Alkylation of 2-phenyl-4-quinolones: Synthetic and structural studies

Article abstract of DOI:10.1248/cpb.49.1352

The alkylation Of 2-phenyl-4-quinolones was investigated and showed that the N-alkylation versus O-alkylation is highly dependent on whether C-5 is hydroxylated or not. N-Alkylation is favoured by the presence of a 5-hydroxyl group. The synthetic and the NMR structural studies are reported.

Full text of DOI:10.1248/cpb.49.1352

1352
Notes
Chem. Pharm. Bull. 49(10) 1352—1355 (2001)
Vol. 49, No. 10
Alkylation of 2-Phenyl-4-quinolones: Synthetic and Structural Studies
Mohamed HADJERI, Anne-Marie MARIOTTE, and Ahcène BOUMENDJEL*
Laboratory of pharmacognosy, UMR-UNRS 5063. Grenoble pharmacy school 3870 La Tornche, FRANCE
Received May 8, 2001; accepted June 18, 2001
The alkylation of 2-phenyl-4-quinolones was investigated and showed that the N-alkylation versus O-alkyla-
tion is highly dependent on whether C-5 is hydroxylated or not. N-Alkylation is favoured by the presence of a 5-
hydroxyl group. The synthetic and the NMR structural studies are reported.
Key words 2-phenyl-4-quinolone; N-alkylation; regioselectivity
2-Phenyl-4-quinolones are a class of molecules used as ence of t-BuOK in THF gave quinolone 3 in 83% yield.
aza analogues of flavones (Fig. 1). Over the last ten years, the Treatment of 3 with BBr3 (1.5 eq) in CH2Cl2 for 24 h af-
interest in 2-phenyl-4-quinolones and related compounds has forded 5-hydroxy-7-methoxy-2-phenyl-4-quinolone 4 in 80%
been the subject of extensive study as potent cytotoxic antim- yield. Under these conditions the 7-methoxy group remained
itotic agents,1) antibacterial agents,2) anti-platelet agents3) and intact.10)
as cardiovascular protectors.4) Replacement of the O1 by a ni-
Quinolones 3 and 4 were treated with an alkyl halide in the
trogen would allow the attachment of groups that may give presence of NaH or K2CO3. The alkylation was conducted
rise to beneficial interactions with the biological active site. under several conditions (NaH/THF, NaH/DMF, K2CO3/ace-
Also, the presence of a nitrogen would allow ammonium tone, K2CO3/DMF) at different temperatures. The K2CO3/
salts to enhance the solubility of the synthesized compound.
DMF system and temperature elevation led to the highest
In an ongoing program aimed at the synthesis and the bio- yields but there was no significant influence on the regiose-
logical activities of flavone analogs, we investigated the syn- lectivity compared to the other systems used.
thesis of N-alkyl-2-phenyl-4-quinolones bearing a 5-hydroxy
In the case of 3 bearing a methoxy group on C-5, treat-
group (III in Fig. 1). The 5-OH group and C2–C3 double ment with K2CO3 in DMF followed with alkyl halide led to
bond in concert with a 4-oxo functionality at the C-ring are the formation of 4-alkoxy-2-phenylquinoline 5 as the only
often required for the activity of flavonoids.5) N-alkyl-4- product (Chart 2, Table 1). It can be postulated that the
quinolones can be prepared by two main methods: starting amino group is deprotonated and equilibrated to give the
from N-alkylaniline derivatives and elaboration of the latter more reactive intermediate 3a which can be alkylated to af-
to N-alkyl-quinolones6,7); by direct alkylation of 2-phenyl-4-
quinolones.8,9) The first method is less convenient, especially
if a large series of N-alkylquinolones is needed. Regarding
the second method, it has been reported that alkylation of 2-
phenyl-4-quinolones leads predominantly to 4-alkoxyquino-
lines. Among N-alkyl-quinolones studied, only N-methyl-2-
phenyl-4-quinolone was obtained.8,9) This has prompted us to
reinvestigate the N-alkylation of 2-phenyl-4-quinolones and
Fig. 1
we have found that the presence of a 5-hydroxyl group is es-
sential for the N-alkylation.
Results and Discussion
While the alkylation of 2-phenyl-4-quinolones was being
studied, we observed that the alkylation regioselectivity (O or
N-alkylation) depends on whether C-5 is hydroxylated or not.
We decided to test and compare the reactivity behavior of 2-
phenyl-4-quinolones where position 5 is either hydroxylated
or methoxylated (masked OH).
5,7-Dimethoxy-2-phenyl-4-quinolone 3 and 5-hydroxy-7-
methoxy-2-phenyl-4-quinolone 4 (Chart 1) were used as
models for this study. They were synthesized starting from
3,5-dimethoxyaniline as shown in Chart 1. Reaction of the
latter with benzoyl chloride in the presence of Et3N gave N-
(3,5-dimethoxyphenyl)benzamide 1 in 96% yield. Friedel–
Crafts acylation with acetyl chloride in 1,2-dichloroethane
and in the presence of SnCl4 gave N-(2-acetyl-3,5-di-
methoxyphenyl)benzamide 2 in 58% yield together with its
a) THF/Et3N; b) CH3COCl, SnCl4, 1,2-dichloroethane; c) t-BuOK, THF,
80 °C; d) BBr3, CH2Cl2.
regioisomer, N-(4-acetyl-3,5-dimethoxyphenyl)benzamide 2a
(isolated in less than 5% yield). Cyclization of 2 in the pres-
Chart 1
To whom correspondence should be addressed. e-mail: Ahcene.Boumendjel@ujf-grenoble.fr
© 2001 Pharmaceutical Society of Japan

October 2001
1353
a) Alkyl halide, K2CO3, DMF.
Chart 2. Alkylation of 5,7-Dimethoxy-2-phenyl-4-quinolone
Table 1. Physicochemical Data of Quinolines 5
5a—d
Compd.
Yield (%)
89
mp (°C) MS m/z
1H-NMR (CDCl3) d:
5a RϭMe
(Me–I)
116
295
8.05 (m, 2H), 7.50 (m, 3H), 7.11 (d, Jϭ2.3 Hz, 1H), 7.05 (s, 1H), 6.50 (d, Jϭ2.3 Hz, 1H), 4.07 (s, 3H),
3. 95 (s, 3H), 3.94 (s, 3H). Anal. Calcd for C18H17NO3: C, 73.20; H, 5.80; N, 4.74. Found: C, 73.14; H,
5.73; N, 4.70.
(AcOEt)
(Mϩ)
5b RϭEt
94
86
76
106
(AcOEt)
309
8.04 (m, 2H), 7.48 (m, 3H), 7.10 (d, Jϭ2.3 Hz, 1H), 7.02 (s, 1H), 6.48 (d, Jϭ2.3 Hz, 1H), 4.29 (q,
Jϭ7 Hz, 2H), 3.94 (s, 3H), 3.93 (s, 3H), 1.58 (t, Jϭ7 Hz, 3H). Anal. Calcd for C19H19NO3: C, 73.77;
H, 6.19; N, 4.53. Found: C, 73.70; H, 6.11; N, 4.49.
8.06 (m, 2H), 7.47 (m, 3H), 7.08 (d, Jϭ2.3 Hz, 1H), 7.02 (s, 1H), 6.47 (d, Jϭ2.3 Hz, 1H), 4.22 (t,
Jϭ6.2 Hz, 2H), 3.94 (s, 3H), 3.92 (s, 3H), 1.93 (m, 2H), 1.65 (m, 2H), 1.04 (t, Jϭ7.3 Hz, 3H). Anal.
Calcd for C21H23NO3: C, 74.75; H, 6.87; N, 4.15. Found: C, 74.69; H, 6.82; N, 4.12.
8.03 (m, 2H), 7.60—7.23 (m, 8H), 7.11 (d, Jϭ2.3 Hz, 1H), 7.07 (s, 1H), 6.47 (d, Jϭ2.3 Hz, 1H), 5.25
(s, 2H), 3.96 (s, 3H), 3.94 (s, 3H). Anal. Calcd for C24H21NO3: C, 77.61; H, 5.70; N, 3.77. Found: C,
77.55; H, 5.66; N, 3.75.
(Et–Br)
(Mϩ)
5c Rϭn-Bu
(nBu–Br)
107
(AcOEt)
337
(Mϩ)
5d RϭBz
amorph.
371
(Bz–Cl)
(Mϩ)
a) Alkyl Halide, K2CO3, DMF.
Chart 3. Alkylation of 5-Hydroxy-7-methoxy-2-phenyl-4-quinolone
ford 5. This observation is in accordance with the reported namely N-alkyl-4-alkoxyquinolines 8 (Table 3), were de-
results regarding the alkylation of 5-unsubstituted-2-phenyl- tected when the reaction was carried out at 80 °C for 3 h and
4-quinolones.8,9)
no similar observation was noticed with 3.
When 4 was treated under the same conditions as 3, com-
As can be seen in Table 2, only the methyl iodide gives ex-
pounds 6 and 7 were produced (Chart 3). In this case, the clusively the N-methylquinolone. Higher alkyl halide led to
amino group was deprotonated to give the intermediate 4. the formation of N-alkylquinolone 6 and 4-alkoxyquinolines
Due to the chelation of the formed enol by the OH-5, compo- 7.
nents (4a, b) were able to co-exist and to be alkylated to give
The structures of 5—8 were confirmed by mass spectrom-
1
quinolone 6 and quinoline 7, respectively (Table 2). In this etry, H- and 13C-NMR (Tables 1—3). N-Alkyl-4-quinolones
1
case, it is worthy to note that the dialkylation products, 6 can be easily identified by comparing their H-NMR spec-

1354
Vol. 49, No. 10
Table 2. Physicochemical Data of Quinolones 6 and Quinolines 7
6a—d
7b—d
Compd.
Yield (%)
mp (°C) MS m/z
1H-NMR (CDCl3) d:
RϭMe (Me–I)
6a
46
26
30
188
CH2Cl2
281
(Mϩ)
7.6—7.30 (m, 5H), 6.35 (d, Jϭ2 Hz, 1H), 6.25 (d, Jϭ2 Hz, 1H), 6.06 (s, 1H), 3.85 (s, 3H), 3.45 (s, 3H).
Anal. Calcd for C17H15NO3: C, 72.58; H, 5.37; N, 4.98. Found: C, 72.54; H, 5.30; N, 4.96.
RϭEt (Et–Br)
295
6b
7b
160
(AcOEt)
7.50 (m, 2H), 7.4 (m, 3H), 6.41 (d, Jϭ2.1 Hz, 1H), 6.35 (d, Jϭ2.1 Hz, 1H), 6.0 (s, 1H), 3.94 (q,
Jϭ7.1 Hz, 2H), 3.89 (s, 3H), 1.26 (t, Jϭ7 Hz, 3H). Anal. Calcd for C18H17NO3: C, 73.20; H, 5.80; N,
4.74. Found: C, 73.14; H, 5.73; N, 4.70.
8.03 (m, 2H), 7.45 (m, 3H), 7.04 (d, Jϭ2.1 Hz, 1H), 7.00 (s, 1H), 6.42 (d, Jϭ2.1, 1H), 4.22 (t, Jϭ6.6 Hz,
2H), 3.95 (s, 3H), 1.64 (t, Jϭ6.6 Hz, 3H). Anal. Calcd for C18H17NO3: C, 73.20; H, 5.80; N, 4.74.
Found: C, 73.16; H, 5.75; N, 4.72.
(Mϩ)
amorph.
295
(Mϩ)
Rϭn-Bu (nBu–Br)
6c
30
amorph.
amorph.
323
7.50—7.35 (m, 5H), 6.41 (d, Jϭ2.1 Hz, 1H), 6.33 (d, Jϭ2.1 Hz, 1H), 6.07 (s, 1H), 3.90 (t, Jϭ6.5 Hz,
2H), 3.89 (s, 3H), 1.65 (m, 2H), 1.26 (m, 2H), 0.76 (t, Jϭ7.2 Hz, 3H). Anal. Calcd for C20H21NO3: C,
74.28; H, 6.55; N, 4.33. Found: C, 74.24; H, 6.53; N, 4.30.
8.06 (m, 2H), 7.47 (m, 3H), 7.08 (d, Jϭ2.2 Hz, 1H), 7.01 (s, 1H), 6.45 (d, Jϭ2.2 Hz, 1H), 4.22 (t,
Jϭ6.4 Hz, 2H), 3.93 (s, 3H), 1.94 (m, 2H), 1.54 (m, 2H), 1.03 (t, Jϭ7.2 Hz, 3H). Anal. Calcd for
C20H21NO3: C, 74.28; H, 6.55; N, 4.33. Found: C, 74.22; H, 6.50; N, 4.29.
(Mϩ)
7c
17
323
(Mϩ)
RϭBz (Ph–CH2–Br)
6d
28
amorph.
358
7.40—7.27 (m, 10H), 6.35 (d, Jϭ2.2 Hz, 1H), 6.18 (s, 1H), 6.13 (d, Jϭ2.2 Hz, 1H), 5.15 (s, 2H), 3.70 (s,
3H). Anal. Calcd for C23H19NO3: C, 77.29; H, 5.36; N, 3.92. Found: C, 77.24; H, 5.31; N, 3.90.
8.06 (m, 2H), 7.63—7.26 (m, 8H), 7.09 (d, Jϭ2.2 Hz, 1H), 7.03 (s, 1H), 6.44 (d, Jϭ2.2 Hz, 1H), 5.28 (s,
2H), 3.95 (s, 3H). Anal. Calcd for C23H19NO3: C, 77.29; H, 5.36; N, 3.92. Found: C, 77.25; H, 5.33; N,
3.88.
(Mϩ1)ϩ
7d
19
96
(AcOEt)
Table 3
8b—d
Compd.
Yield (%)
mp (°C) MS m/z
1H-NMR (CDCl3) d:
8b RϭEt
94
86
76
138
(CH2Cl2)
324
8.06 (dd, J1ϭ1.8 Hz, J2ϭ8.1 Hz, 2H), 7.47 (m, 3H), 7.09 (d, Jϭ2.3 Hz, 1H), 7.01 (s, 1H), 6.46 (d,
Jϭ2.3 Hz, 1H), 4.27 (q, Jϭ7 Hz, 2H), 4.11 (q, Jϭ7 Hz, 2H), 3.93 (s, 3H), 1.59 (t, Jϭ7 Hz, 3H), 1.54
(t, Jϭ7 Hz, 3H).
8.07 (dd, J1ϭ1.8 Hz, J2ϭ8 Hz, 2H), 7.46 (m, 3H), 7.08 (d, Jϭ2.3 Hz, 1H), 7.01 (s, 1H), 6.46 (d,
Jϭ2.3 Hz, 1H), 4.23 (t, Jϭ6.3 Hz, 2H), 4.04 (t, Jϭ6.3 Hz, 2H), 3.93 (s, 3H), 1.93 (m, 4H), 1.65 (m,
4H), 1.04 (m, 6H).
(Et–Br)
(Mϩ)
8c Rϭn-Bu
(nBu–Br)
54
379
(CH2Cl2) (MϪ1)ϩ
8d RϭBz
amorph.
448
8.06 (dd, J1ϭ1.8 Hz, J2ϭ8 Hz, 2H), 7.50—7.21 (m, 13H), 7.15 (s, 1H), 7.12 (d, Jϭ2.2 Hz, 1H), 6.60
(d, Jϭ2.2 Hz, 1H), 5.33 (s, 2H), 5.25 (s, 2H), 3.94 (s, 3H).
(Bz–Cl)
(Mϩ)
tra with the starting quinolone 4. The structure of quinolines 5-OH group is essential for obtaining N-alkylquinolones.
5 and 7 was based on the NMR spectral evidence which in- Thus it is recommended that if N-alkyl-2-phenyl-4-
cluded the appearance of H-3 at 7.00—7.20 ppm instead of quinolones are targeted with the aim of extension at the ni-
6.0—6.2 ppm (in quinolones). Interestingly, the upfield shift trogen, the presence of a 5-hydroxy group in the starting
of H-2Ј and H-6Ј (8.10—8.00 ppm) instead of (7.60— quinolone should be considered.
7.50 ppm) indicated the presence of an electron withdrawing
Experimental
group (imino group) in ortho position. Further, 13C-NMR
Melting points were determined on a Buchi 510 melting points apparatus
1
and are uncorrected. H- and 13C-NMR spectra were recorded on a Bruker
AC200 spectrometer. Chemical shifts are reported in ppm from tetramethyl-
silane as internal standard. J values are given in Hz. Electron impact (EI)
mass spectra and high resolution (HR)-MS were obtained at 70 eV using a
Fisons Trio 1000 instrument. Thin-layer chromatography (TLC) was carried
out using E. Merck silica gel F-254 plates (thickness 0.25 mm) and flash
chromatography was accomplished using Merck silica gel 60, 200—400
confirmed the absence of the C-4 (186—180 ppm).
In summary, 2-phenyl-4-quinolones are being studied as
potential therapeutic agents. Compared to the naturally oc-
curring flavonoids, 2-phenyl-4-quinolones have available ni-
trogen for further extension. In this study, we have shown
that N-alkyl-2-phenyl-4-quinolones cannot be obtained by
applying the standard alkylation conditions. The presence of mesh. All solvents were distilled prior to use. All chemicals and reagents

October 2001
1355
used were obtained from either Aldrich or ACROS and used as received.
room temperature for 24 h, then it was cooled again to 0 °C, and a mixture of
N-(3,5-Dimethoxyphenyl)benzamide (1) To
a solution of 3,5-di- ice and water was added. Extraction with CH2Cl2, drying and concentration
methoxyaniline (3 g, 19.6 mmol) in dry THF (50 ml) was added Et3N afforded a crude 4 which was purified by column chromatography eluted
(4.1 ml, 29.4 mmol). The solution was stirred at 0 °C (ice bath) for 10 min with cyclohexane : AcOEt (7 : 3) to give 0.41 g of 4 as a yellow solid. Yield
and treated by dropwise addition of benzoyl chloride (3.4 ml, 29.4 mmol). 80%; mp 257—259 °C (MeOH). 1H-NMR (acetone-d6) d: 13.45 (1H, s),
The reaction mixture was stirred at room temperature for 1 h then hy- 7.82 (2H, m), 7.56 (3H, m), 6.61 (1H, d, Jϭ2.2 Hz), 6.27 (1H, s), 6.18 (1H,
drolyzed by adding H2O and extracted with EtOAc. The organic layer was d, Jϭ2.2 Hz), 3.84 (3H, s). HR-MS m/z: 266.9856 (Calcd for C16H13NO3:
washed with brine, dried over anhydrous Na2SO4 and evaporated. The 266.9861). EI-MS m/z: 267 (Mϩ). Anal. Calcd for C16H13NO3: C, 71.90; H,
residue was purified by column chromatography eluted with cyclo- 4.90; N, 5.24. Found: C, 71.84; H, 4.83; N, 5.19.
hexane : AcOEt (9 : 1) to yield 4.84 g of pure 1 as a white solid. Yield 96%.
5-Methoxy-4-alkoxyquinolines 5, N-Alkyl-4-quinolones 6 and 5-Hy-
droxy-4- alkoxyquinolines 7: Standard Procedure Quinolone 3 or 4 and
mp 143—145 °C (EtOAc). 1H-NMR (CDCl3) d: 7.86 (2H, m), 7.51 (3H, m),
6.91 (2H, d, Jϭ2 Hz), 6.30 (1H, t, Jϭ2 Hz), 3.81 (6H, s). HR-MS m/z: the alkyl halide (1.5 eq) were dissolved in anhydrous DMF (5 ml/mmol) and
256.9907 (Calcd for C15H15NO3: 256.9909). EI-MS m/z: 257 (Mϩ). Anal. K2CO3 (3 eq) was added. The reaction mixture was stirred at room tempera-
Calcd for C15H15NO3: C, 70.02; H, 5.88; N, 5.44. Found: C, 69.98; H, 5.83; ture for 2 h then heated at 80 °C for 3 h, after heating, the reaction mixture
N, 5.36.
was poured into water, extracted with EtOAc and concentrated. Products
N-(2-Acetyl-3,5-dimethoxyphenyl)benzamide (2) To an ice cold solu- were purified either by chromatography column eluted with hexane : AcOEt
tion of 1 (4.7 g, 18.3 mmol) in freshly distilled 1,2-dichloroethane (60 ml) (9 : 1) or by preparative TLC using hexane : AcOEt (7 : 3) as eluant.
under N2 was added dropwise SnCl4 (4.3 ml, 36.6 mmol). Freshly distilled
acetyl chloride (1.41 ml, 20 mmol) as a solution in 1,2-dichloroethane (5 ml) References and Notes
was also added dropwise. After stirring at room temperature for 1.5 h, the
solution was poured into crushed ice, extracted with AcOEt, washed with
brine, dried over Na2SO4 and concentrated. Purification by column chro-
matography eluted with AcOEt : cyclohexane (1 : 1) afforded 3.18 g of 2 as
1) a) Wang H.-K., Xia Y., Yang Z.-Y., Morris Natschke S. L., Lee K.-H.,
Adv. Exp. Med. Biol., 439, 191—225 (1998); b) Li L., Wang H.-K.,
Kuo S.-C., Wu T.-S., Mauger A., Lin C. M., Hamel E., Lee K.-H., J.
Med. Chem., 37, 3400—3407 (1994); c) Chen K., Kuo S.-C., Hsieh
M.-C., Mauger A., Lin C.-M., Hamel E., Lee K.-H., ibid., 40, 3049—
3056 (1997); d) Xia Y., Yang Z.-Y., Xia P., Bastow K. F., Tachibana
Y., Kuo S.-C., Hamel E., Hackl T., Lee K.-H., ibid., 41, 1155—1162
(1998); e) Zhang S.-X., Feng J., Kuo S.-C., Brossi A., Hamel E., Trop-
sha A., Lee K.-H., ibid., 43, 167—176 (2000); f) Sui Z., Nguyen V.
N., Altom J., Fernandez J., Hilliard J. J., Bernstein J. I., Barrett J. F.,
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3—37.
1
white crystals. Yield 58%. mp 119—121 °C (EtOAc). H-NMR (CDCl3) d:
12.7 (1H, bs), 8.3 (1H, d, Jϭ2.1 Hz), 8.15 (2H, m), 7.50 (3H, m), 6.25 (1H,
d, Jϭ2.1 Hz), 3.96 (3H, s), 3.93 (3H, s), 2.64 (3H, s). HR-MS m/z: 298.9280
(Calcd for C17H17NO4: 298.9284). EI-MS m/z: 299 (Mϩ). Anal. Calcd for
C17H17NO4: C, 68.21; H, 5.72; N, 4.68. Found: C, 68.15; H, 5.63; N, 4.66.
N-(2-Acetyl-3,5-dimethoxyphenyl)benzamide (2a) This regioisomer
(more polar than 2) was obtained with less than 5% yield as white crystals.
mp 137—139 °C (EtOAc). 1H-NMR (CDCl3) d: 8.94 (s, 1H), 7.89 (d,
Jϭ7 Hz, 2H), 7.37 (m, 3H), 7.01 (s, 2H), 3.60 (s, 6H), 2.43 (s, 3H). EI-MS
m/z: 299 (Mϩ). Anal. Calcd for C17H17NO4: C, 68.21; H, 5.72; N, 4.68.
Found: C, 68.18; H, 5.66; N, 4.63.
3) Huang L. J., Hsieh M. C., Teng C. M., Lee K. H., Kuo S. C., Bioorg.
Med. Chem., 6, 1657—1662 (1998).
5,7-Dimethoxy-2-phenyl-4-quinolone (3) To a stirred solution of 2
(3.1 g, 10.3 mmol) in anhydrous THF (30 ml) under N2 atmosphere was
added t-BuOK (5.7 g, 51.5 mmol). The reaction mixture was then refluxed
for 20 h. After cooling, the resultant mixture was added to a saturated aque-
ous solution of NH4Cl and the whole was extracted with AcOEt (3ϫ50 ml),
dried over anhydrous Na2SO4 and evaporated. The crude material was puri-
fied by column chromatography eluted with cyclohexane : AcOEt (3 : 7) to
give 2.41 g of 3 as a yellow solid. Yield 83%. mp 144—145 °C (CH2Cl2).
1H-NMR (CDCl3) d: 7.72 (m, 2H), 7.50 (m, 3H), 6.52 (d, Jϭ2.1 Hz, 1H),
6.29 (s, 1H), 6.21 (d, Jϭ2.1 Hz, 1H), 3.92 (s, 3H), 3.87 (s, 3H). HR-MS m/z:
281.0129 (Calcd for C17H15NO3: 281.0131). EI-MS m/z: 281 (Mϩ). Anal.
Calcd for C17H15NO3: C, 72.58; H, 5.37; N, 4.98. Found: C, 72.52; H, 5.30;
N, 4.97.
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5-Hydroxy-7-methoxy-2-phenyl-4-quinolone (4) To a stirred solution
of 3 (0.54 g, 1.92 mmol) in anhydrous CH2Cl2 (20 ml) at 0 °C under N2 at- 10) Beney C., Hadjeri M., Mariotte A.-M., Boumendjel A., Tetrahedron
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