Synthesis of [1,2,4]-triazolo-annulated 3-aza-A-homocholestanes - A novel class of pentacyclic compounds

Article abstract of DOI:10.1016/j.steroids.2012.01.016

This study was performed to investigate the reactivity of azocarbenium salts derived from 5α-cholestan-3-one towards 1,3-dipolar cycloaddition reactions with inverse electron-demand to produce unprecedented steroidal heterocyclic derivatives, i.e. [1,2,4]

Full text of DOI:10.1016/j.steroids.2012.01.016

Steroids 77 (2012) 521–527
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Steroids
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Synthesis of [1,2,4]-triazolo-annulated 3-aza-A-homocholestanes—A novel
class of pentacyclic compounds
⇑
Hexiang Bai, Shijing Xia, Zhiming Li, Jingmei Wang, Quanrui Wang
Department of Chemistry, Fudan University, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
This study was performed to investigate the reactivity of azocarbenium salts derived from 5a-cholestan-
Received 10 November 2011
Received in revised form 18 January 2012
Accepted 22 January 2012
Available online 31 January 2012
3-one towards 1,3-dipolar cycloaddition reactions with inverse electron-demand to produce unprece-
dented steroidal heterocyclic derivatives, i.e. [1,2,4]-triazolo-annulated 3-aza-A-homocholestanes 8
and 11 and picrates 12. The synthetic steps were comprised of oxidizing hydrazones 3 with tert-butyl
hypochlorite to germinal chloroazo compounds 4, generation of the 1-aza-2-azoniaallene cations 5 by
action with equimolar antimony pentachloride and interception with nitrile and alkyne molecules by
cycloaddition to the triple bond followed by ring enlargement. The structure of the compounds was prin-
cipally established on the basis of the analytical and spectral data along with the previously published X-
ray diffraction analysis on 8a.
Keywords:
5a-Cholestan-3-one
3-Aza-A-homocholestanes
1,3-Dipolar cycloaddition
Ring expansion
Ó 2012 Elsevier Inc. All rights reserved.
1. Introduction
1,2,4-triazolo-fused steroidal azepine compound from
cholestan-3-one [17].
5a-
Steroid heterocycles have interesting biological activities [1–3].
The replacement of one or more carbon atoms in a steroid mole-
cule by a heteroatom, especially nitrogen often results in useful
alterations of its biological activity [4]. On the other hand, azepine
compounds with an additional triazolo ring fused on the seven-
membered ring possess a wide spectrum of important biological
properties, such as anti-tumor agents [5], selective inhibition of
11b-hydroxysteroid dehydrogenase [6], the reduction of beta-
amyloid protein production [7], and even herbicidal activity [8].
In general, the fusion of a triazolo ring plays a vital role in enhanc-
ing the affinities for receptors. To the best of our awareness,
available methods for achieving the expansion of the steroidal
A-ring to an azepine ring seem to be scarce. The most exploited
strategies are the Schmidt reaction [9,10] and the Beckmann
rearrangement [11,12].
In recent years, we have been engaged in a program toward syn-
thesizing novel triazolo annulated heterocycles. We have established
a reliable synthetic pathway to [1,2,4]triazolo[3,2-d][1,5]benzoxaze-
pines and their chalcogen analogs starting from chroman-4-ones and
thiochroman-4-ones [13,14]. We have also successfully applied the
protocol to the synthesis of novel thieno[2,3-f][1,2,4]triazolo[1,5-
a]azepines, furo[3,2-c][1,2,4]triazolo[1,5-a]azepinium salts and
furo[2,3-f][1,2,4]triazolo[1,5-a]azepinum picrates by starting from
the appropriate bicyclic ketones [15,16]. Quite recently, we have also
successfully employed this strategy to achieve a hitherto unknown
In continuation of our long-standing interests on this topic, we
report herein the detailed study on the synthesis of this class of
novel 1,2,4-triazolo-fused steroidal azepine compounds. The syn-
thetic genre shares a common mechanistic scenario: the key step
employs the cycloaddition of 1-aza-2-azoniaallenium ions, posi-
tively charged four-electron, three-center 1,3-dipoles, to the triple
bond of unsaturated compounds followed by ring enlargement and
insertion of a nitrogen atom to furnish the pentacyclic products.
2. Experimental
2.1. General remarks
All commercial materials were used without further purifica-
tion. Solvents were purified and dried by standard methods prior
to use. Reactions were monitored by thin layer chromatography
(TLC) on Silica Gel 60 F254 (Fluka). Infrared spectra were recorded
as KBr disks on a Nicolet-360 IR spectrometer. 1H and 13C NMR
spectra were measured in CDCl3 solutions on a JEOL ECA 400 or a
Bruker AMX 500 spectrometer using TMS as an internal reference
and reported in ppm (d). Coupling constant (J) values are given in
Hz. Multiplicity are expressed as follows: s = singlet, d = doublet,
t = triplet, q = quartet, m = multiplet, br = broad. Elemental analysis
for C, H, N was performed on CAPLO ERBA1106 elemental analyzer.
High resolution mass spectra (HRMS) were recorded on
a
SHIMADZU LCMS-IT-TOF mass spectrometer with ESI ionization.
Melting points were determined in open capillary tubes and are
uncorrected.
⇑
Corresponding author. Fax: +86 21 65641740.
E-mail address: qrwang@fudan.edu.cn (Q. Wang).
0039-128X/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved.
doi:10.1016/j.steroids.2012.01.016

522
H. Bai et al. / Steroids 77 (2012) 521–527
2.2. Organic synthesis
2.2.7. [1R-[1a a,5ab,12aa,12bb,14aa]]-
(R⁄),3ab,3b
1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-tetradecahydro-12a,14a-
dimethyl-1-(1,5-dimethylhexyl)- 8-propyl-9-(2,4,6-trichlorophenyl)-
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepinium
hexachloroantimonate (8b)
2.2.1. General experimental procedure for the synthesis of 5
cholestan-3-one hydrazones
a-
Equimolar amounts of 5a-cholestan-3-one 1 (1.93 g, 5 mmol)
and hydrazine 2a or hydrazide 2b (5 mmol) in EtOH (20 mL) con-
taining HOAc (0.1 mL) were heated under reflux for 3 h and then
left to cool. The solid product 3 formed upon cooling at room tem-
perature was collected by filtration and crystallized from hot EtOH
(95%).
From hydrazone 3a and butyronitrile. Upon completion of the
reaction, all volatiles were removed by distillation under high vac-
uum, the green residue was recrystallized from MeOH and then
from MeOH–MeCN (v/v 5:1) twice to afford pure 8b. Yield 0.29 g
(30%); brown powder; mp 170–172 °C. IR (KBr):
m 2933, 2868,
1560, 1556, 1457, 1386 cmꢀ1 1H NMR (400 MHz, CDCl3): d 0.65–
.
2.50 (m, 47H, steroidal H & CH2CH2CH3), 2.55 (t, J = 7.1 Hz, 2H,
CH2CH2CH3), 3.00 (m, 1H, Hc), 3.33 (m, 1H, Hd), 4.10 (m, 1H, Ha),
4.37 (m, 1H, Hb), 7.73 (s, 2H, Ar–H). 13C NMR (125 MHz, CDCl3):
d 11.9, 12.1, 18.7, 21.3, 22.6, 22.8, 23.82, 24.09, 28.0, 28.2, 28.4,
28.5, 30.3, 31.1, 31.5, 34.6, 34.8, 35.7, 36.1, 37.4, 39.5, 39.6, 39.7,
42.2, 43.7, 45.1, 46.2, 52.6, 56.2, 56.3 (steroidal & n-Pr), 122.4,
130.8, 131.1, 135.6, 136.6, 143.0 (Ar)), 162.6, 163.9 (C@N). HRMS
(ESI): m/z calcd. for the cation [C37H55Cl3N3]+: 646.3462; found:
646.3440.
2.2.2. 5a-Cholestan-3-one (2,4,6-trichlorophenyl)hydrazone (3a)
The physical data and spectral data for 3a were published pre-
viously (Ref. [17]).
2.2.3. 5
a-Cholestan-3-one (N-ethoxycarbonyl)hydrazone (3b)
From 5a-cholestan-3-one 1 and ethyl carbazate 2b. Yield 2.20 g
(93%); white solid; mp 99–100 °C. IR (KBr):
m 3280, 1715, 1557,
1250 cmꢀ1. 1H NMR (500 MHz, CDCl3): d 0.66–2.52 (m, 49H, steroi-
dal H & CO2CH2CH3), 4.27 (q, J = 6.1 Hz, 2H, CO2CH2CH3), 7.62 (s,
1H, NH). Anal. required for C30H52N2O2 (%): C, 76.22; H, 11.09; N,
5.93. Found: C, 76.33; H, 10.95; N, 5.95.
2.2.8. [1R-[1a a,5ab,12aa,12bb,14aa]]-8-benzyl-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-12a,14a-dimethyl-9-(2,4,6-trichlorophenyl)-
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepinium
hexachloroantimonate (8c)
From hydrazone 3a and phenylacetonitrile. Work-up as de-
scribed above furnished 8c. Yield 0.34 g (33%); brown powder;
2.2.4. Preparation of the
procedure
a-chloroazo substrates (4a,b): general
mp 140–142 °C. IR (KBr):
m 2929, 1627, 1562, 1449, 1385,
1106 cmꢀ1. 1H NMR (400 MHz, CDCl3): d 0.66–2.50 (m, 42H, steroi-
dal H), 3.02 (m, 1H, Hc), 3.31 (m, 1H, Hd), 4.05 (s, 2H, Ph-CH2), 4.11
(m, 1H, Ha), 4.30 (m, 1H, Hb), 7.00–7.29 (m, 5H, Ph), 7.65 (s, 2H,
Cl3C6H2). 13C NMR (125 MHz, CDCl3): d 12.0, 18.6, 21.4, 22.5,
22.8, 23.8, 24.0, 24.1, 28.0, 28.2, 29.7, 30.3, 31.5, 33.9, 34.2, 34.6,
34.8, 35.7, 36.1, 39.5, 39.8, 42.2, 43.9, 52.8, 56.2, 56.3 (steroidal &
PhCH2), 122.6, 128.6, 129.2, 129.3, 130.3, 130.8, 131.4, 135.9 (Ar),
160.6, 163.3 (C@N). HRMS (ESI): m/z calcd. for the cation
[C41H55Cl3N3]+: 694.3462; found: 694.3480.
The reaction was carried out in the dark with exclusion of mois-
ture. A solution of t-BuOCl (0.19 g, 1.5 mmol) in dry CH2Cl2 (5 mL)
was added dropwise to an ice-water cooled solution of hydrazone
3 (1 mmol) in dry CH2Cl2 (10 mL) over 10 min. The mixture was
stirred for 15–30 min, and the reaction was monitored by TLC.
After the reaction went to completion, anhydrous CaCl2 was added
to the resultant yellow solution. Substrates 4 could not be purified
without partial decomposition, and therefore the solution contain-
ing 4 was used for next reaction. The solution can be stored at <4 °C
in the dark for <24 h.
2.2.9. [1R-[1
(bromomethyl)phenyl)-1-(1,5-dimethylhexyl)-
a a,5ab,12aa,12bb,14aa]]-8-(2-
(R⁄),3ab,3b
1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-tetradecahydro-12a,14a-
dimethyl-9-(2,4,6-trichlorophenyl)-cyclopenta[5,6]naphtho[2,1-
d][1,2,4]triazolo[1,5-a]azepinium hexachloroantimonate (8d)
From hydrazone 3a and o-(bromomethyl)benzonitrile. Work-up
as described above furnished 8d. Yield 0.99 g (89%); pale-brown
2.2.5. General procedure for the synthesis of the triazolo-fused 3-aza-
A-homocholestanes 8a–f and pyrazolo-fused analog 8g
The reaction was carried out in a nitrogen atmosphere. The
solution containing the chloride 4 was filtered. To the filtrate
was added dropwise the appropriate triple bond compound 6 (ni-
trile or 1-ethynylbenzene, 1.5 mmol). The reaction mixture was
cooled between ꢀ70 and ꢀ60 °C. A solution of SbCl5 (0.37 g,
1.2 mmol) in dry CH2Cl2 (5 mL) was added dropwise to the mixture
over a period of 0.5 h. After being stirred for 2 h between ꢀ60 and
ꢀ30 °C, the mixture was allowed gradually to warm to 30 °C (bath
temperature) and stirred for additional 1.5 h. Different solvent or
solvent combinations should be used depending on solubility of
individual product (see below). This afforded five-membered ring
annulated 3-aza-A-homocholestanes 8a–g. Yields were calculated
based on the employed hydrazone 3.
powder; mp 154–156 °C. IR (KBr):
m 2937, 2866, 1568, 1464,
1382 cmꢀ1. 1H NMR (400 MHz, CDCl3): d 0.66–2.43 (m, 42H, steroi-
dal H), 3.16 (m, 1H, Hc), 3.49 (m, 1H, Hd), 4.26 (m, 1H, Ha), 4.59 (m,
1H, Hb), 4.76–4.87 (m, 2H, BrCH2), 7.10–7.73 (m, 6H, Ar–H). 13C
NMR (125 MHz, CDCl3): d 12.0, 18.6, 21.3, 22.6, 22.8, 23.8, 24.1,
28.0, 29.3, 31.5, 34.8, 36.1, 39.5, 39.7, 42.2, 43.8, 52.8, 56.2 (steroi-
dal & CH2Br), 120.9, 123.7, 128.6, 129.2, 130.8, 131.2, 133.3, 134.0,
142.8 (C6H4, Cl3C6H2), 158.8, 163.1 (C@N). HRMS (ESI): m/z calcd.
for the cation [C41H54BrCl3N3]+: 772.2567; found: 772.2579.
2.2.10. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-12a,14a-dimethyl-9-(2,4,6-trichlorophenyl)-8-vinyl-
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepinium
hexachloroantimonate (8e)
From hydrazone 3a and acrylonitrile. Work-up as described
above furnished 8e. Yield: 0.90 g (93%); pale-yellow powder; mp
2.2.6. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-8,12a,14a-trimethyl-9-(2,4,6-trichlorophenyl)-
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepinium
hexachloroantimonate (8a)
The physical data and spectral data for 8a were published
previously (Ref. [17]).
192–194 °C. IR (KBr):
m 2934, 2866, 1569, 1560, 1477, 1460,
1390 cmꢀ1. 1H NMR (400 MHz, CDCl3): d 0.66–2.43 (m, 42H, steroi-
dal H), 3.00 (m, J = 16.5 Hz, 1H, Hc), 3.35 (m, J = 16.0 Hz, 1H, Hd),

H. Bai et al. / Steroids 77 (2012) 521–527
523
4.14 (m, 1H, Ha), 4.40 (m, 1H, Hd), 6.19 (m, 2H, CH2@CH), 6.91 (m,
2.2.14. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-8-ethy-12a,14a-dimethyl -
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepine (11b)
1H, CH2@CH), 7.74 (s, 2H, Cl3C6H2). 13C NMR (100 MHz, CDCl3): d
12.4, 18.6, 21.2, 23.8, 24.1, 27.7, 28.2, 30.4, 31.2, 31.5, 34.7, 34.8,
35.8, 36.1, 37.5, 39.5, 39.7, 42.2, 43.7, 45.2, 52.3, 56.2, 56.3 (steroi-
dal), 117.5, 121.9 (CH2@CH), 131.1, 131.2, 135.3, 135.9, 136.9,
143.1 (Cl3C6H2), 156.7, 163.9 (C@N). HRMS (ESI): m/z calcd. for
the cation [C36H51Cl3N3]+: 630.3149; found: 630.3166.
From 3b (0.48 g, 1 mmol) and propionitrile (0.11 g, 2 mmol).
The crude product was recrystallized from methanol. Yield 0.30 g
(67%); mp 220–222 °C. IR (KBr, cmꢀ1): 2934, 2869, 1602, 1507,
1520, 1467, 1376. 1H NMR (400 MHz, CDCl3): d (ppm): 0.67–2.14
(m, 45H, steroidal, CH2CH3), 2.90 (q, J = 6.0 Hz, 2H, CH2CH3), 2.97
(m, 1H, Hc), 3.60 (m, 1H, Hd), 4.03 (m, 1H, Ha), 4.21 (m, 1H, Hb).
13C NMR (100 MHz, CDCl3): 11.2, 11.8, 11.9, 18.5, 11.9, 18.5, 19.3,
21.2, 22.5, 22.7, 23.7, 27.9, 28.1, 31.2, 34.8, 35.7, 36.0, 39.4, 39.7,
42.1, 45.6, 52.5, 53.6, 56.1, 56.3 (steroidal, CH2CH3), 154.4, 156.1
(C = N). Anal. required for C30H51N3 (%): C, 79.41; H, 11.33; N,
9.26. Found: C, 79.20; H, 11.64; N, 9.20.
2.2.11. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-12a,14a-dimethyl-8-phenyl-9-(2,4,6-
trichlorophenyl)-cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-
a]azepinium hexachloroantimonate (8f)
From hydrazone 3a and benzonitrile. Work-up as described
above furnished 8f. Yield: 0.91 g (89%); pale-brown solid; mp
2.2.15. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-12a,14a-dimethyl-8-phenyl-
207–208 °C. IR (KBr):
m 2932, 2865, 1574, 1560, 1482, 1460,
1380 cmꢀ1. 1H NMR (500 MHz, CDCl3): d 0.66–2.53 (m, 42H, steroi-
dal H), 3.10 (m, J = 16.3 Hz, 1H, Hc), 3.43 (m J = 13.7 Hz, 1H, Hd),
4.20 (m, J = 14.4 Hz, 1H, Ha), 4.49 (m, J = 13.1 Hz, 1H, Hb), 7.26–
7.67 (m, 5H, Ph), 7.72 (s, 2H, Cl3C6H2). 13C NMR (125 MHz, CDCl3):
d 11.8, 12.0, 18.6, 21.2, 22.5, 22.8, 23.8, 24.1, 28.0, 30.4, 31.2, 31.5,
34.8, 52.8, 56.3 (steroidal), 122.6, 124.3, 128.5, 129.9, 130.8, 131.2,
134.3, 135.9, 136.9, 142.9 (Ar), 159.3, 164.3 (C@N). Anal. required
for C40H53Cl9N3Sb (%): C, 47.25; H, 5.25; N, 4.13. Found: C, 47.13;
H, 5.26; N, 4.21.
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepine (11c)
From 3b (0.48 g, l mmol) and benzonitrile (0.21 g, 2 mmol). The
crude product was recrystallized from MeOH–MeCN (2:1). Yield
0.27 g (54%); mp 197–199 °C. IR (KBr, cmꢀ1): 2953, 2867, 1530,
1487, 1466, 1442, 1350 cmꢀ1 1H NMR (400 MHz, CDCl3): d 0.68–
.
2.11 (m, 42H, steroidal), 2.83–3.09 (m, 2H, Hc/Hd), 4.02–4.35(m,
2H, Ha/Hb), 7.26–8.04 (m, 5H, Ph). 13C NMR (125 MHz, CDCl3)): d
11.7, 12.0, 18.6, 21.2, 21.7, 22.5, 22.8, 23.8, 24.1, 27.5, 28.0, 28.2,
31.5, 35.0, 36.1, 36.2, 40.0, 42.2, 46.4, 52.0, 53.0, 56.2, 56.4 (steroi-
dal), 126.0, 128.4, 128.7, 131.1 (Ph), 157.4, 159.6 (C@N). Anal.
Calcd. for C34H51N3 (%): C, 81.38; H, 10.24; N, 8.37. Found: C,
81.02; H, 10.40; N, 7.92.
2.2.12. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-12a,14a-dimethyl-8-phenyl-9-(2,4,6-
2.2.16. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
trichlorophenyl)-cyclopenta[5,6] naphtho[2,1-d][1,2,4]pyrazolo[1,5-
a]azepinium hexachloroantimonate (8g)
From hydrazone 3a and phenylacetylene. After the reaction was
complete, the mixture was evaporated under reduced pressure,
and the residue was recrystallized from hot MeOH–MeCN (v/v
3:1). The crude product was subjected to a repeated recrystalliza-
tion from hot MeOH–MeCN (v/v 5:1) to give pure 8g. Yield: 0.54 g
(53%); off-white powder; mp 204–206 °C. IR (KBr): 2935, 2866,
tetradecahydro-8,12a,14a-trimethyl-cyclopenta[5,6]naphtho[2,1-
d][1,2,4]triazolo[1,5-a]azepinium picrate (12a)
From 3b and acetonitrile. The crude free base 11a was obtained
as brown oil which was transformed to the picrate by addition of a
1.2 equiv. of picric acid in MeOH with vigorous stirring for 10 min.
The solid formed was filtered and recrystallized from hot MeOH to
furnish the pure picrate 12a. Yield: 0.55 g (82%); yellow crystals;
1562, 1467, 1382 cmꢀ1 1H NMR (400 MHz, CDCl3): d 0.66–2.43
.
(m, 42H, steroidal H), 2.88 (m, 1H, Hc), 3.29 (m, 1H, Hd), 3.99 (m,
1H, Ha), 4.46 (m, 1H, Hb), 6.94 (s, 1H, pyrazole-H), 7.28–7.70 (m,
7H, Ar–H). 13C NMR (500 MHz, CDCl3): d 11.9, 12.0, 18.6, 21.2,
22.5, 22.8, 23.8, 24.1, 28.0, 28.2, 30.2, 30.4, 35.7, 36.1, 38.1, 39.5,
39.7, 39.8, 42.2, 44.9, 45.9, 53.1, 56.2, 56.3, 56.9 (steroidal C),
109.3 (pyrazole C), 124.6, 126.0, 128.2, 128.3, 129.0, 129.6, 130.2,
130.4, 132.1, 136.5, 137.6, 141.4 (Ph, Cl3C6H2), 151.4, 155.1
(C@N). HRMS (ESI): m/z calcd. for the cation [C41H54Cl3N2]+:
679.3353; found: 679.3380.
mp 156–158 °C. IR (KBr):
m 2936, 2866, 1629, 1568, 1364, 1317,
1272 cmꢀ1. 1H NMR (400 MHz, CDCl3): d 0.66–2.43 (m, 42H, steroi-
dal H), 2.57 (s, 3H, CH3), 2.96 (m, 1H, Hc), 3.2–3.55 (m, 1H, Hd),
4.03–4.43 (m, 1H, Ha), 4.19–4.36 (m, 1H, Hb), 8.93 (s, 2H, Ar–H).
13C NMR (100 MHz, CDCl3): d 11.4, 11.7, 11.8, 12.0, 18.59, 18.60,
22.5, 22.8, 23.8, 24.1, 28.0, 28.2, 34.8, 34.9, 35.7, 36.1, 39.47,
39.48, 44.1, 52.6, 56.1, 56.2, 56.3 (steroidal & 3 CH3), 126.4,
129.2, 141.5, 152.0, 154.4 (C6H2N3O7), 154.9, 161.3 (C@N). HRMS
(ESI): m/z calcd. for the cation [C29H50N3]+: 440.4005; found:
440.4007.
2.2.13. General procedure for the synthesis of the triazolo-fused 3-aza-
A-homocholestanes (11) or the picrates (12)
2.2.17. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
The reaction was performed by employing hydrazone 3b in
place of 3a under the condition as described for the synthesis of
8a–g. Instead of precipitating the heterocycles by adding Et2O
upon completion of the reaction, the resulting mixture was cooled
to 0 °C, and an aqueous solution of NaOH (2 N, 10 mL) was added
dropwise with vigorous stirring. After further stirring for 20 min,
the mixture was extracted with CH2Cl2 (3 ꢁ 20 mL), the combined
extracts were washed with H2O (2 ꢁ 20 mL) and dried over
Na2SO4. Removal of the solvent under reduced pressure furnished
the neutral free bases of pentacyclic compounds 11, which was
subjected to recrystallization or salt formation by addition of a sat-
urated picric acid in MeOH to give the corresponding picrate 12.
tetradecahydro-12a,14a-dimethyl-8-propyl-
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepinium picrate
(12c)
From 3b and butyronitrile. The crude oily product 11c was
transformed to the picrate by stirring with 1.2 equiv. of saturated
picric acid in MeOH-MeCN–CH2Cl2 (v/v/v 5:5:1) overnight. The so-
lid product was filtered off and recrystallized several times to give
pure 12c. Yield: 0.06 g (9%); yellow crystals; mp 122–124 °C. IR
(KBr):
m .
2934, 2869, 1602, 1507, 1520, 1467, 1376 cmꢀ1 1H NMR
(400 MHz, CDCl3): d 0.66–2.25 (m, 47H, steroidal & CH3CH2CH2),
2.85 (t, 2H, J = 7.4 Hz, CH3CH2CH2), 2.97 (m, 1H, Hc), 3.23–3.55
(m, 1H, Hd), 4.06–4.40 (m, 1H, Ha), 4.23–4.26 (m, 1H, Hb), 8.91

524
H. Bai et al. / Steroids 77 (2012) 521–527
(s, 2H, Ar–H). 13C NMR (500 MHz, CDCl3) : d 11.6, 11.7, 11.9, 13.4,
18.6, 20.5, 20.6, 22.5, 23.8, 27.3, 27.9, 28.2, 35.7, 36.0, 39.1, 39.4,
42.2, 52.5, 56.1, 56.2, 56.3 (steroidal & Pr), 126.3, 128.8, 141.5,
154.1, 154.6, 155.36 (Ar), 155.39, 161.4 (C@N). HRMS (ESI): m/z
calcd. for the cation [C31H54N3]+: 468.4318; found: 468.4337.
The initial study is outlined in Scheme 1. Cholestanone 1 was
condensed with the aromatic hydrazine 2a in refluxing ethanol
to afford the corresponding hydrazone 3a in 88% yield, which
was then transformed to the
a-chloro azo compound 4a by reac-
tion with t-BuOCl. Unlike the non-steroidal analogs, the oily com-
pound 4a proved to be extremely unstable under ambient
conditions. Thus trials to purify this intermediate were unsuccess-
ful. Nevertheless the intermediate solution can be stored in a
refrigerator and used as obtained by evaporating the solvent. Upon
addition of SbCl5 as the Lewis acid at low temperature (ꢀ60 °C) is
believed to generate the cationic 1,3-dipole intermediate 5a by
departure of the chloride ion of 4a. In the presence of a slight ex-
cess of acetonitrile (6a), the highly reactive species 5a underwent
smooth cycloaddition to the triple bond to produce the 3-spiro-
substituted triazolium salt intermediate 7a. Intermediate 7a
underwent 1,2-shift upon warming to above room temperature
(ꢂ30 °C) in the same vessel affording the novel pentacyclic 1,5-
annulated-1,2,4-triazoloazepinium hexachloroantimonate 8a in
93% isolated yield.
To extend the scope of the reaction, we employed different ni-
triles (6) with diverse electronic and steric characters for the above
reaction sequence. We were pleased to find that the reaction is tol-
erant of the substituent on the cyano group. All reactions per-
formed uniformly well to provide compounds 8b–f, despite the
low-yielding reactions with butyronitrile (30%) and phenylacetoni-
trile (33%). Furthermore, the carbon-carbon triple bond of alkynes
also participated in the cationic [3 + 2] cycloaddition, as demon-
strated by phenylacetylene which delivered the pyrazolo annu-
lated counterpart 8g in 53% yield under the same conditions.
We next considered extending this reaction to the synthesis of
the N(1)-unsubstituted neutral steroidal triazoloazepine com-
pounds (Scheme 2). Likewise, the (N-ethoxycarbonyl)hydrazone
2.2.18. [1R-[1a a,5ab,12aa,12bb,14aa]]-1-(1,5-
(R⁄),3ab,3b
dimethylhexyl)-1,2,3,3a,3b,4,5,11,12,12a,12b,13,14,14a-
tetradecahydro-12a,14a-dimethyl-8-vinyl-
cyclopenta[5,6]naphtho[2,1-d][1,2,4]triazolo[1,5-a]azepine (12e)
From 3b and acrylonitrile. The crude oily product 11e was
transformed to the picrate 12e as described for 11c. The purifica-
tion procedure described for 11c gave 11e as a light yellow. Yield:
0.16 g (23%); light-yellow crystals; mp 98–100 °C. IR (KBr):
m 2942,
2866, 1630, 1567, 1364, 1318, 1271 cmꢀ1 1H NMR (400 MHz,
.
CDCl3): d 0.66–2.43 (m, 42H, steroidal), 2.89 (m, 1H, Hc), 3.35 (m,
1H, Hd), 4.04 (m, 1H, Ha), 4.18 (m, 1H, Hb), 5.70 (d, J = 11.3 Hz,
1H, He), 6.33 (d, J = 17.7 Hz, 1H, Hf), 6.64 (dd, J1 = 17.7,
J2 = 11.3 Hz, 1H, Hg), 8.98 (s, 2H, ArH). 13C NMR (100 MHz, CDCl3):
d 12.0, 12.1, 18.7, 21.5, 22.5, 22.8, 23.8, 24.2, 28.0, 28.2, 29.0, 31.7,
35.4, 35.8, 36.1, 36.2, 38.6, 39.5, 39.9, 44.7, 46.7, 52.7, 53.9, 56.2,
56.3 (steroidal), 121.6, 124.8 (vinyl), 126.3, 130.5, 140.9 (Ar),
153.0, 155.5 (C@N). HRMS (ESI): m/z calcd. for the cation
[C30H50N3]+: 452.4005; found: 452.4009.
3. Results and discussion
The required starting material 5a-cholestan-3-one 1 was read-
ily prepared in high yield according to the reported method
[18,19]. The steroidal ketone 1 has been employed as a substrate
for preparation of thiazolyl and thieno cholestane derivatives with
potent anti-inflammatory effects [20], as well as 3-aza-A-homo-
3b and the
1 by sequential reactions with ethyl carbazate and tert-butyl hypo-
chlorite. Departure of the -chloro group was effected by treat-
a-chloroazo compound 4b were prepared from ketone
cholestanes and 3-aza-A-homo-5a-cholestano[3,4-d]tetrazole ana-
logs [21,22]. In light of our success in the cationic [3 + 2+]
cycloaddition reactions between azocarbenium ions with nitriles,
we decided to employ ketone 1 in the construction of unprece-
dented steroidal heterocycles.
a
ment of 4b with antimony pentachloride at low temperature
(ꢀ60 °C), generating the azocarbenium ion 5b as a reactive inter-
mediate. In the presence of a nitrile molecule 6, 5b could be
(CH2)3CH(CH3)2
H
NHNH2
Cl
H
N
H
Cl
t
-BuOCl
+
EtOH/HOAc
reflux, 3 h
Ar
N
CH2Cl2, 0 °C
H
H
H
20 min
O
H
1
Cl
2a
3a
N
RC X (6)
−60 ~ −30 °C, 2 h
SbCl5
CH2Cl2, −60 °C
Cl
N=N
Ar
N
R
Ar
N
X
H
N
H
30 °C, 1.5 h
H
−
SbCl6
−
Ar
SbCl6
4a
5a
7
(CH2)3CH(CH3)2
H
(CH2)3CH(CH3)2
H
7,8
R
X
H
H
Ar
R
Ar
a
b
c
d
e
f
Me
N
N
N
N
H
H
N
N
H
H
N
n-Pr
Bn
−
−
SbCl6
H
X
SbCl6
H
R
X
2-(BrCH2)C6H4
N
N
vinyl
Ph
8
8'
N
Ar = 2,4,6-trichlorophenyl
g
Ph
CH
Scheme 1. Synthetic pathway to triazolo-fused 3-aza-A-homocholestanes 8a–f and pyrazolo-fused analog 8g.

H. Bai et al. / Steroids 77 (2012) 521–527
525
(CH2)3CH(CH3)2
H
O
H
t
-BuOCl
H
N
+
EtO C NHNH2
EtOH/HOAc
reflux, 3 h
R'
N
CH2Cl2, 0 °C
H
H
H
30 min
O
H
1
2b
3b
N
N
SbCl5
RC N (6)
R'
R'
N
Cl
N=N
N
H
CH2Cl2, −60 °C
−60 ~ −30 °C, 2 h
N
H
−
−
H
4b
SbCl6
R
SbCl6
R'
5b
9
(CH2)3CH(CH3)2
H
R'
R
H
picric acid
MeOH
aq. NaOH
0 °C ~ r.t., 30 min
N
N
30 °C, 1.5 h
N
H
H
N
H
N
−
SbCl6
H
R
N
10
11
9-12
R
(CH2)3CH(CH3)2
H
a
b
c
d
e
Me
O−
Et
H
n-Pr
Ph
O2N
NO2
H
N
H
H
N
vinyl
O
H
R
N
NO2
EtO C
12
R' =
Scheme 2. Synthesis of the N-unsubstituted triazolo-fused 3-aza-A-homocholestane picrates 12a–e.
intercepted by the cationic [3+ + 2] cycloaddition to form the initial
adducts 9a–e, which gave rise to the ring expanded products 10a–e
by 1,2-shift when elevating the temperature to about 35 °C.
Compounds 10a–e were directly treated in the same reaction vial
with an ice-cooled solution of aqueous sodium hydroxide to hydro-
lyze the ester group. The neutral products 11 were obtained after
usual workup as brownish solids. Compounds 11 could be
transformed to the corresponding picrates 12a–e by action with
picric acid (Scheme 2). It has been demonstrated that both ali-
phatic and aromatic nitriles can be applied to furnish acceptable
to good yields of products.
triazoloazepine derivatives reported by us previously [13–16].
Thus, in the 1H NMR spectra, the signals between 4.0 and
4.5 ppm were assigned to the methylene protons Ha/Hb connecting
to the triazolo nitrogen atom. In addition, the corresponding
absorption for compounds 8 was observed somewhat downfield
as compared with 11 or picrates 12. Signals from the methylene
protons (Hc/Hd) were found between 3.0 and 3.5 ppm. These data
verified that the migration took place exclusively with the steroidal
C(2) side upon ring expansion (Scheme 3, route a).
We have recently reported the theoretical investigation on the
parent cycloaddition reaction between azocarbenium ions and
nitriles [23]. The results revealed that the reaction takes place via
an initial formation of a 1:1 complex of the two reactants, followed
by an asynchronous concerted cyclization forming the 3H-[1,2,4]-
triazolium ions, which undergo [1,2]-shift to provide the 1H-
[1,2,4]-triazolium ions. Mechanistically, the five-membered het-
erocyclic ring of the initial spiro-substituted adducts carries a
diazenium function, in which the nitrogen atom N(2) exhibits
latent nitrenium ion character. There are two possibilities for the
subsequent 1,2-shift: the migration of the steroidal C(4) alkyl vs
the C(2) residue. We have reported in the previous work [13–16]
that the 1,2-rearrangement of carbon to electron-deficient
nitrogen in 3H-1,2,4-triazolium ions like 7 and 9 occurs with
complete migrant selectivity, and the migratory aptitude of the
substituents tends to parallel their ability to accommodate the
respective carbocation. In this context, the following migration
sequence could be suggested: H > aryl > 3° alkyl > 2° alkyl > 1°
alkyl > methyl ꢃ cyclopropyl [13–16].
The synthesized products were fully characterized by NMR
spectra along with HRMS analyses. A representative numbering
system is shown in Fig. 1. The 1H or 13C NMR spectra in the given
ranges are very similar to the spectral patterns of the related
C8H17
Hb
Ha
N
N
Hg
He
N
Hd
Hc
Hf
Fig. 1. A schematic illustration of the indicative protons.

526
H. Bai et al. / Steroids 77 (2012) 521–527
C8H17
route a
Ar
N
N
C8H17
H
R
N
C(2)
8
C8H17
N2
Ar
N
H
C(4)
R
N4
N
route b
R
N
H
Ar
N
7
8''
Ar = 2,4,6-trichlorophenyl; R = alkyl, phenyl, vinyl
Scheme 3. Plausible 1,2-shift of the initially formed 3-spiro substituted 3H-1,2,4-triazolium salts 7.
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In the present cases, one would expect that the shift occurs with
no or poor selectivity in view of the electronic similarities of the
two competing migrants. However, we observed that the ring
enlargement proceeded exclusively with migration of the C(2) ali-
phatic chain of the spiro compounds 7 to produce 8, and no iso-
meric products 8 from the C(4) migration (Scheme 3, route b)
were formed. The preferential migration of the C-2 vicinal methy-
lene over the other one C-4 in the Baeyer–Villiger reaction of var-
ious 3-keto-5a-steroids has also been reported by Rivera et al.
[24,25]. According to their theoretical studies, the better migrating
aptitude of C-2 over C-4 in this process is controlled by conforma-
tional effects in the transition state of the Criegee rearrangement.
Nevertheless, an earlier study by Suginome on the Baeyer–Villiger
oxidation of 5
dichloromethane was found to be non-regioselective to produce
a 1:1 mixture of 3-oxa-A-homo-5 -cholestan-4-one and 4-oxa-A-
homo-5 -cholestan-3-one [26]. Factors that govern the migratory
a-cholestan-3-one with m-chloroperbenzoic acid in
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biological evaluation of novel 6,7,8,9-tetrahydro-2-(2-aryloxypyrimidin-4-yl)-
a
2H-[1,2,4]
triazolo[4,3-a]azepin-3(5H)-ones.
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The previously published X-ray diffraction analysis for 8a [17]
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A fully completed Crystallographic Information File deposited
with the CCDC is available (Deposition CCDC No. 754601).
Mannich reactions using azide precursors.
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In conclusion, we have developed a facile strategy for the syn-
thesis of unprecedented steroidal triazoloazepine derivatives 8
and 11 through cycloaddition of the azocarbenium ions accompa-
nied by a consecutive regioselective ring expansion. Our methodol-
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a novel
ogy provides
a useful protocol for the synthesis of novel
pentacyclic steroids with potential biological interests.
[16] Meng QQ, Bai HX, Wang QR, Tao FG.
A general synthesis of furo[3,2-
c][1,2,4]triazolo[1,5-a]azepine and furo[2,3-f][1,2,4]triazolo[1,5-a]azepine
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Acknowledgements
triazolo-annulated
3-aza-A-homocholestane
derivative:
a
novel
pentaheterocyclic ring system. J Chem Crystallogr 2011;41:316–21.
[18] Bruce WF, Ralls JO. Dehydrocholesterol. Org Synth 1943;Coll Vol 2:191–4.
[19] Bruce WF. Cholestanone. Org Synth 1943;Coll Vol 2:139–40.
The authors are indebted to the National Natural Science Foun-
dation of China (Project 20372015) for financial support. We are
also grateful to the anonymous referees for their thoughtful
comments.
[20] Elmegeed GA, Wardakhan WW, Baiuomy AR. Synthesis of thiazolyl and thieno
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[21] Ahmad MS, Alam Z. Synthesis of steroidal tetrazoles: Schimidt reaction on
a novel class of potent antiinflammatory steroid.
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