Nitropyrazoles 16.* the use of methoxymethyl group as a protecting group for the synthesis of 4-methyl-3-nitro-5-R-pyrazoles

Article abstract of DOI:10.1007/s11172-009-0289-7

4-Methyl-3,5-dinitropyrazole prepared by nitration of 1,4-dimethylpyrazole readily reacts with methoxymethyl chloride and methyl vinyl ketone in acetonitrile in the presence of a base giving 1-methoxymethyl-4-methyl-3,5- dinitropyrazole and 4-methyl-3,5-d

Full text of DOI:10.1007/s11172-009-0289-7

Russian Chemical Bulletin, International Edition, Vol. 58, No. 10, pp. 2118—2121, October, 2009
2118
Nitropyrazoles
16.* The use of methoxymethyl group as a protecting group for the synthesis
of 4ꢀmethylꢀ3ꢀnitroꢀ5ꢀRꢀpyrazoles
A. A. Zaitsev,а I. O. Kortusov,b I. L. Dalinger,а V. V. Kachala,а G. P. Popova,а and S. A. Shevelevа
aN. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences,
47 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (499) 135 5328. Eꢀmail: shevelev@ioc.ac.ru
bD. I. Mendeleev University of Chemical Technology of Russia,
9 Miusskaya pl., 125047 Moscow, Russian Federation
4ꢀMethylꢀ3,5ꢀdinitropyrazole prepared by nitration of 1,4ꢀdimethylpyrazole readily reacts
with methoxymethyl chloride and methyl vinyl ketone in acetonitrile in the presence of a base
giving 1ꢀmethoxymethylꢀ4ꢀmethylꢀ3,5ꢀdinitropyrazole and 4ꢀmethylꢀ3,5ꢀdinitroꢀ1ꢀ(3ꢀoxoꢀ
butyl)pyrazole, respectively. The action of the thioglycolanilide anion on 4ꢀmethylꢀ3,5ꢀdiꢀ
nitroꢀ1ꢀ(3ꢀoxobutyl)pyrazole results only in the removal of 1ꢀprotecting group and the formaꢀ
tion of 2ꢀ[(3ꢀoxobutyl)thio]acetanilide, while the action of anionic Sꢀnucleophiles on 1ꢀmethꢀ
oxymethylꢀ4ꢀmethylꢀ3,5ꢀdinitropyrazole leads to the substitution products of the 5ꢀNO2 group
in which the methoxymethyl group can be removed by acid hydrolysis.
Key words: nitropyrazoles, dinitropyrazoles, nitration, nucleophilic substitution, nucleoꢀ
philes, protecting groups.
In our previous work,1 we have demonstrated the posꢀ
sibility of the use of 2,4ꢀdinitrophenyl group as a protectꢀ
ing group in the synthesis of some NHꢀpyrazoles that canꢀ
not be obtained by other methods. The role of the 2,4ꢀdiꢀ
nitrophenyl substituent in the position 1 of the pyrazole
ring consists, from the one hand, of increasing the mobilꢀ
ity of hydrogen atoms of the 4ꢀMe group of 3,5ꢀdinitropyrꢀ
azoles in comparison with 1ꢀMeꢀanalog, and, from the
other hand, of a possibility of easy removal of this substitꢀ
uent by nucleophiles. However, the latter fact does not
allow functionalization of the position 5 of the pyrazole
ring (which can be carried out using nucleophilic substituꢀ
tion of the 5ꢀNO2 group in the case of 1ꢀmethylꢀsubstitutꢀ
ed nitropyrazoles2), since it is the dinitropyrazolate anion
that is substituted instead of the nitro group. At the same
time, nucleophilic substitution is not possible directly in
the Nꢀunsubstituted 3,5ꢀdinitropyrazoles, as the latter are
moderateꢀstrength acids (pKa 3—4)3 and form nonreacꢀ
tive anions under basic conditions of substitution.
Scheme 1
PG is a protecting group
Earlier unknown 4ꢀmethylꢀ3,5ꢀdinitropyrazole (1) was
synthesized by nitration of 4ꢀmethylpyrazole (2) with
nitric—sulfuric acid mixture (Scheme 2), which is in
contradiction with the previous reports that it is impossiꢀ
ble to introduce 4ꢀsubstituted NHꢀpyrazoles in nitration
reaction with the formation of 3,5ꢀdinitropyrazoles.4 It is
worth mentioning that the amount of water in the reaction
medium in the synthesis of 3,5ꢀdinitropyrazole plays the
critical role: to obtain the products in acceptable yields
one has to use, first, concentrated nitric acid with density
d = 1.5 g cm–3, and, second, concentrated sulfuric acid
with concentration of at least 96%. With standard comꢀ
Synthesis of NHꢀ3ꢀnitropyrazoles that have a funcꢀ
tional group in the position 5 can be effected by the inꢀ
troduction of an appropriate protecting group into the
4ꢀmethylꢀ3,5ꢀdinitropyrazole molecule that is resistant
to the action of a nucleophile, subsequent nucleoꢀ
philic substitution, and removal of the protecting group
(Scheme 1).
* For Part 15, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2054—2057, October, 2009.
1066ꢀ5285/09/5810ꢀ2118 © 2009 Springer Science+Business Media, Inc.

Methoxymethyl protecting group in nitropyrazoles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009
2119
mercially available 92.5% sulfuric acid (SSS 4204ꢀ77), the
product yields are negligible (see Ref. 5 for details).
The action of pꢀtoluenethiolate and the thioglycolꢀ
anilide anion on compound 3 affords the corresponding
substitution products of the NO2 group of the pyrazole
ring 6a and 6b (Scheme 5). It is worth noting that
the reactivity of compound 3 in the reaction with the
–SCH2CONHPh anion exceeds that of 1,4ꢀdimethylꢀ3,5ꢀ
dinitropyrazole. In the case with the latter compound, no
total conversion could be attained over reasonable time
when the reaction was carried out in acetonitrile,2c i.e.,
the methoxymethyl group in the position 1 has the actiꢀ
vating influence on the nucleophilic substitution of the
5ꢀNO2 group in comparison with the Me substituent.
However, the attempts to involve compound 3 in reacꢀ
tions with Oꢀnucleophiles (phenolate and glycolic acid
anions), as in the case of 1,4ꢀdimethylꢀ3,5ꢀdinitropyrꢀ
azole, failed: compound 3 did not react.
Scheme 2
i. HNO3 (d = 1.5 g cm–3), H2SO4 (~97.5%), 100 °C, 2 h.
Analysis of literature data on nitroazoles6 allows us to
assume that methoxymethyl and 3ꢀoxobutyl groups might
be used as protecting groups. The corresponding dinitroꢀ
pyrazoles 3 and 4 were easily prepared by the reaction of
dinitropyrazole 1 with methoxymethyl chloride (MOMCl)
and methyl vinyl ketone, respectively in acetonitrile in the
presence of potassium carbonate (Scheme 3).
Scheme 5
Scheme 3
i. MeCOCH=CH2, K2CO3, MeCN, 80 °C, 20 h; ii. MOMCl,
K2CO3, MeCN, 25 °C, 1 h.
2ꢀ[(3ꢀOxobutyl)thio]acetanilide (5) is formed under
the action of the thioglycolanilide anion of on 4ꢀmethylꢀ
3,5ꢀdinitroꢀ1ꢀ(3ꢀoxobutyl)pyrazole (4) instead of the subꢀ
stitution product of the NO2 group (Scheme 4). Apparꢀ
ently, this is due to the substitution of dinitropyrazolate
anion at the Cβ atom rather than the result of sequential
abstraction of the pyrazolate ion and addition of the
PhNHCOCH2S– anion. This can be inferred from the fact
that direct reaction of the thioglycolanilide anion with
methyl vinyl ketone does not result in compound 5.
i. RSH, K2CO3, MeCN, 80 °C; ii. Conc. HCl/EtOH (HOAc),
reflux.
By the example of compound 6b, we demonstrated
that it is the nitro group in the position 5 in dinitropyrꢀ
azole 3 that is substituted. This was established, as in our
previous studies,1,2c using 2D correlation NMR spectrosꢀ
copy on the basis of longꢀrange spinꢀspin coupling conꢀ
stant 1H—13C (HMBC): the spinꢀspin interaction of proꢀ
tons of both the OCH2 and SCH2 groups is observed with the
same carbon atom of the pyrazole ring (δ 135.09), which is
possible only in the case where the PhNHCOCH2S group
is linked to the C(5) carbon atom.
Scheme 4
The methoxymethyl group in compounds 6a and 6b
can be removed by acid hydrolysis. Thus, refluxing of comꢀ
pound 6a in ethanol containing concentrated HCl gives
NHꢀpyrazole 7a. Under these conditions, compound 6b
does not undergo hydrolysis; the use of more drastic conꢀ
ditions, viz., refluxing in acetic acid containing concenꢀ
trated hydrochloric acid at ∼120 °С affords carboxylic acid
i. HSCH2CONHPh, K2CO3, MeCN, 80 °C, 4 h.

2120
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009
Zaitsev et al.
5.8 mmol) in acetonitrile (25 mL). The reaction mixture was
refluxed for 20 h, cooled to ~20 °C, and then poured into 2%
HCl (100 mL) and extracted with ethyl acetate (2×30 mL); the
organic layers were combined, washed with water to neutral pH,
and dried with Na2SO4. The solvent was removed under reduced
pressure, the residue was chromatographed on silica gel (CHCl3).
White crystalline compound 4 was obtained (0.82 g, 58%). M.p.
66—68 °С. Found (%): C, 39.69; H, 4.03; N, 23.16. C8H10N4O5.
Calculated (%): C, 39.67; H, 4.16; N, 23.13. 1Н NMR
((CD3)2SO), δ: 4.76 (t, 2 H, NCH2, J = 6.6 Hz); 3.15 (t, 2 H,
CH2CO, J = 6.6 Hz); 2.53 (s, 3 H, 4ꢀMe); 2.14 (s, 3 H, COMe).
13С NMR ((CD3)2SO), δ: 205.64 (CO); 150.66 (C(3)); 144.21
(C(5)); 114.25 (C(4)); 48.88 (NCH2); 41.04 (CH2CO); 29.76
(CH3CO); 9.65 (4ꢀMe). IR, ν/cm–1: 1720 (CO); 1520, 1336
(NO2). MS, m/z: 242 [M]+.
7b, i.e., hydrolysis of the SCH2CONHPh group accomꢀ
panies removal of the CH2OMe group.
Thus, one can state that the methoxymethyl group can
be successfully used as a protecting group in the synthesis
of some Nꢀunsubstituted 5ꢀRꢀ4ꢀmethylꢀ3ꢀnitropyrazoles.
Experimental
1
H and 13C NMR spectra were recorded on Bruker ACꢀ300
(300.13 MHz) and Bruker DRXꢀ500 (125 MHz) spectrometers,
respectively, at 295 K (unless other temperature is indicated).
Chemical shifts for 1H and 13C are given relative to Me4Si.
IR spectra were recorded on a Specord Mꢀ80 in KBr pellets.
Mass spectra were obtained on a Kratos MSꢀ30 spectrometer
(direct inlet, electron impact, ionization energy 70 eV). The
course of the reactions and purity of compounds were monitored
by TLC on Silufol UVꢀ254 plates, CHCl3—Me2CO (10 : 1).
Elemental analysis was carried out on a Perkin—Elmer Series II
2400 apparatus.
2ꢀ[(3ꢀOxobutyl)thio]acetanilide (5). Potassium carbonate
(0.138 g, 1.0 mmol) was added to a solution of thioglycolanilide
(0.167 g, 1.0 mmol) in acetonitrile (20 mL), the mixture was
stirred for 10 min, then compound 4 (0.242 g, 1.0 mmol) was
added. The reaction mixture was refluxed for 4 h (TLC), cooled
to ~20 °C, poured into water (80 mL) acidified with HCl pH 2—3,
extracted with ethyl acetate (2×20 mL), the organic layers were
combined, washed with water to neutral pH, and dried with
Na2SO4. The solvent was removed under reduced pressure, the
residue was chromatographed on silica gel (CHCl3—Me2CO
(20 : 1)). Compound 5 was obtained in the form of lightꢀyellow
oil (0.178 g, 75%); the yield of compound 1 was (white crystals)
0.077 g (65%). Compound 5. Found (%): C, 60.58; H, 6.30;
N, 5.59; S, 13.42. C12H15NO2S. Calculated (%): C, 60.73; H, 6.37;
N, 5.90; S, 13.51. 1Н NMR ((CD3)2SO), δ: 10.00 (s, 1 H, NH);
7.57 (d, 2 H, oꢀH, Ph, J = 8.1 Hz); 7.30 (t, 2 H, mꢀH, Ph,
J = 8.1 Hz); 7.05 (t, 1 H, pꢀH, Ph, J = 7.3 Hz); 3.30 (s, 2 H,
SCH2СО); 2.78 (br.s, 4 H, COCH2CH2); 2.09 (s, 3 H, Me).
1Н NMR (CDCl3), δ: 8.97 (s, 1 H, NH); 7.62 (d, 2 H, oꢀH, Ph,
J = 8.1 Hz); 7.33 (t, 2 H, mꢀH, Ph, J = 7.7 Hz); 7.12 (t, 1 H, pꢀH,
Ph, J = 7.3 Hz); 3.38 (s, 2 H, SCH2СО); 2.81 (m, 4 H,
COCH2CH2); 2.17 (s, 3 H, Me). 13С NMR (CDCl3), δ: 206.97
(COMe); 167.64 (CONH); 137.39 (ipsoꢀC, Ph); 129.04 (mꢀC,
Ph); 124.85 (pꢀC, Ph); 120.16 (oꢀC, Ph); 42.64 (COCH2CH2);
4ꢀMethylpyrazole,7 methoxymethyl chloride,8 and thioglyꢀ
colanilide9 were prepared as described.
4ꢀMethylꢀ3,5ꢀdinitropyrazole (1). Oleum (41%, d = 1.963 g
cm–3, 12.0 mL) was added to 92.5% sulfuric acid (30.0 mL,
d = 1.826 g cm–3) at a temperature of 30—40 °C; at this temperꢀ
ature, 4ꢀmethylpyrazole (2) (2.00 mL, 24.2 mmol) and then fumꢀ
ing nitric acid (d = 1.5 g cm–3) (3.1 mL, 73.8 mmol) were added
dropwise. The reaction mixture was heated at 100—105 °C for
2 h, cooled to ~20 °C, poured onto ~300 g of crushed ice; air was
passed for 3ꢀ4 h through the suspension thus obtained until total
removal of nitrogen oxides. The precipitate was filtered off, washed
with water and dried in air. White crystalline product 1 (2.22 g)
was obtained. The aqueous layer was extracted with ethyl aceꢀ
tate (2×40 mL), the organic layers were combined, washed with
water to neutral pH, and dried with Na2SO4. The solvent was
removed under reduced pressure, the residue was crystallized
from ethanol. The target product (0.92 g) was obtained additionꢀ
ally. The total yield of compound 1 is 3.14 g (75%), m.p.
211—213 °С. Found (%): C, 27.84; H, 2.18; N, 32.26. C4H4N4O4.
Calculated (%): C, 27.92; H, 2.34; N, 32.56. 1Н NMR ((CD3)2SO),
δ: 2.57 (s, Me). 13C NMR ((CD3)2SO), δ: 149.14 (C(3)); 112.55
(C(4)); 9.13 (Me). IR, ν/cm–1: 3164 (NH); 1548, 1336 (NO2).
MS, m/z: 172 [M]+.
37.15 (SCH2CO); 30.10 (Me); 26.40 (CH2CH2S). IR, ν/cm–1
:
3308 (NH); 1716 (COMe); 1668 (CONH). MS, m/z: 237 [M]+.
1ꢀMethoxymethylꢀ4ꢀmethylꢀ5(3)ꢀ[(4ꢀmethylphenyl)thio]ꢀ
3(5)ꢀnitropyrazole (6a). Potash (0.75 g, 5.4 mmol) was added to
a solution of dinitropyrazole 3 (1.00 g, 5.8 mmol) and pꢀtoluꢀ
enethiol (0.80 g, 6.4 mmol) in acetonitrile (40 mL). The reaction
mixture was refluxed for 15 h in a flow of argon (TLC), cooled to
~20 °C, poured into water (150 mL), extracted with ethyl acetate
(2×30 mL), the organic layers were combined and dried with
Na2SO4. The solvent was removed under reduced pressure, the
residue was chromatographed on silica gel (CCl4, then CHCl3).
Solid yellow compound 6a was obtained (0.79 g, 58%). M.p.
45—47 °С. Found (%): C, 53.62; H, 5.15; N, 13.24; S, 10.16.
C13H15N3O3S. Calculated (%): C, 53.23; H, 5.15; N, 14.32;
S, 10.93. 1Н NMR ((CD3)2SO), δ: 7.16 (d, 2 H, оꢀH, C6H4Meꢀp,
J = 8.1 Hz); 7.12 (d, 2 H, mꢀH, C6H4Meꢀp, J = 8.1 Hz); 5.59
(s, 2 H, CH2); 3.25 (s, 3 H, OMe); 2.27 (s, 3 H, Me), 2.26
(s, 3 H, Me). 13С NMR ((CD3)2SO), δ: 153.41 (C(3)); 136.93
(C(4´)); 134.00 (C(5)); 130.15 (C(2´)); 129.28 (C(1´));
128.01 (C(3´)); 120.36 (C(4)); 80.45 (CH2); 56.58 (OMe); 20.33
(CH3C6H4); 9.79 (4ꢀMe). IR, ν/cm–1: 1560, 1516, 1348 (NO2).
MS, m/z: 293 [M]+.
1ꢀMethoxymethylꢀ4ꢀmethylꢀ3,5ꢀdinitropyrazole (3). Potasꢀ
sium carbonate (4.5 g, 32.6 mmol) and methoxymethyl chloride
(2.4 mL, 31.6 mmol) were added to a solution of dinitropyrazole
1 (5.0 g, 29.1 mmol) in acetonitrile (100 mL). The reaction
mixture was stirred for 1 h (TLC) and then poured into water
(300 mL), extracted with ethyl acetate (2×60 mL), dried with
Na2SO4, and the solvent was removed under reduced pressure.
White crystalline product 3 was obtained (6.1 g, 97%). M.p.
78—80 °С. Found (%): C, 33.38; H, 3.51; N, 25.94. C4H8N4O5.
Calculated (%): C, 33.34; H, 3.73; N, 25.92. 1Н NMR
((CD3)2SO), δ: 5.83 (s, 2 H, CH2); 3.34 (s, 3 H, OMe); 2.57 (s, 3 H,
1
CMe). Н NMR (CDCl3), δ: 5.90 (s, 2 H, CH2); 3.41 (s, 3 H,
OMe); 2.70 (s, 3 H, CMe). 13С NMR ((CD3)2SO), δ: 151.51
(C(3)); 143.63 (C(5)); 115.34 (C(4)); 84.18 (CH2); 57.14 (OMe);
9.60 (Me). IR, ν/cm–1: 1528, 1336 (NO2). MS, m/z: 216 [M]+.
4ꢀ(4ꢀMethylꢀ3,5ꢀdinitropyrazolꢀ1ꢀyl)butanꢀ2ꢀone (4). Methꢀ
yl vinyl ketone (0.50 mL, 6.2 mmol) and potash (0.16 g,
1.2 mmol) were added to a solution of dinitropyrazole 1 (1.00 g,

Methoxymethyl protecting group in nitropyrazoles
Russ.Chem.Bull., Int.Ed., Vol. 58, No. 10, October, 2009
2121
2ꢀ[(1ꢀMethoxymethylꢀ4ꢀmethylꢀ3(5)ꢀnitropyrazoleꢀ5(3)ꢀ
yl)thio]acetanilide (6b). Potassium carbonate (1.06 g, 7.7 mmol)
was added to a solution of dinitropyrazole 3 (1.50 g, 6.9 mmol)
and thioglycolanilide (1.16 g, 6.9 mmol) in acetonitrile (50 mL).
The reaction mixture was refluxed for 4 h (TLC), cooled to
~20 °C, poured into water (200 mL), extracted with ethyl acetate
(2×60 mL), the organic layers were combined and dried with
Na2SO4. The solvent was removed under reduced pressure, the
residue was chromatographed on silica gel (CHCl3). Solid
lightꢀyellow compound 6b was obtained (1.10 g, 52%). M.p.
97—99 °С. Found (%): C, 49.32; H, 4.76; N, 17.74; S, 8.86.
C14H16N4O4S. Calculated (%): C, 49.99; H, 4.79; N, 16.66;
S, 9.53. 1Н NMR ((CD3)2SO), δ: 10.10 (s, 1 H, NH); 7.49 (d, 2 H,
oꢀH, Ph, J = 7.3 Hz); 7.30 (t, 2 H, mꢀH, Ph, J = 7.3 Hz); 7.06
(t, 1 H, pꢀH, Ph, J = 6.7 Hz); 5.65 (s, 2 H, OCH2); 3.64 (s, 2 H,
SCH2); 3.30 (s, 3 H, OMe); 2.30 (s, 3 H, CMe). 13С NMR
((CD3)2SO), δ: 166.04 (CO); 153.11 (C(3)); 138.63 (ipsoꢀC, Ph);
135.09 (C(5)); 128.85 (mꢀC, Ph); 123.67 (pꢀC, Ph);
120.90 (C(4)); 119.16 (oꢀC, Ph); 80.51 (OCH2); 56.71 (OMe);
39.70 (SCH2); 10.10 (CCH3). IR, ν/cm–1: 3296 (NH);
1664 (CO); 1544, 1528, 1336 (NO2). MS, m/z: 336 [M]+.
4ꢀMethylꢀ5(3)ꢀ(4ꢀtolylthio)ꢀ3(5)ꢀnitropyrazole (7a). Conꢀ
centrated HCl (10 mL) was added to a suspension of compound
6a (0.480 g, 1.6 mmol) in ethanol (30 mL). The reaction mixture
was refluxed for 15 h (TLC), cooled to ~20 °C, poured into water
(150 mL), extracted with ethyl acetate (2×40 mL), the organic
layers were combined, washed with water to neutral pH, and
dried with Na2SO4. The solvent was removed under reduced
pressure, the residue was chromatographed on silica gel (CHCl3).
Solid lightꢀyellow compound 7a was obtained (0.254 g, 62%).
M.p. 106—108 °С. Found (%): C, 53.50; H, 4.37; N, 16.55;
S, 12.32. C11H11N3O2S. Calculated (%): C, 53.00; H, 4.45;
N, 16.86; S, 12.86. 1Н NMR ((CD3)2SO), δ: 14.56 (br.s, 1 H, NH);
7.16 (d, 2 H, oꢀH, C6H4Meꢀp, J = 8.1 Hz); 7.11 (d, 2 H, mꢀH,
C6H4Meꢀp, J = 8.1 Hz); 2.26 (s, 3 H, Me); 2.25 (s, 3 H, Me).
13С NMR ((CD3)2SO), δ: 154.28 (C(3)); 136.90 (C(4´)); 132.32
(C(5)); 130.27 (C(2´)); 130.16 (C(1´)); 128.19 (C(3´)); 118.25
(C(4)); 20.47 (CH3C6H4); 9.32 (4ꢀMe). IR, ν/cm–1: 3112, 2928
(NH); 1568, 1548, 1360, 1352, 1344 (NO2). MS, m/z: 249 [M]+.
[(4ꢀMethylꢀ3(5)ꢀnitropyrazoleꢀ5(3)ꢀyl)thio]acetic acid (7b).
Concentrated HCl (10 mL) was added to a solution of amide 6b
(0.200 g, 0.59 mmol) in acetic acid (30 mL). The reaction mixꢀ
ture was refluxed for 2 h (TLC), cooled to ~20 °C, and the solvent
was removed under reduced pressure. Solid lightꢀyellow comꢀ
pound 7b was obtained (0.067 g, 52%). M.p. 92 °С. Found (%):
C, 33.10; H, 3.00; N, 19.75; S, 14.99. C6H7N3O4S. Calculatꢀ
ed (%): C, 33.18; H, 3.25; N, 19.35; S, 14.76. 1Н NMR
((CD3)2SO), δ: 3.62 (s, 2 H, SCH2); 2.29 (s, 3 H, Me). IR,
ν/cm–1: 2920 (NH); 1712 (CO); 1564, 1552, 1360, 1352,
1344 (NO2).
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Received March 11, 2009;
in revised form September 9, 2009
Methoxymethyl protecting group in nitropyrazoles