Expedient synthesis of 2-carboethoxy-4-methylnaphthalenes

Article abstract of DOI:10.1080/00397910500328605

A three-step synthesis of 2-carboethoxy-4-methylnaphthalenes 7a-d from aryl aldehydes is described. Copyright Taylor & Francis LLC.

Full text of DOI:10.1080/00397910500328605

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Expedient Synthesis of
2‐Carboethoxy‐4‐methylnaphthalenes
Chandan P. Amonkar a , Rupesh R. Patre a & Santosh G. Tilve a
a Department of Chemistry , Goa University , Goa, India
Published online: 21 Aug 2006.
To cite this article: Chandan P. Amonkar , Rupesh R. Patre & Santosh G. Tilve (2006) Expedient Synthesis
of 2‐Carboethoxy‐4‐methylnaphthalenes, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 36:1, 13-20, DOI: 10.1080/00397910500328605
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Synthetic Communicationsw, 36: 13–20, 2006
Copyright # Taylor & Francis LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500328605
Expedient Synthesis of 2-Carboethoxy-
4-methylnaphthalenes#
Chandan P. Amonkar, Rupesh R. Patre, and Santosh G. Tilve
Department of Chemistry, Goa University, Goa, India
Abstract: A three-step synthesis of 2-carboethoxy-4-methylnaphthalenes 7a–d from
aryl aldehydes is described.
Keywords: Benzannulations, naphthalene, Wacker reaction, Wittig reaction
The naphthalene structural motif is widely present in nature[1] and in
important biologically active molecules.[2]. For example, 1 is a segment of
anticancer agent neocarzinostatin.[2a] Compound 2 is an orally active leuko-
triene B4 receptor antagonist.[3] Various methods[3,4] are available for the
synthesis of such naphthalene segments. However, most of these methods
are either multistep methods or are useful to synthesize a specific segment.
In view of this, we envisaged developing a convenient method for the
synthesis of substituted 2-carboethoxy-4-methylnaphthalenes, which could
act as common precursors for compounds such as 1 and 2 by carrying out
normal functional-group transformations.
Received in India July 7, 2005
#Dedicated to Professor S. C. Chandrasekaran on the occasion of his 60th Birthday.
Address correspondence to Santosh G. Tilve, Department of Chemistry, Goa
University, Taleigao Plateau, Goa 403206, India. Fax: 91-0832-2451184; E-mail:
santoshtilve@yahoo.com
13

14
C. P. Amonkar, R. R. Patre, and S. G. Tilve
We had earlier used Pd-C–catalyzed ring annulation of the indole ring to
carbazole the precursor of anticancer alkaloid olivacine.[5] Because we were
not able to extend the same method for benzannulations to naphthalene, we
thought that if we could convert the terminal olefin (Scheme 1) to a methyl
ketone group by the Wacker reaction, we may get the naphthalene by ring
annulation. Thus, the pentenoate 5a obtained by Wittig condensation with
phosphorane 4 on Wacker oxidation gave the keto-ester 6a in 70% yield.
The latter compounds are also useful substrates for the synthesis[6] of substi-
tuted g-lactones. Keto ester 6a was then cyclized to 2-carboethoxy-4-methyl
naphthalene (7a) using PPA in good yield. With the facile preparation of
naphthalene 7a, we used this sequence of reactions to synthesize several sub-
stituted 2-carboethoxy-4-methylnaphthalenes (7b–d). In conclusion, we have
developed an efficient three-step method for the synthesis of 2-carboethoxy-4-
methylnaphthalenes (Table 1).
All melting points are uncorrected and were measured by the normal
thiels-tube (paraffin) method. Column chromatography was performed on
silica gel G (13% CaSO4 as binder). IR spectra were recorded on a
Shimadzu FT-IR spectrophotometer (KBr pellet or neat sample). All new
compounds gave satisfactorily microanalysis: C + 0.50; H + 0.30. 1H NMR
and 13CMR spectra were recorded on a Brucker 300-MHz instrument. The
multiplicities of carbon signals were obtained from Distortionless Enhance-
ment by Polarisation Transfer (DEPT) experiments.
GENERAL PROCEDURE FOR THE PREPARATION
OF PENTANOATES 5A–D
A mixture of aryl aldehyde 3a–d (1 mmol), allyl phosphorane 4 (1 mmol), and
chloroform (10 mL) was refluxed for 3 h. The solvent was removed under
reduced pressure, and the residue was chromatographed on silica gel
(hexanes–EtOAc ¼ 95 : 5) to yield unsaturated esters 5a–d.
Scheme 1.

2-Carboethoxy-4-methylnaphthalenes
15
Table 1. Yields of compounds 5, 6, and 7
Compounds
3, 5–7
Compound
5 yield (%)
Compound
6 yield (%)
Compound
7 yield (%)
R1
R2
R3
a
b
c
H
H
H
95
71
69
65
75
77
70
72
70
69
71
66
MeO
MeO
MeO
H
H
MeO
MeO
H
MeO
d
DATA
Ethyl (E)-2-Benzylidenepent-4-enoate (5a)[7]
1
Yield: 95%; liquid; bp 1368C. IR (neat): nmax ¼ 1716, 1635, 1604 cm21. H
NMR (300 MHz, CDCl3): d ¼ 1.33 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 3.28
(d, J ¼ 5.4 Hz, 2H, CH2CH55CH2), 4.26 (q, J ¼ 7.2 Hz, 2H, OCH2CH3),
5.11 (m, 2H, CH2CH55CH2), 6.00 (m, 1H, CH2CH55CH2), 7.30–7.41 (br.s,
5H, Ar-H), 7.80 (s, 1H,55CH). 13C NMR (CDCl3): d ¼ 14.18 (OCH2CH3),
31.56 (CH2CH55CH2), 60.71 (OCH2CH3), 115.55 (CH2CH55CH2), 128.33
(CH), 128.47 (CH), 128.48 (CH), 129.16 (CH), 130.47 (C), 135.43 (C),
135.60 (CH2CH55CH2), 140.04 (CH), 167.83 (CO).
Ethyl (E)-2-(m-Methoxybenzylidene)pent-4-enoate (5b)
Yield: 71%; oily liquid. IR (neat): 1715, 1635, 1600 cm21. 1H NMR (CDCl3):
d ¼ 1.32 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 3.26 (d, J ¼ 5.4 Hz, 2H,
CH2CH55CH2), 3.89 (s, 3H, OCH3), 4.31 (q, J ¼ 7.2 Hz, 2H, OCH2CH3),
5.28 (m, 2H, CH2CH55CH2), 6.03 (m, 1H, CH2CH55CH2), 6.95–7.33
(m, 4H, Ar-H), 7.81 (s, 1H, 55CH). 13C NMR (CDCl3): d ¼ 14.14
(OCH2CH3), 31.02 (CH2CH55CH2), 57.69 (OCH3), 61.23 (OCH2CH3),
111.67 (CH2CH55CH2), 113.12 (CH), 115.32 (CH), 123.03 (C), 128.35
(CH), 128.38 (CH), 135.02 (C), 139.98 (C), 147.74 (CH2CH55CH2), 149.11
(CH), 167.55 (CO). GC/MS: m/z ¼ 246 [M]þ.
Ethyl (E)-2-(3,4-Dimethoxybenzylidene)pent-4-enoate (5c)[7]
Yield: 69%; oily liquid. IR (neat): 1711, 1638, 1606cm21. 1H NMR (CDCl3):
d ¼ 1.33 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 3.33 (d, J ¼ 5.4 Hz, 2H,
CH2CH55CH2), 3.87 (s, 3H, OCH3), 3.90 (s, 3H, OCH3), 4.27 (q, J ¼ 7.2 Hz,
2H, OCH2CH3), 5.13 (m, 2H, CH2CH55CH2), 6.03 (m, 1H, CH2CH55CH2),
6.88 (d, J ¼ 8.4 Hz, 1H, Ar-H), 7.76 (t, J ¼ 8.4, 1.8 Hz, 2H, Ar-H),
7.76 (s, 1H,55CH). 13C NMR (CDCl3): d ¼ 14.16 (OCH2CH3), 31.65

16
C. P. Amonkar, R. R. Patre, and S. G. Tilve
(CH2CH55CH2), 55.87 (OCH3), 60.53 (OCH2CH3), 111.40 (CH2CH55 CH2),
112.80 (CH), 115.30 (CH), 122.83 (C), 128.35 (C), 128.51 (CH), 135.77 (C),
139.89 (C), 148.94 (CH2CH55CH2), 149.81 (CH), 167.95 (CO).
Ethyl (E)-2-(3,4,5-Trimethoxybenzylidene)pent-4-enoate (5d)[7]
Yield: 65%; oily liquid. IR (neat): 1711, 1638, 1585 cm21. 1H NMR (CDCl3):
d ¼ 1.33 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 3.32 (d, J ¼ 5.1 Hz, 2H, CH2CH55
CH2), 3.83 (s, 6H, 2 ꢀ OCH3), 3.86 (s, 3H, OCH3), 4.26 (q, J ¼ 7.2 Hz,
2H, OCH2CH3), 5.15 (m, 2H, CH2CH55CH2), 6.02 (m, 1H, CH2CH55
CH2), 6.66 (s, 2H, Ar-H), 7.74 (s, 1H,55CH). 13C NMR (CDCl3): d ¼ 14.10
(OCH2CH3), 37.71 (CH2CH55CH2), 55.98 (OCH3), 60.58 (OCH2CH3),
106.68 (CH2CH55CH2), 115.30 (CH), 129.44 (C), 130.68 (C), 135.77 (C),
138.65 (C), 140.11 (CH2CH55CH2), 152.95 (CH), 167.74 (CO).
GENERAL PROCEDURE FOR THE PREPARATION
OF KETO-ESTER 6A–D
A mixture of cuprous chloride (1 mmol), palladium chloride (0.1 mmol), and
water (0.2 mL) in DMF (15 mL) was stirred under oxygen atmosphere for 1 h.
Ester 5a–d (1 mmol) in DMF (5 mL) was added, and the mixture was stirred
for 10 h at room temperature under an oxygen atmosphere. The reaction
mixture was then diluted with water and extracted with EtOAc
(3 ꢀ 20 mL). The organic layer was dried over anhyd. Na2SO4, filtered, and
concentrated in vacuo. The residue was purified by column chromatography
on silica gel (hexanes 60–808C–EtOAc ¼ 9 : 1) to yield keto-esters 6a–d.
DATA
Ethyl-2-benzylidene-4-oxo-pentenoate (6a)[8]
1
Yield: 75%; viscous liquid. IR (neat): 1722, 1706 cm21. H NMR (CDCl3):
d ¼ 1.25 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 2.17 (s, 3H, CH2COCH3), 3.53
(s, 2H, CH2COCH3), 4.17 (q, J ¼ 7.2 Hz, 2H, OCH2CH3), 7.32–7.18
(m, 5H, Ar-H), 7.84 (s, 1H,55CH). 13C NMR (CDCl3): d ¼ 14.11
(OCH2CH3), 29.97 (CH3CO), 42.43 (CH2), 61.07 (OCH2CH3), 106.13
(CH), 128.49 (CH), 128.68 (CH), 135.10 (C), 141.89 (CH), 153.13 (C),
167.30 (COOEt), 205.94 (CH3CO).
Ethyl-2-(m-methoxybenzylidene)-4-oxo-pentenoate (6b)
1
Yield: 77%; viscous liquid. IR (neat): 1722, 1700 cm21. H NMR (CDCl3):
d ¼ 1.33 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 2.25 (s, 3H, CH2COCH3), 3.62

2-Carboethoxy-4-methylnaphthalenes
17
(s, 2H, CH2COCH3), 3.80 (s, 3H, OCH3), 4.26 (q, J ¼ 7.2 Hz, 2H, OCH2CH3),
6.86–6.90 (m, 2H, Ar-H), 7.26–7.31 (m, 2H, Ar-H), 7.90 (s, 1H,55CH). 13
C
NMR (CDCl3): d ¼ 14.20 (OCH2CH3), 29.96 (CH3CO), 43.33 (CH2), 54.99
(OCH3), 61.34 (OCH2CH3), 111.46 (CH), 112.40 (CH), 123.23 (CH),
124.80 (C), 127.73 (C), 142.88 (CH), 148.78 (CH), 149.32 (C), 167.63
(COOEt), 205.65 (CH3CO). GC/MS: m/z ¼ 262 [M]þ.
Ethyl-2-(3,4-dimethoxybenzylidene)-4-oxo-pentenoate (6c)
1
Yield: 70%; viscous liquid. IR (neat): 1722, 1700 cm21. H NMR (CDCl3):
d ¼ 1.24 (t, J ¼ 7.1 Hz, 3H, OCH2CH3), 2.17 (s, 3H, CH2COCH3), 3.58
(s, 2H, CH2COCH3), 3.77 (s, 3H, OCH3), 4.17 (q, J ¼ 7.1 Hz, 2H,
OCH2CH3), 6.76–6.84 (m, 3H, Ar-H), 7.84 (s, 1H,55CH). 13C NMR
(CDCl3): d ¼ 14.14 (OCH2CH3), 29.89 (CH3CO), 42.73 (CH2), 55.79
(OCH3), 61.00 (OCH2CH3), 110.96 (CH), 112.04 (CH), 122.23 (CH),
124.88 (C), 127.73 (C), 141.98 (CH), 148.78 (CH), 149.72 (C), 167.53
(COOEt), 206.45 (CH3CO). GC/MS: m/z ¼ 292 [M]þ. HRMS: m/z
[M þ Naþ] calcd. for C16H20O5: 315.3207; found: 315.2845.
Ethyl-2-(3,4,5-trimethoxybenzylidene)-4-oxo-pentenoate (6d)
1
Yield: 72%; viscous liquid. IR (neat): 1722, 1705cm21. H NMR (CDCl3):
d ¼ 1.24 (t, J ¼ 7.1 Hz, 3H, OCH2CH3), 2.17 (s, 3H, CH2COCH3), 3.54
(s, 2H, CH2COCH3), 3.73 (s, 6H, 2 ꢀ OCH3), 3.76 (s, 3H, OCH3), 4.16
(q, J ¼ 7.1 Hz, 2H, OCH2CH3), 6.49 (s, 2H, Ar-H), 7.76 (s, 1H,55CH). 13C
NMR (CDCl3): d ¼ 14.12 (OCH2CH3), 29.78 (CH3CO), 42.77 (CH2), 56.03
(OCH3), 90.76 (OCH3), 61.10 (OCH2CH3), 106.09 (CH), 126.13 (C), 130.43
(C), 138.64 (C), 142.18 (CH), 153.10 (C), 167.29 (COOEt), 206.40 (CH3CO).
HRMS: m/z [M þ Naþ] calcd. for C17H22O6: 345.1314; found: 345.1285.
GENERAL PROCEDURE FOR THE PREPARATION
NAPHTHALENE 7A–D
A slurry of phosphorus pentoxide (5 g) and 88% phosphoric acid (3 mL)
was stirred at 708C on an oil bath. To this slurry, keto-ester 6a–d (2 mmol)
was added in one portion, and the mixture was stirred for 10 min. After
cooling, crushed ice was added, and the reaction mixture was extracted in
EtOAc. The organic layer was dried over anhyd. Na2SO4 and was concen-
trated in vacuo. The residue was purified by column chromatography on
silica gel (petroleum ether 60–808C–EtOAc ¼ 9 : 1) to yield naphthoic
esters 7a–d.

18
C. P. Amonkar, R. R. Patre, and S. G. Tilve
DATA
Ethyl-4-methyl-2-naphthoate (7a)[9]
1
Yield: 70%; white crystals; mp 528C. IR (KBr): 1722, 1630, 1605 cm21. H
NMR (CDCl3): d ¼ 1.46 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 2.73 (s, 3H,
ArCH3), 4.45 (q, J ¼ 7.2 Hz, 2H, OCH2CH3), 7.52–7.65 (m, 2H, Ar-H),
7.93–8.03 (m, 3H, Ar-H), 8.48 (s, 1H, Ar-H). 13C NMR (CDCl3):
d ¼ 14.35 (OCH2CH3), 19.25 (CH3), 60.94 (OCH2CH3), 124.00 (CH),
125.56 (CH), 126.16 (CH), 127.21 (C), 127.95 (CH), 129.35 (CH), 129.94
(CH), 132.61 (C), 134.64 (C), 166.85 (COOEt).
Ethyl-7-methoxy-4-methyl-2-naphthoate (7b)
1
Yield: 69%; white solid; mp 558C. IR (KBr): 1710, 1635, 1600 cm21. H
NMR (CDCl3): d ¼ 1.44 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 2.69 (s, 3H,
ArCH3), 3.94 (s, 3H, OCH3), 4.42 (q, J ¼ 7.2 Hz, 2H, OCH2CH3),
7.26–7.26 (m, 2H, Ar-H), 7.77 (s, 1H, Ar-H), 7.92 (d, J ¼ 9.0 Hz, 1H,
Ar-H), 8.36 (s, 1H, Ar-H). 13C NMR (CDCl3): d ¼ 14.30 (OCH2CH3),
20.45 (CH3), 55.67 (OCH3), 60.78 (OCH2CH3), 102.73 (CH), 106.88
(CH), 124.40 (CH), 126.68 (CH), 127.63 (C), 128.73 (CH), 130.22
(C), 133.77 (C), 149.89 (C), 151.52 (C), 168.11 (COOEt). GC/MS:
m/z ¼ 244 [M]þ.
Ethyl-6,7-dimethoxy-4-methyl-2-naphthoate (7c)
Yield: 70%; white crystals; mp 1448C. IR (KBr): 1716, 1635, 1601 cm21
.
1H NMR (CDCl3): d ¼ 1.43 (t, J ¼ 7.2 Hz, 3H, OCH2CH3), 2.66 (s, 3H,
ArCH3), 4.01 (s, 3H, OCH3), 4.05 (s, 3H, OCH3), 4.41 (q, J ¼ 7.2 Hz,
2H, OCH2CH3), 7.20 (s, 1H, Ar-H), 7.23 (s, 1H, Ar-H), 7.80 (s, 1H,
Ar-H), 8.33 (s, 1H, Ar-H). 13C NMR (CDCl3): d ¼ 14.33 (OCH2CH3),
19.47 (CH3), 55.79 (OCH3), 60.70 (OCH2CH3), 102.73 (CH), 107.98
(CH), 124.42 (CH), 125.62 (C), 127.63 (CH), 128.33 (C), 130.82 (C),
132.78 (C), 149.49 (C), 151.00 (C), 167.05 (COOEt). GC/MS:
m/z ¼ 274 [M]þ. HRMS: m/z [M þ Naþ] calcd. for C16H18O4: 297.1103;
found: 297.1097.
Ethyl-5,6,7-trimethoxy-4-methyl-2-naphthoate (7d)
Yield: 66%; pale yellow crystals; mp 1408C. IR (KBr): 1720, 1638,
1606 cm21
.
1H NMR (CDCl3): d ¼ 1.43 (t, J ¼ 7.2 Hz, 3H, OCH2CH3),
2.88 (s, 3H, ArCH3), 3.95 (s, 3H, OCH3), 3.98 (s, 6H, 2 ꢀ OCH3), 4.41
(q, J ¼ 7.2 Hz, 2H, OCH2CH3), 7.06 (s, 1H, Ar-H), 7.68 (s, 1H, Ar-H),

2-Carboethoxy-4-methylnaphthalenes
19
8.27 (s, 1H, Ar-H). 13C NMR (CDCl3): d ¼ 14.29 (OCH2CH3), 23.34
(CH3), 55.67 (OCH3), 60.79 (OCH3), 61.15 (OCH2CH3), 104.76 (CH),
125.91 (CH), 126.67 (C), 128.01 (CH), 131.13 (C), 134.27 (C), 143.94
(C), 150.46 (C), 152.66 (C), 166.74 (COOEt).
ACKNOWLEDGMENT
We thank CSIR and UGC for support of this work; NIO, Goa, for spectral
analysis; Department of Organic Chemistry IISc, Banglore, for HRMS; and
RSIC, Mumbai, for analysis and GC/MS. C. P. A. thanks CSIR, New
Delhi, for the award of research fellowship.
REFERENCES
1. (a) Meyers, A. G.; Horiguchi, Y. Tetrahedron Lett. 1997, 4363; (b) Pande, A.;
Shukla, Y. N. Phytochemistry 1993, 32, 1350; (c) Charlton, J. L.; Lee, K. A.
Tetrahedron Lett. 1984, 7311; (d) Buta, J. G.; Steffens, G. L. Phytochemistry
1974, 13, 1033; (e) Gupta, R. K.; Dhar, M. M. Phytochemistry 1969, 8, 789;
(f) Chen, C. L.; Hostettler, F. D. Tetrahedron 1969, 25, 3223.
2. (a) Shoji, J. J. Antibiot. 1961, 14, 27; (b) Ishida, N.; Miyazaki, M.; Kumangi, K.;
Rikimaru, M. J. Antibiot. 1965, 18, 68; (c) Sartori, G.; Bigi, F.; Canali, G.;
Mazzi, R.; Casnati, G.; Tao, X. J. Org. Chem. 1993, 58, 840;
(d) Coleman, R. S.; Grant, E. B. J. Org. Chem. 1991, 56, 1357; (e) Yu, K.-L.;
Spinazze, P.; Ostrowski, J.; Currier, S. J.; Pack, E. J.; Hammer, L.; Roalsvig, T.;
Honeyman, J. A.; Tortolani, D. R.; Reczek, P. R.; Mansuri, M. M.;
Starrett, J. E., Jr. J. Med. Chem. 1996, 39 (12), 2411.
3. Huang, F.-C.; Chan, W.-K.; Warus, J. D.; Morrisette, M. M.; Moriarty, K. J.;
Chang, M. N; Travis, J. J.; Mitchell, L. S.; Nuss, G. W.; Sutherland, C. A.
J. Med. Chem. 1992, 35, 4235.
4. (a) Koning, C. B.; Rousseau, A. L.; van Otterlo, W. A. L. Tetrahedron 2003, 59 (7),
and references cited therein; (b) Takahashi, K.; Suzuki, T.; Hirama, M.
Tetrahedron Lett. 1992, 4603; (c) Shibuya, M.; Toyooka, K.; Kubota, S.
Tetrahedron Lett. 1984, 1171; (d) Shishido, K.; Yamashita, A.; Hiroya, K.;
Fukumoto, K.; Kametani, T. Tetrahedron Lett. 1989, 111; (e) Myers, A. G.;
Subramanian, V.; Hammond, M. Tetrahedron Lett. 1996, 587;
(f) Takahashi, K.; Tanaka, T.; Suzuki, T.; Hirama, M. Tetrahedron 1994, 50,
1327; (g) Corey, E. J.; Palani, A. Tetrahedron Lett. 1997, 2397;
(h) Boger, D. L.; Mullican, M. D. J. Org. Chem. 1980, 45, 5002; (i) Ila, H.;
Junjappa, H.; Mohanta, P. K. Prog. Het. Chem. 2001, 13, 1; (j) Krohn, K.;
Bernhard, S. Eur. J. Org. Chem. 1999, 3099; (k) Takaki, K.; Okada, M.;
Yamada, M.; Negoro, K. J. Org. Chem. 1982, 47, 1200; (l) Vorogushhin, A. V.;
Wulff, W. D.; Hansen, H.-J. J. Am. Chem. Soc. 2002, 124, 6512;
(m) Dudley, G. B.; Takaki, K. S.; Cha, D. D.; Danheiser, R. L. Org. Lett.
1994, 35, 1127; (n) Ciufoline, M. A.; Weiss, T. J. Tetrahedron Lett. 1994,
35, 1127; (o) Gordon, D. M.; Danishefsky, S. J.; Schulte, G. K. J. Org.
Chem. 1992, 57, 7052; (p) Parker, K. A.; Coburn, C. A. J. Org. Chem. 1991, 56,
1666.

20
C. P. Amonkar, R. R. Patre, and S. G. Tilve
5. Tilve, S. G.; Tilve, A. S.; Desai, V. D. Synth. Commun. 1996, 26, 1921.
6. Ballini, R.; Bosica, G. Synlett. 1996, 1115.
7. Mali, R. S.; Babu, K. N. Helv. Chim. Acta. 2002, 85, 3525.
8. Kim, J. M.; Im, Y. J.; Kim, T. H.; Nyoung, K. J. Bull. Korean Chem. Soc. 2002,
23 (5), 657.
9. (a) Kim, J. N.; Im, Y. J.; Gong, J. H. Tetrahedron Lett. 2001, 42, 4195;
(b) Im, Y. J.; Chung, Y. M.; Gong, J. H. Bull. Korean Chem. Soc. 2004, 23, 787.