Palladium-Catalyzed Diarylation of Isocyanides with Tetraarylleads for the Selective Synthesis of Imines and α-Diimines.

Using tetraaryllead compounds (PbAr4) as arylating reagents, isocyanides undergo selective diarylation in the presence of palladium catalysts such as Pd(OAc)2 or Pd(PPh3)4 to afford imines and/or α-diimines based on the isocyanide employed. With aliphatic isocyanides, imines are obtained preferentially, whereas α-diimines are formed in the case of electron-rich aromatic isocyanides. The differences in imine/α-diimine selectivity can be attributed to the stability of imidoylpalladium intermediates formed in this catalytic reaction. Compared with other arylating reagents, tetraaryllead compounds are excellent candidates for use in the selective transformations to imines and/or α-diimines, especially in terms of inhibiting the oligomerization of isocyanides, which results in a lower product selectivity in many transition-metal-catalyzed reactions of isocyanides.

Furan- and Thiophene-2-Carbonyl Amino Acid Derivatives Activate Hypoxia-Inducible Factor via Inhibition of Factor Inhibiting Hypoxia-Inducible Factor-1.

Induction of a series of anti-hypoxic proteins protects cells during exposure to hypoxic conditions. Hypoxia-inducible factor-α (HIF-α) is a major transcription factor that orchestrates this protective effect. To activate HIF exogenously, without exposing cells to hypoxic conditions, many small-molecule inhibitors targeting prolyl hydroxylase domain-containing protein have been developed. In addition, suppression of factor inhibiting HIF-1 (FIH-1) has also been shown to have the potential to activate HIF-α. However, few small-molecule inhibitors of FIH-1 have been developed. In this study, we synthesized a series of furan- and thiophene-2-carbonyl amino acid derivatives having the potential to inhibit FIH-1. The inhibitory activities of these compounds were evaluated in SK-N-BE(2)c cells by measuring HIF response element (HRE) promoter activity. Several furan- and thiophene-2-carbonyl amino acid derivatives inhibited FIH-1 based on correlations among the docking score of the FIH-1 active site, the chemical structure of the compounds, and biological HIF-α/HRE transcriptional activity.

Photoinduced synthesis of unsymmetrical diaryl selenides from triarylbismuthines and diaryl diselenides.

A novel method of photoinduced synthesis of unsymmetrical diaryl selenides from triarylbismuthines and diaryl diselenides has been developed. Although the arylation reactions with triarylbismuthines are usually catalyzed by transition-metal complexes, the present arylation of diaryl diselenides with triarylbismuthines proceeds upon photoirradiation in the absence of transition-metal catalysts. A variety of unsymmetrical diaryl selenides can be conveniently prepared by using this arylation method.

Transition-Metal-Catalyzed Diarylation of Isocyanides with Triarylbismuthines for the Selective Synthesis of Imine Derivatives.

The transition-metal-catalyzed diarylation of isocyanides with triarylbismuthines was investigated in detail, and rhodium catalysts such as [RhCl(nbd)]2 were found to selectively afford N-alkyl diaryl ketimines. On the other hand, palladium-catalyzed diarylation proceeded with the incorporation of two molecules of isocyanide, preferentially yielding N,N'-dialkyl or N,N'-diaryl α-diimines. In addition, a cascade synthesis of 2,3-diarylquinoxalines starting from the palladium-catalyzed diarylation of isocyanides with triarylbismuthines was successfully achieved.

Palladium-Catalyzed Synthesis of α-Diimines from Triarylbismuthines and Isocyanides.

In this study, we report a highly selective coupling reaction between triarylbismuthines and isocyanides using palladium diacetate as the catalyst, affording α-diimines, with the formation of three C-C bonds. Among several aryl sources (Ar-YLn: Y = B, Sn, Pb, Sb, Bi, I), only triarylbismuthines successfully undergo coupling with isocyanides to selectively afford α-diimines. The coupling reaction exhibits the advantages of high atom economy and convenient operation, with no need for any additive.

Synthesis of selenium compounds by free radical addition based on visible-light-activated se-se bond cleavage.

Upon irradiation with near-UV or visible light, organic diselenides undergo homolytic cleavage of their selenium-selenium linkage to generate the corresponding seleno radicals, which can add to alkynes, allenes, and related unsaturated compounds. In the case of alkynes, vicinally diselenated alkenes are synthesized successfully. Photoinduced bisselenation of allenes takes place selectively at the terminal double bond of allenes. In sharp contrast, photoinduced addition of organic diselenides to alkenes is an inefficient process. However, combination of diselenides and disulfides under photoirradiation conditions results in highly regioselective thioselenation of alkenes based on the higher reactivity of thio radicals toward alkenes and the higher carbon radical capturing ability of diselenides. Similar conditions can be employed with a variety of unsaturated compounds such as alkynes, allenes, conjugated dienes, vinylcyclopropanes, and isocyanides. This protocol can also be applied to selenotelluration, selenophosphination, and perfluoroalkylselenation of unsaturated compounds. The excellent carbon radical capturing ability of diselenides makes it possible to attain sequential addition of diselenides to several unsaturated compounds by suppression of polymerization of unsaturated compounds. When the sequential addition takes place intramolecularly under photoirradiation conditions, cyclic products are obtained successfully via a radical cyclization process. In addition, novel photoinduced electrocyclic reaction of o-alkynylaryl isocyanides with diselenides efficiently affords diselenated quinoline derivatives.