Radical Cation Diels-Alder Reactions by TiO2 Photocatalysis
Radical cation Diels-Alder reactions by titanium dioxide (TiO2) photocatalysis in lithium perchlorate/nitromethane solution are described. TiO2 photocatalysis promotes reactions between electron-rich dienes and dienophiles, which would otherwise be difficult to accomplish due to electronic mismatching. The reactions are triggered by hole oxidation of the dienophile and are completed by the excited electron reduction of the radical cation intermediate at the dispersed surface in the absence of any sacrificial substrate.
Combining photoredox-catalyzed trifluoromethylation and oxidation with dmso: Facile synthesis of α-trifluoromethylated ketones from aromatic alkenes
Trifluoromethylated ketones are useful building blocks for organic compounds with a trifluoromethyl group. A new and facile synthesis of ketones with a trifluoromethyl substituent in the α-position proceeds through a one-pot photoredox-catalyzed trifluoromethylation-oxidation sequence of aromatic alkenes. Dimethyl sulfoxide (DMSO) serves as a key and mild oxidant under these photocatalytic conditions. Furthermore, an iridium photocatalyst, fac[Ir(ppy)3] (ppy=2-phenylpyridine), turned out to be crucial for the present photoredox process. Valuable α-CF3-substituted ketones can be synthesized from aromatic alkenes by combining photoredox-catalyzed trifluoromethylation and oxidation with DMSO. The iridium photocatalyst fac-[Ir(ppy)3] (ppy=2-phenylpyridine) plays key roles in this keto-trifluoromethylation. SET=single electron transfer.
Wittig reaction: Role of steric effects in explaining the prevalent formation of Z olefin from nonstabilized ylides
For understanding the mechanism involved in the Wittig reaction, it is important to know the factors which influence the stability of 1,2-oxaphosphetane intermediates with pentacoordinate phosphorus; in these intermediates, the steric factor plays a predominant role. Studying the Wittig reaction between nonstabilized ylides and different aldehydes, we noted that the stereochemical outcome driving toward Z-olefin formation was influenced only by different steric factors. The proposed mechanism differs from those previously reported because it underlines the fundamental role of the two cis/trans oxaphosphetane intermediates with the oxygen atom in equatorial position.