ORGANIC
LETTERS
2013
Vol. 15, No. 14
3722–3725
Iridium-Catalyzed Enantioselective
Hydrogenation of r,β-Unsaturated
Carboxylic Acids with
Tetrasubstituted Olefins
Song Song, Shou-Fei Zhu, Yu Li, and Qi-Lin Zhou*
State Key Laboratory and Institute of Elemento-organic Chemistry, Nankai University,
Tianjin 300071, China
Received June 6, 2013
ABSTRACT
A highly efficient asymmetric hydrogenation of R,β-unsaturated carboxylic acids with tetrasubstituted olefin catalyzed by chiral spiro iridium
complexes has been developed for the preparation of chiral R-substituted carboxylic acids in excellent enantioselectivities (up to 99% ee).
Transition-metal-catalyzed asymmetric hydrogenation
of prochiral unsaturated carboxylic acids represents one of
the most efficient and atom-economic methods for pre-
paration of chiral carboxylic acids. In the past decades,
remarkable progress has been achieved in the asymmetric
hydrogenation of unsaturated carboxylic acids with di-1 or
trisubstituted2 olefins by using chiral rhodium, ruthenium,
and iridium catalysts. The asymmetric hydrogenation of
R,β-unsaturated carboxylic acids with highly hindered
tetrasubstituted olefins also draws intense attention, be-
cause its products, chiral carboxylic acids 2 and their
derivatives are core structures of many pharmaceuticals,3
natural products,4 and organocatalysts5 (Figure1).However,
in contrast to the successful hydrogenation of the unsatura-
ted carboxylic acids with di- and trisubstituted olefins,
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10.1021/ol401593a
Published on Web 07/03/2013
2013 American Chemical Society