Regio- and stereoselective access to novel ring-condensed steroidal isoxazolines

Article abstract of DOI:10.1016/j.steroids.2014.05.019

Novel 5α-androstanes containing an isoxazoline moiety condensed to ring A or D were efficiently synthetized by 1,3-dipolar cycloadditions of aryl nitrile oxides to steroidal α,β-unsaturated ketones. During the ring closures, regioisomers in which the O terminus of the nitrile oxide dipoles is attached to the β-carbon of the dipolarophile were formed in a stereoselective manner to furnish exclusively 1α,2α- or 15β,16β-condensed heterocycles. The cyclic enone moiety of the six-membered ring A proved to be less reactive than that of the five-membered ring D, but all the reactions were affected significantly by the substitution pattern of the nitrile oxide. 17-Deacetylation of the primary products resulted in aromatization or simultaneous hydroxylation, depending on the base applied for the ring A-fused heterocycles, while retro-Dieckmann-like fragmentation was observed partially or completely for the ring D-fused analogues during 3-deacetylation.2014 Elsevier Inc. All rights reserved.

Full text of DOI:10.1016/j.steroids.2014.05.019

Accepted Manuscript
Regio- and stereoselective access to novel ring-condensed steroidal isoxazolines
Gergő Mótyán, Zalán Kádár, Dóra Kovács, János Wölfling, Éva Frank
PII:
S0039-128X(14)00132-9
http://dx.doi.org/10.1016/j.steroids.2014.05.019
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Reference:
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Please cite this article as: Mótyán, G., Kádár, Z., Kovács, D., Wölfling, J., Frank, É., Regio- and stereoselective
access to novel ring-condensed steroidal isoxazolines, Steroids (2014), doi: http://dx.doi.org/10.1016/j.steroids.
2014.05.019
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Regio- and stereoselective access to novel ring-condensed steroidal isoxazolines
Gergꢀ Mótyán, Zalán Kádár, Dóra Kovács, János Wölfling and Éva Frank*
Department of Organic Chemistry, University of Szeged, Dóm tér 8, H-6720 Szeged ,
Hungary
Tel: +36-62-544275
Fax: +36-62-544200
E-mail: frank@chem.u-szeged.hu
1

Abstract
Novel 5α-androstanes containing an isoxazoline moiety condensed to ring A or D were
efficiently synthetized by 1,3-dipolar cycloadditions of aryl nitrile oxides to steroidal α,β-
unsaturated ketones. During the ring closures, regioisomers in which the O terminus of the
nitrile oxide dipoles is attached to the β-carbon of the dipolarophile were formed in a
stereoselective manner to furnish exclusively 1α,2α- or 15β,16β-condensed heterocycles. The
cyclic enone moiety of the six-membered ring A proved to be less reactive than that of the
five-membered ring D, but all the reactions were affected significantly by the substitution
pattern of the nitrile oxide. 17-Deacetylation of the primary products resulted in aromatization
or simultaneous hydroxylation, depending on the base applied for the ring A-fused
heterocycles, while retro-Dieckman-like fragmentation was observed partially or completely
for the ring D-fused analogues during 3-deacetylation.
Keywords: 5α-Androstanes, Cycloaddition,Isoxazolines, Stereocontrol, Regioselectivity
2

1. Introduction
In view of the diversity of their biological activities, heterocyclic steroids continue to be
attractive target molecules for stereoselective syntheses [1-6]. The main driving force towards
the preparation of such compounds is the modification of the receptor-binding ability by
chemical transformation of the extant functional groups and therefore the reduction or
elimination of the undesirable hormonal effects [7]. Significant changes in the
pharmacodynamic and pharmacokinetic properties can result from the introduction of a hetero
ring into the sterane core.
Among the five-membered heterocyclic compounds, 2-isoxazolines have attracted interest
as structural building blocks of biologically active molecules and they also serve as versatile
intermediates in organic chemistry [8-10]. Thanks to their stability, the hetero ring can be
functionalized or can be reductively cleaved to furnish a number of important bifunctional
units, such as α,β-unsaturated ketones [11], β-hydroxycarbonyl compounds [12] or 1,3-
aminoalcohols [13]. The outstanding role of 2-isoxazolines, however, is due to their
straightforward synthetic availability from chemically divergent alkenes and nitrile oxides by
1,3-dipolar cycloadditions [14].
In consequence of their instability and high reactivity, most nitrile oxides have to be
prepared in situ. In the absence of a dipolarophile, sterically unhindered nitrile oxides tend to
dimerize to furoxanes at ambient or lower temperatures, or (especially the sterically stabilized
ones) undergo rearrangement to isocyanates at elevated temperature [15]. Although most aryl
nitrile oxides possess relatively long half-lives at room temperature, the presence of an
electron-withdrawing substituent on the aromatic ring facilitates dimerization, while the
resistance to furoxane formation is enhanced by electron-donating groups and sterically by
ortho substituents [5]. These side-reactions may also occur to a certain extent even in the
presence of an alkene component, which can reduce the yield of the desired isoxazoline.
3

Hydroximidoyl chlorides, the most frequently applied precursors of nitrile oxides, are usually
prepared from aldoximes by oxidative halogenation with N-chlorosuccinimide and subsequent
base-induced dehydrohalogenation [16].
A number of steroidal isoxazolines with diverse pharmacological activities (i.e. anti-
inflammatory, hypocholesterolemic, antiviral, antibacterial, antifungal and antiproliferative
effects) have been reported to date [17-19], but there are no examples of isoxazolines
condensed to positions 1,2 or 15,16 of sterane ring A or D. The addition of steric bulk
adjacent to the extant functional groups on C-3 or C-17, essential for hormone-receptor
binding, may contribute to a change in biological activity and these derivatives may therefore
deserve attention from a pharmacological aspect. Moreover, the vicinity of the angular methyl
groups on C-10 and C-13 to the reaction centre and also the rigidity of the sterane skeleton
overall may have a significant influence on the stereo- and regiocontrol of the processes.
As an extension of our work on the synthesis of steroid-fused heterocycles [20-23], we set
out to prepare novel ring-fused isoxazolines from α,β-unsaturated steroidal 17-ketones with
aryl nitrile oxides via intermolecular 1,3-dipolar cycloadditions. A further goal was to
investigate the regio- and stereoselectivity of the processes and to compare the reactivities of
rings A and D against nitrile oxides. The influence of steric and electronic factors on the ring
closures and the behaviour of the cycloadducts under conventional deacetylation conditions
were also studied. Determination of the stereostructures of the synthetized compounds was
also planned.
4

2. Experimental
2.1. General
Melting points (Mps) were determined on an SMS Optimelt digital apparatus. Elemental
analysis data were obtained with a Perkin Elmer CHN analyser model 2400. NMR spectra
were recorded at room temperature with a Bruker DRX 500 instrument. Chemical shifts are
reported in ppm (δ scale), and coupling constants (J) in Hz. For the determination of
multiplicities, the J-MOD pulse sequence was used. Automated flow injection analyses were
performed by using an HPLC/MSD system. The system comprised an Agilent 1100 micro
vacuum degasser, a quaternary pump, a micro-well plate autoinjector and a 1946A MSD
equipped with an electrospray ion source (ESI) operated in positive ion mode. The ESI
parameters: nebulizing gas N2, at 35 psi; drying gas N2, at 350 °C and 12 L/min; capillary
voltage 3000 V; and fragmentor voltage 70 V. The MSD was operated in scan mode with the
−620. Samples (0.2 ꢁL) were injected with an automated needle wash
mass range m/z 60
directly into the solvent flow (0.3 mL/min) of MeCN/H2O 70:30 (v/v) supplemented with
0.1% formic acid. The system was controlled by Agilent LC/MSD Chemstation software. All
solvents were distilled immediately prior to use. Reagents and materials were obtained from
reliable commercial suppliers and were used without purification. The reactions were
monitored by TLC on Kieselgel-G (Merck Si 254 F) layers (0.25 mm thick); solvent systems
(ss): (A) CH2Cl2, (B) EtOAc/CH2Cl2 (2:98 v/v), (C) EtOAc/CH2Cl2 (5:95 v/v) or (D)
EtOAc/CH2Cl2 (10:90 v/v). The spots were detected by spraying with 5% phosphomolybdic
acid in 50% aqueous phosphoric acid. The Rf values were determined for the spots observed
by illumination at 254 and 365 nm. Flash chromatography: Merck silica gel 60, 40–63 ꢁm.
2.2. General procedure for the synthesis of ring-condensed isoxazolines (5, 6, 9 and 11) in the
∆5 androstene series
5

17β-Acetoxy-5α-androst-1-en-3-one (1, 330 mg, 1.00 mmol), 3β-acetoxy-5α-androst-15-en-
17-one (2, 330 mg, 1.00 mmol), 17β-hydroxy-5α-androst-1-en-3-one (13, 288 mg, 1.00
mmol) or 3β-hydroxy-5α-androst-15-en-17-one (14, 288 mg, 1.00 mmol) and the appropriate
aromatic imidoyl chloride (3a−g, 1.50 mmol) were dissolved in toluene (15 mL), and DIPEA
(0.52 mL, 3.00 mmol) was added dropwise to the reaction mixture at room temperature, with
subsequent refluxing for 5 h (for 1 and 13) or for 2 h (for 2 and 14). The solvent was then
evaporated off in vacuo and the resulting crude product was purified by column
chromatography with CH2Cl2 for 5 and 6 and with EtOAc/CH2Cl2 = 5:95 for 9 and 11.
2.2.1.
17β-Acetoxy-3′-phenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one
(5a)
Compound 1 and N-hydroxybenzenecarboximidoyl chloride (3a, 233 mg) were used for the
synthesis as described in the General Procedure. The crude product 5a (247 mg, 55%) was
obtained as a white precipitate. Mp 222−224 °C; Rf = 0.54 (ss B). Anal. Calcd. for C28H35NO4
(449.58): C, 74.80; H, 7.85. Found: C, 74.92; H, 7.97. 1H NMR (500 MHz, CDCl3): δ 0.81 (s,
3H, 18-H3), 0.95 (s, 3H, 19-H3), 0.98 (m, 1H), 1.12 (m, 1H), 1.26−1.32 (m, 3H), 1.40−1.79
(m, 9H), 2.04 (s, 3H, Ac-CH3), 2.12 (m, 1H), 2.19−2.36 (m, 3H), 4.31 (d, 1H, J = 10.0 Hz, 2-
H), 4.59 (t, 1H, J = 8.5 Hz, 17-H), 4.86 (d, 1H, J = 10.0 Hz, 1-H), 7.38 (overlapping m, 3H,
3"-H, 4"-H and 5"-H), 7.75 (d, 2H, J = 7.6 Hz, 2"-H and 6"-H) ppm. 13C NMR (125 MHz,
CDCl3): δ 12.0 (C-18), 12.2 (C-19), 20.4 (CH2), 21.2 (Ac-CH3), 23.6 (CH2), 27.5 (CH2), 28.7
(CH2), 30.5 (CH2), 34.8 (CH), 35.7 (CH), 36.4 (CH2), 38.7 (C-10), 42.4 (C-13), 42.8 (CH2),
46.2 (CH), 50.2 (CH), 58.7 (C-2), 82.7 (C-17), 88.6 (C-1), 127.5 (2C), 128.5 (2C), 128.7 (C-
1"), 130.2 (C-4"), 155.2 (C-5'), 171.1 (Ac-CO), 206.1 (C-3) ppm; ESI-MS 450 [M+H]+.
6

2.2.2. 17β-Acetoxy-3′-4″-methoxyphenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one
(5b)
Compound 1 and N-hydroxy-4-methoxybenzenecarboximidoyl chloride (3b, 279 mg) were
used for the synthesis as described in the General Procedure. The crude product 5b (360 mg,
75%) was obtained as a white precipitate. Mp 166−168 °C; Rf = 0.50 (ss C). Anal. Calcd. for
1
C29H37NO5 (479.61): C, 72.62; H, 7.78. Found: C, 72.85; H, 7.90. H NMR (500 MHz,
CDCl3): δ 0.80 (s, 3H, 18-H3), 0.93 (s, 3H, 19-H3), 0.97 (m, 1H), 1.12 (m, 1H), 1.24−1.32 (m,
−1.79 (m, 9H), 2.03 (s, 3H, Ac
3H), 1.40
−2.34 (m, 3H), 3.81 (s, 3H,
-CH3), 2.10 (m, 1H), 2.16
4"-OCH3), 4.26 (d, 1H, J = 10.3 Hz, 2-H), 4.59 (t, 1H, J = 8.3 Hz, 17-H), 4.82 (d, 1H, J =
10.3 Hz, 1-H), 6.88 (d, 2H, J = 8.7 Hz, 3"-H and 5"-H), 7.70 (d, 2H, J = 8.7 Hz, 2"-H and 6"-
H) ppm. 13C NMR (125 MHz, CDCl3): δ 12.0 (C-18), 12.1 (C-19), 20.4 (CH2), 21.1 (Ac-
CH3), 23.6 (CH2), 27.5 (CH2), 28.7 (CH2), 30.5 (CH2), 34.8 (CH), 35.7 (CH), 36.4 (CH2),
38.7 (C-10), 42.4 (C-13), 42.8 (CH2), 46.3 (CH), 50.3 (CH), 55.3 (OCH3), 59.1 (C-2), 82.7
(C-17), 88.3 (C-1), 114.0 (2C), 121.4 (C-1"), 129.1 (2C), 154.7 (C-5'), 161.2 (C-4"), 171.0
(Ac-CO), 206.2 (C-3) ppm; ESI-MS 480 [M+H]+.
2.2.3.
17β-Acetoxy-3′-2″-tolyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one
(5c)
Compound 1 and N-hydroxy-2-methylbenzenecarboximidoyl chloride (3c, 255 mg) were used
for the synthesis as described in the General Procedure. The crude product 5c (338 mg, 73%)
was obtained as a white precipitate. Mp 182−184 °C; Rf = 0.53 (ss B). Anal. Calcd. for
1
C29H37NO4 (463.61): C, 75.13; H, 8.04. Found: C, 75.20; H, 7.95. H NMR (500 MHz,
−1.34 (m,
CDCl3): δ 0.81 (s, 3H, 18-H3), 0.93 (s, 3H, 19-H3), 0.99 (m, 1H), 1.12 (m, 1H), 1.24
−1.79 (m, 9H), 2.03 (s, 3H, Ac
3H), 1.40
−2.30 (m, 3H), 2.49
-CH3), 2.11 (m, 1H), 2.18
(s, 3H,
2"-CH3), 4.37 (d, 1H, J = 10.1 Hz, 2-H), 4.59 (t, 1H, J = 8.2 Hz, 17-H), 4.84 (d, 1H, J = 10.1
13
−7.29 (overlapping m, 3H), 7.38 (d, 1H,
Hz, 1-H), 7.18
J = 6.9 Hz) ppm. C NMR (125 MHz,
7

CDCl3): δ 12.0 (C-18), 12.2 (C-19), 20.4 (CH2), 21.1 (Ac-CH3), 22.3 (2"-CH3), 23.6 (CH2),
27.5 (CH2), 28.7 (CH2), 30.5 (CH2), 34.8 (CH), 35.8 (CH), 36.4 (CH2), 38.8 (C-10), 42.4 (C-
13), 42.7 (CH2), 46.2 (CH), 50.2 (CH), 60.8 (C-2), 82.7 (C-17), 87.5 (C-1), 125.7 (CH), 127.7
(C-1"), 129.4 (CH), 129.7 (CH), 131.3 (CH), 137.7 (C-2"), 155.9 (C-5'), 171.1 (Ac-CO),
205.4 (C-3) ppm; ESI-MS 464 [M+H]+.
2.2.4. 17β-Acetoxy-3′-3″-tolyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one (5d)
Compound 1 and N-hydroxy-3-methylbenzenecarboximidoyl chloride (3d, 255 mg) were
used for the synthesis as described in the General Procedure. The crude product 5d (260
mg, 56%) was obtained as a white precipitate. Mp 213−216 °C; Rf = 0.48 (ss B). Anal.
1
Calcd. for C29H37NO4 (463.61): C, 75.13; H, 8.04. Found: C, 75.25; H, 8.10. H NMR
(500 MHz, CDCl3): δ 0.81 (s, 3H, 18-H3), 0.94 (s, 3H, 19-H3), 0.98 (m, 1H), 1.13 (m,
−1.33 (m, 3H), 1.39−1.80 (m, 9H), 2.04 (s, 3H, Ac
1H), 1.24
-CH3), 2.12 (m, 1H),
2.17−2.32 (m, 3H), 2.36 (s, 3H, 3"-CH3), 4.30 (d, 1H, J = 10.0 Hz, 2-H), 4.60 (t, 1H, J =
8.4 Hz, 17-H), 4.85 (d, 1H, J = 10.0 Hz, 1-H), 7.20 (d, 1H, J = 7.3 Hz), 7.26 (t, 1H, J =
7.3 Hz, 5"-H), 7.53 (d, 1H, J = 7.3 Hz), 7.58 (s, 1H, 2"-H) ppm; 13C NMR (125 MHz,
CDCl3): δ 12.0 (C-18), 12.1 (C-19), 20.4 (CH2), 21.1 (Ac-CH3), 21.4 (3"-CH3), 23.6
(CH2), 27.5 (CH2), 28.7 (CH2), 30.5 (CH2), 34.8 (CH), 35.8 (CH), 36.4 (CH2), 38.7 (C-
10), 42.4 (C-13), 42.8 (CH2), 46.2 (CH), 50.2 (CH), 58.8 (C-2), 82.7 (C-17), 88.6 (C-1),
124.7 (CH), 127.9 (CH), 128.4 (CH), 128.7 (C-1"), 131.0 (CH), 138.2 (C-3"), 155.4 (C-
5'), 171.1 (Ac-CO), 206.1 (C-3) ppm; ESI-MS 464 [M+H]+.
2.2.5. 17β-Acetoxy-3′-4″-tolyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one (5e)
Compound 1 and N-hydroxy-4-methylbenzenecarboximidoyl chloride (3e, 255 mg) were
used for the synthesis as described in the General Procedure. The crude product 5e (283
8

mg, 61%) was obtained as a white precipitate. Mp 215−217 °C; Rf = 0.60 (ss B). Anal.
1
Calcd. for C29H37NO4 (463.61): C, 75.13; H, 8.04. Found: C, 74.96; H, 8.13. H NMR
(500 MHz, CDCl3): δ 0.80 (s, 3H, 18-H3), 0.93 (s, 3H, 19-H3), 0.97 (m, 1H), 1.12 (m,
−1.31 (m, 3H), 1.38−1.78 (m, 9H), 2.03 (s, 3H, Ac
1H), 1.25
-CH3), 2.11 (m, 1H),
2.15−2.32 (m, 3H), 2.35 (s, 3H, 4"-CH3), 4.28 (d, 1H, J = 10.2 Hz, 2-H), 4.58 (t, 1H, J =
8.5 Hz, 17-H), 4.83 (d, 1H, J = 10.2 Hz, 1-H), 7.17 (d, 2H, J = 7.9 Hz, 3"-H and 5"-H),
7.63 (d, 2H, J = 7.9 Hz, 2"-H and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 12.0 (C-
18), 12.1 (C-19), 20.4 (CH2), 21.2 (Ac-CH3), 21.4 (4"-CH3), 23.6 (CH2), 27.5 (CH2), 28.7
(CH2), 30.5 (CH2), 34.8 (CH), 35.7 (CH), 36.4 (CH2), 38.7 (C-10), 42.4 (C-13), 42.8
(CH2), 46.2 (CH), 50.2 (CH), 58.8 (C-2), 82.7 (C-17), 88.4 (C-1), 125.9 (C-1"), 127.4
(2C), 129.2 (2C), 140.4 (C-4"), 155.2 (C-5'), 171.1 (Ac-CO), 206.1 (C-3) ppm; ESI-MS
464 [M+H]+.
2.2.6. 17β-Acetoxy-3′-4″-chlorophenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one
(5f)
Compound 1 and N-hydroxy-4-chlorobenzenecarboximidoyl chloride (3f, 292 mg) were
used for the synthesis as described in the General Procedure. The crude product 5f (194
mg, 40%) was obtained as a white precipitate. Mp 200−202 °C; Rf = 0.62 (ss B). Anal.
1
Calcd. for C28H34ClNO4 (484.03): C, 69.48; H, 7.08. Found: C, 69.59; H, 6.97. H NMR
(500 MHz, CDCl3): δ 0.80 (s, 3H, 18-H3), 0.95 (s, 3H, 19-H3), 0.98 (m, 1H), 1.12 (m,
−1.33 (m, 3H), 1.39−1.80 (m, 9H), 2.04 (s, 3H, Ac
1H), 1.24
-CH3), 2.13 (m, 1H),
−2.34 (m, 3H), 4.23 (d, 1H,
2.18
J = 10.1 Hz, 2-H), 4.59 (t, 1H, J = 8.3 Hz, 17-H), 4.85 (d,
1H, J = 10.1 Hz, 1-H), 7.34 (d, 2H, J = 8.3 Hz, 3"-H and 5"-H), 7.70 (d, 2H, J = 8.3 Hz,
2"-H and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 12.0 (C-18), 12.2 (C-19), 20.4
(CH2), 21.2 (Ac-CH3), 23.6 (CH2), 27.5 (CH2), 28.6 (CH2), 30.5 (CH2), 34.8 (CH), 35.7
9

(CH), 36.3 (CH2), 38.5 (C-10), 42.4 (C-13), 42.7 (CH2), 46.3 (CH), 50.2 (CH), 58.3 (C-2),
82.7 (C-17), 88.7 (C-1), 127.3 (C-1"), 128.7 (2C), 128.8 (2C), 136.3 (C-4"), 154.6 (C-5'),
171.1 (Ac-CO), 205.8 (C-3) ppm; ESI-MS 485 [M+H]+.
2.2.7. 17β-Acetoxy-3′-4″-nitrophenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one
(5g)
Compound 1 and N-hydroxy-4-nitrobenzenecarboximidoyl chloride (3g, 300 mg) were
used for the synthesis as described in the General Procedure. The crude product 5g (94
mg, 19%) was obtained as a pale-yellow precipitate. Mp 206−209 °C; Rf = 0.64 (ss B).
1
Anal. Calcd. for C28H34N2O6 (494.58): C, 68.00; H, 6.93. Found: C, 68.16; H, 6.82. H
NMR (500 MHz, CDCl3): δ 0.81 (s, 3H, 18-H3), 0.96 (m, 1H), 1.00 (s, 3H, 19-H3), 1.13
(m, 1H), 1.26−1.36 (m, 3H), 1.42−1.80 (m, 9H), 2.04 (s, 3H, Ac-CH3), 2.16−2.27 (m,
3H), 2.32 (m, 1H), 4.25 (d, 1H, J = 9.6 Hz, 2-H), 4.60 (t, 1H, J = 8.6 Hz, 17-H), 4.89 (d,
1H, J = 9.6 Hz, 1-H), 7.94 (d, 2H, J = 8.9 Hz, 3"-H and 5"-H), 8.22 (d, 2H, J = 8.9 Hz, 2"-
H and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 12.0 (C-18), 12.2 (C-19), 20.4 (CH2),
21.1 (Ac-CH3), 23.6 (CH2), 27.5 (CH2), 28.5 (CH2), 30.5 (CH2), 34.8 (CH), 35.9 (CH),
36.3 (CH2), 38.4 (C-10), 42.4 (C-13), 42.7 (CH2), 46.4 (CH), 50.2 (CH), 57.5 (C-2), 82.6
(C-17), 89.3 (C-1), 123.7 (2C), 128.3 (2C), 135.0 (C-1"), 148.4 (C-4"), 154.6 (C-5'), 171.1
(Ac-CO), 205.4 (C-3) ppm; ESI-MS 495 [M+H]+.
2.2.8.
3β-Acetoxy-3′-phenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-one
(6a)
Compound 2 and N-hydroxybenzenecarboximidoyl chloride (3a, 233 mg) were used for the
synthesis as described in the General Procedure. The crude product 6a (423 mg, 94%) was
obtained as a white precipitate. Mp 281−283 °C; Rf = 0.43 (ss A). Anal. Calcd. for C28H35NO4
1
(449.58): C, 74.80; H, 7.85. Found: C, 74.95; H, 7.74. H NMR (CDCl3, 500 MHz): δ 0.82
10

(m, 1H), 0.90 (s, 3H, 19-H3), 1.06 (m, 1H and s, 3H, 18-H3), 1.13−1.33 (overlapping m, 3H),
1.35−1.44 (overlapping m, 4H), 1.52 (m, 1H), 1.61−1.85 (overlapping m, 6H), 2.03 (s, 3H
Ac-CH3), 2.08 (m, 1H), 2.15 (m, 1H), 4.14 (d, 1H, J = 9.2 Hz, 16-H), 4.71 (m, 1H, 3-H), 5.42
(dd, 1H, J = 9.2 Hz, J = 4.3 Hz, 15-H), 7.41 (m, 3H, 3ꢂ-H, 4ꢂ-H and 5ꢂ-H), 7.93 (m, 2H, 2ꢂ-H
and 6ꢂ-H) ppm; 13C NMR (CDCl3, 125 MHz): δ 12.2 (C-19), 17.8 (C-18), 20.2 (CH2), 21.4
(Ac-CH3), 27.4 (CH2), 28.0 (CH2), 30.4 (CH2), 32.1 (CH), 33.3 (CH2), 33.9 (CH2), 35.8 (C-
10), 36.6 (CH2), 44.8 (CH), 48.9 (C-13), 54.3 (CH), 55.0 (CH), 62.1 (CH), 73.4 (C-3), 84.6
(C-15), 127.6 (2C, C-3ꢂ and C-5ꢂ), 128.3 (C-1ꢂ), 128.7 (2C, C-2ꢂ and C-6ꢂ), 130.3 (C-4ꢂ),
155.3 (C-3′), 170.6 (Ac-CO), 212.3 (C-17) ppm; ESI-MS 450 [M+H]+.
2.2.9. 3β-Acetoxy-3′-4″-methoxyphenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-one
(6b)
Compound 2 and N-hydroxy-4-methoxybenzenecarboximidoyl chloride (3b, 279 mg) were
used for the synthesis as described in the General Procedure. The crude product 6b (470 mg,
98%) was obtained as a white precipitate. Mp 232−234 °C; Rf = 0.33 (ss A). Anal. Calcd. for
1
C29H37NO5 (479.61): C, 72.62; H, 7.78. Found: C, 72.45; H, 7.70. H NMR (CDCl3, 500
MHz): δ 0.81 (m, 1H), 0.90 (s, 3H, 19-H3), 1.05 (m, 1H and s, 3H, 18-H3), 1.11−1.32
(overlapping m, 3H), 1.34−1.43 (overlapping m, 4H), 1.52 (m, 1H), 1.59−1.69 (overlapping
m, 3H), 1.75 (m, 2H), 1.83 (m, 1H), 2.02 (s, 3H Ac-CH3), 2.07 (m, 1H), 2.14 (m, 1H), 3.82 (s,
3H, 4ꢂ-OMe), 4.11 (d, 1H, J = 9.1 Hz, 16-H), 4.70 (m, 1H, 3-H), 5.38 (dd, 1H, J = 9.1 Hz, J =
4.2 Hz, 15-H), 6.92 (d, 2H, J = 8.8Hz, 3ꢂ-H and 5ꢂ-H), 7.86 (d, 2H, J = 8.8 Hz, 2ꢂ-H and 6ꢂ-
H) ppm; 13C NMR (CDCl3, 125 MHz): δ 12.1 (C-19), 17.9 (C-18), 20.2 (CH2), 21.4 (Ac-
CH3), 27.4 (CH2), 28.0 (CH2), 30.4 (CH2), 32.1 (CH), 33.2 (CH2), 33.9 (CH2), 35.8 (C-10),
36.6 (CH2), 44.8 (CH), 48.9 (C-13), 54.3 (CH), 55.0 (CH), 55.3 (4ꢂ-OMe), 62.4 (CH), 73.4
11

(C-3), 84.1 (C-15), 114.1 (2C, C-3ꢂ and C-5ꢂ), 120.9 (C-1ꢂ), 129.2 (2C, C-2ꢂ and C-6ꢂ),
154.8 (C-4ꢂ), 161.2 (C-3′), 170.6 (Ac-CO), 212.6 (C-17) ppm; ESI-MS 480 [M+H]+.
2.2.10. 3β-Acetoxy-3′-4″-tolyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-one (6e)
Compound 2 and N-hydroxy-4-methylbenzenecarboximidoyl chloride (3e, 255 mg) were
used for the synthesis as described in the General Procedure. The crude product 6e (450
mg, 97%) was obtained as a white precipitate. Mp 273−276 °C; Rf = 0.27 (ss A). Anal.
1
Calcd. for C29H37NO4 (463.61): C, 75.13; H, 8.04. Found: C, 75.25; H, 8.10. H NMR
(CDCl3, 500 MHz): δ 0.81 (m, 1H), 0.90 (s, 3H, 19-H3), 1.05 (m, 1H and s, 3H, 18-H3),
1.12−1.32 (overlapping m, 3H), 1.35−1.42 (overlapping m, 4H), 1.52 (m, 1H), 1.60−1.67
(overlapping m, 3H), 1.78 (m, 2H), 1.83 (m, 1H), 2.03 (s, 3H Ac-CH3), 2.07 (m, 1H), 2.15
(m, 1H), 2.37 (s, 3H, 4ꢂ-CH3), 4.12 (d, 1H, J = 9.1 Hz, 16-H), 4.71 (m, 1H, 3-H), 5.39
(dd, 1H, J = 9.1 Hz, J = 4.1 Hz, 15-H), 7.21 (d, 2H, J = 7.8 Hz, 3ꢂ-H and 5ꢂ-H), 7.81 (d,
2H, J = 7.8 Hz, 2ꢂ-H and 6ꢂ-H) ppm; 13C NMR (CDCl3, 125 MHz): δ 12.1 (C-19), 17.8
(C-18), 20.1 (CH2), 21.4 (2C, Ac-CH3 and 4ꢂ-CH3), 27.4 (CH2), 28.0 (CH2), 30.4 (CH2),
32.1 (CH), 33.2 (CH2), 33.9 (CH2), 35.8 (C-10), 36.6 (CH2), 44.8 (CH), 48.9 (C-13), 54.3
(CH), 55.0 (CH), 62.2 (CH), 73.4 (C-3), 84.3 (C-15), 125.5 (C-1ꢂ), 127.6 (2C, C-2ꢂ and
C-6ꢂ), 129.4 (2C, C-3ꢂ and C-5ꢂ), 140.6 (C-4ꢂ), 155.3 (C-3′), 170.6 (Ac-CO), 212.4 (C-
17) ppm; ESI-MS 464 [M+H]+.
2.2.11. 3β-Acetoxy-3′-4″-chlorophenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-
one (6f)
Compound 2 and N-hydroxy-4-chlorobenzenecarboximidoyl chloride (3f, 292 mg) were
used for the synthesis as described in the General Procedure. The crude product 6f (378
mg, 78%) was obtained as a white precipitate. Mp 242−245 °C; Rf = 0.50 (ss A). Anal.
12

1
Calcd. for C28H34ClNO4 (484.03): C, 69.48; H, 7.08. Found: C, 69.37; H, 7.18. H NMR
(CDCl3, 500 MHz): δ 0.82 (m, 1H), 0.90 (s, 3H, 19-H3), 1.03 (s, 3H, 18-H3), 1.04 (m,
1H), 1.13−1.43 (overlapping m, 7H), 1.52 (m, 1H), 1.61−1.84 (overlapping m, 6H), 2.02
(s, 3H Ac-CH3), 2.07 (m, 1H), 2.14 (m, 1H), 4.09 (d, 1H, J = 8.9 Hz, 16-H), 4.70 (m, 1H,
3-H), 5.42 (dd, 1H, J = 8.9 Hz, J = 4.2 Hz, 15-H), 8.11 (d, 2H, J = 7.3 Hz, 3ꢂ-H and 5ꢂ-
H), 8.26 (d, 2H, J = 7.3 Hz, 2ꢂ-H and 6ꢂ-H) ppm; 13C NMR (CDCl3, 125 MHz): δ 12.1
(C-19), 17.9 (C-18), 20.1 (CH2), 21.4 (Ac-CH3), 27.3 (CH2), 28.0 (CH2), 30.4 (CH2), 32.1
(CH), 33.2 (CH2), 33.8 (CH2), 35.8 (C-10), 36.6 (CH2), 44.8 (CH), 48.9 (C-13), 54.3
(CH), 54.9 (CH), 61.9 (CH), 73.3 (C-3), 84.8 (C-15), 126.8 (C-1ꢂ), 128.8 (2C, C-3ꢂ and
C-5ꢂ), 128.9 (2C, C-2ꢂ and C-6ꢂ), 136.4 (C-4ꢂ), 154.4 (C-3′), 170.6 (Ac-CO), 212.3 (C-
17) ppm; ESI-MS 485 [M+H]+.
2.2.12. 3β-Acetoxy-3′-4″-nitrophenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-
one (6g)
Compound 2 and N-hydroxy-4-nitrobenzenecarboximidoyl chloride (3g, 300 mg) were
used for the synthesis as described in the General Procedure. The crude product 6g (223
mg, 45%) was obtained as a yellow precipitate. Mp > 250 °C (decomp.); Rf = 0.38 (ss A).
Anal. Calcd. for C28H34N2O6 (494.58): C, 68.00; H, 6.93. Found: C, 67.87; H, 7.05. 1H
NMR (CDCl3, 500 MHz): δ 0.82 (m, 1H), 0.90 (s, 3H, 19-H3), 1.03 (s, 3H, 18-H3), 1.06
(m, 1H), 1.19−1.43 (overlapping m, 7H), 1.51 (m, 1H), 1.65−1.81 (overlapping m, 6H),
2.03 (s, 3H Ac-CH3), 2.08 (m, 1H), 2.14 (m, 1H), 4.14 (d, 1H, J = 9.1 Hz, 16-H), 4.70 (m,
1H, 3-H), 5.50 (dd, 1H, J = 9.1 Hz, J = 4.0 Hz, 15-H), 8.11 (d, 2H, J = 8.6 Hz, 2ꢂ-H and
6ꢂ-H), 8.26 (d, 2H, J = 8.6 Hz, 3ꢂ-H and 5ꢂ-H) ppm; 13C NMR (CDCl3, 125 MHz): δ 12.2
(C-19), 17.9 (C-18), 20.1 (CH2), 21.4 (Ac-CH3), 27.3 (CH2), 28.0 (CH2), 30.4 (CH2), 32.1
(CH), 33.2 (CH2), 33.8 (CH2), 35.8 (C-10), 36.6 (CH2), 44.8 (CH), 49.0 (C-13), 54.4
13

(CH), 54.9 (CH), 61.4 (CH), 73.3 (C-3), 85.8 (C-15), 123.9 (2C, C-3ꢂ and C-5ꢂ), 128.3
(2C, C-2ꢂ and C-6ꢂ), 134.4 (C-1ꢂ), 148.6 (C-4ꢂ), 154.0 (C-3′), 170.7 (Ac-CO), 212.0 (C-
17) pppm; ESI-MS 495 [M+H]+.
2.2.13. 17β-Hydroxy-3′-phenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one (9a)
Compound 13 and N-hydroxybenzenecarboximidoyl chloride (3a, 233 mg) were used for the
synthesis as described in the General Procedure. The crude product 9a (179 mg, 44%) was
obtained as a white precipitate. Mp 206−208 °C; Rf = 0.41 (ss B). Anal. Calcd. for C26H33NO3
(407.55): C, 76.62; H, 8.16. Found: C, 76.77; H, 8.26. 1H NMR (500 MHz, CDCl3): δ 0.76 (s,
3H, 18-H3), 0.95 (s, 3H, 19-H3), 1.04 (m, 1H), 1.18−1.31 (m, 4H), 1.40−1.84 (m, 9H),
2.04−2.16 (m, 2H), 2.23−2.35 (m, 2H), 3.68 (t, 1H, J = 8.5 Hz, 17-H), 4.30 (d, 1H, J = 9.8
Hz, 2-H), 4.86 (d, 1H, J = 9.8 Hz, 1-H), 7.38 (overlapping m, 3H, 3"-H, 4"-H and 5"-H), 7.75
(d, 2H, J = 7.4 Hz, 2"-H and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 11.1 (C-18), 12.2
(C-19), 20.6 (CH2), 23.4 (CH2), 28.7 (CH2), 30.3 (CH2), 30.6 (CH2), 35.1 (CH), 35.9 (CH),
36.2 (CH2), 38.7 (C-10), 42.7 (CH2), 42.8 (C-13), 46.4 (CH), 50.5 (CH), 58.7 (C-2), 81.7 (C-
17), 88.7 (C-1), 127.5 (2C), 128.5 (2C), 128.8 (C-1"), 130.2 (C-4"), 155.4 (C-5'), 206.0 (C-3)
ppm; ESI-MS 408 [M+H]+.
2.2.14. 17β-Hydroxy-3′-4″-methoxyphenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one
(9b)
Compound 13 and N-hydroxy-4-methoxybenzenecarboximidoyl chloride (3b, 279 mg) were
used for the synthesis as described in the General Procedure. The crude product 9b (289 mg,
66%) was obtained as a white precipitate. Mp 225−228 °C; Rf = 0.31 (ss D). Anal. Calcd. for
1
C27H35NO4 (437.57): C, 74.11; H, 8.06. Found: C, 73.96; H, 8.12. H NMR (500 MHz,
CDCl3): δ 0.75 (s, 3H, 18-H3), 0.94 (s, 3H, 19-H3), 1.03 (m, 1H), 1.17−1.30 (m, 4H),
14

−1.84 (m, 9H), 2.02−2.14 (m, 2H), 2.22−2.34 (m, 2H), 3.67 (t, 1H,
1.37
J = 8.3 Hz, 17-H),
3.81 (s, 3H, 4"-OCH3), 4.27 (d, 1H, J = 10.3 Hz, 2-H), 4.83 (d, 1H, J = 10.3 Hz, 1-H), 6.88 (d,
2H, J = 8.7 Hz, 3"-H and 5"-H), 7.70 (d, 2H, J = 8.7 Hz, 2"-H and 6"-H) ppm; 13C NMR (125
MHz, CDCl3): δ 11.0 (C-18), 12.2 (C-19), 20.5 (CH2), 23.4 (CH2), 28.7 (CH2), 30.3 (CH2),
30.6 (CH2), 35.1 (CH), 35.8 (CH), 36.2 (CH2), 38.7 (C-10), 42.7 (CH2), 42.8 (C-13), 46.4
(CH), 50.6 (CH), 55.3 (OCH3), 58.9 (C-2), 81.7 (C-17), 88.3 (C-1), 114.0 (2C), 121.3 (C-1"),
129.1 (2C), 154.8 (C-5'), 161.1 (C-4"), 206.3 (C-3) ppm; ESI-MS 438 [M+H]+.
2.2.15. 17β-Hydroxy-3′-2″-tolyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one (9c)
Compound 13 and N-hydroxy-2-methylbenzenecarboximidoyl chloride (3c, 255 mg) were
used for the synthesis as described in the General Procedure. The crude product 9c (261 mg,
62%) was obtained as a white precipitate. Mp 163−166 °C; Rf = 0.40 (ss B). Anal. Calcd. for
1
C27H35NO3 (421.57): C, 76.92; H, 8.37. Found: C, 77.05; H, 8.25. H NMR (500 MHz,
CDCl3): δ 0.76 (s, 3H, 18-H3), 0.94 (s, 3H, 19-H3), 1.04 (m, 1H), 1.18−1.32 (m, 4H),
1.40−1.85 (m, 9H), 2.04−2.18 (m, 2H), 2.22−2.32 (m, 2H), 2.50 (s, 3H, 2"-CH3), 3.67 (t, 1H,
J = 8.2 Hz, 17-H), 4.38 (d, 1H, J = 10.1 Hz, 2-H), 4.84 (d, 1H, J = 10.1 Hz, 1-H), 7.20−7.30
13
(overlapping m, 3H), 7.38 (d, 1H, J = 6.9 Hz) ppm; C NMR (125 MHz, CDCl3): δ 11.0 (C-
18), 12.2 (C-19), 20.6 (CH2), 22.3 (2"-CH3), 23.4 (CH2), 28.8 (CH2), 30.3 (CH2), 30.6 (CH2),
35.1 (CH), 35.9 (CH), 36.2 (CH2), 38.8 (C-10), 42.7 (CH2), 42.8 (C-13), 46.4 (CH), 50.6
(CH), 60.7 (C-2), 81.7 (C-17), 87.6 (C-1), 125.7 (CH), 127.7 (C-1"), 129.5 (CH), 129.7 (CH),
131.3 (CH), 137.7 (C-2"), 156.0 (C-5'), 205.5 (C-3) ppm; ESI-MS 422 [M+H]+.
2.2.16. 17β-Hydroxy-3′-3″-tolyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one (9d)
Compound 13 and N-hydroxy-3-methylbenzenecarboximidoyl chloride (3d, 255 mg) were
used for the synthesis as described in the General Procedure. The crude product 9d (215
15

mg, 51%) was obtained as a white precipitate. Mp 175−177 °C; Rf = 0.42 (ss B). Anal.
1
Calcd. for C27H35NO3 (421.57): C, 76.92; H, 8.37. Found: C, 76.80; H, 8.22. H NMR
(500 MHz, CDCl3): δ 0.76 (s, 3H, 18-H3), 0.95 (s, 3H, 19-H3), 1.04 (m, 1H), 1.18−1.30
−1.85 (m, 9H), 2.04−2.16 (m, 2H), 2.22−2.31 (m, 2H), 2.36 (s, 3H, 3"
(m, 4H), 1.40
-CH3),
3.68 (t, 1H, J = 8.4 Hz, 17-H), 4.29 (d, 1H, J = 10.0 Hz, 2-H), 4.85 (d, 1H, J = 10.0 Hz, 1-
H), 7.20 (d, 1H, J = 7.3 Hz), 7.26 (t, 1H, J = 7.3 Hz, 5"-H), 7.53 (d, 1H, J = 7.3 Hz), 7.58
(s, 1H, 2"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 11.0 (C-18), 12.2 (C-19), 20.6 (CH2),
21.4 (3"-CH3), 23.4 (CH2), 28.7 (CH2), 30.3 (CH2), 30.6 (CH2), 35.1 (CH), 35.9 (CH),
36.2 (CH2), 38.7 (C-10), 42.8 (C-13), 42.9 (CH2), 46.4 (CH), 50.5 (CH), 58.8 (C-2), 81.7
(C-17), 88.6 (C-1), 124.7 (CH), 127.9 (CH), 128.4 (CH), 128.7 (C-1"), 131.0 (CH), 138.2
(C-3"), 155.5 (C-5'), 206.1 (C-3) ppm; ESI-MS 422 [M+H]+.
2.2.17. 17β-Hydroxy-3′-4″-tolyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-one (9e):
Compound 13 and N-hydroxy-4-methyl-benzenecarboximidoyl chloride (3e, 255 mg)
were used for the synthesis as described in the General Procedure. The crude product 9e
(223 mg, 53%) was obtained as a white precipitate. Mp 232−234 °C; Rf = 0.45 (ss B).
1
Anal. Calcd. for C27H35NO3 (421.57): C, 76.92; H, 8.37. Found: C, 77.08; H, 8.45. H
NMR (500 MHz, CDCl3): δ 0.76 (s, 3H, 18-H3), 0.94 (s, 3H, 19-H3), 1.05 (m, 1H),
−1.31 (m, 4H), 1.40−1.84 (m, 9H), 2.02−2.14 (m, 2H), 2.22−2.33 (m, 2H), 2.36 (s,
1.18
3H, 4"-CH3), 3.68 (t, 1H, J = 8.5 Hz, 17-H), 4.28 (d, 1H, J = 10.2 Hz, 2-H), 4.84 (d, 1H, J
= 10.2 Hz, 1-H), 7.17 (d, 2H, J = 7.9 Hz, 3"-H and 5"-H), 7.63 (d, 2H, J = 7.9 Hz, 2"-H
and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 11.0 (C-18), 12.2 (C-19), 20.5 (CH2),
21.4 (4"-CH3), 23.4 (CH2), 28.7 (CH2), 30.3 (CH2), 30.6 (CH2), 35.1 (CH), 35.9 (CH),
36.2 (CH2), 38.7 (C-10), 42.7 (CH2), 42.8 (C-13), 46.4 (CH), 50.6 (CH), 58.8 (C-2), 81.7
(C-17), 88.5 (C-1), 125.9 (C-1"), 127.4 (2C), 129.2 (2C), 140.5 (C-4"), 155.3 (C-5'), 206.1
16

(C-3) ppm; ESI-MS 422 [M+H]+.
2.2.18. 17β-Hydroxy-3′-4″-chlorophenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-androstan-3-
one (9f):
Compound 13 and N-hydroxy-4-chlorobenzenecarboximidoyl chloride (3f, 292 mg) were
used for the synthesis as described in the General Procedure. The crude product 9f (164
mg, 37%) was obtained as a white precipitate. Mp 210−212 °C; Rf = 0.41 (ss B). Anal.
1
Calcd. for C26H32ClNO3 (441.99): C, 70.65; H, 7.30. Found: C, 70.82; H, 7.52. H NMR
(500 MHz, CDCl3): δ 0.76 (s, 3H, 18-H3), 0.96 (s, 3H, 19-H3), 1.04 (m, 1H), 1.17−1.32
(m, 4H), 1.40−1.84 (m, 9H), 2.04−2.34 (m, 4H), 3.67 (t, 1H, J = 8.3 Hz, 17-H), 4.23 (d,
1H, J = 10.1 Hz, 2-H), 4.85 (d, 1H, J = 10.1 Hz, 1-H), 7.34 (d, 2H, J = 8.3 Hz, 3"-H and
5"-H), 7.70 (d, 2H, J = 8.3 Hz, 2"-H and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 11.1
(C-18), 12.2 (C-19), 20.5 (CH2), 23.4 (CH2), 27.5 (CH2), 28.6 (CH2), 30.5 (CH2), 34.9
(CH), 35.8 (CH), 36.3 (CH2), 38.5 (C-10), 42.4 (C-13), 42.7 (CH2), 46.4 (CH), 50.4 (CH),
58.3 (C-2), 81.7 (C-17), 88.7 (C-1), 127.4 (C-1"), 128.7 (2C), 128.8 (2C), 136.3 (C-4"),
154.7 (C-5'), 205.8 (C-3) ppm; ESI-MS 443 [M+H]+.
2.2.19. 3β-Hydroxy-3′-phenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-one (11a):
Compound 14 and N-hydroxybenzenecarboximidoyl chloride (3a, 233 mg) were used for the
synthesis as described in the General Procedure. The crude product 11a (375 mg, 92%) was
obtained as a white precipitate. Mp > 280 °C (decomp.); Rf = 0.43 (ss D). Anal. Calcd. for
1
C26H33NO3 (407.55): C, 76.62; H, 8.16. Found: C, 76.85; H, 8.22. H NMR (CDCl3, 500
MHz): δ 0.81 (m, 1H), 0.90 (s, 3H, 19-H3), 1.02 (m, 1H), 1.07 (s, 3H, 18-H3), 1.19 (m, 2H),
1.26−1.47 (overlapping m, 6H), 1.62 (m, 2H), 1.68−1.85 (overlapping m, 4H), 2.08 (m, 1H),
2.16 (m, 1H), 3.61 (m, 1H, 3-H), 4.14 (d, 1H, J = 9.2 Hz, 16-H), 5.43 (dd, 1H, J = 9.2 Hz, J =
17

4.3 Hz, 15-H), 7.42 (m, 3H, 3ꢂ-H, 4ꢂ-H and 5ꢂ-H), 7.94 (m, 2H, 2ꢂ-H and 6ꢂ-H) ppm; ESI-
MS 408 [M+H]+.
2.2.20. 3β-Hydroxy-3′-4″-methoxyphenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-
17-one (11b)
Compound 14 and N-hydroxy-4-methoxybenzenecarboximidoyl chloride (3b, 279 mg)
were used for the synthesis as described in the General Procedure. The crude product 11b
(424 mg, 97%) was obtained as a white precipitate. Mp 205−208 °C; Rf = 0.24 (ss D).
1
Anal. Calcd. for C27H35NO4 (437.57): C, 74.11; H, 8.06. Found: C, 73.95; H, 8.22. H
NMR (CDCl3, 500 MHz): δ 0.79 (m, 1H), 0.89 (s, 3H, 19-H3), 1.06 (m, 1H and s, 3H, 18-
H3), 1.12−1.33 (overlapping m, 3H), 1.35−1.43 (overlapping m, 4H), 1.53 (m, 1H), 1.62
(m, 2H), 1.67−1.84 (overlapping m, 4H), 2.08 (m, 1H), 2.14 (m, 1H), 3.61 (m, 1H, 3-H),
3.84 (s, 3H, 4ꢂ-OMe), 4.11 (d, 1H, J = 9.1 Hz, 16-H), 5.39 (dd, 1H, J = 9.1 Hz, J = 4.2
Hz, 15-H), 6.93 (d, 2H, J = 8.8 Hz, 3ꢂ-H and 5ꢂ-H), 7.88 (d, 2H, J = 8.8 Hz, 2ꢂ-H and 6ꢂ-
H) ppm; ESI-MS 438 [M+H]+.
2.2.21.
3β-Hydroxy-3′-4″-tolyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-one
(11e)
Compound 14 and N-hydroxy-4-methylbenzenecarboximidoyl chloride (3e, 255 mg) were
used for the synthesis as described in the General Procedure. The crude product 11e (396
mg, 94%) was obtained as a white precipitate. Mp 221−224 °C; Rf = 0.29 (ss D). Anal.
1
Calcd. for C27H35NO3 (421.57): C, 76.92; H, 8.37. Found: C, 76.80; H, 8.44. H NMR
(CDCl3, 500 MHz): δ 0.79 (m, 1H), 0.89 (s, 3H, 19-H3), 1.06 (m, 1H and s, 3H, 18-H3),
1.14−1.33 (overlapping m, 3H), 1.35−1.43 (overlapping m, 4H), 1.56−1.84 (overlapping
18

m, 7H), 2.07 (m, 1H), 2.15 (m, 1H), 2.37 (s, 3H, 4ꢂ-CH3), 3.61 (m, 1H, 3-H), 4.13 (d, 1H,
J = 9.1 Hz, 16-H), 5.40 (dd, 1H, J = 9.0 Hz, J = 4.1 Hz, 15-H), 7.22 (d, 2H, J = 7.7 Hz,
3ꢂ-H and 5ꢂ-H), 7.82 (d, 2H, J = 7.7 Hz, 2ꢂ-H and 6ꢂ-H) ppm; ESI-MS 422 [M+H]+.
2.2.22. 3β-Hydroxy-3′-4″-chlorophenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-
one (11f):
Compound 14 and N-hydroxy-4-chlorobenzenecarboximidoyl chloride (3f, 292 mg) were
used for the synthesis as described in the General Procedure. The crude product 11f (340
mg, 77%) was obtained as a white precipitate. Mp > 280 °C (decomp.); Rf = 0.31 (ss D).
1
Anal. Calcd. for C26H32ClNO3 (441.99): C, 70.65; H, 7.30. Found: C, 70.47; H, 7.21. H
NMR (CDCl3, 500 MHz): δ 0.80 (m, 1H), 0.89 (s, 3H, 19-H3), 1.04 (m, 1H), 1.05 (s, 3H,
18-H3), 1.18 (m, 2H), 1.26−1.47 (overlapping m, 6H), 1.62 (m, 2H), 1.68−1.85
(overlapping m, 4H), 2.08 (m, 1H), 2.15 (m, 1H), 3.61 (m, 1H, 3-H), 4.09 (d, 1H, J = 9.2
Hz, 16-H), 5.43 (dd, 1H, J = 9.2 Hz, J = 4.3 Hz, 15-H), 7.39 (d, 2H, J = 8.5 Hz, 3ꢂ-H and
5ꢂ-H), 7.87 (d, 2H, J = 8.5 Hz, 3ꢂ-H and 5ꢂ-H) ppm; ESI-MS 442 [M+H]+.
2.2.23. 3β-Hydroxy-3′-4″-nitrophenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-17-
one (11g):
Compound 14 and N-hydroxy-4-nitrobenzenecarboximidoyl chloride (3g, 300 mg) were
used for the synthesis as described in the General Procedure. The crude product 11g (199
mg, 44%) was obtained as a yellow precipitate. Mp 210−212 °C; Rf = 0.30 (ss D). Anal.
1
Calcd. for C26H32N2O5 (452.54): C, 69.01; H, 7.13. Found: C, 69.16; H, 7.01. H NMR
(CDCl3, 500 MHz): δ 0.81 (m, 1H), 0.90 (s, 3H, 19-H3), 1.02 (m, 1H), 1.04 (s, 3H, 18-
H3), 1.19 (m, 2H), 1.26−1.47 (overlapping m, 6H), 1.62 (m, 2H), 1.68−1.85 (overlapping
m, 4H), 2.08−2.17 (m, 2H), 3.61 (m, 1H, 3-H), 4.14 (d, 1H, J = 9.0 Hz, 16-H), 5.51 (dd,
19

1H, J = 9.0 Hz, J = 4.5 Hz, 15-H), 8.12 (d, 2H, J = 9.0 Hz, 2ꢂ-H and 6ꢂ-H), 8.27 (d, 2H, J
= 9.0 Hz, 3ꢂ-H and 5ꢂ-H) ppm; ESI-MS 453 [M+H]+.
2.3. Deacetylation of 17β-acetoxy-3′-4″-methoxyphenyl-2′-isoxazolino[4′,5′-d:2α,1α]-5α-
androstan-3-one (5b)
Method A: Compound 5b (150 mg, 0.31 mmol) was dissolved in MeOH (10 mL), and KOH
(50 mg, 0.89 mmol) was added. The solution was stirred at room temperature for 3 h and then
diluted with water, and the precipitate that formed was filtered off, washed with water and
purified by flash chromatography with EtOAc/CH2Cl2 = 20:80 as eluent to obtain 7b (100
mg, 74%) and 8b (25 mg, 18%) as white crystals (sequence of elution: 7b > 8b).
Method B: Compound 5b (150 mg, 0.31 mmol) was dissolved in DMSO (10 mL), and tBuOK
(80 mg, 0.71 mmol) was added. The solution was stirred at 80 °C for 1 h and then diluted with
water and extracted with EtOAc (2 × 10 mL). The crude product was purified by flash
chromatography with EtOAc/CH2Cl2 = 20:80 as eluent to obtain 7b (120 mg, 89%).
7b: Mp 128−131 °C; Rf = 0.38 (ss D). Anal. Calcd. for C27H33NO4 (435.56): C, 74.45; H,
1
7.64. Found: C, 74.60; H, 7.48. H NMR (500 MHz, CDCl3): δ 0.83 (s, 3H, 18-H3),
0.96−1.11 (m, 3H), 1.32 (s, 3H, 19-H3), 1.40−1.63 (m, 7H), 1.70−1.79 (m, 2H), 1.92 (m, 1H),
2.06 (m, 1H), 2.20 (m, 1H), 2.38 (m, 1H), 2.56−2.68 (m, 2H), 3.68 (t, 1H, J = 8.3 Hz, 17-H),
3.84 (s, 3H, 4"-OCH3), 6.97 (d, 2H, J = 7.7 Hz, 3"-H and 5"-H), 7.94 (d, 2H, J = 7.7 Hz, 2"-H
and 6"-H) ppm; 13C NMR (125 MHz, CDCl3): δ 11.4 (C-18), 13.6 (C-19), 23.4 (CH2), 23.8
(CH2), 26.5 (CH2), 29.7 (C-10), 30.2 (CH2), 30.4 (CH2), 36.2 (CH), 36.6 (CH2), 41.4 (C-13),
42.9 (CH2), 45.1 (CH), 49.5 (CH), 50.8 (CH), 55.3 (4ꢂ-OCH3), 81.6 (C-17), 113.2 (C-2),
113.7 (2C, C-3ꢂ and C-5ꢂ), 119.7 (C-1ꢂ), 130.8 (2C, C-2ꢂ and C-6ꢂ), 159.5 (C-3′), 161.3 (C-
4ꢂ), 189.8 (C-1), 191.9 ppm; ESI-MS 436 [M+H]+.
20

8b: Mp 239−242 °C; Rf = 0.34 (ss E). Anal. Calcd. for C27H35NO5 (453,57): C, 71.50; H,
1
7.78. Found: C 71.37; H, 7.92. H NMR (500 MHz, DMSO-d6): δ 0.64 (s, 3H, 18-H3), 0.66
(s, 3H, 19-H3), 0.88 (m, 2H), 1.01 (m, 1H), 1.12−1.50 (overlapping m, 7H), 1.61 (m, 3H),
1.78 (m, 2H), 1.92 (m, 1H), 2.21 (m, 1H), 2.74 (dd, J = 17.1 Hz, J = 6.4 Hz, 1H), 3.44 (m, 17-
H), 3.78 (s, 3H, 4ꢂ-OMe), 4.19 (s, 1H, 1-H), 4.46 (d, J = 4.3 Hz, 17-OH), 6.95 (d, 2H, J =8.4
Hz, 3ꢂ-H and 5ꢂ-H), 7.02 (s, 1H, 2-OH), 7.64 (d, 2H, J = 8.4 Hz, 2ꢂ-H and 6ꢂ-H) ppm; 13C
NMR (125 MHz, CDCl3): δ 7.3 (C-19), 11.2 (C-18), 22.6 (CH2), 23.0 (CH2), 27.3 (C-10),
29.7 (CH2), 30.4 (2×CH2), 34.6 (CH), 36.4 (CH2), 37.6 (CH), 40.8 (CH2), 42.4 (C-13), 50.1
(CH), 54.7 (CH), 55.1 (4ꢂ-OMe), 79.9 (C-17), 89.0 (C-2), 97.4 (C-1), 113.7 (2C, C-3ꢂ and C-
5ꢂ), 120.8 (C-1ꢂ), 128.8 (2C, C-2ꢂ and C-6ꢂ), 156.3 (C-3′), 160.3 (C-4ꢂ), 207.0 (C-3) ppm;
ESI-MS: 454 [M+H]+.
Method C: Compound 5b (150 mg, 0.31 mmol) was dissolved in DMSO (10 mL), and tBuOK
(80 mg, 0.71 mmol) was added under a N2 atmosphere. The solution was stirred at 80 °C for 1
h and then diluted with water and extracted with EtOAc (2 × 10 mL). The crude product was
purified by flash chromatography with EtOAc/CH2Cl2 = 5:95 as eluent to obtain 9b (115 mg,
85%). See. 2.2.14.
2.4. Deacetylation of 3β-acetoxy-3′-phenyl-2′-isoxazolino[4′,5′-d:16β,15β]-5α-androstan-
17-one (6a)
Method A: Compound 6a (135 mg, 0.30 mmol) was dissolved in MeOH (10 mL), and KOH
(50 mg, 0.89 mmol) was added. The solution was stirred at room temperature for 8 h and then
diluted with water, and the precipitate that formed was filtered off, washed with water and
purified by flash chromatography with EtOAc/CH2Cl2 = 10:90 as eluent to obtain 10a (73 mg,
55%) and 11a (45 mg, 37%) as white crystals (sequence of elution: 11a > 10a).
21

10a: Mp 192−195 °C; Rf = 0.25 (ss D). Anal. Calcd. for C27H37NO4 (439.59): C, 73.77; H,
8.48. Found: C, 73.85; H, 8.60. 1H NMR (CDCl3, 500 MHz): δ 0.82 (m, 3H, 19-H3), 0.85 (m,
1H), 0.98 (m, 1H), 1.11 (m, 2H), 1.29 (m, 4H and s, 3H, 18-H3), 1.39 (m, 1H), 1.55−1.75
(overlapping m, 8H), 1.81 (m, 1H), 2.26 (m, 1H), 3.09 (dd, 1H, J = 16.5 Hz, J = 9.0 Hz, one
of 16-H2), 3.44 (dd, 1H, J = 16.5 Hz, J = 11.2 Hz, the other 16-H2), 3.60 (m, 1H, 3-H), 3.62
(s, 3H, 17-OMe), 4.42 (m, 1H, 15-H), 7.38 (m, 3H, 3ꢂ-H, 4ꢂ-H and 5ꢂ-H), 7.63 (m, 2H, 2ꢂ-H
and 6ꢂ-H) ppm; 13C NMR (CDCl3, 125 MHz): δ 12.3 (C-19), 16.0 (C-18), 20.1 (CH2), 28.5
(CH2), 31.3 (CH2), 32.6 (CH2), 35.6 (C-10), 35.7 (CH), 36.9 (CH2), 37.7 (CH2), 37.8 (CH2),
42.4 (C-16), 44.1 (CH), 45.3 (C-13), 51.7 (17-OMe), 52.7 (CH), 53.7 (CH), 71.0 (C-3), 83.0
(C-15), 126.5 (2C, C-2ꢂ and C-6ꢂ), 128.6 (2C, C-3ꢂ and C-5ꢂ), 129.7 (C-1ꢂ), 129.8 (C-4ꢂ),
156.1 (C-3′), 178.8 (C-17) ppm; ESI-MS: 440 [M+H]+.
t
Method B: Compound 6a (135 mg, 0.30 mmol) was dissolved in BuOH (10 mL), and KOH
(50 mg, 0.89 mmol) was added. The solution was stirred at room temperature for 3 h and then
diluted with water, and the precipitate that formed was filtered off, washed with water and
dried. The crude polar product 12a (111 mg, 87%) was obtained as a white precipitate. Anal.
1
Calcd. for C26H35NO4 (425.56): C, 73.38; H, 8.29. Found: C, 73.27; H, 8.37. H NMR
(DMSO-d6, 500 MHz): δ 0.76 (m, 3H, 19-H3), 0.80 (m, 2H), 0.91 (m, 2H), 1.07 (m, 4H and s,
3H, 18-H3), 1.39 (m, 1H), 1.54−1.74 (overlapping m, 8H), 2.28 (m, 1H), 3.25 (dd, 1H, J =
17.4 Hz, J = 12.3 Hz, one of 16-H2), 3.46 (dd, 1H, J = 17.4 Hz, J = 12.3 Hz, the other 16-H2),
3.60 (m, 1H, 3-H), 4.42 (d, 1H, J = 4.5 Hz, 3-OH), 4.52 (t-like m, 1H, 15-H), 7.43 (m, 3H, 3ꢂ-
H, 4ꢂ-H and 5ꢂ-H), 7.64 (m, 2H, 2ꢂ-H and 6ꢂ-H), 12.13 (bs, 1H, COOH) ppm; ESI-MS: 426
[M+H]+.
Method C: Compound 6a (135 mg, 0.30 mmol) was dissolved in DMSO (10 mL), and tBuOK
(80 mg, 0.71 mmol) was added. The solution was stirred at 80 °C for 1 h and then diluted with
water and extracted with EtOAc (2 × 10 mL). The crude product was purified by flash
22

chromatography with EtOAc/CH2Cl2 = 5:95 as eluent to obtain 11a (106 mg, 87%). See.
2.2.19.
Results and Discussion
Since conjugation of the alkenyl moiety with a C=O bond has been demonstrated to have a
strong promoting effect on the reactivity of the dipolarophile [14], the steroidal unsaturated
ketones 17β-acetoxy-5α-androst-1-en-3-one (1) [24] and 3β-acetoxy-5α-androst-15-en-17-
one (2) [25], readily available from 5α-dihydrotestosterone and dehydroepiandosterone,
respectively, in a multistep pathway, were applied for the transformations (Table 1). Aromatic
hydroximidoyl chlorides (3a−g), as relatively stable precursors of nitrile oxides (4a−g), were
synthetized in two steps by the general protocol from benzaldehyde or its substituted
derivatives [26]. The 1,3-dipoles (4a−g) can be generated in situ from 3a−g by
dehydrochlorination with a base.
Preliminary ring-closure experiments on 1 and 2 with benzonitrile oxide 4a were first
carried out to determine the optimum conditions. The steroidal enone (1 or 2) and an excess of
N-hydroxybenzenecarboximidoyl chloride (3a) were dissolved in toluene and 3 equivalents of
N,N-diisopropylethylamine (DIPEA) was slowly added in order to ensure a low stationary
concentration of the dipole and to minimize undesired furoxane formation. After the
completion of DIPEA addition at room temperature, the solution was refluxed to achieve
complete conversion for compound 2 within 2 h, leading to a single product 6a in a yield of
94% after chromatographic purification (Table 1, entry 8). However, the similar reaction of 1
with 4a was not complete after a 5-h heating period, as indicated by TLC, and the yield of the
purified isoxazoline (5a) was only 55% (entry 1), together with a considerable amount (42%)
of the residual starting material 1. The rate of cycloaddition was much slower at room
temperature or below, and refluxing of the mixtures was therefore necessary for sufficient
23

conversions. Similar cycloadditions of 1 and 2 with various substituted benzonitrile oxides
(4b−g) were subsequently performed under the same conditions to furnish novel ring-
condensed isoxazolines (5b−g, 6b and 6e−g) in moderate to excellent yields (entries 2−7 and
9−12).
Depending on the dipole orientation relative to the double bond, two regioisomers, each
involving four diastereoisomers (two cis and two trans) as concerns the newly-formed
stereogenic centres on C-1 and C-2 in 5a−g or on C-15 and C-16 in 6a−e can be conceived as
possible products of the cycloadditions. However, the trans-like connection of the 1,3-dipole
in both orientations is precluded because of the ring strain. The attack of the dipole from
above the general plane of the sterane framework (the β side) is unlikely in 1 in consequence
of the same spatial orientation of the 18-CH3 [27]. Similarly, the introduction of the nitrile
oxide in 2 is unlikely to occur from beneath (the α side) in consequence of the steric
interaction between the dipole and 14-Hα [28, 29]. Accordingly, for both reactions only two
regioisomers are probable (depicted in Table 1), containing a 1α,2α-cis (5 and 5’) or a
15β,16β-cis ring junction (6 and 6’). The formation of regioisomers (5’ and 6’) in which the
O terminus of the dipole is attached to the α-carbon of the dipolarophile, and the aromatic
ring is therefore bent towards the sterane portion, is considered to be hampered by steric
repulsions. The most facilitated isomers are undoubtedly 5 and 6, in which the anionic pole of
the nitrile oxide is connected to the β carbon of 1 or 2. Both the regio- and the
stereoselectivity of the ring closures are therefore influenced by steric factors, in good
agreement with earlier observations that the electronic character of the dipolarophile has only
a minor effect on such reactions [30].
The overall yields of the products (5a−g, 6a, 6b and 6e−g) were found to depend on the
electronic features of the substituents on the aromatic ring of the dipoles 4a−g (Table 1), and
24

this effect was more pronounced in the case of the ring A-fused derivatives 5a−g. The
electron-donating substituents in 4b and 4e favoured cycloaddition to 1 and 2 (Table 1, entries
2, 5, 9 and 10), in consequence of the lower tendency of these dipoles to undergo dimerization
to furoxanes, while the yields of the desired products (5f and 6f, or 5g and 6g) were decreased
by the presence of the electron-withdrawing groups on the aromatic moiety in 4f and 4g
(entries 6, 7, 11 and 12). The lowest conversions were achieved for the reactions of 1 and 2
with p-nitrobenzonitrile oxide 4g, which resulted in the desired products (5g and 6g) in yields
of only 19% and 45%, respectively. In order to investigate both the electronic and the steric
effects of the substituents on the reactivity of the dipoles, the cycloadditions of o- and m-
methyl-substituted benzonitrile oxides (4c and 4d) to 1 were also carried out (entries 3 and 4).
The highest yield of the tolyl-substituted cycloadducts (5c−e) was that for 5c, which was
comparable to that of the methoxy-substituted analogue 5b (entry 3). This is indicative of the
steric hindrance of the o-methyl group and hence the increased resistance of this dipole (4c)
against dimerization to furoxane [14]. The five-membered ring D of 2 proved to be more
reactive against nitrile oxides than the six-membered ring A of 1, and the related products
were obtained in higher yields within shorter reaction times. A similar difference in reactivity
was earlier observed for the reactions of cyclopentene and cyclohexene, the former being
more reactive due to ring strain and conformational effects [16].
1
The structures of all the synthetized compounds were confirmed by H and 13C NMR
measurements. The presence of the phenyl or substituted phenyl ring derived from the nitrile
oxides (4a−g) was demonstrated by the signals in the aromatic range of the ppm scale in
5a−g, 6a, 6b and 6e−g. In the 1H NMR spectra of 5a−g, the signals of 2-H and 1-H appeared
as two doublets at around 4.27 and 4.85 ppm. The coupling constant 2JH,C,H of about 10.0 Hz
was consistent with the 1α,2α-(cis)-anellation of the hetero ring. At the same time, the
doublet of 16-H and the double doublet of 15-H were detected at around 4.12 and 5.42 ppm in
25

the spectra of 6a, 6b and 6e−g. The exact configurations of the newly formed stereocentres
were established with the aid of homonuclear 2D NMR (COSY and NOESY) and
heteronuclear 2D NMR (HSQC and HMBC) measurements.
The deacetylations of one cycloadduct from both sets of compounds (5b and 6a) were
carried out by using general conditions so as to obtain the corresponding 17-OH analogs of 5
and 3-OH derivatives of 6. However, the transformations led to unexpected products in
particular cases. 17-Deacetylation of 5b in alkaline MeOH at room temperature resulted in the
simultaneous formation of a heteroaromatic isoxazole (7b) and a 4′-hydroxylated isoxazoline
(8b) in an approximate ratio of 4:1, the structures of which were confirmed by NMR
spectroscopy after separation (Scheme 1). The formation of the 4′-OH derivative 8b can be
explained by the oxidation of the corresponding enolate produced in alkaline medium. Such
hydroxylation has already been observed, especially for ketones containing a tertiary carbon
at the α position [31]. The spontaneous aromatization of the isoxazoline ring of 5b to
isoxazole 7b is quite unusual, however, since the oxidation of such rings is more difficult than
that of pyrazolines to pyrazoles [32], and the application of different oxidizing reagents is
usually needed [33] even for the dehydrogenation of six-membered ring-condensed analogues
t
o
[34]. Interestingly, repeated deacetylation of 5b with BuOK in DMSO at 80 C led to the
formation of 7b alone, which can be attributed to the fact that the enolate needed for α-
hydroxylation is less favoured in more polar solvents. Although 8b proved to be quite stable
in alkaline medium, it could be converted to 7b by elimination in the presence of p-
toluenesulfonic acid or sulfuric acid at elevated temperature. However, similar reaction by
applying an inert atmosphere led to the desired product 9b exclusively.
Scheme 1
26

When the 3-deacetylation of the ring D-fused analogue 6a was carried out at room
temperature, the major formation of a D-seco ester (10a) was observed, together with the
desired product (11a) in a ratio of about 6:4 (Scheme 2), while 10a was the sole product when
either 6a or 11a was refluxed in alkaline MeOH. However, exclusively the seco-carboxylic
t
acid 12a was obtained when MeOH was replaced by BuOH presumably due to the poor
t
nucleophilicity of BuO− which precludes its attack on C-17. The desired 3β-hydroxy
t
compound 11a was obtained as sole product by applying BuOK in DMSO for repeated
deacetylation.
Scheme 2
The observed (a1a) fragmentation is similar to the retro-Dieckmann reactions of 1,3-
diketones and ketoesters [35], where the attack of the MeO− or ΗΟ− nucleophile, derived
from either the solvent or the reagent, on the carbonyl-C induces the cleavage of ring D
between C-16 and C-17, as depicted in Figure 1. Simultaneous deacetylation on C-3 also
occurs to furnish 10a or 12a. The formation of the D-seco derivatives (10a and 12a) serves as
indirect evidence of the regioselectivity of the 1,3-cycloaddition of 2 with 4a−e, because the
fragmentation would not be possible in the cases of 6′a−e (see Table 1).
Figure 1
The different behavior observed for 5b and 6a under deacetylation conditions may be
attributed to the higher rigidity and sterically more hindered character of ring D in 6a
compared to the flexible six-membered ring A in 5b. Aromatization of the hetero ring should
27

further enhance the ring strain of ring D in 6a, therefore, fragmentation induced by a
nucleophile attack on C-17 instead of oxidation is more favorable in this case.
The 1,3-cycloadditions of nitrile oxides generated in situ from 3a−g were also carried out
with the corresponding 17- and 3-OH analogues (13 and 14) of 1 and 2 under the same
conditions as applied earlier (Table 2). Similar tendencies concerning the reaction rates and
the electronic and steric effects of the substituents on the aromatic ring of the nitrile oxides
4a−g and therefore the yields of the desired products (9a−g, 11a, 11b and 11e−g) were found
to be repeated here too. The lower reactivity of ring A than that of ring D was again
manifested. Since the p-nitrophenyl-substituted compound 5g was isolated in only a moderate
yield (19%) from the reaction of 1 with 4g, the similar cycloaddition of 13 and 4g was not
performed in this case.
Table 2
Conclusions
In summary, novel types of steroidal isoxazolines condensed to either ring A or ring D of the
sterane framework were synthetized through the 1,3-dipolar cycloaddition of 5α-
androstenones and aromatic nitrile oxides. The ring closures proved to occur in a regio- and
stereoselective manner to furnish a single isomer in all cases, in moderate to excellent yields.
The higher reactivity of the five-membered ring D led to higher yields of the corresponding
products, though all the reactions were affected by the substitution pattern of the nitrile
oxides. The 17- and 3-deacetylation of the isoxazolines in alkaline medium opened the way
for interesting oxidation and fragmentation pathways, resulting in aromatization of the hetero
ring for the ring A-fused derivatives, and skeletal cleavage of the ring D-condensed analogues
without affecting the isoxazoline moiety.
28

Acknowledgements
The financial support by the Hungarian Scientific Research Fund (OTKA K-109107) is
gratefully acknowledged. The research by D. Kovács was supported by the European Union
and the State of Hungary, co-financed by the European Social Fund in the framework of
TÁMOP 4.2.4. A/2-11/1-2012-0001 ꢂNational Excellence Programꢂ.
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