58647-76-0Relevant academic research and scientific papers
(-)-sparteine-mediated asymmetric intramolecular carbolithiation of alkenes: Synthesis of enantiopure cyclopentanes with three consecutive stereogenic centers
Hoppe, Dieter,Weltering, Michael J.,Oestreich, Martin,Froehlich, Roland
, p. 1860 - 1877 (2007/10/03)
An asymmetric intramolecular carbolithiation reaction was developed by combining the (-)-sparteine-mediated enantiotopos-differentiating deprotonation and the anionic 5-exo-trig cyclization. Achiral 6-phenylhex-5- enyl carbamates were efficiently cyclized furnishing regio-, diastereo- (dr >99:1), and enantioselectively (er >98:2) 1,2-trans-substituted cyclopentanes. The intermediate primary benzylic lithium-carbanion pairs were - in spite of their configurative lability - diastercoselectively substituted by versatile electrophiles creating a third consecutive stereogenic center. Additionally, some 4-functionalized 6-phenylhex-5-enyl carbamates were also cyclized in high yield to provide enantiomerically pure cyclopentanes incorporating three adjacent stereogenic centers.
Enantioselective carbanion cyclization of 5-alkenyl carbamates induced by asymmetric lithiation with s-butyllithium/(-)-sparteine system
Tomooka, Katsuhiko,Komine, Nobuyuki,Sasaki, Tomoya,Shimizu, Hideo,Nakai, Takeshi
, p. 9715 - 9718 (2007/10/03)
Treatment of (E)-6-phenyl-5-hexenyl carbamates with s-BuLi/(-)-sparteine is shown to afford the trans-1,2-disubstituted cyclopentane derivatives in high % ee, along with the bicyclo[3.1.0]hexanes (bicyclization products).
Iron Lewis acid catalyzed reactions of phenyldiazomethane and olefins: Formation of cyclopropanes with very high cis selectivity
Seitz, William J.,Hossain, M. Mahmun
, p. 7561 - 7564 (2007/10/02)
The irol Lewis acid, [(η5-C5H5)Fe(CO)2(THF)]+ (1) catalyzes the cyclopropanation reaction of phenyldiazomethane with olefins to provide cis cyclopropanes in high selectivity.
Unconjugated Arylcyclopropanes. Acid-Catalyzed Addition of Acetic Acid to Highly Hindered Arylcyclopropanes
Creary, Xavier
, p. 4653 - 4659 (2007/10/02)
The adduct of 1-naphthylcarbene and norbornene, endo-3-(1-naphthyl)-exo-tricyclo2,4>octane (9) has been prepared. 1H and 13C NMR spectra of this system indicate that the unconjugated arylcyclopropane conformation is favored.Rotation about the naphthyl-cyclopropane bond is restricted.The temperature-dependent NMR indicates a 16.9 kcal/mol barrier to attainment of the conjugated conformation.Acetic acid adds readily under acid catalysis to the phenyl analogue exo-3-phenyl-exo-tricyclo2,4>octane (3) and more slowly to the more strained endo-3-phenyl-exo-tricyclo2,4>octane (4).Kinetic data suggest the involvement of a cationic intermediate with little transition-state charge development at the benzylic carbon.The rates of addition to substituted analogues of 3 and 4 correlate with Hammett ? values, giving ρ values of 2.53 and 2.35, respectively.Product-analysis data support the involvement of a benzylic cation, 23.The slower rate of reaction of the more strained endo isomers has been interpreted in terms of a barrier to attainment of the conjugated conformation which appears to be the favorable conformation for protonation of arylcyclopropanes.This suggestion is supported by the observation that the unconjugated systems, exo- and endo-3-(2,6-dimethylphenyl)-exo-tricyclo-2,4>octanes (27 and 28), add acetic acid 480 and 6.2 x 104 times, respectively, more slowly than 3.
