- Divergent synthesis of (6S,1′S,2′R)-hydroxypestalotin via tandem conjugate addition-lactonization sequence
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The stereoselective synthesis of (6S,1′S,2′R)-hydroxypestalotin from trans-hex-2-en-1-ol utilizing asymmetric dihydroxylation and Luche's reduction and tandem conjugative addition-lactonization as the key steps is reported.
- Mallula, Venkata Satyanarayana,Srinivas, Batthula,Radha Krishna, Palakodety
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p. 1115 - 1117
(2015/02/19)
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- [1,3]-Transfer of chirality during the nicholas reaction in γ-benzyloxy propargylic alcohols
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A highly regio- and stereoselective intramolecular [1.5]-hydrogentransfer process is described. Treatment of γ-benzyl-protccted Co 2(CO)6-α,γ-acetylenic diols with BF 3·OEt2 provides bis-homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the benzyloxy group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair-like transition state substantiated by a theoretical study is also included.
- Diaz, David D.,Ramirez, Miguel A.,Martin, Victor S.
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p. 2593 - 2606
(2008/02/07)
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- Chemoenzymatic total synthesis of the phytotoxic lactone herbarumin III
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Asymmetric total synthesis of phytotoxic nonenolide herbarumin III was accomplished by a chemoenzymatic approach. The main highlight of the synthesis was to fix the hydroxyl stereocenters (C7 and C9) by lipase catalyzed irreversible transesterification.
- Nanda, Samik
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p. 3661 - 3663
(2007/10/03)
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- Synthesis of optically active β,γ-unsaturated α-amino acids of α,β-unsaturated γ-amino acids. S(N)2- vs. S(N)2'-dichotomy of the Mitsunobu amination of allylic alcohols
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Novel and efficient syntheses (6-9 steps, overall yields 10-30%) are described for optically pure β,γ-unsaturated α-amino acids and α,β-unsaturated γ-amino acids, starting from (R)-isopropylidene glyceraldehyde and ethyl (S)-lactate, respectively. The key step is the Mitsunobu reaction of chiral secondary allylic alcohols with phthalimide as the nucleophile, where α,γ allylic transpositions are observed for the first time. The structure-α,γ-ratio-relationship is studied and also the stereochemistry of the allylic transposition. The α-substitution proceeds via clean S(N)2 inversion, whereas the γ-substitution corresponds to an (E)-anti attack of the nucleophilic with varying stereoselectivities.
- Mulzer,Funk
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p. 101 - 112
(2007/10/02)
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- Synthesis of O-Protected (R)-2-Hydroxy Aldehyde and Their Hydrocyanation
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The synthesis of O-silyl- and O-benzyl-protected (R)-2-hydroxy aldehydes (R)-6 from (R)-2-hydroxy carboxylic acids (R)-1 is described.While attempts for their diastereoselective hydrocyanation with hydrocyanic acid and (R)-oxynitrilase as catalyst have not been successful, the cyano silylation with trimethylsilyl cyanide occurred diastereoselectively with a ratio of 81:19 preferring the threo form without racemization at C-2 of the 2-hydroxy aldehyde. Key Words : (R)-2-Hydroxy aldehydes, O-protected / Hydrocyanation
- Effenberger, Franz,Hopf, Martin,Ziegler, Thomas,Hudelmayer, Jochen
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p. 1651 - 1659
(2007/10/02)
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