Asymmetric aldol reactions: a novel model for switching between chelation- and non-chelation-controlled aldol reactions

Yan, Tu Hsin; Tan, Chang Wei; Lee, Hui Chun; Lo, Hua Chi; Huang, Tzung Yu

doi:10.1021/ja00060a010

Cited by 101 publications

(18 citation statements)

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“…This remarkable Lewis acid dependence on the stereochemical outcome of the [4 + 2] cycloaddition has been attributed to a switch in the approach (endo/exo) of one face of the vinyl ether to the enantiotopic faces of the Lewis acid−nitroalkene complex 2b. Interestingly, a number of Lewis acid dependent reversals in selectivity have been documented for a variety of reactions including asymmetric Diels−Alder, aldol, and 1,4-addition reactions . In some examples, the switch in selectivity is rationalized by invoking different coordination modes of the Lewis acids, while in other systems the reversal is believed to result from differing steric requirements of the Lewis acids.…”

Section: Introductionmentioning

confidence: 99%

Tandem Inter [4 + 2]/Intra [3 + 2] Cycloadditions of Nitroalkenes. Asymmetric Synthesis of Highly Functionalized Aminocyclopentanes Using the Bridged Mode (β-Tether) Process

Denmark

Dixon

1998

J. Org. Chem.

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An asymmetric, tandem inter [4 + 2]/intra [3 + 2] bridged mode (beta-tether) cycloaddition of nitroalkenes has been developed. This new sequence involves the Lewis acid-promoted [4 + 2] cycloaddition of nitro olefins with enantiopure 1-alkoxy-1,4-dienes. The resulting nitronates, bearing a C(5) tethered dipolarophile, undergo thermal, intramolecular [3 + 2] cycloaddition to afford stable tricyclic nitroso acetals, which can be subsequently reduced to provide interesting aminocyclopentanes. Thus, in three steps, highly functionalized, enantiomerically enriched aminocyclopentanes can be constructed with good yield and high ee. Additionally, the Lewis acid was found to impart a remarkable influence on the stereochemical outcome of the [4 + 2] cycloaddition.

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Section: Introductionmentioning

confidence: 99%

Tandem Inter [4 + 2]/Intra [3 + 2] Cycloadditions of Nitroalkenes. Asymmetric Synthesis of Highly Functionalized Aminocyclopentanes Using the Bridged Mode (β-Tether) Process

Denmark

Dixon

1998

J. Org. Chem.

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“…No attempt has been made to determine the enolate geometry and the oxidation state of the germanium species in the present reactions. However, on the basis of the absolute configuration of the major products, diastereofacial selection is considered to occur in the same manner as in the aldol reaction of boron enolates derived from enantiomerically pure 2-oxazolidinones. , Thus the observed syn/anti selectivity of the present Reformatsky reaction can be interpreted in terms of the Zimmerman−Traxler model, in which the geometry of enolates correlates with the relative configuration of products. Furthermore, the diastereofacial selectivity achieved can be explained on the basis of a noninternally chelated enolate (Scheme ).…”

Section: Resultsmentioning

confidence: 98%

An Activated Germanium Metal-Promoted, Highly Diastereoselective Reformatsky Reaction

et al. 1998

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Activated germanium metal, prepared by the reduction of germanium(II) iodide with potassium metal, was found to promote the Reformatsky reaction effectively under mild conditions. In the presence of activated germanium metal, the reactions of alpha-bromo ketones 2a and 2b and alpha-bromo imides 2e and 2f with benzaldehyde (1a) proceeded smoothly to give the corresponding beta-hydroxy carbonyl compounds 3a, 3b, 3e and 3f, respectively, in good yields and with good syn diastereoselectivity. The activated germanium metal-promoted, asymmetric Reformatsky reaction of enantiomerically pure-oxazolidinone derivatives 2g-j with various aldehydes 1a-d was also examined; the highest diastereoselectivity was achieved when (1S,2R)-2-amino-1,2-diphenylethanol-derived 2j was used as the Reformatsky donor. The excellent diastereoselectivity could be explained in terms of the formation of a chairlike, six-membered transition state between the aldehyde and enolate as in the Zimmerman-Traxler model. A single recrystallization of the Reformatsky adducts, followed by hydrolysis and subsequent esterification, led to enantiomerically pure methyl 3-hydroxy-2-methylalkanoates 10j-m, with almost quantitative recovery of the enantiomerically pure 2-oxazolidinone 14.

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“…Camphor amino alcohol (1 S ,2 R ,4 R )‐1‐amino‐7,7‐dimethylbi‐cyclo[2.2.1]heptan‐2‐ol 1 was prepared according to the literature process . The amino alcohol 1 reacted with various aldehydes 2a , 2b , 2c , 2d in CH 2 Cl 2 to give the deserved imines, which were directly reduced by sodium borohydride to yield the chiral camphor amino alcohols L1 , L2 , L3 , L4 in high yields (Scheme ) .…”

Section: Resultsmentioning

confidence: 99%

Copper‐Chiral Camphor β‐Amino Alcohol Complex Catalyzed Asymmetric Henry Reaction

Lei

Yan

et al. 2015

Chirality

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Four novel chiral amino alcohols were synthesized from D-(+)-camphor and utilized as ligands in a Cu(I)-catalyzed asymmetric Henry reaction. The reactions were carried out under mild conditions with excellent enantioselectivities and moderate yields without the exclusion of air or moisture. The highest enantioselectivity was observed up to 94% enantiomeric excess (ee) with ligand in toluene at room temperature.

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Asymmetric aldol reactions: a novel model for switching between chelation- and non-chelation-controlled aldol reactions

Cited by 101 publications

References 1 publication

Tandem Inter [4 + 2]/Intra [3 + 2] Cycloadditions of Nitroalkenes. Asymmetric Synthesis of Highly Functionalized Aminocyclopentanes Using the Bridged Mode (β-Tether) Process

Tandem Inter [4 + 2]/Intra [3 + 2] Cycloadditions of Nitroalkenes. Asymmetric Synthesis of Highly Functionalized Aminocyclopentanes Using the Bridged Mode (β-Tether) Process

An Activated Germanium Metal-Promoted, Highly Diastereoselective Reformatsky Reaction

Copper‐Chiral Camphor β‐Amino Alcohol Complex Catalyzed Asymmetric Henry Reaction

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