| 1. |
- Borg, Tessie, et al.
(author)
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Diastereoselective Nucleophilic Addition to Aldehydes with Polar alpha- and alpha,beta-Substituents
- 2011
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In: Advanced Synthesis and Catalysis. - : Wiley. - 1615-4150 .- 1615-4169. ; 353:11-12, s. 2022-2036
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Journal article (peer-reviewed)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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| 2. |
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| 3. |
- Dressel, Martina, et al.
(author)
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Total synthesis of (+)-alexine by utilizing a highly stereoselective 3+2 annulation reaction of an N-tosyl-alpha-amino aldehyde and a 1,3-bis(silyl)propene
- 2008
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 14:10, s. 3072-3077
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Journal article (peer-reviewed)abstract
- A novel route towards the polyhydroxylated pyrrolizidine alkaloid (+)-alexine has been developed. A key step in this synthesis is a highly stereoselective [3+2] annulation reaction of N-Ts-alpha-amino aldehyde 7a (Ts=tosyl) and 1,3-bis(silyl)propene 8a for the construction of the polyhydroxylated pyrrolidine subunit of the target molecule. Previous synthetic strategies rely on carbohydrates that require several protecting-group manipulations, thereby making the total number of steps relatively high. The [3+2] annulation strategy compares favorably with carbohydrate-based syntheses and constitutes a highly efficient entry to polyhydroxylated alkaloids.
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| 4. |
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| 5. |
- Restorp, Per, et al.
(author)
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Diastereoselective Aldol Additions to α-Amino-β-Silyloxy Aldehydes. Divergent Synthesis of Aminodiols
- 2005
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In: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 7:5, s. 893-895
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Journal article (peer-reviewed)abstract
- A divergent protocol for substrate-controlled diastereoselective synthesis of aminodiols has been developed using nucleophilic Mukaiyama aldol additions to alpha-amino-beta-silyloxy aldehydes. The merged stereochemical impact on the diastereoselectivity of the polar alpha- and beta-substituents is highlighted.
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| 6. |
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| 7. |
- Restorp, Per, et al.
(author)
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Regioselective and Divergent Opening of Vinyl Epoxides with Alkyne Nucleophiles
- 2005
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In: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; 18, s. 3946-3951
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Journal article (peer-reviewed)abstract
- A divergent procedure for nucleophilic ring-opening of vinyl epoxides with alkynes has been developed, The combination of lithium acetylides and BF(3)center dot OEt2 afforded the S(N)2 products, whereas alkynylalanes gave S(N)2' addition. The regioselectivity of these processes is affected by the alkyne substituent. Ethoxyacetylene added with complete regiocontrol under both SN2 and SN2' conditions, and the SN2 isomeric adducts could he rearranged into gamma-butyrolactones. The synthetic utility of the process is demonstrated by a short synthesis of gamma-butyrolactone 24, a key intermediate in the synthesis of prostaglandin PGF(20).
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| 8. |
- Restorp, Per, et al.
(author)
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Regioselective and Divergent Opening of Vinyl Epoxides with Ethoxyacetylene
- 2004
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In: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :18, s. 2086-2087
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Journal article (peer-reviewed)abstract
- A divergent protocol for nucleophilic opening of vinyl epoxides with ethoxyacetylide has been developed and demonstrated to give complete regioselectivity depending on reaction conditions.
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| 9. |
- Restorp, Per, 1976-
(author)
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Stereoselective Nucleophilic Additions to α-Amino Aldehydes: Application to Natural Product Synthesis
- 2006
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with the development and application of new synthetic methodology for stereo- or regioselective construction of carbon-carbon bonds in organic synthesis. The first part of this thesis describes the development of a divergent protocol for stereoselective synthesis of chiral aminodiols by employing Mukaiyama aldol additions to syn- and anti-α-amino-β-silyloxy aldehydes. The stereoselectivity of the nucleophilic attack is governed by either chelation to the α-amino moiety or by nucleophilic attack in the Felkin-Anh sense. This study is also directed towards the elucidation of the factors that dictate aldehyde π-facial selectivity in substrate-controlled nucleophilic additions to these and similar systems. In the second part, a highly stereoselective [3 + 2]-annulation reaction of N-Ts-α-amino aldehydes and 1,3-bis(silyl)propenes for stereoselective construction of densely functionalized pyrrolidines is presented. In addition, this methodology is also implemented as a keystep in a synthetic approach towards the polyhydroxylated pyrrolidine and pyrrolizidine alkaloids DGDP and (+)-alexine from a common late pyrrolidine intermediate. Finally, a divergent protocol for regioselective opening of vinyl epoxides using alkyne nucleophiles is described, in which the regioselectivity of the nucleophilic attack is controlled by the choice of reaction conditions. The regioselectivities of the SN2 and SN2’ processes are, however, significantly influenced by the nature of the alkyne substituents and the best results are obtained using ethoxyacetylene. The SN2 opening of vinyl epoxides with ethoxyacetylene as nucleophile is also shown to provide a straightforward entry to functionalized γ-butyrolactones.
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| 10. |
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