- 14. Origin of Diastereoselectivity in the Thermal [4+2] Cycloadditions of Dienophiles Derived from Oppolzer's Sultams: Steric vs. Stereoelectronic Influences
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Comparative semi-empirical PM3 and ab initio STO 3-21G calculations on bornanesultam-derived dienophiles containing the structural moiety SO2-N-C(O)-X(α) = Y(β) suggest that, among the conformers of low energy, the thermodynamically less stable SO2/C(O)-syn,C(O)/X=Y-s-cis conformation is also reactive in terms of LUMO level and atomic coefficients, Furthermore, the X(α), Y(β) LUMO atomic coefficients are nonequivalent with respect to both X(α)-re and X(α)-si faces, and thus have, depending on the conformation, a matching or mismatching stereoelectronic influence with the co-operative steric effect. This dissymmetry is believed to result from the generalized anomeric effect of the N lone pair, itself anomerically stabilized and directed, in the absence of crucial steric interactions, by the pseudo-axial anti-periplanar S=O bond. Five N-acyl-substituted bornanesultams are discussed ((-)-1a: N-acryloyl, X=CH, Y=CH2; (-)-1b: N-crotonoyl, X=CH, Y=CHMe; (-)-1c: N,N'-fumaroyl, X=CH, Y=CH(C(O)-bornanesultam); 2a: N-glyoxyloyl, X=CH, Y=O; 2b: N-acylnitroso, X=N, Y=O). In this context, differences with toluenesultams 3 are pointed out. A previous report on N-(acylnitroso)-bornanesultam 2b is revisited, and the diastereoselectivity observed is shown to result from thermodynamic control.
- Chapuis, Christian,De Saint Laumer, Jean-Yves,Marty, Maurus
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- Asymmetric Electrophilic α-Amination of Silyl Enol Ether Derivatives via the Nitrosocarbonyl Hetero-ene Reaction
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The first example of a general asymmetric nitrosocarbonyl hetero-ene reaction is described. The procedure uses a copper-catalyzed aerobic oxidation of a commercially available chiral nitrosocarbonyl precursor (EleNOr) and is operationally simple. The tran
- Sandoval, David,Samoshin, Andrey V.,Read De Alaniz, Javier
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- Asymmetric multicomponent [C+NC+CC] synthesis of highly functionalized pyrrolidines catalyzed by silver(I)
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Highly functionalized pyrrolidines are obtained in a single chemical step via a mild, efficient, and selective Ag1-catalyzed asymmetric [C+NC+CC] coupling process. Oppolzer's camphorsultam enables the desired reaction cascade and provides a rel
- Garner, Philip,Kaniskan, H. Uemit,Hu, Jieyu,Youngs, Wiley J.,Panzner, Matthew
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p. 3647 - 3650
(2007/10/03)
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- A practical large-scale synthesis of (3R,4R)-4-(Hydroxymethyl)pyrrolidin-3- ol via asymmetric 1,3-dipolar cycloaddition
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(3R,4R)-4-(Hydroxymethyl)pyrrolidin-3-ol (1), which is a useful intermediate for the synthesis of various bioactive molecules, has been synthesized in 51% overall yield by 1,3-dipolar cycloaddition reaction from the dipolarophile, (E)-3-benzyloxypropenoyl-(2′S)-bornane-10,2-sultam (5), and the achiral ylide precursor, N-(benzyl)-N-(methoxymethyl)-N- (trimethylsilylmethyl)amine (6), without using chromatography and the subsequent reduction with LAH and catalytic hydrogenation. The diastereomers 7 and 8 were separated by crystallization, and efficient procedures were developed for the subsequent reactions to afford 1.
- Kotian, Pravin L.,Lin, Tsu-Hsing,El-Kattan, Yahya,Chand, Pooran
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p. 193 - 197
(2012/12/24)
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- Stereocontrolled 1,3-dipolar cycloadditions using Oppolzer's camphor sultam as the chiral auxiliary for carbonyl stabilized azomethine ylides
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Two complementary approaches to substituted pyrrolidines via stereocontrolled 1,3-dipolar cycloaddition reactions of chiral azomethine ylides are described. In one approach, chiral azomethine ylides were generated by thermolysis of aziridine carboxylate sultams and trapped with a variety of dipolarophiles to give good yields of the corresponding cycloadducts. In the second approach, chiral azomethine ylides were generated from glycyl sultams by 'imine tautomerization' and trapped with dipolarophiles to give good yields of the corresponding cycloadducts.
- Garner, Philip,Dogan, ?zdemir,Youngs, Wiley J.,Kennedy, Vance O.,Protasiewicz, John,Zaniewski, Rebecca
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- Progress toward the total synthesis of callipeltin A (I): Asymmetric synthesis of (3S,4R)-3,4-dimethylglutamine
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(equation presented) During the total synthesis of the novel cyclic depsipeptide callipeltin A (1), the unit (3S,4R)-3,4-dimethylglutamine, was successfully synthesized by asymmetric Michael addition and subsequent electrophilic azidation. The key feature of this approach is the generation of three adjacent stereogenic centers using the same camphorsultam chiral auxiliary.
- Liang, Bo,Carroll, Patrick J.,Joullie, Madeleine M.
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p. 4157 - 4160
(2007/10/03)
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- Enantioselective total synthesis of (-)-denticulatins A and B using a novel group-selective aldolization of a meso dialdehyde as a key step
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The diastereoselective synthesis of (-)-denticulatin A (1a) was achieved for the first time in 9 steps (41% yield) based on a novel group-selective aldolization of a meso dialdehyde as a key step. The inherent chirality present in bornanesultam 4 was thus transmitted to the five stereocenters spanning C4-C8 in key intermediate 8. In addition, denticulatin B (1b) was obtained from the common intermediate 8 en route to denticulatin A in 10 steps and 35% overall yield.
- De Brabander, Jef,Oppolzer, Wolfgang
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p. 9169 - 9202
(2007/10/03)
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- Diastereo- and enantiocontrolled synthesis of (-)-allosedamine via cycloaddition of a chiral nitrone
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The piperidine alkaloid (-)-allosedamine (1) has been synthesized, in 21% overall yield, in nine steps starting from the formyl-ester 4. The synthesis features the reaction cascade 7 → 3 → 2, involving asymmetric electrophilic enolate hydroxyamination, hy
- Oppolzer,Tamura,Deerburg
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p. 554 - 560
(2007/10/02)
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- A practical synthesis of (R)-(+)-cyclohex-3-enecarboxylic acid via an asymmetric Diels-Alder reaction
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The polymerisation which complicates the ethylaluminum dichloride-catalysed asymmetric Diels-Alder reaction between N-propenoylbornane-10,2-sultam[10,10-dimethyl-3-thia-4-azatricyclo[5.2 .1.01,5]decane 3,3-dioxide] and butadiene can be suppress
- Thom,Kocienski,Jarowicki
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p. 475 - 477
(2007/10/02)
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- FLUORINATED HETEROCYCLES: TARGETS IN THE SEARCH FOR BIOACTIVE COMPOUNDS AND TOOLS FOR THEIR PREPARATION
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To strategies for the preparation and use of fluorinated heterocycles are discussed: 1.)the building block approach being used mainly for the preparation of target heterocycles with fluorinated substituents, and 2.)the direct fluorination approach in which fluorinated heterocycles are used as tools for the preparation of bioactive compounds.Strategies presented in the building block approach include electrophilic reactions of building blocks derived from trifluoroacetic acid (1), as well as the use of building blocks obtained from trichlorotrifluoroethane (2) and chlorodifluoro acetic acid (3) through organometallic reactions.The preparation and use of N-fluoro sultams 62 and 66 are shown in the direct fluorination approach.Both strategies can be successfully used n the synthesis of bioactive compounds of pharmaceutical and agrochemical interest.
- Differding, E.,Frick, W.,Lang, R. W.,Martin, P.,Schmit, C.,et al.
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p. 647 - 671
(2007/10/02)
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- The Preparation of Optically Active Δ2-Isoxazolines. A Model for Asymmetric Induction in the Non Lewis Acid Catalyzed Reactions of Oppolzer's Chiral Sultam
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Good diastereoselectivity (ca. 90/10) is reported in the cycloaddition reactions of Oppolzer's chiral sultam with nitrile oxides.A model is proposed which may apply to other non Lewis acid promoted reactions of this sultam.
- Curran, Dennis P.,Kim, Byeang Hyean,Daugherty, James,Heffner, Timothy, A.
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p. 3555 - 3558
(2007/10/02)
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- IRIDOIDS : ENANTIOSELECTIVE SYNTHESIS OF LOGANIN VIA AN ASYMMETRIC DIELS-ALDER REACTION
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Starting from (-)-camphor-10-sulfonic acid (5) the crystalline sultam 9 was readily prepared.TiCl4-mediated Diels-Alder addition of the N-crotonyl sultam 11 to cyclopentadiene, crystallization of the resulrting adduct 12 and subsequent reduction gave virtually pure (1S, 4R,5R, 6S)-1 together with recovered auxiliary 9.The loganin precursor 1 was transformed into norbonanone 20, which upon Baeyer-Villiger oxidation led to the suitably substituted cyclopentane 22 from which 1-B-O-methyl loganin aglucone (2) was readily available.
- Vandewalle, M.,Van der Eycken, J.,Oppolzer, W.,Vullioud, C.
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p. 4035 - 4044
(2007/10/02)
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- ASYMMETRIC INTRAMOLECULAR DIELS-ALDER REACTIONS OF N-ACYL-CAMPHOR-SULTAM TRIENES.
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Treatment of triene-imides 4 with EtAlCl2 at -20 deg C gave crystalline cycloadducts 5 which furnished enantiomerically pure bicyclic alcohols 9 with regeneration of the chiral auxilary.
- Oppolzer, Wolfgang,Dupuis, Dominique
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p. 5437 - 5440
(2007/10/02)
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