Chiral sulfinamide-olefin ligands: Switchable selectivity in rhodium-catalyzed asymmetric 1,2-addition of arylboronic acids to aliphatic α-ketoesters

Article abstract of DOI:10.1002/cjoc.201300063

Simple and readily available chiral N-(sulfinyl)allylamines have been developed as efficient novel ligands for the rhodium-catalyzed enantioselective 1,2-addition of arylboronic acids to challenging aliphatic α-ketoesters. By employing the linear or branc

Full text of DOI:10.1002/cjoc.201300063

FULL PAPER
DOI: 10.1002/cjoc.201300063
Chiral Sulfinamide-Olefin Ligands: Switchable Selectivity in
Rhodium-Catalyzed Asymmetric 1,2-Addition of Arylboronic
Acids to Aliphatic α-Ketoesters†
Ting-Shun Zhu and Ming-Hua Xu*
Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
Simple and readily available chiral N-(sulfinyl)allylamines have been developed as efficient novel ligands for
the rhodium-catalyzed enantioselective 1,2-addition of arylboronic acids to challenging aliphatic α-ketoesters. By
employing the linear or branched sulfinamide-olefin ligands, interesting enantioselectivity as well as regioselectiv-
ity reversal in the related asymmetric additions were observed.
Keywords asymmetric catalysis, rhodium, sulfur-olefin ligand, 1,2-addition, stereoselectivity reversal
Introduction
Unlike α-aryl-α-ketoesters, aliphatic α-ketoesters
with the existence of α-H can form enolate esters upon
deprotonation under basic reaction conditions (see
Scheme 1 for an example of 1a). Accordingly, self-
Aldol condensation of the enolate intermediate with
non-enolized aliphatic α-ketoester followed by lactoni-
zation would lead to the formation of an unexpected
heterocyclic side-product. Moreover, the enantioselec-
tivity of the desired 1,2-addition may be affected by the
coordination equilibrium between Rh-ketone oxygen
and Rh-enolate oxygen.
Recently, chiral sulfur-based olefins, including sul-
foxide-olefins and sulfinamide-olefins, have emerged as
a novel class of promising ligands for asymmetric ca-
talysis. As demonstrated in our previous work, they
have shown unique catalytic activity and enantioselec-
tivity in a series of transition-metal-catalyzed asymmet-
ric transformations.[5,6] In comparison to pnictogen-
containing ligands, sulfur-olefins are exceptional be-
cause of the advantages of their easy synthesis, high
stability, good metal-coordination ability and special
S-stereogenic control. In this context, we have been in-
terested in the possible use of chiral sulfur-olefins as
novel ligands for Rh-catalyzed asymmetric 1,2-addition
of aliphatic α-ketoesters. Here, we report that simple
sulfinamide-based branched olefin ligands can be suc-
cessfully employed in Rh-catalyzed enantioselective
addition of arylboronic acids to aliphatic α-ketoesters.
Chiral α-hydroxy esters have attracted much atten-
tion owing to their presence in numerous biologically
interesting compounds and their use as important build-
ing blocks or intermediates for fine chemicals and
pharmaceuticals.[1] Over the past decades, various
methods have been developed for the synthesis of these
valuable chiral compounds.[2] Among these, transition-
metal-catalyzed asymmetric 1,2-nucleophilic addition of
stable, commercially available arylboronic acids to
α-ketoesters is a particularly practical and direct ap-
proach.[3,4] However, despite some remarkable progress
achieved in the rhodium or ruthenium-catalyzed asym-
metric addition employing chiral phosphite,[3a] phos-
phoramidite[3b] or phosphine[3c] ligands, most of the
substrates involved in the reactions are aromatic α-keto-
esters, to the best of our knowledge, catalytic enanti-
oselective addition of aliphatic α-ketoesters remains a
challenging topic.
Scheme 1
O
OH
Ph
COOEt
Ph
base
COOEt
1a
self-Aldol
condensation
[Rh]/Ligand
ArB(OH)2
1,2 addition
O
OH
HO
Ph
O
Ph
COOEt
COOEt
Ar
Results and Discussion
3
4
We began our study by examining the reaction of
Ph
*
E-mail: xumh@simm.ac.cn; Tel.: 0086-021-50807388
Received January 24, 2013; accepted February 24, 2013; published online March 14, 2013.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cjoc.201300063 or from the author.
Dedicated to Professor Guoqiang Lin on the occasion of his 70th birthday.
†
Chin. J. Chem. 2013, 31, 321—328
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321

Zhu & Xu
FULL PAPER
ethyl 2-oxo-4-phenylbutyrate (1a) with 4-anisylboronic
acid (2a) in the presence of [Rh(COE)2Cl]2 (1.5 mol%)
using our recently designed chiral sulfur-olefins L1－L4
as ligands. As expected, the reaction proceeded smoothly
Following up on the encouraging results obtained
with L1 and L4, the effect of ester groups in 2-oxo-
4-phenylbutanoate was investigated (Table 2). Changing
the ester substituent from ethyl to methyl group did not
result in much difference of the enantioselectivity (En-
tries 1－4). Similar with the results of addition to phe-
nylglyoxylate esters reported in our previous work,[5d]
when phenyl ester was employed, an increase of the
enantioselectivity from 33% to 64% ee was observed
using linear N-(sulfinyl)allylamine L1 as the ligand (En-
try 5), but further altering phenyl to 2-naphtyl or
(2,6-dimethyl)phenyl did not improve the enantiose-
lectivity of the reaction (64% ee and 61% ee, respec-
tively; not shown in Table 2). On the contrary, the result
with branched N-(sulfinyl)allylamine L4 showed an
opposite trend. In the case of phenyl ester 1c, a sharp
decline in enantioselectivity was found (Entries 2 and 4
vs. 6). Thus, by simply tuning the ligand structure and
substrate ester moiety, an interesting reversal of enan-
tiofacial selectivity can be achieved to afford the desired
addition product with the same level of enantioselectiv-
ity (64% and 65% ee, Entries 2 and 5). The absolute
configuration of 3a was determined by comparison of
its HPLC chromatogram with the known one (see SI for
details), and others were assigned by analogy. In con-
sideration of the availability, ethyl 2-oxo-4-phenylbu-
tyrate 1a was selected as substrate for further investiga-
tion.
－
1
in aqueous K3PO4 (1.5 mol•L )/THF at room tempera-
ture, but giving the tertiary α-hydroxyester in only mod-
erate yield and ee (Table 1, Entries 1－4). Not surpris-
ingly, compound 4 was obtained as the main byproduct.[7]
Interestingly, a reversal of reaction enantioselectivity[8]
was observed when ligands L3 and L4 with terminal ole-
fin moiety were used, as compared to the results obtained
with L1 and L2 (Table 1, Entries 3－4 vs. 1－2). Solvent
screening among THF, toluene, dichloromethane,
methanol and ethyl acetate showed that THF is the best
choice. In order to avoid side reactions, a further screen-
ing of the reaction conditions was carried out. As shown
in Table 1, employing of weak base such as LiF (1.5
－
1
mol•L , 50 mol%) or less amount of base such as KOH
－
1
(0.1 mol•L , 8 mol%) can obviously prevent the un-
wanted self-Aldol reaction (Entries 5, 10－11).
Table 1 Initial screening of reaction conditionsa
O
B(OH)2 [Rh(COE)2Cl]2
OEt
Ligand
r.t.
+
MeO
O
2a
1a
OH
OEt
O
Table 2 Optimization of reaction conditions for different estersa
3a
MeO
O
[Rh(COE)2Cl]2 (1.5 mol%)
Ligand (3.3 mol%)
B(OH)2
O
O
S
O
Ph
R
+
MeO
S
KOH (0.1 mol L-1), THF, r.t.
Ph
N
O
.
MeO
H
1
MeO
2a
L1
OH
Ph
O
S
MeO
Ph
O
R
L2
Ph
O
S
O
HN
N
MeO
H
3
OBz
L4
L3
Entry
R, 1
Ligand
L1
3
Yieldb/% eec/%
Entry Ligand Solvent
Base
Yieldb/% eec/%
1
2
3
4
5
6
Et, 1a
Et, 1a
Me, 1b
Me, 1b
Ph, 1c
Ph, 1c
3a
3a
3b
3b
3c
3c
67
46
63
53
55
25
33 (S)
65 (R)
35 (S)
61 (R)
64 (S)
41 (R)
－
K3PO4 (1.5 mol•L )
－
K3PO4 (1.5 mol•L )
－
K3PO4 (1.5 mol•L )
－
K3PO4 (1.5 mol•L )
1
1
2
L1
L2
L3
L4
L1
L1
L1
L1
L1
L1
L4
THF
THF
THF
THF
THF
54
40
12
38
71
36
30
48
40
67
46
30
28
L4
1
L1
1
3
−19
−63
30
L4
1
4
L1
－
LiF (1.5 mol•L )
1
5
L4
－
1
a Reaction conditions: 0.25 mmol of 1, 2.0 equiv. of 2a, 1.5 mol%
of [Rh(COE)2Cl]2, 3.3 mol% of ligand, 8 mol% of KOH (0.1
mol•L－1) in 1 mL of THF at room temperature. b Isolated yield.
c Determined by HPLC analysis.
6
toluene LiF (1.5 mol•L )
－
CH2Cl2 LiF (1.5 mol•L )
－
CH3OH LiF (1.5 mol•L )
－
EtOAc LiF (1.5 mol•L )
33
1
7
4
1
8
11
1
9
24
－
KOH (0.1 mol•L )
－
KOH (0.1 mol•L )
1 d
10
THF
THF
33
Having noticed the catalytic property differences
between linear and branched N-(sulfinyl)allylamines,
we decided to further examine the influence of the sub-
stituents on the olefin moiety. As a result, linear ligands
L5－L8 and branched ligands L9－L16 with different
R1 and R2 substituents were designed (Table 3),
1 d
11
a
−65
Reaction conditions: 0.25 mmol of 1a, 2.0 equiv. of 2a, 1.5
mol% of [Rh(COE)2Cl]2, 3.3 mol% of ligand, 0.5 equiv. of base
in 1 mL of solvent at room temperature. b Isolated yield. c Deter-
mined by HPLC analysis. d 8 mol% of KOH was used.
322
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 321—328

Rhodium-Catalyzed Asymmetric 1,2-Addition of Arylboronic Acids to Aliphatic α-Ketoesters
Table 3 Further screening of chiral sulfinamide-olefins for asymmetric 1,2-addtion of ethyl 2-oxo-4-phenylbutyratea,b,c
O
S
R1
N
OH
*
O
H
R2
OEt
OEt
[Rh(COE)2Cl]2
O
O
4-anisylboronic acid
KOH (0.1 mol L-1), THF, r.t.
.
1a
3a
MeO
O
S
O
S
R1
N
N
H
H
R2
L4, R2 = Ph, 46%, 65% ee (R)
L9, R2 = 4-CF3C6H4, 13%, 41% ee (R)
L10, R2 = 2-MeOC6H4, 67%, 41% ee (R)
L11, R2 = CH3, 61%, 47% ee (R)
L1, R1 = Ph, 67%, 33% ee (S)
L5, R1 = 4-MeOC6H4, 57%, 33% ee (S)
L6, R1 = 4-CF3C6H4, 64%, 33% ee (S)
L7, R1 = 4-NO2C6H4, 31%, 32% ee (S)
L8, R1 = CH3, 83%, 3% ee (S)
L12, R2 = iPr, 10%, 19% ee (R)
L13, R2 = CH2Ph, 85%, 40% ee (R)
L14, R2 = CH2(1-naphthyl), 68%, 39% ee (R)
L15, R2 = CH2C(CH3)3, 87%, 63% ee (R)
L16, R2 = CH2(9-anthryl), 18%, 28% ee (R)
－
1
a Reaction conditions: 0.25 mmol of 1a, 2.0 equiv. of 2a, 1.5 mol% of [Rh(COE)2Cl]2, 3.3 mol% of ligand, 8 mol% of KOH (0.1 mol•L )
in 1 mL of THF at room temperature. b Isolated yield. c Determined by HPLC analysis.
synthesized and employed in the rhodium-catalyzed
1,2-additon of 4-anisylboronic acid to ethyl 2-oxo-4-
phenylbutyrate (1a). With all linear N-(sulfinyl)allyl-
amines (L5－L8), unfortunately, no better results in
enantioselectivity was obtained. In the cases of branched
N-(sulfinyl)allylamines, it was also disappointing that
analogues L9－L16 containing substituents with dif-
ferent steric and electronic natures were generally less
effective and gave no higher ee. On the other hand, it
was found that incorporation of an appropriate electron-
rich R2 substituent would be helpful for enhancing the
catalytic activity (L10, L11, L13－L15). With L15
(R2＝neopentyl), significantly improved yield (87%)
together with equally good enantioselectivity (63%)
were achieved.
Table 4 Substrate scope of asymmetric 1,2-addtion to ethyl
2-oxo-4-phenylbutyratea
O
S
N
H
O
(3.3 mol%)
L15
OEt
Ar B(OH)2
+
O
[Rh(COE)2Cl]2 (1.5 mol%)
2
1a
-1
.
KOH (0.1 mol L ), THF, r.t.
OH
OEt
Ar
O
3
Entry Ar
Product
3a
Yieldb/%
87
eec/%
63
With L15 as optimal ligand, we decided to examine
the reaction generality. A wide range of arylboronic acids
were reacted with ethyl 2-oxo-4-phenylbutyrate (1a) in
1
4-MeOC6H4
Ph
2
3b
3c
61
64
－
1
KOH (0.1 mol•L , 8 mol%)/THF at room temperature.
As summarized in Table 4, arylboronic acids bearing
electron-donating group at meta- or para-position of the
phenyl ring can all be employed successfully to afford the
desired products in moderate to good yields and enanti-
oselectivities (Entries 1－3, 7－9), but arylboronic acids
with electron-withdrawing groups are less reactive,
giving low yield of the addition reaction (Entries 4－6).
Among all examples, the highest enantioselectivity of
70% was attained when 4-tert-butylphenylboronic acid
was employed. Notably, in the cases of sterically hin-
dered 2-naphthalenyl- and 1-naphthalenylboronic acids,
the reaction proceeded smoothly to give the adducts 3j
and 3k in moderate yields and with similarly good level
of enantioselectivities (Entries 10 and 11).
3
4-MeC6H4
4-ClC6H4
4-FC6H4
82
61
4
3d
3e
14
57
5
21
61
6
4-PhC6H4
4-tBuC6H4
3-MeOC6H4
3-MeC6H4
2-nathphyl
1-nathphyl
3f
34
61
7
3g
72
70
8
3h
3i
68
65
9
67
51
10
11
3j
62
67
3k
57
65
a Reaction conditions: 0.25 mmol of 1a, 2.0 equiv. of arylboronic
acid, 1.5 mol% of [Rh(COE)2Cl]2, 3.3 mol% of L15, 8 mol% of
－
1
b
KOH (0.1 mol•L ) in 1 mL of THF at room temperature. Iso-
lated yield. c Determined by HPLC analysis.
Chin. J. Chem. 2013, 31, 321—328
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323

Zhu & Xu
FULL PAPER
To further realize the interesting catalytic perform-
ance differences between the linear and branched sulfi-
namide-olefin ligands, we next turned our attention to
the asymmetric addition of styrylglyoxylate. To our
knowledge, there is only one example of enantioselec-
tive addition of arylboronic acids to 2-oxo-4-phenyl-
but-3-enoate been reported by Zhou,[3a] the development
of catalytic asymmetric reactions to afford useful level
of enantioselectivity still represents a challenging task.
As depicted in Scheme 2, the reaction of methyl styryl-
glyoxylate with 4-anisylboronic acid in the presence of
N-(sulfinyl)allylamine L1 and L15 was carried out un-
der rhodium catalysis, respectively. Surprisingly, the
two ligands exhibited very different regioselectivity
propensities.[9] With L1, conjugate addition to the un-
saturated double bond is favored, furnishing β,β-diaryl-
α-ketoester 6a in 43% yield but with only 5% ee. In
sharp contrast, when the branched N-(sulfinyl)allyl-
amine (L15) was used, the reaction took place prefera-
bly at the ketone carbonyl, affording the 1,2-addition
product β,γ-unsatured-α-hydroxyester (7a) in 68% yield
with 52% ee. In both cases, no further 1,2-addition of
product 6a was observed. Though the mechanism re-
mains unknown, these results indicate that the insertion
pathway of the two aryl rhodium intermediates was
clearly different.
ligand L16 was employed (Entry 6).
Table 5 Screening of chiral sulfinamide-olefins for asymmetric
1,2-addtion of (E)-2-oxo-4-phenylbut-3-enoatea
O
S
N
O
H
[Rh]
R
Ph
COOMe
OMe
O
4-anisylboronic acid
5a
-1
.
KOH (0.1 mol L ), THF, r.t.
OH
Ph
COOMe
+
Ph
COOMe
*
MeO
7a
6a
Yieldb/
%
ee of
ee of
Entry R, Ligand
6a/7ac
6ad/%
－
7ad/%
t
1
2
3
4
5
CH2 Bu, L15
72
54
56
76
1∶20
1∶12
52
−23
37
65
68
72
Ph, L4
iPr, L12
5
＜1∶20 －
＜1∶20 －
＜1∶20 －
＜1∶20 －
Bn, L13
CH2(2-Naph), L14 74
CH2(9-anthryl), L16 70
6
a
Reaction conditions: 0.25 mmol of 5a, 2.0 equiv. of 2a, 1.5
Scheme 2
mol% of [Rh(COE)2Cl]2, 3.3 mol% of ligand, 8 mol% of KOH
－
1
(0.1 mol•L ) in 1 mL of THF at room temperature. b Isolated
[Rh(COE)2Cl]2 (1.5 mol%)
O
1
yield. c Determined by H NMR of the crude materials. d Deter-
Ligand (3.3 mol%)
Ph
COOMe
mined by HPLC analysis.
4-anisylboronic acid
KOH (0.1 mol L-1), THF, r.t.
.
5a
Having identified a suitable chiral ligand, we exam-
ined the reaction scope with respect to the styrylglyoxy-
late derivatives under the above optimized conditions.
As shown in Table 6, a range of β,γ-unsatured α-keto-
esters 7a－7j with different R1 or R2 substituent were
evaluated with 4-anisylboronic acids. In general, all re-
actions proceeded smoothly to provide the desired
1,2-addition products in good to moderate yields with
excellent regioselectivity (＞20∶1). It appeared that
varing the ester group could have a dramatic effect on
reaction enantioselectivity. For instance, the isopropyl
(E)-2-oxo-4-phenylbut-3-enoate (5c) gave both lower
yield (65%) and enantioselectivity (64%) compared to
those obtained from their methyl and ethyl esters (5a
and 5b, Entries 1－3). When phenyl (E)-2-oxo-4-phe-
nylbut-3-enoate (5d) was employed, product 7d was
obtained with much improved enantioselectivity (80%,
Entry 4). However, in this case, a sharp decline in the
reaction yield (52%) was found mainly due to signifi-
cant hydrolysis of the aromatic ester substrate. To our
delight, benzyl (E)-2-oxo-4-phenylbut-3-enoate (5e)
underwent clean reaction and could lead to 1,2-adduct in
good yield (81%), albeit in somewhat lower ee (76%,
Entry 5). By comparing the HPLC chromatogram with
known data,[3a] the absolute configuration was deter-
mined as S. Subsequently, the impact of varying the R1
OH
OMe
Ph
COOMe
O
+
Ph
COOMe
*
MeO
7a
6a
L1:
43%, 5% ee
9%, 67% ee
L15:
trace
68%, 52% ee
To attain higher enantioselectivity of the 1,2-addition,
an extensive screening of the branched sulfinamide-
olefin ligands was carried out again (Table 5). Similar
with the previous observations of addition to 2-oxo-4-
phenylbutyrate (1a), electron-rich olefin substituent (R)
with proper steric hinderance was crucial. Phenyl and
bulkyl isopropyl substituent led to poor results in both
regioselectivity and enantioselectivity (Entries 2－3).
Surprisingly, with phenyl substituted L4, 7a with oppo-
site configuration was produced. An improved enanti-
omeric excess (65%) was observed when benzyl-sub-
stituted L13 was used (Entry 4). Further investigation
revealed that the incorporation of a large planar struc-
ture such as 1-naphthyl and 9-anthryl is a little more
beneficial (Entries 5 and 6); and the best 72% ee and
70% yield (＞20∶1 regioselectivity) was attained when
324
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Chin. J. Chem. 2013, 31, 321—328

Rhodium-Catalyzed Asymmetric 1,2-Addition of Arylboronic Acids to Aliphatic α-Ketoesters
substituent on the olefin was also investigated. Elec-
tron-donating as well as electron-withdrawing groups
were all likely applicable and gave the corresponding
tertiary α-hydroxyesters in moderate to good yields and
equally high level of enantioselectivity (80%) (Entries 6
－9). However, when a very bulky 9-anthryl group was
introduced, a dramatic decrease in enantioselectivity
occurred (from 76% to 14% ee, Entries 4 vs. 11). Un-
fortunately, this reaction is very sensitive to the reactiv-
ity of the arylboronic acid. When non-electron rich
phenylboronic acid was employed, a much lower yield
(＜10%) was found.
be dramatically altered by simply tuning the substituent
on the olefin moiety. By employing the readily available
linear or branched sulfinamide-olefin ligands, interest-
ing enantioselectivity as well as regioselectivity reversal
in the related asymmetric additions were observed. Ef-
forts to investigate the insight of the stereoselectivity
reversal mechanism and the further applications of sul-
fur-olefin ligands are currently underway in our labora-
tory.
Experimental
General procedure for Rh-catalyzed 1,2-addition of
arylboronic acids to α-ketoesters
Table
6
Substrate scope of asymmetric 1,2-addtion to
(E)-2-oxo-4-arylbut-3-enoatea
Under Ar atmosphere, a solution of α-ketoester (0.25
mmol), [Rh(COE)2Cl]2 (2.7 mg, 0.0075 mmol of Rh, 1.5
mol%), N-(sulfinyl)allylamine ligand (0.00825 mmol,
3.3 mol%), and arylboronic acid (0.5 mmol for addition
to ethyl 2-oxo-4-phenylbutyrate; 0.375 mmol for addi-
tion to 2-oxo-4-arylbut-3-enoate) in 1.0 mL of THF was
stirred at room temperature for 30 min. To this mixture
[Rh] / L16
4-anisylboronic acid
HO COOR2
O
R1
COOR2
R1
KOH (0.1 mol L-1),
.
5
OMe
7
THF, r.t.
O
S
N
－
1
H
was added aqueous KOH (0.2 mL, 0.1 mol•L , 0.02
mmol). After being stirred at r.t. for 3 h, the mixture was
concentrated under reduced pressure. The residue was
purified by silica gel column chromatography to afford
the corresponding addition product 3 or 7.
L16
(R)-Ethyl 2-hydroxy-2-(4-methoxyphenyl)-4-phe-
nyl-butanoate (3a) Colorless oil, 87% yield, 63% ee;
1H NMR (300 MHz, CDCl3) δ: 1.28 (t, J＝7.2 Hz, 3H),
2.26－2.79 (m, 4H), 3.81 (s, 3H), 3.89 (s, 1H), 4.18－
4.23 (m, 2H), 6.89 (d, J＝9.0 Hz, 2H), 7.18－7.30 (m,
5H), 7.54 (d, J＝8.7 Hz); 13C NMR (100 MHz, CDCl3)
δ: 14.1, 30.1, 41.5, 55.2, 62.4, 75.6, 113.5, 125.8, 126.7,
128.3, 128.4, 133.7, 141.7, 159.0, 175.3. HRMS (ESI)
calcd for C19H22O4Na [M＋Na]＋ : 337.1416, found
337.1418.
Entry R1, R2 (5)
7
1,2/1,4b Yieldc/% eed/%
1
2
Ph, Me (5a)
7a ＞20∶1 70
7b ＞20∶1 72
7c 20∶1 65
7d ＞20∶1 52
7e ＞20∶1 81
7f ＞20∶1 83
7g ＞20∶1 73
7h ＞20∶1 62
7i ＞20∶1 75
7j ＞20∶1 82
72
71
64
80
76
80
80
80
80
14
Ph, Et (5b)
3
Ph, iPr (5c)
4
Ph, Ph (5d)
5
Ph, Bn (5e)
6
4-MeC6H4, Bn (5f)
4-MeOC6H4, Bn (5g)
4-ClC6H4, Bn (5h)
4-BrC6H4, Bn (5i)
9-anthryl, Bn (5j)
7
8
(R)-Ethyl 2-hydroxy-2,4-diphenylbutanoate (3b)
1
Colorless oil, 61% yield, 64% ee; H NMR (300 MHz,
9
CDCl3) δ: 1.30 (t, J＝6.9 Hz, 3H), 2.30－2.80 (m, 4H),
3.93 (s, 1H), 4.17－4.29 (m, 2H), 7.20 (d, J＝6.0 Hz,
3H), 7.29 (t, J＝6.0 Hz, 3H), 7.38 (dd, J＝6.9, 7.5 Hz,
2H), 7.65 (d, J＝6.6 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ: 14.1, 30.2, 41.6, 62.6, 77.9, 125.4, 125.9,
127.7, 128.2, 128.36, 128.43, 141.6, 141.7, 175.1.
10
a Reaction condition: 0.25 mmol of 5, 1.5 equiv. of 2a, 1.5 mol%
of [Rh(COE)2Cl]2, 3.3 mol% of ligand, 8 mol% of KOH (0.1
mol•L－ aq.) in 1 mL of THF at room temperature. b Determined
1
1
by H NMR of the crude materials. c Isolated yield. d Determined
by HPLC analysis.
HRMS (ESI) calcd for C18H20O3Na [M ＋ Na] ＋
:
307.1310, found 307.1318.
Ethyl 2-hydroxy-4-phenyl-2-p-tolylbutanoate (3c)
Colorless oil, 82% yield, 61% ee; H NMR (300 MHz,
Conclusions
1
In summary, we have developed an efficient rho-
dium-catalyzed asymmetric 1,2-addition of aryl boronic
acdis to 2-oxo-4-phenylbuturates and (E)-2-oxo-4-aryl-
but-3-enoates through the use of extremely simple chiral
N-(sulfinyl)allylamine ligands. The method offers a po-
tentially easy and practical access to a variety of opti-
cally active tertiary α-hydroxyesters. Of particular note
is that catalytic enantioselective 1,2-addtion of arylbo-
ronic acids to α-H-containing aliphatic α-ketoesters has
been an important but difficult subject. Moreover, stud-
ies have shown that the ligand catalytic performance can
CDCl3) δ: 1.30 (t, J＝6.9 Hz, 3H), 2.30－2.82 (m, 4H),
2.45 (s, 3H), 3.93 (s, 1H), 4.20－4.26 (m, 2H), 7.18－
7.23 (m, 4H), 7.31 (dd, J＝6.6, 8.1 Hz, 2H), 7.54 (d, J＝
8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ: 14.1, 21.0,
30.1, 41.5, 62.5, 77.8, 125.3, 125.8, 128.3, 128.4, 128.9,
137.4, 138.7, 141.8, 175.3. HRMS (ESI) calcd for
C19H22O3Na [M＋Na]＋: 321.1467, found 321.1462.
(R)-Ethyl 2-(4-chlorophenyl)-2-hydroxy-4-phenyl-
1
butanoate (3d) Colorless oil, 14% yield, 57% ee; H
NMR (300 MHz, CDCl3) δ: 1.28 (t, J＝5.1 Hz, 3H),
Chin. J. Chem. 2013, 31, 321—328
© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
325

Zhu & Xu
FULL PAPER
2.24－2.75 (m, 4H), 3.94 (s, 1H), 4.17－4.26 (m, 2H),
7.19 (dd, J＝8.1, 7.2 Hz, 3H), 7.27－7.35 (m, 5H), 7.59
(d, J＝8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ:
14.1, 30.1, 41.7, 62.8, 77.6, 125.6, 126.0, 127.1, 1284,
1H), 2.38 (s, 3H), 2.45－2.66 (m, 2H), 2.75 (dt, J＝4.8,
11.2 Hz, 1H), 3.90 (s, 1H), 4.18－4.28 (m, 2H), 7.12 (d,
J＝7.5 Hz, 1H), 7.22 (dd, J＝7.2, 5.7 Hz, 3H), 7.27－
7.32 (m, 3H), 7.44 (dd, J＝6.3, 8.1 Hz, 2H); 13C NMR
(100 MHz, CDCl3) δ: 14.1, 21.6, 30.2, 41.5, 62,5. 77.9,
122.5, 125.9, 126.0, 128.1, 128.3, 128.4, 137.9, 141.6,
141.8, 175.2; HRMS (ESI) calcd for C19H22O3Na [M＋
Na]＋: 321.1467, found 321.1461.
128.5, 133.7, 140.2, 141.5, 174.8. HRMS (ESI) calcd
＋
for C18H19O3ClNa [M ＋ Na] : 341.0920, found
341.0925.
(R)-Ethyl 2-(4-fluorophenyl)-2-hydroxy-4-phenyl-
1
butanoate (3e) Colorless oil, 21% yield, 61% ee; H
(R)-Ethyl 2-hydroxy-2-(naphthalen-2-yl)-4-phe-
nylbutanoate (3j) Colorless oil, 62% yield, 67% ee;
1H NMR (300 MHz, CDCl3) δ: 1.30 (t, J＝6.9 Hz, 3H),
2.41－2.82 (m, 4H), 4.06 (s, 1H), 4.18－4.30 (m, 2H),
7.21 (d, J＝8.1 Hz, 3H), 7.29 (dd, J＝6.9, 8.7 Hz, 2H),
7.49－7.52 (m, 2H), 7.74 (d, J＝8.7 Hz, 1H), 7.84－
7.87 (m, 3H), 8.15 (s, 1H); 13C NMR (100 MHz, CDCl3)
δ: 14.1, 30.2, 41.4, 62.7, 78.1, 123.5, 124.6, 125.9,
126.18, 126.20, 127.4, 128.0, 128.3, 128.4, 128.5, 132.8,
133.0, 138.9, 141.7, 175.1; HRMS (ESI) calcd for
C22H22O3Na [M＋Na]＋: 357.1467, found 357.1449.
(R)-Ethyl 2-hydroxy-2-(naphthalen-1-yl)-4-phe-
nylbutanoate (3k) Colorless oil, 57% yield, 65% ee;
1H NMR (300 MHz, CDCl3) δ: 1.17 (t, J＝6.9 Hz, 3H),
2.59－2.78 (m, 3H), 2.88－2.98 (m, 1H), 3.85 (s, 1H),
7.26 (dq, J＝7.5 Hz, JAB＝33.6 Hz, 2H), 7.22－7.32 (m,
5H), 7.42－7.51 (m, 3H), 7.69 (d, J＝8.4 Hz, 1H), 7.82
－7.89 (m, 2H), 8.37 (d, J＝9.6 Hz, 1H); 13C NMR (100
MHz, CDCl3) δ: 14.0, 30.0, 40.5, 62.4, 78.6, 124.2,
124.7, 125.0, 125.5, 126.0, 126.2, 128.5, 129.0, 129.5,
131.2, 134.5, 136.6, 141.6, 176.0; HRMS (ESI) calcd
for C22H22O3Na [M＋Na]＋: 357.1467, found 357.1453.
(S,E)-Methyl 2-hydroxy-2-(4-methoxyphenyl)-4-
phenylbut-3-enoate (7a) Colorless oil, 70% yield,
NMR (300 MHz, CDCl3) δ: 1.29 (t, J＝7.2 Hz, 3H),
2.30－2.36 (m, 1H), 2.46－2.68 (m, 3H), 3.95 (s, 1H),
4.22 (dt, J＝7.2, 1.5 Hz, 2H), 7.05 (dd, J＝9.0 Hz, JF＝
8.7 Hz, 2H), 7.20 (t, J＝8.1 Hz, 3H), 7.29 (dd, J＝7.2,
7.8 Hz, 2H), 7.62 (dd, J＝9.0 Hz, JF＝5.4 Hz, 2H); 13C
NMR (100 MHz, CDCl3) δ: 14.1, 30.1, 41.8, 62.7, 77.5,
115.0 (d, JCF＝17 Hz), 125.9, 127.3 (d, JCF＝6 Hz),
128.4 (d, JCF＝2 Hz), 137.3, 137.4, 141.5, 162.3 (d, J＝
196 Hz), 175.0. HRMS (ESI) calcd for C18H19O3FNa
[M＋ Na]＋: 325.1216, found 325.1212.
(R)-Ethyl 2-(biphenyl-4-yl)-2-hydroxy-4-phenyl-
1
butanoate (3f) Colorless oil, 34% yield, 62% ee; H
NMR (300 MHz, CDCl3) δ: 1.33 (t, J＝6.9 Hz, 3H),
2.35－2.85 (m, 4H), 3.99 (s, 1H), 4.20－4.32 (m, 2H),
7.24 (dd, J＝9.9, 9.0 Hz, 3H), 7.31 (dd, J＝6.9, 7.2 Hz,
2H), 7.38 (d, J＝6.9 Hz, 1H), 7.46 (dd, J＝7.5, 7.2 Hz,
2H), 7.62 (d, J＝6.3 Hz, 4H), 7.72 (d, J＝8.4 Hz, 2H);
13C NMR (100 MHz, CDCl3) δ: 14.1, 30.2, 41.6, 62.6,
77.9, 125.9, 126.0, 127.0, 127.1, 127.35, 127.37, 128.4,
128.8, 140.5, 140.6, 140.7, 141.7, 175.1. HRMS (ESI)
calcd for C24H24O3Na [M＋Na]＋ : 381.1623, found
381.1611.
(R)-Ethyl 2-(4-tert-butylphenyl)-2-hydroxy-4-phe-
nylbutanoate (3g) Colorless oil, 72% yield, 70% ee;
1H NMR (300 MHz, CDCl3) δ: 1.33 (t, J＝6.9 Hz, 3H),
1.35 (s, 9H), 2.33 (dt, J＝4.8, 12.0 Hz, 1H), 2.46－2.66
(m, 2H), 2.79 (dt, J＝4.8, 12.0 Hz, 1H), 3.90 (s, 1H),
4.21－4.27 (m, 2H), 7.21 (d, J＝7.5 Hz, 3H), 7.29 (dd,
J＝6.6, 7.2 Hz, 2H), 7.40 (d, J＝8.1 Hz, 2H), 7.57 (d,
J＝8.1 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ: 14.1,
30.2, 31.3, 34.4, 41.6, 62.5, 77.8, 125.1, 125.2, 125.8,
128.3, 128.4, 138.7, 141.8, 150.5, 175.2; HRMS (ESI)
calcd for C22H28O3Na [M＋Na]＋ : 363.1936, found
363.1934.
1
72% ee; H NMR (300 MHz, CDCl3) δ: 3.81 (s, 3H),
3.84 (s, 3H), 3.94 (s, 1H), 6.71 (d, J＝15.9 Hz, 1H),
6.90 (d, J＝9.0 Hz, 2H), 6.95 (d, J＝15.9 Hz, 1H), 7.28
(d, J＝6.6 Hz, 1H), 7.34 (t, J＝7.5 Hz, 2H), 7.44－7.48
(m, 4H); 13C NMR (100 MHz, CDCl3) δ: 53.6, 55.3,
78.1, 113.8, 126.8, 127.4, 127.9, 128.6, 129.1, 130.4,
133.6, 136.3, 159.4, 174.9; HRMS (ESI) calcd for
C18H18O4Na [M＋Na]＋: 321.1103, found 321.1105.
(S,E)-Ethyl
2-hydroxy-2-(4-methoxyphenyl)-4-
phenylbut-3-enoate (7b) Colorless oil, 72% yield,
1
71% ee; H NMR (300 MHz, CDCl3) δ: 1.31 (t, J＝7.2
(R)-Ethyl 2-hydroxy-2-(3-methoxyphenyl)-4-phe-
nylbutanoate (3h) Colorless oil, 68% yield, 65% ee;
1H NMR (300 MHz, CDCl3) δ: 1.31 (t, J＝7.2 Hz, 3H),
2.34 (dt, J＝5.1, 11.2 Hz, 1H), 2.48 (dt, J＝5.1, 11.2 Hz,
1H), 2.62 (dt, J＝5.1, 11.2 Hz, 1H), 2.75 (dt, J＝5.1,
11.2 Hz, 1H), 3.84 (s, 3H), 3.93 (s, 3H), 4.22－4.26 (m,
2H), 6.86 (d, J＝7.2 Hz, 1H), 7.22 (t, J＝6.6 Hz, 4H),
7.26－7.32 (m, 3H); 13C NMR (100 MHz, CDCl3) δ:
14.1, 30.2, 41.6, 55.2, 62.6, 77.9, 111.3, 113.1, 117.8,
125.9, 128.3, 128.4, 129.2, 141.7, 143.3, 159.6, 175.0;
Hz, 3H), 3.82 (s, 3H), 4.04 (s, 1H), 4.31 (q, J＝7.2 Hz,
2H), 6.74 (d, J＝15.9 Hz, 1H), 6.92 (d, J＝9.0 Hz, 2H),
6.98 (d, J＝15.9 Hz, 1H), 7.29 (d, J＝7.2 Hz, 1H), 7.36
(t, J＝6.9 Hz, 2H), 7.49 (dd, J＝7.5, 9.0 Hz, 4H); 13C
NMR (100 MHz, CDCl3) δ: 14.0, 55.2, 62.8, 77.9, 113.7,
126.8, 127.4, 127.8, 128.5, 129.3, 130.2, 133.7, 136.4,
159.3, 174.3; HRMS (ESI) calcd for C19H20O4Na [M＋
Na]＋: 335.1259, found 335.1251.
(S,E)-Isopropyl 2-hydroxy-2-(4-methoxyphenyl)-
4-phenylbut-3-enoate (7c) Colorless oil, 65% yield,
64% ee; 1H NMR (300 MHz, CDCl3) δ: 1.26 (d, J＝6.0
Hz, 3H), 1.32 (d, J＝6.0 Hz, 3H), 3.82 (s, 3H), 4.08 (s,
1H), 6.72 (d, J＝15.6 Hz, 1H), 6.91 (d, J＝8.7 Hz, 2H),
6.98 (d, J＝15.6 Hz, 1H), 7.29 (d, J＝7.2 Hz, 1H), 7.35
(t, J＝7.2 Hz, 2H), 7.49 (dd, J＝11.7, 8.7 Hz, 4H); 13C
HRMS (ESI) calcd for C19H22O4Na [M ＋ Na] ＋
:
337.1416, found 337.1407.
(R)-Ethyl 2-hydroxy-4-phenyl-2-m-tolylbutanoate
1
(3i) Colorless oil, 67% yield, 57% ee; H NMR (300
MHz, CDCl3) δ: 1.30 (t, J＝7.5 Hz, 3H), 2.28－2.38 (m,
326
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 321—328

Rhodium-Catalyzed Asymmetric 1,2-Addition of Arylboronic Acids to Aliphatic α-Ketoesters
NMR (100 MHz, CDCl3) δ: 21.4, 21.6, 55.2, 77.8, 113.6,
126.7, 127.3, 127.8, 128.5, 129.4, 130.1, 133.8, 136.4,
159.2, 173.8; HRMS (ESI) calcd for C20H22O4Na [M＋
Na]＋: 349.1416, found 349.1423.
3H), 3.97 (s, 1H), 5.27 (s, 2H), 6.70 (d, J＝15.6 Hz, 1H),
6.84－6.89 (m, 3H), 7.24－7.28 (m, 4H), 7.34－7.36 (m,
3H), 7.42－7.46 (m, 4H); 13C NMR (100 MHz, CDCl3)
δ: 55.3, 68.3, 78.0, 113.8, 121.7, 127.4, 128.1, 128.3,
128.57, 128.62, 129.3, 129.9, 131.7, 133.2, 134.8, 135.2,
159.4, 174.0; HRMS (ESI) calcd for C24H21O4BrNa [M
＋Na]＋: 475.0521, found 475.0512.
(S,E)-Benzyl 2-hydroxy-2-(4-methoxyphenyl)-4-
phenylbut-3-enoate (7d)[3a] Colorless oil, 81% yield,
1
76% ee; H NMR (300 MHz, CDCl3) δ: 3.82 (s, 3H),
(S,E)-Benzyl 4-(anthracen-9-yl)-2-hydroxy-2-(4-
methoxyphenyl)but-3-enoate (7j) Colorless oil, 82%
yield, 14% ee; H NMR (300 MHz, CDCl3) δ: 3.84 (s,
4.03 (s, 1H), 5.29 (s, 2H), 6.76 (d, J＝15.3 Hz, 1H),
6.90 (d, J＝8.7 Hz, 2H), 6.97 (d, J＝15.3 Hz, 1H), 7.29
－7.38 (m, 8H), 7.43 (d, J＝7.8 Hz, 2H), 7.48 (d, J＝8.4
Hz, 2H); 13C NMR (100 MHz, CDCl3) δ: 55.2, 68.2,
78.1, 113.7, 126.8, 127.5, 128.9, 128.0, 128.4, 128.52,
128.54, 129.1, 130.5, 133.4, 134.9, 136.2, 159.3, 174.1.
(S,E)-Phenyl 2-hydroxy-2-(4-methoxyphenyl)-4-
phenylbut-3-enoate (7e) Colorless oil, 52% yield,
1
3H), 4.32 (s, 1H), 5.28 (d, J＝12.6 Hz, 1H), 5.44 (d, J＝
11.7 Hz, 1H), 6.66 (d, J＝15.9 Hz, 1H), 6.96 (d, J＝8.7
Hz, 2H), 7.36－7.41 (m, 8H), 7.48 (d, J＝6.9 Hz, 2H),
7.63 (d, J＝8.7 Hz, 2H), 7.75 (d, J＝16.2 Hz, 1H), 8.01
(d, J＝8.1 Hz, 2H), 8.21 (d, J＝9.0 Hz, 2H), 8.40 (s,
1H); 13C NMR (100 MHz, CDCl3) δ: 55.4, 68.6, 78.5,
114.0, 125.2, 125.5, 125.8, 126.6, 127.1, 127.6, 128.3,
128.7, 128.8, 129.5, 131.4, 131.8, 133.5, 134.9, 137.5,
159.5, 174.5; HRMS (ESI) calcd for C32H26O4Na [M＋
Na]＋: 475.0521, found 475.0527.
1
80% ee; H NMR (300 MHz, CDCl3) δ: 3.84 (s, 3H),
3.92 (s, 1H), 6.90 (d, J＝15.6 Hz, 1H), 6.96 (d, J＝8.7
Hz, 2H), 7.06－7.12 (m, 3H), 7.27－7.32 (m, 2H), 7.35
－7.52 (m, 4H), 7.51 (d, J＝7.5 Hz, 2H), 7.61 (d, J＝9.0
Hz, 2H); 13C NMR (100 MHz, CDCl3) δ: 55.3, 78.3,
114.0, 121.0, 126.4, 126.9, 127.6, 128.1, 128.5, 128.6,
129.6, 131.1, 133.2, 136.2, 150.5, 159.6, 173.1; HRMS
(ESI) calcd for C23H20O4Na [M＋Na]＋: 383.1259, found
383.1267.
Acknowledgement
Financial support from the National Natural Science
Foundation of China (Nos. 20972172, 21021063).
(S,E)-Benzyl 2-hydroxy-2-(4-methoxyphenyl)-4-p-
tolylbut-3-enoate (7f) Colorless oil, 83% yield, 80%
ee; 1H NMR (300 MHz, CDCl3) δ: 2.36 (s, 3H), 3.81 (s,
3H), 3.96 (s, 1H), 5.26 (s, 2H), 6.66 (d, J＝15.9 Hz, 1H),
6.86－6.93 (m, 3H), 7.14 (d, J＝7.8 Hz, 2H), 7.27－
7.36 (m, 6H), 7.45 (d, J＝9.0 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ: 21.2, 55.3, 68.2, 78.1, 113.7, 126.7,
127.6, 128.0, 128.1, 128.5, 128.6, 129.2, 130.4, 133.5,
133.6, 135.0, 137.8, 159.3, 174.3; HRMS (ESI) calcd
for C25H24O4Na [M＋Na]＋: 411.1572, found 411.1566.
(S,E)-Benzyl 2-hydroxy-2,4-bis(4-methoxy-phe-
nyl)but-3-enoate (7g) Colorless oil, 73% yield, 80%
ee; 1H NMR (300 MHz, CDCl3) δ: 3.81 (s, 6H), 3.98 (s,
1H), 5.27 (s, 2H), 6.59 (d, J＝15.9 Hz, 1H), 6.84－6.89
(m, 5H), 7.27－7.34 (m, 2H), 7.34－7.37 (m, 5H), 7.46
(d, J＝9.0 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ:
55.2, 68.1, 78.1, 113.7, 113.9, 126.9, 127.6, 127.99,
128.02, 128.4, 128.5, 129.0, 130.0, 133.6, 135.0, 159.3,
159.4, 174.3; HRMS (ESI) calcd for C25H24O5Na [M＋
Na]＋: 427.1521, found 427.1532.
References
[1] (a) Coppola, G. M.; Schuster, H. F. Chiral a-Hydroxy Acids in En-
antioselective Synthesis, Wiley-VCH, Weinheim, 1997; (b) Hanes-
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Pergamon, New York, 1983, Chapter 2.
[2] For reviews, see: (a) Davis, F. A.; Chen, B.-C. Chem. Rev. 1992, 92,
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Zheng, K.; Shi, J.; Liu, X.; Feng, X. J. Am. Chem. Soc. 2008, 130,
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Huang, K.-W.; Lu, Y. Angew. Chem., Int. Ed. 2011, 50, 1861; (l)
Ohshima, T.; Kawabata, T.; Takeuchi, Y.; Kakinuma, T.; Iwasaki, T.;
Yonezawa, T.; Murakami, H.; Nishiyama, H.; Mashima, K. Angew.
Chem., Int. Ed. 2011, 50, 6296.
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Angew. Chem., Int. Ed. 2008, 47, 4351; (b) Yamamoto, Y.; Shirai, T.;
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Chem. Soc. 2011, 133, 18066.
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see: (a) He, P.; Lu, Y.; Dong, C.-G.; Hu, Q.-S. Org. Lett. 2007, 9,
343; (b) He, P.; Lu, Y.; Hu, Q.-S. Tetrahedron Lett. 2007, 48, 5283;
(c) Ganci, G. R.; Chisholm, J. D. Tetrahedron Lett. 2007, 48, 8266;
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2255.
(S,E)-Benzyl 4-(4-chlorophenyl)-2-hydroxy-2-(4-
methoxyphenyl)but-3-enoate (7h) Colorless oil, 61%
1
yield, 80% ee; H NMR (300 MHz, CDCl3) δ: 3.81 (s,
3H), 3.98 (s, 1H), 5.26 (s, 2H), 6.68 (d, J＝15.9 Hz, 1H),
6.87 (d, J＝9.0 Hz, 2H), 6.88 (d, J＝15.9 Hz, 1H), 7.27
－7.36 (m, 9H), 7.42 (d, J＝9.0 Hz, 2H); 13C NMR (100
MHz, CDCl3) δ: 55.2, 68.3, 78.0, 113.7, 128.3, 127.9,
128.0, 128.5, 128.6, 128.7, 129.2, 129.7, 133.2, 133.5,
134.7, 134.8, 159.4, 173.9; HRMS (ESI) calcd for
C24H21O4ClNa [M＋Na]＋: 431.1026, found 431.1039.
(S,E)-Benzyl 4-(4-bromophenyl)-2-hydroxy-2-(4-
methoxyphenyl)but-3-enoate (7i) Colorless oil, 75%
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1
yield, 80% ee; H NMR (300 MHz, CDCl3) δ: 3.81 (s,
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[8] For examples of enantioselectivity reversal in rhodium/sulfur-olefin
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[9] For an example of regioselectivity switch between enantioselective
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[6] For representative recent reports on chiral sulfur-olefin ligands from
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© 2013 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2013, 31, 321—328