A facile synthesis of cis-4-amino-2-cyclopentene-1-methanol, a key intermediate for the synthesis of carbocyclic nucleosides

Article abstract of DOI:10.1081/NCN-120006531

A number of carbocyclic nucleosides can be synthesized from (±)-cis-4-amino-2-cyclopentene-1-methanol (3). Carbocyclic amino alcohol 3 is a key intermediate that makes possible the efficient synthesis of the carbocyclic nucleosides. In this study we wish to report an efficient synthesis of carbocyclic amino alcohol 3 from inexpensive and readily available starting material. The synthetic route employed cyclopentadiene (4) as a starting material and proceeded in 38% overall yield through 6 steps involving a hetero Diels-Alder reaction and an aza-Claisen rearrangement.

Full text of DOI:10.1081/NCN-120006531

This article was downloaded by: [Gazi University]
On: 30 April 2015, At: 14:18
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Nucleosides, Nucleotides and Nucleic Acids
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lncn20
A FACILE SYNTHESIS OF CIS-4-AMINO-2-
CYCLOPENTENE-1-METHANOL, A KEY INTERMEDIATE
FOR THE SYNTHESIS OF CARBOCYCLIC NUCLEOSIDES
a
a
Gwang-il An & Hakjune Rhee
a
Department of Chemistry , Hanyang University , Ansan, Kyunggi-do, 425-791, Korea
Published online: 17 Aug 2006.
To cite this article: Gwang-il An & Hakjune Rhee (2002) A FACILE SYNTHESIS OF CIS-4-AMINO-2-CYCLOPENTENE-1-METHANOL,
A KEY INTERMEDIATE FOR THE SYNTHESIS OF CARBOCYCLIC NUCLEOSIDES, Nucleosides, Nucleotides and Nucleic Acids, 21:1,
65-72, DOI: 10.1081/NCN-120006531
To link to this article: http://dx.doi.org/10.1081/NCN-120006531
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS, 21(1), 65–72 (2002)
A FACILE SYNTHESIS OF CIS-4-AMINO-
2
-CYCLOPENTENE-1-METHANOL, A KEY
INTERMEDIATE FOR THE SYNTHESIS
OF CARBOCYCLIC NUCLEOSIDES
Gwang-il An andHakjune Rhee *
Department of Chemistry, Hanyang University, Ansan,
Kyunggi-do 425-791, Korea
ABSTRACT
A number of carbocyclic nucleosides can be synthesized from (ꢀ)-cis-4-
amino-2-cyclopentene-1-methanol (3). Carbocyclic amino alcohol 3 is
a key intermediate that makes possible the efficient synthesis of the
carbocyclic nucleosides. In this study we wish to report an efficient
synthesis of carbocyclic amino alcohol 3 from inexpensive and readily
available starting material. The synthetic route employed cyclopentadi-
ene (4) as a starting material and proceeded in 38% overall yield through
6
steps involving a hetero Diels-Alder reaction and an aza-Claisen
rearrangement.
INTRODUCTION
Interest in the synthesis of carbocyclic nucleosides and carbocyclic
analogues of normal purine or pyrimidine nucleosides has grown exclusively
1
since the potential antiviral and antitumor therapeutic agents . The repla-
cement of the furanose oxygen by a carbon gives the nucleoside increased
stability to the enzymes that cleave the nucleosidic bonds of the natural
2
nucleosides in addition to modifying the biological activity . Carbocyclic
*Corresponding author. Fax: 82-31-407-3863; E-mail: hrhee@hanyang.ac.kr
65
Copyright # 2002 by Marcel Dekker, Inc.
www.dekker.com

66
AN AND RHEE
0
0
0
0
3
2
in vitro selective inhibitor of HIV-1and exhibited less toxicity than other
,3 -didehydro-2 ,3 -dideoxyguanosine (carbovir, 1) was reported to be an
agents. The analogue of (-)-carbovir, abacavir (1592U89, Ziagen, 2), which
has higher oral bioavailability than carbovir , is currently commercialized for
4
the treatment of HIV infection. Two general synthetic approaches for these
carbocyclic nucleosides are coupling of the intact purine to a carbocycle like
cyclopentenyl derivatives and construction of the purine from the amino
alcohol 3. Among these methods, the coupling of an intact heterocyclic base
to a cyclopentenyl derivative is not efficient for industrial method since
palladium catalyst can be applied just for academic research works. When
the palladium-catalyzed coupling reactions of nucleobase and cyclopentenyl
derivatives were scaled up, the ratio of minor products is getting larger. That
is a major and very serious problem for the first method, but the construction
of the purine from the amino alcohol 3 is relatively suitable for a large scale.
For these reasons and the important biological activity of these carbocyclic
nucleosides, the synthesis of the amino alcohol, a key intermediate for
carbocyclic nucleosides, increasingly important and has been focused and
5
reported by several research groups . In most cases, the amino alcohol 3 was
prepared via a Diels-Alder reaction between a sulfonyl cyanide and cyclo-
pentadiene. We wish to report here a short and an efficient synthetic route for
the hydrochloride salt of carbocyclic amino alcohol 3 starting from cyclo-
pentadiene.
Carbocyclic amino alcohol, 3
RESULTS AND DISCUSSION
Hetero Diels-Alder reaction of cyclopentadiene (4) and glyoxylic acid
(
5) in water was known as a facile method for the synthesis of bicyclic
3j,6
a–hydroxy-g-lactone 6 (Sch. 1) . The products of this reaction were able to
7
be separated by silica-gel column chromatography (6a:6b ¼ 1.72:1) ,

CIS-4-AMINO-2-CYCLOPENTENE-1-METHANOL
67
ꢁ
Scheme 1. a. Toluene, H
6%.
2
O, 40 C, 2 h, 79% (6a:6b ¼ 1.72:1). b. LiAlH
4
, THF, reflux, 2 h,
9
however, we used endo- and exo-hydroxylactone mixture in next step without
separation. Hydroxylactone 6 can be converted to the triol 7 by lithium
3
j,7,8
aluminum hydride reduction (Sch. 1)
.
Cleavage of the vicinal diol moiety with sodium periodate followed by
8
sodium borohydride reduction gave a diol 8 . Treatment of diol 8 with acetic
anhydride in pyridine gave the acetyl mono-protected cyclopentene diol 9
(
Sch. 2).
The conversion of allyl alcohol to allyl amide was achieved via 3,3-
9
sigmatropic rearrangement, known as aza-Claisen rearrangement . We
applied this protocol to the allyl alcohol 9. Thus, the reaction of allyl alcohol
9
with trichloroacetonitrile and the sequential aza-Claisen rearrangement of
imidate 10 gave a desired rearranged product 11 (Sch. 3).
1
1
The compound 11 was identified by H- H COSY spectrum (Fig. 1). In
this spectrum, H4 (d 4.78) is correlated with H3 (d 5.87 or 5.75), H5 (d 2.44
and 1.47: H and H ), and NH (d 9.07). Also, H1( d 2.95) is correlated with
a
b
0
H2 (d 5.87 or 5.75), H5 (d 2.44 and 1.47: H and H ), and H1 (d 4.01). From
a
b
these data, the compound 11 was identified as a 1,4-substituted cyclopentene.
A number of problems were encountered due to the unstable nature of
5a
amino alcohol 3 , especially in the hydrolysis step of the compound 11.
Because free amino alcohol 3 is unstable in light and moisture when con-
centrated from diluted solution, the basic hydrolysis always gave an intractable
mixture. Thus, the hydrolysis of compound 11 with methanolic hydrochloric
acid was attempted and afforded a stable hydrochloride salt 12 (Sch. 4).
Scheme 2. a. i) NaIO
b. pyridine, acetic anhydride, 0 C, 1d, 95%.
4
, diethyl ether=H
ꢁ
2
O, 2 h. ii) ethylene glycol, 1h. iii) NaBH
4
, 2 h, 70%.

68
AN AND RHEE
Scheme 3. a. DBU, trichloroacetonitrile, CHCl , 1 h. b. K CO , p-xylene, reflux, 14 h, 85%.
3
2
3
In summary, a facile synthesis of the compound 12 was achieved from
cyclopentadiene (4) in 38% overall yield through 6 steps. From the result of
the study, an amino alcohol 3 was provided as a valuable key intermediate
for the synthesis of carbocyclic nucleosides.
EXPERIMENTAL
1
Proton ( H) NMR spectra were obtained using a Varian Mercury 300
spectrometer (300 MHz) instrument operating in Fourier transform mode.
13
Carbon-13 ( C) NMR spectra were recorded using a Varian Mercury 300
spectrometer (75.5 MHz) instrument. Infrared spectra were recorded on Bio-
Rad FTS 6000 FT-IR spectrometer. Uncorrected melting points were
determined with a Gallenkamp melting point apparatus. Analytical thin layer
chromatography (TLC) was conducted on E. Merck 60 F254 aluminum
backed silica gel plates (0.2 mm) with a fluorescent indicator. Developed
plates were visualized under UV light, with iodine staining, or by dipping in
1
1
Figure 1. The H- H COSY spectrum of compound 11.

CIS-4-AMINO-2-CYCLOPENTENE-1-METHANOL
69
Scheme 4. a. 3 N methanolic HCl, reflux, 1d, 89%.
2.0% phosphomolybdic acid solution and then heating. Flash column
chromatography was performed using Merck silica gel 60 (230–400 mesh)
10
under positive pressure of air according to the procedure of Still . Reagents
and solvents were of reagent grade, and solvents were purified by the known
11
procedure before use .
cis-5-Hydroxymethyl-cyclopent-2-en-1-ol (8). Diol 8 was prepared
8
from triol 7 by a known procedure: IR (thin film) 3423, 3058, 2930, 1615,
À 1
1
1
1
1
1
441, 1350, 1155, 1019, 951, 891, 723 cm ; H NMR (CDCl ) d 5.98 (m,
3
H), 5.82 (m, 1H), 4.89 (m, 1H), 3.78 (m, 2H), 3.30 (br s, 1H), 3.06 (br s,
H), 2.43 (m, 1H), 2.32 (m, 1H), 2.16 (m, 1H); C NMR (CDCl ) d
13
3
35.01, 132.30, 77.69, 62.69, 42.59, 33.65.
cis-5-Acetoxymethyl-cyclopent-2-en-1-ol (9). To a solution of diol 8
2.00 g, 17.5 mmol) in anhydrous pyridine (15 mL) was added acetic
(
anhydride (1.96 mL, 19.3 mmol) in anhydrous CHCl3 (7 mL) by
ꢁ
cannulation at 0 C. After being stirred for 1d, the reaction mixture was
diluted with CHCl (50 mL) and washed with brine solution (50 mL63).
3
The aqueous phase was extracted with CHCl (20 mL63). The organic
3
phase was collected, dried with anhydrous MgSO and concentrated by
rotary-evaporation. The residue was purified by flash column
4
chromatography (diethyl ether: hexane ¼ 3:2, v=v) to give a colorless oil
(
1
R ¼ 0.25; 2.59 g, 95%): IR (thin film) 3467, 3123, 2889, 2768, 1750, 1610,
f
À 1
1
468, 1432, 1257, 1087, 747 cm ; H NMR (CDCl ) d 6.03 (m, 1H), 5.91
3
(
1
1
m, 1H), 4.71 (m, 1H), 4.35 (m, 1H), 4.20 (m, 1H), 2.44 (m, 1H), 2.37 (m,
13
H), 2.33 (br s, 1H), 2.31 (m, 1H), 2.08 (s, 3H); C NMR (CDCl ) d
3
71.29, 134.73, 132.60, 75.54, 63.85, 41.45, 33.86, 21.04; MS (EI) m=e:
þ
þ
þ
found 156 [M] , 155 [M-H] , 96 [M-(CO CH þH)] .
2
3

70
AN AND RHEE
cis-4-Trichloroacetamido-2-cyclopentene-1-methyl acetate (11). To a
solution of alcohol 9 (0.100 g, 0.641 mmol) in anhydrous CHCl3
(
7.0 mL) was added DBU (0.144 mL, 0.962 mmol) and trichloroacetonitrile
ꢁ
(0.128 mL, 1.28 mmol) at 0 C. After being stirred for 1h, the reaction
mixture was quenched with sat. NH Cl solution. The organic layer was
4
washed with sat. NH Cl solution (10 mL62) and passed through a column
4
packed with celite and silica gel with chloroform. The resulting solution was
evaporated under reduced pressure to give crude trichloroacetimidate that
used in the next reaction without any purification. The crude imidate was
dissolved in anhydrous xylene (10.0 mL). Then, K CO (0.0400 g,
2
3
ꢁ
0
.289 mmol) was added at 0 C to the solution. The mixture was heated at
reflux temperature for 14 h with vigorous stirring. After cooling to room
temperature the reaction mixture was diluted with CHCl (15 mL) and
3
washed with brine solution (15 mL63). The aqueous phase was extracted
with CHCl3 (20 mL63). The organic phase was collected, dried with
anhydrous MgSO , and concentrated by rotary-evaporation. The residue
was purified by flash column chromatography (ethyl acetate:hexane ¼ 1:4,
4
v=v) to give a pale yellow gummy solid (R ¼ 0.25; 0.163 g, 85%): IR (thin
f
À 1
film) 3331, 3058, 2949, 2893, 1741, 1710, 1513, 1243, 1037, 834, 832 cm
;
1
H NMR (DMSO-d ) d 9.07 (d, J ¼ 7.2 Hz, 1H), 5.87 (ddd, J ¼ 5.4, 3.5, 0.9
6
Hz, 1H), 5.75 (dd, J ¼ 4.9, 3.1 Hz, 1H), 4.78 (m, 1H), 4.01 (m, 2H), 2.95 (m,
13
1
(
H), 2.44 (m, 1H), 2.02 (s, 3H), 1.47 (dd, J ¼ 6.9, 6.6 Hz, 1H); C NMR
6
DMSO-d ) d 170.15, 160.73, 133.95, 131.93, 92.81, 66.86, 57.11, 43.62,
3
2
2.89, 20.73; MS (FAB) m=e: calcd for (C H Cl NO ): 299.9961, found
þ
10
13
3
3
99.9945 [MH] .
1
2
.
cis-4-Amino-2-cyclopentene-1-methanol HCl (12) . The rearranged
adduct 11 (0.0400 g, 0.130 mmol) was added to 3.0 N methanolic HCl
ꢁ
solution (10 mL) at À5 C. The reaction mixture was stirred at reflux
temperature for 1d. After removal of solvent by rotary-evaporation, the
residue was washed with mixed solvent (ethanol:diethyl ether ¼ 1:50 , v=v;
2
5 mL). And then the residue was recrystallized to give a pale brown solid
ꢁ
(
ethanol:diethyl ether, 0.0177 g, 89%): m.p. 129–131 C; IR (KBr) 3438,
1
À 1
3
1
1
3
321, 3058, 2927, 2874, 1516, 1337, 820 cm ; H NMR (D O) d 6.12 (m,
2
H), 5.87 (m, 1H), 4.32 (br m, 1H), 3.61 (m, 2H), 3.02 (m, 1H), 2.56 (m,
1
3
H), 1.59 (m, 1H); C NMR (D O) d 138.85, 127.35, 62.19, 55.47, 46.12,
2
0.92.
ACKNOWLEDGMENT
This work was supported by grant No. 2000-1-12300-003-3 from the
Basic Research Program of the Korea Science & Engineering Foundation

CIS-4-AMINO-2-CYCLOPENTENE-1-METHANOL
71
and partially supported by Hanyang University, Korea, made in the program
year of 2000.
REFERENCES
1.
(a) Agrofoglio, L.; Suhas, E.; Farese, A.; Condom, R.; Challand, S.R.; Earl,
R.A.; Guedj, R. Tetrahedron 1994, 50, 10,611–10,670. (b) Borthwick, A.D.;
Biggadike, K. Tetrahedron 1992, 48, 571–623. (c) Huryn, D.M.; Okabe, M.
Chem. Rev. 1992, 92, 1745–1768. (d) Marquez, V.E.; Lim, M.I. Med. Res.
Rev. 1986, 6, 1–40. (e) Hobbs, J.B. In Comprehensive Medicinal Chemistry;
Hansch, C., Sammers, P.G., Taylor, J.B., Eds.; Pergamon: Oxford, 1990;
Vol. 2, 306–322. (f ) Hovi, T. In Antiviral Agents: The Development and
Assessment of Antiviral Chemotherapy; Field, H.J., Ed.; CRC Press: 1988;
Chap. 1, pp 1–12.
2
.
.
Bennet, L.L., Jr.; Shannon, W.M.; Allan, P.W.; Arnett, G. Ann. N.Y. Acad.
Sci. 1975, 255, 342–357.
For some carbovir syntheses, see: (a) Katagiri, N.; Takebayashi, M.;
Kokufuda, H.; Kaneko, C.; Kanehira, K.; Torihara, M.J. Org. Chem. 1997,
3
62, 1580–1581. (b) Berranger, T.; Langlois, Y. Tetrahedron Lett. 1995, 36,
5523–5526. (c) Hildebrand, S.; Troxler, T.; Scheffold, R. Helv. Chim. Acta
1994, 77, 1236–1240. (d) Legraverend, M.; Aubertin, A.M.; Obert, G.;
Huel, C.; Bisagni, E. Nucleosides Nucleotides 1994, 13, 915–923. (e)
Diaz, M.; Ibarzo, J.; Jimenez, J.M.; Ortuno, R.M. Tetrahedron: Asymmetry
1
4
1
994, 5, 129–140. (f) Jung, M.E.; Rhee, H. J. Org. Chem. 1994, 59, 4719–
720. (g) Nokami, J.; Matsuura, H.; Nakasima, K.; Shibata, S. Chem. Lett.
994, 1071–1074. (h) Asami, M.; Takahashi, J.; Inoue, S. Tetrahedron: Asym-
metry 1994, 5, 1649–1652. (i) Hodgson, D.M.; Witherington, J.; Moloney,
B.A. J. Chem. Soc., Perkin Trans. I 1994, 3373–3378. (j) MacKeith, R.A.;
McCague, R.; Olivo, H.F.; Palmer, C.F.; Roberts, S.M. J. Chem. Soc., Perkin
Trans. I 1993, 313–314. (k) Jung, M.E.; Rhee, H. Tetrahedron Lett. 1993, 34,
4449–4452. (l) Evans, C.T.; Roberts, S.M.; Shoberu, K.A.; Sutherland, A.G.
J. Chem. Soc., Perkin Trans. I 1992, 589–592. (m) Trost, B.M.; Li, L.; Guile,
S.D. J. Am. Chem. Soc. 1992, 114, 8745–8747. (n) Peel, M.R.; Sternbach,
D.D.; Johnson, M.R. J. Org. Chem. 1991, 56, 4990–4993.
(a) Daluge, S.M.; Good, S.S.; Faletto, M.B.; Miller, W.H.; Clair, M.H.S.;
Boone, L.R.; Tisdale, M.; Parry, N.R.; Reardon, J.E.; Dornsife, R.E.; Averett,
D.R.; Krenitsky, T.A. Antimicrob. Agents Chemother. 1997, 41, 1082–1093.
4.
(b) Faletto, M.B.; Miller, W.H.; Garvey, E.P.; Clair, M.H.S.; Daluge, S.M.;
Good, S.S. Antimicrob. Agents Chemother. 1997, 41, 1099–1107. (c)
Kimberlin, D.W.; Coen, D.M.; Biron, K.K.; Cohen, J.I.; Lamb, R.A.; McKlin-
lay, M.; Emini, E.A.; Whitley, R. J. Antiviral Res. 1995, 26, 369–401. (d)
Daluge, S.M. U.S. Patent 5,034,394, 1991.
5.
(a) Daluge, S.M.; Martin, M.T.; Sickles, B.R.; Livingston, D.A. Nucleosides
Nucleotides Nucleic Acids 2000, 19, 297–327. (b) Mahmoudian, M.; Lowdon,
A.; Jones, M.; Dawson, M.; Wallis, C. Tetrahedron: Asymmetry 1999, 10,
1201–1206. (c) Katagiri, N.; Ito, Y.; Shiraishi, T.; Maruyama, T.; Sato, Y.;

72
AN AND RHEE
Kaneko, C. Nucleosides Nucleotides 1996, 15, 631–647. (d) Norman, M.H.;
Almond, M.R.; Barbara, E.R.; Rahim, S.G. Synth. Commun. 1992, 22,
3197–3204. (e) Katagiri, N.; Muto, M.; Nomura, M.; Higashikawa, T.;
Kaneko, C. Chem. Pharm. Bull. 1991, 39, 1112–1122. (f ) Vince, R.;
Hua, M.J. Med. Chem. 1990, 33, 17–21. (g) Katagiri, N.; Muto, M.;
Kaneko, C. Tetrahedron Lett. 1989, 30, 1645–1648. (h) Vince, R.;
Daluge, S.M. J. Org. Chem. 1978, 43, 2311–2320. (i) Jagt, J.C.; Van Leusen,
A.M. J. Org. Chem. 1974, 39, 564–566. ( j) Jagt, J.C.; Van Leusen, A.M. Recl.
Trav. Chim. Pays-Bas 1973, 92, 1343–1354.
Lubineau, A.; Auge, J.; Lubin, N. Tetrahedron Lett. 1991, 32, 7529–7530.
An, G.; Rhee, H. Nucleosides Nucleotides Nucleic Acids 2000, 19, 1111–1122.
MacKeith, R.A.; McCague, R.; Olivo, H.F.; Roberts, S.M.; Taylor, S.J.C.;
Xiong, H. Bioorg. Med. Chem. 1994, 2, 387–394.
6.
7.
8.
9.
(a) Martin, C.; Bortolussi, M.; Bloch, R. Tetrahedron Lett. 1999, 40, 3735–
3
1
1
1
736. (b) Nishikawa, T.; Asai, M.; Ohyabu, N.; Isobe, M.J. Org. Chem.
998, 63, 188–192. (c) Wai, J.S.; Fisher, T.E.; Embrey, M.W. Tetrahedron Lett.
¨
995, 36, 3461–3464. (d) Estieu, K.; Ollivier, J.; Salaun, J. Tetrahedron Lett.
995, 36, 2975–2978. (e) Casara, P. Tetrahedron Lett. 1994, 35, 3049–3050.
(f ) Doherty, A.M.; Kornberg, B.E.; Reily M.D. J. Org. Chem. 1993, 58,
795–798. (g) Chen, A.; Savage, I.; Thomas, E.J.; Wilson, P.D. Tetrahedron
Lett. 1993, 34, 6769–6772. (h) Nagashima, H.; Wakamatsu, H.; Ozaki, N.;
Ishii, T.; Watanabe, M.; Tajima, T.; Itoh, K. J. Org. Chem. 1992, 57, 1682–
1689. (i) Metz, P.; Mues, C.; Schoop, A. Tetrahedron 1992, 48, 1071–1080.
(j) Roush, W.R.; Straub, J.; Brown, R.J. J. Org. Chem. 1987, 52, 5127–5136.
(k) Takano, S.; Akiyama, M.; Ogasawara, K. J. Chem. Soc., Chem. Commun.
1984, 770–771. (l) Overman, L.E. Acc. Chem. Res. 1980, 13, 218–224. (m)
Overman, L.E. J. Am. Chem. Soc. 1976, 98, 2901–2910. (n) Yamamoto, Y.;
Shimoda, H.; Oda, J.; Inouye, Y. Bull. Chem. Soc. Jpn. 1976, 49, 3247–3249.
0. Still, W.C.; Kahn, M.; Mitra, A. J. Org. Chem. 1978, 43, 2923–2925.
1
11. Armarego, W.L.F.; Perin, D.D. Purification of Laboratory Chemicals, 4th
Edition, Butterworth-Heinemann, 1996.
12. The compound 12 was identified by checking the spectral data of following
papers: (a) Campbell, J.A.; Lee, W.K.; Rapoport, H. J. Org. Chem. 1995,
6
3
0, 4602–4616. (b) Kam, B.L.; Oppenheimer, N.J. J. Org. Chem. 1981, 46,
268–3272.
Received October 1, 2001
Accepted November 21, 2001