Special Issue "Asymmetric Synthesis"

Guest Editor
Dr. Noureddine Khiar
Instituto de Investigaciones Químicas, C.S.I.C-Universidad de Sevilla, c/. Am rico Vespucio, s/n., Isla de la Cartuja, 41092 Sevilla, Spain
Website: http://www.iiq.cartuja.csic.es/
E-Mail:
Interests: Stereoselectivity, Chiral Pool, Chiral Auxiliary, Asymmetric Catalysis, Enzyme Catalysis, Transition metal Catalysis, Organocatalysis

Submission

All papers should be submitted to molecules@mdpi.org with copy to the guest editor. To be published continuously until the deadline and papers will be listed together at the special websites.

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• stereoselectivity
• chiral pool
• chiral auxiliary
• asymmetric catalysis
• dnzyme catalysis
• transition metal catalysis
• organocatalysis

Manuscript ID: molecules-asychem-20090629-Liu-cn
Type of Paper: Article
Title: The Reduction of Protected 3-Hydroxyglutarimide by L-Selectride: An Efficient Entry to (4S,5S)-4-Benzyloxy-5-hydroxy-N-(4-methoxybenzyl) Amide
Author: Liangxian Liu, lxliu@xmu.edu.cn
Abstract: A general approach to (4S,5S)-4-benzyloxy-5-hydroxy-N-(4-methoxy- benzyl) amide 2 based on a diastereoselective reduction of (5S,6RS)-6-alkyl-5- benzyloxy-6-hydroxy-2-piperidinones 1a and its tautomeric ring-opening keto amides 1b is described. It was uncovered that while the reduction with L-Selectride in -20 ^oC to room temperature led to reductive products 2 in excellent yields and good syn-diastereoselectivities.

Manuscript ID: molecules-asychem-20090708-Acocella-it
Title: Asymmetric Friedel-Crafts Alkylation of Indole with Chalcones Catalyzed by Chiral Phosphoric Acids
Authors: Arrigo Scettri, Rosaria Villano, M.Rosaria Acocella *
Affiliation: Department of Chemistry, University of Salerno, Via Ponte Don Melillo, 84084,Fisciano, Italy. E-mail: acord78@libero.it
Abstract: The reaction of indole with chalcones, to give Michael-type adducts, was found to occur with good efficiency (up to 98% yield) and moderate enentioselectivity (up to 52%ee) in presence of chiral BINOL-based phosphoric acid. Furthermore the alkylation products can be obtained in much higher e.e.s after one only crystallization.

Manuscript ID: Molecules-asychem-20091004-Rindone-it
Type of Paper: Article
Title: Toward the Enantioselective Biomimetic Preparation of Dilignols with Phenylcoumaran Skeleton
Authors: M. Bruschi¹, M. Orlandi¹, M. Rindone², B. Rindone¹, F. Saliu¹, E. L. Tolppa¹ and L. Zoia¹
Affiliations: ¹ Department of Environmental Sciences, University of Milano-Bicocca, Piazza della Scienza, 1, 20126 Milano, Italy
² SIFIT, Milano, Italy; E-Mail: bruno.rindone@unimib.it
Abstract: Organic compounds obtained from radical coupling of phenylpropenoidic phenols have an important biological role. The oxidative phenol coupling is often used as a tool for the preparation of these dilignols. However, the bimolecular phenoxy radical coupling reaction is not under a strictly regio- and stereospecific control. This is due to the fact that phenoxy radicals are very persistent radicals, and the dimerization reaction is slow. Hence the stereogenic carbons formed in the oxidative phenol coupling reaction in vitro are racemic. On the contrary, lignans are homochiral. There is a need for the enantioselective preparation of dilignols, in order to study the mechanism occurring in vivo. We recently reported that regio- and diastereoselectivity in the oxidative phenol coupling reaction may be obtained using the horseradish peroxidase (HRP)-catalyzed oxidative coupling with hydrogen peroxide as the oxidant. Ferulic acid derivatives 1 are dimerized to the phenylcoumaran 2 (Scheme 1) to give almost exclusively the racemic trans isomer if R is achiral. We suggest that this is the result of diastereocontrol in the cyclization of the intermediate quinomethide deriving from the dimerization of a persistent phenoxy radical. An initial single electron transfer from the starting ferulic acid derivative 1 forms a phenoxy radical which undergoes carbon-carbon bond formation in a reversible way to give a mixture of quinomethides isomers 3, possessing, respectively, the (E) and (Z) configuration at the exocyclic quinonoid double bond and the (R) and (S) configuration at the stereogenic C-3 carbon. Ferulic acid derivatized with chiral auxiliaries and oxidized with hydrogen peroxide in the presence of horseradish peroxidase (HRP) as the catalyst gives the phenylcoumaran 2 as different amounts of a diastereisomeric couple. Chromatographic separation and hydrolysis allow to show the enantioselectivity obtained. The conformational analysis and the activation energy of the cyclization reaction using semiempirical PM3 calculations on the intermediate quinomethides 3 is used to explain the observed stereoselectivity.