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146 KiB

Open AccessArticle

From Symmetric Glycerol Derivatives to Dissymmetric Chlorohydrins

by Carmen Solarte, Marc Escribà, Jordi Eras, Gemma Villorbina, Ramon Canela and Mercè Balcells

Molecules 2011, 16(3), 2065-2074; https://doi.org/10.3390/molecules16032065 - 2 Mar 2011

Cited by 7 | Viewed by 6481

Abstract

The anticipated worldwide increase in biodiesel production will result in an accumulation of glycerol for which there are insufficient conventional uses. The surplus of this by-product has increased rapidly during the last decade, prompting a search for new glycerol applications. We describe here [...] Read more.

The anticipated worldwide increase in biodiesel production will result in an accumulation of glycerol for which there are insufficient conventional uses. The surplus of this by-product has increased rapidly during the last decade, prompting a search for new glycerol applications. We describe here the synthesis of dissymmetric chlorohydrin esters from symmetric 1,3-dichloro-2-propyl esters obtained from glycerol. We studied the influence of two solvents: 1,4-dioxane and 1-butanol and two bases: sodium carbonate and 1-butylimidazole, on the synthesis of dissymmetric chlorohydrin esters. In addition, we studied the influence of other bases (potassium and lithium carbonates) in the reaction using 1,4-dioxane as the solvent. The highest yield was obtained using 1,4-dioxane and sodium carbonate. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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194 KiB

Open AccessArticle

A General and Simple Diastereoselective Reduction by L-Selectride: Efficient Synthesis of Protected (4S,5S)-Dihydroxy Amides

by Bo Yin, Dong-Nai Ye, Kai-Hui Yu and Liang-Xian Liu

Molecules 2010, 15(4), 2771-2781; https://doi.org/10.3390/molecules15042771 - 16 Apr 2010

Cited by 2 | Viewed by 10990

Abstract

A general approach to (4S,5S)-4-benzyloxy-5-hydroxy-N-(4-methoxybenzyl) amides 10 based on a diastereoselective reduction of (5S,6RS)-6-alkyl-5-benzyloxy-6-hydroxy-2-piperidinones 6 and their tautomeric ring-opened keto amides 7 is described. The reduction with L-Selectride at -20 °C to [...] Read more.

A general approach to (4S,5S)-4-benzyloxy-5-hydroxy-N-(4-methoxybenzyl) amides 10 based on a diastereoselective reduction of (5S,6RS)-6-alkyl-5-benzyloxy-6-hydroxy-2-piperidinones 6 and their tautomeric ring-opened keto amides 7 is described. The reduction with L-Selectride at -20 °C to room temperature afforded the products 10 in excellent yields and moderate to high syn-diastereoselectivities. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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315 KiB

Open AccessArticle

Organocatalytic Michael Addition of 1,3-Dicarbonyl Indane Compounds to Nitrostyrenes

by Zhen-Yu Jiang, Hua-Meng Yang, Ya-Dong Ju, Li Li, Meng-Xian Luo, Guo-Qiao Lai, Jian-Xiong Jiang and Li-Wen Xu

Molecules 2010, 15(4), 2551-2563; https://doi.org/10.3390/molecules15042551 - 12 Apr 2010

Cited by 14 | Viewed by 9896

Abstract

To map out the efficient organocatalyst requirements in the Michael addition of 1,3-dicarbonyl indane compounds to nitrostyrenes, a dozen different amino organocatalysts containing a p-toluenesulfonyl group (Ts) have been evaluated; excellent enantio-selectivities (up to er 92:8) were obtained with a primary amine-based [...] Read more.

To map out the efficient organocatalyst requirements in the Michael addition of 1,3-dicarbonyl indane compounds to nitrostyrenes, a dozen different amino organocatalysts containing a p-toluenesulfonyl group (Ts) have been evaluated; excellent enantio-selectivities (up to er 92:8) were obtained with a primary amine-based Ts-DPEN catalyst and a plausible catalytic reaction mechanism was proposed on the basis of the experimental results. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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446 KiB

Open AccessArticle

Synthesis and Conformational Study of a Novel Macrocyclic Chiral(Salen) ligand and its Uranyl and Mn Complexes

by Maria E. Amato, Francesco P. Ballistreri, Andrea Pappalardo, Gaetano A. Tomaselli and Rosa M. Toscano

Molecules 2010, 15(3), 1442-1452; https://doi.org/10.3390/molecules15031442 - 9 Mar 2010

Cited by 7 | Viewed by 9182

Abstract

A novel chiral macrocyclic ligand incorporating a chiral salen moiety into a framework containing two biphenyl units was synthesized. Structural properties and conformational aspects of the free ligand and an UO₂ complex were studied by using NMR spectroscopy in solution and MM [...] Read more.

A novel chiral macrocyclic ligand incorporating a chiral salen moiety into a framework containing two biphenyl units was synthesized. Structural properties and conformational aspects of the free ligand and an UO₂ complex were studied by using NMR spectroscopy in solution and MM calculations. The Mn(III) complex was tested as catalyst in enantioselective oxidation of prochiral unfunctionalized olefins to the corresponding optically active epoxides under very mild conditions. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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197 KiB

Open AccessArticle

Protecting-Group-Free Synthesis of 2-Deoxy-Aza-Sugars

by Emma Marie Dangerfield, Catherine Heather Plunkett, Bridget Louise Stocker and Mattie Simon Maria Timmer

Molecules 2009, 14(12), 5298-5307; https://doi.org/10.3390/molecules14125298 - 16 Dec 2009

Cited by 26 | Viewed by 13359

Abstract

The protecting-group-free asymmetric synthesis of 1,2,4-trideoxy-1,4-imino-L-xylitol is readily achieved in five steps from 2-deoxy-D-ribose and with an overall yield of 48%. Key in this synthesis is the application of our recently developed Vasella-reductive amination and carbamate annulation methodologies to the synthesis of 2-deoxy-aza-sugars. [...] Read more.

The protecting-group-free asymmetric synthesis of 1,2,4-trideoxy-1,4-imino-L-xylitol is readily achieved in five steps from 2-deoxy-D-ribose and with an overall yield of 48%. Key in this synthesis is the application of our recently developed Vasella-reductive amination and carbamate annulation methodologies to the synthesis of 2-deoxy-aza-sugars. The carbamate annulation occurred with excellent yield and diastereoselectively (>20:1 d.r.), in favour of the 3,4-cis isomer. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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236 KiB

Open AccessArticle

A Striking Exception to the Chelate Model for Acyclic Diastereocontrol: Efficient Access to a Versatile Propargyl Alcohol for Chemical Synthesis

by Sami F. Tlais, Ronald J. Clark and Gregory B. Dudley

Molecules 2009, 14(12), 5216-5222; https://doi.org/10.3390/molecules14125216 - 15 Dec 2009

Cited by 5 | Viewed by 10534

Abstract

The four-step, asymmetric synthesis of a chiral propargyl alcohol 1 from (R)-pantolactone is described. A key feature of the synthesis is a diastereoselective acetylide addition to a chiral α-alkoxy-aldehyde 7, in which unusual Felkin selectivity is observed, despite the potential [...] Read more.

The four-step, asymmetric synthesis of a chiral propargyl alcohol 1 from (R)-pantolactone is described. A key feature of the synthesis is a diastereoselective acetylide addition to a chiral α-alkoxy-aldehyde 7, in which unusual Felkin selectivity is observed, despite the potential for chelation control. Crystalline propargyl alcohol 1 is valuable for complex molecule synthesis, and is easy to prepare in multi-gram quantities and high diastereomeric purity. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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292 KiB

Open AccessArticle

Asymmetric Friedel-Crafts Alkylation of Indole with Chalcones Catalyzed by Chiral Phosphoric Acids

by Arrigo Scettri, Rosaria Villano and Maria Rosaria Acocella

Molecules 2009, 14(8), 3030-3036; https://doi.org/10.3390/molecules14083030 - 13 Aug 2009

Cited by 27 | Viewed by 16334

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 enantioselectivity (up to 52% e.e.) in the presence of a chiral BINOL-based phosphoric acid. Furthermore, the alkylation products can be [...] Read more.

The reaction of indole with chalcones, to give Michael-type adducts, was found to occur with good efficiency (up to 98% yield) and moderate enantioselectivity (up to 52% e.e.) in the presence of a chiral BINOL-based phosphoric acid. Furthermore, the alkylation products can be obtained in much higher e.e.s after one only crystallization. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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Review

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1044 KiB

Open AccessReview

Synthetic Applications of Chiral Unsaturated Epoxy Alcohols Prepared by Sharpless Asymmetric Epoxidation

by Antoni Riera and María Moreno

Molecules 2010, 15(2), 1041-1073; https://doi.org/10.3390/molecules15021041 - 23 Feb 2010

Cited by 43 | Viewed by 15991

Abstract

An overview of the synthesis and applications of chiral 2,3-epoxy alcohols containing unsaturated chains is presented. One of the fundamental synthetic routes to these compounds is Sharpless asymmetric epoxidation, which is reliable, highly chemoselective and enables easy prediction of the product enantioselectivity. Thus, [...] Read more.

An overview of the synthesis and applications of chiral 2,3-epoxy alcohols containing unsaturated chains is presented. One of the fundamental synthetic routes to these compounds is Sharpless asymmetric epoxidation, which is reliable, highly chemoselective and enables easy prediction of the product enantioselectivity. Thus, unsaturated epoxy alcohols are readily obtained by selective oxidation of the allylic double bond in the presence of other carbon-carbon double or triple bonds. The wide availability of epoxy alcohols with unsaturated chains, the versatility of the epoxy alcohol functionality (e.g. regio- and stereo-selective ring opening; oxidation; and reduction), and the arsenal of established alkene chemistries, make unsaturated epoxy alcohols powerful starting materials for the synthesis of complex targets such as biologically active molecules. The popularization of ring-closing metathesis has further increased their value, making them excellent precursors to cyclic compounds. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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335 KiB

Open AccessReview

Organocatalyzed Asymmetric α-Oxidation, α-Aminoxylation and α-Amination of Carbonyl Compounds

by Tirayut Vilaivan and Worawan Bhanthumnavin

Molecules 2010, 15(2), 917-958; https://doi.org/10.3390/molecules15020917 - 11 Feb 2010

Cited by 155 | Viewed by 16657

Abstract

Organocatalytic asymmetric α-oxidation and amination reactions of carbonyl compounds are highly useful synthetic methodologies, especially in generating chiral building blocks that previously have not been easily accessible by traditional methods. The concept is relatively new and therefore the list of new catalysts, oxidizing [...] Read more.

Organocatalytic asymmetric α-oxidation and amination reactions of carbonyl compounds are highly useful synthetic methodologies, especially in generating chiral building blocks that previously have not been easily accessible by traditional methods. The concept is relatively new and therefore the list of new catalysts, oxidizing and aminating reagents, as well as new substrates, are expanding at an amazing rate. The scope of this review includes new reactions and catalysts, mechanistic aspects and synthetic applications of α-oxidation, hydroxylation, aminoxylation, amination, hydrazination, hydroxyamination and related α-heteroatom functionalization of aldehydes, ketones and related active methylene compounds published during 2005–2009. Full article

(This article belongs to the Special Issue Asymmetric Synthesis)

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