Enantioselective reductive cyclization of 1,6-enynes via rhodium-catalyzed asymmetric hydrogenation: C-C bond formation precedes hydrogen activation.
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.
Jang
Hye-Young
HY
Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
Hughes
Freddie W
FW
Gong
Hegui
H
Zhang
Junmei
J
Brodbelt
Jennifer S
JS
Krische
Michael J
MJ