Samarium(II) iodide-induced tandem reductive coupling-Dieckmann condensation reaction: One-step synthesis of bicyclic oxacyclopentanecarboxylate from bis-α,β-unsaturated esters

Article abstract of DOI:10.1016/S0040-4039(03)01093-1

The tandem cyclization of bis-α,β-unsaturated esters with SmI₂-Sm-THF in the presence of catalytic amount of methanol was found to stereoselectively provide bicyclo[4.3.0]nonan-8-ones and bicyclo[3.3.0]octan-3-ones.

Full text of DOI:10.1016/S0040-4039(03)01093-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 4649–4652
Samarium(II) iodide-induced tandem reductive
coupling-Dieckmann condensation reaction: one-step synthesis of
bicyclic oxacyclopentanecarboxylate from
bis-a,b-unsaturated esters
a
b,†
b
a,
Ikuo Shinohara, Masayuki Okue, Yasuji Yamada and Hiroto Nagaoka *
a
Meiji Pharmaceutical University, Noshio, Kiyose, Tokyo 204-8588, Japan
b
Tokyo University of Pharmacy and Life Science, Horinouchi, Hachioji, Tokyo 192-0392, Japan
Received 27 March 2003; revised 25 April 2003; accepted 25 April 2003
Abstract—The tandem cyclization of bis-a,b-unsaturated esters with SmI -Sm–THF in the presence of catalytic amount of
2
methanol was found to stereoselectively provide bicyclo[4.3.0]nonan-8-ones and bicyclo[3.3.0]octan-3-ones. © 2003 Elsevier
Science Ltd. All rights reserved.
Numerous efforts have been made to produce bicyclic
cyclopentanones, not only in consideration of their
abundance in nature, but also their usefulness as ver-
satile synthetic building blocks. The tandem reductive
coupling-Dieckmann condensation reaction has been
found quite useful as a one-step process for effectively
producing oxacyclopentanecarboxylates from1 a,b-
unsaturated esters. Electrohydrodimerization and
effective method for the SmI -induced tandem cycliza-
2
tion of bis-a,b-unsaturated ester to afford bicy-
clo[4.3.0]octan-8-ones and bicyclo[3.3.0]nonan-3-ones
3
(Scheme 1).
2
metal (Yb or Na)-induced cyclization of cinnamate
derivatives are methods generally applied for this pur-
pose but to our knowledge none has been shown to
produce in an intramolecular manner bicyclic oxacy-
clopentanecarboxylate. The authors have established an
Scheme 1.
Keywords: samarium and compounds; radicals and radical reactions;
annulation; cyclopentanones.
*
Corresponding author. Tel./fax: +81-424-95-8796; e-mail:
nagaoka@my-pharm.ac.jp
Present address: Pharmaceutical Production Technology Laborato-
ries, Meiji Seika Kaisha, Ltd, 788 Kayama, Odawara, Kanagawa
†
2
50-0852, Japan.
Scheme 2.
0
040-4039/03/$ - see front matter © 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4039(03)01093-1

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I. Shinohara et al. / Tetrahedron Letters 44 (2003) 4649–4652
The reaction of bis-a,b-unsaturated ester i (R=Et) with
transformation of bis-a,b-unsaturated ester i to bicyclic
keto ester v possibly via iii and iv, and the a-keto ester
v thus obtained should serve as a new proton source.
SmI –HMPA in the presence of an adequate proton
2
source gives intramolecular reductive coupling product
ii according to Inanaga but formation of bicyclic oxacy4-
clopentanecarboxylate v is not described (Scheme 2).
Appropriate reaction conditions should make possible
Dieckmann condensation subsequent to the intramolec-
ular reductive coupling of i. That is, quantitative
restrictions on the proton source may bring about
Study to clarify conditions for the tandem cyclization
reaction indicated 1.5 equiv. of SmI , 1.5 equiv. of Sm
2
and trace amount of alcohol in THF effective for this
purpose and olefin geometry in substrates and HMPA
as an additive to affect the stereochemistry of the
a
Table 1. SmI -induced tandem reductive coupling-Dieckmann condensation of bis-a,b-unsaturated esters
2

I. Shinohara et al. / Tetrahedron Letters 44 (2003) 4649–4652
4651
Scheme 3.
cyclized products, as evident from Table 1. On treating
temperature under an argon atmosphere. The mixture,
following addition of a solution of bis-a,b-unsaturated
ester 1 (75.3 mg, 0.333 mmol) and methanol (40 mg) in
THF (2 mL) was stirred for 1.5 h at 50°C and the
reaction was terminated with few drops of 30% hydro-
gen peroxide and 1N HCl. The mixture was then
5
bisenoate 1, whose double bonds have the E configura-
6
tion, with SmI –Sm in THF in the presence of a trace
2
amount of methanol at room temperature,
(
8
1R*,6S*,7R*)-7-methoxycarbonylbicyclo[4.3.0]nonan-
-one (3) having a trans ring juncture was obtained as
7
diluted with ether, washed with saturated NaHCO and
the main product along with a small amount of cis
isomer 2 (2:3=1:12) (entry 1). Higher reaction tempera-
3
saturated Na S O , dried and concentrated. The crude
2
2
3
product was purified by silica gel column chromatogra-
phy to give keto ester 3 (51.0 mg, 78% yield) which
contained a small amount of 2 (2:3=1:21).
ture (50°C) improved the value of the ratio of 3/2
8
(
2:3=1:21) and yield (entry 2). HMPA addition
enhanced the reaction rate, though considerably
decreased the ratio of 3/2 (entry 3). Reaction of 4, the
E,Z-isomer of 1, with SmI –Sm gave cis isomer 2 as
9
10
In summary, the authors established an effective and
direct one-step process for obtaining bicy-
clo[4.3.0]nonan-8-ones and bicyclo[3.3.0]octan-3-ones
from simple bis-a,b-unsaturated esters using one elec-
2
the major product, 2:3=14:1 in good yield (entry 4).
This tandem cyclization was found useful for establish-
ing a bicyclo[3.3.0]octane ring system. The cyclization
1
1
tron transfer reagent SmI in the presence of methanol
2
of 5 with SmI –Sm in THF proceeded to completion
2
1
2
in trace amount. By these mild conditions, the use of
strongly basic conditions for the Dieckmann condensa-
tion is avoided and good to excellent stereocontrol over
newly formed ring junctures in the product is possible.
within 15 min at 0°C with only cis isomer 6 formation
entry 5). The presence of HMPA resulted in the
warped trans isomer 7 formation, in addition (entry
). The severely strained 7 was not synthesized from the
corresponding trans cyclopentane diester, methyl 2-
(1R*,2R*)-2-[(methoxycarbonyl)methyl]-4,4-dimethyl-
(
13
6
{
Acknowledgements
cyclopentyl}acetate, by typical conditions for
Dieckmann condensation such as sodium methoxide in
5
toluene or in DMSO. Reaction of bisenoate 8 with
This work was supported in part by a Grant-in Aid for
Scientific Research from Japan Society for the Promo-
tion of Science.
14
15
SmI –Sm provided tricyclic keto esters 9 and 10,
2
each possessing a cis ring juncture, in moderate yield.
Intermolecular cyclization of methyl cinnamate (11)
with SmI –Sm in THF and SmI in THF–HMPA gave
2
2
1
6
1c
cis isomer 12 and trans isomer 13 as major products,
respectively, the former being in contrast to electrohy-
drodimerization and metal-induced coupling of 11
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