Synthesis of chiral pyrimidin-2(1H)-Ones from n-Carbamoyl amino acids

Article abstract of DOI:10.5560/ZNB.2013-3129

A series of previously unknown pyrimidin-2(1H)-ones containing chiral amino acid fragments was synthesized from 1,1,3,3-tetramethoxypropane and N-carbamoyl derivatives of amino acids under acidic conditions.

Full text of DOI:10.5560/ZNB.2013-3129

Synthesis of Chiral Pyrimidin-2(1H)-ones from N-Carbamoyl Amino
Acids
Ilya N. Egorova, Vladimir L. Rusinova,b and Oleg N. Chupakhina,b
a
Institute of Chemistry and Technology, Ural Federal University, Mira St. 19, Ekaterinburg,
620 002, Russia
b
Institute of Organic Synthesis of Russian Academy of Sciences, S. Kovalevskoy St. 22,
Ekaterinburg, 620 041, Russia
Reprint requests to Dr. Ilya Egorov. Fax: +7(343)3740458. E-mail: i.n.egorov@gmail.com
Z. Naturforsch. 2013, 68b, 1253 – 1258 / DOI: 10.5560/ZNB.2013-3129
Received May 1, 2013
A series of previously unknown pyrimidin-2(1H)-ones containing chiral amino acid fragments was
synthesized from 1,1,3,3-tetramethoxypropane and N-carbamoyl derivatives of amino acids under
acidic conditions.
Key words: Heterocycles, Amino Acids, Condensation, Chirality, Pyrimidines
Introduction
acid fragments, but it is known that chirality is im-
portant for bioactivity. To the best of our knowl-
edge only few methods of synthesis of chiral α-amino
acid derivatives of pyrimidines are known [6 – 8]. One
method of synthesis of pyrimidines with chiral α-
amino acid fragments at the heterocyclic ring has been
reported. The alkylation of cytosine with esters of
(S)-lactic acid leads to alkyl derivatives of cytosine
(de = 56) [8].
Amino acid derivatives of pyrimidinones are nucle-
oside analogs and are interesting as biologically ac-
tive compounds or their precursors [1]. It is known
that pyrimidin-2(1H)-ones 1 containing peptide frag-
ments reveal anti-inflammatory activity [2]. Their aza
analogs – 1.2.4-triazin-3(2H)-ones 2 – do not show
or show only low anti-inflammatory activity, however
these compounds have been proved to show strong
analgesic properties [3]. Pyrimidinones 3 are useful in
the treatment or prevention of the diseases mediated by
the activation of the β3-adrenoceptor [4, 5].
Results and Discussion
In this work the synthesis of pyrimidin-2(1H)-
ones with amino acid residues is described. It is
known that N-carbamoyl amino acids easily cyclize to
give hydantoins under acidic conditions [9, 10]. The
condensation of 1,1,3,3-tetramethoxypropane with N-
carbamoyl derivatives of amino acids in the presence
of hydrochloric acid in methanol gives methyl esters
of pyrimidinones 5–11 (Scheme 1, Fig. 1). The change
of solvent from methanol to ethanol, 2-propanol or
water leads to the disappearance of pyrimidinones in
the products of the reaction. In the reactions with N-
carbamoyl derivatives of other amino acids such as L-
valine, L-leucine, L-isoleucine, D,L-tryptophan, or L-
serine we failed to obtain the corresponding pyrimidi-
nones. Acid hydrolysis of the esters 5 and 6 leads to
R1
O
R
O
Ar1
Ar2
N
N
N
COOH
N
COOR2
Ar
N
N
1
2
H
N
OH
Ar
R2
N
R1
O
R3
N
H
O
3
The published methods [1 – 4] for the synthesis of carboxylic acids 12 (67%) and 13 (76%), respectively
compounds 1–3 lead to products with racemic amino (Scheme 1).
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I. N. Egorov et al. · Chiral Pyrimidin-2(1H)-ones from N-Carbamoyl Amino Acids
COOH
COOMe
MeO
MeO
HOOC
∗
∗
∗
OMe
OMe
R
O
H l
C
H
C
HCl
R
N
N
3
HN
+
H2 dioxane
O
,
H
2O
MeOH,
r. t.
O
r. t.
N
N
O
H2N
−
12 13
,
5 11
4
R
Configuration Product Yield (%)
CH3
CH3
(S)
5
43
21
55
15
34
40
52
(R)
6
CH2CH2SCH3
CH2CH2SCH3
CH2CH2SCH3
CH2Ph
(S)
7
(R)
8
(R,S)
(R,S)
9
10
11
CH2(p-C6H4OH) (S)
Scheme 1. Synthesis of pyrimidin-2(1H)-one derivatives.
In addition we tried to prepare 1-substituted
pyrimidin-2-ones from 2-phenylmalonaldehyde 14.
When a mixture of 2-phenylmalonaldehyde and a sub-
stituted urea was refluxed in toluene in the pres-
ence of p-TsOH [11] hydantoins were formed as the
sole products from the N-carbamoyl derivatives of L-
methionine, L-lysine, L-leucine, L-isoleucine, and L-
tyrosine. Using different reaction times in the reaction
with L-valine led to the products 15 and 16 besides the
corresponding hydantoin derivative (Scheme 2).
Obviously the first step of the reaction leads to the
condensation product 15 (Fig. 2). Under forced condi-
tions 15 is cyclized and subsequently decarboxylated
to give 16 (Fig. 3). We could not find conditions which
allowed the isolation of an intermediate. When ben-
zene or p-xylene were used as solvents, hydantoins
were the sole reaction products.
Experimental Section
All commercially obtained solvents and reagents were
Fig. 1. ORTEP diagram of 7.
used as received; N-carbamoyl amino acids [12] and 2-
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I. N. Egorov et al. · Chiral Pyrimidin-2(1H)-ones from N-Carbamoyl Amino Acids
1255
O
COOH
CH3
N
H
N
H
O
HOOC
HN
0.5 h
4 h
Ph
CH3
O
O
p-TsOH
15
Ph
+
toluene, reflux
O
H2N
14
Ph
CH3
CH3
N
N
O
16
Scheme 2.
Fig. 3. ORTEP diagram of 16.
(S)-2-(2-Oxopyrimidin-1(2H)-yl)propionic acid methyl ether
(5)
Fig. 2. ORTEP diagram of 15.
Colorless liquid. Yield 0.39 g (43%). – 1H NMR
(400 MHz, [D6]DMSO): δ = 1.67 (d, J = 7.4 Hz, 3H, CH3),
3.76 (s, 3H, OCH3), 5.41 (q, J = 7.4 Hz, 1H, CH), 6.38 (dd,
J = 6.7, 4.1 Hz, 1H, Py-H), 7.74 (dd, J = 6.7, 2.8 Hz, 1H,
Py-H), 8.60 (dd, J = 3.9, 2.9 Hz, 1H, Py-H). – 13C NMR
(100 MHz, [D6]DMSO) δ = 16.5, 53.0, 55.6, 104.2, 145.4,
155.7, 166.1, 170.4. –C8H10N2O3: calcd. C 52.74, H 5.53,
N 15.38; found C 52.99, H 5.67, N, 15.45.
phenylmalonaldehyde [11] were synthesized by known
1
methods. H, 13C NMR spectra were recorded on a Bruker
DRX-400 spectrometer; tetramethylsilane (TMS) was used
as an internal standard. The optical rotation was measured on
a Perkin Elmer polarimeter. Mass spectra were recorded on
a Bruker Daltonics MicroTOF-Q II mass spectrometer with
electrospray ionization.
General procedure for the synthesis of compounds 5–11
(R)-2-(2-Oxopyrimidin-1(2H)-yl)propionic acid methyl ester
(6)
1,1,3,3-Tetramethoxypropane (821 µL, 5.0 mmol) and
conc. HCl (12 M, 3 mL) were added to a suspension of
the corresponding N-carbamoyl amino acid (5.0 mmol) in
methanol (10 mL). After a few minutes a colorless suspen-
sion resulted, which turned to a clear yellow solution on
stirring at ambient temperature for 1 day. Then it was neu-
tralized with saturated aqueous NaHCO3. After evaporation
of methanol the solution was diluted with 40 mL of water
and extracted three times with CHCl3 (50 mL). The organic
layer was separated, washed with water and brine and dried
over Na2SO4. The CHCl3 was evaporated, and the residue
was chromatographed on a silica gel column with EtOAc as
Colorless liquid. Yield 0.19 g (21%). – 1H NMR
(400 MHz, [D6]DMSO) δ = 1.67 (d, J = 7.4 Hz, 3H, CH3),
3.76 (s, 3H, OCH3), 5.41 (q, J = 7.4 Hz, 1H, CH), 6.38 (dd,
J = 6.7, 4.1 Hz, 1H, Py-H), 7.74 (dd, J = 6.7, 2.8 Hz, 1H,
Py-H), 8.60 (dd, J = 3.9, 2.9 Hz, 1H, Py-H). –C8H10N2O3:
calcd. C 52.74, H 5.53, N 15.38; found C 52.82, H 5.70, N
15.27.
(S)-4-(Methylthio)-2-(2-oxopyrimidin-1(2H)-yl)butyric acid
methyl ester (7)
Colorless crystals. Yield 0.67 g (55%); m. p. 129 ◦C. –
an eluent (5–9). Compounds 10, 11 were crystallized from [α]D = −100.8 (c = 1.0, MeOH). – 1H NMR (400 MHz,
ethanol.
[D6]DMSO): δ = 2.01 (s, 3H, SCH3), 2.32 – 2.44 (m, 4H,
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I. N. Egorov et al. · Chiral Pyrimidin-2(1H)-ones from N-Carbamoyl Amino Acids
Table 1. Crystal structure data
for 7, 15, and 16.
7
15
16
Empirical formula
Mr
C10H14N2O3S
242.29
C15H18N2O4
290.31
C14H16N2O
228.29
Crystal size, mm3
Crystal system
Space group
0.25 × 0.13 × 0.07
orthorhombic
P212121
0.24 × 0.13 × 0.08
monoclinic
P21
0.44 × 0.21 × 0.07
triclinic
¯
P1
˚
a, A
6.1061(3)
13.8993(13)
14.5862(10)
90.0
90.0
90.0
1237.94(16)
4
1.30
0.3
512
6.5984(3)
11.9696(5)
9.9658(4)
90.0
93.980(3)
90.0
785.20(6)
2
1.23
6.2046(12)
9.368(3)
11.194(2)
93.098(19)
103.775(17)
102.96(2)
611.9(2)
2
˚
b, A
˚
c, A
α, deg
β, deg
γ, deg
3
˚
V, A
Z
Dcalcd., g cm−3
µ(MoKα ), cm−1
F(000), e
1.24
0.1
244
0.1
308
hkl range
θ range, deg
Refl. measured/unique 3691/2554
Rint
+8 → −6, ±19, ±20
±8, ±14, +12 → −11 +7 → −6, ±11, ±13
2.79 – 30.52
2.66 – 26.36
1669/1283
0.0161
2.76 – 26.37
2481 /1184
0.0236
0.0165
147
Param. refined
206
154
R(F)/wR(F2)a (all refl.) 0.0575/0.0954
0.0368/0.0557
1.006
0.0870/0.0666
1.007
GoF (F2)b
∆ρfin (max/min), e A
1.002
−0.25/0.22
−3
˚
−0.11/0.09
−0.13/0.10
a R(F) =k Fo|−|F k /Σ|Fo|, wR(F2) = [Σw(F2 −F2)2/Σw(F2)2]1/2, w = [σ2(Fo2)+(AP)2 +BP]−1
,
c
o
o
where P = (Max(Fo2,0)+2F2)/3; b GoF = [Σw(Fo2c−F2)2/(nobs −nparam)]1/2
.
c
c
CH2), 3.65 (s, 3H, OCH3), 5.12 (t, J = 6.9 Hz, 1H, CH), 6.51 MS): m/z = 243.0848 (calcd. 243.0798 for C10H15N2O3S,
(dd, J = 6.5, 4.1 Hz, 1H, Py-H), 8.22 (dd, J = 6.5, 2.8 Hz, [M+H]+). – C10H14N2O3S: calcd. C 49.57, H 5.82, N
1H, Py-H), 8.60 (dd, J = 4.1, 2.8 Hz, 1H, Py-H). – 13C NMR 11.56; found C 49.54, H 5.86, N 11.60.
(100 MHz, [D6]DMSO): δ = 14.9, 28.0, 29.8, 53.0, 61.9,
(R,S)-2-(2-Oxopyrimidin-1(2H)-yl)-3-phenylpropionic acid
104.7, 149.9, 155.6, 167.3, 169.7. – C10H14N2O3S: calcd.
methyl ester (10)
C 49.57, H 5.82, N 11.56; found C 49.52, H 5.88, N 11.89.
Colorless crystals. Yield 0.52 g (40%); m. p. 162 ◦C.
(R)-4-(Methylthio)-2-(2-oxopyrimidin-1(2H)-yl)butyric acid
methyl ester (8)
– [α]D = 0 (c = 1.0, MeOH). – 1H NMR (400 MHz,
[D6]DMSO): δ = 3.36 – 3.46 (m, 2H, CH2), 3.71 (s, 3H,
Colorless crystals. Yield 0.18 g (15%); m. p. 133 ◦C. – OCH3), 5.19 (dd, J = 10.1, 5.7 Hz, 1H), 6.16 (dd, J = 6.5,
[α]D = +94.3 (c = 1.0, MeOH). – 1H NMR (400 MHz, 4.1 Hz, 1H), 7.04 – 7.11 (m, 2H), 7.12 – 7.21 (m, 3H), 7.74
[D6]DMSO): δ = 2.04 (s, 3H, SCH3), 2.29 – 2.44 (m, 4H, (dd, J = 6.5, 2.8 Hz, 1H), 8.42 (dd, J = 4.1, 2.8 Hz, 1H).
CH2), 3.69 (s, 3H, OCH3), 5.05 – 5.08 (m, 1H, CH), 6.43 (dd,
–
13C NMR (100 MHz, [D6]DMSO): δ = 33.5, 52.4, 64.0,
J = 6.5, 4.1 Hz, 1H, Py-H), 8.15 (dd, J = 6.5, 2.8 Hz, 1H, Py- 103.5, 126.7, 128.4, 128.9, 136.1, 149.5, 154.9, 166.6, 168.7.
H), 8.55 (dd, J = 4.0, 2.8 Hz, 1H, Py-H). – C10H14N2O3S: – HRMS ((+)-ESI-MS): m/z = 259.1094 (calcd. 259.1077
calcd. C 49.57, H 5.82, N 11.56; found C 49.64, H 5.93, N for C14H15N2O3, [M+H]+).
11.70.
(S)-3-(4-Hydroxyphenyl)-2-(2-oxopyrimidin-
(R,S)-4-(Methylthio)-2-(2-oxopyrimidin-1(2H)-yl)butyric
1(2H)-yl)propionic acid methyl ester (11)
acid methyl ester (9)
Colorless crystals. Yield 0.71 g (52%); m. p. 166 ◦C. –
Colorless crystals. Yield 0.41 g (34%); m. p. 105 ◦C. – [α]D = −242.9 (c = 1.0, MeOH). – 1H NMR (400 MHz,
1H NMR (400 MHz, [D6]DMSO): δ = 2.04 (s, 3H, SCH3), [D6]DMSO): δ = 3.22 – 3.33 (m, 2H), 3.67 (s, 3H, OCH3),
2.32 – 2.43 (m, 4H, CH2), 3.69 (s, 3H, OCH3), 4.97 – 5.16 5.16 (dd, J = 10.2, 5.6 Hz), 6.28 (dd, J = 6.5, 4.2 Hz), 6.59
(m, 1H, CH), 6.43 (dd, J = 6.5, 4.1 Hz, Py-H), 8.15 (dd, J = (d, J = 8.3 Hz, 2H, 4-OH-Ph), 6.85 (d, J = 8.3 Hz, 2H,
6.5, 2.8 Hz, Py-H), 8.56 (dd, J = 4.1, 2.8 Hz, Py-H). – 13C 4-OH-Ph), 7.81 (dd, J = 6.5, 2.7 Hz, 1H), 8.47 – 8.49 (m,
NMR (100 MHz, [D6]DMSO): δ = 14.9, 28.1, 29.9, 53.0, 1H), 9.22 (s, 1H). – 13C NMR (100 MHz, [D6]DMSO):
61.9, 104.6, 149.8, 155.6, 167.3, 169.7. – HRMS ((+)-ESI- δ = 32.7, 52.3, 64.1, 103.5, 115.2, 125.9, 129.8, 149.5,
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I. N. Egorov et al. · Chiral Pyrimidin-2(1H)-ones from N-Carbamoyl Amino Acids
1257
154.9, 156.0, 166.5, 168.8. – HRMS ((+)-ESI-MS): m/z = 1H, CH), 4.17 – 4.20 (m, 1H, CH), 7.21 – 7.23 (m, 2H, Ph),
275.1044 (calcd. 275.1026 for C14H15N2O4, [M+H]+).
7.34 – 7.46 (m, 4H, Ph), 7.77 (d, J = 12.4 Hz, 1H), 9.14 (d,
J = 12.4 Hz, 1H), 9.31 (s, 1H, COOH), 12.63 (br.s, 1H, NH).
– HRMS ((+)-ESI-MS): m/z = 291.1320 (calcd. 291.1339
for C15H19N2O4, [M+H]+).
Procedure for the synthesis of 12 and 13
Conc. HCl (3 mL) was added to the solution of pyrim-
idinone 5 or 6 (200 µg) in dioxane (10 mL). The reaction
mixture was stirred for 1 day, and then it was evaporated in
a Petri dish to dryness and crystallized from 2-propanol.
1-Isobutyl-5-phenylpyrimidin-2(1H)-one (16)
1
Yellow crystals. Yield 0.20 g (13%); m. p. 177 ◦C. – H
NMR (400 MHz, [D6]DMSO): δ = 0.95 (d, J = 6.7 Hz, 6H,
2 × CH3), 2.10 – 2.28 (m, 1H, CH), 3.77 (d, J = 7.4 Hz,
1H, CH2), 7.29 – 7.33 (m, 1H, Ph), 7.40 – 7.44 (m, 2H, Ph),
7.55 – 7.57 (m, 2H, Ph), 8.48 (d, J = 3.4 Hz, 1H), 8.87 (d,
J = 3.4 Hz, 1H). – 13C NMR (100 MHz, [D6]DMSO): δ =
164.8, 155.6, 147.4, 133.7, 129.5, 127.9, 125.8, 116.6, 57.9,
27.4, 19.9. – HRMS ((+)-ESI-MS): m/z = 229.1352 (calcd.
229.1335 for C14H17N2O, [M+H]+).
(S)-2-(2-Oxopyrimidin-1(2H)-yl)propionic acid (12)
Colorless crystals. Yield 0.12 g (67%); m. p. 179 ◦C. –
[α]D = −39.4 (c = 1.0, MeOH). – 1H NMR (400 MHz,
[D6]DMSO): δ = 1.66 (d, J = 7.3 Hz, 3H, CH3), 5.21 (q, J =
7.2 Hz, 1H), 6.72 (dd, J = 6.4, 5.0 Hz, 1H), 8.63 – 8.70 (m,
1H), 8.73 (dd, J = 4.7, 2.6 Hz, 1H). – 13C NMR (100 MHz,
[D6]DMSO): δ = 15.4, 59.0, 104.7, 150.5, 156.0, 162.3,
170.6. – HRMS ((+)-ESI-MS): m/z = 169.0616 (calcd.
169.0608 for C7H9N2O3, [M+H]+). – C7H8N2O3: calcd.
C 50.00, H 4.80, N 16.66; found C 50.12, H 4.93, N 16.77.
Crystal structure determinations
X-Ray analyses were carried out on an Oxford Diffraction
Xcalibur S CCD diffractometer using the software package
CRYSALISPRO [13]. X-Ray data collection was carried out
at 295(2) K with graphite-monochromatized MoKα radiation
(R)-2-(2-Oxopyrimidin-1(2H)-yl)propionic acid (13)
Colorless crystals. Yield 0.14 g (76%); m. p.
183 – 184 ◦C. – [α]D = +37.1 (c = 1.0, MeOH). – 1H
NMR (400 MHz, [D6]DMSO): δ = 1.65 (d, J = 7.3 Hz,
3H, CH3), 5.20 (q, J = 7.3 Hz, 1H, CH), 6.70 (dd, J = 6.3,
5.0 Hz, 1H, Py-H), 8.66 (dd, J = 6.4, 2.5 Hz, 1H, Py-H),
8.72 (dd, J = 4.8, 2.6 Hz, 1H, Py-H). – C7H8N2O3: calcd.
C 50.00, H 4.80, N 16.66; found C 49.59, H 5.02, N 16.72.
˚
(λ = 0.71073 A). The structures were solved with Direct
Methods using SHELXS-97 [14] and refined by full-matrix
least-squares procedures on F2 with SHELXL-97 [15]. Non-
H atoms were refined anisotropically, hydrogen atoms were
placed in idealized positions and were constrained to ride on
their parent atoms. Due to the absence of heavy atoms in the
non-centrosymmetric crystal structures of 7 and 15, Friedel
pairs were merged, and Flack parameters were not refined.
Table 1 summarizes the crystal data and numbers pertinent
to data collection and structure refinement.
Procedure for the synthesis of compounds 15 and 16
2-Phenylmalonaldehyde (1.0 g, 6.75 mmol) and N-
carbamoyl L-valine (1.62 g, 10.12 mmol) were mixed with
toluene (60 mL). The mixture was refluxed with a Dean-Stark
trap. Then it was cooled to 40 ◦C, the toluene solution was
decanted, and the resin residue was crystallized from ethanol.
CCDC 873468 (7), CCDC 936498 (15) and CCDC
936499 (16) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.
cam.ac.uk/data request/cif.
(2S)-3-Methyl-2-((E)-3-(3-oxo-2-phenylpropylidene)-
ureido)butyric acid (15)
Acknowledgement
Colorless crystals. Yield 0.15 g (8%); m. p. 203 – 204 ◦C.
– 1H NMR (400 MHz, [D6]DMSO): δ = 0.85 (d, J = 6.8 Hz,
We are pleased to thank Dr. P. Slepukhin for assistance
3H, CH3), 0.92 (d, J = 6.8 Hz, 3H, CH3), 2.04 – 2.21 (m, with the X-ray analyses.
[1] T. Nishitani, T. Iwasaki, Y. Mushika, M. Miyoshi, J.
[4] R. Berger, L. Chang, S. D. Edmondson, S. D. Goble,
Org. Chem. 1979, 44, 2019.
[2] G. E. Hardtmann, F. Park, H. Ott, US Pat. 3829422,
S. N. Ha, N. F. Kar, I. E. Kopka, B. Li, G. J. Morriello,
C. R. Moyes, D.-M. Shen, L. Wang, C. Zhu, US Pat.
2009/0253705A1, 2009.
1974.
[3] P. Guy, H. Cousse, G. Mouzin, US Pat. 4677105,
[5] R. Berger, L. Chang, S. D. Edmondson, S. D. Goble,
1987.
B. Harper, N. F. Kar, I. E. Kopka, I. I. Bing, G. J. Mor-
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I. N. Egorov et al. · Chiral Pyrimidin-2(1H)-ones from N-Carbamoyl Amino Acids
riello, C. R. Moyes, D.-M. Shen, L. Wang, H. Wendt, [11] G. M. Coppola, G. E. Hardtmann, B. S. Huegi, J. Het.
C. Zhu, WO Pat. 2009/123870A1, 2009.
Chem. 1974, 11, 51.
[6] K. Papadopoulos, D. W. Young, Tetrahedron Lett. [12] V. F. Gonko, N. D. Shustova, G. M. Anoshina, T. E.
2002, 43, 3951.
[7] P. B. Hitchcock, K. Papadopoulos, D. W. Young, Org.
Biomol. Chem. 2003, 1, 2670.
[8] C. G. Overberger, J. Y. Chang, Tetrahedron Lett. 1989,
30, 51.
Zubova, L. B. Radina, Pharm. Chem. J. 1978, 12, 601
(Engl. transl. from Khim.-Farm. Zh. 1978, 12, 53).
[13] CRYSALIS PRO, Oxford Diffraction Ltd., Abingdon,
Oxford (U. K.) 2008.
[14] G. M. Sheldrick, Acta Crystallogr. 1990, A46, 467.
[15] G. M. Sheldrick, Acta Crystallogr. 2008, A64, 112.
[9] V. Stella, T. Higuchi, J. Org. Chem. 1973, 38, 1527.
[10] E. Ware, Chem. Rev. 1950, 403.
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