Efficient electrophilic cobromination of alkenes and bromination of activated arenes with bromodichloroisocyanuric acid under mild conditions

Article abstract of DOI:10.1055/s-2007-982575

Efficient methodologies for the preparation of bromodichloroisocyanuric acid were developed (70-75%). This new reagent is very efficient for regioselective electrophilic bromination of activated arenes (86-93%) and cobromination of alkenes with oxygenated nucleophiles (31-98%). The reaction of bromodichloroisocyanuric acid with anisole, acetanilide, N-methylacetanilide leads to 4-substituted monobromoarene and with 2-methoxynaphthalene leads to 1-bromo-2-methoxynaphthalene. Alkenes were cobrominated in the presence of oxygenated nucleophilic solvents (water, alcohols, and acetic acid), leading to the corresponding bromohydrins, β-bromoethers and β-bromoacetates. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-982575

LETTER
1687
Efficient Electrophilic Cobromination of Alkenes and Bromination of
Activated Arenes with Bromodichloroisocyanuric Acid under Mild Conditions
B
L
rominations w
e
ith Bromod
o
ichloroisocy
n
anuric
A
cid ardo S. de Almeida, Pierre M. Esteves,* Marcio C. S. de Mattos*
Instituto de Química, Departamento de Química Orgânica, Universidade Federal do Rio de Janeiro, Cx. Postal 68545, 21945-970,
Rio de Janeiro, Brazil
Fax +55(21)25627133; E-mail: pesteves@iq.ufrj.br; E-mail: mmattos@iq.ufrj.br
Received 27 March 2007
silver salts and elementary bromine. This generates a mix-
Abstract: Efficient methodologies for the preparation of bromo-
ture of AgBr and TBCA or DBCA, which are insoluble in
most solvents making their separation difficult. A green
alternative methodology developed by us for the prepara-
dichloroisocyanuric acid were developed (70–75%). This new
reagent is very efficient for regioselective electrophilic bromination
of activated arenes (86–93%) and cobromination of alkenes with
oxygenated nucleophiles (31–98%). The reaction of bromodi- tion of TBCA in 87%, consists of the reaction of cyanuric
®
chloroisocyanuric acid with anisole, acetanilide, N-methyl- acid with KBr and Oxone in the presence of NaOH for
acetanilide leads to 4-substituted monobromoarene and with 2-
methoxynaphthalene leads to 1-bromo-2-methoxynaphthalene.
Alkenes were cobrominated in the presence of oxygenated nucleo-
philic solvents (water, alcohols, and acetic acid), leading to the cor-
responding bromohydrins, b-bromoethers and b-bromoacetates.
9
2
4 hours at room temperature. This methodology is quite
simple and the product is obtained by vacuum filtration
needing no further purification. A previous work showed
that TBCA is a very good regioselective brominating
9
2a
agent for alkenes and activated aromatic rings.
Key words: alkenes, arenes, electrophilic addition, electrophilic
aromatic substitution, halogenation
O
1
1
1
1
1
2
3
X
X
X
X
X
= X = X = Cl (TCCA)
X1
O
X2
O
= X = Cl, X3 = H (DCCA)
2
N
N
2
= X = X3 = Br (TBCA)
Organic halides are a very important class of compounds
with applications in many fields of chemistry, specially as
synthetic intermediates. Many techniques for halo-
2
3
N
X3
= X = Br, X = H (DBCA)
2
3
= X = Cl, X = Br (BDCCA)
1
Figure 1 Haloisocyanuric acids
genation of organic compounds employing alternative
2
reagents are found in the literature, once direct halogena-
tion with X (X = Cl, Br, I) generates HX which are
polluting and corrosive strong acids. The use of N-halo-
imides is a good alternative for halogenation of organic
2
In this paper we introduce the preparation of bromo-
dichloroisocyanuric acid (BDCCA, Figure 1) and its ap-
plication on regioselective bromination of alkenes and
activated aromatic rings.
3
molecules, due to their lower toxicity compared to X and
2
furnish the corresponding imides as byproduct after work-
up. In this class of compounds, the halogen has a stronger
electrophilic character because it is directly bonded to the
The first step of this work was the preparation of BDCCA
from the commercially available sodium dichloroiso-
cyanurate (65% pure). The two methodologies employed
to prepare BDCCA are shown in Scheme 1. In the former,
a solution of 100 mmol of sodium dichloroisocyanurate in
4
nitrogen of the imide.
Trichloroisocyanuric acid (TCCA, Scheme 1), a white
solid sold at 99% of purity at supermarkets and used as
pool disinfectant and bleaching agent, has shown to be a
very good reagent in organic synthesis, finding applica-
1
L of water reacted with 107 mmol of Br . The formation
2
of BDCCA can easily be observed by the rapid precipita-
tion of a white solid with simultaneous discoloration of
the solution. After a vacuum filtration and drying over
P O , the pure product is obtained in 75% yield. The
5
6
tion in oxidative and chlorinating reactions. It was
formerly prepared by Chattaway and Wadmore in 1902 by
2
5
7
®
the reaction of cyanuric acid with Cl /NaOH. Similarly,
2
second alternative route used KBr and Oxone to generate
the disubstituted analogue, dichloroisocyanuric acid
Br in situ and led to BDCCA in 70% yield.
2
(
DCCA, Figure 1) can be prepared by the stoichiometric
Both methodologies lead to the same product in good
control. Its monosodic salt, sodium dichloroisocyanurate,
is also sold for pool disinfection in 65% purity. Other in-
teresting analogues of TCCA are the tribromoisocyanuric
yields. The reaction with Br is faster, but worst to
2
manipulate. On the other hand, the reagents used on the
®
second methodology (KBr and Oxone ) are solids, much
acid (TBCA, Figure 1) and dibromoisocyanuric acid
less toxic and easier to handle. The reactivity of BDCCA
towards arene brominations and alkenes cobrominations
was investigated.
8
(
DBCA, Figure 1), formerly prepared by Gottardi using
a difficult and tedious methodology employing expensive
Alkenes are rapidly converted into the corresponding bro-
mohydrins in excellent yields (Table 1), when 2 mmol of
substrate react with 2 mmol of BDCCA in 15 mL of aque-
ous acetone (1:5) at room temperature. The substrates
SYNLETT 2007, No. 11, pp 1687–1690
Advanced online publication: 25.06.2007
DOI: 10.1055/s-2007-982575; Art ID: S01707ST
0
3
.0
7
.2
0
0
7
©
Georg Thieme Verlag Stuttgart · New York

1
688
L. S. de Almeida et al.
LETTER
a
bromoarenes were obtained in excellent yields (Table 2).
The regioselectivity was very high, leading to 4-substitut-
ed monobromoarene and 1-bromo-2-methoxynaphtha-
lene. No regioisomers or chlorinated products could be
O
75%
O
Cl
Cl
Br
N
N
N
N
1
detected by analytical procedures (GCMS and H NMR
O
N
O
O
N
O
1
3
and C NMR spectroscopy).
Cl
Cl
b, c
0%
In a previous work, the brominations of the same sub-
strates using TBCA or TCCA/KBr system were per-
7
Scheme 1 Preparation of BDCCA. Reagents and conditions: a) Br ,
H O, r.t.; b) Na CO , KBr, H O, r.t.; c) Oxone , r.t., 24 h.
2a
2
formed in longer reaction times (0.5–72 h), whilst in the
®
2
2
3
2
present work all the reactions with the arenes were carried
out in just 30 minutes (Table 2). This higher reactivity of
BDCCA compared to TBCA seems to be associated to the
dipole of the BDCCA molecule. The chlorine atoms
increase the dipole toward the carbonyl between them,
and consequently the electrophilicity of the bromine atom
increases, too.
used in these reactions were a-methylstyrene, styrene, 1-
methylcyclohexene, and cyclohexene. The cobromination
of styrene and cyclohexene with BDCCA in methanol,
isopropanol, and acetic acid has led to the corresponding
b-bromoethers and b-bromoacetates in moderate to good
yields. The reactions are regioselective, forming products
in Markownikoff’s fashion, and featuring trans-configu- Table 2 Bromination of Arenes with BDCCA
ration, which were analyzed by analytical procedures
O
1
13
(
GCMS and H NMR and C NMR spectroscopy). The
Cl
Br
N
N
solvent
results (Table 1) show that reactions in water–acetone
system are faster than in alcohol or acid media. No chlori-
nated products were detected by analytical techniques.
Ar
H
+
Ar Br
r.t., 30 min
O
N
O
Cl
Yield (%)a
93
Table 1 Cobromination of Alkenes with BDCCA
Arene
Product
Solvent
O
OMe
OMe
MeOH
R1
R2
H
Cl
4
H
Br
4
R O
R1
R3
N
N
R OH
+
R3
r.t.
R2
O
N
O
Br
Cl
Br
R1
Me
H
R2
Ph
Ph
Ph
Ph
Ph
R3
H
H
H
H
H
R4
T (min) Yield (%)a
NMeAc
NHAc
NMeAc
H O
2
94
86
95
Hb
5
120
120
30
5
98
Me
i-Pr
Ac
Hb
71
Br
H
77
NHAc
MeOH
MeOH
H
97
H
97
Me
H
–(CH ) –
Hb
5
95c
79c
31c
69c
97c
Br
2
4
OMe
Br
–(CH ) –
Me
i-Pr
Ac
Hb
15
1200
5
2
4
OMe
H
–(CH ) –
2 4
H
–(CH ) –
2 4
a
Isolated yield based on the arene.
H
–(CH ) –
5
2
4
a
Isolated yield based on the alkene.
In conclusion, the present work describes two prepara-
tions of the bromodicloroisocyanuric acid. Both methods
are efficient, but the alternative one, with KBr/Oxone , is
b
c
H O–acetone (1:5) used as nucleophile.
2
trans-Product.
®
more ecofriendly, because these reagents are not polluting
Brominations of activated arenes were performed at room and not corrosive. The reactions of BDCCA with arenes
temperature using 2 mmol substrate (anisole, acetanilide, and alkenes present high regioselectivity, forming mono-
N-methylacetanilide, and 2-methoxynaphthalene) in 10 bromo arenes and bromohydrins, b-bromoethers and b-
mL of methanol or 20 mL of water (just for N-methyl- bromoacetates in moderate to excellent yields.
acetanilide). After workup, the corresponding mono-
Synlett 2007, No. 11, 1687–1690 © Thieme Stuttgart · New York

LETTER
Brominations with Bromodichloroisocyanuric Acid
1689
Preparation of Bromodichloroisocyanuric Acid (BDCCA)
Procedure 1 (Using Br2)
(4) (a) De Souza, S. P. L.; da Silva, J. F. M.; de Mattos, M. C. S.
Quim. Nova 2006, 29, 1061. (b) Koval, I. V. Russ. J. Org.
Chem. 2002, 38, 301.
(5) (a) Barros, J. C. Synlett 2005, 2115. (b) Tilstam, U.;
Weinmann, H. Org. Process Res. Dev. 2002, 6, 384.
(c) Yamaoka, H.; Moriya, N.; Ikunaka, M. Org. Process Res.
Dev. 2004, 8, 931.
To a well-stirred solution of sodium dichloroisocyanurate (100
mmol) in H O (1 L) was added dropwise Br (107 mmol). A white
2
2
solid precipitates forming a dense suspension. Then, the product
was isolated by filtration, washed with cold H O and dried over
2
1
0
P O , needing no further purification. Yield 75%; mp not deter-
2
5
mined because it decomposes on heating.
(6) (a) Juenge, E. C.; Beal, D. A.; Duncan, W. P. J. Org. Chem.
1
970, 35, 719. (b) Mendonca, G. F.; Sanseverino, A. M.; de
Procedure 2 (Using KBr/oxone®)
Mattos, M. C. S. Synthesis 2003, 45. (c) Mendonca, G. F.;
Magalhães, R. M.; de Mattos, M. C. S.; Esteves, P. M.
J. Braz. Chem. Soc. 2005, 16, 695.
To a well-stirred solution of sodium dichloroisocyanurate (10
mmol), Na CO (10 mmol) and KBr (10 mmol) in H O (150 mL)
2
3
2
®
cooled in an ice bath a solution of Oxone (10 mmol) in H O (40
(7) Chattaway, F. D.; Wadmore, J. M. J. Chem. Soc. 1902, 81,
191.
2
mL) was added dropwise. A white solid precipitates during the ad-
dition of the oxidant solution forming a dense suspension, which
was stirred for 24 h. The product was isolated by filtration, washed
with cold H O and dried over P O . No further purification is
(8) (a) Gottardi, W. Monatsh. Chem. 1967, 98, 1613.
(b) Gottardi, W. Monatsh. Chem. 1968, 99, 815.
(9) de Almeida, L. S.; Esteves, P. M.; de Mattos, M. C. S. Synlett
2006, 1515.
2
2
5
necessary.10 Yield 70%; mp not determined because it decomposes
on heating.
(10) CP-MAS 13C NMR: d = 159.5 (br, C=O) ppm. IR: 1697,
1
654, 1620, 1484, 1450, 1421, 1409, 1349, 1319, 1203,
–
1
Typical Procedure for Cobromination of Alkenes
1149, 1110, 1074, 1047, 796, 755, 725, 602, 555 cm .
To a stirred solution of the alkene (2 mmol) in the appropriated sol-
(11) Selected Analytical Data
vent (12.5 mL of acetone and 2.5 mL of H O for bromohydrins, or
1-Bromo-2-phenylpropan-2-ol
2
1
5
mL of alcohols or AcOH for b-bromoethers or b-bromoacetates,
H NMR (CDCl ): d = 1.68 (s, 3 H), 2.63 (s, 1 H), 3.73 (dd,
3
respectively), was added BDCCA (2 mmol) at r.t. in small portions.
After the elapsed time in Table 1 (the termination of the reaction
was determined by gas chromatography), CH Cl (10 mL) and H O
2 H, J = 12.45 Hz, J = 10.20 Hz), 7.25–7.49 (m, 5 H) ppm.
1
2
1
3
C NMR (CDCl ): d = 28.0, 46.2, 73.1, 124.8, 127.5, 128.4,
3
+
+
144.2 ppm. MS (70 eV): m/z = 216 [M + 2], 214 [M ], 199,
2
2
2
(
10 mL) were added, dichlorocyanuric acid was filtered off, and the
201, 121 (100), 77, 43.
resulting solution was treated with 10% aq Na SO (30 mL). The
(2-Bromo-1-methoxyethyl)benzene
2
3
1
aqueous phase was washed with CH Cl (2 × 10 mL) and the com-
H NMR (CDCl ): d = 3.31 (s, 3 H), 3.42–3.59 (m, 2 H), 4.39
2
2
3
bined organic layer was dried over anhyd Na SO . After the evapo-
ration of the solvent on a rotatory evaporator, the product was
collected.11
(dd, 1 H, J = 7.86 Hz, J = 4.44 Hz), 7.34–7.43 (m, 5 H)
2
4
1
2
1
3
ppm. C NMR (CDCl ): d = 36.2, 57.2, 83.4, 126.7, 128.6,
3
+
+
139.0 ppm. MS (70 eV): m/z = 216 [M + 2], 214 [M ], 121
100), 91, 77, 51.
(
Typical Procedure for Bromination of Arenes
To a stirred solution of the arene (2 mmol) in MeOH (10 mL) or
(2-Bromo-1-isopropoxyethyl)benzene
1
H NMR (CDCl ): d = 1.12 (d, 3 H, J = 6.15 Hz), 1.23 (d, 3
3
H O (20 mL, for N-methylacetanilide) was added BDCCA (2
2
H, J = 6.14 Hz), 3.38–3.48 (m, 2 H), 3.57 (hept, 1 H,
mmol). The reaction was monitored by GC. After 30 min, CH Cl
J = 6.14 Hz), 4.58 (dd, 1 H, J = 7.86 Hz, J = 4.78 Hz) 7.35
2
2
1
2
1
3
(
30 mL) and H O (20 mL) were added, dichlorocyanuric acid was
(s, 5 H) ppm. C NMR (CDCl ): d = 21.2, 23.1, 37.0, 70.4,
2
3
filtered off, and the resulting solution was treated with 10% aq
Na SO (30 mL). The aqueous phase was washed with CH Cl
79.3, 126.7, 128.2, 128.5, 140.6 ppm. MS (70 eV): m/z =
185, 183, 149, 107 (100), 79, 43.
2
3
2
2
(
2 × 10 mL) and the combined organic layer was dried over anhyd
2-Bromo-1-phenylethyl Acetate
1
Na SO . After evaporation of the solvent on a rotatory evaporator,
the product was collected.
H NMR (CDCl ): d = 2.13 (s, 3 H), 3.54 (m, 2 H), 5.98 (dd,
2
4
3
1
2
13
1 H, J = 7.41 Hz, J = 5.12 Hz), 7.36 (s, 5 H) ppm. C NMR
1
2
(
CDCl ): d = 20.9, 34.2, 74.8, 126.5, 128.6, 137.6, 169.8
3
+
+
ppm. MS (70 eV): m/z = 244 [M + 2], 242 [M ], 162, 121,
Acknowledgment
120, 103, 77, 43 (100).
2
-Bromo-1-phenylethanol
The authors thank CAPES, CNPq and FAPERJ for the financial
support.
1
H NMR (CDCl ): d = 2.81 (d, 1 H, J = 2.73 Hz) 3.48–3.64
3
1
3
(
(
(
m, 2 H), 4.89–4.94 (m, 1 H), 7.37 (s, 5 H) ppm. C NMR
CDCl ): d = 40.1, 73.7, 125.9, 128.4, 128.6, 140.3 ppm. MS
70 eV): m/z = 202 [M + 2], 200 [M ], 107 (100), 79, 77, 51.
3
+
+
References and Notes
trans-2-Bromo-1-methylcyclohexanol
1
(
1) (a) Johnsson, R.; Meijer, A.; Ellervik, U. Tetrahedron 2005,
H NMR (CDCl ): d = 1.25–1.48 (m, 5 H), 1.68–2.05 (m, 4
3
61, 11657. (b) Liu, Y. H.; Zhou, S. L. Org. Lett. 2005, 7,
H), 2.15 (br s, 1 H), 2.21–2.27 (m, 1 H), 4.15 (dd, 1 H,
1
3
4609.
J = 11.52 Hz, J = 4.10 Hz) ppm. C NMR (CDCl ): d =
1
2
3
(
2) (a) de Almeida, L. S.; Esteves, P. M.; de Mattos, M. C. S.
Synthesis 2006, 221. (b) Gallou, F.; Reeves, J. T.; Tan, Z.;
Song, J. J.; Yee, N. K.; Campbell, S.; Jones, P.-J.;
22.8, 23.2, 26.3, 34.7, 38.2, 66.0, 72.5. MS (70 eV): m/z =
194 [M + 2], 192 [M ], 177, 179, 113, 95, 71 (100), 43 ppm.
+
+
trans-1-Bromo-2-methoxycyclohexane
1
Senanayake, C. H. Synlett 2005, 2400. (c) Moghaddan, F.
M.; Boeini, H. Z. Synlett 2005, 1612. (d) de Souza, S. P. L.;
da Silva, J. F. M.; de Mattos, M. C. S. J. Braz. Chem. Soc.
H NMR (CDCl ): d = 1.20–1.40 (m, 3 H), 1.64–1.88 (m, 3
3
H), 2.15–2.34 (m, 2 H), 3.17–3.28 (m, 1 H), 3.42 (ddd, 1 H,
1
3
J = 9.56 Hz, J = 8.53 Hz, J = 4.44 Hz) ppm. C NMR
1
2
3
2003, 14, 832.
(CDCl ): d = 23.1, 25.3, 29.9, 35.4, 55.2, 57.1, 83.1 ppm. MS
(70 eV): m/z = 194 [M + 2], 192 [M ], 113, 81, 71 (100), 41.
3
+
+
(
3) The Merck Index, 13rd ed; Merck & Co. Inc.: Whitehouse
Station, 2001.
trans-1-Bromo-2-isopropoxycyclohexane
1
H NMR (CDCl ): d = 1.13–1.43 (m, 9 H), 1.62–1.90 (m,
3
3
H), 2.02–2.11 (m, 1 H), 2.30–2.37 (m, 1 H), 3.33–3.40 (m,
Synlett 2007, No. 11, 1687–1690 © Thieme Stuttgart · New York

1
690
L. S. de Almeida et al.
LETTER
1
H), 3.78 (hept, 1 H, J = 6.15 Hz), 3.90 (ddd, 1 H, J = 9.76
4-Bromo-N-methylacetanilide
Mp 91 °C (lit. 95 °C). H NMR (CDCl ): d = 1.83 (s, 3 H),
1
1
3
13
1
Hz, J = 8.93 Hz, J = 4.43 Hz) ppm. C NMR (CDCl ): d =
2
3
3
3
2
7.5, 23.0, 23.5, 25.5, 32.5, 35.8, 56.6, 71.2, 79.7 ppm. MS
3.20 (s, 3 H), 7.04, (d, J = 8.30 Hz, 2 H), 7.50 (d, J = 8.30
+
+
13
(
(
70 eV): m/z = 222 [M + 2], 220 [M ], 178, 180, 99, 81
100), 57, 43.
Hz, 2 H). C NMR (CDCl ): d = 22.4, 37.0, 121.4, 128.7,
3
+
132.9, 143.5, 205.6. MS (70 eV): m/z = 229 [M + 2], 227
[M ], 187 (100), 185 (100), 186, 184, 157, 155, 104, 77, 56,
+
trans-2-Bromocyclohexyl acetate
1
H NMR (CDCl ): d = 1.27–1.47 (m, 3 H), 1.74–1.96 (m, 3
43.
3
H), 2.08 (s, 3 H), 2.13 (m, 1 H), 2.32–2.39 (m, 1 H), 3.96
4-Bromoacetanilide
Mp 166 °C (lit. 167 °C). H NMR (DMSO-d ): d = 2.03 (s,
1
4
1
(
ddd, 1 H, J = 10.45 Hz, J = 9.29 Hz, J = 4.26 Hz), 4.84–
1
2
3
6
1
3
4
3
2
.93 (m, 1 H) ppm. C NMR (CDCl ): d = 21.0, 23.3, 25.6,
3 H), 7.43, (d, J = 8.92 Hz, 2 H), 7.54 (d, J = 8.92 Hz, 2 H)
3
+
13
5.7, 52.8, 75.8, 170.0 ppm. MS (70 eV): m/z = 222 [M +
], 220 [M ], 160, 162, 81, 43 (100).
ppm. C NMR (DMSO-d ): d = 24.0, 114.5, 120.8, 131.5,
6
+
+
138.7, 168.5 ppm. MS (70 eV): m/z = 215 [M + 2], 213
+
trans-2-Bromocyclohexanol
[M ], 173 (100), 171 (100), 157, 155, 92, 43.
1
H NMR (CDCl ): d = 1.24–1.37 (m, 3 H), 1.67–1.86 (m, 3
1-Bromo-2-methoxynaphthalene
3
1
5
1
H), 2.10–2.20 (m, 1 H), 2.25–2.60 (m, 2 H), 3.50–3.70 (m, 1
Mp 82 °C (lit. 85 °C). H NMR (CDCl ): d = 4.03 (s, 3 H),
3
H), 3.90 (ddd, 1 H, J = 11.68 Hz, J = 9.57 Hz, J = 4.35
7.26 (d, J = 9.67 Hz, 1 H), 7.41 (t, J = 7.90 Hz, 1 H), 7.59 (t,
1
2
3
1
3
Hz) ppm. C NMR (CDCl ): d = 24.1, 26.6, 33.5, 36.2, 61.8,
J = 7.90 Hz, 1 H), 7.80 (d, J = 7.9 Hz, 1 H), 7.81 (d, J = 9.67
3
+
+
13
7
5.3 ppm. MS (70 eV): m/z = 180 [M + 2], 178 [M ], 99, 81
100), 57, 41.
12) Selected Analytical Data
-Bromoanisole
Hz, 1 H), 8.26 (d, J = 7.90 Hz, 1 H) ppm. C NMR (CDCl ):
3
(
d = 56.9, 108.6, 113.6, 124.2, 126.0, 127.7, 128.0, 128.9,
+
(
129.8, 133.0, 153.7 ppm. MS (70 eV): m/z = 238 [M + 2],
+
4
236 [M ], 223, 221, 195 (100), 193 (100), 127, 114.
1
H NMR (CDCl ): d = 3.77 (s, 3 H), 6.78 (d, J = 8.90 Hz, 2
(13) Olah, G.; Ohannesian, L.; Arvanaghi, M. Synthesis 1986,
868.
3
1
3
H), 7.37 (d, J = 8.90 Hz, 2 H) ppm. C NMR (CDCl ): d =
3
5
5.4, 112.8, 115.7, 139.2, 158.7 ppm. MS (70 eV): m/z = 188
(14) Yamasaki, R.; Tanatani, A.; Azumaya, I.; Saito, S.;
Yamagushi, K.; Kagechika, H. Org. Lett. 2003, 5, 1265.
(15) Miyano, S.; Okada, S.; Suzuki, T.; Handa, S.; Hashimoto, H.
Bull. Chem. Soc. Jpn. 1986, 59, 2044.
+
+
(
100) [M + 2], 186 (100) [M ], 173, 171, 145, 143, 119,
17, 84, 63, 49 ppm.
1
Synlett 2007, No. 11, 1687–1690 © Thieme Stuttgart · New York

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