A general uncatalyzed method for the synthesis of O-silylated oximes

Article abstract of DOI:10.1081/SCC-120015717

Aldoximes and ketoximes were smoothly and efficiently 0-silylated at room temperature with diverse chlorosilanes such as TMSCl, TBSCl, or TIPSCl in dichloromethane or THF, using imidazole as a base to trap the generated hydrochloric acid.

Full text of DOI:10.1081/SCC-120015717

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A General Uncatalyzed Method for the Synthesis of O-
Silylated Oximes
Margarita Ortiz-Marciales a b , Melvin De Jesús a , Dyliana Figueroa a , Jesús Hernández a ,
Leslie Vázquez a , Rafael Vega a , Eduardo M. Morales a & José A. López a
a Department of Chemistry, University of Puerto Rico, CUH Station, Humacao, PR, USA
b Department of Chemistry, University of Puerto Rico, CUH Station, Humacao, PR, 00791,
USA
Published online: 21 Aug 2006.
To cite this article: Margarita Ortiz-Marciales , Melvin De Jesús , Dyliana Figueroa , Jesús Hernández , Leslie Vázquez , Rafael
Vega , Eduardo M. Morales & José A. López (2003) A General Uncatalyzed Method for the Synthesis of O- Silylated Oximes,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 33:2, 311-323,
DOI: 10.1081/SCC-120015717
To link to this article: http://dx.doi.org/10.1081/SCC-120015717
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 2, pp. 311–323, 2003
A General Uncatalyzed Method for the
Synthesis of O-Silylated Oximes
*
Margarita Ortiz-Marciales, Melvin De Jesus,
Dyliana Figueroa, Jesus Hernandez, Leslie Vazquez,
Rafael Vega, Eduardo M. Morales, and Jose A. Lopez
Department ofChemistry, University ofPuerto Rico,
CUH Station, Humacao, PR, USA
ABSTRACT
Aldoximes and ketoximes were smoothly and efficiently O-silylated
at room temperature with diverse chlorosilanes such as TMSCl,
TBSCl, or TIPSCl in dichloromethane or THF, using imidazole as
a base to trap the generated hydrochloric acid.
Oximes and oxime ethers are used as convenient intermediates for the
[1–7]
preparation ofa variety oforganic molecules
and pharmaceutical
products[8–10] due to their convenient preparation from carbonyl com-
pounds and their facile transformations to other functional groups.
O-Silylated aldoximes and ketoximes are widely known stable derivatives
*Correspondence: Margarita Ortiz-Marciales, Department ofChemistry,
University ofPuerto Rico, CUH Station, Humacao, PR 00791, USA. Fax:
(787) 850-9422; E-mail: m_ortiz@cuhac.upr.clu.edu.
311
DOI: 10.1081/SCC-120015717
Copyright & 2003 by Marcel Dekker, Inc.
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312
Ortiz-Marciales et al.
used as intermediates for the synthesis of nitrogen containing compounds
such as: hydroxylamines,[5] amines,[11–13] nitrones,[14] isoxazoles,[15]
nitriles,[16] and other compounds.[17–20]
A large number ofprocedures are reported of r the direct hydroxyl
[21]
group silylation ofalcohols,
phenols,[22] and carboxylic acids[23] using
the commercially available silyl chlorides as silylating reagents. However,
there is a need ofwell established methods for the synthesis ofO -silylhy-
droxylamines[24] and oximes.[25] Most ofthe known procedures of r the
silylation ofoximes were directed toward the characterization ofderiva-
tives by gas chromatographic analysis,[26a,b] or for the in situ preparations
ofaldoxime intermediates in multi-step synthesis without their complete
characterization.[27]
In general, the synthesis of O-trimethylsilyl oximes has been accom-
plished by refluxing the oximes with hexamethyldisilazane in the presence
[14,28a]
ofa catalytic amount oftrimethylchlorosilane;
or by the oxime
reaction with trimethylchlorosilane using different liquid bases, such as
pyridine (used also as solvent),[28b] or triethylamine in CCl4,[27c,28c,d,29]
CH2Cl2,[27b] or ether.[28e]
Although the bulkier aldoximes and ketoximes silylethers are more
stable and potentially useful as synthetic intermediates, methods for their
preparation have been less studied.[25b] In 1983, Barret and coworker[30a]
applied to oximes the conditions used by Corey et al.[21a] for the tert-
butyldimethylsilyl (TBS) group protection ofalcohols, e.g., TBSCl/
imidazole/N,N-dimethylformamide. However, this silylating method
has been reported to be sluggish[26] and requires forcing reaction condi-
tions such as: excess ofchlorosilane and imidazole, longer reaction
times,[30a,30b] molecular sieves as catalyst[31] or heating.[32]
We report here an efficient silylating procedure that presents several
advantages over the existing methods. It requires shorter reaction times
of r the large-scale preparation ofa variety ofsilylethers (TMS-, TBS-,
TIPS-, or MDPS-groups) at room temperature without the need for a
catalyst and it has a simple workup that produces highly pure aliphatic
and aromatic aldoximes and ketoximes derivatives in very good yield.
In a preliminary experiment, the formation of the silyl ether 1 and
the corresponding oxime hydrochloride 2 was observed by GC when
4-methoxyacetophenone oxime was mixed in an equal molar ratio with
TBSCl in CH2Cl2, (Sch. 1). Product 2 was isolated and characterized by
1
its IR, H and 13C NMR spectra.[33,34]
To optimize this method, the silylation of4-methoxyacetophenone
oxime using one equivalent ofTBSCl with the subsequent addition of1.5
equivalents ofimidazole as a base was carry out in CH Cl2, THF, and
2

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O-Silylated Oximes
313
Scheme 1.
diethyl ether, accomplishing a 98%, 90%, and 88% yield, respectively,
in 15 min as analyzed by GC/MS. We extended our approach to the
synthesis ofother silylated oximes using one equivalent ofthe oxime,
one equivalent ofthe chlorosilane in CH Cl2 (or THF depending on
2
the solubility ofthe oxime ), of llowed by the addition of1–2 equivalent
ofimidazole in CH Cl2. Immediately after the reagents were mixed, the
2
imidazolinium hydrochloride salt precipitated. Analysis ofthe solutions
by GC indicated that the reactions were completed in less than 1 h with
excellent product purity. The precipitate was removed from the mixture
by filtration, the crystals were washed with a small amount ofCH Cl2
2
and the filtrate was concentrated under vacuum. The oily residue was re-
dissolved in dry hexane and passed through a short pad ofsilica gel in
hexane. In an alternative pre-purification wet process, the filtrated was
washed with cold bicarbonate and/or a brine solution, dried and concen-
trated to afford the silylated oxime. Further purification by vacuum dis-
tillation, recrystallization, or column chromatography on silica gel with
hexane as eluting phase, yielded a highly pure product (GC/MS).
By this procedure, a variety ofoximes were conveniently and effi-
ciently silylated with different silyl groups, as indicated in Table 1. As
expected, benzaldoximes provided the silylated oximes without a trace of
the corresponding nitrile due to the mild reaction conditions. One impor-
tant feature of our reported silylating method is that the substitution
reaction at the silicon atom proceeds swiftly even for the bulky tert-
butyldimethyl- and triisopropylsilyl groups. We have observed that
when the addition ofimidazole to the oxime and chlorosilane reaction
mixture is too abrupt, the reaction rate decreases significantly. Therefore,

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314
Ortiz-Marciales et al.
Table 1. Synthesis ofoxime silyl ethers.
E/Z Yield
ratioa (%)b Entry
E/Z Yield
ratioa (%)b
Entry
Silyl ether
Silyl ether
1a
90/10
77
1g
92/8
77
1b
1c
1d
93/7
84/16
92/8
87
88
66
1h
1i
1j
99/1
96/4
99/1
68
69
80
1e
1f
98/2
97/3
81
79
1k
1l
100
87
66
99/1
aE/Z ratios.
bIsolated yields ofpure products characterized by their FT-IR, 1H, and 13C NMR
and GC/MS spectroscopic data.
a hypothesis for the high efficiency of our method with these bulky silyl
groups is the prevention ofthe in situ ofrmation ofthe less reactive
R1R2R3Si-imidazole intermediates.[25a]
In conclusion, we have described a general uncatalyzed, inexpensive,
facile, and efficient method for the synthesis of new ketoximes and
aldoximes silylethers.

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O-Silylated Oximes
315
EXPERIMENTAL SECTION
All experiments were carried out under an atmosphere ofdry nitro-
gen, and using standard procedures for handling air sensitive compounds.
1H and 13C NMR spectra were recorded on a GE 500 MHz in CDCl3
solution using TMS as internal reference. Mass spectra were measured at
70 eV on a HP 5996 instrument. Analytical gas chromatography (GC)
was performed using a flame ionization detector and a capillary column
(25 mm ꢀ 0.33 mm bonded 5% phenyl methylsilicone). Commercial
grade reagents and solvents were used after standard purification pro-
cedures. The silica gel, used for column chromatography was Merck,
230–400 mesh from Aldrich. Dry THF was distilled from sodium benzo-
phenone ketyl. Dichoromethane was distilled over CaH2, prior to use.
Representative procedure for silylation of oximes used for the synthesis
of O-triisopropylsilyl camphor oxime (1k): To a stirred solution of
camphor oxime (3.0 g, 18 mmol) and triisopropylsilyl (TPS) chloride
(3.84 mL, 3.45 g, 18 mmol) in CH2Cl2 (5 mL) was added dropwise
(30 min) a solution ofimidazole (2.44 g, 36 mmol) in CH Cl2 (15 mL) at
2
room temperature. GC analysis indicated the complete formation of the
product after one hour. The white precipitate was removed by filtration
under nitrogen, the solution was concentrated in a rotorevaporator
(20 mmHg) and then under high vacuum (0.01 mmHg). The crude pro-
duct (5.8 g, 99%) was passed through a silica gel pad (28 g) with hexane
and fractional distilled under vacuum. Yield 87% (5.1 g); B.p. 94–97ꢁC
(0.05 mmHg); IR (neat): 1665 (C¼N); 1H NMR (CDCl3) ꢀ (ppm): 2.5 (dt,
1H, CH), 2.0 (d, 1H, CH), 1.86 (t, 1H), 1.8 (m, 1H), 1.6 (m, 1H), 1.4 (m,
1H), 1.2 (m, 1H), 1.2 (m, 3H, Si–CH), 1.0 (d, 18H), 0.97 (s, 3H), 0.87 (s,
3H), 0.77 (s, 3H); and 13C NMR ꢀ: 172.1 (C¼N), 51.8 (C1), 48.0 (C7), 43.7
(C4), 33.4 (C3), 32.8 (C6), 27.3 (C5), 19.4 (C8), 18.6 (C9), 18.0 (CH3–CH–
Si), 11.9 (C10), 11.1 (Si–CH); MS m/z: 324.2 (Mþ), 298 (100). Anal. calcd.
for C19H37NOSi: C, 70.52; H, 11.53; N, 4.33. Found: C, 70.12; H, 11.62;
N, 4.37.
O-(tert-Butyldimethylsilyl)-2-methoxybenzaldoxime (1a): Compound
1a was prepared from 2-methoxybenzaldoxime (5.4 g, 39.6 mmol) using
the previous procedure for silylation. The clear oily crude product (8.4 g,
80%, E/Z ratio: 92/8 by GC, Rt 10.3 min and 9.5 min) was purified by
column chromatography on silica gel (2 cm diameter,15 cm length, 30 g)
in hexane (8.0 g, 77% yield, 97% purity by GC): FT-IR (neat, cmꢂ1) 1605
(C¼N), 1250 (SiMe, vs); 1H NMR ꢀ: 8.65 (s, 1H), 6.89–7.89 (m, 4H), 3.8
(s, 3H), 1.05 (s, 9H), 0.30 (s, 6H); 13C NMR ꢀ: 149.1, 157.4, 126.3, 131.0,
120.6, 121.2, 110.9, 55.4, 26.1, 18.2, 5.2; MS m/z: 266.5 (Mþ, 100), 208

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316
Ortiz-Marciales et al.
(M. þ-t-Bu), 134 (M. þ ꢂ OTBS). Anal. calcd. for C14H23NO2Si: C, 63.35;
H, 8.73; N, 5.28. Found: C, 63.45; H, 9.07; N, 5.23.
O-(Triisopropylsilyl)benzaldoxime (1b): Compound 1b was prepared
from benzaldoxime (2.2 g, 18 mmol) using the described procedure for
silylation. The clear oily crude product (4.7 g, 94%, E/Z ratio: 93/7 by
GC, Rt 12.2 min and 11.9 min) was purified by column chromatography
1
on silica (16 cm ꢀ 2.0 cm diameter) /hexane (4.3 g, 87%): H NMR ꢀ: 8.3
(s, 1H), 7.7–7.4 (m, 5H), 1.41 (m, 3H), 1.27 (d, 18H); 13C NMR ꢀ: 152.9,
149.6, 130.8, 129.6, 128.6, 126.9, 17.9, 11.9; MS m/z: 278 (M.þ), 252 (100).
Anal. Calcd. for C16H27NOSi: C, 69.26; H, 9.81; N, 5.05. Found: C, 69.02;
H, 10.18; N, 4.84.
O-(tert-Butyldimethylsilyl)-2-methoxyacetophenone oxime (1c): This
compound was obtained from 2-methoxyacetophenone oxime (5.0 g,
30 mmol) using the described procedure for silylation, followed by
dilution with hexane, filtration ofthe imidazole hydrochloride salt,
extraction with a cold brine solution (50 mL) and subsequent drying
the organic phase with MgSO4, as a clear liquid (7.8 g, 93%, E/Z ratio:
87/13 by GC, Rt 10.6 min and 8.6 min). After purification by fractional
distillation, 1c was obtained (7.4 g, 88%): B.p. 88ꢁC/0.45 mmHg. IR
1
(film, cmꢂ1) 1248 (SiMe, vs); H NMR (CDCl3, TMS) ꢀ: 7.4 (m, 2H),
6.9 (m, 2H), 3.8 (s, 3H), 2.2 (s, 3H), 1.1 (s, 9H), 0.26 (s, 6H); 13C NMR ꢀ:
160.9, 157.4, 129.9, 129.6, 127.4, 120.4, 111.0, 55.3, 26.1, 18.1, 15.8, ꢂ5.1;
MS m/z: 280.4 (M. þ þ 1) 149.2 (M. þ ꢂ HOTBS, 100). Anal. calcd. for
C15H25NO2Si: C, 64.47; H, 9.02; N, 5.01. Found: C, 64.30; H, 8.79; N, 5.03.
O-(tert-Butyldimethylsilyl)-2,4-dimethoxyacetophenone oxime (1d):
This compound was prepared as described above from 2,4-dimethoxya-
cetophenone oxime (4.0 g, 20 mmol), followed by filtration of the imida-
zole hydrochloride salt, concentration ofthe filtrate under vacuum,
extraction with a cold brine solution (40 mL) and subsequent drying
the organic phase with Na2SO4. The crude product was a clear colorless
liquid (5.36 g, 85%, E/Z ratio: 92/8 by GC, Rt 12.6 min and 10.8 min).
After purification by fractional distillation, 1d was obtained as a clear
liquid (4.2 g, 66%, 98% purity): B.p. 123ꢁC/0.85 mmHg; IR (film, cmꢂ1
)
1248 (SiMe, vs); 1 H NMR (CDCl3, TMS) ꢀ: 7.3 (d, 1H), 6.4 (m, 2H), 3.8
(s, 3H), 3.8 (s, 3H), 2.2 (s, 3H), 1.0 (s, 9H), 0.23 (s, 6H); 13C NMR ꢀ:
161.4, 160.6, 158.6, 130.1, 120.4, 104.2, 98.8, 55.3, 26.1, 18.1, 15.9, ꢂ5.1;
.
MS m/z: 310.1 (Mþ ), 177.8 (M. þ ꢂ HOTBS, 100). Anal. calcd. for
C16H27NO3Si: C, 62.10; H, 8.79; N, 4.53. Found: C, 61.82; H, 9.02;
N, 4.50.
O-(tert-Butyldimethylsilyl)-4-methylacetophenone oxime (1e): Prepared
by the typical silylation method described previously from the 4-methyl-

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O-Silylated Oximes
317
acetophenone oxime (3.00 g, 20.2 mmol) as an oily clear product (5.1 g,
95%, E/Z ratio: 98/2 by GC, Rt 11.6 min and 10.1 min): After purifica-
tion by fractional distillation, 1e was obtained as a clear liquid (4.3 g,
81%): B.p. 40ꢁC/0.2 mmHg. The spectral data corresponded exactly to
the previous reported values.[32]
O-(tert-Butyldimethylsilyl)-4-methoxyacetophenone oxime (1f ): Pre-
pared by the typical silylation method described previously from 4-meth-
oxyacetophenone oxime (6.00 g, 36.4 mmol) as a clear oily product. After
purification by fractional distillation, 1f was obtained as a viscous liquid
(8.0 g, 79%): B.p. 116ꢁC/0.1 mmHg, (E/Z ratio: 97/3 by GC, Rt 11.5 min
and 10.6 min). The spectral data corresponded exactly to the previous
reported values.[12b]
O-(Triisopropylsilyl)-4-
methoxyacetophenone oxime (1g): Prepared from 4-methoxyacetophe-
none oxime (1.5 g, 26 mmol) as an oily clear product (2.6 g, 90%, E/Z
ratio: 92/8 by GC, Rt 18.1 min and 16.2 min). After purification by frac-
tional distillation, 1g was obtained as a clear viscous liquid (2.2 g, 77%,
99% purity, E/Z ratio: 95/5): B.p. 180ꢁC/0.3 mmHg; H NMR ꢀ: 7.7 (d,
1
J ¼ 8.8 Hz,1H), 6.9 (d, J ¼ 8.8 Hz, 2H), 3.8 (s, 3H), 2.3 (s, 3H), 1.3 (m,
3H), 1.2 (d, 18H); 13C NMR ꢀ: 160.2, 157.7, 129.6, 127.2, 6, 113.6, 55.2,
12.1, 11.9; MS m/z: 148 (100). Anal. calcd. for C18H31NO2Si: C, 67.31; H,
9.73; N, 4.36. Found: C, 67.21; H, 10.05; N, 4.27.
O-(Trimethylsilyl)-4-methoxyacetophenone oxime (1h): Prepared from
the 4-methoxyacetophenone oxime (3.5 g, 21.1 mmol) as an oily viscous
product (4.4 g, 88%, 93% purity, E/Z ratio: 99/1 by GC, Rt 10.8 min and
9.3 min). After purification by fractional distillation, 1h was obtained
as a clear viscous liquid, (3.0 g, 68%, 99.7% purity by GC), b.p.
78ꢁC/0.05 mmHg; IR (film, cmꢂ1) 1249 (SiMe, vs); H NMR ꢀ: 7.7 (d,
1
J ¼ 9 Hz, 2H), 6.9 (d, J ¼ 9 Hz, 2H), 3.8 (s, 3H), 2.3 (s, 3H), 0.3 (s, 3H);
13C NMR ꢀ: 160.4, 158.2, 129.5, 127.4, 113.6, 55.2, 12.2, ꢂ0.60; MS m/z:
237 (M. þ), 148 (M. þ ꢂ OSiMe3, 100). Anal. calcd. for C12H19NO2Si:
C, 60.72; H, 8.07; N, 5.90. Found: C, 61.04; H, 8.17; N, 6.08.
O-(Trimethylsilyl)camphor oxime (1i): Compound 1i was prepared
from camphor oxime (4.2 g, 25.2 mmol) using the previous procedure
for silylation. The clear oily crude product (5.1 g, 85%, 90% purity by
GC, Rt 7.96 min) was purified by fractional distillation (4.1 g, 69%, only
E isomer by GC/MS): B.p. 94–98ꢁC/4 mmHg; FT IR (film, cmꢂ1) 1664
1
(C¼N), 1250 (SiMe, vs); H NMR (CDCl3) ꢀ (ppm): 2.47 (dt, 1H, CH),
2.0 (d, 1H, CH), 1.85 (t, 1H), 1.8 (m, 1H), 1.7 (m, 1H), 1.4 (m, 1H), 1.2
(m, 1H), 0.99 (s, 3H), 0.89 (s, 3H), 0.76 (s, 3H), 0.16; 13C NMR ꢀ: 173.83
(C¼N), 51.7, 48.0, 43.7 , 33.8, 32.7, 27.3, 19.4, 18.5, 11.1, 0.72; MS m/z:

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Ortiz-Marciales et al.
239 (M. þ), 75 (100). Anal. calcd. for C13H25NOSi: C, 65.21; H, 10.52;
N, 5.85. Found: C, 65.30; H, 11.00; N, 5.63.
O-(tert-Butyldimethylsilyl)camphor oxime (1j): Compound 1j was
prepared from camphor oxime (2.8 g, 16.8 mmol) using the previous
procedure for silylation. The clear oily crude product (4.7 g, 99%, only
one peak, 95% purity, Rt 9.2 min) was purified by fractional distillation
(3.6 g, 80%, >98%, E/Z ratio: 95/5 by GC/MS, Rt 18.1 and 17.9 min):
B.p. 70–73ꢁC/0.3 mmHg; FT IR (film, cmꢂ1) 1666 (C¼N), 1249 (SiMe,
vs); 1H NMR (CDCl3) ꢀ (ppm): 2.5 (tt, 1H, CH), 2.0 (s, 1H, CH), 1.85 (t,
1H), 1.81 (m, 1H), 1.68 (m, 1H), 1.44 (m, 1H), 1.23 (m, 1H), 1.0 (m, 3H),
0.92 (s, 9H), 0.89 (s, 3H), 0.90 (s, 3H), 0.77 (s, 3H), 0.13 (s, 6H); 13C NMR
ꢀ: 173.28 (C¼N), 51.8, 48.1, 43.7, 33.7, 32.7, 27.3, 26.2, 19.4, 18.6, 11.1,
ꢂ5.2; MS m/z: 280 (M. þ), 75 (100). Anal. calcd. for C16H31NOSi: C, 68.26;
H, 11.10; N, 4.98. Found: C, 67.97; H, 11.35; N, 4.79.
O-(tert-Butyldimethylsilyl)-6-methoxytetralone oxime (1l): This com-
pound was prepared as described above from 6-methoxytetralone oxime
(3.6 g, 18.8 mmol) in CH2Cl2 (35 mL), tert-butyldimethylsilyl chloride
(3.12 g, 20.7 mmol) and a solution ofimidazole (2.56 g, 37.6 mmol) in
CH2Cl2 (25 mL). After Schlenk filtration of the imidazole hydrochloride
salt, the filtrate was concentrated under vacuum. The clear oily residue
was dissolved in hexane (20 mL), extracted the organic phase with a cold
NaHCO3 aqueous solution (20 mL), and dried with Na2SO4. The crude
product was an oily compound (4.76 g, 83%, E/Z ratio: 99/1 by GC/MS,
Rt 15.9 min and 15.3 min) that was purified by column chromatography
on silica gel (2 cm diameter, 13 cm length, 24 g) in hexane (3.76 g, 66%
yield, 99% purity by GC): IR (film, cmꢂ1) 1613 (C¼N); 1H NMR (CDCl3,
TMS) ꢀ: 8.0 (d, J ¼ 8.7 Hz, 1H), 6.8 (d, J ¼ 8.7 Hz,1H), 6.6 (s, 1H), 3.8 (s,
3H), 2.83 (t, J ¼ 6.5 Hz, 2H), 2.76 (t, J ¼ 5.9 Hz, 2H), 1.87 (m, J ¼ 6.3 Hz,
2H), 1.0 (s, 9H), 0. 27 (s, 6H); 13C NMR ꢀ: 160.1, 157.7, 141.1, 125.8,
124.0, 112.8, 112.6, 55.1, 30.1, 26.2, 24.0, 21.2, 18.2, ꢂ5.1; MS m/z:
.
306.3 (Mþ , 100). Anal. calcd. for C17H27NO2Si: C, 66.84; H, 8.91;
N, 4.59. Found: C, 66.87; H, 9.16; N, 4.66.
ACKNOWLEDGMENTS
This work was supported by the National Institute ofHealth, MBRS
Program Grant (GM 08216) and AREA Grant (GM 59829). ONR and
NSF-AMP undergraduate’s support is also gratefully acknowledged. We
thank Mr. Jose Martınez (University ofPuerto Rico, Rı o Piedras) for
obtaining the NMR spectra.

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O-Silylated Oximes
323
5.6 mmol, 77% yield) as a crystalline salt: M.p. 115–118ꢁC, IR
(KBr): 2695.7 (broad, NHþ, OH) cmꢂ1 1H NMR (CDCl3) ꢀ
;
(ppm): 2.47 (s, 3H, CH3), 3.85 (s, 3H, CH3 O), 7.8 (d, 2H, Ar),
7.0 (d, 2H, Ar), 12.4 (s, 2H, NH, OH); and 13C NMR: 164.23
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15.68 (CH3).
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Chem. Scand. Ser. B 1987, 41, 184.
Received in the USA February 22, 2002

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