Highly active 3-oxobutylideneaminatocobalt complex catalysts for an enantioselective hetero Diels-Alder reaction

Article abstract of DOI:10.1246/bcsj.74.1333

Optically active 3-oxobutylideneaminatocobalt(III) complexes were developed as effective catalysts for the enantioselective hetero Diels-Alder reaction of aromatic and aliphatic aldehydes with 3-(t-butyldimethylsilyloxy)-1-methoxy-1,3-butadiene. In the presence of the highly active cationic cobalt(III) complex, the hetero Diels-Alder reactions proceeded to afford the corresponding dihydropyran-4-ones with high performance and high enantioselectivities. The reaction with aromatic aldehydes substituted by a coordinating group at the ortho position proceeded more smoothly.

Full text of DOI:10.1246/bcsj.74.1333

Bull. Chem.
Soc. Jpn.
7
4
7
The Chemical © 2001 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 74, 1333–1342 (2001) 1333
Society of Ja-
pan
The Chemical
Society of Ja-
Highly Active 3-Oxobutylideneaminatocobalt Complex Catalysts
pan
OB
7
for an Enantioselective Hetero Diels–Alder Reaction
Chiral Cobalt Catalyst for Hetero DA Reaction
S. Kezuka et al.
1
5
Satoko Kezuka, Tsuyoshi Mita, Natsuki Ohtsuki, Taketo Ikeno, and Tohru Yamada*
2
1
1
001
333
342
Department of Chemistry, Faculty of Science and Technology, Keio University,
Hiyoshi, Kohoku-ku, Yokohama 223-8522
BCSJA8
0
0
1
3
2
3
1
2
009-2673
1030
(
Received January 30, 2001)
0
001
Optically active 3-oxobutylideneaminatocobalt(Ⅲ) complexes were developed as effective catalysts for the enanti-
oselective hetero Diels–Alder reaction of aromatic and aliphatic aldehydes with 3-(t-butyldimethylsilyloxy)-1-methoxy-
1,3-butadiene. In the presence of the highly active cationic cobalt(Ⅲ) complex, the hetero Diels–Alder reactions pro-
ceeded to afford the corresponding dihydropyran-4-ones with high performance and high enantioselectivities. The reac-
tion with aromatic aldehydes substituted by a coordinating group at the ortho position proceeded more smoothly.
6
001
3
4
.2
.9.3
Among the various carbon–carbon bond-forming reactions,
the enantioselective hetero Diels–Alder reaction has emerged
as an important method in synthetic organic chemistry, be-
1
cause carbon–carbon and carbon–oxygen bonds are both
formed to stereoselectively afford six-membered pyran deriva-
tives. Lewis acids have been versatile catalysts for the Diels–
Alder reaction; therefore, much effort has been made to devel-
op efficient organometallic complex catalysts for the enanti-
oselective hetero Diels–Alder reaction. The first report on an
enantioselective catalytic hetero Diels–Alder reaction was at-
Fig. 1. (S)-MPAC (1a).
and selectivity as a catalyst, the choice of the center metal, the
design of the chiral ligand, and the combination of the ligand
with the metal are essential.
2
tempted by Danishefsky et al. The available chiral lanthanide
β-diketonato complex Eu(hfc)
3
was employed as a Lewis acid
Optically active 3-oxobutylideneaminato ligands derived
from the corresponding 3-oxoalkanals and optically active 1,2-
diarylethylenediamines were also employed as effective cata-
lysts in various enantioselective reactions. Their manga-
nese(Ⅲ) complexes catalyzed the aerobic enantioselective oxi-
to achieve 58% ee in the hetero Diels–Alder reaction of ben-
zaldehyde with 1-t-butoxy-2-methyl-3-(trimethylsilyloxy)-1,3-
butadiene (Eq. 1).
1
5
16
dation of alkenes and sulfides, and their corresponding co-
balt(Ⅱ) complexes (Fig. 1) effectively catalyzed the enantiose-
1
7
lective borohydride (tetrahydroborate) reductions of ketones,
1
8
19
imines, and α,β-unsaturated carboxamides, and the enanti-
oselective cyclopropanation of styrene derivatives with diaz-
oacetate. In our previous paper, it was observed that the cor-
2
0
(
1)
responding cobalt(Ⅱ) complexes employed as a chiral Lewis
acid catalyst for the hetero Diels-Alder reactions of aromatic
21
Recently, several groups have reported promising Lewis
acid catalysts for catalytic enantioselective versions of this re-
action. For instance, as typical Lewis acids, high performance
and aliphatic aldehydes with electron-rich diene (Danishef-
sky’s diene) afforded the corresponding dihydropyran-4-ones
3
22
was achieved by chiral (acyloxy)borane catalysts, optically
with high yields and high enantioselectivities. By designing
4
pure binaphthol (BINOL) aluminum catalysts, and chiral
optically active 3-oxobutylideneaminato cationic cobalt(Ⅲ)
complex catalysts, high performance was achieved for the cat-
alytic enantioselective reaction. In this paper, we disclose the
detailed results of a highly enantioselective hetero Diels–Alder
reaction of aromatic and aliphatic aldehydes with electron-rich
dienes catalyzed by optically active 3-oxobutylideneaminato-
cobalt(Ⅲ) complexes.
5
BINOL titanium catalysts. Rare earth metal catalysts, such as
6
chiral yttrium bis-trifluoromethanesulfonylamides and chiral
7
ytterbium(Ⅲ) phosphate, were also proposed for use as effec-
tive Lewis acids. Remarkable development was recently re-
ported for the chiral transition-metal-based Lewis acid cata-
8
lysts; e.g., the chiral salen chromium(Ⅲ) complex, the corre-
9
10
sponding cobalt and ruthenium complexes, bis(3-acylcam-
1
1
12
13
Results and Discussion
phorato)oxovanadium, bis(oxazoline)copper and zinc
complexes, and the BINAP-palladium(Ⅱ) complex were em-
1
4
Various Metal Complexes with the Optically Active 3-
ployed as a chiral Lewis acid. In order to achieve a high ability
Oxobutylideneaminato Ligand. Various metal complexes

1
334 Bull. Chem. Soc. Jpn., 74, No. 7 (2001)
Chiral Cobalt Catalyst for Hetero DA Reaction
4
with the optically active 3-oxobutylideneaminato ligand were
prepared and their catalytic activities for the hetero Diels–Al-
der reaction were examined. In the presence of 5.0 mol% of
each complex catalyst, the hetero Diels–Alder reaction of o-
methoxybenzaldehyde (3a) with 3-(t-butyldimethylsilyloxy)-
aluminum complexes were often employed as effective Lewis
acid catalysts, their optically active 3-oxobutylideneaminato
complexes were not efficient catalysts for the present hetero
Diels-Alder reaction (Entries 1 and 2). The copper(Ⅱ) com-
1
2
plexes with the bis(oxazoline) ligands and the chromium(Ⅲ)
complexes with salen-type ligands were reported to be effec-
2
3
8
1
-methoxy-1,3-butadiene (2) was tried in dichloromethane
solution at −20 °C (Table 1). After the treatment of the crude
product with trifluoroacetic acid, the optical yield of the ob-
tained dihydropyran-4-one derivative was determined by
tive as Lewis acid catalysts for the hetero Diels-Alder reaction;
however, the corresponding 3-oxobutylideneaminato complex-
es were not employed (Entries 3 and 4). When the 3-oxobutyl-
ideneaminatomanganese(Ⅲ), nickel(Ⅱ), or oxovanadium(Ⅳ)
complex catalyst was subjected to the reaction, the racemic
product was only obtained in low yield (Entries 5, 6, and 7).
On the contrary, in the presence of a catalytic amount of the
optically active 3-oxobutylideneaminatocobalt(Ⅱ) complex
catalyst ((S)-MPAC), the hetero Diels–Alder reaction smoothly
proceeded to afford the corresponding dihydropyran-4-one
with moderate enantioselectivity (Entry 8).
5
HPLC analysis (Chiralpak AD). Although titanium and
Table 1. Various Metal Complex Catalysts with Optically
Active 3-Oxobutylideneaminato Ligand for Asymmetric
Hetero Diels–Alder Reaction
Enantioselective Hetero Diels–Alder Reaction in Various
Solvents. Solvation influences the steric factor of the Lewis
acid catalysts and the stereochemistry. A nonpolar solvent was
conventionally used for Lewis acid catalyzed reactions, while
the coordination of the solvent would be sometimes effective
a)
Entry
Time/h
Yield/
%
Ee/
%
b)
c)
3a,12f,24
for the stereoselectivities.
As shown in Table 2, the
product yields and enantiomer excesses were quite dependent
on the solvent used. In dichloromethane, fluorobenzene, and
toluene, a more than 95% yield of the product was obtained
and the optical yields were 62%, 57%, and 50%, respectively
(Entries 2–4). The solvents, such as acetonitrile, diethyl ether,
and tetrahydrofuran, however, decreased the catalytic activity,
since their coordination to the cobalt complexes changed the
stereochemical configuration in the intermediate (Entries 5–7).
The 3-oxobutylideneaminatocobalt catalysts were not dis-
solved in hexane and afforded the products in low yield with
low enantioselectivities (Entry 8). In order to avoid lowering
the yield and the enantiomer excess, a halogenated or aromatic
solvent was utilized. Dichloromethane was chosen as the reac-
tion solvent due to its high yield and high enantioselectivity.
Temperature Effect in Enantioselective Hetero Diels–
Alder Reaction. The reaction temperature dependence was
examined for the hetero Diels-Alder reaction using o-methox-
ybenzaldehyde (3a) (Table 3). At room temperature, 80% of
1
2
3
4
5
6
7
8
Ti(Ⅳ)Cl
A Ⅲ)Cl
Cu(Ⅱ)
Cr(Ⅲ)Cl
Mn(Ⅲ)Cl
Ni(Ⅱ)
V(Ⅳ)wO
Co(Ⅱ)
2
92
92
30
30
30
41
92
55
23
23
trace
10
15
41
4
1
—
0
0
0
l(
32
96
6
62
a) Reaction conditions: metal complex catalyst 0.025 mmol
5.0 mol%), dienophile 0.5 mmol, and diene 1.0 mmol at
20 °C in CH Cl . b) Isolated yield after the treatment with
CF COOH. c) Determined by HPLC analysis using Chiral-
(
−
2
2
3
pak AD (0.5% 2-propanal in hexane).
Table 2. Various Solvents for Asymmetric Hetero Diels–
Alder Reaction
Table 3. Temperature Effect for Asymmetric Hetero Diels–
Alder Reaction o-Methoxybenzaldehyde
a)
b)
c)
Entry
Solvent
—
Time/h
Yield/%
Ee/%
1
2
3
4
5
6
7
8
24
55
72
47
95
47
70
98
89
96
96
quant
44
32
51
62
57
50
59
56
—
46
CH
PhF
Toluene
CH CN
Et
2
Cl
2
a)
b)
c)
Entry
Temp/°C
Time/h
Yield/%
Ee/%
3
1
2
3
4
r.t.
30
55
55
77
80
96
85
23
25
62
60
38
2
O
−20
−40
−78
THF
Hexane
trace
28
a) Reaction conditions: Co(Ⅱ) complex catalyst 0.025
mmol (5.0 mol%), dienophile 0.5 mmol, and diene 1.0
mmol at −20 °C. b) Isolated yield after the treatment with
a) Reaction conditions: Co(Ⅱ) complex catalyst 0.025
mmol (5.0 mol%), dienophile 0.5 mmol, and diene 1.0
mmol in CH Cl . b) Isolated yield after the treatment with
2
2
CF
3
COOH. c) Determined by HPLC analysis using Chiral-
CF COOH. c) Determined by HPLC analysis using Chiral-
3
pak AD (0.5% 2-propanol in hexane).
pak AD (0.5% 2-propanol in hexane).

S. Kezuka et al.
Bull. Chem. Soc. Jpn., 74, No. 7 (2001) 1335
the products were obtained and the optical yield was 25% (En-
try 1). In order to enhance the stereoselectivity of the pyra-
none derivatives, the reaction was tried at −20 °C and −40 °C
(
6
Entries 2 and 3), and the optical yields increased to 62 and
0%, respectively. However, both the yield and the ee de-
creased at −78 °C after a long reaction (Entry 4). In the reac-
tion of o-fluorobenzaldehyde (3b), more than 70% of the prod-
ucts were obtained, and the optical yield was 40% at room
temperature (Table 4, Entry 1). Then, the reaction was tried at
−
50 °C and −78 °C (Entries 2 and 3), and the optical yields
increased to 70 and 78%, respectively.
Various Optically Active 3-Oxobutylideneaminatoco-
balt(ꢀ) Complexes and Effective Axial Ligands. A variety
of optically active 3-oxobutylideneaminatocobalt complexes
(
Fig. 2) were examined for the asymmetric hetero Diels–Alder
reaction of o-fluorobenzaldehyde (Table 5). These complexes
1a, 5a, and 6a) were respectively prepared from the corre-
Fig. 2. Various 3-oxobutylideneaminato cobalt(Ⅱ) and co-
balt(Ⅲ) complexes.
(
sponding optically active 1,2-diarylethylenediamines and 1,3-
dicarbonyl compounds. When the optically active cobalt(Ⅱ)
complex 5a was employed as the catalyst, the yield and the op-
tical yield of the product were slightly improved compared
with complex 1a (Entries 1 and 2). On the contrary, both the
activity and enantioselectivity unexpectedly decreased when
complex 6a was used. A variety of axial ligands were next ex-
amined to enhance the Lewis acidity. The cobalt(Ⅲ) complex-
Table 4. Temperature Effect for Asymmetric Hetero Diels–
Alder Reaction of o-Fluorobenzaldehyde
2
5
es, 1b and 1c, were obtained by the oxidation of the cobalt(Ⅱ)
complex 1a with Br and I , respectively. In the presence of
a)
b)
c)
Entry
Temp/°C
Time/h
Yield/%
Ee/%
2
2
complexes 1b, though the optical yield of the product signifi-
cantly decreased, the reaction smoothly proceeded (Entry 4).
When the cobalt(Ⅲ) complex 1c was employed, the reaction
time was shortened and the optical yield of the product was
maintained (Entry 5). Furthermore, the cationic cobalt(Ⅲ)
complex 1d, obtained by treating the corresponding cobalt(Ⅲ)
iodide 1c with silver trifluoromethanesulfonate (AgOTf) (Eq.
1
2
3
r.t.
−50
−78
22
48
50
76
68
62
40
70
78
a) Reaction conditions: Co(Ⅱ) complex catalyst 0.025
mmol (5.0 mol%), dienophile 0.5 mmol, and diene 1.0
mmol in CH
2 2
Cl . b) Isolated yield after the treatment with
CF COOH. c) Determined by HPLC analysis using Chiral-
3
2
), was proved to be a highly active catalyst for the hetero Di-
pak AD (1.0% 2-propanol in hexane).
els-Alder reaction. In the presence of the 5 mol% complex
catalyst 1d, the reaction was completed in 12 h to give pyra-
Table 5. Various Cobalt Complex Catalysts for Asymmetric
Hetero Diels–Alder Reaction of o-Fluorobenzaldehyde
26
none 4b with 85% ee (Entry 6). The addition of MS 4A to
the reaction mixture improved both the yield and the optical
yield of the product, and the cationic cobalt(Ⅲ) triflate com-
plex 5d, prepared from complex 5c, significantly accelerated
the hetero Diels–Alder reaction to produce the corresponding
dihydropyran-4-one with high enantioselectivity (Entries 7,8,
and 9).
a)
b)
c)
Entry
Catalysts
Time/h
Yield/%
Ee/%
1
2
3
4
5
6
7
1a
5a
6a
1b
1c
1d
5c
50
72
31
36
36
12
24
24
3
62
71
9
84
87
89
83
91
89
78
83
14
73
78
85
81
86
87
(
2)
Various Counter Anions of the Cationic Cobalt(ꢁ) Com-
plexes. In the previous section, it was mentioned that the het-
ero Diels–Alder reaction proceeded smoothly in the presence
of the cationic cobalt(Ⅲ) trifluoromethanesulfonate complex
catalyst. Other counter anions have also been screened to
achieve high reactivities and high selectivities (Table 6). The
cationic cobalt(Ⅲ) complexes (1e, 1f, 1g, 1h, and 1d) were
synthesized by the treating the cobalt(Ⅲ) complex 1c with the
corresponding silver salts. The yield of 2,3-dihydro-4H-pyran-
d)
8
9
d)
5d
a) Reaction conditions: 0.025 mmol (5.0 mol%) cobalt cat-
alyst, 0.5 mmol dienophile (o-fluorobenzaldehyde), and 1.0
mmol diene in CH
treatment with CF
sis using Chiralpak AD (1.0% 2-propanol in hexane). d)
Powdered 4 Å molecular sieves (MS 4A) were added.
2
Cl
2
(2.5 mL). b) Isolated yield after the
COOH. c) Determined by HPLC analy-
3

1
336 Bull. Chem. Soc. Jpn., 74, No. 7 (2001)
-one was higher than 90% when complexes 1e and 1f were
Chiral Cobalt Catalyst for Hetero DA Reaction
4
dide, and little difference in the catalytic activity was found
among the cationic cobalt(Ⅲ) complexes.
used as catalysts (Entries 1 and 2). On the other hand, the
product was obtained with about an 80% yield when 1g, 1d,
and 1h were employed. As a result of these experiments, the
cationic cobalt(Ⅲ) complexes catalyzed the hetero Diels–Alder
reaction more effectively than the corresponding cobalt(Ⅲ) io-
X-ray Analysis of the Cationic Cobalt(ꢁ) Complex. An
X-ray analysis of the cationic cobalt(Ⅲ) complex was carried
out. Screening of the various combinations of the cobalt(Ⅲ)
complexes and solvent for the formation of single crystals re-
vealed that when the cationic cobalt(Ⅲ) 5d was recrystallized
from a mixed solvent of tetrahydrofuran–hexane, single crys-
tals of sufficient size were obtained for a structural analysis.
Figure 3 shows the crystal structure of cobalt(Ⅲ) trifluo-
romethanesulfonate 5d. The structure of the optically active 3-
oxobutylideneaminato cationic cobalt(Ⅲ) trifluoromethane-
sulfonate 5d was found to be very similar to that of the corre-
Table 6. Various Cationic Cobalt Complex Catalysts for
Asymmetric Hetero Diels–Alder Reaction
27
sponding cobalt(Ⅲ) iodide complex previously reported.
Two oxygen atoms and two nitrogen atoms coordinating to the
central cobalt atoms are on the same plane. This is evidence in
support of similar transition states to the corresponding co-
balt(Ⅲ) iodide. Two water molecules occupy each of the oppo-
site axial positions perpendicular to the coplanar formed by the
oxygen and nitrogen atoms on the cobalt complex. Tetrahy-
drofuran, a solvent for recrystallization, was 2.58 Å (2.61 Å
for another independent cobalt complex in a unit cell) from the
water oxygen and trifluoromethanesulfonate ion was 2.67 Å
a)
b)
c)
Entry
Catalysts
1e(SbF
1f(PF
1g(BF
1d(OTf)
1h(OTs)
Yield/%
Ee/%
1
2
3
4
5
6
)
90
98
77
89
81
82
85
82
85
80
6
)
4
)
a) Reaction conditions: 0.025 mmol (5.0 mol%) cobalt cat-
alyst, 0.5 mmol dienophile (o-fluorobenzaldehyde), and 1.0
mmol diene in CH
treatment with CF
sis using Chiralpak AD (1.0% 2-propanol in hexane). d)
Powdered 4 Å molecular sieves (MS 4A) were added.
(
2.86 Å) from the water oxygen. As compared with the length
27
of the cobalt–iodine bond of 1c (2.57 Å), it is reasonable to
consider that the 3-oxobutylideneaminatocobalt(Ⅲ) cation was
completely separated from the trifluoromethanesulfonate ion;
therefore, its Lewis acidity was enhanced. The FAB mass-
2
Cl
2
(2.5 mL). b) Isolated yield after the
COOH. c) Determined by HPLC analy-
3
Table 7. The Asymmetric Hetero Diels–Alder Reaction of
Various Dienophiles
a)
b)
Entry
R-CHO
Time/h Yield/%
Ee/%
1
2
3
3
89
81
87
81
3
4
5
6
7
7
24
59
94
88
81
83
94
91
91
90
Fig. 3.
ylphenyl)-N,Nꢀ-bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyl-
idene]ethylenediaminato}cobalt(Ⅲ) trifluoromethane-
Crystal structure of {(1S,2S)-1,2-bis(3,5-dimeth-
c)
7
8
96
96
69
89
90
88
d)
sulfonate dihydrate (5d): Selected bond lengths (Å) and
bond angles (°) are as follows: Co–O1, 1.899(7); Co–O2,
1
1
.912(8); Co–N1, 1.864(8); Co–N2, 1.853(8); Co–O3,
.939(8); Co–O4, 1.931(8); O1-Co-N2, 179.1(3); O2-Co-
a) Reaction conditions: 0.025 mmol (5.0 mol%) cobalt(Ⅲ)-
OTf catalyst 5d, 0.5 mmol dienophile (aldehyde), 150 mg
N1, 178.8(4); O1-Co-O2, 86.0(3); O1-Co-N1, 93.3(3); O2-
Co-N2, 94.8(4); N1-Co-N2, 85.8(4); O1-Co-O4, 89.4(3);
O2-Co-O4, 88.6(3); O4-Co-N1, 90.5(3); O4-Co-N2,
MS 4A, and 1.0 mmol diene in CH
2
2
Cl (2.5 mL). b) Isolated
yield after the treatment with CF
3
COOH. c) 9.0 mol%
9
0.2(4); (Two molecules exist in each unit cell, and one of
cobalt(Ⅲ)-OTf complex 1d and 200 mg MS 4A was
employed. d) 8.0 mol% complex 1d was employed.
−
2 3
them and OSO CF ion were omitted for clarity).

S. Kezuka et al.
Bull. Chem. Soc. Jpn., 74, No. 7 (2001) 1337
spectra data also indicated that cobalt(Ⅲ) iodide and cobalt(Ⅲ)
bromide provided their own molecular weight, while the cat-
ionic cobalt(Ⅲ) complex showed their cationic cobalt species
and their anions.
1a was employed in the reaction. For the ortho-chloro substi-
tuted aromatic aldehyde, the reaction was completed in 24 h
and the optical yield was 75% ee. On the contrary, when para-
chloro derivatives were used, the reactions proceeded slower
and did not finish even after 48 h, but the optical yields were
83% ee.
Enantioselective Hetero Diels–Alder Reaction of Various
Aldehydes. The highly active cationic cobalt(Ⅲ) triflate
complexes 1d and 5d were successfully applied as effective
chiral catalysts for the enantioselective hetero Diels–Alder re-
action of various aldehydes with the electron-rich diene. As
shown in Table 7, the hetero Diels–Alder reactions of the o-flu-
oro- and o-chlorobenzaldehydes (3b and 3c) smoothly pro-
ceeded to afford the corresponding dihydropyran-4-ones in
high yield with high enantioselectivity (Entries 1 and 2). By
using the cationic cobalt(Ⅲ) complex 5d as a Lewis acid cata-
lyst, aromatic aldehydes substituted by an electron-withdraw-
ing group at the para position reacted with Danishefsky’s di-
ene, and was completely consumed in 7–24 h. The enantiose-
lectivities in these reactions of the p-nitro-, p-trifluoromethyl-,
and p-chlorobenzaldehydes (3d, 3e, and 3f) were 94, 91, and
Absolute Configuration of Optically Active Pyranone
Derivatives. In the previous section, it was mentioned that
the reaction proceeded rapidly when a methoxy or halogen
substituent was at the ortho position of the aromatic aldehyde.
These phenomena made us suspect that the stereocourses were
different for the ortho and para substituted aromatic aldehydes.
The absolute configurations of the hetero Diels-Alder adducts
were then determined (Fig. 5). The absolute configurations of
the hetero Diels–Alder adducts, 2-(4-nitrophenyl)-2,3-dihy-
dro-4H-pyran-4-one (4d) and 2-phenyl-2,3-dihydro-4H-pyran-
4-one (4g), were determined by comparing their optical rota-
2
9
tions with the reported values. For 2-(2-bromophenyl)-2,3-
dihydro-4H-pyran-4-one (4j), the optical rotation was com-
pared after conversion by a dehalogenation reaction to 2-phe-
nyl-2,3-dihydro-4H-pyran-4-one. The value of the enantiomer
excess calculated from the specific rotation agreed with that by
the high-performance liquid chromatography (HPLC) method.
These observations indicated that a pyranone derivative of (S)-
configuration was obtained from either the ortho-substituted,
para-substituted or non-substituted aromatic aldehyde in the
presence of the (S,S)-cobalt complex catalysts. Therefore, it is
possible to assume that similar stereocourses occurred for each
aldehyde except for the reaction rate.
9
1% ee, respectively (Entries 3–5). The hetero Diels–Alder re-
action of benzaldehyde (3g) also proceeded to afford the corre-
sponding pyranone derivative in 83% yield with 90% ee (Entry
6
). In the presence of a catalytic amount of the cationic co-
balt(Ⅲ) triflate complex 1d, the hetero Diels–Alder reaction of
-phenylpropionaldehyde (3h) and octanal (3i) smoothly pro-
3
ceeded to afford the corresponding dihydropyran-4-ones with
high enantioselectivity (90 and 88% ee, Entries 7 and 8, re-
spectively).
Acceleration of the Reaction for the Ortho Substituted
Aromatic Aldehydes. The reaction proceeded rapidly when
a methoxy group or halogen atom was substituted at the ortho
position of the aromatic aldehyde. For instance, the 2-(2-chlo-
rophenyl)-2,3-dihydro-4H-pyran-4-one was obtained in 81%
within 3 h, whereas the 2-(4-chlorophenyl)-2,3-dihydro-4H-
It is presumed that both the o- and p-substituted aldehydes
were activated by the coordination of the cobalt atom to form a
similar intermediate. The computational experiment on the
structure of the (S,S)-cobalt complex with benzaldehyde was
then attempted by a semi-empirical method with a Mac Spar-
tan Pro (PM3(tm)). After examining the energy surface and
the optimization of the structure, it was revealed that the lone
pair of oxygen atoms anti to the phenyl group in the aldehyde
contributed to coordinate the cobalt atom, and that the phenyl
group was oriented between two coordinating oxygen atoms,
2
8
pyran-4-one was obtained in 81% yield after 24 h. These re-
sults suggest that the hetero Diels–Alder reaction was acceler-
ated due to the coordination of the cobalt complex by a substit-
uent group at the ortho position. The time-course of the prod-
ucts’ yields was then investigated (Fig. 4). The cobalt complex
1
2
O and O , on the planar 3-oxobutylideneaminato ligand (Fig.
). The diene should approach the si-face of the activated di-
6
enophile mentioned above to afford the (S)-endo adduct in
high selectivities because the re-face is blocked by the aryl
group of the chiral diamine and the bulky alkyl or aryl group
Fig. 4. Time-course of hetero Diels–Aider reaction for o-
and p-cholorobenzaldehydes.
Fig. 5. Absolute configurations of hetero Diels–Alder prod-
ucts.

1
338 Bull. Chem. Soc. Jpn., 74, No. 7 (2001)
Chiral Cobalt Catalyst for Hetero DA Reaction
Fig. 6. The optimized structure of (S,S)-cobalt/PhCHO complex by semi-empirical method with Mac Spartan Pro (PM3(tm)).
Side view (left) and top view (right).
Experimental
General: The melting points were measured on an Electro-
thermal IA9100 apparatus or a Rigaku DSC-8230 apparatus and
were uncorrected.
(
a) Spectrometers: Infrared (IR) spectra were recorded on a
JASCO Model FT/IR-410 infrared spectrometer on KBr pellets or
1
13
liquid film on NaCl. H NMR spectra and C NMR spectra were
measured on a JEOL Model GX-400 spectrometer using CDCl or
as a solvent and with tetramethylsilane as an internal stan-
3
6 6
C D
dard. High-resolution mass spectra were obtained with a HITA-
CHI M-8013. FAB mass spectra were recorded with a JEOL
MStation JMS-700 spectrometer using 3-nitrobenzyl alcohol
(
NBA) as a matrix agent.
b) Chromatography: For the thin-layer chromatography
TLC) analysis used throughout this work, Merck precoated TLC
(
(
plates (silica gel 60 F254, 0.25 mm) were used. The products
were purified by preparative column chromatography on silica gel
(
(
silica gel 60 N). High-performance liquid chromatography
HPLC) analyses were performed with a Shimadzu LC-6A chro-
matograph using an optically active column (Chiralcel OD-H, and
Chiralpak AD columns, Daicel Ltd., Co.); the peak areas were ob-
tained with a Shimadzu chromatopack CR-4A or Varian Dynamax
MacIntegrator.
Fig. 7. Reasonable explanation for the endo-selection and
the enantioselection in the hetero Diels–Alder reaction cat-
alyzed by (S,S)-cobalt complex.
(
c) Optical Rotations: Optical rotations were measured with
on the side chain of the 3-oxobutylideneaminato ligand. These
explanations are in full accord with the enantioselection of the
present hetero Diels–Alder reaction (Fig. 7).
a JASCO DIP-370 digital polarimeter.
Aldehydes: o-Methoxybenzaldehyde (3a), o-chlorobenzalde-
hyde (3c), p-nitrobenzaldehyde (3d), p-trifluoromethylbenzalde-
hyde (3e), p-chlorobenzaldehyde (3f), 3-phenylpropionaldehyde
Conclusion
(
3h), octanal (3i) were purchased from Tokyo Kasei Kogyo (TCI)
The cationic cobalt(Ⅲ) complexes with optically active 3-
oxobutylideneaminato ligands effectively catalyzed the hetero
Diels–Alder reaction of various aromatic and aliphatic alde-
hydes with Danishefsky’s diene to afford the corresponding di-
hydropyran-4-one derivatives in high yield with high enanti-
oselectivity.
Co., Ltd., respectively. o-Fluorobenzaldehyde (3b) was purchased
from ACROS Organics. Benzaldehyde ( 3g) was purchased from
Kanto Chemical Co., Inc. o-Bromobenzaldehyde (3j) was pur-
chased from Wako Pure Chemical Industries, Ltd.
Diene: 3-(t-Butyldimethylsilyloxy)-1-methoxy-1,3-butadi-
ene (2) was prepared by a reported method.
23
Tetrakis(triphenylphosphine)palladium(0) was purchased from
Kanto Chemical Co., Inc.
Preparation of Optically Active 3-Oxobutylideneaminato
Ligands: Ligands 1, 5, and 6 were prepared by a reported
The authors thank Professor Shigeru Ohba and Dr. Masano-
bu Tsuchimoto, Keio University, for X-ray analysis of cobalt
complex 5d.

S. Kezuka et al.
Bull. Chem. Soc. Jpn., 74, No. 7 (2001) 1339
1
5
method from 3-oxo-2-(2,4,6-trimethylbenzoyl)butanal and opti-
cally active 1,2-diarylethylenediamines.
cobalt(ꢁ) Complexes: Cobalt(Ⅲ) complexes type-A 1b, 1c,
and 5c were prepared by a reported method.
27
(
1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
1
dene]-1,2-diphenylethylenediamine (1): H NMR (400 MHz)
δ 1.92 (6H, s), 1.98 (6H, s), 2.26 (6H, s), 2.63 (6H, brs), 4.41 (2H,
d, J = 7.2 Hz), 6.72–6.74 (4H, m), 6.98–7.00 (6H, m), 7.24–7.26
1
3
(
6H, m), 11.98 (2H, brs); C NMR (100 MHz) δ 19.1, 21.1, 31.8,
6
1
1
9.4, 112.6, 126.5, 128.0, 128.2, 128.6, 128.9, 133.3, 133.4,
35.4, 137.4, 161.0, 196.2, 201.1; IR (KBr) 2971, 2917, 1615,
454, 1405, 1353, 1299, 1252, 1200, 981, 849, 697 cm−1. Found:
(4)
Bromo{N,Nꢂ-bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
C, 78.55; H, 6.91; N, 4.39%. Calcd for C42
H
44
N
2
O
4
: C, 78.72; H,
dene]-(1S,2S)-1,2-diphenylethylenediaminato}cobalt(ꢁ) (1b):
2
8
6
.92; N, 4.37%. Mp 210.4–211.2 °C. [α]
CHCl ).
1S,2S)-1,2-Bis(3,5-dimethylphenyl)-N,Nꢂ-bis[3-oxo-2-
2,4,6-trimethylbenzoyl)butylidene]ethylenediamine (5):
NMR (400 MHz) δ 1.82 (6H, s), 1.99 (6H, s), 2.23–2.25 (18H, m),
D
+72.3° (c 0.507,
IR (KBr) 2917, 1591, 1496, 1398, 1352, 1298, 1268, 1199, 994,
−
1
+
3
879, 847, 701, 592 cm . MS (FAB) m/z 777 (M+H) .
ꢂ
(
Iodo{N,N -bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butylidene]-
1
(
H
(1S,2S)-1,2-diphenylethylenediaminato}cobalt(ꢁ) (1c):
IR
.
−
1
(KBr) 2919, 1588, 1398, 1353, 1268, 994, 880, 848, 701, 592cm
+
2
6
1
1
2
.66 (6H, brs), 4.34 (2H, d, J = 6.8 Hz), 6.63 (4H, s), 6.70 (4H, s),
MS (FAB) m/z 825 (M+H) .
1
3
.83–6.95 (4H, m), 11.91 (2H, br); C NMR (100 MHz) δ 19.0,
9.2, 21.1, 21.3, 31.8, 69.5, 112.5, 124.1, 128.0, 130.2, 133.3,
33.4, 135.4, 137.3, 138.6, 161.3, 196.2, 200.9; IR (KBr) 2921,
860, 1620, 1407, 1352, 1307, 1257, 1200, 1169, 980, 849, 802
Iodo{(1S,2S)-1,2-bis(3,5-dimethylphenyl)-N,Nꢂ-bis[3-oxo-2-
(2,4,6-trimethylbenzoyl)butylidene]ethylenediaminato}co-
balt(ꢁ) (5c): IR (KBr) 2918, 1590, 1398, 1352, 1285, 1199,
−
1
1125, 996, 872, 849, 745, 723, 600 cm . MS (FAB) m/z 881
−
1
+
+
cm . HRMS: Calcd for C46
z 696.3914. Mp 211.3–213.3 °C. [α]
CHCl ).
1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
dene]-1,2-bis(2,4,6-trimethylphenyl)ethylenediamine (6):
H NMR (400 MHz) δ 1.42 (6H, s), 2.02 (6H, s), 2.10 (6H, s),
H
52
N
2
O
4
: (M ), 696.3927. Found: m/
(M+H) .
2
2
D
+106.3° (c 1.006,
Cobalt(Ⅲ) complexes type-B 1d–h and 5d were prepared as fol-
lows.
3
(
1
2
.18 (6H, s), 2.23 (6H, brs), 2.28 (6H, s), 2.64 (6H, brs), 4.84 (2H,
brs), 6.54 (2H, s), 6.73 (2H, s), 6.79 (4H, s), 7.07 (2H, brs), 11.52
1
3
(
2H, brs); C NMR (100 MHz) δ 19.01, 19.05, 19.9, 20.4, 20.8,
(5)
2
1
2
9
1.2, 31.6, 61.6, 112.7, 127.7, 128.1, 129.38, 129.44, 131.4,
33.0, 133.6, 134.8, 136.7, 137.5, 138.3, 140.7, 161.2, 196.3,
00.2; IR (KBr) 2921, 1624, 1404, 1350, 1305, 1257, 1200, 1171,
83, 849, 820 cm− . Found: C, 79.27; H, 7.70; N, 3.83%. Calcd
(1S,2S)-1,2-Bis(3,5-dimethylphenyl)-N,Nꢂ-bis[3-oxo-2-
(2,4,6-trimethylbenzoyl)butylidene]ethylenediaminatoco-
balt(ꢁ) trifluoromethanesulfonate (5d): To a solution of the
cobalt complex 5c (259.9 mg, 0.295 mmol) in dichloromethane
(10.0 mL) was added AgOTf (84.4 mg, 0.329 mmol) in dichlo-
romethane (1.0 mL). The mixture was stirred for 1.5 h, and the re-
sulting AgI and excess AgOTf were filtered off. The solvent were
removed under reduced pressure and the crude product was puri-
fied by reprecipitation from dichloromethane/hexane to afford the
cationic cobalt(Ⅲ) complex 5d (231.4 mg) in 87% yield as a green
solid. IR (KBr) 2921, 1592, 1472, 1399, 1355, 1290, 1171, 1030,
1
56 2 4
for C48H N O : C, 79.52; H, 7.79; N, 3.86%. Mp 171.4–173.2
2
4
30
°
C. [α]
Preparation of Optically Active 3-Oxobutylideneaminatoco-
balt(ꢀ) Complexes: Catalysts 1a, 5a, and 6a were prepared by
D 3
+27.5° (c 1.019, CHCl ).
27
a reported method.
−
1
9
97, 874, 849, 640, 601 cm . MS (FAB(positive)) m/z 754 (M−
+
−
OTf+H) , (FAB (negative)) m/z 149 (OTf) .
1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
(
(
3)
dene]-1,2-diphenylethylenediaminatocobalt(ꢁ) trifluorometh-
anesulfonate (1d): IR (KBr) 2921, 1589, 1399, 1355, 1271,
−
1
(
1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
1171, 1031, 995, 881, 849, 701, 639, 593 cm . MS (FAB(posi-
+
−
dene]-1,2-diphenylethylenediaminatocobalt(ꢀ) (1a):
IR
KBr) 2919, 1640, 1571, 1454, 1397, 1354, 1284, 1267, 993, 880,
8
tive)) m/z 698 (M−OTf+H) , (FAB(negative)) m/z 149 (OTf) .
(1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
dene]-1,2-diphenylethylenediaminatocobalt(ꢁ) hexafluoroan-
timonate (1e): IR (KBr) 2922, 1583, 1456, 1398, 1355, 1301,
(
47, 700, 593 cm− . MS (FAB) m/z 698 (M+H) . Mp 299.2 °C
1
+
(
DSC).
−
1
(
1S,2S)-1,2-Bis(3,5-dimethylphenyl)-N,Nꢂ-bis[3-oxo-2-
1270, 1200, 994, 882, 849, 701, 669, 593 cm . MS (FAB(posi-
+
−
(
2,4,6-trimethylbenzoyl)butylidene]ethylenediaminatoco-
tive)) m/z 698 (M−SbF
(1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
dene]-1,2-diphenylethylenediaminatocobalt(ꢁ) hexafluoro-
phoshpate (1f): IR (KBr) 2922, 1587, 1456, 1399, 1355, 1296,
6 6
+H) , (FAB(negative)) m/z 235 (SbF ) .
balt(ꢀ) (5a): IR (KBr) 2917, 1644, 1610, 1572, 1428, 1388,
−
1
1
(
354, 1275, 1256, 995, 873, 845, 802 cm . MS (FAB) m/z 754
+
M+H) . Mp 334.1 °C (DSC).
1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
−
1
(
1271, 995, 880, 702, 593, 558 cm . MS (FAB(positive)) m/z 698
+
−
dene]-1,2-bis(2,4,6-trimethylphenyl)ethylenediaminatoco-
(M−PF
6 6
+H) , (FAB(negative)) m/z 145 (PF ) .
balt(ꢀ) (6a): IR (KBr) 2921, 1623, 1587, 1398, 1353, 1261, 849
(1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
−
1
+
cm . MS (FAB) m/z 782 (M+H) . Mp 248.8 °C (DSC).
dene]-1,2-diphenylethylenediaminatocobalt(ꢁ)
tetrafluoro-
Preparation of Optically Active 3-Oxobutylideneaminato-
borate (1g): IR (KBr) 2921, 1587, 1455, 1399, 1355, 1299,

1
340 Bull. Chem. Soc. Jpn., 74, No. 7 (2001)
Chiral Cobalt Catalyst for Hetero DA Reaction
1
1
270, 1124, 1084, 994, 881, 847, 701, 593 cm− . MS (FAB(posi-
yield was determined by Chiralpak AD (1.0% 2-propanol in hex-
ane, Flow1.0mL/min), 23.2 min (minor), 25.7 min (major).
2-(4-Trifluoromethylphenyl)-2,3-dihydro-4H-pyran-4-one
+
−
4 4
tive)) m/z 698 (M−BF +H) , (FAB(negative)) m/z 87 (BF ) .
(
1S,2S)-N,Nꢂ-Bis[3-oxo-2-(2,4,6-trimethylbenzoyl)butyli-
dene]-1,2-diphenylethylenediaminatocobalt(ꢁ) p-toluenesul-
fonate (1h): IR (KBr) 2919, 1592, 1455, 1398, 1353, 1269,
158, 1123, 1035, 1010, 880, 847, 701, 682, 639, 592, 567 cm .
MS (FAB(positive)) m/z 698 (M−OTs+H) , (FAB(negative)) m/z
1
(4e): H NMR (400 MHz) δ 2.70 (1H, ddd, J = 1.0, 3.4, 17.0
Hz), 2.86 (1H, dd, J = 14.2, 17.0 Hz), 5.50 (1H, dd, J = 3.4, 14.2
Hz), 5.56 (1H, dd, J = 1.0, 6.1 Hz), 7.51 (1H, d, J = 6.1 Hz), 7.54
−
1
1
+
13
(2H, d, J = 8.3 Hz), 7.69 (2H, d, J = 8.3 Hz); C NMR (100
−
1
71 (OTs) .
MHz) δ 43.4, 80.1, 107.6, 123.7 (q, JCF = 272 Hz), 125.7 (q, JCF
= 4 Hz), 126.1, 130.8 (q, JCF = 33 Hz), 141.6, 162.6, 191.0; IR
(KBr) 3060, 2896, 1665, 1623, 1597, 1411, 1326, 1285, 1178,
General Procedure for the Enantioselective Hetero Diels–
Alder Reaction of 2-(4-Nitrophenyl)-2,3-dihydro-4H-pyran-4-
one (4d): To a solution of the cobalt complex 5d (22.9 mg, 5.0
mol%) in dichloromethane (0.5 mL) in the presence of molecular
sieves 4A was added p-nitrobenzaldehyde (75.4 mg, 0.50 mmol)
in dichloromethane (1.0 mL). A solution of the 3-(t-butyldimeth-
ylsilyloxy)-1-methoxy-1,3-butadiene (200 µL, 0.97 mmol) in
dichloromethane (1.0 mL) was then added at −78 °C. The mix-
ture was stirred for 7 h at −78 °C, followed by a treatment with
trifluoroacetic acid (0.2 mL) at rt for 5 h. After neutralization with
1127, 843 cm− . HRMS: Calcd for C12
1
H O F : (M ), 242.0555.
+
9 2 3
24
Found: m/z 242.0544. Mp 72.2–74.4 °C. [α]
CHCl ). Optical yield was determined by Chiralpak AD (1.0% 2-
D
+44.4° (c 0.630,
3
propanol in hexane, Flow 1.0 mL/min), 36.1 min (minor), 51.1
min (major).
1
2-(4-Chlorophenyl)-2,3-dihydro-4H-pyran-4-one (4f):
H
NMR (400 MHz) δ 2.65 (1H, ddd, J = 1.2, 3.4, 16.6 Hz), 2.86
(1H, dd, J = 14.2, 16.6 Hz), 5.41 (1H, dd, J = 3.4, 14.2 Hz), 5.54
(1H, dd, J = 1.2, 5.9 Hz), 7.33–7.35 (2H, m), 7.39–7.41 (2H, m),
3
a sat. NaHCO solution, a standard workup and chromatography
13
on silica gel afforded 2,3-dihydro-2-(4-nitrophenyl)-4H-pyran-4-
one (102.5 mg) in 94% yield. The optical yield of the product was
determined by an HPLC analysis (Chiralcel OD-H, 10% 2-pro-
panol in hexane, Flow 1.0 mL/min, 35.3 min (major), 49.0 min
7.47 (1H, d, J = 5.9 Hz); C NMR (100 MHz) δ 43.4, 80.3,
107.4, 127.3, 128.9, 134.6, 136.2, 162.8, 191.4; IR (neat) 3068,
2901, 1682, 1596, 1495, 1402, 1272, 1227, 1039, 933, 834 cm−
1
.
Found: C, 63.05; H, 4.48%. Calcd for C11
H
9
O
2
Cl: C, 63.32; H,
27
(
minor)) to be 94% ee.
4.35%. [α] +91.2° (c 0.548, CHCl ). Optical yield was deter-
D
3
The products 2-(4-nitrophenyl)-2,3-dihydro-4H-pyran-4-one
mined by Chiralcel OD-H (1.0% 2-propanol in hexane, Flow 1.0
29b,31
3b,8a,29a
(4d)
and 2-phenyl-2,3-dihydro-4H-pyran-4-one (4g)
were identified with the corresponding material reported previous-
ly.
-(2-Methoxyphenyl)-2,3-dihydro-4H-pyran-4-one
H NMR (400 MHz) δ 2.71–2.81 (2H, m), 3.84 (3H, s), 5.52 (1H,
d, J = 6.4 Hz), 5.81 (1H, dd, J = 5.9, 11.7 Hz), 6.92 (1H, d, J =
mL/min), 43.9 min (major), 58.1 min (minor).
2-(2-Phenylethyl)-2,3-dihydro-4H-pyran-4-one (4h):
1
H
NMR (400 MHz) δ 1.84–1.92 (1H, m), 2.04–2.13 (1H, m), 2.36
(1H, ddd, J = 1.0, 3.9, 16.6 Hz), 2.48 (1H, dd, J = 13.7, 16.6 Hz),
2.64–2.80 (2H, m), 4.29–4.36 (1H, m), 5.34 (1H, dd, J = 1.0, 6.4
Hz), 7.11–7.16 (3H, m), 7.21–7.25 (2H, m), 7.31 (1H, d, J = 6.4
2
(4a):
1
13
7
2
4
1
1
.8 Hz), 7.01–7.05 (1H, m), 7.32–7.37 (1H, m), 7.48 (1H, dd, J =
Hz); C NMR (100 MHz) δ 31.0, 36.1, 41.8, 78.4, 107.0, 126.1,
1
3
.0, 7.6 Hz), 7.52 (1H, d, J = 6.4 Hz); C NMR (100 MHz) δ
2.4, 55.4, 76.4, 107.1, 110.4, 120.7, 126.2, 126.4, 129.5, 155.7,
63.4, 192.7; IR (neat) 3071, 2940, 2840, 1678, 1595, 1496, 1464,
128.2, 128.4, 140.5, 162.9, 192.2; IR (neat) 3025, 2952, 1673,
−
1
1591, 1414, 1271, 1228, 1045, 726, 699 cm . HRMS: Calcd for
+
27
C
13
H
14
O
2
: (M ), 202.0994. Found: m/z 202.1000. [α]
D
+97.0°
−
1
28a
404, 1273, 1226, 1040, 756 cm . HRMS: Calcd for C12
H
12
O
3
:
(c 1.021, CHCl
3
).
Optical yield was determined by Chiralpak
+
26
(
M ), 204.0786. Found: m/z 204.0801. [α]
D
−48.1° (c 0.883,
AD (1.0% 2-propanol in hexane, Flow 1.0 mL/min), 23.1 min (mi-
CHCl
3
). Optical yield was determined by Chiralpak AD (0.5% 2-
propanol in hexane, Flow 1.0 mL/min), 45.8 min (minor), 57.9
nor), 30.9 min (major).
2-Heptyl-2,3-dihydro-4H-pyran-4-one (4i):
1
H NMR
min (major).
(400 MHz) δ 0.80–0.94 (3H, m), 1.19–1.57 (10H, m), 1.60–1.72
(1H, m), 1.75–1.89 (1H, m), 2.43 (1H, dd, J = 3.9, 16.6 Hz), 2.52
(1H, dd, J = 13.7, 16.6 Hz), 4.32–4.48 (1H, m), 5.40 (1H, d, J =
1
2
-(2-Fluorophenyl)-2,3-dihydro-4H-pyran-4-one (4b):
H
NMR (400 MHz) δ 2.70 (1H, ddd, J = 1.0, 3.4, 16.7 Hz), 2.90
13
(
(
1H, dd, J = 14.2, 16.7 Hz), 5.55 (1H, dd, J = 1.0, 6.1 Hz), 5.73
1H, dd, J = 3.4, 14.2 Hz), 7.09–7.14 (1H, m), 7.20–7.24 (1H, m),
5.9 Hz), 7.37 (1H, d, J = 5.9 Hz); C NMR (100 MHz) δ 14.2,
22.7, 24.8, 29.2, 29.3, 31.8, 34.4, 41.9, 79.6, 106.8, 163.2, 192.7;
IR (neat) 2927, 2857, 1684, 1597, 1466, 1406, 1275, 1227, 1040,
1
3
7
4
.35–7.40 (1H, m), 7.49–7.53 (2H, m); C NMR (100 MHz) δ
2.4, 75.5 (d, JCF = 3 Hz), 107.4, 115.7 (d, JCF = 21 Hz), 124.5
791 cm− . HRMS: Calcd for C12
1
H
20
O
2
: (M ), 196.1463. Found:
+
25
(
1
(
d, JCF = 4 Hz), 125.1 (d, JCF = 13 Hz), 127.3 (d, JCF = 3 Hz),
30.4 (d, JCF = 8 Hz), 159.5(d, JCF = 248 Hz), 162.9, 191.5; IR
neat) 3070, 2920, 1681, 1619, 1597, 1496, 1272, 1224, 1038, 761
m/z 196.1446. [α]
determined by Chiralpak AD (0.5% 2-propanol in hexane, Flow
D
+105.5° (c 0.727, CHCl ). Optical yield was
3
1.0 mL/min), 19.6 min (minor), 28.6 min (major).
2-(2-Bromophenyl)-2,3-dihydro-4H-pyran-4-one (4j):
−
1
+
1
cm . HRMS: Calcd for C11
H O
9 2
F: (M ), 192.0587. Found: m/z
+52.4° (c 0.887, CHCl ). Optical yield was de-
H
2
9
1
92.0557. [α]
D
3
NMR (400 MHz) δ 2.59 (1H, dd, J = 14.2, 16.8 Hz), 2.73 (1H,
dd, J = 3.4, 16.8 Hz), 5.47 (1H, d, J = 5.9 Hz), 5.69 (1H, dd, J =
3.4, 14.2 Hz), 7.12–7.17 (1H, m), 7.30–7.33 (1H, m), 7.43 (1H, d,
termined by Chiralpak AD (1.0% 2-propanol in hexane, Flow 1.0
mL/min), 32.7 min (minor), 41.4 min (major).
1
13
2
-(2-Chlorophenyl)-2,3-dihydro-4H-pyran-4-one (4c):
H
J = 5.9 Hz), 7.48–7.51 (2H, m); C NMR (100 MHz) δ 42.2,
NMR (400 MHz) δ 2.72 (1H, dd, J = 13.7, 16.8 Hz), 2.81 (1H,
ddd, J = 1.0, 3.9, 16.8 Hz), 5.56 (1H, dd, J = 1.0, 5.9 Hz), 5.83
80.1, 107.4, 121.2, 127.1, 127.8, 129.9, 132.8, 137.2, 162.8,
191.2; IR (neat) 3068, 2905, 1680, 1597, 1401, 1272, 1226, 1038,
995, 932, 757 cm−
251.9786.
CHCl ). Optical yield was determined by Chiralcel OD-H (2.0%
1
.
Br: (M ),
−116.8° (c 1.147,
+
(
5
7
1
1H, dd, J = 3.9, 13.7 Hz), 7.30–7.42 (3H, m), 7.52 (1H, d, J =
9 2
HRMS: Calcd for C11H O
1
3
23
.9 Hz), 7.58–7.61 (1H, m); C NMR (100 MHz; C
6
D
6
) δ 42.2,
Found: m/z 251.9767. [α]
D
8.1, 107.7, 127.3, 127.5, 129.7, 129.8, 132.0, 136.2, 162.3,
90.4; IR (neat) 3069, 2905, 1683, 1598, 1402, 1273, 1227, 1038,
3
2-propanol in hexane, Flow 1.0 mL/min), 19.2 min (major), 22.5
min (minor).
1
+
9
32, 758 cm− . HRMS: Calcd for C11
H
9
O
2
Cl: (M ), 208.0291.
2
8
32
Found: m/z 208.0282. [α]
D
−95.6° (c 0.812, CHCl ). Optical
3
Debromination of 2-(2-Bromophenyl)-2,3-dihydro-4H-py-

S. Kezuka et al.
Bull. Chem. Soc. Jpn., 74, No. 7 (2001) 1341
coordinating oxygen atoms.
ran-4-one (4j) to 2-Phenyl-2,3-dihydro-4H-pyran-4-one (4g):
A mixture of the 2-(2-bromophenyl)-2,3-dihydro-4H-pyran-4-one
(
113.1 mg, 0.45 mmol), sodium formate (67.0 mg, 0.99 mmol),
References
tetrakis(triphenylphosphine)palladium(0) (51.7 mg, 44.7 µmol) in
DMF (3.0 mL). The mixture was stirred for 1.5 h at 100 °C. A
standard workup and chromatography on silica gel afforded 2,3-
dihydro-2-phenyl-4H-pyran-4-one (54.8 mg) in 70% yield. The
optical yield of the product was determined by an HPLC analysis
1
K. Maruoka and H. Yamamoto, “Catalytic Asymmetric
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(
3
Chiralcel OD-H, 2.0% 2-propanol in hexane, 28.0 min (major),
2
3
4.6 min (minor)) to be 75% ee. [α]
D 3
+77.2° (c 0.548, CHCl ).
X-ray Crystallography of Cobalt(ꢁ) Trifluoromethane-
sulfonate (5d): The crystals were grown from a THF solution
by diffusion of a small amount of hexane. A crystal specimen was
sealed in a capillary with the mother liquor to avoid efflorescence.
The X-ray intensities were measured on a Rigaku AFC-7R diffrac-
tometer with Mo Kα radiation. The structure was refined by full-
3
3
matrix least-squares calculations. The crystal structure had a
pseudo center of symmetry and the space group was approximate-
2
M. Bednarski, C. Maring, and S. Danishefsky, Tetrahedron
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/a. There was an orientational disorder of the trifluo-
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positions and two oxygen atoms are four disordered sites with
5
0% probability each; also the positional disorder was modeled
only tentatively. Crystal data for [Co(C46 )•(H O) ]•
CF SO •C 10S, Formula weight = 1011.05,
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H
50
N
2
O
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Org. Chem., 57, 1951 (1992). b) Q. Gao, K. Ishihara, T.
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3
3
4 8 3 2
H O: C51H62CoF N O
1
3
1
1
9.285(2) Å, β = 97.619(10)°, V = 5346.7(11) Å , Z = 4, Dcalc =
3 −1
.256 g cm− , T = 296(1) K, µ (Mo Kα) = 0.425 mm , no. of
4
a) K. Maruoka, T. Itoh, T. Shirasaka, and H. Yamamoto, J.
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2
rameters 547, R(F) = 0.116, R
−
w
(F ) = 0.313, Flack parameter =
0.01(3).
Computational Details:
The computations were per-
3
4
formed using the GAUSSIAN-98 package and Mac Spartan Pro
3
5
(
PM3(tm)).
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5
M. Terada, K. Mikami, and T. Nakai, Tetrahedron Lett., 32,
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(
cobalt atom), 3-21G (ethylenediamine bridge, formyl groups of
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other atoms. To the optimized complex, the benzaldehyde mole-
cule was attached at the axial position. The distance between the
cobalt atom and the carbonyl oxygen was optimized by a semi-
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6
K. Mikami, O. Kotera, Y. Motoyama, and H. Sakaguchi,
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7
J. Inanaga, Y. Sugimoto, and T. Hanamoto, New J. Chem.,
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0
1
1
1
2
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nato]cobalt(Ⅲ) (7).

1
342 Bull. Chem. Soc. Jpn., 74, No. 7 (2001)
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pyran-4-one was obtained in 13% yield after 45 h. Similarly the
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in 96% within 55 h at −20 °C, whereas the 2-(4-methoxyphenyl)-
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5
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2
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3
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6
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