Enantioselective synthesis of arylglycine derivatives by Asymmetric Addition of arylboronic acids to imines

Article abstract of DOI:10.1071/CH11225

Rhodium-catalyzed enantioselective 1,2-additions of arylboronic acids to N-tosyl furanylimine and lithium 5-methyl-2-furanyltriolborate to N-tosyl arylimines giving aryl(2-furanyl)methanamines were developed for enantioselective synthesis of arylglycines

Full text of DOI:10.1071/CH11225

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2011, 64, 1447–1453
Full Paper
http://dx.doi.org/10.1071/CH11225
Enantioselective Synthesis of Arylglycine Derivatives
by Asymmetric Addition of Arylboronic Acids to Imines
A B
,
A
A
Yasunori Yamamoto,
and Norio Miyaura
Yoshinori Takahashi, Kazunori Kurihara,
A
A
Division of Chemical Process Engineering, Graduate School of Engineering,
Hokkaido University, Sapporo 060-8628, Japan.
B
Corresponding author. Email: yasuyama@eng.hokudai.ac.jp
Rhodium-catalyzed enantioselective 1,2-additions of arylboronic acids to N-tosyl furanylimine and lithium 5-methyl-
2-furanyltriolborate to N-tosyl arylimines giving aryl(2-furanyl)methanamines were developed for enantioselective
synthesis of arylglycines by ozonolysis of the furyl ring. A chiral N-linked C2-symmetric bidentate phosphoramidite
(N-Me-BIPAM) achieved high enantioselectivities up to 99 % ee. For the direct synthesis of arylglycines, the asymmetric
addition of arylboronic acids to ethyl N-p-methoxyphenyl iminoester was carried out at 808C in dioxane in the presence of
Rh(acac)(C2H4)2/(R,R)-N-Me-BIPAM. The reaction gave optically active arylglycines in up to 99 % ee.
Manuscript received: 2 June 2011.
Manuscript accepted: 24 August 2011.
Published online: 16 November 2011.
Introduction
attempts to arylate imines with heteroarylboronic acids, such as
2-fulylboronic acid, were unsuccessful because of competitive
B–C bond cleavage with water relative to the addition reaction.
This is attributable to the high coordination ability of hetero-
atoms to catalysts and slow transmetalation and insertion of
electron-deficient heteroaryl rings. Thus, we recently developed
tetracoordinated ate-complexes of boronic esters for metal
catalyzed reactions in non-aqueous media.[35–40] Initially, we
chose arylation of N-tosyl-2-furylimine for the synthesis of
N-tosyl-aryl(furyl)methanamine (Table 1). The Rh(acac)(C2H4)2
(acac ¼ acetylacetonate) previously used for addition of aryl-
boronic acids to N-tosylaldimines resulted in lower selectivities
(75 % ee, entry 1).[30] The reaction took place smoothly in
dimethoxyethane (DME) at 508C for 16 h in the presence
of Rh(acac)((R,R)-N-Me-BIPAM) with 97 % yield and
96 % ee (entry 2). Results of the arylation of N-tosyl-2-
furylimine with representative arylboronic acids at 508C in
DME are summarized in Table 1. High enantioselectivities
were achieved with donating or withdrawing substituents at the
boronic acids.
Next, we tried the addition reaction of 2-furylboronic acid
derivatives (4a–d) to 4-methoxybenzylaldehyde N-tosylimine
(2c) (Table 2). The best selectivity was obtained with lithium
5-methylfuryltriolborate (4c) (entry 3), whereas 2-furyboronic
acid or 2-furyltriolborate resulted in lower selectivities than that
of 4c. Furthermore, no desired product was obtained with
lithium 5-methoxyfuryltriolborate (4d) (entry 8). By further
investigation of the reaction conditions, 4c was finally obtained
in 62 % yield and 99 % ee using 3 mol-% Rh(acac)(C2H4)2/
3.3 mol-% (R,R)-N-Me-BIPAM in toluene (4 mL) at 1008C for
16 h (entry 6).
Arylglycines are a particularly important class of amino acids
because they are components of several pharmaceutical agents,
including glycopeptide antibiotics, antibacterial agents, and
cardiovascular drugs.[1] The synthesis of a-amino acids has been
dominated by the Strecker reaction and variants thereof.[2]
Multicomponent reactions based on isonitriles (Ugi reaction)
have also been developed but they are usually multistep and
suffer from side reactions.[3,4] The addition of arylboronic acids
to imino acids by Petasis reaction is a powerful method for
arylglycine synthesis.[5,6] The asymmetric rhodium-catalyzed
addition of arylboron reagents and arylstannanes to imines has
been reported.[7–19] Recently, Ellman has reported an elegant
method for the asymmetric synthesis of a-amino acids by the
rhodium-catalyzed addition of arylboronic acids to N-tert-
butanesulfinylimine, which precedes in high yield with high
diastereoselectivity for both electron-rich and electron-poor
arylboronic acids.[20–23] N-tert-butanesulfinyl protected aryl-
glycine derivatives have also been synthesized by the transition
metal-catalyzed addition of arylboronic acids to N-tert-butane-
sulfinyl imino esters.[23–25] We recently reported a chiral
N-linked C2-symmetric bidentate phosphoramidite ((R,R)-N-
Me-BIPAM)[26–29] that was newly developed for the rhodium-
catalyzed enantioselective addition of arylboronic acids to
N-sulfonylimines. This ligand achieved high enantioselec-
tivities.[30] As part of our program to develop a catalyzed
reaction of organoboronic acids with a rhodium or palladium
catalyst, we report here the synthesis of chiral arylglycine
derivatives by using enantioselective addition of arylboron
reagents to imines (Scheme 1).
Results and Discussion
Lithium 5-methyl-2-furyltriolborate (4c) was smoothly added
to N-tosyl-arylimines in moderate yields and with excellent
enantiomeric excess under optimized conditions (Table 3).
Furyl rings are excellent synthons of the hydroxycarbonyl group
that allow various syntheses of amino acids.[31–35] However,
Journal compilation Ó CSIRO 2011
www.publish.csiro.au/journals/ajc

1448
Y. Yamamoto et al.
PG
H
N
ArB(OH)2 (3)
PG
O
HN
*
Rh catalyst
O
[O]
R
PG
1
FG
HN
*
PG
H
5
N
CO2RЈ
4a–d
R ϭ H, Me, MeO
FG
Rh catalyst
FG
PG
N
7
ArB(OH)2 (3)
PG ϭ Ts or PMP
RЈ ϭ H or Et
2
Rh catalyst
EtO2C
H
6
Liϩ
Liϩ
O
Liϩ
O
B
O
BϪ
BϪ
B(OH)2
O
O
O
O
O
O
N
O
O
O
O
O
O
O
P
MeO
O
P
4a
4b
4c
4d
NMe2 Me2N
8: (R,R)-N-Me-BIPAM
Scheme 1. FG: functional group, PG: protecting group.
Table 1. Arylation of N-tosyl-2-furylimine (1)A
Rh(acac)((R,R)-N-Me-BIPAM)
NHTs
NTs
O
(3 mol-%)
O
ϩ
ArB(OH)2
Ar
DME, 50ЊC, 16 h
H
3 (1.5 eq.)
1
5
Entry
Ar
Yield [%]
ee [%]
1
C6H5 (3a)
C6H5 (3a)
89 (5a)
97 (5a)
91 (5b)
93 (5c)
99 (5d)
86 (5e)
75 (5f)
76 (5g)
84 (5h)
93 (5i)
54 (5j)
75B (S)
96 (S)
2
3
4-MeC6H4 (3b)
4-MeOC6H4 (3c)
3-MeOC6H4 (3d)
4-CF3C6H4 (3e)
3-CF3C6H4 (3f)
3-ClC6H4 (3g)
93 (ꢀ)
99B (þ)
95B (ꢀ)
98B (ꢀ)
98 (ꢀ)
95 (ꢀ)
99 (þ)
90 (þ)
95C (ꢀ)
4
5
6
7
8
9
3-BrC6H4 (3h)
10
11
3,4-(CH2O2)C6H3 (3i)
3-F-4-BrC6H4 (3j)
AA mixture of furylimine (0.5 mmol), ArB(OH)2 (0.75 mmol), Rh(acac)((R,R)-N-Me-BIPAM) (3 mol-%) in dimethoxyethane (2 mL)
was stirred at 508C for 16 h.
BRh(acac)(C2H4)2 (3 mol-%)/(R,R)-N-Me-BIPAM (3.3 mol-%) was used instead of Rh(acac)((R,R)-N-Me-BIPAM) (from ref. [30]).
CDetermined at 808C.
The furyl rings thus synthesized are excellent synthons of a
carboxylic acid group in various syntheses of carboxylic
acids.[31–35] Ozone is used for the oxidation of the furyl rings
because a combination of RuCl3 and NaIO4 resulted in a complex
mixture of several products. Thus, ozonolysis of 5h and 5m in
methanol smoothly occurred at ꢀ788C to yield the corresponding
arylglycine derivatives in 87 and 82 % NMR yield, respectively
(Scheme 2).
For the direct synthesis of arylglycines, then we tried the
asymmetricaddition of arylboronicacids toiminoesters (Table 4).
We investigated the reaction of ethyl N-tosyliminoacetate
with phenylboronic acid in the presence of Rh(acac)(C2H4)2
(3 mol-%) and (R,R)-N-Me-BIPAM (3.3. mol-%) in DME at
508C for 16 h; the addition product was obtained in only 19 %
yield. The p-methoxyphenyl (PMP)-protected iminoester could
be synthesized in one step and in high yield from ethyl
glyoxylate.[41] The resulting products could be deprotected
under mild conditions using cerium ammonium nitrate.
Moreover, the PMP-protected iminoesters are more stable than
their corresponding imines such as tosylimine. When ethyl
N-p-methoxyphenyliminoester was used, the yield increased
to 51 %. Finally, the reaction took place smoothly in dioxane at
508C in the presence of 3.0 equivalents of phenylboronic acid
with 74 % yield and 96 % ee (entry 4). High enantioselectivities
were achieved in most arylboronic acids having donating or
withdrawing substituents at the para or meta carbons. In

Asymmetric Addition of Arylboronic Acids to Imines
1449
Table 2. Addition of 2-furylboron reagent to aryliminesA
Rh catalyst (3 mol-%)
(R,R)-N-Me-BIPAM (3.3 mol-%)
NHTs
BX
NTs
H
O
O
ϩ
MeO
R
solvent, 16 h
R
MeO
2c
4
5
Entry
4 (eq.)
Rh catalystB
SolventC
Temp. [8C]
Yield [%]
ee [%]
1
2
3
4
5
6
7
8
4a (1.5)
4b (2.0)
4c (2.0)
4c (2.0)
4c (2.0)
4c (2.0)
4c (2.0)
4d (2.0)
Rh(acac)(C2H4)2
Rh(acac)(C2H4)2
Rh(acac)(C2H4)2
Rh(acac)(C2H4)2
Rh(acac)(coe)2
Rh(acac)(coe)2
[Rh(nbd)2]BF4
Rh(acac)(C2H4)2
DME
80
80
34
30
65
85
89
92
99
96
ND
DME
71
DME
80
34
Toluene
Toluene
Toluene
Toluene
DME
80
56
80
50
100
80
62
43
80
Trace
AA mixture of arylimine (0.5 mmol), 3, Rh catalyst (3 mol-%)/(R,R)-N-Me-BIPAM (3.3 mol-%) in solvent (2 mL) was stirred for 16 h.
Bacac: acetylacetonate, coe: cyclooctene, nbd: 2,5-norbornadiene.
CDME (dimethoxyethane) or toluene (4 mL) was used.
Table 3. Addition of lithium 5-methyl-2-furyltriolborate (4c) to aryliminesA
Liϩ
NHTs
Rh(acac)(coe)2 (3 mol-%)
O
NTs
H
(R,R)-N-Me-BIPAM (3.3 mol-%)
BϪ
O
Ar
O
O
Ar
ϩ
toluene, 16 h
O
2
4c (2.0 eq.)
5
Entry
Ar
Temp. [8C]
Yield [%]
ee [%]
1
2
3
4
5
6
7
8
9
C6H5 (2a)
100
90
62 (5k)
56 (5l)
62 (5m)
44 (5n)
64 (5o)
41 (5p)
51 (5q)
45 (5r)
44 (5s)
93 (þ)
89 (þ)
99 (þ)
96 (þ)
96 (þ)
66 (þ)
96 (ꢀ)
94 (þ)
98 (þ)
4-MeC6H4 (2b)
4-MeOC6H4 (2c)
3-MeOC6H4 (2d)
2-MeOC6H4 (2e)
4-CF3C6H4 (2f)
4-BrC6H4 (2g)
3-ClC6H4 (2h)
2-ClC6H4 (2i)
100
100
100
70
70
70
70
AA mixture of arylimine (0.5 mmol), 3 (1.0 mmol), Rh(acac)(coe)2 (3 mol-%)/(R, R)-N-Me-BIPAM (3.3 mol-%)
in toluene (4 mL) was stirred for 16 h (acac: acetylacetonate, coe: cyclooctene).
Rh catalyst
(R,R)-N-
Me-BIPAM
NHTs
Br
NTs
NHTs
Br
O
O3
O
H
Br
ϩ
B(OH)2
HO2C
MeOH
Ϫ78ЊC
30 min
5h (76 %, 95 % ee)
7a (82 % NMR yield)
1
3h
Liϩ
Rh catalyst
(R,R)-N-
Me-BIPAM
NTs
NHTs
O
O
NHTs
CO2H
BϪ
O3
H
O
O
ϩ
O
MeOH
Ϫ78ЊC
30 min
MeO
MeO
5m (62 %, 99 % ee)
Scheme 2.
MeO
7b (87 % NMR yield)
2c
4c

1450
Y. Yamamoto et al.
Table 4. Arylation of iminoestersA
Rh(acac)(C2H4)2 (3 mol-%)
NHPG
NPG
H
(R,R)-N-Me-BIPAM (3.3 mol-%)
EtO2C
ArB(OH)2
ϩ
EtO2C
Ar
solvent, 80ЊC, 22 h
6
3
7
(PG: protecting group, Ts: p-toluenesulfonyl, PMP: p-methoxyphenyl, DME: dimethoxyethane)
Entry
PG
Ar (eq.)
Solvent
Yield [%]
ee [%]
1
Ts
C6H5 (3a) (1.5)
DME
19B (7c)
51B (7c)
60B (7c)
74 (7c)
84 (7d)
73 (7e)
67 (7f)
47 (7g)
77 (7h)
57 (7i)
68 (S)
98 (S)
2
PMP
PMP
PMP
PMP
PMP
PMP
PMP
PMP
PMP
PMP
PMP
C6H5 (3a) (1.5)
DME
3
C6H5 (3a) (1.5)
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
96 (S)
4
C6H5 (3a) (3.0)
96 (S)
5
4-MeC6H4 (3b) (3.0)
4-MeOC6H4 (3c) (3.0)
3-MeOC6H4 (3d) (3.0)
4-ClC6H4 (3k) (3.0)
3,4-(CH2O2)C6H3 (3i) (3.0)
4-HOC6H4 (3l) (3.0)
3-HOC6H4 (3m) (3.0)
3-BocHNC6H4 (3n) (3.0)
97 (þ)
97 (þ)
96 (þ)
98 (þ)
96 (þ)
90 (þ)
99.7 (þ)
99 (þ)
6
7
8
9
10
11
12
61 (7j)
54 (7k)
AA mixture of iminoester (0.5 mmol), ArB(OH)2, Rh(acac)(C2H4)2 (3 mol-%)/(R,R)-N-Me-BIPAM (3.3 mol-%) in dioxane (2 mL) was stirred at 808C for 22 h.
BDetermined after 16 h.
addition, functional groups such as hydroxy and amino groups
were tolerated (entries 10–12).
(s, 3H), 2.37 (s, 3H), 5.39 (d, J 7.7, 1H), 5.56 (d, J 7.7, 1H),
5.99 (d, J 3.2, 1H), 6.17 (dd, J 1.8, 3.2, 1H), 7.02–7.06 (m, 4H),
7.14 (d, J 8.2, 2H), 7.20 (d, J 1.4, 1H), 7.57 (d, J 8.2, 2H).
dC (CDCl3, 100 MHz) 21.2, 21.6, 55.4, 108.3, 110.3, 127.2,
129.3, 129.4, 135.4, 137.4, 137.9, 142.6, 143.2, 152.5. m/z
(HR-ESI) Calc. for C19H19NO3SNa: 364.0983 [M þ Na]þ.
Found: 364.0977.
Conclusion
In summary, we have developed an efficient and highly
enantioselective synthesis of arylglycines by using asymmetric
addition of arylboronic acids to N-tosyl 2-furylimines or ethyl
PMP-iminoesters. Furthermore, asymmetric addition of lithium
5-methyl-2-furyltriolborate to N-tosyl aryl imines has been
achieved with high enantioselectivity. We have demonstrated
the high efficiency of (R,R)-N-Me-BIPAM and lithium
2-furyltriolborate for enantioselective 1,2-addition to imines.
With this catalyst system, a broad range of enantiopure aryl-
glycines are easily prepared.
N-[2-(Furanyl)(4-methoxyphenyl)methyl]-4-methylbenzene-
sulfonamide (5c):[30] [a]D24 þ2.54 (c 0.65, CHCl3), 88 % ee,
{lit.:[30] [a]2D2 þ2.79 (c 0.45, CHCl3) (99 % ee)}.
N-[2-(Furanyl)(3-methoxyphenyl)methyl]-4-methylbenzene-
sulfonamide (5d):[30] [a]D24 ꢀ5.88 (c 0.26, CHCl3), 89 % ee
{lit.:[30] [a]2D4 ꢀ150.71 (c 0.32, CHCl3) (95 % ee)}.
N-[2-(Furanyl)(4-trifluoromethylphenyl)methyl]-4-methyl-
benzenesulfonamide (5e):[30] [a]D24 ꢀ10.24 (c 0.57, CHCl3),
95 % ee {lit.:[30] [a]D23 ꢀ10.95 (c 0.56, CHCl3) (98 % ee)}.
N-[2-(Furanyl)(3-trifluoromethylphenyl)methyl]-4-methyl-
benzenesulfonamide (5f): [a]2D4 ꢀ5.80 (c 0.85, CHCl3), 98 % ee
(HPLC analysis: Chiralcel AS-H, hexane/EtOH ¼ 10/1, flow ¼
0.5 mL minꢀ1, l 230 nm, tR 38.3 and 53.8 min). dH (CDCl3,
400 MHz) 2.35 (s, 3H), 5.66 (d, J 7.7, 1H), 5.74 (d, J 7.7, 1H),
5.99 (d, J 3.2, 1H), 6.18–6.20 (m, 1H), 7.12 (d, J 8.2, 2H),
7.24 (t, J 0.9, 1H), 7.33–7.47 (m, 4H), 7.55 (d, J 8.2, 2H). dC
(CDCl3, 100 MHz) 21.5, 55.2, 108.8, 110.5, 124.1, 124.2, 124.9
(2C), 127.1, 129.2, 129.5, 130.9, 137.0, 139.2, 143.1, 143.7,
151.4. m/z (HR-ESI) Calc. for C19H16F3NO3SNa: 418.0701
[M þ Na]þ. Found: 418.0695.
Experimental
Arylation of N-Tosyl-2-furylimine
A flask was charged with Rh(acac)((R,R)-N-Me-BIPAM)
(0.015 mmol, 3 mol-%), N-tosyl-2-furylimine (0.5 mmol), and
arylboronic acid (0.75 mmol) under a nitrogen atmosphere.
DME (2.0 mL) was added to the flask and the mixture was then
stirred at 508C for 16 h, at which time the crude reaction mixture
was extracted using ethyl acetate, washed with saturated NH4Cl
and brine, and dried over MgSO4. Chromatography of the crude
reaction mixture on silica gel gave (S)-N-(2-(furanyl)(phenyl)
methyl)-4-methylbenzenesulfonamide (5a)[14,16,18,19,30] in 97 %
yield and 96 % ee. [a]D24 ꢀ10.66 (c 0.83, CHCl3) {lit.[14] for
(S)-5a: [a]2D0 ꢀ21.6 (c 1.03, CHCl3) (99 % ee); lit.[16] for (R)-5a:
[a]D20 þ4.6 (c 0.50, CHCl3) (85 % ee); lit.[18] for (S)-5a:
[a]2D0 ꢀ14.9 (c 0.98, CHCl3) (99 % ee); lit.[19] for (S)-5a: [a]2D0
ꢀ9.6 (c 0.76, CHCl3) (81 % ee); lit.:[14] [a]D25 ꢀ10.8 (c 0.37,
CHCl3) (75 % ee)}.
N-[(3-Chlorophenyl)(2-furanyl)methyl]-4-methylbenzene-
sulfonamide (5g): [a]2D4 ꢀ2.81 (c 0.51, CHCl3), 95 % ee (HPLC
analysis: Chiralcel AS-H, hexane/propan-2-ol ¼ 4/1, flow ¼
0.5 mL minꢀ1, l 230 nm, tR 51.2 and 62.0 min). dH (CDCl3,
400 MHz) 2.37 (s, 3H), 5.56 (d, J 8.2, 1H), 5.61 (d, J 8.2, 1H),
5.98 (d, J 3.2, 1H), 6.18 (dd, J 1.8, 3.2, 1H), 7.09–7.22 (m, 7H),
7.56 (d, J 8.6, 2H). dC (CDCl3, 100 MHz) 21.6, 55.1, 108.7,
110.4, 125.6, 127.1, 127.6, 128.2, 129.5, 129.9, 134.5, 137.1,
140.2, 142.9, 143.6, 151.5. m/z (HR-ESI) Calc. for
C18H16ClNO3SNa: 384.0437 [M þ Na]þ. Found: 384.0432.
N-(2-(Furanyl)(p-tolyl)methyl)-4-methylbenzenesulfonamide
(5b): [a]2D4 ꢀ1.43 (c 1.31, CHCl3), 93 % ee (HPLC analysis:
Chiralcel AS-H, hexane/propan-2-ol ¼ 4/1, flow ¼ 0.5 mL minꢀ1
,
l 230 nm, tR 48.6 and 56.1 min). dH (CDCl3, 400 MHz) 2.29

Asymmetric Addition of Arylboronic Acids to Imines
1451
N-[(3-Bromophenyl)(2-furany)methyl]-4-methylbenzene-
sulfonamide (5h): [a]2D4 þ0.93 (c 0.67, CHCl3), 99 % ee
(HPLC analysis: Chiralcel AS-H, hexane/propan-2-ol ¼ 4/1,
flow ¼ 0.5 mL minꢀ1, l 230 nm, tR 55.2 and 73.8 min).
dH (CDCl3, 400 MHz) 2.39 (s, 3H), 5.19 (d, J 7.3, 1H), 5.58
(d, J 7.3, 1H), 6.00 (d, J 3.2, 1H), 6.21 (dd, J 1.8, 3.2, 1H),
7.10–7.18 (m, 4H), 7.25 (d, J 9.1, 2H), 7.34–7.36 (m, 1H),
7.56 (d, J 8.6, 2H). dC (CDCl3, 100 MHz) 21.6, 55.0, 108.8,
110.4, 122.7, 126.1, 127.2, 129.5, 130.2, 130.4, 131.2,
137.1, 140.3, 143.0, 143.6, 151.4. m/z (HR-ESI) Calc. for
C18H16BrNO3SNa: 427.9932 [M þ Na]þ. Found: 427.9926.
N-[(5-Benzo[1,3]dioxolyl)(2-furanyl)methyl]-4-methyl-
benzenesulfonamide (5i): [a]2D4 þ13.61 (c 0.56, CHCl3), 90 %
ee (HPLC analysis: Chiralcel OD-H, hexane/propan-2-ol ¼
95/5, flow ¼ 0.5 mL minꢀ1, l 230 nm, tR 90.0 and 97.5 min).
(HPLC analysis: Chiralcel OD-H, hexane/EtOH ¼ 9/1, flow¼
1.0 mLminꢀ1, l 230 nm, tR 12.9 and 14.7min). dH (CDCl3,
400 MHz) 2.09 (s, 3H), 2.38 (s, 3H), 3.77 (s, 3H), 5.14
(d, J 7.3, 1H), 5.50 (d, J 7.7, 1H), 5.74 (dd, J 0.9, 3.2, 1H), 5.83
(d, J 3.2, 1H), 6.76 (d, J 8.6, 2H), 7.11 (d, J 8.6, 2H), 7.16 (d, J 7.7,
2H), 7.57 (d, J 8.6, 2H). dC (CDCl3, 100 MHz) 13.5, 21.6,
55.2, 55.3, 106.1, 109.3, 113.9, 127.2, 128.6, 129.3, 130.6,
137.5, 143.1, 150.5, 152.3, 159.3. m/z (HR-ESI) Calc. for
C20H21NO4SNa: 394.1089 [Mþ Na]þ. Found: 394.1086.
N-[(3-Methoxyphenyl)(5-methyl-2-furanyl)methyl]-4-methyl-
benzenesulfonamide (5n): [a]2D4 þ0.60 (c 0.05, CHCl3), 96 % ee
(HPLC analysis: Chiralcel OD-H, hexane/EtOH¼ 10/1, flow ¼
0.5 mL minꢀ1, l 230 nm, tR 20.0 and 21.0 min). dH (CDCl3,
400MHz) 2.10 (s, 3H), 2.38 (s, 3H), 3.71 (s, 3H), 5.18 (d, J 7.7,
1H), 5.53 (d, J 7.3, 1H), 5.74 (d, J 2.3, 1H), 5.85 (d, J 3.2, 1H),
6.72–6.80 (m, 3H), 7.14–7.18 (m, 3H), 7.58 (d, J 8.2, 2H).
dC (CDCl3, 100 MHz) 13.5, 21.6, 55.3, 55.6, 106.2, 109.5,
112.9, 113.6, 119.7, 127.2, 129.3, 129.6, 137.5, 139.9, 143.1,
150.1, 152.4, 159.7. m/z (HR-ESI) Calc. for C20H21NO4SNa:
394.1089 [M þ Na]þ. Found: 394.1084.
d
H (CDCl3, 400 MHz) 2.37 (s, 3H), 5.45 (d, J 7.3, 1H), 5.50
(d, J 7.7, 1H), 5.89 (dd, J 1.4, 5.9, 2H), 6.00 (d, J 3.2, 1H),
6.18 (dd, J 1.8, 3.2, 1H), 6.63–6.67 (m, 3H), 7.16 (d, J 8.2,
2H), 7.21 (d, J 1.4, 1H), 7.58 (d, J 8.2, 2H). dC (CDCl3,
100 MHz) 21.6, 55.4, 101.3, 107.9, 108.2, 108.3, 110.3,
121.0, 127.2, 129.4, 132.2, 137.4, 142.6, 143.3, 147.4,
147.8, 152.3. m/z (HR-ESI) Calc. for C19H17NO5SNa:
394.0725 [M þ Na]þ. Found: 394.0721.
N-[(2-Methoxyphenyl)(5-methyl-2-furanyl)methyl]-4-methyl-
benzenesulfonamide (5o): [a]2D3 þ11.86 (c 0.23, CHCl3), 96% ee
(HPLC analysis: Chiralcel OD-H, hexane/EtOH ¼ 10/1, flow¼
1.0 mLminꢀ1, l 230 nm, tR 8.9 and 10.2min). dH (CDCl3,
400 MHz) 2.12 (s, 3H), 2.34 (s, 3H), 3.69 (s, 3H), 5.66 (d, J 9.1,
1H), 5.74 (d, J 9.5, 2H), 5.80 (d, J 2.7, 1H), 6.71 (d, J 8.2, 1H),
6.81 (ddd, J 0.9, 7.7, 15.0, 1H), 7.09 (d, J 7.7, 3H), 7.15–7.19
(m, 1H), 7.56 (d, J 8.2, 2H). dC (CDCl3, 100MHz) 13.6, 21.5,
52.9, 55.4, 106.2, 108.3, 111.0, 120.8, 126.2, 127.1, 129.1, 129.2
(2C), 137.7, 142.8, 150.8, 151.9, 156.6. m/z (HR-ESI) Calc. for
C20H21NO4SNa: 394.1089 [Mþ Na]þ. Found: 394.1083.
4-Methyl-N-[(5-methyl-2-furanyl)(4-trifluoromethylphenyl)
methyl]-benzenesulfonamide (5p): [a]2D4 þ7.45 (c 0.25, CHCl3),
66 % ee (HPLC analysis: Chiralcel OD-H, hexane/EtOH ¼ 10/1,
flow ¼ 1.0 mL minꢀ1, l 230 nm, tR 11.9 and 14.5 min). dH
(CDCl3, 400 MHz) 2.12 (s, 3H), 2.37 (s, 3H), 5.37 (d, J 7.3,
1H), 5.60 (d, J 7.3, 1H), 5.75 (dd, J 0.9, 3.2, 1H), 5.82 (d, J 3.2,
1H), 7.13 (d, J 8.2, 2H), 7.33 (d, J 8.2, 2H), 7.46 (d, J 8.2, 2H),
7.54 (d, J 8.6, 2H). dC (CDCl3, 100 MHz) 13.5, 21.5, 55.3, 106.3,
109.8, 125.4, 125.5(2C), 127.2, 127.9, 129.4, 137.2, 142.2,
143.5, 149.3, 153.0. m/z (HR-ESI) Calc. for C20H18F3NO3SNa:
432.0857 [M þ Na]þ. Found: 432.0853.
N-[(4-Bromo-3-fluorophenyl)(2-furanyl)methyl]-4-methyl-
benzenesulfonamide (5j): [a]2D4 ꢀ4.35 (c 0.59, CHCl3), 96 % ee
(HPLC analysis: Chiralcel AS-H, hexane/propan-2-ol ¼ 4/1,
flow ¼ 0.5 mL minꢀ1, l 230 nm, tR 43.1 and 48.2 min). dH
(CDCl3, 400 MHz) 2.39 (s, 3H), 5.55 (d, J 7.7, 1H), 5.67
(d, J 7.7, 1H), 5.98 (d, J 3.2, 1H), 6.19 (dd, J 1.8, 3.2, 1H),
6.89 (dd, J 1.8, 8.2, 1H), 6.92–6.95 (m, 1H), 7.16 (d, J 8.6, 2H),
7.23 (d, J 1.8, 1H), 7.39 (dd, J 7.3, 8.2, 1H), 7.56 (d, J 8.2, 2H).
dC (CDCl3, 100 MHz) 21.6, 54.7, 108.8, 110.5, 115.5, 115.8,
124.3, 127.1, 129.5, 133.6, 137.0, 140.0, 143.1, 143.8, 151.0,
158.9. m/z (HR-ESI) Calc. for C18H15BrFNO3SNa: 445.9838
[M þ Na]þ. Found: 445.9832.
Addition of Lithium 5-Methyl-2-furyltriolborate
to Arylimines
A flask was charged with Rh(acac)(coe)2 (coe ¼ cyclooctene)
(0.015mmol, 3 mol-%) and (R,R)-N-Me-BIPAM (0.0165mmol,
3.3 mol-%) under a nitrogen atmosphere. Toluene (4.0 mL)
was added to the flask and the mixture was then stirred at
room temperature for 1 h to prepare the catalyst. Arylimine
(2a, 0.5 mmol) and lithium 5-methyl-2-furyltoriolborate (4c,
1.0 mmol) were then added to this catalyst solution. The reaction
mixture was stirred at 1008C for 16h, at which time the crude
reaction mixture was extracted using ethyl acetate, washed with
saturated NH4Cl and brine, and dried over MgSO4. Chromatog-
raphy of the crude reaction mixture on silica gel gave 4-methyl-
N-[(5-methyl-2-furanyl)(phenyl)methyl]benzenesulfonamide[42]
(5k) in 65% yield and 93% ee. [a]2D4 þ37.25 (c 0.15, CHCl3).
4-Methyl-N-[(5-methyl-2-furanyl)(p-tolyl)methyl]-benzene-
sulfonamide (5l): [a]2D4 þ14.62 (c 0.63, CHCl3), 89 % ee (HPLC
analysis: Chiralcel OD-H, hexane/EtOH ¼ 10/1, flow ¼ 1.0 mL
minꢀ1, l 230 nm, tR 7.1 and 9.7 min). dH (CDCl3, 400 MHz)
2.09 (s, 3H), 2.30 (s, 3H), 2.38 (s, 3H), 5.11 (d, J 7.7, 1H), 5.51
(d, J 7.3, 1H), 5.73 (dd, J 0.9, 3.1, 1H), 5.84 (d, J 3.2, 1H), 7.01–
7.10 (m, 4H), 7.15 (d, J 8.2, 2H), 7.58 (d, J 8.2, 2H). dC (CDCl3,
100 MHz) 13.5, 21.2, 21.6, 55.4, 106.1, 109.3, 127.2, 129.2,
129.3, 135.5, 137.8, 143.1, 150.4, 152.3. m/z (HR-ESI) Calc. for
C20H21NO3SNa: 378.1140 [M þ Na]þ. Found: 378.1134.
N-[(4-Methoxyphenyl)(5-methyl-2-furanyl)methyl]-4-methyl-
benzenesulfonamide (5m): [a]2D4 þ13.73 (c 0.12, CHCl3), 99 % ee
N-[(4-Bromophenyl)(5-methyl-2-furanyl)-methyl]-4-methyl-
benzenesulfonamide (5q): [a]2D4 ꢀ5.43 (c 0.07, CHCl3), 96 % ee
(HPLC analysis: Chiralcel OD-H, hexane/EtOH ¼ 10/1, flow ¼
1.0 mL minꢀ1, l 230 nm, tR 8.1 and 11.4 min). dH (CDCl3,
400 MHz) 2.09 (s, 3H), 2.39 (s, 3H), 5.46 (d, J 7.7, 1H), 5.49
(d, J 7.7, 1H), 5.74 (d, J 2.3, 1H), 5.81 (d, J 3.2, 1H), 7.08 (d,
J 8.6, 2H), 7.15 (d, J 8.6, 2H), 7.33 (d, J 8.6, 2H), 7.55 (d, J 8.2,
2H). dC (CDCl3, 100 MHz) 13.4, 21.5, 55.0, 106.1, 109.5, 121.9,
127.1, 129.0, 129.3, 131.5, 137.1, 137.3, 143.3, 149.5, 152.6. m/z
(HR-ESI) Calc. for C19H18BrNO3SNa: 442.0088 [M þ Na]þ.
Found: 442.0087.
N-[(3-Chlorophenyl)(5-methyl-2-furanyl)methyl]-4-methyl-
benzenesulfonamide (5r): [a]2D4 þ91.35 (c 0.21, CHCl3), 94 % ee
(HPLC analysis: Chiralcel OD-H, hexane/EtOH ¼ 10/1, flow ¼
0.5 mL minꢀ1, l 230 nm, tR 17.1 and 18.9 min). dH (CDCl3,
400 MHz) 2.10 (s, 3H), 2.38 (s, 3H), 5.44 (d, J 7.7, 1H), 5.52 (d,
J 7.7, 1H), 5.74 (d, J 2.3, 1H), 5.83 (d, J 3.2, 1H), 7.11–7.18
(m, 6H), 7.56 (d, J 8.2, 2H). dC (CDCl3, 100 MHz) 13.5, 21.6,
55.2, 106.3, 109.6, 125.7, 127.2, 127.6, 128.1, 129.4, 129.8,
134.4, 137.2, 140.4, 143.4, 149.5, 152.8. m/z (HR-ESI) Calc. for
C19H18ClNO3SNa: 398.0588 [M þ Na]þ. Found: 398.0591.

1452
Y. Yamamoto et al.
N-[(2-Chlorophenyl)-(5-methyl-2-furanyl)methyl]-4-methyl-
(4-Hydroxyphenyl)(4-methoxyphenylamino)acetic acid ethyl
ester (7i): [a]2D4 þ78.80 (c 0.46, CHCl3), 90 % ee (HPLC analysis:
benzenesulfonamide (5s): [a]2D4 þ4.45 (c 0.20, CHCl3), 98 % ee
(HPLC analysis: Chiralcel OD-H, hexane/EtOH¼ 10/1, flow ¼
0.5 mL minꢀ1, l 230nm, tR 16.0 and 17.0 min). dH (CDCl3,
400 MHz) 2.11 (s, 3H), 2.37 (s, 3H), 5.47 (d, J 7.3, 1H), 5.75
(d, J 2.7, 1H), 5.77 (d, J 3.2, 1H), 5.96 (d, J 7.3, 1H), 7.14–7.17
(m, 4H), 7.24–7.27 (m, 1H), 7.34–7.37 (m, 1H), 7.63 (d, J 8.2,
2H). dC (CDCl3, 100MHz) 13.5, 21.6, 52.8, 106.4, 109.5, 127.0,
127.3, 129.1, 129.2, 129.4, 129.7, 132.9, 135.9, 137.1, 143.3,
149.2, 152.7. m/z (HR-ESI) Calc. for C19H18ClNO3SNa:
398.0588 [M þ Na]þ. Found: 398.0592.
Chiralcel OD-H, hexane/EtOH ¼ 10/1, flow ¼ 0.5 mL minꢀ1
,
l 230 nm, tR 29.7 and 32.6 min). dH (CDCl3, 400MHz) 1.20
(t, J 7.3, 3H), 3.71 (s, 3H), 4.08–4.26 (m, 2H), 4.93 (s, 1H), 6.53
(d, J 9.1, 2H), 6.71–6.78 (m, 4H), 7.32 (d, J 8.6, 2H).
dC (CDCl3, 100 MHz) 14.2, 55.8, 61.2, 61.8, 114.9, 115.8,
128.7, 129.8, 140.3, 152.5, 155.7, 172.6. m/z (HR-ESI) Calc.
for C17H19NO4Na: 324.1206 [M þ Na]þ. Found: 324.1212.
(3-Hydroxyphenyl)(4-methoxyphenylamino)acetic acid ethyl
ester (7j): [a]2D4 þ7.38 (c 1.10, CHCl3), 99.7% ee (HPLC
analysis: Chiralcel As-H, hexane/propan-2-ol¼ 4/1, flow ¼ 0.5
mLminꢀ1, l 230 nm, tR 24.1 and 30.8 min). dH (CDCl3,
400MHz) 1.22 (t, J 7.3, 3H), 3.72 (s, 3H), 4.15–4.31 (m, 2H),
4.73 (br s, 1H), 5.00 (s, 1H), 6.73–6.75 (m, 4H), 6.85–6.92
(m, 2H), 7.20–7.26 (m, 2H). dC (CDCl3, 100MHz) 14.1,
55.7, 62.5, 62.9, 114.8, 117.6, 117.9, 120.3, 121.2, 129.4,
129.9, 139.1, 154.6, 156.8, 171.4. m/z (HR-ESI) Calc. for
C17H19NO4Na: 324.1206 [Mþ Na]þ. Found: 324.1212.
Arylation of Iminoesters
A flask was charged with Rh(acac)(C2H4)2 (0.015 mmol, 3 mol-%)
and (R,R)-N-Me-BIPAM (0.0165 mmol, 3.3 mol-%) under a
nitrogen atmosphere. Dioxan (2.0 mL) was added to the flask
and the mixture was then stirred at room temperature for 1 h to
prepare the catalyst. PMP iminoester (6, 0.5 mmol) and phe-
nylboronic acid (3a, 1.5 mmol) were then added to this catalyst
solution. The reaction mixture was stirred at 808C for 22 h, at
which time the crude reaction mixture was extracted using ethyl
acetate, washed with saturated NH4Cl and brine, and dried over
MgSO4. Chromatography of the crude reaction mixture on silica
gel gave (S)-(4-methoxyphenylamino)phenylacetic acid ethyl
ester[43,44] (7c) in 74 % yield and 96 % ee. [a]2D4 þ69.33 (c 0.31,
CHCl3) {lit.[43] for (R)-7c: [a]D20 ꢀ107.8 (c 0.68, CHCl3) (96 %
ee); lit.[44] for (R)-7c: [a]D20 ꢀ77.0 (c 0.4, CHCl3) (92 % ee)}.
(4-Methoxyphenylamino)(p-tolyl)acetic acid ethyl ester[43,44]
(7d): [a]2D4 þ90.20 (c 0.31, CHCl3), 97 % ee, {lit.:[43] [a]2D0 ꢀ74.5
(c 0.92, CHCl3) (96 % ee); lit.:[44] [a]D20 ꢀ86.4 (c 0.4, CHCl3)
(93 % ee)}.
(3-tert-Butoxycarbonylaminophenyl)(4-methoxyphenylamino)
acetic acid ethyl ester (7k): [a]2D4 þ61.73 (c 0.08, CHCl3),
99% ee (HPLC analysis: Chiralcel AD-H, hexane/propan-2-ol
¼ 4/1, flow¼ 1.0 mL minꢀ1, l 230 nm, tR 13.3 and 18.1 min). dH
(CDCl3, 400 MHz) 1.20 (t, J 7.3, 3H), 1.50 (s, 9H), 3.69 (s, 3H),
4.07–4.26 (m, 2H), 4.67 (br s, 1H), 4.95 (s, 1H), 6.51 (d, J 9.1, 2H),
6.69–6.73 (m, 2H), 7.15 (d, J 7.7, 1H), 7.24–7.28 (m, 1H), 7.39–
7.41 (m, 2H). dC (CDCl3, 100 MHz): 14.2, 28.4, 55.8, 61.6, 61.9,
80.7, 114.8, 114.9, 116.9, 118.3, 121.9, 129.5, 139.0 (2C), 140.3,
152.5, 152.7, 172.0. m/z (HR-ESI) Calc. for C22H28N2O5Na:
423.1890 [Mþ Na]þ. Found: 423.1892.
Acknowledgements
(4-Methoxyphenyl)(4-methoxyphenylamino)acetic acid ethyl
ester[43,44] (7e): [a]D24 þ86.05 (c 0.22, CHCl3), 97 % ee, {lit.:[43]
[a]2D0 ꢀ64.4 (c 0.46, CHCl3) (94 % ee); lit.:[44] [a]2D0 ꢀ82.0 (c 0.2,
CHCl3) (91 % ee)}.
This work was supported in part by the Global COE Program (Project
No. B01, Catalysis as the Basis for Innovation in Materials Science) from the
Ministry of Education, Culture, Sports, Science, and Technology, Japan.
(3-Methoxyphenyl)(4-methoxyphenylamino)acetic acid ethyl
ester (7f): [a]2D4 þ71.71 (c 0.30, CHCl3), 96 % ee (HPLC
analysis: Chiralcel AD-H, hexane/propan-2-ol ¼ 4/1, flow ¼
1.0 mL minꢀ1, l 230 nm, tR 12.8 and 15.1 min). dH (CDCl3,
400 MHz) 1.21 (t, J 7.3, 3H), 3.70 (s, 3H), 3.78 (s, 3H), 4.08–
4.26 (m, 2H), 4.63 (br s, 1H), 4.96 (s, 1H), 6.51–6.55 (m, 2H),
6.70–6.74 (m, 2H), 6.83 (ddd, J 0.9, 1.8, 8.2, 1H), 7.03–7.04
(m, 1H), 7.08 (d, J 7.7, 1H), 7.24–7.28 (m, 1H). dC (CDCl3,
100 MHz) 14.2, 55.3, 55.8, 61.8, 61.9, 112.8, 113.8, 114.8,
114.9, 119.7, 129.9, 139.6, 140.3, 152.5, 160.0, 172.0. m/z
(HR-ESI) Calc. for C18H21NO4Na: 338.1363 [M þ Na]þ.
Found: 338.1366.
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4.65 (br s, 1H), 4.90 (s, 1H), 5.92–5.93 (m, 2H), 6.52 (d, J 7.7,
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100 MHz) 14.2, 55.8, 61.3, 61.9, 101.3, 107.6, 108.5, 114.8,
114.9, 120.9, 131.9, 140.2, 147.6, 148.1, 152.5, 172.1. m/z
(HR-ESI) Calc. for C18H19NO5Na: 352.1155 [M þ Na]þ.
Found: 352.1156.

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