Lithiation of 2-(chloroaryl)-2-aryl-1,3-dioxolanes with butyllithium activated by N,N,N′,N″,N″-pentamethyldiethylenetriamine

Article abstract of DOI:10.1016/j.tet.2007.08.086

Intramolecular competition of variously substituted phenyl rings of benzophenone ketals in lithiation reactions proved to be?a useful tool to study both ortho-directing ability and long-range effects of the substituents. The regioselectivities observed in the reaction of benzophenone ketals having one or two chloro substituents in one of the aryl rings with butyllithium complexed to N,N,N′,N″,N″-pentamethyldiethylenetriamine demonstrate the significance of both ortho- and meta-acidifying effect of the chloro substituents. The lithio species thus generated were carboxylated resulting in new polysubstituted benzoic acids.

Full text of DOI:10.1016/j.tet.2007.08.086

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 1029–1033
Lithiation of 2-(chloroaryl)-2-aryl-1,3-dioxolanes with
butyllithium activated by N,N,N0,N00,N00-
pentamethyldiethylenetriamine
*
Marta Porcs-Makkay, Anna Komaromi, Gyula Lukacs and Gyula Simig
ꢀ
ꢀ
ꢀ
Chemical Research Division, EGIS Pharmaceuticals PLC., PO Box 100, 1475 Budapest, Hungary
Received 5 July 2007; revised 14 August 2007; accepted 21 August 2007
Available online 4 September 2007
ꢀ
Dedicated to Professor Csaba Szantay on the occasion of his 80th birthday
Abstract—Intramolecular competition of variously substituted phenyl rings of benzophenone ketals in lithiation reactions proved to be a
useful tool to study both ortho-directing ability and long-range effects of the substituents. The regioselectivities observed in the reaction
of benzophenone ketals having one or two chloro substituents in one of the aryl rings with butyllithium complexed to N,N,N0,N00,N00-penta-
methyldiethylenetriamine demonstrate the significance of both ortho- and meta-acidifying effect of the chloro substituents. The lithio species
thus generated were carboxylated resulting in new polysubstituted benzoic acids.
Ó 2007 Published by Elsevier Ltd.
1. Introduction
aptitude of the ketal group (a factor present in both phenyl
rings).9
Relative ortho-directing abilities of directed metalation
groups (DMGs) in lithiation reactions have been investigated
in several studies using intramolecular or intermolecular
competitions.1 Optional site selectivity has been achieved in
the lithiation reactions of arene substrates through matching
of reagents and neighbouring groups.2,3 Some results pub-
lished recently called the attention to the long-range effects
of some DMGs resulting in unexpected regioselectivity of
the metalation reactions.4–7
We now report the extension of this work to the metalation of
benzophenone ketals with butyllithium complexed to
N,N,N0,N00,N00-pentamethyldiethylenetriamine (PMDTA).
This reagent is expected to abstract a proton preferentially
or exclusively from the most acidic site contrary to butyl-
lithium, which is seeking coordinative assistance by a
substituent of the substrate in order to accomplish deproto-
nation.3,10 Nevertheless, in most cases it is hardly predict-
able, which is the most acidic site of benzophenone ketals 1.
Intramolecular competition of variously substituted phenyl
rings of benzophenone ketals in lithiation reactions proved
to be a useful tool to study both ortho-directing ability and
long-range effects of the substituents.8 Thus lithiation of ke-
tals 1a–e with butyllithium in THF at 0 to ꢀ20 ꢁC occurred
in the 4-chlorophenyl ring ortho to the ketal substituent (2a–
e) as demonstrated by the formation of products 3a–e and
4a–e after functionalization (Scheme 1). Intramolecular
competition between the aryl rings was observed in the lith-
iation of compound 1f with butyllithium in THF at ꢀ50 ꢁC
as indicated by the formation of 3f and 5 in a 1:2 ratio.
The observed regioselectivities were explained by the
long-range (meta) electron-withdrawing (acidifying) effect
of the chloro substituent in addition to the ortho-directing
2. Results and discussion
Lithiation of ketals 1a–e with butyllithium complexed with
PMDTA in THF at ꢀ78 ꢁC followed by carboxylation af-
forded benzoic acids 8 in good yield (Scheme 2), which
demonstrates that lithiation occurred exclusively in the
4-chlorophenyl ring, ortho to the chloro substituent. The
formation of benzoic acids 8b–d indicates that chloro substit-
uent exhibits superior inductive effect relative to methoxy
group at the ortho position favouring the formation of lithi-
ated intermediates 7b–d contrary to lithiations at the me-
thoxy adjacent sites.3,11 With the knowledge of the stronger
inductive effect of fluorine relative to chloro substituent it
was expected that lithiation of ketal 1f under similar condi-
tions followed by carboxylation gave compound 6 as the
single product in 73% yield.12–14
Keywords: Lithiation; Substituent effects; Benzophenones; 1,3-Dioxolanes.
* Corresponding author. Tel.: +36 1 2655555; fax: +36 1 2655613; e-mail:
pmmarta@freemail.hu
0040–4020/$ - see front matter Ó 2007 Published by Elsevier Ltd.
doi:10.1016/j.tet.2007.08.086

1030
M. Porcs-Makkay et al. / Tetrahedron 64 (2008) 1029–1033
Cl
Li
O
Cl
Cl
El
O
O
electrophilic
reagent
BuLi, THF
2h
O
O
O
R2
R2
R2
R1
R1
R1
2
1
3 (El=SO2Cl)
4 (El=COOH)
Cl
O
R1
H
R2
H
H
a
b
c
d
e
O
MeO
H
MeO MeO
Cl
F
MeO
El
H
H
F
f
5 (El=SO2Cl)
6 (El=COOH)
Scheme 1.
Li
COOH
Cl
Cl
Cl
BuLi, PMDTA
O
O
O
O
CO2
THF
O
O
-78 °C, 20 min
R2
R2
R2
R1
R1
R1
1
7
8
R1, R2: see Scheme 1
Scheme 2.
Butyllithium in THF at ꢀ78 ꢁC abstracts a proton from
compounds 9a–c at the common ortho position of the
chlorine and ketal groups.9 Lithiation of benzophenone
ketals 9a–c with butyllithium complexed with PMDTA
in THF at ꢀ78 ꢁC followed by carboxylation afforded
products 11a–c (Scheme 3) indicating that metalation oc-
curs solely at the sterically uncongested 4-position of the
meta-chlorophenyl ring (10a–c). The oily product 11b
was hydrolyzed to crystalline benzophenone derivative
14. It is worth mentioning that 1H NMR analysis of
Cl
Li
Cl
HOOC
O
O
CO2
O
O
Cl
R2
R2
Cl
a-c
e-f
BuLi, PMDTA
THF
-78 °C, 20 min
O
R1
10
R1
HOOC
11
O
O
Cl
Cl
R2
R1, R2: see Scheme 1
R1
O
O
CO2
O
O
9
OMe
14
Li
COOH
R1
12
R1
13
Scheme 3.

M. Porcs-Makkay et al. / Tetrahedron 64 (2008) 1029–1033
COOH
1031
Cl
Cl
Cl
Cl
Cl
Cl
1. BuLi, PMDTA
THF
-78 °C, 20 min
HOOC
+
O
O
O
O
+
HOOC
O
O
O
O
2. CO2
R2
R2
R2
R2
R1
8
R1
R1
R1
11
15
16
Cl
Cl
R1, R2: see Scheme 1
O
HOOC
OMe
17
Scheme 4.
Table 1. Products formed in the lithiation reaction of compounds 15
followed by carboxylation
the crude acid fractions did not indicate the presence of
regioisomers.
Starting
compound
Product mixture
Yield (%) 16:8:11a
Recov. 15 (%) Yield of
isolated 16 (%)
Simultaneous proton abstraction from the 4-position of the
meta-chlorophenyl and 3-position of the para-chlorophenyl
ring was observed in similar lithiation of compound 9e. 1H
NMR analysis of the product mixture isolated after carbox-
ylation demonstrated the formation of acids 11e and 13e in
a 1:3.5 ratio, demonstrating that in the course of the lithiation
reaction the developing negative charge is more destabilized
by the electron-donating ketal group in the para than meta
position. Benzoic acid 13e was isolated in pure form and
the structure 11e could be unambiguously assigned to the
minor product on the basis of the doublet at d 7.94 ppm in
the 1H NMR spectrum of the product mixture, characteristic
to the proton adjacent to a carboxylic function (see also com-
pounds 11a–c). As expected, fluoro derivative 9f was lithi-
ated exclusively at the 3-position of the para-fluorophenyl
ring (12f), resulting in benzoic acid 13f as the single product.
15a
15b
15e
15f
79
83
54
75
9:1.3:1
7.5:1.5:1 15
9:1.5:1
8:1.5:1
4
27
31b
22
42
20
26
The ratios were assessed by 1H NMR spectroscopy. In the case of 8a,b,e
and 11a,b the structure assignment based on 1H NMR spectra of the prod-
uct mixtures is supported also with a comparison of the 1H NMR data of
authentic samples.
a
b
Isolated as the benzophenone 17, see Section 3.
ortho- and meta-acidifying effect of the adjacent chlorine
substituents on the less crowded ortho position determined
the regioselectivity of the deprotonation. The preferred for-
mation of by-products 8 versus 11 can be explained by a sim-
ilar electrical effect of the ketal group as discussed in the
case of the deprotonation reaction of compound 9e.
Ketals 15a, 15b, 15e and 15f were lithiated with butyllithium
in THF at ꢀ78 ꢁC at the site between the 1,3-interrelated
chlorine and ketal group.9 Lithiation of ketals 15a with bu-
tyllithium complexed to PMDTA followed by carboxylation
afforded a mixture of acids in 79% combined yield, the ma-
jor product 16a being isolated in 27% yield (Scheme 4). The
metalation at the uncongested site next to the chlorine was
accompanied with minor chlorine–lithium exchange reac-
tions resulting acids 16a, 8a and 11a in a 9:1.3:1 ratio, as in-
dicated by the 1H NMR analysis of the product mixture (see
Table 1).
More strikingly, ketal 15f was also found to react with butyl-
lithium complexed to PMDTA exclusively in the 3,4-
dichlorophenyl ring affording after carboxylation 16f as
the main product. 1H NMR spectrum of the product mixture
indicated that the compounds formed contain ‘intact’ 4-
fluorophenyl moiety. Deprotonation occurred at the 5-posi-
tion of the 3,4-dichlorophenyl ring rather than at the fluorine
adjacent site of the 4-fluorophenyl moiety and chlorine-
lithium exchange products 8f and 11f were formed in minor
As expected, ketal 15b produced similar result: acids 16b,
8b and 11b were obtained in a 7.5:1.5:1 ratio and in
a 83% combined yield. Since the major product 16b could
not be isolated in crystalline form, the mixture was hydro-
lyzed and benzophenone 17 was prepared in 31% yield.
Cl
Cl
Cl
O
O
O
O
Surprisingly, 3,4,40-trichlorobenzophenone ketal 15e was
deprotonated exclusively at the 5-position of the dichloro-
phenyl ring as shown by the formation of 16e as the main
product in addition to minor products 8e and 11e originating
from chlorine–lithium exchange reactions. The cooperating
F
F
1f
15f
Scheme 5.

Table 2. Experimental data for compounds 6, 8, 11, 13 and 16 synthesized according to the general procedure
R1
R2
Yield Recov.
Mp (ꢁC)
Molecular formula
Elemental analysis
Found
IR (KBr):
n (cmꢀ1
1H NMR (CDCl3, 200 MHz, 25 ꢁC)
(%)
starting
material
(%)
)
Calcd
4
6
F
H
73
19
159–160 (EtOAc/hexane 1:3)
C16H12ClFO4 (322.72) C 59.55, H 3.75,
Cl 10.99
C 59.00, H 3.81,
Cl 10.68
1686 (C]O)
8.17 (dd, JHF¼7.0 Hz, J¼2.4 Hz, 1H), 7.67 (ddd,
4
J¼8.6 Hz, JHF¼4.5 Hz, J¼2.4 Hz, 1H), 7.44 (d,
J¼8.7 Hz, 2H), 7.32 (d, J¼8.7 Hz, 2H), 7.13 (dd,
3JHF¼10.4 Hz, J¼8.6 Hz, 1H), 4.11–3.96 (m, 4H)
8.19 (d, J¼2.2 Hz, 1H), 7.59 (dd, J¼8.4, 2.2 Hz,
1H), 7.54–7.47 (m, 2H), 7.43 (d, J¼8.4 Hz, 1H),
7.40–7.24 (m, 3H), 4.07 (s, 4H)
8a
H
H
H
73
60
21
19
144–146 (EtOAc/hexane 1:1)
139–144 (EtOAc/hexane 3:7)
C16H13ClO4 (304.73)
C17H15ClO5 (334.76)
C 63.06, H 4.30,
Cl 11.63
C 62.97, H 4.36,
Cl 11.57
1684 (C]O)
1691 (C]O)
8b MeO
C 61.00, H 4.52,
Cl 10.59
C 62.97, H 4.36,
Cl 11.57
8.17 (d, J¼2.2 Hz, 1H), 7.58 (dd, J¼8.0, 2.2 Hz,
1H), 7.43 (d, J¼8.0 Hz, 1H), 7.41 (d, J¼9.1 Hz,
2H), 6.84 (d, J¼8.8 Hz, 2H), 4.06 (br s, 4H), 3.79 (s,
3H)
8c
H
MeO 59
40
35
107–109 (EtOAc/hexane 3:7)
171–173 (EtOAc/hexane 1:3)
C17H15ClO5 (334.76)
C18H17ClO6 (364.78)
C 61.00, H 4.52,
Cl 10.59
C 60.63, H 4.72,
Cl 10.67
1689 (C]O)
1698 (C]O)
8.18 (d, J¼2.2 Hz, 1H), 7.58 (dd, J¼8.4, 2.2 Hz,
1H), 7.44 (d, J¼8.1 Hz, 1H), 7.26 (t, J¼8.1 Hz, 1H),
7.10–7.04 (m, 2H), 6.84 (dq, J¼8.1, 1.1 Hz, 1H),
4.08 (s, 4H), 3.80 (s, 3H)
8.18 (d, J¼2.2 Hz, 1H), 7.58 (dd, J¼8.4, 2.2 Hz,
1H), 7.44 (d, J¼8.4 Hz, 1H), 7.00 (s, 1H), 6.99 (d,
J¼2.2 Hz, 1H), 6.82 (d, J¼8.8 Hz, 1H), 4.08 (s,
4H), 3.87 (s, 3H), 3.86 (s, 3H)
8d MeO MeO 63
C 59.27, H 4.70,
Cl 9.72
C 59.64, H 4.64,
Cl 9.60
8e Cl
11a
11b MeO
H
H
H
73
81
40
25
16
43
152–153 (EtOAc/hexane 1:3)
79–80 (EtOAc/hexane 1:3)
C16H12Cl2O4 (339.18) C 56.66, H 3.57,
Cl 20.91
C 56.32, H 3.61,
Cl 20.31
C 62.68, H 4.60,
Cl 12.06
1693 (C]O)
1704 (C]O)
9.30 (br s, 1H), 7.50–7.44 (m, 3H), 7.34–7.26 (m,
3H), 4.15–4.05 (m, 2H), 4.05–3.95 (m, 2H)
7.95 (d, J¼8.0 Hz, 1H), 7.69 (d, J¼1.5 Hz, 1H),
7.54–7.45 (m, 3H), 7.36–7.28 (m, 3H), 4.01 (s, 4H)
7.94 (d, J¼8.4 Hz, 1H), 7.66 (d, J¼1.5 Hz, 1H),
7.48 (dd, J¼8.1, 1.5 Hz, 1H), 7.40 (d, J¼8.8 Hz,
2H), 6.85 (d, J¼8.8 Hz, 2H), 4.14–4.01 (m, 4H),
3.78 (s, 3H)
H
C16H13ClO4 (304.73)
C 63.06, H 4.30,
Cl 11.63
Isolated in crystalline form as benzophenone 14
11c
H
MeO 60
40
99–101 (EtOAc/hexane 3:7)
C17H15ClO5 (334.76)
C 61.00, H 4.52,
Cl 10.59
C 60.79, H 4.52,
Cl 10.44
1705 (C]O)
7.95 (d, J¼8.1 Hz, 1H), 7.68 (d, J¼1.5 Hz, 1H),
7.48 (dd, J¼8.1, 1.5 Hz, 1H), 7.27 (t, J¼8.1 Hz,
1H), 7.11–7.03 (m, 2H), 6.85 (dd, J¼8.1, 2.2 Hz,
1H), 4.08 (br s, 4H), 3.80 (s, 3H)
13e Cl
H
H
31
86
33
14
128–130 (EtOAc/hexane 1:2)
130–132 (EtOAc/hexane 1:3)
C16H12Cl2O4 (339.18) C 56.66, H 3.57,
Cl 20.91
C, 56.85, H, 3.71, 1719 (C]O)
Cl, 20.81
8.16 (d, J¼2.2 Hz, 1H), 7.58 (dd, J¼8.4, 2.2 Hz,
1H), 7.54–7.51 (m, 1H), 7.45 (d, J¼8.4 Hz, 1H),
7.40–7.27 (m, 3H), 4.08 (s, 4H)
4
13f
F
C16H12ClFO4 (322.72) C 59.55, H 3.75,
Cl 10.99
C 59.36, H 3.82,
Cl 10.84
1709, 1688
(C]O)
8.20 (dd, JHF¼7.0 Hz, J¼2.2 Hz, 1H), 7.68 (ddd,
4
J¼8.6 Hz, JHF¼4.4 Hz, J¼2.2 Hz, 1H), 7.53 (br s,
3
1H), 7.41–7.25 (m, 3H), 7.13 (dd, JHF¼10.2 Hz,
J¼8.8 Hz, 1H), 4.08 (s, 4H)
16a
H
H
H
27
4
142–144 (EtOAc/hexane 1:3)
C16H12Cl2O4 (339.18) C 56.66, H 3.57,
Cl 20.91
Isolated in crystalline form as benzophenone 17
C 56.28, H 3.72,
Cl 19.89
1711, 1688
(C]O)
8.00 (d, J¼2.2 Hz, 1H), 7.81 (d, J¼2.2 Hz, 1H),
7.53–7.45 (m, 2H), 7.42–7.30 (m, 3H), 4.08 (s, 4H)
7.99 (d, J¼2.2 Hz, 1H), 7.79 (d, J¼2.2 Hz, 1H),
7.39 (d, J¼8.8 Hz, 2H), 6.87 (d, J¼8.8 Hz, 2H),
4.10–4.08 (m, 2H), 4 08–4.07 (m, 1H), 3.80 (s, 3H)
7.97 (d, J¼2.2 Hz, 1H), 7.78 (d, J¼2.2 Hz, 1H),
7.44 (d, J¼8.8 Hz, 2H), 7.32 (d, J¼8.8 Hz, 2H),
4.07 (s, 4H)
16b MeO
16e Cl
15
H
H
22
26
42
20
175–177 (EtOAc/hexane 1:2)
129–130 (EtOAc/hexane 1:3)
C16H11CI3O4 (373.62) C 51.44, H 2.97,
Cl 28.47
C 51.93, H 3.09,
Cl 27.43
1710, 1681
(C]O)
16f
F
C16H11Cl2FO4 (357.17) C 53.81, H 3.10,
Cl 19.85
C 53.97, H 2.94,
Cl 19.21
1698 (C]O)
7.96 (d, J¼2.2 Hz, 1H), 7.78 (d, J¼2.2 Hz, 1H),
7.47 (ddd, J¼8.8 Hz, JHF¼5.5 Hz, J¼2.2 Hz, 2H),
7.04 (tm, J¼8.8 Hz, 2H), 4.07 (s, 4H)

M. Porcs-Makkay et al. / Tetrahedron 64 (2008) 1029–1033
1033
amounts. In the 1H NMR spectrum of the mixture no signals
3.3. 2,3-Dichloro-5-(4-methoxybenzoyl)-benzoic acid
(17)
characteristic for 2-fluoro-substituted benzoic acid could
be detected. The contrasting reactivity of 4-chlorophenyl-
4-fluorophenyl ketal and 3,4-dichlorophenyl-4-fluorophenyl
ketal (1f and 15f) in deprotonation reaction with butyl-
lithium complexed to PMDTA (Scheme 5) provides further
evidence for the strong meta-acidifying effect of the chloro
substituent.
The product mixture obtained after lithiation and carboxyl-
ation of 15b in an aqueous solution of hydrochloric acid
(10%, 25 ml) was refluxed for 4 h. The crystalline product
was filtered and recrystallized from ethyl acetate to give
17 (1.35 g, 31%, based on 15b) as colourless crystals, mp
1
195–197 ꢁC (ethyl acetate). H NMR (CDCl3, 200 MHz,
25 ꢁC): d¼8.19 (d, J¼2.2 Hz, 1H), 8.05 (d, J¼2.2 Hz, 1H),
7.81 (d, J¼8.8 Hz, 2H), 7.00 (d, J¼8.8 Hz, 2H), 3.91 (s,
3. Experimental section
3.1. General procedure
3H). IR (KBr): n¼1735, 1707 cmꢀ1
. Anal. Calcd
C15H10C12O4 (325.15) C 55.41, H 3.10, Cl 21.81; found C
55.76, H 3.25, Cl 21.59.
N,N,N0,N00,N00-pentamethyldiethylenetriamine (PMDTA)
(11.5 mmol) was added at ꢀ78 ꢁC under argon to buthyl-
lithium (4.6 ml of a 2.5 M solution in hexane, 11.5 mmol)
followed by addition dropwise of the ketal (10 mmol) in
THF (10 ml). The reaction mixture was stirred at ꢀ78 ꢁC
for an additional 20 min, then it was poured onto a large ex-
cess of dry ice (200 g). After 3 h, water (30 ml) was added
and the layers were separated. The aqueous layer was ex-
tracted with diethyl ether (30 ml). An aqueous solution of
hydrochloric acid (10%, 20 ml) was added to the aqueous
layer and it was extracted with diethyl ether (2ꢂ30 ml).
The solvent was evaporated and the oil thus obtained was
crystallized from suitable solvent affording the correspond-
ing carboxylated derivative. For yields, melting points, sol-
References and notes
1. Snieckus, V. Chem. Rev. 1990, 90, 879–933.
2. Schlosser, M. Organometallics in Synthesis: A Manual;
Schlosser, M., Ed.; Wiley: Chichester, UK, 2002; pp 253–257.
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4. Castagnetti, E.; Schlosser, M. Chem.—Eur. J. 2002, 8, 799–
804.
5. Lulinski, S.; Serwatowski, J.; Zaczek, A. Eur. J. Org. Chem.
2006, 5167–5173.
6. Heiss, Ch.; Cottet, F.; Schlosser, M. Eur. J. Org. Chem. 2005,
5236–5241.
1
vents of recrystallization, elemental analyses and H NMR
data see Table 2.
7. Heiss, Ch.; Leroux, F.; Schlosser, M. Eur. J. Org. Chem. 2005,
5242–5247.
8. For ortho-directing ability of aromatic acetals and ketals in
ꢀ
lithiation reactions see Refs. 8–13 quoted in: Lukacs, Gy.;
Porcs-Makkay, M.; Simig, Gy. Tetrahedron Lett. 2003, 44,
3.2. 2-Chloro-4-(4-methoxybenzoyl)-benzoic acid
hemihydrate (14)
3211–3214.
ꢀ
2-Chloro-4-[2-(4-methoxyphenyl)-1,3-dioxolane-2-yl]-ben-
zoic acid (11b) (3.34 g, 0.01 mol) (prepared according the
general procedure) in an aqueous solution of hydrochloric
acid (10%, 25 ml) was refluxed for 4 h. The crystalline prod-
uct was filtered to give 14 (2.61 g, 90% based on 11b and
36% based on 8b) as colourless crystals, mp 203–204 ꢁC
9. Lukacs, Gy.; Porcs-Makkay, M.; Simig, Gy. Eur. J. Org. Chem.
2004, 4130–4140.
10. Katsoulos, G.; Takagishi, S.; Schlosser, M. Synlett 1991, 731–
732.
11. Slocum, D. W.; Dietzel, P. Tetrahedron Lett. 1999, 40, 1823–
1826.
12. Moyroud, J.; Guesnet, J.-L.; Bennetau, B.; Mortier, J.
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13. Moyroud, J.; Guesnet, J.-L.; Bennetau, B.; Mortier, J. Bull. Soc.
Chim. Fr. 1996, 133, 133–141.
1
(ethyl acetate). H NMR (CDCl3, 200 MHz, 25 ꢁC):
d¼8.07 (d, J¼8.1 Hz, 1H), 7.83 (d, J¼1.5 Hz, 1H), 7.81
(d, J¼8.8 Hz, 2H), 7.67 (dd, J¼8.1, 1.5 Hz, 1H), 7.00 (d,
J¼8.8 Hz, 2H), 3.91 (s, 3H). IR (KBr): n¼1702,
1642 cmꢀ1. Anal. Calcd C15H11ClO4 (299.71) C 60.11, H
4.04, Cl 11.83; found C 60.52, H 3.92, Cl 11.73.
14. Mongin, F.; Schlosser, M. Tetrahedron Lett. 1996, 37, 6551–
6554.