condensation of aldehyde or chalcone with (R)-tert-buta-
nesulfinamide followed by addition with a vinyl Grignard
reagent or reduction with DIBAL-H.1,16,17 Selected chiral
ligands are listed in Figure 2, and it is worth noting that some
of them are already well-known compounds, but none of
them has been utilized as an effective ligand for asymmetric
catalysis.
Figure 1. Representative N-sulfinyl-based chiral ligands for
metal-catalyzed asymmetric reactions.
oxygenactsas the coordination atom. However, tothe best
of our knowledge, few chiral ligands with the sulfur of tert-
butanesulfinamide as the coordination atom have been
developed for asymmetric catalysis, even though the chir-
ality is actually at sulfur, which will probably provide a
better chiral environment.7À9 Exploring novel N-sulfinyl-
based chiral sulfur ligands is therefore of great interest.
As one type of lately emerging ligand, chiral olefin
ligands have witnessed significant progress since the pio-
neering contribution by Hayashi and Carreira.10,11 Both
chiral diene12 and hybrid ligands combined olefins with
heteroatoms such as phosphorus13 and nitrogen14 have
been well developed. However, other coordination atoms
except P and N have seldom been incorporated in chiral
olefin ligands. As part of our interest in exploring new,
effective, and accessible chiral olefin ligands, in our pre-
vious work, a variety of acyclic chiral diene ligands as well
as P/olefin ligands has been developed for Rh- or Pd-
catalyzed asymmetric additions or allylic alkylation.15
Inspired by the perfect character of tert-butanesulfina-
mide, we envision that the combination of tert-butanesul-
finamide and olefin in chiral ligands will provide
an excellent opportunity for the development of novel
N-sulfinyl-based chiral sulfurÀolefin ligands. Herein, we
wish to report our efforts on this subject.
Figure 2. Selected N-sulfinyl-based chiral sulfurÀolefin ligands.
To test the possibility for application of these novel
ligands in asymmetric catalysis, ligand 4a was subjected to
Rh(I)-catalyzed 1,4-addition18 of phenylboronic acid (6a)
to 2-cyclohexenone (5a) in the presence of K3PO4 3H2O
3
with water as solvent at ambient temperature for 3 h
(Scheme 1). We were pleased to find that this reaction
proceeded smoothly to give the desired adduct 7a in 99%
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