Best Synthetic Methods: Reactions of Alkenes
Swadeshmukul Santra of the University of Central Florida described (Tetrahedron Lett. 2009, 50, 124. ) a simple preparation of silica nanoparticles that efficiently catalyzed the anti-Markovnikov addition of thiophenol to alkenes (illustrated), and also to alkynes. Akiya Ogawa of Osaka Prefecture University devised (Tetrahedron Lett. 2009, 50, 624. ) a protocol for the photoinduced hydrophosphinylation of an alkene 3 to the phosphine oxide 4. Xavi Ribas and Miquel Costas of the University of Girona developed (Adv. Synth. Catal. 2009, 351, 348. ) a manganese catalyst for the epoxidation of alkenes with 30% H2O2. Masahito Ochiai of the University of Tokushima established (J. Am. Chem. Soc. 2009, 131, 1382. ) an iodoarene-catalyzed oxidation of an alkene 7 to the keto acid 9. If, as is likely, isolated alcohols are stable under these conditions, this will be a useful complement to RuO4 cleavage.
Several methods are available for homologating unactivated alkenes. Sven Doye of the Universität Oldenburg observed (Angew. Chem. Int. Ed. 2009, 48, 1153. ) that a Ti catalyst could effect the addition of N-methyl aniline 10 to the alkene 3, to give the branched product 11. The reaction also worked well in an intramolecular sense. Note that in this process, a C-H bond is also converted to a C-C bond. Kiyoshi Tomioka of Kyoto University reported (Org. Lett. 2009, 11, 2007. ) that the Suzuki coupling of the hydroboration product from 12 with the iodo alkene 13 was best supported by AsPh3.
Teck-Peng Loh of Nanyang Technological University showed (J. Am. Chem. Soc. 2009, 131, 1372. ) that the homologation of an isolated alkene 15 with an acrylate ester 16 could also be carried out under oxidative conditions, to give the diene 17. Weiping Su of the Fujian Institute of Research on the Structure of Matter found (Org. Lett. 2009, 11, 2341. ) that similar oxidative conditions effected the decarboxylative addition of an aromatic acid such as 18 to an alkene to give the substituted styrene 19.
Kian L. Tan of Boston College took advantage (Org. Lett. 2009, 11, 2764. ) of a chelating ligand to direct the regioselective hydroformylation of an allylic sulfonamide 20. Isolated internal alkenes were stable under these conditions. Barry M. Trost of Stanford University described (Org. Lett. 2009, 11, 1071. ) the Ru-catalyzed cross coupling of an alkynyl ester 23 with a protected allylic alcohol 22 to give the 1,3-diene 24. The process is highly Z-selective, as would be expected for alkene formation by β-hydride elimination.
Sylvain Darses of the Ecole National Supériore de Chimie de Paris devised (Adv. Synth. Catal. 2009, 351, 153. ) a Ru catalyst for the addition of an alkenyl silane such as 26 to an alkene 25 bearing an electron-withdrawing group, leading to the homologated product 27. Kazuhiko Takai of Okayama University uncovered (Org. Lett. 2009, 11, 2711. ) a conceptually related process for the directed homologation of the alkenyl H of 28 to give 29. The imidazole of 30 is interesting in its own right and could also be hydrolyzed to the corresponding carboxylic acid.