Studies on the diastereoselectivity in the IMDA reactions of terminally activated (E,E,E)-nona-1,6,8-trienes

Article abstract of DOI:10.1016/j.tetlet.2005.12.118

The structure-diastereoselectivity relationships in the IMDA reactions of the terminally activated (E,E,E)-nona-1,6,8-trienes have been studied. It is found that the configuration of the C3 position bearing the protected hydroxyl group is crucial to the diastereoselectivity, and the magnitude of the ratio depends on the relative configuration of the C3-C5 positions. The results obtained in this study including the new successful IMDA reactions would be useful for the stereoselective synthesis of natural products containing a bicyclo[4.3.0]non-2-ene carbon skeleton.

Full text of DOI:10.1016/j.tetlet.2005.12.118

Tetrahedron
Letters
Tetrahedron Letters 47 (2006) 1593–1598
Studies on the diastereoselectivity in the IMDA reactions
of terminally activated (E,E,E)-nona-1,6,8-trienes
Takahiro Suzuki, Natsumi Tanaka, Takehiko Matsumura, Yosuke Hosoya and
Masahisa Nakada*
Department of Chemistry, Faculty of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan
Received 22 November 2005; revised 14 December 2005; accepted 22 December 2005
Available online 19 January 2006
Abstract—The structure–diastereoselectivity relationships in the IMDA reactions of the terminally activated (E,E,E)-nona-1,6,8-tri-
enes have been studied. It is found that the configuration of the C3 position bearing the protected hydroxyl group is crucial to the
diastereoselectivity, and the magnitude of the ratio depends on the relative configuration of the C3–C5 positions. The results
obtained in this study including the new successful IMDA reactions would be useful for the stereoselective synthesis of natural prod-
ucts containing a bicyclo[4.3.0]non-2-ene carbon skeleton.
Ó 2006 Elsevier Ltd. All rights reserved.
IMDA
The intramolecular Diels–Alder (IMDA) reaction in
which the diene and dienophile are tethered by a con-
necting chain has become a most versatile method for
the synthesis of polycyclic natural products.1 Of parti-
cular interest is the selective introduction of stereogenic
centers because the IMDA reaction simultaneously gen-
erates upto four new stereogenic centers, making this
reaction valuable in natural products synthesis.
3
1
5
CO2Me
TBSO
4
2
reaction
TIPSO
OH
1
OH
TIPSO
OH
TIPSO
H
H
H
H
H
H
CO2Me
OTBS
OH
OTBS
H
H
3
2
y. 82%, >10 : 1
We reported synthesis of the AB ring moiety 3 (Scheme
1) of (+)-FR182877 (Fig. 1) via 2, which was success-
fully prepared by the stereoselective IMDA reaction of
1 (>10:1, Scheme 1).2 In that work, the IMDA reaction
of 10, which was a diastereomer of 1 at the C3 position,
was found to show the low diastereoselectivity (20 and 200
in a ratio of 1:1.2). Hence, this dramatic change in the
diastereoselectivity interested us greatly.
IMDA
3
1
5
CO2Me
4
TBSO
2
reaction
TIPSO
OH
OH
1'
4
5
4
3
2
5
OH
TIPSO
+
TIPSO
3
H
H
H
H
H
H
2
CO2Me
CO2Me
OTBS
1
1
OTBS
2'' y. 49%
H
H
y. 42%
2'
Although many IMDA reactions of the terminally acti-
vated (E,E,E)-nona-1,6,8-trienes have been reported,2–8
there have been no studies on the structure–diastereo-
selectivity relationships in the IMDA reactions of the
above substrates possessing stereogenic centers at the
C3, C4, and C5 positions so far as we know. Such stud-
ies are useful for the stereoselective total synthesis of the
reported bioactive natural products incorporating a
Scheme 1. IMDA reactions of 1 and 10.2
OH
O
O
O
H
E
H
A
H
H
HO
H
D
B
C
H
H
(-)-FR182877
*
Corresponding author. Tel./fax: +81 3 5286 3240; e-mail: mnakada@
waseda.jp
Figure 1. Structure of (ꢀ)-FR182877.
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.12.118

1594
T. Suzuki et al. / Tetrahedron Letters 47 (2006) 1593–1598
bicyclo[4.3.0]non-2-ene carbon skeleton8,9 as well as
the forthcoming congeners. Consequently, we were
prompted to study the IMDA reactions of the deriva-
tives of 1, and we wish to report the structure–diastereo-
selectivity relationships of the terminally activated
(E,E,E)-nona-1,6,8-trienes, which include new successful
examples and suggest that the configuration of the C3
position bearing the protected hydroxyl group is crucial
to the diastereoselectivity in the IMDA reaction of the
above substrates.
We additionally prepared the simplified racemic sub-
strates IIIa–d, which lack the C4 methyl group, and
IVa–c which possess only the C3 stereogenic centers
(Schemes 4 and 5). Thus, addition of methyl lithium to
aldehyde 8, and the following MnO2 oxidation gener-
ated methyl ketone 13. An aldol reaction of 13 with
methyl (E)-4-oxo-2-butenoate14 afforded 14, which was
converted to benzoate 15, followed by Luche reduc-
tion15 to give a separable mixture of 16-syn and 16-anti.
Compounds IIIa–d were prepared from 16-syn by the
conventional methods as shown in Scheme 4, and their
relative configuration was successfully determined by
13C NMR of the corresponding acetonides.16 Prepara-
tion of IVa–b is shown in Scheme 5. Acetate 19, pre-
pared from 8 via Luche reduction and following
acetylation, was coupled with the Weinreb amide of
phenylsulfonylacetic acid using Pd(0), followed by
removal of the phenyl sulfonyl group and subsequent
DIBAL-H reduction affording 20. Kishi–Nozaki
coupling of 20 with methyl (E)-3-iodoacrylate generated
21, and the benzoate IVa and TBS ether IVb were
prepared in the usual manner.
We prepared all the diastereomers and congeners of 1
derived from the C3, C4, and C5 stereogenic centers,10
and examined their IMDA reactions. The C4,5-syn
series, Ia–d, was prepared from 42 according to the
reported method for preparing 1 and 10 (Scheme 2).2
The structures of Ia–d were determined by comparing
1
their H NMR spectrums with those of 1 and 10.11
The C4,5-anti series, IIa–d, was prepared as shown in
Scheme 3, starting from the anti-selective aldol reaction
of aldehyde 812 and ketone 9.13 The resultant alcohol 10
was protected as the triethylsilyl ether, followed by
reduction with LiBH4 and oxidative cleavage with
NaIO4 to afford aldehyde 11. Kishi–Nozaki coupling
of 11 with methyl (E)-3-iodoacrylate gave separable dia-
stereomers 12-syn and 12-anti, which were converted to
benzoates IIa and IIc, respectively, and were also con-
verted to silyl ethers IId and IIb, respectively.
The IMDA reactions of the C4,5-syn series, Ia–d, are
summarized in Table 1; the IMDA reaction of Ia gener-
ated AIa and BIa in a ratio of 1.1:1 (entry 1), and the
IMDA reaction of Ib generated AIb and BIb in a ratio
of 2.5:1 (entry 2). On the other hand, the IMDA reac-
tions of Ic and Id, possessing C3,4-anti relative configu-
a, b
N
c
d
TBSO
CHO
6-syn + 6-anti
7
TBSO
OMe
6-anti +
O
HO
TESO
5
4
e
g-i
6-syn (R1=H, R2=OH), 6-anti (R1=OH, R2=H), 7 (R1=R2=O)
f
j
Ia
Ic
6
-anti
Ib
Id
1
CO2Me
5
3
2
4
TBSO
Ia (R1= H, R2= OBz), Ib (R1= H, R2= OTBS)
k
Ic (R1= OBz, R2= H), Id (R1= OTBS, R2= H)
TESO R1 R2
6-anti
Scheme 2. Reagents and conditions: (a) TESCl, imidazole, DMAP, DMF, rt, 92%; (b) DIBAL-H, THF, ꢀ78 °C, 92%; (c) NiCl2 (cat.), CrCl2, methyl
(E)-3-iodoacrylate, NaHCO3, THF, rt, 96%, syn/anti = 2:5; (d) MnO2, CH2Cl2, rt, 6-anti (47%, anti only), 7 (47%); (e) NaBH(OMe)3, MeOH, rt,
30 min, 64%, syn/anti = 1:1; (f) PPh3, DEAD, BzOH, toluene, rt, 74% (at 70% conversion); (g) PPh3, DEAD, CH2ClCO2H, toluene, rt, 80% (at 82%
conversion); (h) K2CO3, MeOH, rt, 86%; (i) TBSCl, imidazole, DMAP, DMF, CH2Cl2, rt, 95% (at 75% conversion); (j) Bz2O, DMAP, CH2Cl2, rt,
7 h, 83% (at 88% conversion); (k) TBSCl, imidazole, DMAP, DMF, CH2Cl2, rt, 94% (at 71% conversion).
a
b, c, d
TBSO
CHO
OBz
+
TBSO
OBz
TBSO
e
CHO
TESO
O
8
OH
O
9
11
10
CO2Me
CO2Me
TBSO
+
TBSO
TESO
OH
12-anti
TESO
OH
12-syn
1
CO2Me
5
3
4
2
TBSO
f
g
i
12-syn
12-anti
IIa
IIc
12-syn
12-anti
IIb
IId
TESO R1 R2
h
IIa (R1 = OBz, R2 = H), IIIb (R1 = OTBS, R2 = H)
IIc (R1 = H, R2 = OBz), IIId (R1 = H, R2 = OTBS)
Scheme 3. Reagents and conditions: (a) c-Hex2BCl, Me2NEt, Et2O, ꢀ78 °C then ꢀ20 °C; (b) TESCl, imidazole, DMAP, CH2Cl2, DMF, 96% (two
steps); (c) LiBH4, THF, ꢀ78 °C, rt; (d) NaIO4, NaHCO3, MeOH, H2O, 89% (two steps); (e) methyl (E)-3-iodoacrylate, NiCl2, CrCl2, THF, 12-syn
(42%), 12-anti (53%); (f) Bz2O, DMAP, CH2Cl2, rt, 72%; (g) TBSOTf, DIPEA, CH2Cl2, rt, 79%; (h) Bz2O, DMAP, CH2Cl2, rt, 71%; (i) TBSOTf,
DIPEA, CH2Cl2, rt, 83%.

T. Suzuki et al. / Tetrahedron Letters 47 (2006) 1593–1598
1595
g
f
h
16-syn
i, j
17
3
IIIa
k
IIIb
CO2Me
R
c
TBSO
TBSO
l
O
OR
O
IIIc
17
18
18
IIId
8 (R=H)
13 (R=CH3)
14 (R=H)
15 (R=Bz)
a, b
d
1
CO2Me
5
4
2
TBSO
TESO R1 R2
e
CO2Me
CO2Me
TBSO
+
TBSO
17 (R1 = H, R2 = OH), 18 (R1 = OH, R2 = H)
IIIa (R1 = H, R2 = OBz), IIIb (R1 = H, R2 = OTBS)
IIIc (R1 = OBz, R2 = H), IIId (R1 = OTBS, R2 = H)
HO
OBz
16-anti
HO
OBz
16-syn
Scheme 4. Reagents and conditions: (a) MeLi, THF, ꢀ78 °C, 83%; (b) MnO2, CH2Cl2, rt, 91%; (c) LDA, then methyl (E)-4-oxo-2-butenoate, THF,
ꢀ78 °C, 69%; (d) BzCl, DMAP, pyridine, CH2Cl2, rt, 62%; (e) CeCl3Æ6H2O, NaBH4, MeOH, rt, 16-syn (41%), 16-anti (14%); (f) TESOTf, TEA,
CH2Cl2, rt, 93%; (g) K2CO3, MeOH, rt, 75% (at 56% conversion); (h) imidazole, DMAP, TBSCl, DMF, rt, 89%; (i) PPh3, ClCH2COOH, DEAD,
toluene, rt, 87%; (j) K2CO3, MeOH, rt, 77%; (k) BzCl, DMAP, pyridine, CH2Cl2, rt, 92% (at 44% conversion); (l) imidazole, DMAP, TBSCl, DMF,
rt, 80%.
c-e
1
f
CO2Me
3
2
TBSO
TBSO
CHO
TBSO
a,b
R
R1
8 (R=CHO)
19 (R=CH2OAc)
20
h
g
IVa (R1=OBz)
21 (R1=OH)
IVb (R1=OTBS)
Scheme 5. Reagents and conditions: (a) NaBH4, CeCl3Æ7H2O, MeOH, rt, 90%; (b) Ac2O, pyridine, DMAP, CH2Cl2, rt, 95%; (c)
PhSO2CH2CONMe(OMe), NaH, Pd2(dba)3, PPh3, reflux, 94%; (d) Mg, MeOH, rt, 94%; (e) DIBAL-H, THF, ꢀ78 °C, 99%; (f) methyl (E)-3-
iodoacrylate, NiCl2, CrCl2, NaHCO3, THF, rt, 91%; (g) Bz2O, DMAP, CH2Cl2, rt, 97%; (h) TBSOTf, DIPEA, CH2Cl2, rt, 98%.
Table 1. IMDA reactions of Ia–da
R1
R2
R1
R2
anti
anti
4
4
CO2Me
3
TESO
TESO
2
4
3
3
TBSO
BHT (0.05 eq)
H
H
BIa (R1 = H; R2 = OBz)
BIb (R1 = H; R2 = OTBS)
BIc (R1 = OBz; R2 = H)
AIa (R1 = H; R2 = OBz)
AIb (R1 = H; R2 = OTBS)
AIc (R1 = OBz; R2 = H)
TESO R1 R2
H
H
H
H
2
+
2
toluene, 80 oC, 24 h
CO2Me
CO2Me
Ia (R1 = H; R2 = OBz); Ib (R1 = H; R2 = OTBS)
Ic (R1 = OBz; R2 = H); Id (R1 = OTBS; R2 = H)
OTBS AId (R1 = OTBS; R2 = H)
H
OTBS BId (R1 = OTBS; R2 = H)
H
Entry
R1
R2
Substrate
Yield (%) of Ab
Yield (%) of Bb
A:B
1
2
3
4
H
H
OBz
OTBS
OBz
OTBS
H
Ia
Ib
Ic
Id
46
68
16
11
40
27
65
77
1.1:1
2.5:1
1:4.1
1:7.0
H
a The IMDA reactions of Ia–d were carried out under the same conditions as those for the IMDA reaction of 1.2
b Isolated yield.
ration, showed the reversed diastereoselectivity; that is,
the IMDA reaction of Ic generated AIc and BIc in a
ratio of 1:4.1 (entry 3), and the IMDA reaction of Id
generated AId and BId in a ratio of 1:7.0 (entry 4).
the C4 methyl group (Table 3), and nor also in the reac-
tions of IVa–b which possess only the C3 stereogenic
center (Table 4).
In addition to the trend in the diastereoselectivity
described above, the relationships between the relative
configuration and the diastereomeric ratio in Table 3
are quite similar to those in Table 1, thereby suggesting
that the steric effect of the C4 methyl group on the dia-
stereoselectivity is negligible in the case of the C4,5-syn
series. In contrast, compared with the results in Tables
1, 3 and 4, the high diastereoselectivity (1:>10, entries
3 and 4) in the IMDA reactions of the C4,5-anti IIc
and IId (Table 2) is noteworthy, clearly indicating that
the relative configuration of the C3–C5 positions is cru-
cial to the high selectivity.
The IMDA reactions of the C4,5-anti series, IIa–d, were
carried out under the same conditions as those for 12
(Table 2). The IMDA reactions of IIa–d showed the
same trend in their diastereoselectivity as that of Ia–d.
Thus, CIIa and DIIa formed in a ratio of 1.8:1 (entry
1), and CIIb and DIIb formed in a ratio of 1.9:1 (entry
2). The IMDA reactions of IIc and IId afforded the cor-
responding CII and DII in a high diastereomeric ratio of
1:>10 (entries 3 and 4).
The preferential formation of the products with the anti-
relative configuration between the C–H bond at the C2
position and the C–O bond at the C3 position did not
change in the IMDA reactions of IIIa–d, which lack
The transition state models which can explain the pref-
erential formation of the major products in the IMDA

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T. Suzuki et al. / Tetrahedron Letters 47 (2006) 1593–1598
Table 2. IMDA reactions of IIa–da
R1
R2
R1
anti
anti
3
CO2Me
TESO
TESO
4
R2
4
4
2
3
3
TBSO
BHT (0.05 eq)
H
H
DIIa (R1 = H; R2 = OBz)
DIIb (R1 = H; R2 = OTBS)
DIIc (R1 = OBz; R2 = H)
CIIa (R1 = H; R2 = OBz)
CIIb (R1 = H; R2 = OTBS)
CIIc (R1 = OBz; R2 = H)
TESO R1 R2
H
H
H
H
2
+
2
toluene, 80 oC, 24 h
CO2Me
CO2Me
IIa (R1 = H; R2 = OBz); IIb (R1 = H; R2 = OTBS)
IIc (R1 = OBz; R2 = H); IId (R1 = OTBS; R2 = H)
OTBS CIId (R1 = OTBS; R2 = H)
H
OTBS DIId (R1 = OTBS; R2 = H)
H
Entry
R1
R2
Substrate
Yield (%) of Cb
Yield (%) of Db
C:D
1
2
3
4
H
H
OBz
OTBS
OBz
OTBS
H
IIa
IIb
IIc
IId
50
60
—
28
31
72
74
1.8:1
1.9:1
1:>10d
1:>10d
c
c
H
—
a,bSee the footnotes to Table 1.
c Yield was not calculated because the product contained impurity.
d Ratio determined by 1H NMR.
Table 3. IMDA reactions of IIIa–da
R1
anti
R1
R2
anti
R2
3
TESO
CO2Me
TESO
EIIIa (R1 = H; R2 = OBz)
EIIIb (R1 = H; R2 = OTBS)
EIIIc (R1 = OBz; R2 = H)
EIIId (R1 = OTBS; R2 = H)
FIIIa (R1 = H; R2 = OBz)
FIIIb (R1 = H; R2 = OTBS)
3
3
2
TBSO
BHT (0.05 eq)
H
H
H
H
TESO R1 R2
2
+
H
H
2
CO2Me FIIIc (R1 = OBz; R2 = H)
FIIId (R1 = OTBS; R2 = H)
OTBS
toluene, 80 oC, 24 h
CO2Me
IIIa (R1 = H; R2 = OBz); IIIb (R1 = H; R2 = OTBS)
IIIc (R1 = OBz; R2 = H); IIId (R1 = OTBS; R2 = H)
H
H
OTBS
Entry
R1
R2
Substrate
Yield (%) of Eb
Yield (%) of Fb
E:F
1
2
3
4
H
H
OBz
OTBS
OBz
OTBS
H
IIIa
IIIb
IIIc
IIId
44
66
15
11
31
15
67
72
1.4:1
4.4:1
1:4.5
1:6.5
H
a,bSee the footnotes to Table 1.
Table 4. IMDA reactions of IVa–da
anti
H
H
R
3
R
CO2Me
3
3
TBSO
BHT (0.05 eq)
H
H
H
H
H
H
2
R
2
+
HIVa (R = OBz)
HIVb (R = OTBS)
GIVa (R = OBz)
GIVb (R = OTBS)
toluene, 80 oC, 24 h
CO2Me
CO2Me
IVa (R = OBz); IVb (R = OTBS)
H
OTBS
H
OTBS
Entry
R
Substrate
Yield (%) of Gb
Yield (%) of Hb
G:H
1
2
OBz
OTBS
IVa
IVb
61
57
23
15
2.7:1
3.8:1
a,bSee the footnotes to Table 1.
reactions of Ia–d and IIa–d are proposed in Figure 2.
Since all the products in Tables 1 and 2 are the endo-
adducts, the transition states are limited to TS-1 and
TS-2 for the reactions of Ia, Ib, IIa, and IIb, and TS-3
and TS-4 for the reactions of Ic, Id, IIc, and IId. Since
a carbon–oxygen bondꢁ possesses a rather low-lying
rꢁCO, when the allylic rCO orbital of the dienophile is
aligned anti to the forming bonding in the IMDA reac-
tion, its overlap with the HOMO of the transition state,
consisting of a mixture of the HOMO of diene and the
LUMO of dienophile, is maximized.17 Consequently,
considering the above stereoelectronic effect, TS-2 and
TS-3 shown in Figure 2 are surmised to be energetically
moreꢁfavored than TS-1 and TS-4, respectively, because
the rCO orbital at C3 position is surmised to align nearly
anti to the forming bonding in the IMDA reaction.
However, the major products formed in Tables 1 and 2
must generate through TS-1 or TS-4; hence, other factors
stabilizing TS-1 and TS-4 or destabilizing TS-2 and TS-3
should exist in the IMDA reactions in Tables 1 and 2.
The stereoelectronic effect as described above cannot
explain the outcome of the IMDA reactions of IIIa–d
and IVa–b again, however, the reactions of IVa–b were
suggestive because the products GIVa–b, which possess
the anti relative configuration between C–H bond at
the C2 position and C–O bond at the C3 position, were
preferentially generated. These results clearly indicate
that the configuration of the C3 stereogenic center bear-
ing the protected hydroxyl group is crucial to the
observed diastereoselectivity because IVa–b possess only
one protected hydroxyl group at the stereogenic C3

T. Suzuki et al. / Tetrahedron Letters 47 (2006) 1593–1598
1597
R
H
R
H
OP
H
TESO
OP
OTES
H
OTES
TESO
OP
H
H
H
H
H
H
H
H
H
TBSO
H
TBSO
PO
H
CO2Me
MeO2C
Me
CO2Me
MeO2C
Me
H
R
H
R
R
R
3
9
OP
3
9
OP
OTBS
5
5
H
OTBS
TESO
TESO
TS-3
TS-4
disfavored
TS-1
favored
AIc, AId, EIIIc, EIIId
R
AIa, AIb, EIIIa, EIIIb
1
1
CO2Me
OTBS
CO2Me
OTBS
R
Me
Me
TESO
OP
H
H
TESO
OP
H
H
OTES
OTES
H
H
MeO2C
TBSO
H
H
H
MeO2C
TBSO
H
Ia, Ib, IIIa, IIIb
R=Me, H
Ic, Id, IIIc, IIId
R=Me, H
H
H
CO2Me
CO2Me
R
R
H
PO
H
H
OP
H
H
OTBS
H
OTBS
TS-2
disfavored
favored
BIa, BIb, FIIIIa, FIIIb
BIc, BId, FIIIc, FIIId
Figure 2.
ences cited therein; (b) Takao, K.; Munakata, R.; Tadano,
K. Chem. Rev. 2005, 105, 4779–4807.
position. Nevertheless, a careful analysis and discussion
is required to account for the observed diastereoselectiv-
ity because various factors were surmised to influence
the diastereoselectivity and the rationale as well as quan-
titative analysis for the diastereoselectivity awaits fur-
ther studies on the IMDA reactions and theoretical
calculations.
2. Suzuki, T.; Nakada, M. Tetrahedron Lett. 2002, 43, 3263–
3267. Absolute configuration shown in Scheme 1 and
Table 2 is reversed to avoid confusion. For total synthesis
and synthetic studies on FR182877, see Refs. 3–7.
3. (a) Vanderwal, C. D.; Vosburg, D. A.; Weiler, S.;
Sorensen, E. J. Org. Lett. 1999, 1, 645–648; (b) Vosburg,
D. A.; Vanderwal, C. D.; Sorensen, E. J. Org. Lett. 2001,
3, 4307–4310; (c) Vosburg, D. A.; Vanderwal, C. D.;
Sorensen, E. J. J. Am. Chem. Soc. 2002, 124, 4552–4553;
(d) Vanderwal, C. D.; Vosburg, D. A.; Weiler, S.;
Sorensen, E. J. J. Am. Chem. Soc. 2003, 125, 5359–
5373.
4. (a) Evans, D. A.; Starr, J. T. Angew. Chem., Int. Ed. 2002,
41, 1787–1790; (b) Evans, D. A.; Starr, J. T. J. J. Am.
Chem. Soc. 2003, 125, 13531–13540.
5. Methot, J. E.; Roush, W. R. Org. Lett. 2003, 43, 3263–
3267.
In conclusion, we found that the configuration of the
stereogenic C3 position bearing the protected hydroxyl
group is crucial to the diastereoselectivity in the IMDA
reaction of the terminally activated (E,E,E)-nona-1,6,8-
trienes, and also found the new successful IMDA reac-
tion of the diastereomer of 1 which produced the prod-
ucts in a ratio of 1:>10. These results would be useful for
constructing bioactive natural products containing a
bicyclo[4.3.0]non-2-ene carbon skeleton. Further studies
on the structure–diastereoselectivity relationships as
well as the studies with the aid of theoretical calculations
are in progress, and the results will be reported in due
course.
6. Armstrong, A.; Goldberg, F. W.; Sandham, D. A.
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A. J. Tetrahedron 2005, 61, 353–363.
Acknowledgements
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We thank the Material Characterization Central Labo-
ratory, Waseda University, for its technical support of
the X-ray crystallographic analysis. This work was
financially supported in part by a Waseda University
Grant for Special Research Projects, and a Grant-in-
Aid for Scientific Research (C) from the Ministry
of Education, Science, Sports, Culture and Technology,
Japan. We are also indebted to 21COE ‘Practical Nano-
Chemistry’.
Supplementary data
The structure determination of all the products based on
1
the H NMR experiments and CIF files for the X-ray
crystallographic analysis. Supplementary data associ-
ated with this article can be found, in the online version,
at doi:10.1016/j.tetlet.2005.12.118.
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