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Chiral Borate Esters in Asymmetric Synthesis. Part 2
Author(s) -
Liu Dejun,
Shan Zixing,
Zhou Yan,
Wu Xiaojun,
Qin Jingui
Publication year - 2004
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.200490206
Subject(s) - chemistry , borane , chirality (physics) , diol , catalysis , stereoselectivity , enantioselective synthesis , boron , stereochemistry , boranes , organic chemistry , medicinal chemistry , chiral symmetry , physics , quantum mechanics , nambu–jona lasinio model , quark
Asymmetric catalytic activity of the chiral spiroborate esters 1 – 9 with a O 3 BN 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 1 ). 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.