Enantioselective addition of allyltin reagents to amino aldehydes catalyzed with bis(oxazolinyl)phenylrhodium(III) aqua complexes

Article abstract of DOI:10.3390/molecules16075387

Bis(oxazolinyl)phenylrhodium(III) aqua complexes, (Phebox)RhX₂ (H₂O) [X = Cl, Br], were found to be efficient Lewis acid catalysts for the enantioselective addition of allyl- and methallyltributyltin reagents to amino aldehydes. The

Full text of DOI:10.3390/molecules16075387

Molecules 2011, 16, 5387-5401; doi:10.3390/molecules16075387
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molecules
ISSN 1420-3049
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Article
Enantioselective Addition of Allyltin Reagents to Amino
Aldehydes Catalyzed with Bis(oxazolinyl)phenylrhodium(III)
Aqua Complexes
Yukihiro Motoyama 1,*, Takatoshi Sakakura 2, Toshihide Takemoto 2, Kayoko Shimozono 2,
Katsuyuki Aoki 2 and Hisao Nishiyama 3
1
Institute for Materials Chemistry and Engineering, Kyushu University, 6-1 Kasuga-koen, Kasuga,
Fukuoka 816-8580, Japan
2
School of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi,
Aichi 441-8580, Japan
3
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa,
Nagoya 464-8603, Japan
* Author to whom correspondence should be addressed; E-Mail: motoyama@cm.kyushu-u.ac.jp;
Tel.: +81-92-583-7821; Fax: +81-92-583-7839.
Received: 30 May 2011; in revised form: 20 June 2011 / Accepted: 23 June 2011 /
Published: 27 June 2011
Abstract: Bis(oxazolinyl)phenylrhodium(III) aqua complexes, (Phebox)RhX2(H2O)
[X = Cl, Br], were found to be efficient Lewis acid catalysts for the enantioselective
addition of allyl- and methallyltributyltin reagents to amino aldehydes. The reactions
proceed smoothly in the presence of 5–10 mol % of (Phebox)RhX2(H2O) complex at
ambient temperature to give the corresponding amino alcohols with modest to good
enantioselectivity (up to 94% ee).
Keywords: allylation; amino aldehydes; Lewis acids; pincer ligands; rhodium
1. Introduction
The development of enantioselective synthesis of chiral homoallylic alcohols containing amino-
functional groups is of great importance to synthetic organic and medicinal chemistry. Despite much
effort directed at enantioselective allylation of aldehydes [1-3], there are only a few systems for
enantioselective allylation of amino aldehydes as substrates because the high coordination ability of

Molecules 2011, 16
5388
amino groups to the metal species often leads to deactivation of chiral allylmetals or catalysts.
Therefore, most of these reactions need a stoichiometric amount of chiral sources. For examples,
Brown [4] and Chen [5] reported the utility of allylboron reagents (Figure 1, A–C) for the reaction
with pyridinecarboxaldehydes and 1-methyl-2-pyrrolecarboxaldehyde [4,5]. Denmark and co-workers
developed a new reaction system for the allylation of aldehydes, but the enantioselectivity of the
reaction with 4-dimethylaminobenzaldehyde was not so high (Figure 1, D) [6]. The other one is a
catalytic reaction using 20 mol % of BINOL-derived chiral titanium complex/allyltributyltin via
transmetalation mechanism reported by Umani-Ronchi (Figure 1, E) [7].
Figure 1. Chiral allylmetal reagents for the asymmetric allylation of amino aldehydes.
CHO
CHO
N
Me
N
N
CHO
96–>99% ee (78–85%)
>99% ee (85%)
94% ee (92%)
BnHNOC
B
B
2
2
O
BnHNOC
B
O
A
B
C
Me2N
N
CHO
CHO
33% ee (69%)
80% ee (90%)
Me
N
O
O
Cl3Si
P
Bu3Sn
N
TiCl2
N
Me
O
D
E
We have previously developed a meridional tridentate ligand, 2,6-bis(oxazolinyl)phenyl derivative
(abbreviated to Phebox) as a chiral N–C–N pincer type ligand with one central covalent bond to a
metal [8-14], and have demonstrated that rhodium(III) aqua complexes bearing the Phebox ligand,
(Phebox)RhX2(H2O) [1: X = Cl, 2: X = Br], acted as recoverable chiral Lewis acid catalysts for the
enantioselective addition of allylic tributyltin reagents to aldehydes [15-17] and the asymmetric hetero
Diels-Alder reactions of Danishefsky’s dienes and glyoxylates [18]. During the course of our studies
on the Phebox-Rh(III) system as a chiral transition metal Lewis acid, we have found that tertiary
amines such as N,N-diisopropylethylamine or triethylamine cannot bind to the rhodium atom [19]. This
discovery encouraged us to use these air-stable and water-tolerant complexes 1 and 2 for the allylation
of amino aldehydes as substrates. We wish to report herein the Lewis acid-catalyzed enantioselective
addition of allyl- and methallyltributyltin reagents to aldehydes containing amino-functional groups
(Scheme 1).

Molecules 2011, 16
Scheme 1. Enantioselective addition of allyltin reagents to amino aldehydes catalyzed with
5389
(Phebox)RhX2(H2O) complexes (X = Cl, Br).
O
O
X
1 or 2
(5 ~ 10 mol%)
N
N
R2
H
R2
Rh
O
+
R2N
R2N
R
R
MS 4A
CH2Cl2
25 °C, 24 h
X
O
OH
SnBu3
H
H
3
4a: R2 = H
b: R2 = Me
5: R2 = H
6: R2 = Me
1: X = Cl
2: X = Br
Me2N
Me2N
N
CHO
R1
N
CHO
CHO
CHO
3a
3b: R1 = H
c: R1 = Me
3d
3e
2. Results and Discussion
2.1. NMR Studies, Isolation, and X-ray Analysis of Phebox-Rh(III)–Amino Aldehyde Complexes
First, we checked the complexation between Phebox-Rh(III) complex i-Pr-1 and amino aldehydes
1
13
1
13
3a–e by H and C-NMR. Selected H and C-NMR data in CDCl3 are listed in Table 1. Although
rigid complexation was not clearly observed between i-Pr-1 and 6-methyl-2-pyridinecarboxaldehyde
(3c) (Entry 3), 1H- and 13C-NMR spectra of the other cases showed formation of new complexes. From
the NMR spectra of a mixture of i-Pr-1 and 3a, the pyridine’s nitrogen atom exclusively forms
σ-complexes with the (i-Pr-Phebox)RhCl2 fragment; the signals of the protons for 2- and 6-positions of
the pyridine ring (H2 and H6) appeared at lower field than those of the uncomplexed (free) 3a (from δ
9.08 to 10.30 ppm for H2, and from δ 8.85 to 10.08 ppm for H6, respectively) (Entry 1). This amine
complex was stable enough to be purified by silica gel chromatography and was eventually
characterized by a single-crystal X-ray diffraction (Figure 2, Table 2). In the case of the reaction of
i-Pr-1 and 3b, H6 and the formyl proton (Hf) both appeared as broad signals at lower field (δ 9.11 for
H6 and 10.34 ppm for Hf) than those of free 3b (δ 8.77 for H6 and 10.07 ppm for Hf) (Entry 2). These
results indicate that the coordination of 3b to the (i-Pr-Phebox)RhCl2 fragment is an equilibrium
between the pyridinic nitrogen and carbonyl oxygen. In contrast to the pyridinecarboxaldehydes,
solutions of 4-dimethylaminobenzaldehyde (3d) and 4-dimethylaminocinnamaldehyde (3e) in the
presence of i-Pr-1 showed rigid formation of C=O/σ type aldehyde complexes. For example, the
signals assignable to the dimethylamino group were not changed, but the signals of the formyl proton
(Hf) and carbon (Cf) of coordinated 3d appeared at lower field than the uncomplexed (free) 3d (from δ
9.74 to 9.92 ppm for Hf, and from δ 190.4 to 207.2 ppm for Cf, respectively) (Entry 4). Similar lower
field shifts of Hf and Cf along with the olefinic protons Hα and Hβ (Hα = α-proton, Hβ = β-proton) were
1
also observed for the mixture of i-Pr-1 and 3e in H and 13C NMR (ΔHα = +0.27 ppm,
ΔH = +0.14 ppm, ΔHf = +0.77 ppm, ΔCf = +2.9 ppm, respectively) (Entry 5). It is widely known that
β
chemical shifts of vinylic protons (Hα and Hβ), formyl proton (Hf) and carbon (Cf) of enals bound

Molecules 2011, 16
5390
to Lewis acids by the carbonyl oxygen appear at lower field than those of free enals [20-22]. These
lower-field shifts of Hα, Hβ, Hf and Cf are also observed in the reaction of i-Pr-1 and
(E)-cinnamaldehyde [16]. The above NMR and X-ray studies thus indicated that the (Phebox)RhCl2
fragment, generated by releasing H2O from (Phebox)RhCl2(H2O), captures amino aldehydes 3b–e at
the carbonyl oxygen to form aldehyde complexes (Scheme 2).
Table 1. Selected spectroscopic data for free amino aldehydes 3 and mixtures of i-Pr-1 and 3.
δ (ppm) a
Entry
Δ (ppm) b
3
i-Pr-1 and 3
H2: 10.30
H6: 10.08
Hf: 10.27
Cf: 189.8
H2: 9.08
H6: 8.85
Hf: 10.12
Cf: 190.8
+1.22
+1.23
+0.15
–1.0
H6
1
N
Hf
Hf
Hf
Cf
O
3a
3b
3c
H2
N
H6: 8.77
Hf: 10.07
H6: 9.11 (br)
+0.34
Hf: 10.34 (br) +0.27
2
3
H6
Cf
O
HMe: 2.66
Hf: 10.04
CMe: 24.5
Cf: 193.1
HMe: 2.66
Hf: 10.06
CMe: 24.5
Cf: 194.1
0.00
+0.02
0.0
HMe
HMe
CMe
HMe
N
Cf
O
+1.0
HMe: 3.09
Hf: 9.74
CN: 40.2
Cf: 190.4
HMe: 3.11
Hf: 9.92
CN: 40.2
Cf: 207.2
+0.02
+0.18
0.0
Me
N
HMe
CN
4
5
HMe
HMe
Hf
+16.8
Cf
O
3d
Hα: 6.54
Hβ: 7.38
HMe: 3.05
Hf: 9.09
CN: 40.2
Cf: 193.8
Hα: 6.81
Hβ: 7.52
HMe: 3.07
Hf: 9.86
CN: 40.2
Cf: 196.7
+0.27
+0.14
+0.02
+0.77
0.0
Me
HMe
HMe
N
CN
HMe
Hα
Hf
Cf
O
3e
Hβ
+2.9
a Observed at 400 MHz for 1H-NMR and 100 MHz for 13C-NMR in CDCl3 at ambient temperature;
b Calculated by δ (i-Pr-1 and 3) – δ (3).
Scheme 2. Complexation between (Phebox)RhCl2 fragment ([Rh]) and amino aldehydes.
[Rh]
– H2O
OH2
H
H
3a
R2N
[Rh]
+ H2O
O
O
+ 3b or 3c
– 3b or 3c
H
H
+
[Rh]
R2N
[Rh]
R2NH
O
O
3d or 3e
R2N
[Rh]
[Rh]

Molecules 2011, 16
Figure 2. Molecular structure of (i-Pr-Phebox)RhCl2(κ-3a): there are two independent
5391
molecules and one H2O in the unit cell.
O1
C1
O2
Cl2
N2
N1
C2
Rh
N3
Cl1
C3
C4
O3
Table 2. Selected bond distances (Å) and angles (deg) for (i-Pr-Phebox)RhCl2(κ-3a).a
Rh–C1
Rh–Cl1
Rh–Cl2
1.93(1) [1.89(1)]
2.340(4) [2.334(4)]
2.334(4) [2.351(4)]
Rh–N1
Rh–N2
Rh–N3
2.05(1) [2.06(1)]
2.05(1) [2.09(1)]
2.21(1) [2.27(1)]
1.25(3) [1.27(4)]
54(1) [90(1)]
C4–O3
C1–Rh–N3
Cl1–Rh–Cl2
N1–Rh–N2
175.2(6) [178.0(5)]
178.0(2) [177.2(2)]
158.4(5) [157.6(5)]
N1–Rh–N3–C2
O3–C4–C3–C2
−175(2) [19(3)]
a Bond distances and angles of the second molecule are given in brackets.
2.2. Phebox-Rh(III)-Catalyzed Enantioselective Addition of Allyltributyltin to Amino Aldehydes
We also examined the Phebox-Rh(III)-catalyzed reaction of amino aldehydes and allyltributyltin.
Allyltributyltin (4a) was added to a suspension of 4Å molecular sieves (MS 4A), amino aldehydes
3b–e and 5–10 mol % of (S,S)-(Phebox)RhX2(H2O) complexes (1 or 2) in dichloromethane at 25 °C
for 24 h. These results are summarized in Table 3. First, the reaction of pyridine-2-carboxaldehyde
(3b) proceeded smoothly, but the isolated yield of the allylated product 5b was only 14% after
purification of the crude material by silica gel chromatography (Entry 1). This result indicates that the
alkoxystananne 5b-Sn formed in the reaction mixture is stable and hardly hydrolyzed under the usual
workup process (see Experimental section). Consequently, we adopted a new procedure for conversion
of 5b-Sn to the acetate derivative 5b-Ac by treatment with acetic anhydride (Scheme 3). In this
manner, 5b-Ac was obtained in good to high yields and with moderate enantioselectivity (Entries 2, 3,
5, and 6). The absolute configuration of 5b-Ac obtained by (S,S)-Phebox-derived Rh(III) complexes
was determined to be S by comparison of the optical rotation value with literature data [23]. In the case
of the reaction using (S,S)-Ph-1, however, ca. 50% of 3b was recovered after silica gel chromatography
and (R)-5b-Ac was formed as a major enantiomer (Entry 4). Finally, an enantioselectivity of up to
59% ee was achieved using 10 mol % of the i-Pr- and Me-Phebox-derived dibromide complexes
(Entries 5 and 6). In the cases of the other aldehydes 3c–e, the products were obtained as a homoallylic
alcohol in good to high yields. The reactions of 6-methyl-2-pyridinecarboxaldehyde (3c) and
4-dimethylaminocinnamaldehyde (3e) afforded the corresponding amino alcohols 5c and 5e with good

Molecules 2011, 16
5392
enantioselectivity by using the dibromide complexes (5c: 84% ee with Ph-2, and 5e: 88% ee with
Bn-2, respectively) (entries 9 and 15). In sharp contrast, the dichloride complexes showed higher
enantioselectivity (84% ee for Me-1, and 81% ee for s-Bu-1, respectively) than the parent dibromide
one (72% ee for Me-2) in the allylation reaction of 4-dimethylamino- benzaldehyde (3d) (Entries 10–12).
We also examined the reaction of 3-pyridinecarboxaldehyde (3a), however, no allylated product was
obtained and the amine complex, (i-Pr-Phebox)RhCl2(κ-3a), free 3a, and allyltributyltin (4a) were
detected by 1H-NMR of the crude material.
Scheme 3. Conversion of 5b-Sn to 5b-Ac by treatment with Ac2O.
Ac2O
+
Bu3Sn(OAc)
N
N
5b-Sn
5b-Ac
OAc
O
Bu3Sn
Table 3. Enantioselective addition of allyltributyltin 4a to amino aldehydes 3b–e.a
Entry
1
Aldehyde
Catalyst
i-Pr-1
i-Pr-1
Me-1
Ph-1
i-Pr-2
Me-2
Product
5b
% Yield % eeb (config.) c
14
99
99
45
81
85
42 (S)
53 (S)
56 (S)
21 (R)
59 (S)
59 (S)
69 (S)e
75 (S)e
84 (S)e
2 d
5b-Ac
5b-Ac
5b-Ac
5b-Ac
5b-Ac
3 d
4 d
5 d
6 d
N
N
CHO 3b
CHO 3c
7
8
9
i-Pr-1
Ph-1
Ph-2
5c
5c
5c
94
89
97
10
11
12
Me-1
s-Bu-1
Me-2
5d
5d
5d
80
67
42
84 (S)
81 (S)
72 (S)
Me2N
CHO 3d
13
14
15
Bn-1
s-Bu-1
Bn-2
5e
5e
5e
80
61
44
81 (S)e
80 (S)e
88 (S)e
Me2N
CHO 3e
a All reactions were carried out using 0.5 mmol of 3, 0.75 mmol of 4, and 0.025 mmol (5 mol %) of
1 or 0.05 mmol (10 mol %) of 2 in 2 mL of dichloromethane in the presence of MS 4A (250 mg)
b
at 25 °C for 24 h; Determined by chiral HPLC analysis using Daicel CHIRALCEL OD;
c
d
Assignment by comparison of the sign of optically rotation with reported value; 0.6 mmol of
acetic anhydride was added; e Assignment by analogy.

Molecules 2011, 16
5393
2.3. Phebox-Rh(III)-Catalyzed Enantioselective Addition of Methallyltributyltin to Amino Aldehydes
Table 4 summarizes the results obtained for the methallylation of amino aldehydes 3b–e catalyzed
with Phebox-Rh(III) complexes in dichloromethane in the presence of MS 4A at 25 °C for 24 h. In the
reactions of pyridinecarboxaldehydes 3b and 3c, the enantiomeric excesses of the methallylated
products 6b-Ac and 6c were moderate (51% ee for 6b-Ac, and 45% ee for 6c, respectively)
(Entries 1–10). Similar to the reaction of pyridine-2-carboxaldehyde 3b and allyltributyltin (Table 2,
Entry 4), (S,S)-Ph-1 afforded the opposite (R)-6b-Ac as a major enantiomer (Entry 3). Compared to the
reactions with pyridinecarboxaldehydes 3b and 3c, the (S,S)-Phebox-Rh-catalyzed reactions of
4-dimethyl-aminobenzaldehyde (3d) and 4-dimethylaminocinnamaldehyde (3e) with methallyltributyltin
(4b) afforded the corresponding (S)-products with good to high enantioselectivity (90% ee for 6d and
94% ee for 6e, respectively) (Entries 11–17). Incidentally, the Phebox-Rh(III) aqua complexes 1 and 2
can be recovered almost quantitatively from the reaction media by silica gel column chromatography.
Table 4. Enantioselective addition of methallyltributyltin 4b to amino aldehydes 3b–e.a
Entry
1 d
2 d
3 d
4 d
5 d
6 d
7
Aldehyde
Catalyst
Bn-1
Product % Yield % ee b (config.) c
6b-Ac
6b-Ac
6b-Ac
6b-Ac
6b-Ac
6b-Ac
6c
79
76
18
52
48
22
60
36
21
26
84
79
68
52
52
74
20
15 (S)
41 (S)
24 (R)
<2 (–)
45 (S)
51 (S)
45 (S)e
11 (S)e
10 (S)e
26 (S)e
85 (S)e
90 (S)e
87 (S)e
63 (S)e
80 (S)e
84 (S)e
94 (S)e
Me-1
Ph-1
s-Bu-1
Me-2
s-Bu-2
Me-1
s-Bu-1
Me-2
s-Bu-2
i-Pr-1
Bn-1
s-Bu-1
Bn-2
i-Pr-1
s-Bu-1
s-Bu-2
N
CHO 3b
8
9
6c
6c
6c
6d
6d
6d
6d
6e
N
CHO 3c
10
11
12
13
14
15
16
17
Me2N
CHO 3d
Me2N
6e
6e
CHO 3e
a All reactions were carried out using 0.5 mmol of 3, 0.75 mmol of 4, and 0.025 mmol (5 mol %) of
1 or 0.05 mmol (10 mol %) of 2 in 2 mL of dichloromethane in the presence of MS 4A (250 mg) at
b
25 °C for 24 h;
Determined by chiral HPLC analysis using Daicel CHIRALCEL OD;
c
d
Assignment by comparison of the sign of optically rotation with reported value; 0.6 mmol of
acetic anhydride was added; e Assignment by analogy.

Molecules 2011, 16
5394
3. Experimental
3.1. General
Anhydrous dichloromethane was purchased from Kanto Chemical Co. Carbon tetrabromide, all
1
13
aldehydes and allyltributyltin were purchased from Tokyo Chemical Industry Co., Ltd. H and C
NMR spectra were measured on a VARIAN Inova-400 (400 MHz) spectrometer. 1H-NMR (400 MHz)
chemical shifts were described in parts per million downfield from tetramethylsilane used as an
internal standard (δ = 0) in CDCl3, unless otherwise noted. 13C-NMR (100 MHz) chemical shifts were
expressed in parts per million with reference to the residual solvent peak as an internal standard
(δ = 77.1 for CDCl3), unless otherwise noted. IR spectra were measured on a JASCO FT/IR-230
spectrometer. Melting points were measured on a Yanaco MP-J3 apparatus. Elemental analyses were
measured on a Yanaco CHN CORDER MT-6 instrument. High performance liquid chromatography
(HPLC) analyses were performed with a JASCO PU-980 HPLC pump, UV-975 and 980 UV/VIS
detector, and CO-966 column thermostat (at 25 °C) using a Daicel CHIRALCEL OD column. Optical
rotations were measured on a JASCO DIP-140 polarimeter. Column chromatography was performed
with silica gel (Merck, Art. No. 7734). Analytical thin-layer chromatography (TLC) was performed on
glass plates and aluminum sheets pre-coated with silica gel (Merck, Kieselgel 60 F-254, layer
thicknesses 0.25 and 0.2 mm, respectively). Visualization was accomplished by UV light (254 nm),
anisaldehyde, and phosphomolybdic acid. All reactions were carried out under a nitrogen or argon
atmosphere. (Phebox)SnMe3, (Phebox)RhCl2(H2O) 1 and (Bn-Phebox)RhBr2(H2O) (Bn-2) were
prepared by our method [16,18,24]. [(c-octene)2RhCl]2 [25] and methallyltributyltin [26] were
prepared by the literature methods.
3.2. General Procedure for the Synthesis of (Phebox)RhBr2(H2O) Complexes
To a stirred solution of (R-Phebox)SnMe3 and [(c-octene)2RhCl]2 in dichloromethane was added
tetrabromomethane [ca. 8 equivalents with respect to (R-Phebox)SnMe3] at ambient temperature for 24
h. Then the reaction mixture was concentrated under reduced pressure. Purification of the residue by
silica gel chromatography gave (R-Phebox)RhBr2(H2O) (R-2).
(i-Pr-Phebox)RhBr2(H2O) (i-Pr-2). 51% yield. Pale yellow solid. mp. 167 °C (decomp); IR (KBr) ν
1
3474, 2959, 1622, 1485, 1391, 961, 745 cm−1; H-NMR (CDCl3) δ 0.94 (d, J = 6.5 Hz, 6H), 0.96 (d,
J = 7.0 Hz, 6H), 2.42 (qqd, J = 7.0, 6.5, 2.5 Hz, 2H), 3.43 (bs, 2H), 4.30 (td, J = 8.3, 2.5 Hz, 2H), 4.71
(d, J = 8.3 Hz, 4H), 7.25 (t, J = 7.6 Hz, 1H), 7.58 (d, J = 7.6 Hz, 2H); 13C-NMR (CDCl3) δ 15.4, 19.6,
29.1, 67.5, 71.3, 123.1, 128.1, 131.5, 170.9 (d, JRh-C = 4.1 Hz), 178.8 (d, JRh-C = 24.2 Hz); Anal.
C18H25N2O3Br2Rh: Found C 37.31, H 4.33, N 4.74%; Calcd C 37.27, H 4.34, N 4.83%.
(Me-Phebox)RhBr2(H2O) (Me-2). 58% yield. Orange solid; mp. >300 °C (decomp); IR (KBr) ν 3397,
1
3009, 2822, 1617, 1485, 1397, 1148, 958, 739 cm−1; H-NMR (CD3OD) δ 1.50 (d, J = 6.7 Hz, 6H),
3.32 (bs, 2H), 4.34 (ddq, J = 8.8, 7.7, 6.7 Hz, 2H), 4.45 (dd, J = 8.5, 7.7 Hz, 2H), 5.02 (dd, J = 8.8, 8.5
13
Hz, 2H), 7.24 (t, J = 7.7 Hz, 1H), 7.58 (d, J = 7.7 Hz, 2H); C-NMR (CD3OD) δ 19.3, 58.6, 77.7,

Molecules 2011, 16
5395
122.3, 126.9, 132.4, 171.1 (d, JRh-C = 3.7 Hz), 182.2 (d, JRh-C = 20.0 Hz); Anal. C14H17N2O3Br2Rh:
Found C 32.04, H 3.39, N 5.27%; Calcd C 32.09, H 3.27, N 5.35%.
(Ph-Phebox)RhBr2(H2O) (Ph-2). 37% yield. Pale yellow solid. mp. 189 °C (decomp); IR (KBr) ν
1
3452, 2980, 2825, 1613, 1485, 1326, 1149, 968 cm−1; H-NMR (CDCl3) δ 1.79 (bs, 2H), 4.58 (dd,
J = 10.4, 8.6 Hz, 2H), 5.18 (dd, J = 10.2, 8.6 Hz, 2H), 5.31 (dd, J = 10.4, 10.2 Hz, 2H), 7.35-7.46
13
(m, 7H), 7.46-7.74 (m, 4H), 7.72 (d, J = 7.7 Hz, 2H); C-NMR (CDCl3) δ 31.7, 67.1, 76.8, 123.3,
128.5, 128.8, 128.9, 131.4, 137.4, 172.5 (d, JRh-C = 4.2 Hz), 180.4 (d, JRh-C = 21.1 Hz); Anal.
C24H21N2O3Br2Rh: Found C 44.48, H 3.19, N 4.30%; Calcd C 44.47, H 3.27, N 4.32%.
(s-Bu-Phebox)RhBr2(H2O) (s-Bu-2). 21% yield. Pale yellow solid. mp. 119 °C (decomp); IR (KBr) ν
1
3448, 2968, 2822, 1617, 1484, 1394, 1145, 963 cm−1; H-NMR (CDCl3) δ 0.96 (d, J = 6.8 Hz, 6H),
1.00 (t, J = 7.3 Hz, 6H), 1.24 (m, 2H), 1.39 (m, 2H), 2.17 (m, 2H), 3.43 (bs, 2H), 4.34 (ddd,
J = 9.9, 6.7, 3.2 Hz, 2H), 4.69 (dd, J = 8.8, 6.7 Hz, 2H), 4.74 (dd, J = 9.9, 8.8 Hz, 2H), 7.26 (t, J = 7.7
Hz, 1H), 7.59 (d, J = 7.7 Hz, 2H); 3C-NMR (CDCl3) δ 12.0, 12.8, 35.8, 66.4, 71.4, 77.4, 123.4, 128.2,
131.4, 170.7 (d, JRh-C = 4.2 Hz), 176.9 (d, JRh-C = 24.5 Hz); Anal. C20H29N2O3Br2Rh: Found C 39.51, H
4.73, N 4.63%; Calcd C 39.50, H 4.81, N 4.61%.
3.3. General Procedure for the Catalytic Enantioselective Addition of Allyl- or Methallyltributyltin to
Aldehydes Catalyzed with (Phebox)RhX2(H2O) Complexes
To a suspension of MS 4A (250 mg) in dichloromethane (2 mL) was added (Phebox)RhX2(H2O)
complex (0.025-0.05 mmol, 5-10 mol %), amino aldehyde (0.5 mmol) and allyl- or methallyltributyltin
(0.75 mmol) at 25 °C. After it was stirred for 24 h at that temperature, the reaction mixture was
concentrated under reduced pressure. Purification of the residue by silica gel chromatography gave
homoallylic alcohol: the enantioselectivity was determined by chiral HPLC analysis.
20
23
1-(2-Pyridyl)-3-buten-1-ol (5b) [4,5]. [α]D −27.1° (c 1.22, CHCl3) for 42% ee: lit. 4 [α]D −32.5°
(c 3.5, EtOH) for ≥99% ee, 1S; IR (neat) ν 3267, 2922, 1733, 1699, 164, 1562, 1474, 1066, 702 cm−1;
1H- NMR (CDCl3) δ 2.48 (ddddd, J = 14.5, 7.3, 6.9, 1.3, 1.1 Hz, 1H), 2.63 (ddddd, J = 14.5, 6.9, 4.7,
1.4, 1.2 Hz, 1H), 4.07 (bs, 1H), 4.81 (bs, 1H), 5.09 (dddd, J = 10.1, 2.0, 1.2, 1.1 Hz, 1H), 5.11 (dddd,
J = 17.2, 2.0, 1.4, 1.3 Hz, 1H), 5.83 (dddd, J = 17.2, 10.1, 7.3, 6.9 Hz, 1H), 7.20 (ddd, J = 7.5, 4.9, 1.2
Hz, 1H), 7.28 (ddd, J = 7.8, 1.2, 1.0 Hz, 1H), 7.68 (ddd, J = 7.8, 7.5, 1.5 Hz, 1H), 8.54 (ddd,
13
J = 4.9, 1.5, 1.0 Hz, 1H); C-NMR (CDCl3) δ 43.0, 72.3, 118.1, 120.5, 122.4, 134.2, 136.7, 148.4,
161.4. Enantiomeric excess was determined by after conversion to the corresponding acetate 5b-Ac.
1-Acetoxy-1-(2-pyridyl)-3-butene (5b-Ac) [23]. IR (neat) ν 1738, 1592, 1372, 1235, 1047, 921 cm−1;
1H-NMR (CDCl3) δ 2.13 (s, 3H), 2.69 (ddddd, J = 14.3, 7.5, 6.9, 1.3, 1.1 Hz, 1H), 2.76 (ddddd,
J = 14.3, 7.1, 5.8, 1.4, 1.2 Hz, 1H), 5.04 (dddd, J = 10.2, 1.9, 1.2, 1.1 Hz, 1H), 5.08 (dddd, J = 17.2,
1.9, 1.4, 1.3 Hz, 1H), 5.74 (dddd, J = 17.2, 10.2, 7.1, 6.9 Hz, 1H), 5.86 (dd, J = 7.5, 5.8 Hz, 1H), 7.20
(ddd, J = 7.6, 4.8, 1.3 Hz, 1H), 7.30 (ddd, J = 7.9, 1.3, 0.9 Hz, 1H), 7.67 (ddd, J = 7.9, 7.6, 1.8 Hz,
13
1H), 8.60 (ddd, J = 4.8, 1.8, 0.9 Hz, 1H); C-NMR (CDCl3) δ 21.2, 39.2, 75.7, 118.2, 121.3, 122.8,
20
25
133.2, 136.7, 149.5, 158.9, 170.4; [α]D −40.8° (c 1.10, CHCl3) for 59% ee: lit. [α]D +75° (c 2.01,

Molecules 2011, 16
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CHCl3) for 92% ee, 1R [23]; Daicel CHIRALCEL OD, UV Detector 254 nm, hexane/i-PrOH = 9:1,
flow rate 0.5 mL/min. tR = 10.2 min (R), 12.8 min (S).
1-(6-Methyl-2-pyridyl)-3-buten-1-ol (5c). IR (neat) ν 3417, 2907, 1642, 1594, 1459, 1066, 799 cm−1;
1H-NMR (CDCl3) δ 2.45 (dtt, J = 14.2, 7.0, 1.1 Hz, 1H), 2.55 (s, 3H), 2.61 (dddt, J = 14.2, 6.9, 4.8, 1.1
Hz, 1H), 4.40 (d, J = 4.8 Hz, 1H), 4.76 (dt, J = 7.0, 4.8 Hz, 1H), 5.01 (ddt, J = 10.1, 2.0, 1.2 Hz, 1H),
5.12 (ddt, J = 17.1, 2.0, 1.5 Hz, 1H), 5.85 (ddt, J = 17.1, 10.1, 7.0 Hz, 1H), 7.04 (d, J = 7.7 Hz, 1H),
7.06 (d, J = 7.7 Hz, 1H), 7.56 (t, J = 7.7 Hz, 1H); 13C-NMR (CDCl3) δ 24.4, 43.1, 71.9, 117.3, 117.8,
121.9, 134.5, 136.9, 157.1, 160.5; Anal. C10H13NO: Found C 73.69, H 8.15, N 8.49%; Calcd C 73.59,
25
H 8.03, N 8.58%; [α]D −14.7° (c 0.95, CHCl3) for 84% ee; Daicel CHIRALCEL OD, UV Detector
254 nm, hexane/i-PrOH = 30:1, flow rate 0.5 mL/min. tR = 12.0 min (R), 13.8 min (S).
1-(p-Dimethylaminophenyl)-3-buten-1-ol (5d) [7]. IR (neat) ν 3435, 2802, 1614, 1522, 1348, 1162,
1
1052, 915, 819 cm−1; H-NMR (CDCl3) δ 1.89 (d, J = 2.6 Hz, 1H), 2.45-2.58 (m, 2H), 2.95 (s, 6H),
4.65 (ddd, J = 7.1, 6.2, 2.6 Hz, 1H), 5.11 (dm, J = 10.2 Hz, 1H), 5.15 (dm, J = 17.2 Hz, 1H), 5.82
13
(dddd, J = 17.2, 10.2, 7.3, 6.9 Hz, 1H), 6.72 (d, J = 8.8 Hz, 2H), 7.24 (d, J = 8.8 Hz, 2H); C-NMR
(CDCl3) δ 40.7, 73.4, 112.6, 117.9, 126.9, 131.9, 135.1, 150.3; [α]D24 −51.8° (c 0.35, CHCl3) for 84%
ee; Daicel CHIRALCEL OD, UV Detector 254 nm, hexane/i-PrOH = 9:1, flow rate 0.5 mL/min.
tR = 15.9 min (minor), 18.5 min (major).
(E)-1-(p-Dimethylaminophenyl)-1,5-hexadien-3-ol (5e). IR (neat) ν 3674, 1730, 1610, 1522, 1437,
1352, 968, 806 cm−1; 1H-NMR (CDCl3) δ 1.75 (d, J = 3.7 Hz, 1H), 2.36 (ddddd, J = 14.0, 7.4, 6.9, 1.1,
1.0 Hz, 1H), 2.43 (ddddd, J = 14.0, 6.8, 5.4, 1.4, 1.2 Hz, 1H), 2.95 (s, 6H), 4.31 (dddd, J = 7.2, 6.9,
5.4, 3.7 Hz, 1H), 5.14 (dddd, J = 10.2, 2.1, 1.2, 1.0 Hz, 1H), 5.17 (dddd, J = 17.1, 2.1, 1.4, 1.1 Hz, 1H),
5.86 (dddd, J = 17.1, 10.2, 7.4, 6.8 Hz, 1H), 6.03 (dd, J = 15.8, 6.9 Hz, 1H), 6.50 (d,
13
J = 15.8 Hz, 1H), 6.67 (d, J = 8.9 Hz, 2H), 7.27 (d, J = 8.9 Hz, 2H); C-NMR (CDCl3) δ 40.6, 42.2,
72.4, 112.5, 118.2, 125.1, 127.2, 127.5, 130.8, 134.5, 150.3; Anal. C14H19NO: Found C 77.30, H 8.89,
25
N 6.44%; Calcd C 77.38, H 8.81, N 6.45%; [α]D −21.5° (c 1.08, CHCl3) for 88% ee; Daicel
CHIRALCEL OD, UV Detector 254 nm, hexane/i-PrOH = 9:1, flow rate 0.5 mL/min. tR = 20.0 min
(minor), 21.1 min (major).
1-Acetoxy-1-(2-pyridyl)-3-methyl-3-butene (6b-Ac). IR (neat) ν 3076, 2933, 1742, 1651, 1591, 1472,
1236, 894 cm−1; 1H-NMR (CDCl3) δ 1.77 (s, 3H), 2.11 (s, 3H), 2.65 (d, J = 6.8 Hz, 2H), 4.72 (bs, 1H),
4.79 (bs, 1H), 5.98 (t, J = 6.8 Hz, 1H), 7.20 (dd, J = 7.7, 4.8 Hz, 1H), 7.31 (d, J = 7.7 Hz, 1H), 7.67
13
(td, J = 7.7, 1.7 Hz, 1H), 8.60 (dd, J = 4.8, 1.7 Hz, 1H); C-NMR (CDCl3) δ 21.1, 22.6, 74.7, 113.7,
121.2, 122.8, 136.7, 141.2, 149.5, 159.3, 170.4; Anal. C12H15NO2: Found C 70.29, H 7.29, N 6.76%;
Calcd C 70.22, H 7.37, N 6.82%; [α]D26 −37.5° (c 1.08, CHCl3) for 51% ee; Daicel CHIRALCEL OD,
UV Detector 254 nm, hexane/i-PrOH = 50:1, flow rate 0.5 mL/min. tR = 17.8 min (R), 21.0 min (S).
1-(6-Methyl-2-pyridyl)-3-methyl-3-buten-1-ol (6c). IR (neat) ν 3399, 2924, 1645, 1591, 1458, 1156,
1
889 cm−1; H-NMR (CDCl3) δ 1.82 (bs, 3H), 2.37 (dd, J = 14.0, 8.8 Hz, 1H), 2.52 (dd, J = 14.0,
4.4 Hz, 1H), 2.55 (s, 3H), 4.14 (d, J = 4.4 Hz, 1H), 4.81 (bs, 1H), 4.85 (dt, J = 8.8, 4.4 Hz, 1H), 4.89
13
(bs, 1H), 7.04 (d, J = 7.8 Hz, 1H), 7.08 (d, J = 7.8 Hz, 1H), 7.56 (t, J = 7.8 Hz, 1H); C- NMR

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(CDCl3) δ 22.7, 24.4, 47.4, 70.9, 113.6, 117.3, 121.9, 136.9, 142.5, 157.2, 161.1; Anal. C11H15NO:
Found C 74.58, H 8.53, N 7.80%; Calcd C 74.54, H 8.53, N 7.90%; [α]D20 −29.1° (c 1.37, CHCl3) for
45% ee; Daicel CHIRALCEL OD, UV Detector 254 nm, hexane/i-PrOH = 30:1, flow rate 0.5 mL/min.
tR = 12.5 min (R), 13.5 min (S).
1-(p-Dimethylaminophenyl)-3-methyl-3-buten-1-ol (6d). White solid. mp. 28–30 °C; IR (neat) ν 3251,
2886, 2800, 1524, 1442, 1350, 1162, 1054, 816 cm−1; 1H-NMR (CDCl3) δ 1.79 (bs, 3H), 1.98 (bs, 1H),
2.39 (dd, J = 14.1, 4.4 Hz, 1H), 2.48 (dd, J = 14.1, 9.2 Hz, 1H), 2.94 (s, 6H), 4.74 (ddd, J = 9.2, 4.4,
1.5 Hz, 1H), 4.85 (bs, 1H), 4.90 (bs, 1H), 6.73 (d, J = 8.8 Hz, 2H), 7.26 (d, J = 8.8 Hz, 2H); 13C-NMR
(CDCl3) δ 22.5, 40.8, 48.0, 71.4, 112.6, 113.7, 126.9, 132.0, 142.9; Anal. C13H19NO: Found C 76.07,
H 9.29, N 6.77%; Calcd C 76.06, H 9.33, N 6.82%; [α]D19 −55.7° (c 1.41, CHCl3) for 90% ee; Daicel
CHIRALCEL OD, UV Detector 254 nm, hexane/i-PrOH = 9:1, flow rate 0.5 mL/min. tR = 15.0 min
(R), 17.4 min (S).
(E)-1-(p-Dimethylaminophenyl)-3-methyl-1,5-hexadien-3-ol (6e). IR (neat) ν 3631, 3397, 2926, 2801,
1
1611, 1447, 1167, 965, 804 cm−1; H-NMR (CDCl3) δ 1.79 (d, J = 2.8 Hz, 1H), 1.80 (bs, 3H), 2.34
(d, J = 6.6 Hz, 2H), 2.96 (s, 6H), 4.40 (tdd, J = 6.6, 6.6, 2.8 Hz, 1H), 4.85 (bs, 1H), 4.90 (bs, 1H), 6.03
(dd, J = 15.7, 6.6 Hz, 1H), 6.54 (d, J = 15.7 Hz, 1H),6.68 (d, J = 8.8 Hz, 2H), 7.28 (d,
13
J = 8.8 Hz, 2H); C-NMR (CDCl3) δ 22.7, 40.6, 46.5, 70.6, 112.5, 113.6, 125.3, 127.6, 130.0, 130.5,
142.4, 150.3; Anal. C15H21NO: Found C 76.07, H 9.29, N 6.77%; Calcd C 76.06, H 9.33, N 6.82%;
20
[α]D −30.2° (c 1.66, CHCl3) for 84% ee; Daicel CHIRALCEL OD, UV Detector 254 nm,
hexane/i-PrOH = 9:1, flow rate 0.5 mL/min. tR = 20.0 min (R), 21.1 min (S).
3.4. Synthesis and X-ray Analysis of (i-Pr-Phebox)RhCl2 (κ-3a)
(i-Pr-Phebox)RhCl2 (κ-3a). To a stirred solution of i-Pr-1 (200 mg, 0.41 mmol) in dichloromethane
(5 mL) was added 3a (39 μL, 0.41 mmol) at ambient temperature. After it was stirred for 2 h, the
mixture was concentrated under reduced pressure. Purification of the residue by silica gel
chromatography (dichloromethane/ether = 1:1) gave (i-Pr-Phebox)RhCl2(κ-3a) in 84% yield (200 mg).
Orange solid. mp. 203-205 °C (decomp); IR (KBr) ν 2958, 1711, 1620, 1485, 1394, 1214, 963,
739 cm−1; 1H-NMR (CDCl3) δ 0.64 (d, J = 6.8 Hz, 6H), 0.73 (d, J = 6.8 Hz, 6H), 1.37 (dsept, J = 2.8,
6.8 Hz, 2H), 4.04 (ddd, J = 10.0, 6.4, 2.8 Hz, 2H), 4.62 (dd, J = 8.8, 6.4 Hz, 2H), 4.74 (dd, J = 10.0,
8.8 Hz, 2H), 7.30 (t, J = 7.6 Hz, 1H), 7.65 (d, J = 7.6 Hz, 2H), 7.79 (dd, J = 7.6, 5.6 Hz, 1H), 8.49 (dd,
J = 7.6, 1.6 Hz, 1H), 10.07 (dd, J = 5.6, 1.6 Hz, 1H), 10.27 (s, 1H), 10.30 (d, J = 1.6 Hz, 1H);
13C-NMR (CDCl3) δ 15.1, 19.2, 29.4, 66.9, 71.1, 123.3, 125.2, 128.1, 131.6, 132.6, 136.6, 155.1,
157.2, 172.4 (JRh-C = 3.4 Hz), 185.9 (JRh-C = 19.7 Hz), 189.8; Anal. C24H28Cl2N3O3Rh: Found C 49.62,
H 4.86, N 7.22%; Calcd C 49.67, H 4.86, N 7.24%. X-ray-quality crystals of (i-Pr-Phebox)RhCl2(κ-3a)
was obtained from benzene-ether-hexane at room temperature and mounted in glass capillary.
Diffraction experiments were performed on a Rigaku AFC-7R four-circle diffractometer equipped with
graphite-monochromated Mo K〈 radiation; ⎣ = 0.71069 Å. The lattice parameters and an orientation
matrix were obtained and refined from 25 machine-centered reflections with 29.82 < 2⎝ < 29.97°.
Intensity data were collected using a ⎤-2⎝ scan technique, and three standard reflections were recorded

Molecules 2011, 16
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every 150 reflections. The data were corrected for Lorentz and polarization effects. The structure was
solved by direct methods [27] and expanded using Fourier techniques [28]. The non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included but not refined. The final cycle of full-
matrix least-squares refinement was based on 5306 observed reflections (I > 3⌠(I)) and 598 variable
parameters. Neutral atom scattering factors were taken from Cromer and Waber [29]. All calculations
were performed using the teXsan crystallographic software package [30]. Final refinement details are
collected in Table 5 and the numbering scheme employed is shown in Figure 2, which was drawn with
ORTEP at 30% probability ellipsoid. Crystallographic data (excluding structure factors) for the
structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre
as supplementary publication no. CCDC-826794. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK (fax: (+44)1223-336-033; e-mail:
deposit@ccdc.cam.ac.uk).
Table 5. Crystallographic data and structure refinement for (i-Pr-Phebox)RhCl2(κ-3a).
Empirical Formula
Formula Weight
C48H58N6O7Cl4Rh2
1178.65
Temperature
Scan type
23.0 °C
ω-2θ
Crystal Dimensions
Crystal System
Lattice Type
Lattice Parameters: a
0.15 × 0.5 × 0.5 mm
monoclinic
C-centered
18.307(4) Å
14.886(5) Å
21.056(4) Å
106.55(2) deg
5500(2) Å3
C2 (#5)
Scan Width
2θmax
No. of Reflection
94 3tanθ deg
55.0 deg
Total: 6787
measured
b
c
No. of Unique data
Structure Solution
Refinement
6581 (Rint = 0.018)
Direct methods
Full-matrix
least squares
5306 (I>3σ(I))
598
β
Volume
Space Group
Z value
Dcalcd
F(000)
No. of Observations
No. of Variables
Reflection/Parameter
Ratio
4
1.423 g/cm3
2408.00
8.87
μ(Mo Kα)
λ
8.44 cm−1
Residuals: R; Rw
0.058; 0.077
0.71069 Å
4. Conclusions
In this paper, we have described the catalytic enantioselective addition of allyl- and
methallyltributyltin reagents to amino aldehydes catalyzed with air-stable and water tolerant chiral
Phebox-Rh(III) aqua complexes. The reactions proceed under mild conditions to afford the
corresponding homoallylic alcohols with modest to good enantioselectivity (up to 94% ee), and these
aqua complexes can be recovered from the reaction media by column chromatography. We have
clarified that the chiral (Phebox)RhX2 fragments (X = Cl, Br), generated by releasing water molecule
from (Phebox)RhX2(H2O), capture amino aldehydes at the carbonyl oxygen and the reaction proceeded
via a Lewis acid mechanism.

Molecules 2011, 16
5399
Acknowledgements
This work was partly supported by a Grant-in-Aid for Scientific Research from the Ministry of
Education, Science and Culture, Japan.
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Sample availability: Samples of the complexes 1 and 2 are available from the authors.
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distributed under the terms and conditions of the Creative Commons Attribution license
(http://creativecommons.org/licenses/by/3.0/).