- Asymmetric Acetalization: A Simple Method for the Synthesis of Chiral α-Monosubstituted Cyclopentanones
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Acetalization of α-monosubstituted cyclopentanones with chiral hydroxy thiols under equilibrating conditions afforded a mixture of acetals in a highly diastereoselective manner, and deacetalization of the product affords optically active α-monosubstituted cyclopentanones.
- Nishida, Mayumi,Nakaoka, Kazuyo,Ono, Shizuka,Yonemitsu, Osamu,Nishida, Atsushi,et al.
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- Enantioselective protonation of prochiral enolates with chiral imides
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New chiral proton sources possessing an asymmetric 2-oxazoline ring, (S,S)-imide 1 and related imides, were synthesized from Kemp's triacid and optically active 2-amino alcohols. With these chiral imides, various lithium enolates of α-monoalkylated cycloalkanones were effectively protonated with excellent to moderate enantioselectivity. An increase in enantioselectivity was observed in the asymmetric protonation of prochiral enolates with (S,S)- imide 1 using lithium salt as an additive. For example, (R)-enriched 2-n- pentylcyclopentanone 35 was obtained in high yield with 90% ee when the silyl enol ether 33 was treated with n-BuLi in the presence of 5 equiv of LiBr in Et2O, and the resulting lithium enolate 34 was then protonated by a solution of (S,S)-imide 1 in THF. In contrast, the product 35 obtained without LiBr exhibited a lower enantiomeric excess (74% ee).
- Yanagisawa, Akira,Kikuchi, Tetsuo,Kuribayashi, Takeshi,Yamamoto, Hisashi
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p. 10253 - 10264
(2007/10/03)
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- Enantioselective Synthesis of (R)-(+)-5-Hexadecanolide, the Pheromone of Queen of Oriental Hornet, Vespa orientalis Linn
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An enantioselective synthesis of (R)-(+)-5-hexadecanolide (1) using cyclopentanone, and (R)-2-aminobutyl-n-undecyl iodide (as electrophile) is reported.
- Gadkari, R. G.,Kapadi, A. H.
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p. 814 - 815
(2007/10/02)
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