leads to the corresponding secondary alkyllithiums with high retention of configuration. Subsequent quenching with various electrophiles such as Bu2S2, DMF, MeOB(OR)2, or Et2CO provides the desired products with retention of configuration. Furthermore, a transmetalation with CuBr⋅P(OEt)3 also allows retentive trapping with acid chlorides and ethylene oxide. The quenching of the resulting alkyllithiums
Remarkably Facile Borane-Promoted, Rhodium-Catalyzed Asymmetric Hydrogenation of Tri- and Tetrasubstituted Alkenes
作者:Veronika M. Shoba、James M. Takacs
DOI:10.1021/jacs.7b02581
日期:2017.4.26
Oxime-directed catalytic asymmetric hydroboration is diverted to catalytic asymmetrichydrogenation (CAH) upon the addition of a proton source, such as MeOH, or by running the reaction under a hydrogen atmosphere. A borane (e.g., pinacolborane) is required to promote CAH. Tri- and tetrasubstituted alkenes, including the challenging all-alkyl tetrasubstituted alkenes, undergo CAH with enantiomer ratios (er) as
Asymmetric Conjugate Addition of Crotylstannane: Synthesis of (-)-Lasiol
作者:Richard Mullins、Emily Wilding、John Gregg
DOI:10.1055/s-0029-1219381
日期:2010.3
the primary sexattractant of the male ant, Lasius meridionalis. Our interest in lasiol stems from the stereochemistry of the chiral methyl substituents and the synthetic challenges posed by this common structural motif. As such, an asymmetric 1,4-conjugate addition of an allylic stannane to produce the 1,2-anti-dimethyl arrangement with high stereocontrol has resulted in the synthesis of (-)-lasiol
Catalytic Enantioselective Synthesis of Vicinal Dialkyl Arrays
作者:Anthoni W. van Zijl、Wiktor Szymanski、Ferrnando López、Adriaan J. Minnaard、Ben L. Feringa
DOI:10.1021/jo8010649
日期:2008.9.19
With a consecutive "asymmetric allylic alkylation (AAA)/cross-metathesis (CM)/conjugate addition (CA)" protocol it is possible to synthesize either stereoisomer of compounds containing a vicinal dialkyl array with excellent stereoselectivity. The versatility of this protocol in natural product synthesis is demonstrated in the preparation of the ant pheromones faranal and lasiol.
Synthesis of Vicinal Dimethyl Chirons by Asymmetric Hydrogenation of Trisubstituted Alkenes
作者:Jian Zhao、Kevin Burgess
DOI:10.1021/ja905458n
日期:2009.9.23
Roche ester derivatives were converted to trisubstituted alkenes with allylic chiral centers. Hydrogenation of these substrates with chiral analogues of Crabtree's catalyst, specifically, an optically active carbene oxazoline derivative, were found to be mostly catalyst controlled. However, the peripheral functionalities and protecting groups had significant effects and could be adjusted to give high stereoselectivities. The upshot of this work is that alpha,omega-functionalized chirons to introduce 1,2-dimethyl functionalities into acyclic chains have been developed.