Stereoselective synthesis of spiro and condensed pyrazolines of steroidal α,β-unsaturated ketones and nitrilimines by 1,3-dipolar cycloaddition

Article abstract of DOI:10.1016/j.steroids.2009.02.001

Effective syntheses of endo- and exocyclic α,β-unsaturated ketones as C{double bond, long}C dipolarophiles were carried out in the 13α-estrone series. The 1,3-dipolar cycloadditions of 15,16α,β-unsaturated ketones of 13α-estrone 3-methyl and 3-benzyl ethe

Full text of DOI:10.1016/j.steroids.2009.02.001

Steroids 74 (2009) 520–525
Contents lists available at ScienceDirect
Steroids
journal homepage: www.elsevier.com/locate/steroids
Stereoselective synthesis of spiro and condensed pyrazolines of steroidal
␣
,␤-unsaturated ketones and nitrilimines by 1,3-dipolar cycloaddition
a,∗
a
b
c
Erzsébet Mernyák , Eszter Kozma , Anasztázia Hetényi , László Márk ,
a
a
Gyula Schneider , János Wölfling
Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary
Department of Medicinal Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged, Hungary
Department of Biochemistry and Medical Chemistry, University of Pécs, Szigeti út 12, H-7624 Pécs, Hungary
a
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Effective syntheses of endo- and exocyclic ␣,␤-unsaturated ketones as C C dipolarophiles were carried
out in the 13␣-estrone series. The 1,3-dipolar cycloadditions of 15,16␣,␤-unsaturated ketones of 13␣-
estrone 3-methyl and 3-benzyl ether with nitrilimines stereoselectively furnished two regioisomers of
new condensed pyrazolines in a ratio of 2:1. The main product was the isomer obtained by the attack
of the N-terminus of the 1,3-dipole on the carbon atom ␤ to the carbonyl group of the dipolarophile.
The nitrilimine cycloadditions to the 16-methylene-17-ketones of 13␣-estrone 3-methyl and 3-benzyl
ether stereo- and regioselectively furnished spiropyrazolines. The attack of the N-terminus of the dipole
occurred on the ␣-carbon of the ␣,␤-unsaturated ketones. The reactions were performed under both
homogeneous and heterogeneous conditions. Silver acetate as a base proved more effective than its tri-
ethylamine counterpart. Changes in regio- and stereoselectivities were not observed on variation of the
conditions of the cycloaddition reactions. The structures of the new products were determined by NMR
Received 31 October 2008
Received in revised form 30 January 2009
Accepted 2 February 2009
Available online 13 February 2009
Keywords:
Cycloadditions
Nitrilimines
Pyrazolines
MALDI
C70 fullerenes
(one- and two-dimensional) and MALDI TOF MS techniques, with C70 fullerenes as matrix in the latter
case.
©
2009 Elsevier Inc. All rights reserved.
1
. Introduction
-tetralones leads to spiropyrazolines with high regioselectivity, but
differences in diastereoselectivity, depending on the conforma-
tional arrangement of substituents of the dipolarophile [10–12].
13␣-Estrone derivatives possess a quasi-equatorial angular
methyl group and their conformation depends on the substitu-
tion pattern of ring D [13–17]. The target binding properties of
these derivatives are strongly dependent on the conformation.
The conformational control provides an option to influence the
binding activities of the molecules. Only two types of condensed
N-containing heterocyclic 13␣-estrone derivatives (condensed aza-
D-homoestrones and tetrahydroquinolines) are known [18–20];
accordingly, we are interested in the synthesis and stereochem-
ical investigation of such compounds. A few 16,17-condensed
steroidal pyrazolines of pharmacological significance have been
described [21–24], but steroidal 16-spiro- or 15,16-condensed 17-
ketopyrazolines are not known.
Synthesis of derivatives of naturally occurring terpenes includ-
ing pyrazolo analogs has recently received considerable attention.
Natural terpenes can suppress the proliferation of murine B16
melanoma and other carcinogenic processes [1–3]. Moreover,
the pyrazole ring comprises the core structure of a number of
drugs [4]. The reactions of nitrilimine 1,3-dipoles with dipo-
larophiles provide an option for the construction of substituted
pyrazoles [5]. Nitrilimines are well-known intermediates generated
in situ by base-promoted dehydrohalogenation of the correspond-
ing hydrazonoyl halides [6–9]. The nitrilimine cycloadditions of
certain enones or allylic alcohols were recently reported under
both homogeneous and heterogeneous conditions [7,8]. For ␣,␤-
unsaturated ketones containing a trisubstituted C C bond, only the
cycloadducts in which the C-terminus of the 1,3-dipole is bonded
to the carbon atom ␣ to the carbonyl group were obtained. This
structure results from the electronic demands of the cycloaddi-
tion. Nitrilimine cycloaddition to 2-arylmethylidene-indanones or
2. Experimental
Melting points (mps) were determined with a Kofler hot-stage
apparatus and are uncorrected. Elemental analyses were performed
with a PerkinElmer CHN analyzer model 2400. Thin-layer chro-
matography: silica gel 60 F254; layer thickness 0.2 mm (Merck);
∗ Corresponding author. Fax: +36 62 544199.
E-mail address: bobe@chem.u-szeged.hu (E. Mernyák).
0
039-128X/$ – see front matter © 2009 Elsevier Inc. All rights reserved.
doi:10.1016/j.steroids.2009.02.001

E. Mernyák et al. / Steroids 74 (2009) 520–525
521
detection with iodine or UV (365 nm) after spraying with 5% phos-
phomolybdic acid in 50% aqueous phosphoric acid and heating
OCH ), 112.7 (C-4), 114.5 (C-2), 120.8 (C-17), 127.4 (2C) and 128.5
2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(2C): C-2 , C-3 , C-5 and C-6 , 127.7 and 127.8 (C-1 and C-4 ), 130.5
◦
ꢀ
at 100–120 C for 10 min. Flash chromatography: silica gel 60,
and 139.1 (C-15 and C-16), 132.9 (C-10), 137.4 (C-1 ), 138.1 (C-5),
1
+
4
0–63 ␮m (Merck). H NMR spectra were recorded in CDCl3 solu-
156.5 (C-3). MS positive mode: 403 (20%, [M+H] ).
tion (if not otherwise stated) with a Bruker DRX-500 instrument at
13
5
00 MHz, with Me Si as internal standard. C NMR spectra were
2.3. Synthesis of 5a or 5b
4
recorded with the same instrument at 125 MHz under the same
conditions. The mass spectrometer used was an Autoflex II TOF/TOF
To a solution of 4a (1.30 g, 4 mmol) or 4b (1.61 g, 4 mmol) in ace-
tone (25 ml), formalin (5 ml, 60 mmol formaldehyde) and a catalytic
amount of p-TsOH were added. The mixture was stirred for 1.5 h at
rt, and then poured into water (100 ml). The precipitate formed was
filtered off, washed with water and dried in the air. The crude prod-
uct 5a or 5b was subjected to chromatographic separation, with
(
Bruker Daltonics, Bremen, Germany) operated in reflector mode.
The ions were accelerated under delayed extraction conditions
80 ns) in positive and negative ion modes, with an acceleration
(
voltage of 20.00 kV. The instrument uses a 337 nm pulsed (50 Hz)
nitrogen laser. 1 ␮l aliquots of the standard solutions were loaded
onto the target plate (MTP 384 target plate ground steel TF, Bruker
Daltonics, Bremen, Germany) by mixing with the same volume of a
saturated matrix solution prepared by dissolving C70 fullerenes in
toluene.
50% diisopropyl ether/50% hexane as eluent.
◦
Data for 5a: 1.10 g, 98%; mp 70–73 C; R = 0.25 (CH Cl ). Anal.
f
2
2
1
Calcd. for C19 H22O : C, 80.82; H, 7.85. Found: C, 80.97; H, 7.72.
H
2
NMR 1.21 (s, 3H, 18-H ), 2.81 (m, 2H, 6-H ), 3.76 (s, 3H, 3-OMe),
3
2
6
.17 (dd, 1H, J = 5.8 Hz, J = 1.4 Hz, 16-H), 6.59 (d, 1H, J = 2.4 Hz, 4-H),
6.73 (dd, 1H, J = 8.6 Hz, J = 2.4 Hz, 2-H), 7.14 (d, 1H, J = 8.6 Hz, 1-H),
.78 (dd, 1H, J = 5.8 Hz, J = 2.5 Hz, 15-H). 13C NMR 24.2 (C-18), 27.0,
2.1. Synthesis of 3a or 3b
7
To a suspension of 1a (10 g, 44 mmol) or 1b (15.9 g, 44 mmol) in
28.2, 29.1, 29.8, 38.4, 41.2, 46.5 (C-13), 55.2 (3-OMe), 56.6, 112.3 (C-
4), 113.2 (C-2), 128.0 (C-1), 131.2 (C-15), 132.7 (C-10), 137.2 (C-5),
157.4 (C-3), 163.9 (C-16), 214.1 (C-17). MS positive mode: 282 (15%,
triethyl orthoformate (15 ml, 88 mmol) and ethylene glycol (6 ml,
10 mmol), a catalytic amount of p-TsOH was added, and the mix-
ture was gently heated until the suspension became a clear solution
0.5 h). The warm reaction mixture was then poured into a saturated
solution of sodium bicarbonate (100 ml). The white precipitate
formed was filtered off, washed with water and dried in the air.
To a solution of the crude product 2a (10 g, 30 mmol) or 2b (15 g,
1
+
[M+H] ).
◦
(
Data for 5b: 1.38 g, 96%; mp 111–113 C; R = 0.24 (CH Cl ). Anal.
Calcd. for C25H26O : C, 83.76; H, 7.31. Found: C, 83.94; H, 7.26. H
f
2
2
1
2
NMR 1.21 (s, 3H, 18-H ), 2.80 (m, 2H, 6-H ), 5.03 (s, 2H, OCH ), 6.18
3
2
2
(dd, 1H, J = 5.8 Hz, J = 1.7 Hz, 16-H), 6.68 (d, 1H, J = 2.6 Hz, 4-H), 6.80
(dd, 1H, J = 8.6 Hz, J = 2.6 Hz, 2-H), 7.14 (d, 1H, J = 8.6 Hz, 1-H), 7.31
3
7 mmol) in abs. tetrahydrofuran (100 ml), 10 g (30 mmol) of pyri-
ꢀ ꢀ ꢀ
(t, 1H, J = 7.0 Hz, 4 H), 7.38 (t, 2H, J = 7.0 Hz, 3 -H and 5 -H), 7.42 (d,
dinium hydrobromide perbromide was added. A white precipitate
was formed immediately from the yellow solution. The reaction
mixture was stirred for 2 h at rt, and then diluted with a saturated
aqueous solution of sodium bicarbonate (0.5 l). The precipitate
formed was filtered off, washed with water and dried in the air.
The crude product 3a or 3b was transformed without purifica-
tion.
ꢀ
ꢀ
2H, J = 7.0 Hz, 2 -H and 6 -H), 7.77 (dd, 1H, J = 5.8 Hz, J = 2.5 Hz, 15-H).
13
C NMR 24.2 (C-18), 27.0, 28.2, 29.2, 29.9, 38.4, 41.2, 46.5 (C-13),
56.7, 70.0 (OCH ), 113.1 (C-4), 114.4 (C-2), 127.4 and 128.5 (2 × 2C,
2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
C-2 , C-3 , C-5 and C-6 ), 127.8 and 128.0 (C-1 and C-4 ), 131.3 (C-
15), 133.1 (C-10), 137.1 (C-1 ), 137.2 (C-5), 156.7 (C-3), 163.9 (C-16),
ꢀ
214.1 (C-17).
+
MS positive mode: 357 (10%, [M−H] ), 91 (100%, benzylic
2
.2. Synthesis of 4a or 4b
cation).
To a solution of 3a (4.07 g, 10 mmol) or 3b (4.83 g, 10 mmol)
2.4. Synthesis of 7a or 7b
in dimethyl sulfoxide (40 ml) potassium tert-butylate (2.24 g,
2
0 mmol) was added. The suspension was vigorously stirred and
To a suspension of 6a (3.12 g, 10 mmol) or 6b (3.72 g, 10 mmol)
in acetone (50 ml), formalin (31 ml, 372 mmol formaldehyde) was
added, and the mixture was maintained at rt for 0.5 h. Powdered
sodium carbonate (7.13 g, 66 mmol) was next added and the mix-
ture was vigorously stirred for 24 h, diluted with water, and acidified
with hydrochloric acid until pH 5. The resulting precipitate was
filtered off, washed with water, and dried in the air. The crude prod-
uct 7a or 7b was subjected to chromatographic purification, with
◦
heated (80 C) until it became a clear yellow-brown solution (5 h).
The mixture was poured into ice-water (1 l), and the resulting pre-
cipitate was filtered off, washed with water and dried in the air. The
crude product 4a or 4b was subjected to chromatographic separa-
tion, with 30% diisopropyl ether/70% hexane as eluent.
◦
Data for 4a: 2.45 g, 75%; mp 92–95 C; R = 0.47 (CH Cl ). Anal.
f
2
2
1
Calcd. for C21H26O : C, 77.27; H, 8.03. Found: C, 77.42; H, 7.92.
H
3
NMR 1.10 (s, 3H, 18-H ), 2.80 (m, 2H, 6-H ), 3.77 (s, 3H, 3-OMe),
dichloromethane as eluent.
3
2
◦
3
.90 (m, 3H) and 4.00 (m, 1H): ketal-OCH , 5.71 (d, 1H, J = 5.9 Hz,
Data for 7a: 26.6 g, 90%; mp 120–124 C; R = 0.52 (CH Cl ). Anal.
2
f
2
2
1
1
6-H), 6.33 (m, 1H, 15-H), 6.58 (d, 1H, J = 2.3 Hz, 4-H), 6.71 (dd, 1H,
Calcd. for C20H24O : C, 81.04; H, 8.16. Found: C, 80.95; H, 8.27. H
2
13
J = 8.5 Hz, J = 2.3 Hz, 2-H), 7.20 (d, 1H, J = 8.5 Hz, 1-H). C NMR 27.7
C-18), 28.1, 29.6, 30.3, 31.3, 40.5, 44.5, 44.9 (C-13), 55.2 (3-OMe),
NMR 1.06 (s, 3H, 18-H ), 2.80 (m, 2H, 6-H ), 3.76 (s, 3H, 3-OMe),
3 2
(
5.38 and 6.08 (2 × s, 2s1H, 16a-H ), 6.57 (d, 1H, J = 2.6 Hz, 4-H), 6.68
2
13
5
7.3, 64.5 and 64.9 (2× OCH ), 111.9 (C-4), 113.4 (C-2), 120.8 (C-
(dd, 1H, J = 8.6 Hz, J = 2.6 Hz, 2-H), 7.16 (d, 1H, J = 8.6 Hz, 1-H).
C
2
17), 127.6 (C-1), 130.5 and 139.1 (C-15 and C-16), 132.6 (C-10), 138.1
NMR 25.1 (18-Me), 28.0, 28.1, 29.9, 30.2, 32.1, 41.2, 42.2, 46.5, 50.1
(C-13), 55.1 (3-OMe), 111.6 (C-4), 113.4 (C-2), 119.3 (C-16a), 126.8 (C-
1), 131.8 (C-10), 137.9 (C-5), 143.0 (C-16), 157.4 (C-3), 208.5 (C-17).
+
(
C-5), 157.2 (C-3). MS positive mode: 327 (20%, [M+H] ).
◦
Data for 4b: 3.42 g, 85%; mp 137–140 C; R = 0.58 (CH Cl ). Anal.
f
2
2
1
+
Calcd. for C27H30O : C, 80.56; H, 7.51. Found: C, 80.68; H, 7.66.
H
MS positive mode: 296 (50%, [M] ).
3
◦
NMR 1.12 (s, 3H, 18-H ), 2.81 (m, 2H, 6-H ), 3.90 (m, 3H) and 4.02 (m,
Data for 7b: 34.2 g, 92%; mp 155–158 C; R = 0.64 (CH Cl ). Anal.
3
2
f
2
2
1
1
H): ketal-OCH , 5.04 (s, 2H, benzyl-OCH ), 5.72 (d, 1H, J = 5.8 Hz,
Calcd. for C26H28O : C, 83.83; H, 7.58. Found: C, 83.65; H, 7.38. H
2
2
2
16-H), 6.34 (m, 1H, 15-H), 6.69 (d, 1H, J = 2.3 Hz, 4-H), 6.80 (dd, 1H,
NMR 1.08 (s, 3H, 18-H ), 2.84 (m, 2H, 6-H ), 5.02 (s, 2H, OCH ), 5.39
3 2 2
J = 8.5 Hz, J = 2.3 Hz, 2-H), 7.22 (d, 1H, J = 8.5 Hz, 1-H), 7.32 (t, 1H,
(s, 1H) and 6.10 (s, 1H): 16a-H , 6.68 (d, 1H, J = 2.4 Hz, 4-H), 6.77
2
ꢀ
ꢀ
ꢀ
J = 7.1 Hz, 4 -H), 7.39 (t, 2H, J = 7.1 Hz, 3 -H and 5 -H), 7.44 (d, 2H,
(dd, 1H, J = 8.6 Hz, J = 2.4 Hz, 2-H), 7.18 (d, 1H, J = 8.6 Hz, 1-H), 7.31 (t,
ꢀ
ꢀ
13
ꢀ ꢀ ꢀ
1H, J = 7.3 Hz, 4 -H), 7.37 (t, 2H, J = 7.3 Hz, 3 -H and 5 -H), 7.41 (d, 2H,
J = 7.1 Hz, 2 -H and 6 -H). C NMR 27.7 (C-18), 28.1, 29.6, 30.2, 31.3,
ꢀ
ꢀ
13
4
0.5, 44.5, 45.0 (C-13), 57.3, 64.5 and 64.9 (2× OCH ), 70.0 (benzyl-
J = 7.3 Hz, 2 -H and 6 -H). C NMR 25.3 (C-18), 28.1, 28.2, 30.1, 30.3,
2

5
22
E. Mernyák et al. / Steroids 74 (2009) 520–525
3
2
2.3, 41.3, 42.3, 46.6, 50.2 (C-13), 70.0 (OCH ), 112.5 (C-4), 114.6 (C-
157.7 (C-3), 161.7 (COOCH CH ), 212.2 (C-17). MS positive mode:
2 3
2
ꢀ
+
+
), 119.4 (C-16a), 126.9 and 127.8 (C-1 and C-4 ), 127.4 and 128.5
486 (10%, M ), 441 (50%, M -C H5O).
2
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(
5
2 × 2C, C-2 , C-3 C-5 and C-6 ), 132.2 (C-10), 137.3 (C-1 ), 138.0 (C-
), 143.1 (C-16), 156.8 (C-3), 208.5 (C-17). MS positive mode: 371
2.6.2. Synthesis of 9b and 10b
+
(
5%, [M−H] ), 91 (100%, benzylic cation).
Following the reaction of 5b with 8 as in General Procedure B, the
chromatographic elution first yielded 9b, which was obtained as a
◦
2.5. Synthesis of 8
white solid (136 mg, 48%). Mp 186–190 C; R = 0.55 (CH Cl ). Anal.
f
2
2
Calcd. for C36H38N O : C, 76.84; H, 6.81. Found: C, 76.73; H, 6.98.
2
4
1
Diazonium salt of p-toluidine: 1.9 g (18 mmol) of p-toluidine
H NMR 1.06 (s, 3H, 18-H ), 1.43 (t, 3H, J = 7.1 Hz, OCH CH ), 2.30
3
2
3
was suspended in water (25 ml) and cc. sulfuric acid (2.5 ml,
(s, 3H, tolyl-Me), 2.88 (m, 2H, 6-H ), 4.16 (d, 1H, J = 13.1 Hz, 16-H),
2
◦
47 mmol) was added. The mixture was cooled below 10 C, and
4.41 (m, 2H, OCH CH ), 4.68 (d, 1H, J = 13.1 Hz, 15-H), 5.03 (s, 2H,
2
3
1
.25 g (18 mmol) of sodium nitrite in water (6 ml) was added in 5
benzyl-OCH ), 6.72 (d, 1H, J = 2.4 Hz, 4-H), 6.79 (dd, 1H, J = 8.6 Hz,
2
ꢀ ꢀ
J = 2.4 Hz, 2-H), 7.12 (d, 2H, J = 9.4 Hz, 2 -H and 6 -H), 7.18 (d, 1H,
amounts under vigorous stirring. After 20 min of stirring, a brown
solution was obtained. A solution of 2.5 ml (18 mmol) of ethyl-2-
chloroacetoacetate in 50% pyridine-water (20 ml) was added and
the mixture was stirred for an additional 15 min. The orange pre-
cipitate that resulted was filtered off, washed with water, dried in
the air and recrystallized from methanol.
ꢀ
ꢀ
J = 8.6 Hz, 1-H), 7.32 (t, 1H, J = 7.3 Hz, 4 -H), 7.38 (t, 2H, J = 7.3 Hz,
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀ
3 -H and 5 -H), 7.41 (overlapping multiplets, 4H, 2 -H, 6 -H, 3 -
H and 5 -H). C NMR ı ppm 14.4 (OCH CH ), 20.6 (tolyl-Me),
ꢀ
13
2
3
26.3 (18-Me), 27.8, 27.9, 30.3, 33.5, 41.2, 46.1, 50.6 (C-13), 50.7, 51.1
(C-16), 61.4 (OCH CH ), 67.8 (C-15), 70.0 (benzyl-OCH ), 112.6 (C-
2
3
2
ꢀ ꢀ
), 114.4 (C-4), 114.9 (2C, C-2 and C-6 ), 126.9 (C-1), 127.4 and
2
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
ꢀꢀ
2.6. General procedures for the synthesis of condensed
128.5 (2 × 2C, C-2 , C-3 , C-5 and C-6 ), 127.9 (C-4 ), 129.6 (2C,
ꢀ
ꢀ
ꢀ
ꢀꢀ
pyrazolines and spiropyrazolines
C-3 and C-5 ), 131.4 (C-4 ), 131.7 (C-10), 137.0 (C-1 ), 137.9 (C-5),
ꢀ
1
39.9 (C-1 ), 141.2 (C N), 156.8 (C-3), 162.3 (COOCH CH ), 212.4
(C-17). MS positive mode: 562 (20%, [M] ), 517 (40%, M -C H5O),
2
3
+
+
Procedure A: a solution of hydrazonoyl chloride 8a (170 mg,
2
+
1
mmol) and enone 5a (140 mg, 0.5 mmol) or 5b (180 mg, 0.5 mmol)
or 7a (150 mg, 0.5 mmol) or 7b (186 mg, 0.5 mmol) in dry toluene
5 ml) was treated with triethyl amine (0.28 ml, 2 mmol) and
304 (25%, M −259), 91 (100%, benzylic cation). Continued elu-
◦
tion yielded 10b (68 mg, 24%). Mp 216–220 C; R = 0.20 (CH Cl ).
f
2
2
(
Anal. Calcd. for C36H38N O : C, 76.84; H, 6.81. Found: C, 76.63; H,
2 4
1
refluxed under a nitrogen atmosphere for 48 h. The solvent was
then evaporated off and the residue was subjected to column chro-
matography with 30% diisopropyl ether/70% hexane.
6.95. H NMR 1.05 (s, 3H, 18-H ), 1.38 (t, 3H, J = 7.1 Hz, OCH CH ),
3 2 3
2.33 (s, 3H, tolyl-Me), 2.91 (m, 2H, 6-H ), 4.22 (d, 1H, J = 11.8 Hz,
2
15-H), 4.37 (m, 2H, OCH CH ), 5.03 (s, 2H, benzyl-OCH ), 5.11 (d,
2
3
2
Procedure B: a solution of hydrazonoyl chloride 8a (170 mg,
1H, J = 11.8 Hz, 16-H), 6.71 (d, 1H, J = 2.4 Hz, 4-H), 6.79 (dd, 1H,
ꢀ
1
mmol) and enone 5a (140 mg, 0.5 mmol) or 5b (180 mg, 0.5 mmol)
or 7a (150 mg, 0.5 mmol) or 7b (186 mg, 0.5 mmol) in dry toluene
5 ml) was treated with silver acetate (200 mg, 1 mmol) and stirred
in the dark at rt under a nitrogen atmosphere for 24 h. The solvent
was then evaporated off and the residue was subjected to column
chromatography with 30% diisopropyl ether/70% hexane.
J = 8.6 Hz, J = 2.4 Hz, 2-H), 7.18 (overlapping doublets, 3H, 1-H, 2 -
ꢀ
ꢀ
ꢀ
H and 6 -H), 7.25 (d, 2H, J = 8.7 Hz, 3 -H and 5 -H), 7.32 (t, 1H,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(
J = 7.3 Hz, 4 -H), 7.38 (t, 2H, J = 7.3 Hz, 3 -H and 5 -H), 7.42 (d, 2H,
ꢀꢀ ꢀꢀ
J = 7.3 Hz, 2 -H and 6 -H). C NMR ı ppm 14.3 (OCH CH ), 20.6
2 3
13
(tolyl-Me), 26.8 (18-Me), 28.1, 28.3, 30.3, 33.9, 41.3, 44.0, 50.6,
51.8 (C-13), 56.4 (C-15), 61.3 (OCH CH ), 68.5 (C-16), 70.0 (benzyl-
2
3
ꢀ
ꢀ
OCH ), 112.9 (C-4), 114.5 (C-2), 115.4 (2C, C-2 and C-6 ), 127.1
2
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
2
.6.1. Synthesis of 9a and 10a
Following the reaction of 5a with 8 as in General Procedure B, the
and 127.8 (C-1 and C-4 ), 127.4 and 128.5 (2 × 2C, C-2 , C-3 , C-
ꢀꢀ ꢀꢀ ꢀ ꢀ ꢀ
5 and C-6 ), 129.9 (2C, C-3 and C-5 ), 131.2 (C-4 ), 132.1 (C-10),
ꢀ
ꢀ
ꢀ
chromatographic elution first yielded 9a, which was obtained as a
135.2 (C N), 137.0 (C-1 ), 137.2 (C-5), 139.7 (C-1 ), 157.0 (C-3),
161.6 (COOCH CH ), 212.1 (C-17). MS positive mode: 562 (10%,
[M] ), 517 (50%, M -C H5O), 304 (20%, M -259), 91 (100%, benzylic
◦
white solid (106 mg, 44%). Mp 179–182 C; R = 0.62 (CH Cl ). Anal.
f
2
2
2
3
+
1
+
+
Calcd. for C30H34N O : C, 74.05; H, 7.04. Found: C, 73.92; H, 7.18. H
2
4
2
NMR 1.06 (s, 3H, 18-H ), 1.43 (t, 3H, J = 7.0 Hz, OCH CH ), 2.30 (s,
cation).
3
2
3
3
H, tolyl-Me), 2.88 (m, 2H, 6-H ), 3.77 (s, 3H, 3-OMe), 4.16 (d, 1H,
2
J = 13.1 Hz, 16-H), 4.42 (m, 2H, OCH CH ), 4.69 (d, 1H, J = 13.1 Hz, 15-
2.6.3. Synthesis of 11a
2
3
H), 6.62 (d, 1H, J = 2.3 Hz, 4-H), 6.71 (dd, 1H, J = 8.5 Hz, J = 2.3 Hz, 2-H),
Following the reaction of 7a with 8 as in General Procedure B,
11a was obtained as a white solid (198 mg, 78%). Mp 178–180 C;
ꢀ
ꢀ
◦
7
.11 (d, 2H, J = 8.3 Hz, 2 -H and 6 -H), 7.18 (d, 1H, J = 8.5 Hz, 1-H), 7.41
ꢀ
ꢀ
13
(
d, 2H, J = 8.3 Hz, 3 -H and 5 -H). C NMR ␦ ppm 14.4 (OCH CH ),
R = 0.40 (CH Cl ). Anal. Calcd. for C31H36N O : C, 74.37; H, 7.25.
2
3
f
2 2 2 4
1
2
0.6 (tolyl-Me), 26.3 (18-Me), 28.0 (2C), 30.4, 33.6, 41.3, 46.2, 50.6
Found: C, 74.46; H, 7.18. H NMR 0.59 (s, 3H, 18-H ), 1.32 (t, 1H,
3
(
1
C-13), 50.9, 51.4, 55.2 (3-OMe), 61.3 (OCH CH ), 67.9, 111.9 (C-4),
J = 7.1 Hz, OCH CH ), 2.32 (s, 3H, tolyl-Me), 2.85 (m, 2H, 6-H ), 3.06
2
3
2
3
2
ꢀ
ꢀ
ꢀ
13.6 (C-2), 115.1 (2C, C-2 and C-6 ), 126.9 (C-1), 129.6 (2C, C-3 and
and 3.41 (2 × d, 2 × 1H, J = 16.9 Hz): 16a-H , 3.78 (s, 3H, 3-OMe), 4.28
2
ꢀ
ꢀ
ꢀ
C-5 ), 131.3 (C-4 ), 131.8 (C-10), 137.9 (C-5), 140.2 and 141.4 (C-1 and
(m, 2H, OCH CH ), 6.63 (d, J = 2.4 Hz, 4-H), 6.72 (dd, 1H, J = 8.6 Hz,
2
3
C N), 157.7 (C-3), 162.4 (COOCH CH ), 212.3 (C-17). MS positive
J = 2.4 Hz, 2-H), 7.11 (s, 4H, tolyl aromatic protons), 7.17 (d, 1H,
J = 8.6 Hz, 1-H). MS positive mode: 501 (5%, [M+H] ), 455 (40%, M -
C2H5O).
2
3
+
+
+
+
mode: 486 (20%, [M] ), 441 (80%, M -C H5O).
2
◦
Continued elution yielded 10a (53 mg, 22%). Mp 210–215 C;
R = 0.18 (CH Cl ). Anal. Calcd. for C30H34N O : C, 74.05; H, 7.04.
f
2
2
2
4
1
Found: C, 74.18; H, 6.95. H NMR 1.05 (s, 3H, 18-H ), 1.38 (t, 3H,
2.6.4. Synthesis of 11b
3
J = 7.0 Hz, OCH CH ), 2.34 (s, 3H, tolyl-Me), 2.90 (m, 2H, 6-H ), 3.78
Following the reaction of 7b with 8 as in General Procedure B,
11b was obtained as a white solid (233 mg, 81%). Mp 221–223 C;
2
3
2
◦
(
s, 3H, 3-OMe), 4.22 (d, 1H, J = 13.1 Hz, 15-H), 4.37 (m, 2H, OCH CH ),
2
3
5
1
2
.12 (d, 1H, J = 13.1 Hz, 16-H), 6.62 (d, 1H, J = 2.4 Hz, 4-H), 6.73 (dd,
R = 0.55 (CH Cl ). Anal. Calcd. for C31H36N O : C, 74.37; H, 7.25.
f
2 2 2 4
1
H, J = 8.6 Hz, J = 2.4 Hz, 2-H), 7.18 (overlapping doublets, 3H, 1-H,
Found: C, 74.51; H, 7.38. H NMR ı ppm 0.62 (s, 3H, 18-H ), 0.96 (m,
3
ꢀ
ꢀ
ꢀ
ꢀ
13
-H and 6 -H), 7.25 (d, 2H, J = 8.6 Hz, 3 -H and 5 -H). C NMR ı
1H, one 11-H), 1.10 (m, 1H, 8-H), 1.35 (t, 3H, COOCH CH ), 1.38 (over-
2
3
ppm 14.3, 20.6, 26.8, 28.1, 28.3, 30.3, 33.9, 41.3, 44.0, 50.6, 51.8, 55.2
lapping multiplets, 2H, one 7-H and 12-H), 1.66 (m, 1H, 14-H), 2.11
(m, 1H, other 7-H), 2.20 (m, 1H, 9-H), 2.23 (m, 1H, one 15-H), 2.25
(
3-OMe), 56.4 (C-15), 61.3 (OCH CH ), 68.4 (C-16), 112.1 (C-2), 113.5
2 3
ꢀ
ꢀ
ꢀ
(
C-4), 115.4 (2C, C-2 and C-6 ), 127.1 (C-1), 129.9 (2C, C-3 and C-
(m, 1H, 11-H), 2.33 (t, 1H, tolyl-H ), 2.35 (m, 1H, other 12-H), 2.46
3
ꢀ
ꢀ
ꢀ
5
), 130.9 (C-4 ), 132.1 (C-10), 135.2 (C N), 137.1 (C-5), 139.7 (C-1 ),
(m, 1H, other 15-H), 2.85 (m, 2H, 6-H ), 3.09 and 3.45 (2 × d, 2 × 1H,
2

E. Mernyák et al. / Steroids 74 (2009) 520–525
523
Scheme 1. Reagents and conditions: (i) 2.5 equiv. of ethylene glycol; 2 equiv. of triethyl orthoformate; catal. amount of p-TsOH; rt; 2 h; (ii) 1 equiv. of pyridinium hydrobromide
◦
perbromide; THF; rt; (iii) 2 equiv. of KOtBu; DMSO; 80 C; 5 h; (iv) 15 equiv. of H2CO; catal. amount of p-TsOH; acetone; rt; 30 min; (v) 2 equiv. of NaOCH3; 15 equiv. of HCOOEt;
◦
benzene; 50 C; 6 h; (vi) 50 equiv. of H2CO; 8 equiv. of Na2CO3; acetone; 24 h.
Scheme 2. 1,3-Dipolar cycloadditions of steroidal ␣,␤-unsaturated ketones with nitrilimines.
J = 16.9 Hz, 16a-H ), 4.30 (q, 2H, J = 7.0 Hz, OCH CH ), 5.06 (s, 2H,
The first step was the protection of the 17-keto function in
the form of ethylene ketal in order to prevent the formation of
undesired side-products (Scheme 1). Ketals are commonly used to
protect the carbonyl function during multistep syntheses, because
of the ease of removal of the ketal protecting group [28]. After
protection of the 17-keto function, ␣-bromination was carried
out with pyridinium hydrobromide perbromide, which yielded a
stereoisomeric mixture of 16-bromo derivatives 3 [29]. Subsequent
dehydrohalogenation with potassium tert-butylate and deprotec-
tion of the 17-ketone led to endocyclic ␣,␤-unsaturated ketone
dipolarophiles 5. 3-Benzyloxy derivative 5b is of value for phar-
macological experiments, because of the ease of removal of the
benzyl function. 3-Methoxy- and 3-benzyloxy-estra-1,3,5(10),15-
tetraen-17-one have been reported previously, but their 13␣
counterparts are unknown [30]. The new exocyclic unsaturated
ketones 7 were synthesized in excellent yields from the known 16-
2
2
3
benzyl-OCH ), 6.71 (d, 1H, J = 2.0 Hz, 4-H), 6.79 (dd, 1H, J = 8.4 Hz,
2
ꢀ
ꢀ
ꢀ
ꢀ
J = 2.0 Hz, 2-H), 7.10 (s, 4H, 2 -H, 3 -H, 5 -H and 6 -H), 7.16 (d, 1H,
J = 8.4 Hz, 1-H), 7.32 (t, 1H, J = 7.2 Hz, 4 -H), 7.38 (t, 2H, J = 7.2 Hz, 3 -
H and 5 -H), 7.42 (d, 2H, J = 7.2 Hz, 2 -H and 6 -H). C NMR ı ppm
ꢀ
ꢀ
ꢀꢀ
ꢀ
ꢀ
ꢀꢀ
ꢀꢀ
13
1
4.4 (OCH CH ), 21.0 (tolyl-CH ), 25.6 (C-18), 28.3 (C-7), 28.5 (C-11),
2
3
3
3
0.2 (C-6), 33.3 (C-12), 34.0 (C-15), 41.1 (C-9), 42.4 (C-8), 46.2 (C-
1
4), 47.9 (C-16a), 49.4 (C-13), 61.0 (OCH CH ), 70.0 (benzyl-OCH ),
2
3
2
ꢀ
ꢀ
7
8.2 (C-16), 112.9 (C-2), 114.7 (C-4), 127.1 (3C, C-1 and C-2 ,6 ), 127.4
ꢀꢀ ꢀꢀ ꢀꢀ ꢀꢀ ꢀꢀ
(
2C) and 128.5 (2C): C-2 , C-3 , C-5 and C-6 , 127.9 (C-4 ), 129.4 (2C,
ꢀ
ꢀ
ꢀ
ꢀꢀ
C-3 and C-5 ), 131.6 (C-10), 136.9 (C N), 137.2 (C-4 ), 137.3 (C-1 ),
ꢀ
137.8 (C-5), 139.0 (C-1 ), 157.0 (C-3), 162.5 (COOEt), 218.8 (C-17).
+
+
MS positive mode: 576 (10%, [M] ), 531 (30%, M -C H5O), 91 (100%,
2
benzylic cation).
3. Results and discussion
Table 1
Our aim was to build up pyrazolines from steroidal ␣,␤-
Synthesis of unsaturated ketones 5 and 7.
unsaturated ketone dipolarophiles and hydrazonoyl chlorides as
nitrilimine precursors. Two different types of dipolarophiles (endo-
and exocyclic C C) were synthesized.
The new endocyclic ␣,␤-unsaturated ketones were prepared
from 13␣-estrone-3-methyl or 3-benzyl ether 1a or 1b, which
were obtained by the epimerization of estrone 3-methyl or 3-
benzyl ether by the method of Yaremenko and Khvat [13,25,26].
Entry
Substrate
Product
Yield (%)
1
2
3
4
5
6
7
8
1a
1b
3a
3b
4a
4b
6a
6b
3a
3b
4a
4b
5a
5b
7a
7b
75
79
75
85
98
96
90
92
13␣-Estrone is available in one step by irradiation of estrone with
monochromatic ultraviolet light [27].

5
24
E. Mernyák et al. / Steroids 74 (2009) 520–525
Table 2
Reactions between hydrazonoyl chloride 8 and enones 5 and 7 in dry toluene.
◦
Entry
Substrate
Base (equiv.) + reagent
Reaction time (h)
Temperature ( C)
Products
Yields (%)
1
2
3
4
5
6
8
9
5a
5a
5b
5b
7a
7a
7b
7b
Et3N (4) + 8
AgOAc (2) + 8
Et3N (4) + 8
AgOAc (2) + 8
Et3N (4) + 8
AgOAc (2) + 8
Et3N (4) + 8
AgOAc (2) + 8
48
24
48
24
48
24
48
24
110
25
110
25
110
25
110
25
9a + 10a
9a + 10a
9b + 10b
9b + 10b
11a
11a
11b
11b
27 + 13
44 + 22
30 + 15
48 + 24
39
78
56
81
hydroxymethylidene derivatives 6 in one step, using formalin and
sodium carbonate in acetone [31]. No side-products were formed,
in contrast to the similar reactions in the natural estrone series
4. Structure determination
The structures of the newly formed cycloadducts 9, 10 and 11
were determined by NMR spectroscopy. The H NMR spectra of 9a
1
[
31].
The hydrazonoyl chloride 8 was prepared via the Japp–
and 9b displayed two doublets, at around ı = 4.2 and 4.7 ppm, due
to 16-H and 15-H with a coupling constant of 13 Hz. In the simi-
lar spectra of the other regioisomer 10a and 10b, an upfield shift
and the reversed sequence of the signals of 15-H (4.22 ppm) and
16-H (5.12 ppm) were observed, with a coupling constant of 12 Hz.
The regio- and stereochemistry of the pyrazoline products 9, 10
and 11 were established from 2D NMR (NOESY, COSY, HSQC and
HMBC) measurements. NOESY experiments on cycloadducts 9 and
10 showedcross-peaks betweenthe signals of15-Hand16-H, which
proved cis ring junctions in the condensed pyrazolines 9 and 10.
The stereochemistry of spiropyrazolines 11 was established from
the NOE cross-peaks: 18-H3 and 15␣-H; 18-H3 and tolyl aromatic
Klingemann reaction [32–34]. The diazonium sulfate of 4-
methylaniline was coupled to ethyl 2-chloroacetoacetate. The
nitrilimine precursor 8 was formed in high yield in a short reaction
time and was purified by crystallization from methanol.
The 1,3-dipolar cycloadditions were carried out in dry toluene,
under both homogeneous and heterogeneous reaction conditions,
with triethylamine or silver(I) acetate as base (Scheme 2). Reac-
tions with triethylamine were carried out under reflux, but only
poor yields were obtained (Table 1). The silver salt proved more
effective: the reaction mixture was stirred in the dark at rt, under a
nitrogen atmosphere. Some starting enone was always recovered
and some tarry material was always formed under both condi-
tions.
ꢀ
proton 2 -H; 8␤-H and cis 16a-H; 15␤-H and trans 16a-H (cis and
trans referring to the orientation relative to the carbonyl group).
The NOE effects between the marked protons in rings C, D and E
are indicative of the S configuration of C-16 (Fig. 1). In the HMBC
spectra of spiro derivatives 11, the cross-peak between C-16a and
C N reflects the structure in which the carbon atom of the dipole
is connected to the ␤-carbon of the enone.
The reaction of 5 with 8 led to a regioisomeric mixture of 9 and
10. The main product was the pyrazoline 9 in which the N-terminus
of the 1,3-dipole is attached to the ␤-carbon of the enone 5. The
ratio of the products 9 and 10 was 2:1. The condensed pyrazolines
9
and 10 were formed stereoselectively with the same type of D/E
ring junction. The two regioisomers could be easily separated by
flash chromatography. The cycloaddition of 7 to 8 under hetero-
geneous conditions was completely regio- and diastereoselective,
yielding one spiropyrazoline, 11. The dipole and the dipolarophile
were joined in the same way as in the minor product of the previous
reaction (Table 2).
Neutral steroids are difficult to analyze by matrix-assisted laser
desorption/ionization (MALDI) TOF, and there have been only a few
literature reports on the analysis of derivatized steroids through the
MALDI TOF technique [35–37]. We reported earlier the successful
measurement of some heterocyclic steroids with a MALDI TOF mass
spectrometer without further chemical derivatization, using C70
fullerenes as a matrix. We now describe the results of the positive
mode detections of the synthesized non-heterocyclic and hetero-
cyclic compounds. The analytical method applied was similar to
that used in our previous work. We observed that non-heterocyclic
derivatives were also effectively detected: molecular or positively
charged quasimolecular ions appeared in all cases. In the spectra of
the 3-benzylic derivatives, the benzylic cation was always seen. The
regioisomeric counterparts of the heterocyclic cycloadducts exhib-
ited similar fragmentations. In the spectra of condensed pyrazolines
9a and 10a, molecular ions and fragment ions resulting from the
cleavage of the O-ethyl function from the ester group were seen.
Two additional characteristic peaks could be observed in the spec-
tra of 3-benzyl ethers 9b and 10b: that of the benzylic cation and
that of the fragment ion obtained by cleavage of the O-ethyl, benzyl
and tolyl groups and two oxygen atoms.
5. Conclusion
In summary, we have presented a simple and highly stereose-
lective method for the preparation of novel condensed pyrazolines
and spiropyrazolines of 13␣-estrone ethers. The reaction rates and
yields are strongly influenced by the structure of the starting enone
and the nature of the base used. Through substitution of the enone,
various derivatives can be synthesized. Known 13␣-estrone deriva-
tives with 17␣ substituents or a 17-keto group possess the usual ring
Fig. 1. NOE effects between the relevant protons in rings C, D and E.

E. Mernyák et al. / Steroids 74 (2009) 520–525
525
C chair conformation, whereas 17␤ substituents or double bonds
in ring D are responsible for the unusual, twist-boat conformation
in ring C [13–17]. Conformational analysis of the ␣,␤-unsaturated
ketones 5 and 7 prepared and the cycloadducts 9, 10 and 11 would
be of particular interest, because there are no literature indications
of the conformations of such compounds. Recent investigations
have shown that benzyl ester cleavage in pyrazoline, or benzyl
ether cleavage in pyrazol derivatives under hydrogen pressure in
methanol ortetrahydrofurane, in thepresence ofpalladium onchar-
coal catalyst can be successfully performed, while the pyrazoline
or pyrazol moiety remains unchanged [23,38]. Thus, the removal
of the benzyl protecting group under similar reaction conditions
in the compounds synthetized, is expected to lead to steroids of
potential pharmacological significance.
[16] Nambara T, Kudo T, Hosoda H, Titaka Y, Kikutani N. The crystal structure of 3-
methoxy-16-hydroxy-13␣-estra-1,3,5(10),15-tetraen-17-one
p-
bromobenzoate. Chem Pharm Bull 1975;23:320–5.
[
17] Nambara T, Kudo T. The synthesis and conformational analysis of ␣-bromo-16-
ketones of 13␣-estratriene. Chem Pharm Bull 1972;20:2156–62.
18] Mernyák E, Benedek G, Schneider Gy, Wölfling J. Stereoselective synthesis of
condensed aza-D-homo-estrone derivatives by 1,3-dipolar cycloaddition. Syn-
lett 2005:637–9.
[
[19] Mernyák E, Bikádi Zs, Hazai E, Márk L, Schneider Gy, Wölfling J. Steroidal ␦-
alkenyl oximes as ambident nucleophiles: electrophile induced formation of
oxazepane derivatives in the bis-estrone series. Lett Org Chem 2008;5:17–21.
[
20] Mernyák E, Schneider Gy, Herbst-Irmer R, Kubas M, Wölfling J. Synthesis
and stereochemical investigations of novel nitrogen-containing 13␣-estrone
derivatives. Steroids 2006;71:558–64.
[
21] Schaub RE, Van den Hende JH, Weiss MJ. The reaction of 16-hydroxymethylene-
1
7-keto steroids with semicarbazide and thiosemicarbazide to give 17␣-
1ꢀ(5ꢀ)
hydroxy[17␤,16␤-c]-ꢀ
-pyrazoline derivatives. 17␣-Hydroxy-3-methoxy-
ꢀ ꢀ
1 (5 )
ꢀ
2
-thiocarbamoylestra-1,3,5(10)-trieno[17␤,
16␤-c]-ꢀ
-pyrazoline,
a
potential nonfeminizing hypocholesterolemic agent. J Org Chem 1965;30:
234–40.
22] Vicker N, Lawrence H, Rithma R, Allan GM, Bubert C, Fischer DSM, et al. 17Beta-
hydroxysteroid dehydrogenase inhibitors. U.S. Pat Appl Publ 145 (2006).
2
Acknowledgement
[
We are grateful for the support of the Hungarian Scientific
Research Fund (OTKA grants D 048294 and K 72309).
[23] Fischer DS, Allan GM, Bubert C, Vicker N, Smith A, Tutill HJ, et al. E-ring modified
steroids as novel potent inhibitors of 17beta-hydroxysteroid dehydrogenase
type 1. J Med Chem 2005;48:5749–70.
[
24] Green B, Sheu K. Synthesis of steroidal D-ring fused pyrazolines: study of regio-
chemistry of addition. Steroids 1994;59:479–84.
References
[
25] Yaremenko FG, Khvat AV. A new one-pot synthesis of 17-oxo-13␣-steroids
of the androstane series from their 13␤-analogues. Mendeleev Commun
[
[
1] Rajesh D, Stenzell RA, Howard SP. Perillyl alcohol as a radio-/chemosensitizer
in malignant glioma. J Biol Chem 2003;278:35968–78.
2] Wagner JE, Huff JL, Rust WL, Kingsley K, Plopper GE. Perillyl alcohol inhibits
breast cell migration without affecting cell adhesion. J Biomed Biotechnol
1994;4:187–8.
[
26] Wölfling J, Mernyák E, Frank É, Falkay G, Márki Á, Minorics R, et al. Synthesis
and receptor-binding examinations of the normal and 13-epi-D-homoestrones
and their 3-methyl ethers. Steroids 2003;68:277–88.
2
002;2:136–40.
[
27] Butenandt A, Wolff A, Karlson P. Lumiestrone. Ber Dtsch Chem Ges
[
3] Tatman D, Mo H. Volatile isoprenoid constituents of fruits, vegetables and herbs
cumulatively suppress the proliferation of murine B16 melanoma and human
HL-60 leukemia cells. Cancer Lett 2002;175:129–39.
1941;74:1308–13.
[28] Greene TW, Wuts PGM. Protective groups in organic synthesis. 3rd ed. New
York: John Wiley and Sons; 1999.
29] Schneider Gy. Personal communication.
30] Messinger J, Thole HH, Husen B, Van Steen BJ, Schneider Gy, Hulshof JBE, et al.
Preparation of novel 17␤-hydroxysteroid dehydrogenase type I inhibitors. PCT
Int Appl 2005:190.
[
[
4] Elguero J, Goya P, Najerovic N, Silva AMS. Targets Heterocycl Syst 2002;6:52–98.
5] Caramella P, Grünanger P. In: Padwa A, editor. 1,3-Dipolar cycloaddition chem-
istry, vol. 1. New York: Wiley; 1984. p. 291–392.
[
[
[
[
[
[
6] Molteni G. Silver(I) salts as useful reagents in pyrazole synthesis. Arkivoc
2
007;ii:224–46.
[
31] Schneider Gy, Vincze I, Hackler L, Dombi Gy. A convenient method for the
7] De Benasutti L, Garanti L, Molteni G. Oxygenated monoterpenes as dipo-
larophiles for nitrilimine cycloadditions. Tetrahedron 2004;60:4627–33.
8] Del Buttero P, Molteni G, Pilati T. Nitrilimine cycloaddition onto 2-azetidinones
bearing alkenyl dipolarophile(s). Tetrahedron 2005;61:2413–9.
9] Molteni G, Del Buttero P. A bicyclo[3.1.1]heptano[4,3-c]pyrazole derived chi-
ral auxiliary for dipolar cycloadditions. Tetrahedron: Asymm 2005;16:1983–
formation of 16-methylene-17-ketosteroids. Synthesis 1983;8:665–9.
32] Yao HC, Resnick P. Azo-hydrazone conversion. I. The Japp–Klingemann reaction.
J Am Chem Soc 1962;84:3514–7.
33] Barrett GC, El-abadelah MM, Hargreaves MK. Cleavage of 2-acetyl-2-
phenylazopropionanilide and related compounds by boron trifluoride. New
Japp–Klingemann reactions. J Chem Soc (C) 1970:1986–9.
[
[
7
.
[
34] El-abadelah MM, Hussein AQ, Kamal MR, Al-Adhami KH. Heterocycles
[
10] Kerbal A, Tshiamala K, Vebrel J, Laude B, Mercier MF. Reaction of diarylnitrilim-
ines with substituted 2-arylidene-1-tetralones. Effect of conformation on the
diastereochemistry of the reaction. Bull Soc Chim Belg 1991;100:159–68.
1
from nitrile imines. Part I . 1,2,3,4-tetrahydro-1,2,4,5-tetrazines. Heterocycles
1988;27:917–24.
[
35] Khan MA, Wang Y, Heidelberger S, Alvelius G, Liu S, Sjövall J, et al. Analysis of
derivatised steroids by matrix-assisted laser desorption/ionisation and post-
source decay mass spectrometry. Steroids 2006;71:42–53.
[11] Jedlovska E, Levai A, Toth G, Balazs B, Fisera L. Synthesis of spiropyrazolines via
1,3-dipolar cycloaddition of nitrilimines. J Heterocycl Chem 1999;36:1087–90.
[12] Mishriky N, Girgis AS, Ibrahim YA. Regioselective synthesis of spiro[naph-
ꢀ
[36] Griffiths WJ, Alvelius G, Sjovall J. Derivatisation for the characterisation of neu-
tral oxosteroids by electrospray and matrix-assisted laser desorption/ionisation
tandem mass spectrometry: the Girard P derivative. Rapid Commun Mass Spec-
trom 2003;17:924–35.
thalene-2(1H),3 -[3H]pyrazol]-1-ones utilizing 1,3-dipolar cycloaddition of
nitrilimines. J Chem Res S 2000;1:101–11.
[13] Schönecker B, Lange C, Kötteritzsch M, Günther W, Weston J, Anders E, et al.
Conformational design for 13alpha-steroids. J Org Chem 2000;65:5487–97.
[
37] Wang Y, Hornshaw M, Alvelius G, Bodin K, Liu S, Sjovall J, et al. Matrix-
assisted laser desorption/ionization high-energy collision-induced dissociation
of steroids: analysis of oxysterols in rat brain. Anal Chem 2006;78:164–73.
38] Jun MA, Park WS, Kang SK, Kim KY, Kim KR, Rhee SD, et al. Synthesis and biologi-
cal evaluation of pyrazoline analogues with beta-amino acyl group as dipeptidyl
peptidase IV inhibitors. Eur J Med Chem 2008;43:1889–902.
[
14] Altona C, Geise HJ, Romers C. Conformation of non-aromatic ring compounds—
XXV geometry and conformation of ring D in some steroids from X-ray structure
determinations. Tetrahedron 1968;24:13–32.
[
[15] Mernyák E, Schönecker B, Lange C, Kötteritzsch M, Görls H, Wölfling J. Schneider
Gy addition reactions at the 16(17) double bond of 3-methoxy-13␣-estra-
1,3,5(10),16-tetraene. Steroids 2003;68:289–95.