Nickel-Catalyzed Cross-Coupling Reaction of Aryl Methyl Sulfides with Aryl Bromides.

A nickel-catalyzed cross-coupling reaction of aryl methyl sulfides with aryl bromides has been developed to access biaryls in yields of up to 86%. The reactions proceeded well using Ni(COD)2 as catalyst with the ligand BINAP (2,2'-bis(diphenylphosphanyl)-1,1'-binaphthalene) in the presence of magnesium. The method has a broad scope of substrates and is scalable. The wide availability of commercially available aryl bromides and the absence of preparation and preparation of organometallic reagents make the reaction of high application value.

Dearomatization Silylation of Benzofurans and Furopyridines via Silyl Radical Addition and Endocyclic C-O Bond Scission.

Direct introduction of silyl radicals to forge C-Si bonds is of central importance in organic synthesis, owing to the formidable potential of silyl groups as coupling partners for further derivatization reactions to achieve more valuable compounds. Cleavage of heteroaromatic endocyclic carbon-heteroatom bonds to assemble C-Si bonds is scarce. Here, we demonstrate a dearomatization silylation of benzofurans and furopyridines via silyl radical addition and C(2)-O bond scission under metal-catalyst-free and mild conditions. Preliminary mechanistic experiments suggest that these transformations involve radical/single-electron transfer and [1,5]-Brook rearrangement processes. This protocol for the total synthesis of Doxepin and oxyresveratrol derivatives is carried out. The silylated products in several transformation reactions have proven to be useful as synthetic intermediates.

Palladium-Catalyzed Cyanation of Aryl Sulfonium Salts.

A palladium-catalyzed cyanation of aryl dimethylsulfonium salts using cheap, nontoxic, and bench-stable K4[Fe(CN)6]·3H2O as the cyanating reagent has been developed. The reactions proceeded well under base-free conditions with various sulfonium salts and provided aryl nitrile with yields of up to 92%. Aryl sulfides can be transformed to aryl nitriles directly via a one-pot process, and the protocol is scalable. Density functional theory calculations were performed to investigate the reaction mechanism that involved a catalytic cycle involving oxidative addition, ligand exchange, reductive elimination, and regeneration to yield the product.

Defluorosilylation of fluoroarenes and fluoroalkanes.

Direct activation of carbon-fluorine bonds (C-F) to introduce the silyl or boryl groups and generate valuable carbon-silicon (C-Si) or carbon-boron (C-B) bonds is important in the development of synthetically useful reactions, owing to the unique opportunities for further derivatization to achieve more complex molecules. Despite considerable progress of C-F bond activation to construct carbon-carbon (C-C) and carbon-heteroatom (C-X) bond formation, the defluorosilylation via C-F cleavage has been rarely demonstrated. Here, we report an ipso-silylation of aryl fluorides via cleavage of unactivated C-F bonds by a Ni catalyst under mild conditions and without the addition of any external ligand. Alkyl fluorides are also directly converted into the corresponding alkyl silanes under similar conditions, even in the absence of the Ni catalyst. Applications of this protocol in late-stage defluorosilylation of potentially bioactive pharmaceuticals and in further derivatizations are also carried out.

Silver-induced self-immolative Cl-F exchange fluorination of arylsulfur chlorotetrafluorides: synthesis of arylsulfur pentafluorides.

A novel strategy for the synthesis of arylsulfur pentafluorides by silver carbonate-induced Cl-F exchange fluorination of arylsulfur chlorotetrafluorides is reported. This fluorination does not require any exogenous fluoride sources. Rather, the reaction proceeds via the self-immolation of the substrate Ar-SF4Cl.

The opioid receptor triple agonist DPI-125 produces analgesia with less respiratory depression and reduced abuse liability.

Opioid analgesics remain the first choice for the treatment of moderate to severe pain, but they are also notorious for their respiratory depression and addictive effects. This study focused on the pharmacology of a novel opioid receptor mixed agonist DPI-125 and attempted to elucidate the relationship between the δ-, µ- and κ-receptor potency ratio and respiratory depression and abuse liability. Five diarylmethylpiperazine compounds (DPI-125, DPI-3290, DPI-130, KUST202 and KUST13T02) were selected for this study. PKA fluorescence redistribution assays in CHO cells individually expressing δ-, µ- or κ-receptors were used to measure the agonist potency. The respiratory safety profiles were estimated in rats by the ratio of ED50 (pCO2 increase)/ED50 (antinociception). The abuse liability of DPI-125 was evaluated with a self-administration model in rhesus monkeys. The observed agonist potencies of DPI-125 for δ-, µ- and κ-opioid receptors were 4.29±0.36, 11.10±3.04, and 16.57±4.14 nmol/L, respectively. The other four compounds were also mixed agonists with varying potencies. DPI-125 exhibited a high respiratory safety profile, clearly related to its high δ-receptor potency. The ratio of the EC50 potencies for the µ- and δ-receptors was found to be positively correlated with the respiratory safety ratio. DPI-125 has similar potencies for µ- and κ-receptors, which is likely the reason for its reduced abuse potential. Our results demonstrate that the opioid receptor mixed agonist DPI-125 is safer and less addictive than traditional µ-agonist analgesics. These findings suggest that the development of δ>µâˆ¼κ opioid receptor mixed agonists is feasible, and such compounds could represent a promising class of potent analgesics with wider therapeutic windows.

IF5 affects the final stage of the Cl-F exchange fluorination in the synthesis of pentafluoro-λ6-sulfanyl-pyridines, pyrimidines and benzenes with electron-withdrawing substituents.

A difficult chlorine-fluorine (Cl-F) exchange fluorination reaction in the final stage of the preparation of pentafluoro-λ6-sulfanyl-(hetero)arenes having electron-withdrawing substituents has now been elucidated through the use of iodine pentafluoride. A major side-reaction of C-S bond cleavage was sufficiently inhibited by the potential interaction between F and I with a halogen bonding.

Importance of a Fluorine Substituent for the Preparation of meta- and para-Pentafluoro-λ(6) -sulfanyl-Substituted Pyridines.

Although there are ways to synthesize ortho-pentafluoro-λ(6) -sulfanyl (SF5 ) pyridines, meta- and para-SF5 -substituted pyridines are rare. We disclose herein a general route for their synthesis. The fundamental synthetic approach is the same as reported methods for ortho-SF5 -substituted pyridines and SF5 -substituted arenes, that is, oxidative chlorotetrafluorination of the corresponding disulfides to give pyridylsulfur chlorotetrafluorides (SF4 Cl-pyridines), followed by chloride/fluoride exchange with fluorides. However, the trick in this case is the presence on the pyridine ring of at least one fluorine atom, which is essential for the successful transformation of the disulfides into m-and p-SF5 -pyridines. After enabling the synthesis of an SF5 -substituted pyridine, ortho-F groups can be efficiently substituted by C, N, S, and O nucleophiles through an SN Ar pathway. This methodology provides access to a variety of previously unavailable SF5 -substituted pyridine building blocks.