| 11. |
- Borg, Tessie, et al.
(författare)
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Mukaiyama aldol addition to α-chloro-substituted aldehydes. Origin of the unexpected syn selectivity.
- 2010
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 46:8, s. 1281-1283
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Tidskriftsartikel (refereegranskat)abstract
- The addition of sterically demanding enolsilanes to alpha-chloro aldehydes results unexpectedly in preferential formation of the anti-PFA product (1,2-syn), while the addition of the corresponding boron enolate furnishes the expected polar Felkin-Anh product (1,2-anti). A stereoinduction model explaining these observations is proposed.
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| 12. |
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| 13. |
- Danielsson, Jakob, et al.
(författare)
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1,3-Dipolar Cycloaddition of Azomethine Ylides to Aldehydes : Synthesis of anti alpha-Amino-beta-Hydroxy Esters
- 2011
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :3, s. 607-613
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Tidskriftsartikel (refereegranskat)abstract
- A 1,3-dipolar cycloaddition reaction of azomethine ylides to aldehydes is described. The azomethine ylides, generated by thermal electrocyclic ring opening of aziridines, adds to aldehydes in good yields with moderate to good selectivities to furnish oxazolidines. The oxazolidines were subsequently hydrolyzed to the corresponding amino alcohols, giving the anti diastereomer as the major product.
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| 14. |
- Danielsson, Jakob, 1985-
(författare)
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Stereoselective Nucleophilic Additions to Aldehydes and Synthesis of α-Amino-β- Hydroxy-Esters
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the development of new reaction methodology as well as stereochemical investigations. The first part concerns the investigation of 1,2- and merged 1,2- and 1,3- asymmetric induction in Mukaiyama aldol additions to α-heteroatom and α,β- heteroatom substituted aldehydes respectively. In particular, the unexpected 1,2-syn selectivity obtained in the addition of sterically hindered nucleophiles to α-chloroaldehydes is examined, and an explanation for the observed stereochemical trends is proposed. The second part describes the development of a novel entry to α-amino-β- hydroxy esters by a 1,3-dipolar cycloaddition reaction of aldehydes and azomethine ylides, generated by thermolysis of aziridines. The third part deals with our efforts to develop a novel entry to vicinal all- carbon quaternary centers, based on an intramolecular domino Heck- carbonylation reaction using tetrasubstituted olefins.
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| 15. |
- Danielsson, Jakob, et al.
(författare)
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Studies Toward Communesin F: A Diels-Alder Approach.
- 2014
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7052 .- 1523-7060. ; 16:3, s. 784-787
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Tidskriftsartikel (refereegranskat)abstract
- A Diels-Alder reaction is used as a key step in a synthetic study toward communesin F, in order to simultaneously introduce both of the all-carbon quaternary stereocenters with complete control of relative stereochemistry. Further manipulations of the cycloadduct, toward the hexacyclic core-structure of communesin F, are also disclosed.
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| 16. |
- Danielsson, Jakob, et al.
(författare)
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Total Synthesis of Dehaloperophoramidine : Evolution of a Synthesis
- 2017
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Ingår i: Strategies and Tactics in Organic Synthesis. - 1874-6004. ; 13, s. 217-242
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Bokkapitel (refereegranskat)abstract
- This account describes our efforts toward developing a stereodivergent entry to perophoramidine and the communesin alkaloids. The original approach toward our simplified model substrates relied on a palladium-catalyzed carbopalladation–carbonylation of a tetrasubstituted olefin to install the vicinal all-carbon quaternary stereocenters present in the target molecules, the olefin's stereochemistry thus dictating the relative stereochemistry of the quaternary stereocenters. Although the carbonylation–carbopalladation sequence worked well for trisubstituted olefins, only premature esterification was observed when using tetrasubstituted alkene substrates. Our second approach made use of the latent symmetry embedded in our target molecules. A Diels–Alder reaction or SmI2-mediated bis-alkylation of isoindigo was to be used to access the communesin and perophoramidine scaffolds, respectively. We found that due to unfavorable thermodynamics, it was not possible to reach the communesin scaffold. However, two new complexity-generating, cascade reactions were encountered en route to the synthesis of dehaloperophoramidine, resulting in a short and efficient synthesis.
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| 17. |
- Dressel, Martina, et al.
(författare)
-
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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Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 14:10, s. 3072-3077
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Tidskriftsartikel (refereegranskat)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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| 18. |
- Hirner, Sebastian, et al.
(författare)
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Microwave-Assisted Rearrangement of Vinylaziridines to 3-Pyrrolines : Formal Synthesis of (-)-Anisomycin
- 2005
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Ingår i: Synlett. - : Georg Thieme Verlag KG. - 0936-5214 .- 1437-2096. ; :20, s. 3099-3102
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Tidskriftsartikel (refereegranskat)abstract
- An efficient microwave-assisted rearrangement of activated vinylaziridines to 3-pyrrolines is described. The rearrangement proceeds in good to excellent yields and is mediated by NaI or LiI in MeCN at elevated temperatures. The synthetic utility of this reaction is shown in an efficient formal total synthesis of the antibiotic (-)-anisomycin.
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| 19. |
- Hirner, Sebastian, 1979-
(författare)
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New Methodologies in Organic Chemistry: Applications to the Synthesis of α-Amino Acids and Natural Products
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the development and application of new synthetic methodology in organic chemistry. The first part describes the development of a new protocol for the synthesis of 3-pyrrolines by means of a microwave-assisted ring-expansion reaction of 2-vinylaziridines. In addition, this methodology is implemented as a key-step in a formal total synthesis of the antibiotic (-)-anisomycin. In the second part, a new methodology for the synthesis of arylglycines from Weinreb amides is described. In this procedure, a Grignard reagent is added to the iminium ion formed from the Weinreb amide upon treatment with a base. When a chiral amide is used, the nucleophilic addition proceeds with high diastereoselectivity. Finally, an easy and straightforward synthesis of α-amino amides via a base-mediated rearrangement of modified Weinreb amides into N,O-acetals is presented. Subsequent arylation, alkylation, alkenylation or alkynylation of this intermediate affords the corresponding α-amino amides in excellent yields. Furthermore, a more generalized protocol for the α-arylation of Weinreb amides lacking an α-amino moiety is also discussed.
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| 20. |
- Hirner, Sebastian, et al.
(författare)
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Synthesis of alpha-Amino Acids by Umpolung of Weinreb Amide Enolates
- 2008
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Ingår i: European Journal of Organic Chemistry. - : Wiley. - 1434-193X .- 1099-0690. ; :33, s. 5583-5589
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Tidskriftsartikel (refereegranskat)abstract
- An efficient and diastereoselective synthesis of alpha-amino acids from readily available starting materials has been developed. The key feature of this reaction is an umpolung of a glycine-derived enolate, providing an alternative approach for the synthesis of alpha-amino acids.
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