title: Enantioselective reductive cyclization of 1,6-enynes via rhodium-catalyzed asymmetric hydrogenation: C-C bond formation precedes hydrogen activation.
abstract: Asymmetric hydrogenation of 1,6-enynes using chirally modified cationic rhodium precatalysts enables enantioselective reductive cyclization to afford alkylidene-substituted carbocycles and heterocycles in a completely atom economical fashion. Good to excellent yields and exceptional levels of asymmetric induction are observed across a structurally diverse set of substrates. Mechanistic studies involving hydrogen-deuterium crossover experiments, along with the observance of nonconjugated cycloisomerization products 14c and 15c, suggest rhodium(III) metallocyclopentene formation occurs in advance of hydrogen activation. This oxidative coupling-hydrogenolytic cleavage motif should play a key role in the design of related hydrogen-mediated couplings.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: Hye-Young
authors.initials: HY
authors.lastname: Jang
authors.forename: Freddie W
authors.initials: FW
authors.lastname: Hughes
authors.forename: Hegui
authors.initials: H
authors.lastname: Gong
authors.forename: Junmei
authors.initials: J
authors.lastname: Zhang
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Brodbelt
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Krische