| 1. |
- Blid, Jan, et al.
(författare)
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Lewis Acid Mediated [2,3]-Sigmatropic Rearrangement of Allylic alpha-Amino Amides
- 2004
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 69:9, s. 3043-3049
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Tidskriftsartikel (refereegranskat)abstract
- Boron trifluoride and BBr3 mediated [2,3]-sigmatropic rearrangements of allylic alpha-amino amides have been developed affording secondary amines in good yields. (E)-Crotyl and (E)-cinnamyl alpha-amino amides 2b and 2c exhibit excellent syn-diastereoselectivity upon rearrangement with either Lewis acid. The allylic amine 2a forms upon treatment with BF3 or BBr3 a five-membered heterocylic complex in which a single halide anion has been displaced by the carbonyl oxygen atom. The structures of the Lewis acid-amine complexes were elucidated using NMR spectroscopy. A plausible reaction mechanism, based on DFT calculations, is presented. Thus, BF3- or BBr3-complexed allylic amines 2 are shown to preferentially proceed, after deprotonation, via an endo transition state.
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| 2. |
- Blid, Jan, et al.
(författare)
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Lewis Acid Mediated [2,3]-Sigmatropic Rearrangement of Allylic Ammonium Ylides
- 2003
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Ingår i: Tetrahedron Letters. - 0040-4039 .- 1359-8562. ; 44:15, s. 3159-3162
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Tidskriftsartikel (refereegranskat)abstract
- An investigation of the Lewis acid mediated [2,3]-sigmatropic rearrangement of allylic ammonium ylides has been conducted by employing various bases and boron Lewis acids. Using BBr3 together with the phosphazene base 6, various allylic amines could be rearranged in good yields with low to excellent diastereoselectivity.
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| 3. |
- Lindquist, Charlotta, et al.
(författare)
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Microwave-Assisted Coupling of Carboxylic Acids to a Polymer Bound Hydrazine Linker
- 2003
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Ingår i: Synthetic Communications. - New York : Marcel Dekker, Inc.. - 0039-7911 .- 1532-2432. ; 33:13, s. 2257-2262
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Tidskriftsartikel (refereegranskat)abstract
- A set of carboxylic acids, all being potential scaffolds for combinatorial chemistry or peptide synthesis, were coupled to a polymer bound aryl hydrazine linker using microwave irradiation in good yields. Improved yields and reduced reaction times were achieved byusing microwave-assisted heating compared to conventional heating.
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| 4. |
- Lindström, U. M., et al.
(författare)
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Aza- 3,3 -claisen enolate rearrangement in vinylaziridines : Stereoselective synthesis of mono-, di-, and trisubstituted seven-membered lactams
- 2001
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Ingår i: Chemistry - A European Journal. - 0947-6539 .- 1521-3765. ; 7:1, s. 94-98
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Tidskriftsartikel (refereegranskat)abstract
- Several 2,3-disubstituted vinylaziridines have been N-acylated and subjected to LiHMDS in THF at - 78 degreesC. Upon warming to room temperature, the resulting amide enolates underwent a highly stereoselective [3,3]-sigmatropic rearrangement to give mono-, di-, and trisubstituted seven-membered lactams in good yields. The scope and limitations of the process have been investigated by using variously substituted vinylaziridines. A kinetically controlled process proceeding through a six-membered boatlike transition state assembly has been invoked to explain the stereochemical outcome of the reaction.
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| 5. |
- Neimert-Andersson, Kristina, et al.
(författare)
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Stereoselective Synthesis of Polyhydroxyl Surfactants. Stereochemical Influence on Langmuir Monolayers
- 2004
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 69:11, s. 3746-3752
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Tidskriftsartikel (refereegranskat)abstract
- Herein is described the synthesis of surfactants featuring polyhydroxylated head groups. Three head groups were prepared via consecutive stereoselective dihydroxylations of a diene. By coupling of these with lipophilic tail groups six novel surfactants have been prepared. The monolayers prepared from four of these have been investigated at the air-water interface. Significant differences were observed between monolayers consisting of enantiomerically pure surfactants contra racemates as well as between diastereomers.
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| 6. |
- Olofsson, Berit, et al.
(författare)
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A regio- and stereodivergent route to all isomers of vic-amino alcohols
- 2002
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 67:24, s. 8574-8583
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Tidskriftsartikel (refereegranskat)abstract
- Vicinal amino alcohols are substructures in several important natural products. They are also frequently employed ligands in asymmetric synthesis. Many enantioselective syntheses of vic-amino alcohols have been reported, but each structure has required its own synthetic route. This study presents a synthetic strategy leading to all eight possible isomers of a given beta-amino alcohol, starting from vinyl epoxides. The developed strategy focuses on the propensity of vinyl epoxides and vinylaziridines to be selectively ring-opened at the allylic position by suitable hard nucleophiles. Within this strategy, a novel large-scale aminolysis reaction and the synthesis of a trisubstituted N-H vinylaziridine are detailed.
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| 7. |
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| 8. |
- Olofsson, Berit, et al.
(författare)
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A regio- and stereodivergent synthesis of vic-amino alcohols
- 2000
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 2:25, s. 4087-4089
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Tidskriftsartikel (refereegranskat)abstract
- [GRAPHICS] A regio- and stereodivergent synthesis of vic-amino alcohols starting from vinylepoxides is described. The developed strategy focuses on the propensity of vinylepoxides and vinylaziridines to be ring-opened at the allylic position by suitable nucleophiles and makes use of reactions that perform such tasks selectively with either retention or inversion of configuration.
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| 9. |
- Olofsson, Berit, et al.
(författare)
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Determination of the relative configuration of vic-amino alcohols
- 2003
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Ingår i: Tetrahedron Letters. - 0040-4039 .- 1359-8562. ; 44:6, s. 1279-1281
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Tidskriftsartikel (refereegranskat)abstract
- A large set of syn- and anti-1,2-amino alcohols has been synthesized. Upon comparison of the CHO and CHN H-1 NMR shifts a general trend has been observed, making it possible to determine the relative configuration of 1,2-amino alcohols without derivatization or shift reagents.
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| 10. |
- Olofsson, Berit, et al.
(författare)
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Divergent synthesis of D-erythro-sphingosine, L-threo-sphingosine, and their regioisomers
- 2003
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 68:6, s. 2514-2517
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Tidskriftsartikel (refereegranskat)abstract
- Starting from a vinyl epoxide, a divergent synthesis of four sphingosine isomers is described. The remaining four isomers can easily be synthesized using the same methodology. Although numerous syntheses of sphingosine have been published, this is the first general route leading to all eight isomers in this important compound class. The synthetic strategy relies on regioselective opening of a vinyl epoxide and a vinylaziridine in the allylic position.
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