| Autor: |
Li Z; Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, USA., Boyarskikh V, Hansen JH, Autschbach J, Musaev DG, Davies HM |
| Jazyk: |
angličtina |
| Zdroj: |
Journal of the American Chemical Society [J Am Chem Soc] 2012 Sep 19; Vol. 134 (37), pp. 15497-504. Date of Electronic Publication: 2012 Sep 11. |
| DOI: |
10.1021/ja3061529 |
| Abstrakt: |
Rhodium-catalyzed reactions of tertiary propargylic alcohols with methyl aryl- and styryldiazoacetates result in tandem reactions, consisting of oxonium ylide formation followed by [2,3]-sigmatropic rearrangement. This process competes favorably with the standard O-H insertion reaction of carbenoids. The resulting allenes are produced with high enantioselectivity (88-98% ee) when the reaction is catalyzed by the dirhodium tetraprolinate complex, Rh(2)(S-DOSP)(4). Kinetic resolution is possible when racemic tertiary propargylic alcohols are used as substrates. Under the kinetic resolution conditions, the allenes are formed with good diastereoselectivity and enantioselectivity (up to 6.1:1 dr, 88-93% ee), and the unreacted alcohols are enantioenriched to 65-95% ee. Computational studies reveal that the high asymmetric induction is obtained via an organized transition state involving a two-point attachment: ylide formation between the alcohol oxygen and the carbenoid and hydrogen bonding of the alcohol to a carboxylate ligand. The 2,3-sigmatropic rearrangement proceeds through initial cleavage of the O-H bond to generate an intermediate with close-lying open-shell singlet, triplet, and closed-shell singlet electronic states. This intermediate would have significant diradical character, which is consistent with the observation that the 2,3-sigmatropic rearrangement is favored with donor/acceptor carbenoids and more highly functionalized propargylic alcohols. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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