Letteratura scientifica selezionata sul tema "Carbon-Hydrogen (C-H) Functionalization"

AbstractThe generation of carbon-centered radicals via intermolecular hydrogen-atom transfer (HAT) from C—H bonds to an abstracting species (HAT reagent) represents a significant challenge in terms of reactivity, site-selectivity and stereoselectivity. The radical species resulting from such a transfer can then engage in carbon—carbon or carbon—heteroatom bond formation, possibly through the intervention of transition-metal catalysts, leading to a variety of functionalized products. This chapter aims to provide the reader with useful guidelines to understand, predict, and design selective radical transformations based upon initial HAT from a C—H bond coupled to different radical-capture strategies. A selection of examples that illustrate different approaches to implement HAT reactions in synthetically useful procedures are presented.

AbstractRecent advances in intramolecular hydrogen-atom transfer (HAT) have demonstrated significant utility in C—H functionalization through highly reactive open-shell intermediates. The intramolecular transposition of radical reactivity from select functional groups to generate more stable carbon-centered radicals often proceeds with high regioselectivity, providing novel bond disconnections at otherwise inert and largely indistinguishable positions. This chapter explores the functional groups capable of intramolecular HAT to generate remote radicals and the transformations currently available to the synthetic chemist.

Janine Cossy of ESPCI Paris (Org. Lett. 2011, 13, 4084) and Yasushi Obora of Kansai University (Chem. Lett. 2011, 40, 1055) independently developed conditions for the “borrowed hydrogen” condensation of acetonitrile with an alcohol 1 to give the nitrile 2. Akio Baba of Osaka University showed (Angew. Chem. Int. Ed. 2011, 50, 8623) that a ketene silyl acetal 4 could be condensed with a carboxylic acid 3 to give the β-keto ester 5. Timothy W. Funk of Gettysburg College found (Tetrahedron Lett. 2010, 51, 6726) that the cyclopropanol 6, readily prepared by Kulinkovich condensation of an alkene with an ester, opened with high regioselectivity to give the branched ketone 7. In an elegant application of C–H functionalization, Yong Hae Kim of KAIST and Kieseung Lee of Woosuk University added (Tetrahedron Lett. 2011, 52, 4662) the acetal 9 in a conjugate sense to 8 to give 10. Hitoshi Kuniyasu and Nobuaki Kambe of Osaka University devised (Tetrahedron Lett. 2010, 51, 6818) conditions for the Pd-catalyzed carbonylation of a silyl alkyne 11 to the ester 12 with high geometric control. Dennis G. Hall of the University of Alberta also observed (Chem. Sci. 2011, 2, 1305) good geometric control in the rearrangement of the vinyl carbinol 13 to the alcohol 14. Takashi Tomioka of the University of Mississippi condensed (J. Org. Chem. 2011, 76, 8053) the anion 16, prepared in situ from lithio acetonitrile and 1-iodobutane, with the aldehyde 15 to give a nitrile, which was carried onto the aldehyde 17, again with good control of geometry. Bruce H. Lipshutz of the University of California, Santa Barbara established (Org. Lett. 2011, 13, 3818) conditions for the Negishi coupling of an alkenyl halide 18 to give 20 with retention of alkene geometry. Daesung Lee of the University of Illinois, Chicago found (J. Am. Chem. Soc. 2011, 133, 12964) that a Pt catalyst rearranged a silyl cyclopropene 21 to the allene 22. Jan Deska of the Universität zu Köln prepared (Angew. Chem. Int. Ed. 2011, 50, 9731) the enantiomerically enriched allene 25 by lipase-mediated esterification of the prochiral 23.