Enantioselective Diels-Alder Reaction Induced by Chiral Supramolecular Lewis Acid Catalysts Based on CN?B and PO?B Coordination Bonds

Article abstract of DOI:10.1055/s-0035-1561362

Chiral supramolecular boron Lewis acid catalysts were prepared from chiral 3-phosphoryl-1,1′-bi-2-naphthols, (2-cyanophenyl)boronic acids, and tris(pentafluorophenyl)borane, bound through CN···B and PO···B coordination bonds. In particular, the coordinated tris(pentafluorophenyl)boranes increase the Lewis acidity of the active center in the manner of a Lewis acid assisted Lewis acid catalyst system. A possible cavity in these catalysts was highly suitable for several Diels-Alder probe reactions of acroleins with cyclic or acyclic dienes, which gave the corresponding adducts in good to high yields and high enantio-selectivities.

Full text of DOI:10.1055/s-0035-1561362

SYNLETT
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©
Georg Thieme Verlag Stuttgart · New York
2016, 27, A–G
A
cluster
Synlett
M. Hatano et al.
Cluster
Enantioselective Diels–Alder Reaction Induced by Chiral Supra-
molecular Lewis Acid Catalysts Based on CN···B and PO···B Coordi-
nation Bonds
Manabu Hatano
Kazushi Hayashi
Tatsuhiro Sakamoto
Yuma Makino
Kazuaki Ishihara*
Graduate School of Engineering, Nagoya University, Furo-cho,
Chikusa, Nagoya 464-8603, Japan
shihara@cc.nagoya-u.ac.jp
Received: 09.12.2015
Accepted: 12.01.2016
Published online: 05.02.2016
DOI: 10.1055/s-0035-1561362; Art ID: st-2015-u0955-c
tion bond to generate a new type of chiral supramolecular
catalyst. In particular, the CN moiety would be an attractive
option at the ortho-position of arylboronic acids, where it
should exert both a steric effect and an electron-withdraw-
ing effect on the active boron center (Figure 1, b). Here, we
report the chiral Lewis acid catalysts 2, based on CN···B and
PO···B coordination bonds, for enantioselective Diels–Alder
reactions of various acroleins with cyclic or acyclic dienes.
Abstract Chiral supramolecular boron Lewis acid catalysts were pre-
pared from chiral 3-phosphoryl-1,1′-bi-2-naphthols, (2-cyanophe-
nyl)boronic acids, and tris(pentafluorophenyl)borane, bound through
CN···B and PO···B coordination bonds. In particular, the coordinated
tris(pentafluorophenyl)boranes increase the Lewis acidity of the active
center in the manner of a Lewis acid assisted Lewis acid catalyst system.
A possible cavity in these catalysts was highly suitable for several Diels–
Alder probe reactions of acroleins with cyclic or acyclic dienes, which
gave the corresponding adducts in good to high yields and high enantio-
selectivities.
Key words supramolecular catalysts, asymmetric catalysis, Diels–Al-
der reactions, Lewis acids, dienes, aldehydes
Making the most of coordinative interactions is the
principal approach used in the construction of conforma-
tionally flexible complexes based on supramolecular chem-
istry, as reflected in early work by Lehn and others.1 If
suitable small molecules are added through acid–base
,2
3
chemistry, tailor-made chiral supramolecular catalysts can
be fine-tuned in situ without producing any associated
waste. In this regard, we previously developed chiral supra-
molecular Lewis acid catalysts such as 1 (Figure 1, a), which
are highly effective for enantioselective Diels–Alder reac-
4–6
tions with anomalous endo/exo-selectivities.
In catalyst
1
, two bulky tris(pentafluorophenyl)borane moieties are
7,8
coordinated to phosphoryl (PO) groups to form a deep
chiral cavity. Moreover, the coordinated tris(pentafluoro-
phenyl)boranes increase the Lewis acidity of the active bo-
ron center by means of a Lewis acid assisted Lewis acid cat-
alyst system. In this context, we surmised that we might be
possible to use CN···B(C F )
9
Figure 1 Design of chiral supramolecular catalysts containing
10
as another useful coordina-
6
5
3
PO···B(C F ) and CN···B(C F ) coordination bonds
6 5 3 6 5 3
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–G

B
Synlett
M. Hatano et al.
Cluster
First, we examined the Diels–Alder reaction of meth-
acrolein (4a) with cyclopenta-1,3-diene (3) in dichloro-
O
11
methane at –78 °C in the presence of the chiral supramo-
lecular catalyst 6 (10 mol%). Catalyst 6 is a simple analogue
of catalyst 1, prepared in situ from (R)-3,3′-bis(phosphor-
yl)-BINOL (BINOL = 1,1′-bi-2-naphthol), (2-cyano-5-fluoro-
phenyl)boronic acid, and tris(pentafluorophenyl)borane
O
P
O
B(C6F5)3
O
B(C6F5)3
B
N
O
C
(Scheme 1). Unfortunately, the enantioselectivity toward
O
the product exo-(2S)-5a was low (6% ee).
O
P
O
B(C6F5)3
F
2a
93%, 89% ee (exo-(2S)-5a)
endo-5a:exo-5a = 4:96
O
B(C6F5)3
O
P
B(C6F5)3
B(C6F5)3
B
O
N
O
O
C
O
O
N
O
O
P
O
6 5 3
B(C F )
C
F
B
2b
9
4%, 91% ee (exo-(2S)-5a)
endo-5a:exo-5a = 4:96
O
B(C6F5)3
B
N
O
P
O
C
F
O
O
B(C6F5)3
O
O
6
(10 mol%)
F3C
P
O
6 5 3
B(C F )
+
(2SC) HO
2c
+
CHO
4a
MS 4Å, CH2Cl2
–78 ºC, 3 h
(2S)
CHO
endo-(2S)-5a
8
9%, 98% ee (exo-(2S)-5a)
endo-5a:exo-5a = 3:97
O
3
B(C6F5)3
B
exo-(2S)-5a
N
a
96%, 90% ee (exo-(2S)-5a)
O
>
99% (endo-5a:exo-5a = 9:91)
C
6
% ee (exo)
endo-5a:exo-5a = 4:96
Scheme 1 Diels–Alder reaction of methacrolein (4a) with cyclopenta-
1,3-diene (3) in the presence of chiral supramolecular catalyst 6
2d
O
O
CF3
P
O
B(C6F5)3
88%, 94% ee (exo-(2S)-5a)
endo-5a:exo-5a = 4:96
To avoid excessive interaction between the three bulky
tris(pentafluorophenyl)borane moieties, we replaced (R)-
,3′-bis(phosphoryl)-BINOL with (R)-3-phosphoryl-BINOL
Figure 2). As a result, the enantioselectivity toward 5a was
dramatically improved: 5a was obtained in 93% yield and
9% ee when we used catalyst 2a. Replacement of the
O
B(C6F5)3
B
3
(
N
O
C
O
O
2e
P
O
B(C6F5)3
8
binaphthyl skeleton in 2a with the octahydrobinaphthyl
skeleton in 2b slightly improved the enantioselectivity to-
ward 5a (91% ee). Moreover, replacement of the 5-fluoro
group in the arylboronic acid moiety of 2b with a 5-trifluo-
romethyl moiety in 2c improved the enantioselectivity to-
99%, 77% ee (exo-(2S)-5a)
endo-5a:exo-5a = 4:96
O
B(C6F5)3
B
N
O
C
Me
2f
11
ward 5a to 98% ee. In a control experiment, catalyst 2d,
with a 4-trifluoromethyl moiety, was slightly less effective
than catalyst 2c in terms of its enantioselectivity. Moreover,
catalyst 2e with no substituents and catalyst 2f with a 5-
methyl group were both much less effective than 2c.
9
7%, 49% ee (exo-(2S)-5a)
endo-5a:exo-5a = 6:94
Figure 2 Chiral supramolecular catalysts 2 for the Diels–Alder reaction
of methacrolein (4a) with cyclopenta-1,3-diene (3). The reaction was
carried out in the presence of 2 (10 mol%) and 4 Å MS at –78 °C for 3 h.
The reaction was carried in the presence of 2c (10 mol%) and an addi-
tional 5 mol% of B(C F ) .
We next examined the effect of a bulky 3-substituent on
the binaphthyl skeleton of the catalyst. In place of
PO···B(C F ) in catalyst 2c, we used a bulky electron-with-
a
6
5 3
6
5 3
drawing 3,5-[3,5-(F C) C H ] C H moiety in catalyst 7a
3
2
6
3
2
6
3
(
Figure 3). Catalyst 7a was also found to be effective in the
reaction of methacrolein (4a) with cyclopenta-1,3-diene
3), and gave 5a in 96% yield and 84% ee. In sharp contrast,
catalyst 7b with a less bulky 3,5-(F C) C H moiety was less
than that in the presence of 7a (84% ee). Moreover, the cata-
lytic activity of 2c might also be higher than that of 7a, be-
cause the enantioselectivity with catalyst 2c in the pres-
ence of an additional 5 mol% of B(C F ) was still high (90%
(
3
2
6
3
6 5 3
effective in inducing enantioselectivity, and gave 5a in 50%
ee. Overall, when we compared 2c with 7a, the enantiose-
lectivity of 5a in the presence of 2c (98% ee) was higher
ee), unlike the case of 7a with an additional 5 mol% of
B(C F ) (66% ee) [see footnotes a in Figures 2 and 3].
6
5 3
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Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–G

C
Synlett
M. Hatano et al.
Cluster
CF3
(a)
F3C
(2SC) HO
Et
catalyst (10 mol%)
+
Et
2S)
+
(
Et
CHO
MS 4Å, CH2Cl2
–78 ºC, 3 h
CHO
CF3
3
4b
endo-(2S)-5b
exo-(2S)-5b
2
7
c (10 mol%):
a (10 mol%):
>99% (endo-5b:exo-5b = 3:97), 85% ee (exo)
>99% (endo-5b:exo-5b = 2:98), 92% ee (exo)
O
CF3
B(C6F5)3
(b)
B
(2RC) HO
N
catalyst (10 mol%)
+
O
Br
C
+
(
2R)
Br
Br
CHO
MS 4Å, CH2Cl2
–78 ºC, 3 h
CHO
3
4c
endo-(2R)-5c
exo-(2R)-5c
F3C
7a
2
c (10 mol%):
98% (endo-5c:exo-5c = 10:90), 44% ee (exo)
[96% (endo-5c:exo-5c = 8:92), 52% ee (exo)]a
98% (endo-5c:exo-5c = 9:91), 0% ee (exo)
9
6%, 84% ee (exo-(2S)-5a)
endo-5a:exo-5a = 2:98
7a (10 mol%):
a
9
1%, 66% ee (exo-(2S)-5a)
endo-5a:exo-5a = 4:96
(c)
(2SC) HO
catalyst (10 mol%)
+
+
(2S)
F3C
CHO
CHO
MS 4Å, CH2Cl2
–78 ºC, 3 h
3
4d
endo-(2S)-5d
exo-(2S)-5d
CF3
2c (10 mol%):
80% (endo-5d:exo-5d = 1:>99), 91% ee (exo)
16% (endo-5d:exo-5d = 1:>99), 28% ee (exo)
7a (10 mol%):
(
d)
O
B
B(C6F5)3
(2SC) HO
N
catalyst (10 mol%)
+
H
O
+
(2S)
H
C
H
CHO
MS 4Å, CH2Cl2
–78 ºC, 3 h
CHO
3
4e
endo-(2S)-5e
exo-(2S)-5e
F3C
7b
2c (10 mol%):
89% (endo-5e:exo-5e = 76:24), 86% ee (endo)
89% (endo-5e:exo-5e = 73:27), 42% ee (endo)
7a (10 mol%):
8
7%, 50% ee (exo-(2S)-5a)
endo-5a:exo-5a = 7:93
(
e)
CO2Et
CHO
EtO2C
(2R)
3R)
(3R)
(2R)
Figure 3 Chiral supramolecular catalysts 7 for the Diels–Alder reaction
of methacrolein (4a) with cyclopenta-1,3-diene (3). The reaction was
carried out in the presence of 10 mol% of 7a and an additional 5 mol%
+
(
a
catalyst (10 mol%)
+
CHO
endo-(2R,3R)-5f
2
CO Et
H
CHO
MS 4Å, CH2Cl2
–78 ºC, 3 h
of B(C F ) .
exo-(2R,3R)-5f
6
5 3
3
4f
2
7
c (10 mol%):
a (10 mol%):
72% (endo-5f:exo-5f = 86:14), 85% ee (endo)
78% (endo-5f:exo-5f = 86:14), 10% ee (endo)
Next, we investigated the range of substrates that are
suitable for use with catalysts 2c and 7a (Scheme 2). The α-
substituted acroleins 2-ethylacrylaldehyde (4b), 2-bromoa-
crylaldehyde (4c), and (2E)-2-methylbut-2-enal (4d; tiglic
aldehyde) were examined. Catalyst 7a was found to be as
effective as catalyst 2c for the reaction of aldehyde 4b with
cyclopenta-1,3-diene (3) (Scheme 2, a). However, for the re-
actions of aldehydes 4c and 4d with diene 3, catalyst 7a was
less effective than catalyst 2c (Scheme 2, b and c). 2-Bromo-
acrylaldehyde (4c) was extremely reactive, and the enantio-
selectivity was low (44% ee) at –78 °C. However, the use of
catalyst 2c at –98 °C improved the enantioselectivity to 52%
ee. Catalyst 2c was also more effective than catalyst 7a in
reactions of α-unsubstituted acroleins, such as acrolein (4e;
Scheme 2, d) or ethyl (2E)-4-oxobut-2-enoate (4f; Scheme
Scheme 2 Reactions of various acroleins 4 with cyclopenta-1,3-diene
(3) in the presence of chiral supramolecular catalysts 2c and 7a. The
reaction was carried out at –98 °C for 3 h.
a
(2RC) HO
H
catalyst (10 mol%)
+
CHO MS 4Å, CH2Cl2
MeO
MeO
–78 ºC, 3 h
8
4a
endo-(2R)-9
2c (10 mol%):
97% (endo-9:exo-9 = >99:1), 85% ee (endo)
95% (endo-9:exo-9 = >99:1), 80% ee (endo)
7a (10 mol%):
Scheme 3 Diels–Alder reaction of methacrolein (4a) with acyclic diene
in the presence of chiral supramolecular catalyst 2c or 7a
8
2
, e).
We also examined the effect of replacing cyclopenta-
,3-diene with the acyclic diene 8 (Scheme 3). As a result,
Overall, in these Diels–Alder reactions of 4a–f in the
presence of catalyst 2c, anomalous endo/exo-selectivities
1
endo-9 was obtained exclusively in 97% yield and 85% ee
when we used catalyst 2c, whereas catalyst 7a gave endo-9
in 95% yield and 80% ee.
were not observed, unlike the case with our previous cata-
lyst 1. Although catalyst 2c might contain a chiral cavity
(see Figure 6), its structure might be too flexible to permit
control of anomalous endo/exo-selectivities. Therefore, the
use of moderately rigid conformationally flexible supramo-
4
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D
Synlett
M. Hatano et al.
Cluster
lecular catalysts such as 1 might be essential to induce
anomalous endo/exo-selectivities. The more flexible cata-
lyst 2c, on the other hand, induced high enantioselectivities
with a relatively wide range of substrates, whereas the
more rigid catalyst 1 showed substrate specificity in induc-
ing high enantioselectivities with anomalous endo/exo-se-
lectivities.
1
4 (10 mol%)
CHO
+
+
CHO
4a
MS 4Å, CH2Cl2
r.t., 30 min
CHO
endo-13
12
exo-13
O
O
B(C F )
O
O
6 5 3
B(C F )
To confirm the roles of the main parts in the optimized
6
5
3
B
B
N
N
12
supramolecular catalysts 2c and 7a, we performed control
experiments with simplified model compounds. First, we
investigated the effect of the CN···B(C F ) moiety in 2c and
C
C
1
4a
14b
39%
Me
6
5 3
6
3%
7a by conducting the reaction of 4a with 3 in the presence
endo-13:exo-13 = 62:38
endo-13:exo-13 = 62:38
of catalyst 10 or 11 (Figure 4); these showed a low catalytic
activity and no catalytic activity, respectively.1 Moreover,
3
5
a was produced as a racemate when catalyst 10 was used.
O
O
O
O
5 3
B(C F )
B(C6F5)3
6
B
B
N
N
The CN···B(C F ) moiety in 2c and 7a is therefore essential
for obtaining the Diels–Alder products in high yields and
high enantioselectivities.
6
5 3
C
C
14
F3C
14c
14d
98%
CF3
9
8%
CF3
endo-13:exo-13 = 61:39
endo-13:exo-13 = 62:38
F3C
a
a
3
3% (–40 °C, 48 h)
15% (–40 °C, 48 h)
endo-13:exo-13 = 65:35
endo-13:exo-13 = 60:40
O
O
CF3
P
O
B(C6F5)3
Scheme 4 Diels–Alder reaction of methacrolein (4a) with cyclohexa-
,3-diene (12) catalyzed by achiral supramolecular catalysts 14. Addi-
a
1
tional control experiments.
O
B
CF3
O
O
O
B
16
CD Cl at –40 °C (Figure 5). We did not observe any shifts
2
2
of the formyl proton (δ = 9.50 ppm) or the formyl carbon
H
10
(
δ = 195.3 ppm) of 4a when we used 2-borylbenzonitrile
3
0%, 0% ee (exo-5a)
11
0%
C
17
endo-5a:exo-5a = 12:88
in the absence of B(C F ) (Figure 5, b). In contrast, when
6
5 3
we used complexes 14a and 14b, a slight upfield shift of the
formyl proton (Δ = –0.02 to Δ = –0.04 ppm) and a slight
downfield shift of the formyl carbon (Δ = +0.3 to Δ = +0.5
ppm) were observed (Figure 5, c and d). Moreover, when we
used complex 14c, which has an electron-withdrawing 5-
trifluoromethyl moiety, a large upfield shift of the formyl
proton (Δ = –0.14 ppm) and a large downfield shift of the
formyl carbon (Δ = +1.6 ppm) were observed (Figure 5, e).
Similar shifts ( H: Δ = –0.14 ppm; C: Δ = +0.8 ppm) were
observed for 14d, which has an electron-withdrawing 4-tri-
fluoromethyl moiety (Figure 5, f). These results suggest that
methacrolein (4a) coordinates better to complex 14c than
to complex 14a, 14b, or 14d. Overall, methacrolein (4a)
should be more activated by 14c than by 14a, 14b, or 14d,
and this observation agrees well with the reaction yields, as
shown in Scheme 4. Moreover, the enantioselectivities in
the reaction of methacrolein (4a) with cyclopenta-1,3-di-
ene (3) in the presence of catalysts 2c–f in Figure 2 can be
rationalized in part, since stronger Lewis acids should acti-
vate the substrate in a shorter distance with low electronic
energies and should better assist in enantiofacial discrimi-
nation of the substrate in comparison with weaker Lewis
acids.18
Figure 4 Control experiments to examine the effect of the
CN···B(C F ) moiety on the yield and enantioselectivity in the reaction
of cyclopenta-1,3-diene (3) with methacrolein (4a). The reaction was
carried out in the presence of catalyst 10 or 11 (10 mol%) and 4 Å MS in
dichloromethane at –78 °C for 3 h.
6
5 3
We conducted our next fundamental control experi-
ments by using the achiral supramolecular catalysts 14a–d,
which contain 4- or 5-substituted arylboronic acid moi-
eties, in the reaction of methacrolein (4a) with the less-re-
active cyclohexa-1,3-diene (12) at room temperature for 30
1
13
15
minutes (Scheme 4). Catalysts 14c and 14d with electron-
withdrawing 5- and 4-trifluoromethyl groups, respectively,
showed high yields, whereas the unsubstituted catalyst 14a
and catalyst 14b with an electron-donating 5-methyl sub-
stituent showed much lower yields. Therefore, an electron-
withdrawing group such as trifluoromethyl appears to be
effective in producing high yields in the Diels–Alder reac-
tions. Moreover, additional control experiments at –40 °C
for 48 hours showed that catalyst 14c has a higher activity
than catalyst 14d (Scheme 4, footnote a).
Additional control experiments by 1H and 13C NMR
spectroscopic analyses were performed by using the achiral
supramolecular catalysts 14a–d and methacrolein 4a in
©
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E
Synlett
M. Hatano et al.
Cluster
(
a)
(b)
Δ(13C): 0 ppm
from TS-15 and TS-16. More information based on experi-
1
Δ( H): 0 ppm
mental and theoretical studies will be needed to discuss
13C: 195.3 ppm
1H: 9.50 ppm
20
further possible structures.
H
O
O
H
B
O
N
C
O
4a
[14a w/o B(C6F5)3] + 4a
(
c)
(d)
Δ(13C): +0.3 ppm
Δ(13C): +0.5 ppm
1
Δ( H): –0.02 ppm
1
Δ( H): –0.04 ppm
H
O
H
O
O
O
B(C6F5)3
B(C6F5)3
B
B
O
N
O
N
C
C
1
4a + 4a
Me
14b + 4a
Δ(13C): +0.8 ppm
(
e)
(f)
Δ(13C): +1.6 ppm
Δ( H): –0.14 ppm
1
Δ( H): –0.07 ppm
1
H
H
O
O
O
O
B(C6F5)3
B(C6F5)3
B
B
O
N
O
N
C
C
F3C
14c + 4a
14d + 4a
CF3
Figure 5 1H and 13C NMR analysis of achiral complexes 14a–d with
methacrolein (4a) in CD Cl at –40 °C
2
2
Finally, we considered possible transition-state struc-
tures for the Diels–Alder reaction of methacrolein (4a) with
cyclopenta-1,3-diene (3) in the presence of supramolecular
catalysts 2c and 7a (Figure 6). For the C -symmetric (R)-3-
1
R-BINOLs, two major intermediates with 4a are shown in
Figure 6 (a and b, respectively). The R substituent of (R)-3-
R-BINOL is located far from the Ar moiety of the arylboronic
acid in Figure 6 (a), whereas it is close to the Ar moiety in
Figure 6 (b). For steric reasons, the intermediate shown in
Figure 6 (a) might be more favored than that shown in Fig-
ure 6 (b). On the basis of this hypothesis, TS-15 in Figure 6
Figure 6 Possible structures and chiral cavities of supramolecular cata-
lysts in transition states (Ar = C F ). (a) Favored intermediate with R far
F
6 5
from the Ar moiety. (b) Disfavored intermediate with R close to the Ar
moiety. (c) Possible TS-15 with catalyst 2c. (d) Possible TS-16 with cata-
lyst 7a.
(c) might be a favored transition state for catalyst 2c. TS-15
has a syn-conformation for the two bulky tris(pentafluoro-
In summary, we have developed conformationally flexi-
ble chiral supramolecular Lewis acid catalysts based on chi-
ral 3-substituted-BINOLs, (2-cyanophenyl)boronic acids,
and tris(pentafluorophenyl)borane and containing a coor-
dination bond between the cyano moiety and tris(pentaflu-
orophenyl)borane. Moreover, a second coordination bond
between the phosphoryl moiety at the 3-position of the
BINOL and tris(pentafluorophenyl)borane might increase
both the catalytic reactivity and enantioselectivity in some
Diels–Alder reactions21 by providing a chiral cavity. In par-
ticular, chiral supramolecular catalyst 2c was effective in
inducing high enantioselectivities in reactions of a variety
of acroleins with cyclic or acyclic dienes. Further investiga-
19
phenyl)borane moieties, which would provide a chiral
cavity around the active boron Lewis acid center. On the
other hand, the much less bulky catalyst 7a might be much
more conformationally flexible than catalyst 2c, and a simi-
lar TS-16, shown in Figure 6 (d), might be a favored transi-
tion state. Consequently, the possible chiral cavity in TS-16
for 7a might be less effective than TS-15 for 2c, which
might explain why catalyst 2c induced generally higher en-
antioselectivity than did catalyst 7a. Through a re-face at-
tack on 4a, which is activated by means of noncovalent in-
17
teractions, exo-(2S)-5a might be reasonably provided
©
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tions of mechanistic aspects and application to other sub-
strates and/or other catalytic asymmetric reactions are cur-
rently underway.
Shibasaki, M. Angew. Chem. Int. Ed. 2000, 39, 1650.
(c) Takamura, M.; Funabashi, K.; Kanai, M.; Shibasaki, M. J. Am.
Chem. Soc. 2000, 122, 6327. (d) Hamashima, Y.; Kanai, M.;
Shibasaki, M. J. Am. Chem. Soc. 2000, 122, 7412. (e) Funabashi,
K.; Ratni, H.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2001,
123, 10784.
Acknowledgment
(
8) We have used the coordinating P=O moiety in some catalytic
processes; see: (a) Hatano, M.; Miyamoto, T.; Ishihara, K. Adv.
Synth. Catal. 2005, 347, 1561. (b) Hatano, M.; Miyamoto, T.;
Ishihara, K. Synlett 2006, 1762. (c) Hatano, M.; Miyamoto, T.;
Ishihara, K. J. Org. Chem. 2006, 71, 6474. (d) Hatano, M.; Takagi,
E.; Ishihara, K. Org. Lett. 2007, 9, 4527. (e) Hatano, M.;
Miyamoto, T.; Ishihara, K. Org. Lett. 2007, 9, 4535. (f) Hatano,
M.; Ishihara, K. Chem. Rec. 2008, 8, 143. (g) Hatano, M.; Ikeno, T.;
Matsumura, T.; Torii, S.; Ishihara, K. Adv. Synth. Catal. 2008, 350,
1776. (h) Hatano, M.; Mizuno, T.; Ishihara, K. Chem. Commun.
Financial support was provided in part by JSPS KAKENHI (15H05755,
2
6288046, and 26105723), Program for Leading Graduate Schools
‘
IGER Program in Green Natural Sciences’, MEXT, Japan.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1561362.
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
2010, 46, 5443. (i) Hatano, M.; Mizuno, T.; Ishihara, K. Synlett
2010, 2024. (j) Hatano, M.; Mizuno, T.; Ishihara, K. Tetrahedron
2011, 67, 4417. (k) Hatano, M.; Gouzu, R.; Mizuno, T.; Abe, H.;
References and Notes
Yamada, T.; Ishihara, K. Catal. Sci. Technol. 2011, 1, 1149.
l) Hatano, M.; Goto, Y.; Izumiseki, A.; Akakura, M.; Ishihara, K.
(
1) Lehn, J.-M. Science 1985, 227, 849.
(
(
2) For recent reviews on supramolecular catalysis, see: (a) Ma, L.;
Abney, C.; Lin, W. Chem. Soc. Rev. 2009, 38, 1248. (b) Corma, A.;
García, H.; Llabrés i Xamena, F. X. Chem. Rev. 2010, 110, 4606.
J. Am. Chem. Soc. 2015, 137, 13472. (m) Hatano, M.; Ishihara, H.;
Goto, Y.; Ishihara, K. Synlett DOI: 10.1055/s-0035-1560369.
9) Yamamoto developed the pioneering concept of combined acid
catalysis. For reviews, see: (a) Ishibashi, H.; Ishihara, K.;
Yamamoto, H. Chem. Rec. 2002, 2, 177. (b) Yamamoto, H.;
Futatsugi, K. Angew. Chem. Int. Ed. 2005, 44, 1924.
(
(c) Meeuwissen, J.; Reek, J. N. H. Nat. Chem. 2010, 2, 615.
(d) Raynal, M.; Ballester, P.; Vidal-Ferran, A.; van Leeuwen, P. W.
N. M. Chem. Soc. Rev. 2014, 43, 1660. (e) Raynal, M.; Ballester, P.;
Vidal-Ferran, A.; van Leeuwen, P. W. N. M. Chem. Soc. Rev. 2014,
(c) Yamamoto, H.; Futatsugi, K. In Acid Catalysis in Modern
43, 1734. (f) Brown, C. J.; Toste, F. D.; Bergman, R. G.; Raymond,
Organic Synthesis; Vol. 1; Yamamoto, H.; Ishihara, K., Eds.;
Wiley-VCH: Weinheim, 2008, 1.
K. N. Chem. Rev. 2015, 115, 3012.
(3) For reviews on acid–base combination chemistry, see: (a) Kanai,
(
10) Focante, F.; Mercandelli, P.; Sironi, A.; Resconi, L. Coord. Chem.
Rev. 2006, 250, 170.
M.; Kato, N.; Ichikawa, E.; Shibasaki, M. Synlett 2005, 1491.
(b) Ishihara, K.; Sakakura, A.; Hatano, M. Synlett 2007, 686.
(c) Ishihara, K. Proc. Jpn. Acad., Ser. 2009, 85, 290.
(d) Shibasaki, M.; Kanai, M.; Matsunaga, S.; Kumagai, N. Acc.
(
11) Dichloromethane was essential for inducing good reactivity and
enantioselectivity in this catalytic system. Toluene, as another
nonpolar solvent, was also effective in promoting the reaction,
although the enantioselectivity decreased significantly (~60%
ee). In contrast, the use of coordinative polar solvent such as
B
Chem. Res. 2009, 42, 1117.
(
4) For anomalous endo-selective Diels–Alder reactions of α-substi-
tuted acroleins, see: (a) Hatano, M.; Mizuno, T.; Izumiseki, A.;
Usami, R.; Asai, T.; Akakura, M.; Ishihara, K. Angew. Chem. Int.
Ed. 2011, 50, 12189. (b) Hatano, M.; Ishihara, K. Chem. Commun.
Et O or THF resulted in almost no catalytic activity.
2
(
(
12) In the ESI-MS (positive mode) analysis of catalyst 2c, a peak for
+
[
2a + H O + H] was observed. See the Supporting Information.
2
2012, 48, 4273.
13) When we compared the catalytic activity of 10, which has a
phosphoryl moiety, to that of 11, which has 3,5-[3,5-
F C) C H ] C H moiety, 10 showed a higher yield. This ten-
(
5) For anomalous exo-selective Diels–Alder reactions of α-nonsub-
stituted acroleins, see: (a) Maruoka, K.; Imoto, H.; Yamamoto, H.
J. Am. Chem. Soc. 1994, 116, 12115. (b) Kündig, E. P.; Saudan, C.
M.; Alezra, V.; Viton, F.; Bernardinelli, G. Angew. Chem. Int. Ed.
a
(
3
2
6
3
2
6
3
dency should be correlated to the reaction using 2c or 7a in the
presence of a competing 5 mol% of B(C F ) (see footnotes a in
6
5 3
2
2
001, 40, 4481. (c) Kano, T.; Tanaka, Y.; Maruoka, K. Org. Lett.
006, 8, 2687. (d) Hayashi, Y.; Samanta, S.; Gotoh, H.; Ishikawa,
Figures 2 and 3).
(
14) The position of the CN group influenced the enantioselectivity.
The use of (3-cyanophenyl)boronic acid or (4-cyanophe-
nyl)boronic acid in place of (2-cyanophenyl)boronic acid in cat-
alyst 10 gave exo-(2S)-5a in ~80% yield with 9% and 11% ee,
respectively.
H. Angew. Chem. Int. Ed. 2008, 47, 6634. (e) Sibi, M. P.; Nie, X.;
Shackleford, J. P.; Stanley, L. M.; Bouret, F. Synlett 2008, 2655.
6) For reviews on the Diels–Alder reaction, see: (a) Kagan, H. B.;
Riant, O. Chem. Rev. 1992, 92, 1007. (b) Du, H.; Ding, K. In Hand-
book of Cyclization Reactions; Ma, S., Ed.; Wiley-VCH: Wein-
heim, 2010, Chap. 1, 1. (c) Ishihara, K.; Sakakura, A. In Science of
Synthesis, Stereoselective Synthesis 3: Stereoselective Pericyclic
Reactions, Cross Coupling, C–H and C–X Activation; Evans, P. A.,
Ed.; Thieme: Stuttgart, 2011, Chap. 3.2, 67.
(
(
(
(
15) Because cyclopentadiene 3 is too reactive to permit the evalua-
tion of meaningful differences in catalytic activity in 14a–d, we
used cyclohexa-1,3-diene (12).
16) 1H and 13C NMR (CD Cl ) analyses of 14 and 4a at room tem-
2
2
perature did not show clear interactions, because a somewhat
broad chart was observed.
17) The C(=O)H···O hydrogen-bonding interaction is well known,
see: (a) Corey, E. J.; Lee, T. W. Chem. Commun. 2001, 1321.
(
7) As a strong Lewis base moiety, a phosphoryl group (P=O) is
highly attractive in asymmetric catalysis. Shibasaki pioneered
the development of catalytic asymmetric cyanosilylation and a
Strecker-type reaction in which Me SiCN is effectively activated
by coordination of a phosphoryl group; see: (a) Hamashima, Y.;
Sawada, D.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 1999, 121,
3
(b) Corey, E. J.; Shibata, T.; Lee, T. W. J. Am. Chem. Soc. 2002, 124,
3808. (c) Ryu, D. H.; Lee, T. W.; Corey, E. J. J. Am. Chem. Soc.
2002, 124, 9992.
2641. (b) Takamura, M.; Hamashima, Y.; Usuda, H.; Kanai, M.;
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M. Hatano et al.
Cluster
(18) Energy profiles and bond distances in boron Lewis acid com-
for 2 h. The resulting substance was cooled to r.t. under N and
2
plexes with coordinating substrates such as aldehydes, ketones,
or pyridines have been studied; see: (a) Reetz, M. T.;
Huellmann, M.; Massa, W.; Berger, S.; Rademacher, P.;
Heymanns, P. J. Am. Chem. Soc. 1986, 108, 2405. (b) LePage, T. J.;
Wiberg, K. B. J. Am. Chem. Soc. 1998, 110, 6642. (c) Wu, D.; Jia,
D.; Liu, L.; Zhang, L.; Guo, J. J. Phys. Chem. A 2010, 114, 11738.
19) The previous supramolecular catalyst 1 was calculated to be in
tris(pentafluorophenyl)borane (51.2 mg, 0.10 mmol) and
freshly distilled CH Cl (2 mL) were added under argon in a
2
2
glove box. The pale-brown mixture was stirred at r.t. for 1 h,
then cooled to –78 °C, and methacrolein 4a (95% purity, 43.4 μL,
0.50 mmol) was added. Freshly distilled cyclopenta-1,3-diene
(3; 210 μL, 2.5 mmol) was then added over 15 min at –78 °C,
and the mixture was stirred at –78 °C for 3 h. To quench the
(
(
(
a
similar C1-symmetric syn-conformation for two bulky
reaction, Et N (0.5 mL) was poured into the reaction mixture at
3
4
tris(pentafluorophenyl)boranes.
–78 °C. The product mixture was directly purified by column
20) Other possible transition states are discussed in the Supporting
Information, which also gives the results for other supramolec-
ular catalysts.
chromatography [silica gel, pentane–Et O (100:1 to 8:1)]. Sol-
2
vents were removed on a rotary evaporator at 15 °C and <200
1
torr to give 5a; yield: 60.8 mg (89%). H NMR (400 MHz, CDCl ):
3
21) Diels–Alder Reaction of Methacrolein (4a) with Cyclopenta-
δ = 0.76 (d, J = 12.0 Hz, 1 H), 1.01 (s, 3 H), 1.39 (m, 2 H), 2.25 (dd,
J = 12.0, 3.9 Hz, 1 H), 2.82 (br s, 1 H), 2.90 (br s, 1 H), 6.11 (dd, J =
1,3-diene (3); Typical Procedure
A
solution of (R)-3-(5,5-dimethyl-2-oxido-1,3,2-dioxaphos-
6.0, 3.0 Hz, 1 H), 6.30 (dd, J = 6.0, 3.0 Hz, 1 H), 9.69 (s, 1 H). 13
C
phorinan-2-yl)-5,5′,6,6′,7,7′,8,8′-H -BINOL (22.1 mg, 0.050
mmol) and [2-cyano-5-(trifluoromethyl)phenyl]boronic acid
NMR (100 MHz, CDCl ): δ = 20.1, 34.6, 43.2, 47.6, 48.5, 53.9,
8
3
+
133.1, 139.6, 205.9. HRMS (EI): m/z [M] calcd for C H12O:
9
(
10.7 mg, 0.050 mmol) in CH Cl (1 mL), THF (0.3 mL), and H O
136.0888; found: 136.0893.
2
2
2
(9 μL, 0.5 mmol) was stirred at r.t. for 12 h in a Pyrex Schlenk
The endo/exo ratio of 5a was determined by 1H NMR (CDCl3)
analysis: δ = 9.40 [s, 1 H, CHO (endo-5a)], 9.69 [s, 1 H, CHO (exo-
5a)] (see ref. 4a). The enantioselectivity and absolute stereo-
chemistry of 5a were determined by GC analysis according to
the reported method (see ref. 4a).
tube under N . Volatile compounds were removed under
2
reduced pressure, and powdered 4 Å MS (250 mg, used as
received from a commercial source) was added. The resulting
white solid was heated at 100 °C (bath temperature) and <5 torr
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2016, 27, A–G