfluorocarboxylic acids in the presence of pyridine and subsequent cyclization with concentrated H2SO4 gave the corresponding 1,3-dialkyl-5-(polyfluoroalkyl)pyrimido[4,5-b]quinoline-2,4(1H,3H)-diones (5-polyfluoroalkyl-5-deazaalloxazines). The reactivity of these compounds towards nucleophilic reagents, such as sodium cyanoborohydride, acetophenone, nitromethane, potassium cyanide, indole and p-thiocresol, as well as Suzuki and Sonogashira couplings are described. The nucleophilic addition takes place at the 5-position of the 5-deazaalloxazine system and is in many cases irreversible to give 5,10-dihydropyrimido[4,5-b]quinoline-2,4(1H,3H)-dione derivatives in good to excellent yields.

Synthesis of N,N'-diglycosylated isoindigos.

The first N,N'-diglycosylated isoindigos were prepared by P(NEt(2))(3)-mediated dimerization of acetyl protected N-glycosyl-5-alkylisatins. Subsequent deacetylation yielded the corresponding deprotected N,N'-diglycosylated isoindigos. Isatine-N-glycosides containing an unsubstituted or alkyl-substituted heterocyclic moiety and ß-D-manno- and ß-L-rhamno configured carbohydrate substituents were successfully transformed into the corresponding isoindigos. In contrast, isatins with ß-D-gluco- or ß-D-xylo configured substituents failed to give the desired products.

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.

Pyrrole versus quinoline formation in the palladium catalyzed reaction of 2-alkynyl-3-bromothiophenes and 2-alkynyl-3-bromofurans with anilines. A combined experimental and computational study.

Benzofuroquinolines were prepared by a new type of Pd catalyzed annulation reaction. In the first step, 2-alkynyl-3-bromobenzofurans were prepared by Sonogashira reactions of 2,3-dibromobenzofuran. Their Pd catalyzed reaction with electron-rich anilines afforded benzofuroquinolines by a domino C-N coupling/annulation process. This reaction proceeds as a C,N-cyclization via the nitrogen atom and the ortho-carbon of the aniline. Similarly, furoquinolines were prepared from 2,3-dibromofuran. In contrast, benzofuropyrroles and furopyrroles were formed by N,N-cyclization when electron-poor anilines were used. Earlier, we reported results related to the thiophene and benzothiophene series. Quinolines were formed from 2,3-dibromobenzothiophene when electron rich anilines were used. In contrast, pyrroles were obtained in the case of electron-poor anilines. On the other hand, pyrroles were generally obtained, not depending on the type of aniline, when 2,3-dibromothiophene was employed as the starting material. In the present article, a detailed DFT study related to the mechanism (quinoline versus pyrrole formation) is reported which provides a rationalization of the selectivities observed for the furan, benzofuran, thiophene and benzothiophene series and for the different selectivities observed for electron-rich and -poor anilines.

Reactions of 3-acylchromones with dimethyl 1,3-acetonedicarboxylate and 1,3-diphenylacetone: one-pot synthesis of functionalized 2-hydroxybenzophenones, 6H-benzo[c]chromenes and benzo[c]coumarins.

Reactions of 3-methoxalyl-, 3-polyfluoroacyl- and 3-aroylchromones with dimethyl 1,3-acetonedicarboxylate and 1,3-diphenylacetone in the presence of DBU proceed at the C-2 atom of the chromone system with pyrone ring-opening and subsequent formal [3 + 3] cyclocondensation to functionalized 2-hydroxybenzophenones, 6H-benzo[c]chromenes and benzo[c]coumarins, depending on the substituent at the 3-position. An NMR study and X-ray crystallographic analysis are reported. The compounds synthesized can be considered as promising scaffolds for the design of the novel UV-A/B and UV-B filters.

Efficient [5 + 1]-strategy for the assembly of 1,8-naphthyridin-4(1H)-ones by domino amination/conjugate addition reactions of 1-(2-chloropyridin-3-yl)prop-2-yn-1-ones with amines.

A facile synthetic approach for the synthesis of 1,8-naphthyridine-4(1H)-one derivatives via a catalyst free and Pd-supported tandem amination sequence is developed and described. In a case of aliphatic amines reaction proceeds in a catalyst free mode, however anilines demand Pd-supported reaction conditions.

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.