Regioselective 1,3-dipolar cycloadditions of (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines to acetylenic dipolarophiles

Article abstract of DOI:10.1002/1522-2675(20010131)84:1<146::AID-HLCA146>3.0.CO;2-7

The 5,5-dimethylpyrazolidin-3-one (4), prepared from ethyl 3-methylbut-2-enoate (3) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a-i to give the corresponding (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a-i. The 1,3-dipolar cycloaddition reactions of azomethine imines 6a-h with dimethyl acetylenedicarboxylate (=dimethyl but-2-ynedioate; 7) afforded the corresponding dimethyl pyrazolo[1,2-a]pyrazoledicarboxylates 8a-h, while by cycloaddition of 6 with methyl propiolate (= methyl prop-2-ynoate: 9), regioisomeric methyl pyrazolo[1,2-a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a- i with methyl propiolate (9) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a-e derived from benzaldehydes 5a-e with a single substituent or without a substituent at the orthopositions in the aryl residue, led to mixtures of regioisomers 10a-e and 11a-e. Azomethine imines 6f-i derived from 2,6-disubstituted benzaldehydes 5f-i gave single regioisomers 10f-i.

Full text of DOI:10.1002/1522-2675(20010131)84:1<146::AID-HLCA146>3.0.CO;2-7

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Regioselective 1,3-Dipolar Cycloadditions of
(1Z)-1-(Arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide
Azomethine Imines to Acetylenic Dipolarophiles
by Cvetka Turka), Jurij Svetea)*, Branko Stanovnika)*, Ljubo GolicÏ a), Simona GolicÏ-Grdadolnikb),
Amalija GolobicÏ a), and Lovro SelicÏ a)
a) Faculty of Chemistry and Chemical Technology, University of Ljubljana, Ljubljana, Slovenia
b) National Institute of Chemistry, Ljubljana, Slovenia
The 5,5-dimethylpyrazolidin-3-one (4), prepared from ethyl 3-methylbut-2-enoate (3) and hydrazine
hydrate, was treated with various substituted benzaldehydes 5a ± i to give the corresponding (1Z)-1-
(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a ± i. The 1,3-dipolar cyclo-
addition reactions of azomethine imines 6a ± h with dimethyl acetylenedicarboxylate (ˆdimethyl but-2-
ynedioate; 7) afforded the corresponding dimethyl pyrazolo[1,2-a]pyrazoledicarboxylates 8a ± h, while by
cycloaddition of 6 with methyl propiolate (ˆ methyl prop-2-ynoate; 9), regioisomeric methyl pyrazolo[1,2-a]-
pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine
imines 6a ± i with methyl propiolate (9) was influenced by the substituents on the aryl residue. Thus, azomethine
imines 6a ± e derived from benzaldehydes 5a ± e with a single substituent or without a substituent at the ortho-
positions in the aryl residue, led to mixtures of regioisomers 10a ± e and 11a ± e. Azomethine imines 6f ± i derived
from 2,6-disubstituted benzaldehydes 5f ± i gave single regioisomers 10f ± i.
Introduction. ± Since the beginning of a systematic work on the chemistry of
substituted pyrazolidin-3-ones more than four decades ago, the importance of this
initially relatively neglected type of heterocycle significantly rose in the last two
decades (for a review on pyrazolidin-3-ones, see [1]). Pyrazolidin-3-ones are an
important class of compounds that exhibit biological activity and a wide applicability
for industrial and synthetic purposes. For example, phenidone (1a) and its derivatives
and analogues such as BW357U (1b) are used as super-additive developers in
photographic applications1) [2] and as inhibitors of cyclooxygenase, lipooxygenase, and
g-aminobutyrate transferase [3]. Another important pyrazolidinone is Lillyꢀs bicyclic
pyrazolidinone 2, which is a g-lactam antibiotic [4]. On the other hand, pyrazolidin-3-
ones and closely related homologues, perhydropyridazin-3-ones, can also serve either
as building blocks, or as precursors for the preparation of b-turn mimics [5], azatropane
derivatives [6], and natural products such as saxitoxin, celacinnine, and glidobactin
antibiotics [7].
Previously, we have reported the stereoselective 1,3-dipolar cycloaddition reactions
of azomethine imines derived from rel-(4R,5R)-4-(benzoylamino)-5-phenylpyrazoli-
din-3-one and on the utilization of rel-(4R,5R)-4-(benzoylamino)-5-phenylpyrazolidin-
3-one in the synthesis of 3-(alkylamino)-3-phenyl- and 3-phenyl-3-(pyrazol-1-yl)-
substituted alanine derivatives [8 ± 11]. Recently, we reported an unusual two-step
1
)
There are many publications and patents on this topic. Just few examples are given in [2].

Helvetica Chimica Acta ± Vol. 84 (2001)
147
transformation of 5,5-dimethylpyrazolidin-3-one into an alkaloid-like tetracyclic
system [12]. On the other hand, Chuang and Sharpless reported the preparation of
N4,N4-disubstituted (4S*,5S*)-5-phenyl-4-aminopyrazolidin-3-ones and their stereo-
selective transformations into substituted 1H,5H-pyrazolo[1,2-a]pyrazol-1-one deriv-
atives via N4,N4-disubstituted (4S*,5S*)-1-(arylmethylidene)-5-phenyl-4-amino-3-oxo-
pyrazolidin-1-ium-2-ide azomethine imines as the key intermediates [13]2).
Results and Discussion. ± In continuation of our work on the chemistry of
pyrazolidin-3-ones, we now report 1,3-dipolar cycloaddition sof (1Z)-1-(arylmethyli-
dene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a ± i with di-
methyl acetylenedicarboxylate (ˆdimethyl but-2-ynedioate; 7) and methyl propiolate
(ˆ methyl prop-2-ynoate; 9). The 5,5-dimethyl pyrazolidin-3-one (4), prepared from
ethyl 3-methylbut-2-enoate (3) and hydrazine hydrate [14], was treated with various
substituted benzaldehydes 5a ± i to give the corresponding (1Z)-1-(arylmethylidene)-
5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a ± i (cf. Scheme 1).
The (Z)-configuration of the exocyclic CˆN bond in azomethine imine 6b, which is
otherwise usual for oxopyrazolidiniumide azomethine imines [1], was confirmed by
NMR spectroscopy (NOESY experiment, d(H C(1') ´´´ Me C(5)) ˆ 0.27 nm). The
1,3-dipolar cycloadditions of 1,3-dipoles 6a ± h to dimethyl acetylenedicarboxylate (7)
gave the corresponding dimethyl 1-aryl-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyra-
zolo[1,2-a]pyrazole-2,3-dicarboxylates (8a ± h) in 70 ± 97% yields. In the cycloadditions
of azomethine imines 6a ± i with methyl propiolate (ˆ methyl prop-2-ynoate; 9),
regioselectivity was found to be dependent on the substituents attached to the aryl
residue. With azomethine imines 6a ± e, unsubstituted or monosubstituted at one of the
ortho-positions of the benzene ring, ca. 3 :1 mixtures of regioisomers 10a ± e and 11a ± e
were formed. In the cases of 6a,b,e, both regioisomers were separated, isolated, and
fully characterized, whereas in the cases of 6c,d, the minor isomers 11c,d were only
detected by 1H-NMR. On the other hand, azomethine imines 6f ± i, substituted at both
ortho-positions of the aromatic ring, afforded single regioisomers 10f ± i upon
treatment with methyl propiolate (9) (Scheme 1).
2
)
We are grateful to the referee for informing us about this article, which was published after submission of
our manuscript. The numbering of the 1H,5H-pyrazolo[1,2-a]pyrazole derivatives 7 ± 10 in [13] should be
revised (cf. numbering of 8a ± h in Scheme 1).

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Helvetica Chimica Acta ± Vol. 84 (2001)
Scheme 1
Ar
10/11a)
5a, 6a, 8a, 10a, 11a
5b, 6b, 8b, 10b, 11b
5c, 6c, 8c, 10c, 11c
5d, 6d, 8d, 10d, 11d
5e, 6e, 8e, 10e, 11e
5f, 6f, 8f, 10f
5g, 6g, 8g, 10g
5h, 6h, 8h, 10h
5i, 6i, 10i
2-nitrophenyl
4-nitrophenyl
71 : 29
67: 33
70 : 30
75 : 25
80 : 20
100 : 0
100 : 0
100 : 0
100 : 0
2-methoxyphenyl
3,4,5-trimethoxyphenyl
2,4-dichlorophenyl
2,6-dichlorophenyl
2,4,6-trimethylphenyl
2,4,6-trimethoxyphenyl
2,6-dimethoxyphenyl
a
1
) Determined by H-NMR spectroscopy.
i) Hydrazine hydrate, EtOH, reflux. ii) ArCHO (5a ± i), EtOH, CF3COOH, r.t. iii) MeOOCCꢀCCOOMe (7),
100 ± 1508. iv) HCꢀCCOOMe (9), 100 ± 1508.
Spectroscopic and analytical data for compounds 6 ± 11 are in accordance with the
data for similar compounds described in [1]. Structures of compounds 6f and 10g were
also confirmed by X-ray diffraction analysis (Figs. 1 and 2).
So far, we do not have a firm explanation for the regioselectivity of these
cycloadditions. Since the ratios of the regioisomers formed from the dipole 6a with an
acceptor substituent and from 6c with a donor substituent are the same, the electronic
effects of the substituents at the aromatic ring seem to have a negligible effect on the
regioselectivity (cf. Scheme 1). Presumably, the electronic distribution in azomethine
imines 6a ± i is reflected at best by the resonance structures 6 and 6' as the negative

Helvetica Chimica Acta ± Vol. 84 (2001)
149
Fig. 1. ORTEPIII View of the molecular structure of compound 6f, showing the labelling of the non-H-atoms.
Ellipsoids are drawn at the 50% probability level.
Fig. 2. ORTEPII View of the molecular structure of compound 10g, showing the labelling of the non-H-atoms.
Ellipsoids are drawn at the 50% probability level.

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charge at the N(1) atom is stabilized by the carbonyl group (Scheme 2). In the case of at
least one free ortho-position in the aromatic ring, the dipole can adopt a planar
conformation 6'', which allows both regioisomeric transition states. To the contrary, the
planar conformation is not accessible in the case of two ortho-substituents; therefore,
the transition state for the concerted 1,3-dipolar cycloaddition is prohibited. In this
case, a two-step Michael-type mechanism is feasible. Consequently, the formation of
mixtures of regioisomers 10a ± e and 11a ± e from ortho-unsubstituted or ortho-
monosubstituted azomethine imines 6a ± e could be explained by the concerted 1,3-
dipolar cycloaddition mechanism with the ꢁplanarꢀ dipole conformation 6'' as the
reactive species, whereas the regiospecific formation of cycloadducts 10f ± i from ortho-
disubstituted azomethine imines 6f ± i could be explained by a two-step Michael-type
mechanism including the ꢁnonplanarꢀ dipole conformation as the reactive species and
dipolar adducts 12f ± i as intermediates (Scheme 2).
Scheme 2
Experimental Part
General. 5,5-Dimethylpyrazolidin-3-one (4) was prepared according to the procedure described in [14].
Ratios of regioisomers 10a ± i and 11a ± i were determined in the following manner: after completion of the
1
reaction, volatile components were evaporated and the H-NMR spectra of the residue recorded. All starting
materials were commercially available (in most cases from Fluka) and purified according to the standard
techniques. Column chromatography (CC): silica gel (Fluka, silica gel 60; column dimensions 40 Â 5 cm). TLC:
alu foils coated with silica gel 60 F 254 (0.2 mm; Merck). M.p.: Kofler micro hot stage. IR: Perkin-Elmer-1310
spectrophotometer. 1H- and 13C-NMR: Bruker-Avance DPX-300 spectrometer. Elemental analyses: Perkin-
Elmer CHN Analyser 2400.

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(1Z)-1-(Arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide Azomethine Imines 6a ± i: General
Procedure. CF3COOH (1 ml) was added to a stirred mixture of 5,5-dimethyl pyrazolidin-3-one (4; 1.14 g,
10 mmol), substituted benzaldehyde 5a ± i (10 mmol), and anh. EtOH (40 ml). The mixture was stirred at r.t. for
3 ± 72 h. Volatile compounds were evaporated, Et2O (30 ml) added to the residue, and the precipitate collected
by filtration: azomethine imines 6a ± i.
(1Z)-5,5-Dimethyl-1-[(2-nitrophenyl)methylidene]-3-oxopyrazolidin-1-ium-2-ide (6a). From 2-nitrobenz-
aldehyde (5a) (24 h): 2.10 g (85%). M.p. 194 ± 1968 (EtOH). IR (KBr): 1670 (CˆO). 1H-NMR (300 MHz,
(D6)DMSO): 1.78 (s, 2 Me C(5)); 2.78 (s, 2 H C(4)); 7.60 (ddd, J ˆ 8.3, 7.5, 0.8, 1 arom. H); 7.68 (s, H C(1'));
7.76 (ddd, J ˆ 7.9, 7.5, 1.1, 1 arom. H); 8.14 (dd, J ˆ 8.3, 1.1, 1 arom. H); 9.06 (dd, J ˆ 7.9, 1.1, 1 arom. H of Ph).
Anal. calc. for C12H13N3O3 (247.26): C 58.29, H 5.29, N 16.99; found: C 58.02, H 5.50, N 16.98.
(1Z)-5,5-Dimethyl-1-[(4-nitrophenyl)methylidene]-3-oxopyrazolidin-1-ium-2-ide (6b). From 4-nitrobenz-
aldehyde (5b) (3 h): 2.30 g (93%). M.p. >2708 (EtOH). IR (KBr): 1680 (CˆO). 1H-NMR (300 MHz,
(D6)DMSO): 1.68 (s, 2 Me C(5)); 2.63 (s, 2 H C(4)); 7.93 (s, H C(1')); 8.30 (d, J ˆ 9.0, 2 arom. H); 8.59
(d, J ˆ 9.0, 2 arom. H). Anal. calc. for C12H13N3O3 (247.26): C 58.29, H 5.29, N 16.99; found: C 58.01, H 5.14,
N 16.92.
(1Z)-1-[(2-Methoxyphenyl)methylidene]-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide (6c). From 2-methox-
ybenzaldehyde (5c) (72 h): 2.11 g (91%). M.p. 160 ± 1658 (PhMe). IR (KBr): 1650 (CˆO). 1H-NMR
(300 MHz, CDCl3): 1.71 (s, 2 Me C(5)); 2.73 (s, 2 H C(4)); 3.92 (s, MeO); 6.93 (dd, J ˆ 8.3, 0.8, 1 arom. H);
7.06 (ddd, J ˆ 7.9, 7.5, 0.8, 1 arom. H); 7.44 (ddd, J ˆ 8.3, 7.5, 1.9, 1 arom. H); 7.64 (s, H C(1')); 9.25 (dd, J ˆ 7.9,
1.9, 1 arom. H). Anal. calc. for C13H16N2O2 (232.29): C 67.22, H 6.94, N 12.06; found: C 67.26, H 6.93, N 12.18.
(1Z)-5,5-Dimethyl-3-oxo-1-[(3,4,5-trimethoxyphenyl)methylidene]pyrazolidin-1-ium-2-ide (6d). From
3,4,5-trimethoxybenzaldehyde (5d) (24 h): 2.87 g (98%). M.p. 134 ± 1368 (heptane/EtOH 5 :1). IR (KBr):
1
1660 (CˆO). H-NMR (300 MHz, (D6)DMSO): 1.63 (s, 2 Me C(5)); 2.56 (s, 2 H C(4)); 3.76, 3.83 (2s, 1:2,
3 MeO); 7.71 (s, H C(1')); 7.84 (s, 2 arom. H). Anal. calc. for C15H20N2O4 (292.34): C 61.63, H 6.89, N 9.58;
found: C 61.69, H 6.99, N 9.77.
(1Z)-1-[(2,4-Dichlorophenyl)methylidene]-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide (6e). From 2,4-di-
chlorobenzaldehyde (5e) (24 h): 2.30 g (85%). M.p. 180 ± 1848 (Et2O). IR (KBr): 1670 (CˆO). 1H-NMR
(300 MHz, CDCl3): 1.77 (s, 2 Me C(5)); 2.77 (s, 2 H C(4)); 7.39 (dd, J ˆ 8.7, 1.9, 1 arom. H); 7.50 (d, J ˆ 1.9,
1 arom. H); 7.52 (s, H C(1')); 9.36 (d, J ˆ 8.7, 1 arom. H). Anal. calc. for C12H12Cl2N2O (271.15): C 53.16,
H 4.46, N 10.33; found: C 52.92, H 4.44, N 10.31.
(1Z)-1-[(2,6-Dichlorophenyl)methylidene]-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide (6f). From 2,6-di-
chlorobenzaldehyde (5f) (24 h): 2.43 g (90%). M.p. 246 ± 2488 (Et2O). IR (KBr): 1650 (CˆO). 1H-NMR
(300 MHz, CDCl3): 1.79 (s, 2 Me C(5)); 2.77 (s, 2 H C(4)); 7.18 (s, H C(1')); 7.29 ± 7.37 (m, 3 arom. H).
Anal. calc. for C12H12Cl2N2O (271.15): C 53.16, H 4.46, N 10.33; found: C 53.05, H 4.66, N 10.17.
(1Z)-5,5-Dimethyl-3-oxo-1-[(2,4,6-trimethylphenyl)methylidene]pyrazolidin-1-ium-2-ide (6g). From 2,4,6-
1
trimethylbenzaldehyde (5g) (48 h): 2.17 g (89%). M.p. 206 ± 2108 (PhMe). IR (KBr): 1660 (CˆO). H-NMR
(300 MHz, CDCl3): 1.75 (s, 2 Me C(5)); 2.22, 2.28 (2s, 2 :1, Me3C6H2); 2.75 (s, 2 H C(4)); 6.86 (s, 2 arom. H);
7.35 (s, H C(1')). Anal. calc. for C15H20N2O (244.34): C 73.74, H 8.25, N 11.46; found: C 73.91, H 8.23, N 11.40.
(1Z)-5,5-Dimethyl-3-oxo-1-[(2,4,6-trimethoxyphenyl)methylidene]pyrazolidin-1-ium-2-ide (6h). From
2,4,6-trimethoxybenzaldehyde (5h) (24 h): 2.72 g (93%). M.p. 206 ± 2078 (PhMe). IR (KBr): 1650 (CˆO).
1H-NMR (300 MHz, CDCl3): 1.72 (s, Me C(5)); 2.99 (s, H C(4)); 3.85, 3.86 (2s, 1:2, 3 MeO); 6.11
(s, 2 arom. H); 7.56 (s, H C(1')). Anal. calc. for C15H20N2O4 (292.34): C 61.63, H 6.89, N 9.58; found: C 61.31,
H 6.97, N 9.74.
(1Z)-1-[(2,6-Dimethoxyphenyl)methylidene]-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide (6i). From 2,6-
1
dimethoxybenzaldehyde (5i) (24 h): 2.26 g (86%). M.p. 195 ± 1998 (Et2O). IR (KBr): 1650 (CˆO). H-NMR
(300 MHz, CDCl3): 1.72 (s, 2 Me C(5)); 2.75 (s, 2 H C(4)); 3.85 (s, 2 MeO); 6.55 (d, J ˆ 8.3, 2 arom. H); 7.20
(s, H C(1')); 7.34 (t, J ˆ 8.3, 1 arom. H). Anal. calc. for C14H18N2O3 (262.31): C 64.10, H 6.92, N 10.68; found:
C 64.03, H 7.07, N 10.40.
Dimethyl 1-Aryl-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-dicarboxylates 8a ± h:
General Procedure. A mixture of dimethyl acetylenedicarboxylate (7; 1.2 ml, 10 mmol) and (1Z)-1-
(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide 6a ± h (10 mmol) in an appropriate solvent
(PhMe, xylene, or PhOMe; 40 ml) was heated under reflux for 20 min to 4 h. Volatile components were
i
evaporated, the residue was triturated with Et2O or Pr2O, and the precipitate was collected by filtration;
cycloadducts 8a ± h.
Dimethyl 6,7-Dihydro-7,7-dimethyl-1-(2-nitrophenyl)-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-dicarbox-
ylate (8a). From 6a (xylene, 20 min): 3.55 g (91%). M.p. 164 ± 1668 (iPr2O). 1H-NMR (300 MHz, CDCl3):

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1.25 (s, 1 Me C(7)); 1.36 (s, 1 Me C(7)); 2.43 (d, J ˆ 15.8, 1 H C(6)); 2.87 (d, J ˆ 15.8, 1 H C(6)); 3.53
(s, MeOOC C(2)); 3.97 (s, MeOOC C(3)); 6.44 (s, H C(1)); 7.42 (ddd, J ˆ 8.7,8.3, 1.5, 1 arom. H); 7.64
(ddd, J ˆ 8.7, 7.5, 1.1, 1 arom. H); 7.77 (dd, J ˆ 7.9, 1.1, 1 arom H); 7.89 (dd, J ˆ 7.9, 1.5, 1 arom. H). Anal. calc. for
C18H19N3O7 (389.37): C 55.53, H 4.92, N 10.79; found: C 55.47, H 4.87, N 10.47.
Dimethyl 6,7-Dihydro-7,7-dimethyl-1-(4-nitrophenyl)-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-dicarbox-
ylate (8b). From 6b (xylene, 4 h): 3.77 g (97%). M.p. 167 ± 1688 (heptane/EtOH 5 :2). 1H-NMR (300 MHz,
CDCl3): 1.15 (s, 1 Me C(7)); 1.30 (s, 1 Me C(7)); 2.43 (d, J ˆ 15.8, 1 H C(6)); 2.87 (d, J ˆ 15.8, 1 H C(6));
3.61 (s, MeOOC C(2)); 3.98 (s, MeOOC C(3)); 5.61 (s, H C(1)); 7.68 (d, J ˆ 8.8, 2 arom. H); 8.22
(d, J ˆ 8.8, 2 arom. H). Anal. calc. for C18H19N3O7 (389.37): C 55.53, H 4.92, N 10.79; found: C 55.36, H 4.80,
N 10.81.
Dimethyl 6,7-Dihydro-1-(2-methoxyphenyl)-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-dicar-
boxylate (8c). From 6c (xylene, 2 h): 3.10 g (83%). M.p. 104 ± 1058 (iPr2O). 1H-NMR (300 MHz, CDCl3):
1.19 (s, 1 Me C(7)); 1.31 (s, 1 Me C(7)); 2.34 (d, J ˆ 15.4, 1 H C(6)); 2.79 (d, J ˆ 15.8, 1 H C(6)); 3.57
(s, MeOOC C(2)); 3.88 (s, MeOC6H4); 3.98 (s, MeOOC C(3)); 6.02 (s, H C(1)); 6.89 (d, J ˆ 8.3, 1 arom. H);
6.98 (dd, J ˆ 7.9, 7.5, 1 arom. H); 7.26 (m, 1 arom. H); 7.36 (dd, J ˆ 7.5, 1.9, 1 arom. H). Anal. calc. for
C19H22N2O6 (374.40): C 60.95, H 5.92, N 7.48; found: C 60.98, H 5.98, N 7.37.
Dimethyl 6,7-Dihydro-7,7-dimethyl-5-oxo-1-(3,4,5-trimethoxyphenyl)-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-
dicarboxylate (8d). From 6d (xylene, 30 min): 3.82 g (88%). M.p. 147 ± 1498 (EtOH). 1H-NMR (300 MHz,
CDCl3): 1.21 (s, 1 Me C(7)); 1.27 (s, 1 Me C(7)); 2.41 (d, J ˆ 15.7, 1 H C(6)); 2.88 (d, J ˆ 15.7, H C(6)); 3.63
(s, MeOOC C(2)); 3.84, 3.88 (2s, 1:2, 3 MeOC6H2); 3.97 (s, MeOOC C(3)); 5.45 (s, H C(1)); 6.68
(s, 2 arom. H). Anal. calc. for C21H26N2O8 (434.45): C 58.06, H 6.03, N 6.45; found: C 58.01, H 6.21, N 6.48.
Dimethyl 1-(2,4-Dichlorophenyl)-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-di-
carboxylate (8e). From 6e (PhMe, 25 min): 2.91 g (70%). M.p. 76 ± 798 (heptane). 1H-NMR (300 MHz,
CDCl3): 1.15 (s, 1 Me C(7)); 1.34 (s, 1 Me C(7)); 2.40 (d, J ˆ 15.8, 1 H C(6)); 2.80 (d, J ˆ 15.8, H C(6));
3.59 (s, MeOOC C(2)); 3.98 (s, MeOOC C(3)); 6.07 (s, H C(1)); 7.29 (dd, J ˆ 8.7, 1.9, 1 arom. H); 7.36
(d, J ˆ 1.9, 1 arom. H); 7.52 (d, J ˆ 8.7, 1 arom. H). Anal. calc. for C18H18Cl2N2O5 (413.26): C 52.31, H 4.39,
N 6.78; found: C 52.27, H 4.36, N 6.76.
Dimethyl 1-(2,6-Dichlorophenyl)-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-di-
carboxylate (8f). From 6f (PhOMe, 3 h): 3.18 g (77%). M.p. 152 ± 1538 (EtOH). 1H-NMR (300 MHz, CDCl3):
1.15 (s, 1 Me C(7)); 1.40 (s, 1 Me C(7)); 2.40 (d, J ˆ 15.8, 1 H C(6)); 2.83 (d, J ˆ 15.8, 1 H C(6)); 3.59
(s, MeOOC C(2)); 3.97 (s, MeOOC C(3)); 6.54 (s, H C(1)); 7.17 (dd, J ˆ 8.3, 7.9, 1 arom. H); 7.32 (dd, J ˆ
8.3, 1.1, 1 arom. H); 7.33 (dd, J ˆ 7.9, 1.1, 1 arom. H). 13C-NMR (75.5 MHz, CDCl3): 19.7; 24.9; 49.4; 52.2; 53.9;
62.4; 65.7; 112.0; 128.5; 129.9; 131.1; 134.6; 135.9; 136.2; 137.4; 159.9; 163.0; 166.6. Anal. calc. for C18H18Cl2N2O5
(413.26): C 52.31, H 4.39, N 6.78; found: C 52.33, H 4.34, N 6.48.
Dimethyl 6,7-Dihydro-7,7-dimethyl-5-oxo-1-(2,4,6-trimethylphenyl)-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-di-
carboxylate (8g). From 6g (PhMe, 90 min): 3.15 g (82%). M.p. 114 ± 1158 (heptane). 1H-NMR (300 MHz,
CDCl3): 1.07 (s, 1 Me C(7)); 1.36 (s, 1 arom. Me); 2.24 (s, 1 Me C(7)); 2.40 (d, J ˆ 15.8, 1 H C(6)); 2.46
(s, 1 arom. Me); 2.48 (s, 1 arom. Me); 2.80 (d, J ˆ 15.8, 1 H C(6)); 3.57 (s, MeOOC C(2)); 3.96
(s, MeOOC C(3)); 6.06 (s, H C(1)); 6.78 (s, 1 arom. H); 6.83 (s, 1 arom. H). Anal. calc. for C21H26N2O5
(386.45): C 65.27, H 6.78, N 7.25; found: C 65.22, H 6.94, N 7.06.
Dimethyl 6,7-Dihydro-7,7-dimethyl-5-oxo-1-(2,4,6-trimethoxyphenyl)-1H,5H-pyrazolo[1,2-a]pyrazole-2,3-
dicarboxylate (8h). From 6h (xylene, 20 min): 3.13 g (72%). M.p. 186 ± 1888 (EtOH). 1H-NMR (300 MHz,
CDCl3): 1.18 (s, 1 Me C(7)); 1.30 (s, 1 Me C(7)); 2.31 (d, J ˆ 15.5, 1 H C(6)); 2.82 (d, J ˆ 15.5, 1H C(6));
3.57 (s, MeOOC C(2)); 3.79, 3.82 (2s, 2 :1, 1 arom. Me); 3.96 (s, MeOOC C(3)); 6.09 (s, H C(1)); 6.12
(s, 2 arom. H). 13C-NMR (75.5 MHz, CDCl3): 18.9; 24.3; 49.1; 51.6; 53.2; 55.2; 55.7; 56.1; 65.5; 91.4; 109.8; 115.1;
135.0; 160.6; 161.1; 163.4; 167.7. Anal. calc. for C21H26N2O8 (434.45): C 58.06, H 6.03, N 6.45; found: C 58.14,
H 6.12, N 6.74.
Methyl 1-Aryl-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxylates 10a ± i and
Methyl 1-Aryl-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-3-carboxylates 11a ± e: General
Procedure. A mixture of methyl propiolate (9; 0.5 ml, 6 mmol) and (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-
oxopyrazolidin-1-ium-2-ide 6a ± i (5 mmol) in an appropriate solvent (PhMe, xylene, or PhOMe; 20 ml) was
heated under reflux for 1 ± 8 h. Volatile components were evaporated to afford mixtures of isomers 10a ± e and
11a ± e or single regioisomers 10f ± i. Regioisomers 10a,b,e and 11a,b,e were then separated by CC. In the cases
of mixtures of 10c,d and 11c,d, the minor isomers 11c,d were detected by 1H-NMR spectroscopy. In the case of
10f ± i, the residue was triturated with an appropriate solvent to give the pure compounds.

Helvetica Chimica Acta ± Vol. 84 (2001)
153
Methyl 6,7-Dihydro-7,7-dimethyl-1-(2-nitrophenyl)-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxylate
(10a) and Methyl 6,7-Dihydro-7,7-dimethyl-1-(2-nitrophenyl)-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-3-carbox-
ylate (11a). From 6a (PhMe, 1 h), after CC (Et2O).
Data of Major Isomer 10a: Yield: 0.930 g (56%). M.p. 110 ± 1158 (Et2O). 1H-NMR (300 MHz, CDCl3): 1.23
(s, 1 Me C(7)); 1.31 (s, 1 Me C(7)); 2.44 (d, J ˆ 15.8, 1 H C(6)); 2.88 (d, J ˆ 15.8, 1 H C(6)); 3.56
(s, MeOOC C(2)); 6.38 (d, J ˆ 1.5,
H
C(1)); 7.41 (ddd, J ˆ 1.5, 7.5, 7.9, 1 arom. H); 7.51 (d, J ˆ 1.5,
H
C(3)); 7.62 (ddd, J ˆ 1.2, 7.5, 7.5, 1 arom. H); 7.77 (dd, J ˆ 1.2, 7.9, 1 arom. H); 7.85 (dd, J ˆ 1.5, 7.9,
1 arom. H). Anal. calc. for C16H17N3O5 (331.33): C 58.00, H 5.17, N 12.68; found: C 58.25, H 5.36, N 12.68.
Data of Minor Isomer 11a: Yield: 0.174 g (11%). M.p. 180 ± 1858 (Et2O). 1H-NMR (300 MHz, CDCl3): 1.14
(s, 1 Me C(7)); 1.24 (s, 1 Me C(7)); 2.42 (d, J ˆ 15.7, 1 H C(6)); 2.98 (d, J ˆ 15.7, 1 H C(6)); 3.85
(s, MeOOC C(3)); 5.95 (d, J ˆ 2.5, H C(1)); 6.07 (d, J ˆ 2.3, H C(2)); 7.47 (ddd, J ˆ 1.5, 7.5, 7.9, 1 arom. H);
7.73 (ddd, J ˆ 1.2, 7.5, 7.5, 1 arom. H); 8.01 (dd, J ˆ 1.2, 7.9, 1 arom. H); 8.22 (dd, J ˆ 1.5, 7.9, 1 arom. H). Anal.
calc. for C16H17N3O5 (331.33): C 58.00, H 5.17, N 12.68; found: C 58.06, H 5.37, N 12.54.
Methyl 6,7-Dihydro-7,7-dimethyl-1-(4-nitrophenyl)-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxylate
(10b) and Methyl 6,7-Dihydro-7,7-dimethyl-1-(4-nitrophenyl)-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-3-carbox-
ylate (11b). From 6b (PhOMe, 1 h), after CC (CHCl3/MeOH 25 :1).
Data of Major Isomer 10b: Yield 0.730 g (44%). M.p. 119 ± 1208 (CHCl3/MeOH 25 :1). 1H-NMR
(300 MHz, CDCl3): 1.14 (s, Me C(7)); 1.25 (s, Me C(7)); 2.44 (d, J ˆ 15.8, 1 H C(6)); 2.89 (d, J ˆ 15.8,
H
C(5)); 3.64 (s, MeOOC C(2)); 5.58 (d, J ˆ 1.2, H C(1)); 7.53 (d, J ˆ 1.2, H C(3)); 7.69 (d, J ˆ 8.8,
2 arom. H); 8.21 (d, J ˆ 8.8, 2 arom. H). 13C-NMR (75.5 MHz, CDCl3): 19.3; 25.2; 49.5; 52.0; 64.3; 65.0; 115.9;
124.0; 129.3; 130.4; 148.0; 149.6; 164.1; 166.9. Anal. calc. for C16H17N3O5 (331.33): C 58.00, H 5.17, N 12.68;
found: C 58.23, H 5.36, N 12.58.
Data of Minor Isomer 11b: Yield 0.296 g (18%). M.p. 101 ± 1028 (CHCl3/MeOH, 25 :1). 1H-NMR
(300 MHz, CDCl3): 1.15 (s, 1 Me C(7)); 1.29 (s, 1 Me C(7)); 2.43 (d, J ˆ 15.7, 1H C(6)); 2.98 (d, J ˆ 15.7,
1 H C(6)); 3.87 (s, MeOOC C(3)); 5.50 (d, J ˆ 2.5, H C(1)); 5.87 (d, J ˆ 2.5, H C(2)); 7.65 (d, J ˆ 8.7,
2 arom. H); 8.24 (d, J ˆ 8.7, 2 arom. H). Anal. calc. for C16H17N3O5 (331.33): C 58.00, H 5.17, N 12.68; found:
C 57.96, H 5.02, N 12.73.
Methyl 6,7-Dihydro-1-(2-methoxyphenyl)-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxyl-
ate (10c). From 6c (PhMe, 3 h), after CC (Et2O).
Data of Major Isomer 10c: Yield 0.320 g (20%). M.p. 112 ± 1148 (Et2O). 1H-NMR (300 MHz, CDCl3): 1.17
(s, 1 Me C(7)); 1.27 (s, 1 Me C(7)); 2.37 (d, J ˆ 15.4, 1 H C(6)); 2.81 (d, J ˆ 15.4, 1 H C(6)); 3.61
(s, MeOOC C(2)); 3.88 (s, MeOC6H4); 6.02 (d, J ˆ 1.5, H C(1)); 6.89 (dd, J ˆ 1.1, 8.3, 1 arom. H); 6.97
(ddd, J ˆ 1.1, 7.5, 7.5, 1 arom. H); 7.26 (ddd, J ˆ 1.7, 7.5, 8.3, 1 arom. H); 7.35 (dd, J ˆ 1.5, 7.5, 1 arom. H); 7.57
(d, J ˆ 1.5, H C(3)). Anal. calc. for C17H20N2O4 (316.35): C 64.54, H 6.37, N 8.86; found: C 64.88, H 6.35,
N 8.90.
Data of Minor Isomer 11c: 1H-NMR (300 MHz, CDCl3): 1.48 (s, 1 Me C(7)); 2.97 (d, J ˆ 15.4, 1 H C(6));
3.13 (d, J ˆ 15.4, 1 H C(6)); 3.76 (s, MeOOC C(3)).
Methyl 6,7-Dihydro-7,7-dimethyl-5-oxo-1-(3,4,5-trimethoxyphenyl)-1H,5H-pyrazolo[1,2-a]pyrazole-2-car-
boxylate (10d). From 6d (PhMe, 2 h), after CC (Et2O).
Data of Major Isomer 10d: Yield 0.885 g (47%). M.p. 105 ± 1078 (Et2O). 1H-NMR (300 MHz, (D6)DMSO):
1.21 (s, 1 Me C(7)); 1.22 (s, 1 Me C(7)); 2.40 (d, J ˆ 15.7, 1 H C(6)); 2.89 (d, J ˆ 15.7, 1 H C(6)); 3.66
(s, MeOOC C(2)); 3.84, 3.87 (2s, 1:2, 1 arom. MeO); 5.41 (d, J ˆ 1.2, H C(1)); 6.69 (s, 2 arom. H); 7.50
(d, J ˆ 1.2, H C(3)). Anal. calc. for C19H24N2O6 (376.41): C 60.63, H 6.43, N 7.44; found: C 60.79, H 6.60,
N 7.49.
1
Data of Minor Isomer 11d: H-NMR (300 MHz, CDCl3): 1.18 (s, 1 Me C(7)); 1.29 (s, 1 Me C(7)); 5.33
(d, J ˆ 2.6, H C(1)); 5.93 (d, J ˆ 2.6, H C(2)).
Methyl 1-(2,4-Dichlorophenyl)-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxyl-
ate (10e) and Methyl 1-(2,4-Dichlorophenyl)-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-3-
carboxylate (11e). From 6e (PhMe, 2 h), after CC (Et2O).
Data of Major Isomer 10e: Yield 1.156 g (65%). M.p. 140 ± 1488 (Et2O). 1H-NMR (300 MHz, CDCl3): 1.14
(s, 1 Me C(7)); 1.30 (s, 1 Me C(7)); 2.40 (d, J ˆ 15.8, 1 H C(6)); 2.82 (d, J ˆ 15.8, 1 H C(6)); 3.62
(s, MeOOC C(2)); 6.03 (d, J ˆ 1.5, H C(1)); 7.27 (dd, J ˆ 2.0, 7.9, 1 arom. H); 7.36 (d, J ˆ 1.9, 1 arom. H);
7.48 (d, J ˆ 8.7, 1 arom. H); 7.56 (d, J ˆ 1.5, H C(3)). Anal. calc. for C16H16Cl2N2O3 (355.22): C 54.10, H 4.54,
N 7.89; found: C 54.34, H 4.65, N 7.74.
Data of Minor Isomer 11e: Yield 0.176 g (10%). M.p. 124 ± 1268 (Et2O). 1H-NMR (300 MHz, CDCl3): 1.16
(s, 1 Me C(7)); 1.28 (s, 1 Me C(7)); 2.42 (d, J ˆ 16.0, 1 H C(6)); 2.97 (d, J ˆ 16.0, 1 H C(6)); 3.85

154
Helvetica Chimica Acta ± Vol. 84 (2001)
(s, MeOOC C(2)); 5.74 (d, J ˆ 1.6, H C(1)); 5.98 (d, J ˆ 1.6, H C(2)); 7.32 (dd, J ˆ 1.9, 8.2, 1 arom. H); 7.37
(d, J ˆ 1.9, 1 arom. H); 7.81 (d, J ˆ 8.7, 1 arom. H). 13C-NMR (75.5 MHz, CDCl3): 20.5; 25.8; 50.2, 53.1; 61.0;
64.3; 122.3; 128.3; 129.4; 131.0; 131.1; 132.7; 134.6; 137.6; 159.5; 166.8. Anal. calc. for C16H16Cl2N2O3 (355.22):
C 54.10, H 4.54, N 7.89; found: C 54.27, H 4.69, N 7.84.
Methyl 1-(2,6-Dichlorophenyl)-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-carboxy-
late (10f). From 6f (xylene, 7 h): 1.510 g (85%). M.p. 145 ± 1478 (Et2O). 1H-NMR (300 MHz, CDCl3): 1.14
(s, 1 Me C(7)); 1.34 (s, 1 Me C(7)); 2.40 (d, J ˆ 15.8, 1 H C(6)); 2.84 (d, J ˆ 15.8, 1 H C(6)); 3.62
(s, MeOOC C(2)); 6.47 (d, J ˆ 1.7, H C(1)); 7.16 (dd, J ˆ 8.3, 7.9, 1 arom. H); 7.31 (dd, J ˆ 8.3, 1.1, 1 arom. H);
7.32 (dd, J ˆ 7.9, 1.1, 1 arom. H); 7.53 (d, J ˆ 1.7, H C(3)). 13C-NMR (75.5 MHz, CDCl3): 19.6; 25.0; 49.9; 52.0;
61.9; 65.2; 114.5; 128.6; 129.7; 131.1; 131.2; 134.9; 135.9; 137.4; 164.1; 166.4. Anal. calc. for C16H16Cl2N2O3
(355.22): C 54.10, H 4.54, N 7.89; found: C 54.02, H 4.63, N 7.85.
Methyl 6,7-Dihydro-7,7-dimethyl-5-oxo-1-(2,4,6-trimethylphenyl)-1H,5H-pyrazolo[1,2-a]pyrazole-2-car-
boxylate (10g). From 6g (PhMe, 8 h): 1.443 g (88%). M.p. 135 ± 1368 (Et2O). 1H-NMR (300 MHz, CDCl3):
1.06 (s, 1 Me C(7)); 1.30 (s, 1 Me C(7)); 2.24 (s, 1 arom. Me); 2.40 (d, J ˆ 15.4, 1 H C(6)); 2.42 (s, 1 ar-
om. Me); 2.47 (s, 1 arom. Me); 2.81 (d, J ˆ 15.4, 1H C(6)); 3.60 (s, MeOOC C(2)); 6.00 (d, J ˆ 1.9, H C(1));
6.80 (br. s, 2 arom. H); 7.46 (d, J ˆ 1.9, H C(3)). Anal. calc. for C19H24N2O3 (328.41): C 69.49, H 7.37, N 8.53;
found: C 69.81, H 7.34, N 8.72.
Methyl 6,7-Dihydro-7,7-dimethyl-5-oxo-1-(2,4,6-trimethoxyphenyl)-1H,5H-pyrazolo[1,2-a]pyrazole-2-car-
boxylate (10h). From 6h (PhMe, 3 h): 1.204 g (64%). M.p. 162 ± 1658 (PhMe). 1H-NMR (300 MHz,
(D6)DMSO): 1.16 (s, 1 Me C(7)); 1.28 (s, 1 Me C(7)); 2.32 (d, J ˆ 15.6, 1 H C(6)); 2.84 (d, J ˆ 15.6,
1 H C(6)); 3.61 (s, MeOOC C(2)); 3.79 (br. s, 1 arom. MeO); 6.06 (d, J ˆ 1.8, H C(1)); 6.13 (s, 2 arom. H);
7.43 (d, J ˆ 1.8, H C(3)). 13C-NMR (75.5 MHz, CDCl3): 19.4; 24.8; 50.1; 51.6; 55.5; 55.6; 56.4; 65.2; 91.3; 92.7;
110.3; 118.1; 129.2; 161.3; 164.8; 166.8. Anal. calc. for C19H24N2O6 (376.41): C 60.63, H 6.43; N 7.44; found:
C 60.50, H 6.78, N 7.64.
Methyl 1-(2,6-Dimethoxyphenyl)-6,7-dihydro-7,7-dimethyl-5-oxo-1H,5H-pyrazolo[1,2-a]pyrazole-2-car-
boxylate (10i). From 6i (toluene, 4 h): 1.386 g (80%). M.p. 159 ± 1628 (heptane).1H-NMR (300 MHz, CDCl3):
1.16 (s, 1 Me C(7)); 1.29 (s, 1 Me C(7)); 2.33 (d, J ˆ 15.5, 1 H C(6)); 2.85 (d, J ˆ 15.8, 1 H C(6)); 3.60
(s, MeOOC C(2)); 3.81 (br. s, 1 arom. Me); 6.16 (d, J ˆ 1.9, H C(1)); 6.56 (d, J ˆ 8.3, H C(3'), H C(5'));
7.21 (t, J ˆ 8.4, H C(4')); 7.46 (d, J ˆ 1.9, H C(3)). Anal. calc. for C18H22N2O5 (346.39): C 62.42, H 6.40, N 8.09;
found: C 62.65, H 6.42, N 8.17.
X-Ray Structure Determination of Compounds 6f and 10g. The crystallographic data are presented in the
Table. The pictures of the molecular structures of compounds 6f and 10g are shown in Figs. 1 and 2. Both
structures were solved by direct methods with the SIR92 [15] program. The positions of H-atoms were obtained
from difference Fourier maps. We employed full-matrix least-squares refinement on Fo with anisotropic
temperature factors for all non-H atoms. For compound 10g, H-atoms were refined isotropically; for compound
6f, the positions of H-atoms were refined with fixed displacement parameters of atoms of attachment. For
compound 10g, the correction for secondary extinction [16] was applied with g ˆ 2.5(9) ´ 104. The Xtal3.4 [17]
system of crystallographic programs was used for the correlation and reduction of data, structure refinement,
and interpretation. ORTEPII [18] and ORTEPIII [19][20] programs were used to produce molecular graphics.
Further details of crystal structures of compounds 6f and 10g can be obtained, free of charge, on application to
CCDC, 12 Union Road, Cambridge CB21EZ, UK (e-mail: deposit@ccdc.cam.ac.uk), quoting the deposition
numbers CCDC 145358 and CCDC 145359, resp.

Helvetica Chimica Acta ± Vol. 84 (2001)
155
Table 1. Crystallographic Data for Compounds 6f and 10g
6f
10g
Crystal data
Chemical formula
Mr
C12H12Cl2N2O
271.15
C19H24N2O3
328.4
Crystal system
Space group
monoclinic
P21/c
triclinic
P1
Å
a [Š]
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š3]
11.630(1)
8.343(1)
13.069(1)
90.00
96.49(1)
90.00
1260.0(1)
4
1.429
8.315(1)
10.077(1)
11.634(1)
74.43(1)
82.65(1)
72.72(1)
895.4(2)
2
1.218
MoKa
0.71069
100
Z
3
Calc. density Dx [Mg m
Radiation type
Wavelength (l)
]
MoKa
0.71069
75
No. of refl. for cell parameters
q range [8]
8.9 ± 15.9
0.4994
8.26 ± 17.87
0.0772
1
m [mm
]
Temperature [K]
Crystal shape
293(1)
prism
293(1)
prism
Crystal size [mm]
Crystal color
0.95 Â 0.53 Â 0.39
0.56 Â 0.45 Â 0.28
colorless
yellow
Data collection
Diffractometer
Enraf Nonius CAD-4
Enraf Nonius CAD-4
Data collection method
Absorption correction
No. of measured refl.
No. of independent refl.
No. of observed refl.
Criterion of observed refl.
Rint
w/2q scans
none
12127
3020
2630
I > 2.5s(I)
0.0244
28
w/2q scans
none
8683
4298
3204
I > 2.5s(I)
0.0067
28
qmax [8]
No. of standard refl.
Frequency of standard refl.
Intensity decay [%]
3
3
every 333.3 min of scan time
0.05
every 333.3 min of scan time
0.58
Refinement
R
wR
0.041
0.036
2630
190
0.004
0.274
0.668
0.040
0.047
3806
314
0.008
0.259
0.182
No. of contributing refl.
No. of parameters
(D/s)max
D1max
D1min
Financial support of the Ministry of Science and Technology of Slovenia is gratefully acknowledged.

156
Helvetica Chimica Acta ± Vol. 84 (2001)
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Received June 15, 2000