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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 12, Number 6
BKCSDE 12(6)
June 20, 1991 

 
Title
New Chiral Borohydrides. 2. Preparation of Potassium B-Methoxydiisopinocampheylborohydride and Its Asymmetric Reducing Properties
Author
Byung Tae Cho
Keywords
Abstract
In order to prepare new chiral borohydrides (4) possessing chirality on dialkyl moieties, a series of B-alkoxydiisopinocampheylborinates (3) were synthesized by treatment of diisopinocampheylborane (Ipc2BH) with alcohols (R in ROH: Me, Et, i-Pr, t-Bu) and reacted with excess of potassium hydride. Of these chiral borinic esters, only B-methoxydiisopinocampheyl borinate (3a) was converted into the corresponding dialkylmonoalkoxyborohydride (4a). For the other borinic esters, hydride uptake reactions were very slow at room temperature, accompanying disproportionation products at 65℃. The hydride (4a) formed is stable at 0℃ and can be stored over potassium hydride for few months. In the asymmetric reduction of the selected ketones, 4a provided the corresponding alcohols, such as 21% ee for 3-methyl-2-butanone, 11% ee for 2,2-dimethylcyclopentanone, 24% ee for acetophenone, 32% ee for 3-acetylpyridine, 30% for methyl benzoylformate, 31% ee for 4-phenyl-3-butyn-2-one, 39% ee for 3-butyn-2-one, and 34% ee for 3-hexyn-2-one.
Page
662 - 665
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