Chiral borate esters in asymmetric synthesis - Part 2 - Asymmetric borane reduction of prochiral ketones in the presence of a chiral spiroborate ester

Asymmetric catalytic activity of the chiral spiroborate esters 1-9 with a O3BN framework (see Fig. 1) toward borane reduction of prochiral ketones was examined. In the presence of 0.1 equiv. of a chiral spiroborate ester, prochiral ketones were reduced by 0.6 equiv. of borane in THF to give (R)-seco...

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Published inHelvetica chimica acta Vol. 87; no. 9; pp. 2310 - 2317
Main Authors Liu, DJ, Shan, ZX, Zhou, Y, Wu, XJ, Qin, JG
Format Journal Article
LanguageEnglish
Published WEINHEIM Wiley 01.01.2004
Subjects
Chemistry
Chemistry, Multidisciplinary
Physical Sciences
Science & Technology
ALCOHOLS
ACIDS
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Summary:Asymmetric catalytic activity of the chiral spiroborate esters 1-9 with a O3BN framework (see Fig. 1) toward borane reduction of prochiral ketones was examined. In the presence of 0.1 equiv. of a chiral spiroborate ester, prochiral ketones were reduced by 0.6 equiv. of borane in THF to give (R)-secondary alcohols in up to 92% ee and 98% isolated yields (Scheme 7). The stereoselectivity of the reductions depends on the constituents of the chiral spiroborate ester (Table 2) and the structure of the prochiral ketones (Table 1). The configuration of the products is independent of the chirality of the diol-derived parts of the catalysts. A mechanism for the catalytic behavior of the chiral spiroborate esters (R,S)-2 and (S,S)-2 during the reduction is also suggested.
ISSN:0018-019X
1522-2675
DOI:10.1002/hlca.200490206