Reactions of Alkenes
One of the most powerful of alkene transformations is enantioselective epoxidation. Tsutomu Katsuki of Kyushu University has developed (Angew. Chem. Int. Ed. 2007, 46, 4559. ) a Ti catalyst that with H2O2, selectively epoxidized terminal alkenes with high ee. The same catalyst converted a Z 2-alkene such as 3 into the epoxide. This is significant, because such epoxides are opened with nucleophiles selectively at the less congested center.
Novel procedures for alkene functionalization have been put forward. Philippe Renaud of the University of Berne has developed (Adv. Synth. Catal. 2008, 350, 1163. ) a simple protocol for terminal halogenation, based on catalyzed addition of catecholborane, followed by free radical substitution. Sulfides and selenides were also prepared. H. Zoghlami of the Faculty of Sciences of Tunis has devised (Tetrahedron Lett. 2007, 48, 5645. ) an oxidative sulfinylation, converting a terminal alkene 7 to the sulfide 8. M. Christina White of the University of Illinois (J. Am. Chem. Soc. 2008, 130, 3316. ) and Guosheng Liu of the Shanghai Institute of Organic Chemistry (Angew. Chem. Int. Ed. 2008, 47, 4733. ) independently developed Pd catalysts for the oxidation of a terminal alkene 9 to the terminal allylic amine 10. Shannon S. Stahl of the University of Wisconsin-Madison has established (Org. Lett. 2007, 9, 4331. ) conditions for the complementary transformation of a terminal alkene 11 to the enamide 12. Douglas B. Grotjahn of San Diego State University has optimized (J. Am. Chem. Soc. 2007, 129, 9592. ) Ru-catalyzed alkene (“zipper”) migration, effecting the conversion of 13 to 14 and of 15 to 16.
There have been several new observations on alkene cleavage. Marcus A. Tius of the University of Hawaii and Bakthan Singaram of the University of California, Santa Cruz have found (Tetrahedron Lett. 2008, 49, 2764. ) that epoxides such as 17 are cleaved directly by NaIO4, providing a simple alternative to ozonolysis. Rolando A. Spanevello of the Universidad Nacional de Rosario has extended (Tetrahedron 2007, 63, 11410. ) unsymmetrical ozonolysis to highly substituted norbornene derivatives such as 19, observing 20 as the only product. Patrick H. Dussault of the University of Nebraska-Lincoln has established (J. Org. Chem. 2008, 73, 4688. ) that alkene ozonolysis in wet acetone delivered the ketone or aldehyde directly, without reductive workup.
In a very simple procedure, Takashi Kamitanaka and Tadao Harada of Ryukoku University and the Industrial Research Center of Shiga Prefecture have found (Tetrahedron Lett. 2008, 48, 8460. ) that acetone, acetonitrile or an alcohol added without catalyst to a terminal alkene at 340°C. Yoshiji Takemoto of Kyoto University has reported (J. Org. Chem. 2007, 72, 5898. ) Pd-catalyzed acylation of 9-BBN adducts, and Michael G. Organ of York University has described (Chem. Commun. 2008, 735. ) a convenient Pd catalyst for coupling of 9-BBN adducts with primary alkyl bromides at ambient temperature. Dieter Vogt of the Eindhoven University of Technology (Adv. Synth. Catal. 2008, 350, 332. ) and Maurizio Taddei of the Universitā degli Studi di Siena (Tetrahedron Lett. 2008, 48, 8501. ) have reported hydroformylation in the presence of a secondary amine to give net aminomethylation, and Bernhard Breit of the Albert-Ludwigs-Universität Freiburg has found (Adv. Synth. Catal. 2008, 350, 989. ) that hydroformylation can be followed by Knoevenagel condensation, to give three-carbon homologation, to 28. Melanie S. Sanford of the University of Michigan has devised (J. Am. Chem. Soc. 2008, 130, 2150. ) strategies for interrupting Heck arylation, to give selectively either 29 or 30, and Andrew J. Phillips of the University of Colorado has taken advantage of Kulinkovich cyclopropanation to give selectively either 31 or 32 (Org. Lett. 2007, 9, 2717, ); 2008, 10, 1083. ).