| 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, 1970-
(författare)
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Asymmetric [2,3]-Sigmatropic Rearrangement of Allylic Ammonium Ylides
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis describes the realization of an asymmetric [2,3]-sigmatropic rearrangement of achiral allylic amines. It is divided into two parts; the first part deals with the development of a Lewis acid-mediated [2,3]-sigmatropic rearrangement and the second the asymmetric version thereof. Quaternization of an -amino amide with various Lewis acids established BBr3 and BF3 to be the most appropriate ones. Various allylic amines were subsequently rearranged into the corresponding homoallylic amines in good to excellent syn-diastereoselectivities, revealing the endo-transition state to be the preferred pathway. The structures of the intermediate Lewis acid-amine complexes were confirmed by NMR spectroscopy studies and DFT calculations. Based on this investigation a chiral diazaborolidine was chosen as Lewis acid and was shown to efficiently promote the asymmetric [2,3]-sigmatropic rearrangement furnishing homoallylic amines in good yields and excellent enantiomeric excesses. In contrast to the achiral rearrangement mediated by BBr3 and BF3, the asymmetric version gave the opposite major diastereomer, revealing a preference for the exo-transition state in the asymmetric rearrangement. To account for the observed selectivities, a kinetic and thermodynamic pathway was presented. On the basis of a deuterium exchange experiment on a rearranged Lewis acid-amine complex and an NMR spectroscopic investigation, the kinetic pathway was shown to be favored.
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| 3. |
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| 4. |
- Blid, Jan, et al.
(författare)
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Asymmetric [2,3]-sigmatropic rearrangement of allylic ammonium ylides
- 2005
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 127:26, s. 9352-9353
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Tidskriftsartikel (refereegranskat)abstract
- An asymmetric Lewis acid-mediated [2,3]-sigmatropic rearrangement of allylic amines has been developed, affording the corresponding homoallylic amines in good yield and excellent enantioselectivities. The rearrangement proceeds by complexation of the chiral Lewis acid to the amine followed by deprotonation and rearrangement.
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| 5. |
- 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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| 6. |
- Blid, Jan, et al.
(författare)
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Lewis acid mediated asymmetric 2,3 -sigmatropic rearrangement of allylic amines. Scope and mechanistic investigation
- 2007
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 72:4, s. 1294-1300
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Tidskriftsartikel (refereegranskat)abstract
- [GRAPHIC] The first asymmetric [2,3]-sigmatropic rearrangement of achiral allylic amines has been realized by quaternization of the amines with an enantiomerically pure diazaborolidine and subsequent treatment with Et3N. The resultant homoallylic amines were obtained in good yields and excellent ee's. The observed diastereo- and enantioselectivities were rationalized by invoking a kinetically controlled process, and support for this model was obtained from an NMR spectroscopic investigation of the chiral Lewis acid-substrate complex. The structure of the Lewis acid-product complex was established by X-ray crystallographic analysis and supported the proposed mechanism.
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| 7. |
- Borg, Tessie, et al.
(författare)
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Diastereoselective formation of 2,3,4,5-tetrasubstituted tetrahydrofurans by a Lewis acid promoted addition of C3-substituted 1,3-bis(silyl)propenes to aldehydes
- 2013
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Ingår i: Tetrahedron Letters. - : Pergamon Press. - 0040-4039 .- 1359-8562. ; 54:30, s. 3916-3918
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Tidskriftsartikel (refereegranskat)abstract
- A mild, efficient, Lewis acid promoted addition of C3-substituted 1,3-bis(silyl)propenes to aldehydes to provide the corresponding 2,3,4,5-tetrasubstituted tetrahydrofurans in excellent stereoselectivity is reported.
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| 8. |
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| 9. |
- Borg, Tessie, et al.
(författare)
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Diastereoselective Nucleophilic Addition to Aldehydes with Polar alpha- and alpha,beta-Substituents
- 2011
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Ingår i: Advanced Synthesis and Catalysis. - : Wiley. - 1615-4150 .- 1615-4169. ; 353:11-12, s. 2022-2036
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Tidskriftsartikel (refereegranskat)abstract
- The stereoselectivities obtained in Lewis acid-promoted Mukaiyama aldol additions and Sakurai allylations of mono-, and syn- and anti-disubstituted aldehydes possessing various polar alpha- and beta-substituents under non-chelating conditions are presented. The stereochemical outcome in the nucleophilic addition to alpha-substituted aldehydes containing an alpha-benzyloxy, alpha-fluoro or alpha-sulfonamide substituent are accurately predicted by current stereoinduction models. In contrast, the selectivitites obtained from addition of sterically demanding nucleophiles to alpha-chloro-substituted aldehydes cannot be rationalized by the same models and an alternative is discussed. The stereochemichal outcome in the additions to alpha, beta-disubstituted aldehydes is more complex and cannot be predicted using current models.
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| 10. |
- Borg, Tessie, et al.
(författare)
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Lewis Acid-Promoted Addition of 1,3-Bis(silyl)propenes to Aldehydes : A Route to 1,3-Dienes
- 2011
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 76:19, s. 8070-8075
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Tidskriftsartikel (refereegranskat)abstract
- The Lewis acid-promoted addition of 1,3-bis(silyl)-propenes to aldehydes to provide the corresponding (E)-1,3-dienes in excellent stereoselectivity and good to excellent yields is reported. The procedure is mild, base-free, and operationally straightforward.
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