Synthesis of 17β-isoxazolyl steroids and spiro[steroid-17,2′-furanone]s

Article abstract of DOI:10.1135/cccc19981564

Synthesis of 17β-isoxazolyl steroids and their transformations into the corresponding spiro[steroid-17,2′-furanone]s are described. The reaction sequence consists of the 1,3-dipolar cycloaddition of a nitrile oxide to mestrenol, dehydration, epoxidation or dihydroxylation, cleavage of the isoxazole moiety and cyclization of intermediate enamino ketones.

Full text of DOI:10.1135/cccc19981564

1564
Baranovsky, Groen, de Groot, Litvinovskaya, Khripach:
SYNTHESIS OF 17β-ISOXAZOLYL STEROIDS AND SPIRO[STEROID-
17,2′-FURANONE]S
a
b
c
Alexander V. BARANOVSKY , Marinus B. GROEN , Aede de GROOT ,
Raissa P. LITVINOVSKAYAa1 and Vladimir A. KHRIPACH
*
a2,
a Institute of Bioorganic Chemistry, National Academy of Sciences, Zhodinskaya str. 5/2,
220141 Minsk, Belarus; e-mail: 1 litvin@ns.iboch.ac.by, 2 steroids@ns.iboch.ac.by
b Scientific Development Group, N. V. Organon, P.O. Box 20, 5340 BH Oss, The Netherlands
c Laboratory of Organic Chemistry, Agricultural University, Dreijenplein 8, 6703 HB Wageningen,
The Netherlands; e-mail: aede.degroot@sg1.oc.wau.nl
Received May 5, 1998
Accepted July 3, 1998
This paper is dedicated to Dr Jan Fajkos on the occasion of his 1998 jubilee and his significant
contribution to chemistry of natural products.
Synthesis of 17β-isoxazolyl steroids and their transformations into the corresponding spiro[steroid-
17,2′-furanone]s are described. The reaction sequence consists of the 1,3-dipolar cycloaddition of a
nitrile oxide to mestrenol, dehydration, epoxidation or dihydroxylation, cleavage of the isoxazole
moiety and cyclization of intermediate enamino ketones.
Key words: Steroids; Isoxazoles; Spiro[steroid-17,2′-furanone]s; Steroidal spirofuranones; Nitrile oxides.
At present, only a few 17-isoxazolyl steroids are known1–4 and there are no data in the
literature on 17α-hydroxy-17-isoxazolyl steroids. To our best knowledge, only one at-
tempt was undertaken to open the heterocycle ring in 17-isoxazolyl steroids5. We de-
scribe here a new approach to 17β-isoxazolyl steroids and the cleavage of their
heterocyclic moiety to the corresponding spirofuranones. A number of (17R)- and
(17S)- steroidal spirofuranones can be found in literature, but they were prepared via
intramolecular condensation of derivatives of 17-hydroxypregnenolone6–8 or mercury-
catalyzed cyclization of 17-diyne steroids9.
* The author to whom correspondence should be addressed.
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Synthesis of 17β-Isoxazolyl Steroids
1565
EXPERIMENTAL
Melting points are uncorrected. Infrared spectra (wavenumbers in cm–1) were recorded on a UR-20
spectrometer and only characteristic absorptions are reported. 1H NMR spectra were measured in
deuteriochloroform solutions with residual CHCl3 as internal standard on Bruker AC-200, operating
at 200 MHz. 13C NMR spectra were recorded on Bruker AC-200 operating at 50 MHz. Chemical
shifts are reported in ppm (δ-scale) and coupling constants (J) are in Hz. MS data were determined
at 70 eV on a Shimadzu QP-5000 mass spectrometer. The ratios m/z are indicated for the significant
peaks. Optical rotations were recorded in chloroform on a JASCO-20 polarimeter at 20 °C and [α]D
values are given in 10–1 deg cm2 g–1. Column chromatography was performed on Merck silica gel 60.
All reactions were carried out under a positive pressure of nitrogen. Reactions were monitored by
TLC silica gel plates (Merk Kieselgel 60 F-254) and visualization of the compounds was accom-
plished by UV light, and/or spraying with an acidic cerium ammonium sulfate solution.
3-Methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-trien-17β-ol (2)
To a stirred suspension of N-chlorosuccinimide (9.35 g, 70 mmol) in CHCl3 (60 ml), pyridine (0.1 ml)
and acetaldehyde oxime (4.54 g, 77 mmol) were added. The mixture was stirred for 15 min until it
became clear. A solution of mestrenol (1) (6.2 g, 20 mmol) in CHCl3 (70 ml) was added to the mix-
ture. After stirring of the resulting mixture for 5 min a solution of Et3N (8.24 g, 77 mmol) in CHCl3
(30 ml) was added dropwise during 10 h. The mixture was washed with water and dried over
Na2SO4. The solvent was evaporated. The residue was chromatographed on silica gel (toluene–AcOEt
20 : 90) to afford 2 (6.53 g, 89%), m.p. 157–159°C (MeOH–CH2Cl2) (literature1 gives 155–157 °C).
1H NMR spectrum: 1.03 s, 3 H (3 × H-18); 2.32 s, 3 H (Me-3′); 3.78 s, 3 H (OMe); 6.03 s, 1 H
(H-4′); 6.62 d, 1 H, J = 2 (H-4); 6.70 dd, 1 H, J1 = 8, J2 = 2 (H-2); 7.16 d, 1 H, J = 8 (H-1). IR
spectrum (KBr): 3 410, 2 935, 1 605, 1 590.
3-Methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10),16-tetraene (3)
To a stirred solution of 2 (336 mg, 0.92 mmol) and pyridine (0.3 ml, 3.68 mmol) in THF (20 ml),
thionyl chloride (0.33 ml, 1.84 mmol) in THF (5 ml) was added at –50 °C. The temperature was
allowed to rise to ambient for 1 h and 5% NaHCO3 was added. The organic phase was extracted with
ethyl acetate, washed with water, brine, dried (Na2SO4) and concentrated. The obtained oil was chro-
matographed on silica gel (toluene–AcOEt 95 : 5) to give 3 (270 mg, 84%), m.p. 141–143 °C
1
(MeOH–CH2Cl2), [α]D –65 (c 1.10). H NMR spectrum: 1.01 s, 3 H (3 × H-18); 2.33 s, 3 H (Me-3′);
2.95 m, 2 H (2 × H-6); 3.79 s, 3 H (OMe); 6.07 s, 1 H (H-4′); 6.43 brs, 1 H (H-16); 6.68 d, 1 H, J =
2.6 (H-4); 6.73 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.22 d, 1 H, J = 8.8 (H-1). 13C NMR spectrum: 12.1 q,
17.1 q, 27.2 t, 28.4 t, 30.3 t, 32.4 t, 35.8 t, 37.8 d, 44.8 d, 47.6 s, 55.9 q, 56.6 d, 100.9 d, 112.1 d,
114.5 d, 126.7 d, 133.1 d, 133.2 s, 138.5 s, 142.6 s, 158.2 s, 160.4 s, 167.2 s. IR spectrum (KBr): 1 620,
1 605, 1 570, 1 550, 1500. Mass spectrum: 349 [M+], 334.
17β-(3-Amino-1-oxobut-2-en-1-yl)-3-methoxyestra-1,3,5(10)-triene (4)
To a stirred solution of nickel chloride hydrate (226 mg, 1 mmol) in methanol (5 ml), compound 3
(175 mg, 0.5 mmol) in THF (7 ml) was added. The resulting mixture was cooled to 0 °C and sodium
borohydride (76 mg, 2 mmol) was added portionwise. Aqueous ammonia was added in 10 min and
the solution was evaporated to a small volume. The organic phase was extracted with ethyl acetate,
washed with water and brine, dried (Na2SO4) and concentrated. The obtained oil was crystallized to
1
give enaminoketone 4 (94 mg, 53%), m.p. 182–184 °C (MeOH), [α]D +106 (c 0.48). H NMR spec-
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

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Baranovsky, Groen, de Groot, Litvinovskaya, Khripach:
trum: 0.62 s, 3 H (3 × H-18); 1.91 s, 3 H (H-4′); 2.88 m, 2 H (2 x H-6); 3.78 s, 3 H (OMe); 4.90 brs,
1 H (NH); 5.03 s, 1 H (H-2′); 6.62 d, 1 H, J = 2 (H-4); 6.70 dd, 1 H, J1 = 8.5, J2 = 2 (H-2); 7.16 d,
1 H, J = 8.5 (H-1); 9.78 brs, 1 H (NH). 13C NMR spectrum: 13.4 q, 22.6 q, 22.7 t, 24.3 t, 26.7 t,
27.8 t, 29.9 t, 38.9 t, 38.9 d, 43.9 d, 44.8 s, 55.2 q, 55.7 d, 62.2 d, 100.0 d, 111.5 d, 113.7 d, 126.3 d,
132.8 s, 138.1 s, 157.4 s, 159.8 s, 199.1 s. IR spectrum (KBr): 3 400, 2 940, 1 610, 1 520. Mass
spectrum: 353 [M+], 310, 268.
Cleavage of Isoxazole 3 with Mo(CO)6
A solution of 3 (524 mg, 1.5 mmol) and hexacarbonyl molybdenum (436 mg, 1.65 mmol) in aceto-
nitrile (35 ml) and water (0.6 ml) was refluxed for 1 h. The solution was then cooled and the solvent
was evaporated. The brown residue was dissolved in chloroform (5 ml) and silica gel was added.
Then the solvent was evaporated and the residue absorbed on silica gel, was chromatographed on a
silica gel column (toluene–AcOEt 95 : 5).
17-(3-Hydroxy-1-oxobut-2-en-1-yl)-3-methoxyestra-1,3,5(10),16-tetraene (6) (168 mg, 32%), m.p.
120–121 °C (MeOH). 1H NMR spectrum: 0.92 and 1.00 s, 3 H (3 × H-18); 2.12 and 2.25 s, 3 H
(H-4′); 2.88 m, 2 H (2 × H-16); 3.78 s, 3 H (OMe); 5.87 s, 1 H (H-2′); 6.64 m, 2 H (H-4 and H-16);
6.70 dd, 1 H, J1 = 8.5, J2 = 2 (H-2); 7.16 d, 1 H, J = 8.5 (H-1); 15.66 brs, 1 H (OH). IR spectrum
(KBr): 1 730, 1 660, 1 610, 1 600, 1 510. 13C NMR spectrum: 15.9 and 16.3 q, 25.6 and 30.3 q, 26.4
and 26.5 t, 27.7 t, 29.6 t, 31.9 and 32.3 t, 34.7 and 35.1 t, 37.0 d, 44.1 d, 46.7 s, 55.1 q, 55.5 and
55.9 d, 97.7 d, 111.4 d, 113.9 d, 126.1 d, 132.6 s, 137.8 s, 140.1 d, 151.9 s, 157.5 s, 182.0 s, 192.2 s.
Mass spectrum: 352 [M+], 337.
17-(3-Amino-1-oxobut-2-en-1-yl)-3-methoxyestra-1,3,5(10),16-tetraene (5) (299 mg, 57%), m.p.
200–202 °C (MeOH), [α]D +66 (c 0.56). 1H NMR spectrum: 1.02 s, 3 H (3 × H-18); 1.91 s, 3 H
(H-4′); 2.88 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 5.00 brs, 1 H (NH); 5.38 s, 1 H (H-2′); 6.43 brs, 1 H
(H-16); 6.62 d, 1 H, J = 2 (H-4); 6.70 dd, 1 H, J1 = 8.5, J2 = 2 (H-2); 7.16 d, 1 H, J = 8.5 (H-1);
9.80 br s, 1 H (NH). IR spectrum (KBr): 3 430, 1 610, 1 520, 1 510.
16α,17α-Epoxy-3-methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-triene (7)
A solution of 3 (450 mg, 1.29 mmol), 3-chloroperoxy benzoic acid (267 mg, 1.55 mmol), and
NaHCO3 (236 mg, 2.8 mmol) in dichloromethane (50 ml) was stirred at room temperature. After 4 h,
it was treated with a solution of Na2S2O3. The organic phase was diluted with dichloromethane,
washed with saturated NaHCO3, brine, dried (Na2SO4) and concentrated. The obtained residue was
chromatographed on silica gel (toluene–AcOEt 95 : 5) to give the starting material 3 (113 mg) fol-
1
lowed by epoxide 7 (269 mg, 57 %), m.p. 179–181 °C (MeOH–CH2Cl2), [α]D +96 (c 1.59). H NMR
spectrum: 0.92 s, 3 H (3 × H-18); 2.29 s, 3 H (Me-3′); 2.88 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe);
3.88 s, 1 H (H-16β); 6.16 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6
(H-2); 7.20 d, 1 H, J = 8.8 (H-1). 13C NMR spectrum: 12.1 q, 16.3 q, 26.7 t, 27.7 t, 28.2 t, 30.3 t, 32.4 t,
37.5 d, 43.5 s, 44.7 d, 45.1 d, 55.9 q, 61.7 d, 64.4 s, 105.2 d, 112.2 d, 114.6 d, 126.7 d, 132.9 s,
138.3 s, 158.3 s, 160.3 s, 168.5 s. IR spectrum (KBr): 1 600, 1 500, 1 235. Mass spectrum: 365 [M+],
322.
3-Methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)trien-16α,17α-diol (8)
A mixture of 3 (1.222 g, 3.5 mmol), OsO4 (79 mg, 0.31 mmol), and 4-methylmorpholine N-oxide
(747 mg, 5.6 mmol) in acetone (50 ml) and water (2.5 ml) was stirred at room temperature for 18 h.
Then the solvent was evaporated and the residue was dissolved in ethyl acetate. The organic phase
was washed with water, brine, dried (Na2SO4) and concentrated. Crystallization of the obtained ma-
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Synthesis of 17β-Isoxazolyl Steroids
1567
terial from aqueous methanol and chromatography on silica gel of the mother liquor gave diol 8
1
(1.099 g, 82%), m.p. 191–192 °C (EtOAc). H NMR spectrum: 0.66 s, 3 H (3 × H-18); 2.21 s, 3 H
(Me-3′); 2.86 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 5.08 dd, 1 H, J1 = 10, J2 = 3 (H-16 β); 6.10 s,
1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8
(H-1). IR spectrum (KBr): 3 590; 1 600, 1 500. Mass spectrum: 383 [M+], 365.
17α-Hydroxy-3-methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-trien-16α-yl Acetate (9)
A mixture of diol 8 (958 mg, 2.5 mmol) and Ac2O (0.4 ml, 3.9 mmol) in pyridine (8 ml) reacted for
15 h at 20 °C. Then it was poured into ice water and extracted with ethyl acetate. The organic phase
was washed with 1 M HCl, saturated NaHCO3, brine, dried (Na2SO4) and concentrated. The obtained
oil was purified on a short silica gel column (toluene–AcOEt 80 : 20) to give acetate 9 (1.02 g, 96%),
1
m.p. 215–217 °C (EtOAc), [α]D –12 (c 1.34). H NMR spectrum: 0.68 s, 3 H (3 × H-18); 2.10 s, 3 H,
(OAc); 2.30 s, 3 H (Me-3′); 2.86 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 5.81 dd, 1 H, J1 = 10, J2 = 3
(H-16β); 6.10 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d,
1 H, J = 8.8 (H-1). 13C NMR spectrum: 11.5 q, 15.5 q, 21.1 q, 25.6 t, 27.8 t, 29.5 t, 29.8 t, 32.1 t,
38.7 d, 43.5 d, 47.8 d, 49.0 s, 55.2 q, 81.2 s, 103.4 d, 111.5 d, 113.6 d, 126.2 d, 132.3 s, 137.8 s,
157.5 s, 159.6 s, 169.6 s, 172.7 s. IR spectrum (KBr): 3 450, 1 730, 1 600, 1 500, 1 250. Mass
spectrum: 425 [M+], 365.
17α-Hydroxy-3-methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-trien-16α-yl Benzoate (10)
A mixture of diol 8 (502 mg, 1.31 mmol), benzoyl chloride (0.38 ml, 2.62 mmol) and 4-dimethylami-
nopyridine (425 mg, 3.93 mmol) in dichloromethane (15 ml) reacted for 48 h at room temperature.
The precipitate was filtered off, and the mother liquor was washed with water, dried (Na2SO4),
evaporated and the residue was crystallized from methanol to give the second crop. Both crops were
combined to afford benzoate 10 (531 mg, 83%), m.p. 262–264 °C (MeOH), [α]D –27 (c 0.64). 1H NMR
spectrum: 0.77 s, 3 H (3 × H-18); 2.30 s, 3 H (Me-3′); 2.86 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe);
6.10 dd, 1 H, J1 = 10, J2 = 3 (H-16β); 6.15 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8,
J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8 (H-1); 7.42 and 7.55 and 8.00 m, 5 H (Ph). IR spectrum (KBr):
3 540, 1 710, 1 600, 1 500, 1 250.
17α-Hydroxy-3-methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-trien-16-one (11) and
3-Methoxy-17α-(methylsulfanyl)methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-trien-16-one (12).
To a stirred solution of oxalyl chloride (127 mg, 1.0 mmol) in dichloromethane (3 ml) at –70 °C,
dimethyl sulfoxide (117 mg, 1.5 mmol) in dichloromethane (3 ml) was added dropwise. After stirring
for 20 min, diol 8 (192 mg, 0.5 mmol) in dichloromethane (5 ml) was added and stirring was conti-
nued for 20 min. Subsequently, triethylamine (505 mg, 5.0 mmol) was added, the temperature was
risen slowly to 20 °C and stirring was continued for another hour. Then the mixture was poured in
saturated NaHCO3 and extracted with chloroform. The extract was washed with brine, dried
(Na2SO4) and evaporated. The residue was chromatographed on silica gel (toluene–AcOEt 1 : 1) to
give following compounds.
Ether 12 as oil (46 mg, 21%). 1H NMR spectrum: 0.62 s, 3 H (3 × H-18); 2.14 s, 3 H (CH3S);
2.33 s, 3 H (Me-3′); 2.90 m, 2 H (H-6); 3.80 s, 3 H (OMe); 4.38 d, 2 H, J = 3 (OCH2S); 6.42 s, 1 H
(H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.18 s, 1 H, J = 8.8 (H-1).
IR spectrum (KBr): 1 740, 1 600, 1 500, 1 040. Mass spectrum: 441 [M+], 394, 380.
1
Ketone 11 (120 mg, 63%), m.p. 221–222 °C (benzene–EtOAc), [α]D –138 (c 0.84). H NMR spectrum:
0.66 s, 3 H (3 × H-18); 2.29 s, 3 H (Me-3′); 2.90 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 6.25 s, 1 H
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Baranovsky, Groen, de Groot, Litvinovskaya, Khripach:
(H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.18 d, 1 H, J = 8.8 (H-1).
13C NMR spectrum (C5D5N): 11.2 q, 15.6 q, 26.0 t, 28.5 t, 30.0 t, 30.0 t, 37.1 t, 38.4 d, 43.9 d, 44.2 d,
47.2 s, 55.2 q, 80.4 s, 105.2 s, 112.2 d, 114.2 d, 126.7 d, 132.6, 138.0 s, 158.3 s, 159.2 s, 171.3 s,
212.4 s. IR spectrum (KBr): 3 450, 1 740, 1 605, 1 500. Mass spectrum: 381 [M+], 227.
17α-Hydroxy-3-methoxy-17-(3-methylisoxazol-5-yl)estra-1,3,5(10)-trien-16β-yl Acetate (13)
To a stirred solution of ketone 11 (70 mg, 0.18 mmol) in THF (7 ml) lithium tri-tert-butoxyaluminium-
hydride (127 mg, 0.5 mmol) was added portionwise. The resulting solution was stirred at room tem-
perature for 1 h and water (0.1 ml) was added. The slurry was filtered through a plug with Na2SO4
and the precipitate was washed several times with chloroform. The filtrate and the washings were
combined and evaporated. The residue was chromatographed on silica gel (toluene–AcOEt 80 : 20)
to give diol (60 mg, 87%), which was acetylated to acetate 13 as described above, m.p. 107–110 °C
1
(MeOH–water), [α]D +22.5 (c 1.02). H NMR spectrum: 0.88 s, 3 H (3 × H-18); 2.08 s, 3 H, (OAc);
2.32 s, 3 H (Me-3′); 2.88 m, 2 H (2 × H-6); 3.80 s, 3 H (OMe); 5.20 dd, 1 H, J1 = 8, J2 = 6 (H-16α);
6.12 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J =
8.8 (H-1). 13C NMR spectrum: 11.4 q, 14.9 q, 21.1 q, 25.7 t, 27.8 t, 29.7 t, 30.4 t, 32.8 t, 38.6 d, 43.3 d,
46.3 d, 48.5 s, 55.2 q, 82.0 d, 83.0 s, 103.8 d, 111.5 d, 113.8 d, 126.3 d, 132.3 s, 137.8 s, 157.5 s,
159.2 s, 170.7 s, 172.2 s. IR spectrum (KBr): 3 450, 1 730, 1 600, 1 500, 1 250. Mass spectrum: 425
[M+], 365.
Cleavage of Epoxide 7
To a stirred solution of epoxide 7 (114 mg, 0.31 mmol) in THF (10 ml), perchloric acid (46%, 0.6 ml)
was added, and the resulting mixture was stirred for 20 h at room temperature. Saturated NaHCO3
was added and the mixture was evaporated to 10% of its original volume. The organic material was
extracted with chloroform and the organic phase was washed with brine, dried (Na2SO4) and evap-
orated. The residue was chromatographed on silica gel (toluene–AcOEt 70 : 30) to give two isoxa-
zoles (96 mg, 85%).
3-Methoxy-17-methyl-17α-(3-methylisoxazol-5-yl)-18-nor-8α,13α,14β-estra-1,3,5(10),9(11)-tetraen-16α-ol (15),
1
m.p. 176–179 °C (EtOAc). H NMR spectrum: 1.46 s, 3 H (Me-17); 2.26 s, 3 H (Me-3′); 2.85 m, 2 H
(H-6); 3.78 s, 3 H (OMe); 4.15 m, 1 H (H-16β); 5.71 m, 1 H (H-11); 5.98 s, 1 H (H-4′); 6.63 d, 1 H,
J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8 (H-1).
3-Methoxy-17-methyl-17α-(3-methylisoxazol-5-yl)-18-norestra-1,3,5(10),13-tetraen-16α-ol
(14),
1
m.p. 188–190 °C (MeOH–CH2Cl2), [α]D –11 (c 1.09). H NMR spectrum: 1.46 s, 3 H (Me-17); 2.26 s,
3 H (Me-3′); 2.95 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 4.27 t, 1 H, J = 7 (H-16β); 5.88 s, 1 H
(H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8 (H-1).
IR spectrum (KBr): 3 350, 1 600, 1 585, 1 500. Mass spectrum: 365 [M+].
3-Methoxy-17-methyl-17α-(3-methylisoxazol-5-yl)-18-norestra-1,3,5(10),13-tetraen-16α-yl Acetate (16)
Title compound was prepared from 14 by the above described procedure in 83% yield, m.p. 119–120 °C
1
(aqueous MeOH), [α]D +12 (c 0.26). H NMR spectrum: 1.53 s, 3 H (3 × H-18); 1.94 s, 3 H (OAc);
2.29 s, 3 H (Me-3′); 2.87 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 5.30 t, 1 H, J = 7 (H-16β); 5.83 s,
1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8
(H-1). 13C NMR spectrum: 11.6 q, 20.9 q, 21.5 q, 22.4 t, 26.3 t, 26.8 t, 29.9 t, 36.7 t, 39.6 d, 40.9 d,
53.1 s, 55.2 q, 80.7 d, 102.8 d, 111.4 d, 114.0 d, 125.8 d, 132.1 s, 136.5 s, 137.6 s, 138.0 s, 157.7 s,
159.4 s, 170.9 s, 173.7 s. IR spectrum (KBr): 1 740, 1 600, 1 500, 1 270, 1050. Mass spectrum: 407
[M+], 347.
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Synthesis of 17β-Isoxazolyl Steroids
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3-Methoxy-17-methyl-17α-(3-methylisoxazol-5-yl)-18-nor-8α,13α,14β-estra-1,3,5(10),9(11)-tetraen-
16α-yl Acetate (17)
Title compound was prepared from 15 by the above described procedure in 84% yield, m.p. 157–159 °C
1
(MeOH–CH2Cl2). H NMR spectrum: 1.52 s, 3 H (Me-17); 1.87 s, 3 H (OAc); 2.28 s, 3 H (Me-3′);
2.85 obsc m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 5.18 dd, 1 H, J1 = 6, J2 = 3 (H-16β); 5.71 m, 1 H
(H-11); 5.95 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d,
1 H, J = 8.8 (H-1). 13C NMR spectrum: 11.5 q, 20.9 q, 24.9 q, 27.8 t, 29.9 t, 32.7 t, 34.8 t, 39.7 d,
42.9 d, 45.1 d, 49.9 s, 55.2 q, 81.0 d, 102.6 d, 112.1 d, 113.4 d, 120.8 d, 127.5 d, 131.9 s, 137.7 s,
146.1 s, 157.4 s, 159.2 s, 170.3 s, 174.9 s. IR spectrum (KBr): 1 740, 1 600, 1 500, 1 270, 1 050.
Mass spectrum: 407 [M+], 346.
17β-(3-Amino-1-oxobut-2-en-1-yl)-16α,17α-epoxy-3-methoxyestra-1,3,5(10)-triene (18)
A solution of compound 7 (435 mg, 1.19 mmol), Mo(CO)6 (333 mg, 1.26 mmol) and water (0.5 ml)
in acetonitrile (30 ml) was refluxed for 1 h. The solution then was cooled and the solvent was evap-
orated. The brown residue was dissolved in chloroform (5 ml) and silica gel was added. Then the
solvent was evaporated in vacuo and the residue absorbed on silica gel, was purified on a silica gel
column (toluene–AcOEt 90 : 10) to give enamino ketone 18 (301 mg, 69%), m.p. 222–224 °C
1
(MeOH–CH2Cl2), [α]D + 109 (c 0.51). H NMR spectrum: 1.11 s, 3 H (3 × H-18); 1.95 s, 3 H (H-4′);
2.84 m, 2 H (2 × H-6); 3.62 s, 1 H (H-16β); 3.78 s, 3 H (OMe); 5.08 brs, 2 H (H-2′ and NH); 6.63 d,
1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8 (H-1); 9.82 brs, 1 H
(NH). IR spectrum (KBr): 3 280, 1 610, 1 550.
Spiro [((17R)-16β-bromo-3-methoxyestra-1,3,5(10)-triene)-17,2′-(5′-methylfuran-3′(2′H)-one)] (19)
To a stirred solution of compound 18 (130 mg, 0.35 mmol) in THF (5 ml), HBr (48%, 0.2 ml) was
added at 0 °C. In 1 h the temperature was allowed to rise to ambient and stirring was continued for
24 h. The solution was diluted with ethyl acetate, washed with saturated NaHCO3, brine, dried
(Na2SO4) and concentrated. The obtained material was purified on a silica gel column (toluene–
AcOEt 90 : 10) to give product 19 (136 mg, 90%), m.p. 177–180 °C (MeOH–CH2Cl2), [α]D +43 (c 0.56).
1H NMR spectrum: 1.21 s, 3 H (3 × H-18); 2.26 s, 3 H (Me-5′); 2.86 m, 2 H (2 × H-6); 3.78 s, 3 H
(OMe); 4.32 t, 1 H, J = 7 (H-16α); 5.45 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 =
8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J = 8.8 (H-1). 13C NMR spectrum: 14.0 q, 17.1 q, 26.1 t, 28.5 t,
30.3 t, 31.3 t, 38.7 d, 40.0 t, 43.9 d, 49.0 d, 50.2 s, 51.2 d, 55.9 q, 97.2 s, 106.6 d, 112.3 d, 114.4 d,
126.9 d, 132.4 s, 138.3 s, 158.3 s, 187.2 s, 200.0 s. IR spectrum (KBr): 1 700, 1 620, 1 510. Mass
spectrum: 430 and 432 [M+], 351, 253, 227.
Spiro[((17R)-3-methoxyestra-1,3,5(10)-triene)-17,2′-(5′-methylfuran-3′(2′H)-one)] (20)
A solution of compound 19 (64 mg, 0.15 mmol), tributylstannane (87 mg, 0.3 mmol) and AIBN (98 mg,
0.6 mmol) in benzene (2 ml) was refluxed for 1 h. The solution then was cooled and the solvent was
evaporated. The obtained material was purified on a silica gel column (toluene–AcOEt 90 : 10) to
give product 20 (50 mg, 95%), m.p. 169–170 °C (MeOH–CH2Cl2), [α]D +139 (c 1.11). 1H NMR
spectrum: 0.96 s, 3 H (3 × H-18); 2.25 s, 3 H (Me-5′); 2.88 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe);
5.42 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.20 d, 1 H, J =
8.8 (H-1). 13C NMR spectrum: 13.6 q, 17.3 q, 24.9 t, 26.6 t, 28.5 t, 30.5 t, 30.8 t, 33.8 t, 39.3 d, 44.0 d,
50.5 s, 52.4 d, 55.9 q, 101.4 s, 106.0 d, 112.2 d, 114.4 d, 126.9 d, 132.9 s, 138.5 s, 158.1 s, 187.7 s,
204.8 s. IR spectrum (KBr): 1 690, 1 610, 1 510. Mass spectrum: 352 [M+].
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1570
Baranovsky, Groen, de Groot, Litvinovskaya, Khripach:
Spiro[((17S)-16α-acetoxy-3-methoxyestra-1,3,5(10)-triene)-17,2′-(5′-methylfuran-3′(2′H)-one)] (21)
To a stirred solution of nickel chloride hydrate (135 mg, 0.6 mmol) in methanol (5 ml), compound 9
(107 mg, 0.25 mmol) in THF (10 ml) was added. The resulting mixture was cooled to 0 °C and
sodium borohydride (70 mg, 1.8 mmol) was added portionwise. Aqueous ammonia was added in 10 min
and the solution was evaporated to a small volume. The organic phase was extracted with ethyl acetate,
washed with water and brine, dried (Na2SO4) and concentrated. The obtained oil was dissolved in
ethanol (7 ml) contained HCl (0.1 ml) and the solution was stirred at room temperature. After 24 h,
the solvent was evaporated to 10% of its original volume and silica gel was added. Then the rest of
solvent was evaporated in vacuo and the residue absorbed on silica gel, was purified on a silica gel
column (toluene–AcOEt 80 : 20) to give acetate 21 (72 mg, 70%), m.p. 187–190 °C (MeOH–
1
CH2Cl2), [α]D +87 (c 1.0). H NMR spectrum: 1.04 s, 3 H (3 × H-18); 2.00 s, 3 H (OAc); 2.29 s, 3
H (Me-5′); 2.86 m, 2 H (2 × H-6); 3.78 s, 3 H (OMe); 5.44 s, 1 H (H-4′); 5.48 obsc m, 1 H (H-16β);
6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.18 d, 1 H, J = 8.8 (H-1). IR
spectrum (KBr): 1 735. 1 685, 1 600, 1 500, 1 250. Mass spectrum: 410 [M+], 350.
Spiro[((17S)-16α-benzoyloxy-3-methoxyestra-1,3,5(10)-triene)-17,2′-(5′-methylfuran-3′(2′H)-one)] (22)
A solution of compound 10 (325 mg, 0.67 mmol), Mo(CO)6 (195 mg, 0.74 mmol) and water (0.8 ml)
in acetonitrile (60 ml) was refluxed for 1 h. The solution was cooled and concentrated hydrochloric
acid (0.3 ml) was added. A resulted mixture was refluxed for another hour, cooled and the solvent
was evaporated. The brown residue was dissolved in chloroform (5 ml) and silica gel was added.
Then the solvent was evaporated in vacuo and the residue adsorbed on silica gel was purified on a
silica gel column to give benzoate 22 (288 mg, 91%), m.p. 182–183 °C (MeOH–CH2Cl2), [α]D +54
(c 0.99). 1H NMR spectrum: 1.13 s, 3 H (3 × H-18); 2.29 s, 3 H (Me-5′); 2.86 m, 2 H (2 × H-6);
3.78 s, 3 H (OMe); 5.46 s, 1 H (H-4′); 5.84 m, 1 H (H-16β); 6.63 d, 1 H, J = 2.6 (H-4); 6.70 dd, 1 H,
J1 = 8.8, J2 = 2.6 (H-2); 7.18 d, 1 H, J = 8.8 (H-1); 7.42 and 7.55 and 8.00 m, 5 H (Ph). IR spectrum
(KBr): 1 730, 1 700, 1 600, 1 500, 1 250. Mass spectrum: 472 [M+], 350.
Spiro[((17S)-16α-hydroxy-3-methoxyestra-1,3,5(10)-triene)-17,2′-(5′-methylfuran-3′(2′H)-one)] (23)
To a stirred solution of compound 21 (68 mg, 0.17 mmol) in methanol (10 ml), 1 M KOH in methanol
(0.5 ml) was added. After stirring for 20 min, 5% aqueous HCl (0.5 ml) was added and the mixture
was evaporated to a small volume. The organic material was extracted with chloroform. The organic
phase was washed with brine, dried (Na2SO4) and evaporated. The residue was chromatographed on
silica gel (toluene–AcOEt 50 : 50) to give product 23 (42 mg, 67%), m.p. 209–211 °C (aqueous
1
MeOH), [α]D +74 (c 0.65). H NMR spectrum: 1.03 s, 3 H (3 × H-18); 2.33 s, 3 H (Me-5′); 2.86 m,
2 H (2 × H-6); 3.78 s, 3 H (OMe); 4.72 m, 1 H (H-16β); 5.49 s, 1 H (H-4′); 6.63 d, 1 H, J = 2.6
(H-4); 6.70 dd, 1 H, J1 = 8.8, J2 = 2.6 (H-2); 7.18 d, 1 H, J = 8.8 (H-1). 13C NMR spectrum: 13.7 q,
17.3 q, 26.1 t, 28.5 t, 30.9 t, 31.1 t, 35.6 t, 38.9 d, 44.0 d, 50.4 s, 51.2 d, 55.9 q, 77.4 d, 100.2 s,
107.3 d, 112.3 d, 114.5 d, 126.8 d, 132.7 s, 138.5 s, 158.2 s, 188.7 s, 203.9 s. Mass spectrum: 368
[M+], 350.
RESULTS AND DISCUSSION
Our approach is based on the elimination of the 17-hydroxy group in mestrenol (1) and
introduction of the chiral center at C-17 bearing in mind that the attack of the reagent
will take place from the α-side of the steroid skeleton. However, direct dehydration of
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Synthesis of 17β-Isoxazolyl Steroids
1571
mestrenol did not give the desired enyne as it was also reported previously10. However,
elimination of water from hydroxyisoxazole 2 with thionyl chloride was successful and
led to alkene 3 exclusively in 84% yield (Scheme 1). No products of skeletal rearrange-
ment were detected. The cleavage of the isoxazole ring was effected by reduction with
OH
O
O
H
NH
NH
2
2
5
MeO
1
4
(i)
(iii)
N
N
O
O
O
(iv)
OH
OH
(ii)
6
2
3
(vi)
(v)
N
N
N
O
O
O
OH
OR
OR
(ix)
O
O
(xi)
11, R = H
12, R = CH SCH
8, R = H
9, R = Ac
7
(vii)
(viii)
2
3
10, R = Bz
(x), (vii)
N
N
O
N
O
O
H
OH
OAc
OR
OR
H
H
14, R = H
16, R = Ac
15, R = H
17, R = Ac
13
(vii)
(vii)
Bz = benzoyl
o
(i) CH C=NOH, N-chlorosuccinimide, Et N/CHCl ; (ii) SOCl , pyridine/THF, -50 C; (iii) NiCl , NaBH /THF;
3
3
3
2
2
4
(iv) Mo(CO) /CH CN, H O, reflux; (v) 3-chloroperoxybenzoic acid, NaHCO /CH Cl ; (vi) OsO , 4-methyl-
6
3
2
3
2
2
4
morpholine N-oxide/Me CO, H O; (vii) Ac O/pyridine; (viii) benzoyl chloride, DMAP/CH Cl ; (ix) (COCl) ,
2
2
2
2
2
2
o
DMSO, Et N/CH Cl , -70 C; (x) LiAlH(tBuO) /THF; (xi) HClO , H O/THF
3
2
2
3
4
2
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

1572
Baranovsky, Groen, de Groot, Litvinovskaya, Khripach:
nickel boride, but in these conditions, the saturation of the ∆16-bond also occurred,
giving enaminoketone 4. To avoid this reduction, the cleavage with Mo(CO)6 was em-
ployed. The reaction of alkene 3 with Mo(CO)6 afforded enamino ketone 5 along with
1
compound 6 in a good yield. From the H and 13C NMR spectra, it could be concluded
that diketone 6 exists in solution mostly in its 22-en-23-ol tautomeric form. Unfortu-
nately, all further attempts to electrophilic and free-radical cyclization of compounds 5
or 6 into a spirofurane were unsuccessful. This turned us to try the formation of the
chiral center at C-17 before opening of the ring.
Two approaches were examined for this purpose, dihydroxylation and epoxidation.
It is known that the attack of a reagent on the ∆16-bond usually occurs from the
α-side and also in our reactions, only epimers 7 and 8 were isolated. The epoxidation
route was not entirely satisfactory since appreciable amounts of side products, resulting
from opening of the epoxide ring and further rearrangements, were obtained. Thus,
when epoxide 7 was treated with perchloric acid in THF, compounds 14 and 15 were
isolated in a 3 : 1 ratio. Such backbone rearrangement induced by boron trifluoride is
known for 5α,6α- and 16α,17α-epoxy steroids11,12. Because of their low solubility,
compounds 14 and 15 were converted in their acetates 16 and 17 for spectroscopic
correlations. The assignment of the structure of acetate 17 was based on analysis of its
13C NMR spectrum13,14
.
The dihydroxylation gave a better yield (82% vs 57% for the epoxide) but also re-
quired a strict control of conditions. It was found that excess of oxidant (4-methylmor-
pholine N-oxide) led to oxidative cleavage of diol 8. The secondary hydroxy group in
diol 8 was protected as esters 9 or 10 to ensure the formation of spirofurans after
cleavage of the isoxazole ring and to prevent the cyclization at C-16. In an attempt to
prepare the 16β-epimer of diol 8, we examined its oxidation to ketone 11. It was found
that chromium reagents were unsuitable for this oxidation and led to complex mixtures
due to cleavage of the D ring of the steroid. Swern oxidation afforded the desired
ketone in 63% yield along with some ketone 12 as a result of the Pummerer rearrange-
ment. Finally, the reduction of ketone 11 with the bulky lithium tri-tert-butoxyalumi-
niumhydride followed by acetylation gave acetate 13 exclusively.
In acidic conditions, epoxide 7 suffered from rearrangement and therefore we de-
cided to open the epoxy ring after cleavage of the isoxazole ring. Indeed, compound 18
treated with HBr in THF was converted smoothly and without rearrangement to bromo-
furanone 19 in 90% yield, via trans-opening of the epoxy ring8,15–18 followed by intra-
molecular cyclization (Scheme 2).
Debromination of bromofuranone 19 was performed with tributylstannane and pro-
duct 20 was isolated in a good yield. Comparison of the spectral data of compound 20
with those of analogs given in literature6,9 unambiguously confirms the 17R-configura-
tion of the chiral center at C-17. The signals of the protons at C-18 and C-4′ in the 1H NMR
spectra are the most suitable for structure assignment. Thus, for furanone 20, the sig-
Collect. Czech. Chem. Commun. (Vol. 63) (1998)

Synthesis of 17β-Isoxazolyl Steroids
1573
nals of the protons at C-18 resonate at higher field in comparison with those of the
17-epimer (ca 0.07 ppm) and the signal of the proton at C-4′ appears at lower field (ca
0.11 ppm).
N
O
O
O
O NH
2
(ii)
(i)
O
O
Br
18
19
7
(iii)
O
O
OR
O
O
(iv)
(v)
9
21, R = Ac
22, R = Bz
23, R = H
20
(vi)
10
Bz = benzoyl
(i) Mo(CO) /CH CN, H O, reflux; (ii) 48% aq. HBr/THF; (iii) tributylstannane, AIBN/benzene, reflux;
6
3
2
(iv) NiCl , NaBH /THF, MeOH; (v) a) Mo(CO) /CH CN, H O, reflux, b) 37% aq. HCl/THF; (vi) KOH/MeOH
2
4
6
3
2
SCHEME 2
The 16-substituted spirofuranones 21 and 22 were prepared from the corresponding
isoxazoles 9 and 10. The cleavage of isoxazole 9 was carried out with nickel boride
and, after cyclization, furanone 21 was isolated in 70% yield. The protection of the
C-16 hydroxy group as benzoate and the use of Mo(CO)6 as reducing agent allowed to
obtain furanone 22 in 91% yield after cyclization. Cyclization of the enamino ketones
was performed with HCl in ethanol. Hydrolysis of the acetate in furanone 21 with KOH
in methanol gave alcohol 23 in 67% yield along with some by-products.
We are grateful to the Laboratory for Physical and Chemical Analysis of the Institute of Bioorganic
chemistry for the acquisition of spectral data.
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