Studies on stereocontrolled epoxidations of bis-alicyclic alcohols in steroidal skeletons: Preparation of eight diastereomerically pure epoxides from cholest-4-en-3β,6β-; -3β,6α-; -3α,6β- and -3α,6α-diols

Article abstract of DOI:10.1016/S0957-4166(01)00174-4

Eight diastereomerically pure epoxides have been prepared from cholest-4-en-3β,6β -3β,6α-; -3α,6β- and -3α,6α-diols via a combination of steric, protecting group and oxidant effects on stereocontrolled epoxidations of a bis-alicyclic alcohol system within

Full text of DOI:10.1016/S0957-4166(01)00174-4

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 12 (2001) 1211–1217
Studies on stereocontrolled epoxidations of bis-alicyclic alcohols
in steroidal skeletons: preparation of eight diastereomerically
pure epoxides from cholest-4-en-3b,6b-; -3b,6a-; -3a,6b- and
-3a,6a-diols
Kejun Zhao, Yongfeng Wang* and David C. Billington
Pharmaceutical Sciences Research Institute, Aston University, Aston Triangle, Birmingham B4 7ET, UK
Received 4 April 2001; accepted 18 April 2001
Abstract—Eight diastereomerically pure epoxides have been prepared from cholest-4-en-3b,6b; -3b,6a-; -3a,6b- and -3a,6a-diols
via a combination of steric, protecting group and oxidant effects on stereocontrolled epoxidations of a bis-alicyclic alcohol system
within the steroidal skeleton. © 2001 Elsevier Science Ltd. All rights reserved.
with examples of cis- or trans-selectivity. Henbest10
reported the epoxidation of 3b, 6b-dihydroxy-cholest-4-
1. Introduction
ene 1 with a peracid, showing that the syn-directing
effect of the hydroxyl functions is significant enough to
drive the epoxidation to occur predominantly from the
b-side. However, no investigation of the coordination
effect of the dihydroxy substrates in bis-allylic and
bis-alicyclic alcohol systems and of the effects of
hydroxyl protecting groups and oxidants on the stereo-
control of such epoxidations has been reported.
Herein we describe such an investigation into the epox-
idation of the bis-alicyclic alcohols 1, 6, 10 and 16 and
their acylated derivatives.
In recent years, oxysterols have attracted a great deal of
interest from biological scientists due to their effects on
gene regulation,1 cytotoxicity,2 atherogenesis,3 mutage-
nesis,4 etc. It is generally believed that the activities are
attributed to the numbers and configurations (steric
effects) of the oxygenated functional groups (such as
hydroxyl and ketone) on the rings as well as on the side
chain. Because the availability of oxysterols is limited,
both in number and quantity, studies in this field have
been seriously hampered. As part of our project toward
the development of robust synthetic methods for the
preparation of polyhydroxylsterols, we have under-
taken the synthesis of all possible stereoisomers of
cholestan-3,4,5,6-tetrols, after our discovery of the
potent activity of cholestan-3b,5a,6b,7b-tetrol against a
number of cancer cell lines.5 We have developed an
efficient preparative syntheses of the cholest-4-en-3b,6b-;
-3b,6a-; -3a,6b- and -3a,6a-diols 1, 6, 10 and 166 (Table
1). Studies of stereocontrolled epoxidations to gain the
eight diastereomerically pure epoxides are described
herein.
2. Results and discussion
The preparations of cholest-4-en-3,6-diols 1, 6, 10 and
16, the diacetate 8 and the monoacetate 17 have been
reported in our preceding paper.6 The monoacetates 2,
3, 7 and 11 and the benzoyl esters 5, 9, 14, 15, 19 and
20 used in this paper were prepared either by the partial
hydrolysis of the appropriate diacetates 4, 8, 13 and 18
or by reaction of benzoyl chloride or acetic anhydride
with the appropriate alcohols in pyridine at room
temperature.
The syn-directing effect of the hydroxyl of allylic and
alicyclic alcohols is well known,7 and the removal of
this effect after alkylation to form ethers8 or acylation
to esters is also well documented.9 In contrast to allylic
alcohols, there have only been sporadic reports of
epoxidations of bis-allylic and bis-alicyclic alcohols
Three typical epoxidation conditions, m-CPBA,11
VO(acac)2/TBHP12 and Sharpless,13 were investigated
with cholest-4-en-diols 1, 6, 10 and 16 and their acetates
2, 3, 4, 7, 8, 11, 12, 13, 17 and 18, benzoates 5, 9 and
20 and acetate-benzoates 14, 15 and 19 (Scheme 1). The
results are summarised in Table 1.
* Corresponding author. E-mail: y.f.wang@aston.ac.uk
0957-4166/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(01)00174-4

Table 1. The summary of the results of the epoxidationsa
Substrate
3R
6R%
i mCPBA
ii VO(acac)2/TBHP
iii Ti(OiPr)4/TBHP/(−)DET
iv Ti(OiPr)4 /TBHP/(+)DET
a/b Ratioc
Yieldb (%)
Time (h)
a/b Ratioc
Yieldb (%)
Time (h)
a/b Ratioc
Yieldb (%)
a/b Ratioc
Yieldb (%)
Time (h)
d
d
e
e
e
e
1
2
3
4
5
b-OH
b-OAc
b-OH
b-OAc
b-OBz
b-OH
b-OH
b-OAc
b-OAc
b-OBz
0:100
7:93
2:98
82:18
75:25
98
94
94
71
75
2
4
4
288
96
0:100
0:100
0:100
95
90
90
3
5
5
–
–
–
–
–
–
–
–
–
e
e
d
e
–
–
d
e
–
/
d
d
e
e
e
6
7
8
9
a-OH
a-OH
a-OAc
a-OBz
b-OH
38:62
91:9
76:34
50:50
70
84
73
80
1
5
120
48
33:67
100:0
93
90
0.5
1
–
–
–
–
–
–
–
–
e
b-OAc
b-OAc
b-OBz
d
e
–
–
d
e
10
11
12
13
14
15
b-OH
b-OAc
b-OH
b-OAc
b-OAc
b-OBz
a-OH
a-OH
a-OAc
a-OAc
a-OBz
a-OBz
12:88
42:58
2:98
73:27
95:5
69
88
78
74
77
81
4
11
11
120
48
48
0:100
13:87
0:100
98
82
86
2
5
5
0:100
52
43
94:6
60
55
12
12
d
d
e
e
e
e
–
–
–
–
–
–
–
–
–
e
d
e
–
–
–
d
e
2
d
e
87:13
–
1
16
17
18
19
20
a-OH
a-OH
a-OH
a-OAc
a-OBz
a-OBz
100:0
27:73
25:75
52:48
75:25
98
75
80
83
84
2
4
72
48
48
100:0
0:100
82
95
3
5
100:0
100:0
d
d
e
e
e
a-OAc
a-OAc
a-OAc
a-OBz
–
–
–
–
–
–
–
–
1
d
e
–
–
–
d
e
127
d
e
a Epoxidations were performed using the standard protocols.
b Yields of a+b.
c Calculated from 1H NMR spectra.
d No reaction after 3 days.
e Did not test.

K. Zhao et al. / Tetrahedron: Asymmetry 12 (2001) 1211–1217
1213
In this particular group of substrates, MCPBA showed
superior reactivity to VO(acac)2/TBHP and Sharpless
conditions, and induced satisfactory stereoselectivity.
MCPBA effected epoxidation of all substrates with
good to excellent yields. The reaction rates with diace-
tate substrates 4, 5, 8, 9, 13, 14, 15, 18, 19 and 20 were
dramatically lower because of increased steric hin-
drance and lack of coordination between MCPBA and
the free hydroxyl group. The VO(acac)2/TBHP oxidant
generally gave better stereoselectivity than MCPBA
with substrates 1, 2, 3, 6, 7, 10, 11, 12, 16 and 17, which
bear one or two free hydroxyl groups but failed to react
with the diacetates 4, 5, 8, 9, 13, 14, 15, 18, 19 and 20.
This demonstrates the importance of coordination
between the oxidant and the hydroxyl group in the
VO(acac)2/TBHP epoxidation reactions. Sharpless con-
ditions effected epoxidations of 10 and 16 only,
possibly due to steric hindrance of the steroidal skele-
tons blocking the approach of the oxidant complex to
the double bond.
steroids,14 resulted in a reorientation of peracid epoxi-
dations from cis- to trans-stereoselectivity. This is gen-
erally attributed to steric hindrance created on the
normally favoured cis-side by the acetate group, and to
prevention of coordination between the oxidant and the
hydroxyl group of the substrate.15
However, in this study we found that the effect of
acylation is much more complicated. When the 3- and
6-hydroxyl groups are b oriented, epoxidation of
monoacetates 2 and 3 led to only slightly reduced
stereoselectivity in reactions with MCPBA. However,
when the 3- and 6-hydroxyl groups are a configured,
reaction of a monoacylated substrate with VO(acac)2/
TBHP surprisingly led to a total reorientation of
stereoselectivity from a-side to b-side, furnishing a sin-
gle b-isomer in the reaction of 17. In the cases of the
3a- and 6b-hydroxyl substrates, e.g. 7, after acylation of
the 6b-hydroxyl group, the 3a-OH directed cis-epoxida-
tion product dominated; with MCPBA the a-epoxide
formed in 91% yield and with VO(acac)2/TBHP the
a-epoxide formed with 100% stereoselectivity. In con-
trast, in the substrates with 3b- and 6a-OH, acylation
of the 3b-OH, (compound 11) failed to increase a-side
stereoselectivity. Again, this demonstrated that the 6a-
OH exerts little a-side directing effect. In the epoxida-
tion of the 6a-O-acylated substrate 12, b-side
epoxidation predominated, a result of the directing
influence of the 3b-OH.
When the 3- and 6-hydroxyl groups are of the same
configuration (both b or a), 1 and 16, MCPBA and
VO(acac)2/TBHP afforded 100% cis-epoxidation prod-
ucts, resulting from an enhanced syn directing effect,
implying that when the two hydroxyl groups are of the
same configuration they are involved in anchoring the
active oxygen of MCPBA or VO(acac)2/TBHP to
approach the C-CꢀC plane from the same side (if this
was not so there should be less cis-epoxidation because
of increased cis-side congestion).
In general, when both 3-OH and 6-OH were acetylated,
epoxidation occurred selectively from the opposite side
to that of its free hydroxy congener, such as the epoxi-
dations of 4, 8, 13 and 18, which were opposite to 1, 6,
10 and 16.
When the 3- and 6-hydroxyl groups are opposite in
configuration the epoxidation with all three oxidants
occurred with surprisingly high stereoselectivity. Thus,
epoxidation of 6 furnished a 1:2 mixture of a-isomer:b-
isomer with both MCPBA and VO(acac)2/TBHP.
Epoxidation of 10 with MCPBA gave rise to 88%
b-isomer and with VO(acac)2/TBHP the b-isomer was
formed with 100% selectivity. This result indicates that
the a configured hydroxyl group exerts less syn direct-
ing effect than the b hydroxyl. In particular, the influ-
ence of the 6a-hydroxyl group on the reaction is
minimal. This is reminiscent of Lavie’s findings that
both 4a-hydroxycholest-5-ene and 6b-hydroxycholest-4-
ene underwent cis-epoxidation with a peracid, but 6a-
hydroxycholest-4-ene gave a mixture of products.14
The effect of replacement of the acetyl group with the
larger Bz was investigated with the expectation max-
imising reorientation and selectivity in the epoxidation
reactions. The experiments showed Bz apparently
exerted less steric hindrance than acetate, e.g. 5, 9 and
20 furnished less of the re-oriented epoxides compared
to 4, 8 and 18. Surprisingly, epoxidation of the mixed
esters 14 and 19 (with the 3- and 6-OH protected as Ac
and Bz esters) resulted in higher levels of the re-ori-
ented epoxides. In particular 14 afforded almost a
single isomer on oxidation with MCPBA.
It has been observed that acylation of the hydroxyl
group of alicyclic alcohols, cyclohexenol10 and oxy-
The importance of transition state geometries of allylic7
and alicyclic17 alcohols, and in particular, the torsion
i, ii, iii, iva
+
RO
RO
RO
O
OR'
OR'
O
OR'
1-20
Scheme 1. Epoxidations. a See Table 1.

1214
K. Zhao et al. / Tetrahedron: Asymmetry 12 (2001) 1211–1217
epoxycholest-3a,6b-diol from the crude product of 6 via
di-acetylation, recrystallisation and deprotection. The
results show that in this particular group of bis-alicyclic
steroidal alcohols, the 3a, 3b and 6b-OH exert syn
directing effects with MCPBA and VO(acac)2/TBHP,
and the enhanced syn directing effect was observed
when two hydroxyl groups are of the same configura-
tion. In directing the orientation of epoxidations, the
6a-OH behaves differently, trans-directing with VO(ac-
ac)2/TBHP in particular, e.g. 11 and 17. Overall, the
study shows that by acylation of the hydroxyl func-
tions, the directing effects of the substituents can be
manipulated and with careful selection of oxidant high
stereoselectivities can be achieved in the epoxidation
reactions of these steroid substrates.
(dihedral) angle of O-C-CꢀC in the determination of
the orientations of epoxidation products has been
demonstrated with peracids16 and VO(acac)2/TBHP.7
Whitham16 first proposed a transition state geometry
for peracid epoxidations of alicyclic alcohols. In his
cyclohexenol model, the optimal arrangement for high
cis-stereoselectivity and a faster reaction is that the OH
occupies a pseudo-equatorial conformation, with a tor-
sion angle of about 150°.17 Later with the same group
of compounds he found a pseudo-axial OH, with a
torsion angle of approximately 90°17 to be responsible
for rapid cis-selective epoxidation with VO(acac)2/
TBHP.18 A number of epoxidations of the allylic frag-
ments of steroids have been reported, some of which
were clearly cis-stereoselective,10 while some were not.14
We calculated torsion angles of O-C(3)-C(4)ꢀC(5) and
O-C(6)-C(5)ꢀC(4) fragments in the substrates 1, 6, 10,
16 and some of their acetates (Fig. 1). The torsion angle
of the 3a-OH is about 108°, while 3b is about −140° (on
the opposite side). The torsion angle of the 6a-OH is
very small (about 5°), implying that O-C(6)-C(5)ꢀC(4)
are almost in the same plane; while 6b is about −105°.
Mono- or diacylation has little effect on the torsion
angles. None of these torsion angles match those for
cis-stereoselectivity proposed above, however, the rea-
son for the behaviour of the 6a-OH substrates is clear:
Because the oxygen of the 6a-OH is in the same plane
with the C(6)-C(5)ꢀC(4) fragment, its transition state
geometry is out of line with all predictions. Still, its
predominant trans-directing effect in the VO(acac)2/
TBHP epoxidations of 11 and 17 remains a question,
because, in this case, the transition state geometry is
perfect for oxidation of an alicyclic alcohol into its
enone form according to Ternaishi’s model.17 The dom-
inant cis-directing effect of the 3a, 3b and 6b-OH in the
epoxidations of this group of substrates with MCPBA
and VO(acac)2/TBHP means the torsion angles of their
transition states are not that restrictive.
3. Experimental
3.1. General
Melting points were obtained on a Reichert-Jung
Microthermal apparatus, and are uncorrected. IR spec-
tra were recorded on a Mattson 3000 instrument and
NMR spectra at 250 MHz on a Bruker AC-250. Mass
spectra (MS) were obtained on a HP G1034C GC/LC-
MS Chemstation using atmospheric chemical-ionisation
(APCI) method. High-resolution mass spectra (HRMS)
were measured on Finnigan MAT 900 XLT high-reso-
lution double-focusing mass spectrometer using electro-
spray method. Flash chromatography was performed
on 200–400 mesh silica-gel and thin-layer chromato-
graphy (TLC) was performed using 0.25 mm Merck
Kieselgel 60 F254 precoated silica gel plates.
The semi-empirical program MOPAC (ChemOffice
Ver. 4.0) was used for the calculations throughout this
work. The structure optimisation of compound 10 was
also done by ab initio methods at RHF 3-21G level by
using the program Gamess (Ver. 6.0) on a PC.
Other epoxidation conditions including chloral hydrate/
hydrogen peroxide19 and dioxarine/oxone/acetone,20
were also tested on this bis-alicyclic alcohol system, but
were found to be ineffective.
3.2. General procedure of MCPBA epoxidations
The cholest-4-en-3,6-diol or its derivative (1 mmol) and
MCPBA (207 mg, 1.2 mmol) were dissolved in DCM
(10 mL) and the mixture was stirred at room tempera-
ture for a given period (see Table 1). The resulting
mixture was washed with 10% aqueous sodium hydrox-
ide and water, then dried over sodium sulphate.
Removal of the solvent gave the crude product for
further purification (see individual compounds below
for details).
In summary, the eight target epoxides have been syn-
thesised in a diastereomerically pure form from the free
alcohols 1, 7, 10 and 16, the monoacetate 17 and the
di-acetate 14. The remaining two were formed indi-
rectly; 4,5a-epoxycholest-3b,6b-diol from
4
after
hydrolysis and recrystallisation from MeOH, and 4,5b-
-140 o
-105 o
H
OH
H
OH
H
H
HO
H
5o
108o
H
OH
3α-OH, O-C3-C4=C5
Figure 1. Torsion angles of 3a-, 3b-,6a- and 6b-OH of cholest-4-en-3,6-diols.
H
H
6α-OH, O-C6-C5=C4
3β-OH, O-C3-C4=C5
6β-OH, O-C6-C5=C4

K. Zhao et al. / Tetrahedron: Asymmetry 12 (2001) 1211–1217
1215
3.3. General procedure of VO(acac2)2/TBHP
epoxidations
3.6. 4a,5-Epoxy-5a-cholestane-3b,6b-diol, 3,6-diacetate
Obtained via recrystallisation from methanol as white
needles. Mp 157–158°C (lit.22 158–160°C); [h]D15=+18
(c 10.0, CHCl3); IR: wmax 2954, 2850, 1743, 1465,
To a solution of the cholest-4-en-3,6-diol or its
derivative (1 mmol) and vanadyl acetylacetonate (5.3
mg) in DCM (10 mL) was added dropwise the
TBHP/toluene solution (4 M, 0.75 mL, 3.0 mmol).
The resulting homogeneous solution was stirred at
room temperature for a given period (Table 1). When
TLC showed completion of the reaction, the mixture
was washed with saturated sodium bicarbonate (2×20
mL) and brine (2×20 mL), then dried over MgSO4.
After removal of the solvent, the residue was sub-
jected to further purification (see individual com-
pounds below for details).
1
1367, 1240 and 1027; H NMR (CDCl3): lH 4.93 (dd,
J=8.2 and 0.6 Hz, 1H, H-3), 4.28 (m, 1H, H-6), 3.16
(s, 1H, H-4), 1.19 (s, 3H, CH3-19), 0.70 (s, 3H, CH3-
18); 13C NMR (CDCl3): lC 11.9, 17.0, 18.5, 20.4,
20.9, 22.4 and 22.6 (7×CH3), 20.4, 22.8, 23.7, 23.9,
28.0, 29.3, 33.6, 36.0, 39.3 and 39.4 (10×CH2), 27.8,
30.8, 35.6, 49.4, 55.2, 56.0, 62.2, 66.9 and 74.2 (9×
CH), 34.5, 42.4, 63.2, 169.5 and 169.7 (5×C); MS
(ES+): m/z 503 (M+H+, 40), 525 (M+Na+, 100).
3.7. 4b,5-Epoxy-5b-cholestane-3b,6b-diol
3.4. General procedure of Sharpless epoxidations
Obtained directly from the reaction without further
purification. Mp 162–163°C (lit.23 164–165°C); [h]D15=
−7 (c 10.0, CHCl3, lit.23 [h]D20=−7.5, c 0.6, CHCl3);
IR: wmax 3500–3300, 2960, 2848, 1463, 1380 and 1059;
1H NMR (CDCl3): lH 3.96 (m, 1H, H-3), 3.32 (m,
1H, H-6), 3.22 (d, J=3.2 Hz, 1H, H-4), 1.16 (s, 3H,
CH3-19), 0.70 (s, 3H, CH3-18); 13C NMR (CDCl3):
lC 11.9, 18.5, 19.6, 22.5 and 22.7 (5×CH3), 21.3, 23.7,
24.1, 25.5, 28.7, 32.5, 36.0, 36.8, 39.4 and 39.7 (10×
CH2), 27.9, 29.2, 35.6, 50.6, 55.9, 56.1, 65.1, 66.1 and
74.0 (9×CH), 35.1, 42.4 and 69.4 (3×C); MS (ES+):
m/z 441 (M+Na+, 100).
Freshly distilled titanium tetra-iso-propoxide (426 mg,
1.5 mmol) was added to DCM (2 mL, with the
appropriate amount of pre-activated and powdered
molecular sieves). The resulting mixture was cooled to
−20°C (dry ice/acetone). Freshly distilled (S,S)-(−)-di-
iso-propyl tartrate (DIPT) or (R,R)-(+)-DIPT (352
mg, 1.5 mmol) was then added. The resulting mixture
was stirred for 15 min, then a solution of the cholest-
4-en-3,6-diol or its derivative (1.0 mmol) in DCM (10
mL) was added. After 10 min of stirring, tert-butyl
hydroperoxide solution (3.0 mmol) was added drop-
wise, and the reaction mixture was then stirred at a
temperature between −10 and 0°C for 48 h. The
resulting mixture was poured into a pre-cooled (0°C)
aqueous solution of tartaric acid (10% w/v) (20 mL),
then the mixture was vigorously stirred for 30 min,
followed by dilution with diethyl ether (50 mL),
washing with 10% aqueous tartaric acid (2×25 mL)
and brine (2×40 mL), and dry over (MgSO4). After
the solvent was removed, the resulting crude epoxide
was subjected to further purification (see individual
compounds below for details).
3.8. 4b,5-Epoxy-5b-cholestane-3b,6b-diol, 3,6-diacetate
Obtained via recrystallisation from methanol as off-
white needles. Mp 160–161°C (lit.23 154–155°C);
[h]1D5=−60 (c 10.0, CHCl3; lit.23 [h]1D9=−58.5, c 1.0,
CHCl3); IR: wmax 2948, 2871, 1743, 1463, 1369, 1239
1
and 1027; H NMR (CDCl3): lH 5.01 (m, 1H, H-3),
4.51 (m, 1H, H-6), 3.27 (d, J=3.0 Hz, 1H, H-4), 1.14
(s, 3H, CH3-19), 0.68 (s, 3H, CH3-18); 13C NMR
(CDCl3): lC 11.8, 18.4, 18.9, 20.7, 21.0, 22.4 and 22.6
(7×CH3), 21.9, 22.3, 23.6, 24.0, 27.9, 32.2, 35.2, 35.9,
39.2 and 39.4 (10×CH2), 27.7, 29.9, 35.5, 50.0, 55.4,
55.9, 60.8, 68.6 and 75.4 (9×CH), 35.6, 42.3, 64.8,
169.3 and 170.1 (5×C); MS (ES+): m/z 525 (M+Na+,
100).
3.5. 4a,5-Epoxy-5a-cholestane-3b,6b-diol21
4a,5-Epoxy-5a-cholestane-3b,6b-diol 3,6-diacetate (2.0
g, 4.0 mmol) was dissolved in DCM (15 mL) and
ethanol (50 mL). 15% Aqueous NaOH solution (8
mL) was added with stirring. The solution was stirred
at room temperature for 1.5 h, then poured into
water (40 mL). The DCM layer was separated and
washed with water then dried over sodium sulphate.
The solvent was removed under reduced pressure to
give a solid product, which was recrystallised from
ether/petroleum ether (yield: 70 g, 91%). Mp 166–
167°C; [h]1D5=+23 (c 10.0, CHCl3); IR: wmax 3500–
3300, 2949, 2865, 1469, 1385 and 1051; 1H NMR
(CDCl3): lH 4.02 (dd, J=8.0 and 0.5 Hz, 1H, H-3),
3.22 (s, 1H, H-6), 2.93 (s, 1H, H-4), 1.26 (s, 3H,
CH3-19), 0.67 (s, 3H, CH3-18); 13C NMR (CDCl3):
lC 12.0, 17.7, 18.6, 22.5 and 22.7, (5×CH3), 20.6,
23.8, 24.1, 26.5, 28.1, 29.4, 35.9, 36.1, 39.4 and 39.5
(10×CH2), 27.9, 30.4, 35.7, 49.7, 55.4, 56.1, 63.6, 64.6
and 73.5 (9×CH), 34.7, 42.5 and 65.9 (3×C); MS (ES+):
m/z 441 (M+Na+, 100).
3.9. 4a,5-Epoxy-5a-cholestane-3a,6b-diol
Obtained via hydrolysis of its 6b-acetate, then recrys-
tallisation from chloroform/hexane as granular crys-
tals. Mp 152–154°C; [h]2D0=+57 (c 10.0, CHCl3);
HRMS (ES+): m/z 419.3528 (M+H+, C24H47O3
requires 419.3525); IR: wmax 3500–3300, 2939, 2865,
1
1469, 1380 and 1034; H NMR (CDCl3): lH 4.06 (m,
1H, H-3), 3.26 (m, 2H, H-6, H-4), 1.18 (s, 3H, CH3-
19), 0.68 (s, 3H, CH3-18); 13C NMR (CDCl3): lC
12.0, 17.3, 18.5, 22.5 and 22.7 (5×CH3), 20.6, 23.8,
24.1, 26.8, 28.1, 29.5, 35.7, 36.0, 39.4 and 39.6 (10×
CH2), 27.9, 30.3, 35.7, 50.2, 55.5, 56.1, 62.8, 63.3 and
73.8 (9×CH), 34.6, 42.5 and 67.7 (3×C); MS (ES+):
+
m/z 436 (M+NH4 , 55), 236 (50), 214 (100).

1216
K. Zhao et al. / Tetrahedron: Asymmetry 12 (2001) 1211–1217
3.10. 4a,5-Epoxy-5a-cholestane-3a,6b-diol, 3,6-diacetate
64.9 and 65.4 (9×CH), 36.2, 42.6 and 69.3 (3×C); MS
(ES+): m/z 441 (M+Na+, 100).
Obtained via acetylation of the crude 6b-acetate with
acetic anhydride and pyridine in toluene at reflux for 2
h, subsequent recrystallisation from methanol afforded
the product as white crystals. Mp 98–99°C; [h]2D0=+60
3.14. 4a,5-Epoxy-5a-cholestane-3b,6a-diol, 3,6-diacetate
Obtained via acetylation of the correspondent diol as a
colourless gum. [h]D20=+47 (c 2.9, CHCl3); HRMS (ES+):
m/z 503.3738 (M+H+, C31H51O5 requires 503.3736);.
IR: wmax 2948, 2865, 1733, 1465, 1379, 1246 and 1033;
1H NMR (CDCl3): lH 5.23 (dd, J=11.9 and 4.7 Hz,
1H, H-6), 4.93 (m, 1H, H-3), 3.08 (s, 1H, H-4), 1.11 (s,
3H, CH3-19), 0.60 (s, 3H, CH3-18); 13C NMR (CDCl3):
lC 11.9, 17.0, 18.5, 21.0, 21.2, 22.4, 22.7 (7×CH3), 20.6,
22.8, 23.7, 23.9, 27.9, 28.4, 34.0, 35.9 and 39.3 (two
carbons) (10×CH2), 27.8, 34.1, 35.6, 49.2, 55.1, 55.9,
57.5, 67.1 and 67.2 (9×CH); 36.4, 42.5, 66.0, 169.2 and
169.6 (5×C); MS (ES+): m/z 525 (M+Na+, 100).
(c 10.0, CHCl3); HRMS (ES+): m/z 520.4002 (M+NH4 ,
+
C31H54NO5 requires 520.4002); IR: wmax 2942, 1753,
1
1467, 1383, 1220 and 1026; H NMR (CDCl3): lH 5.15
(m, 1H, H-3), 4.30 (m, 1H, H-6), 3.44 (d, J=3.5 Hz,
1H, H-4), 1.09 (s, 3H, CH3-19), 0.70 (s, 3H, CH3-18);
13C NMR (CDCl3): lC 12.0, 16.8, 18.5, 21.0, 21.3, 22.5
and 22.7 (7×CH3), 20.5, 23.6, 23.7, 24.0, 28.0, 30.0,
33.8, 36.0, 39.4 and 39.5 (10×CH2), 27.9, 30.8, 35.7,
49.9, 55.3, 55.9, 60.4, 66.4 and 74.8 (9×CH), 34.8, 42.5,
63.8, 169.8 and 170.5 (5×C); MS (ES+): m/z 525 (M+
Na+, 100).
3.11. 4b,5-Epoxy-5b-cholestane-3a,6b-diol
3.15. 4b,5-Epoxy-5b-cholestane-3b,6a-diol
Obtained via hydrolysis of its 3,6-diacetate and recrys-
tallisation from DCM/hexane which afforded the
product as a white solid. Mp 137–138°C; [h]2D0=+10 (c
1.0, CHCl3); HRMS (ES+): m/z 419.3517 (M+H+,
C24H47O3 requires 419.3525); IR: wmax 3500–3300, 2942,
Obtained via flash chromatography (ether as eluent) as
white solids. Mp 66–67°C; [h]2D0=−3 (c 10.0, CHCl3);
HRMS (ES+): m/z 436.3787 (M+NH4 , C24H50NO3
+
requires 436.3791); IR: wmax 3500–3300, 2938, 2865,
1
1463, 1378 and 1066; H NMR (CDCl3): lH 3.95 (m,
1
2865, 1463, 1378 and 1058; H NMR (CDCl3): lH 3.94
2H, H-3, H-6), 3.65 (s, 1H, H-4), 0.95 (s, 3H, CH3-19),
0.62 (s, 3H, CH3-18); 13C NMR (CDCl3): lC 11.8, 18.5,
19.0, 22.5 and 22.7 (5×CH3), 21.3, 23.7, 24.1, 25.3, 27.9,
28.0, 36.0, 37.8, 39.3 and 39.5 (10×CH2), 27.9, 29.4,
35.7, 46.4, 55.9, 56.1, 65.8, 66.1 and 74.3 (9×CH), 36.4,
42.4 and 71.0 (3×C); MS (ES+): m/z 441 (M+Na+, 100).
(dd, J=9.1 and 2.6 Hz, 1H and H-3), 3.35 (m, 1H,
H-6), 2.93 (s, 1H, H-4), 1.14 (s, 3H, CH3-19), 0.69 (s,
3H, CH3-18); 13C NMR (CDCl3): lC 11.9, 18.5, 20.6,
22.5 and 22.7 (5×CH3); 21.0, 23.8, 24.2, 25.3, 27.3, 28.1,
35.8, 36.0, 39.4 and 39.6 (10×CH2), 7.9, 29.4, 35.7, 46.4,
55.9, 56.1, 65.8, 66.1 and 74.3 (9×CH2), 35.8, 42.5 and
67.6 (3×C); MS (ES+): m/z 441 (M+Na+, 100), 419
(M+H+, 39), 236 (61), 214 (37).
3.16. 4b,5-Epoxy-5b-cholestane-3b,6a-diol, 3,6-diacetate
Obtained via acetylation of the corresponding diol.
Isolated as a colourless gum. [h]2D0=−15 (c 10.0,
CHCl3); HRMS (ES+): m/z 503.3733 (M+H+, C31H51O5
requires 503.3736); IR: wmax 2948, 2865, 1733, 1465,
3.12. 4b,5-Epoxy-5b-cholestane-3a,6b-diol, 3,6-diacetate
Obtained via recrystallisation from methanol as small
white plates. Mp 72–73°C; HRMS (ES+): m/z 520.3988
1378, 1246 and 1033; H NMR (CDCl3): lH 5.20 (dd,
1
+
(M+NH4 , C31H54NO5 requires 520.4002); [h]2D0=−24 (c
J=12.2 and 4.8 Hz, 1H, H-6), 5.10 (m, 1H, H-3), 3.54
(d, J=3.6 Hz, 1H, H-4), 1.06 (s, 3H, CH3-19), 0.65 (s,
3H, CH3-18); 13C NMR (CDCl3): lC 11.7, 18.4, 18.6,
20.7, 20.8, 22.3 and 22.6 (7×CH3), 21.2, 22.2, 23.6, 23.9,
27.9, 28.9, 35.9, 36.0, 39.2 and 39.3 (10×CH2), 27.7,
33.6, 35.5, 47.8, 54.6, 55.5, 55.9, 66.3 and 66.9 (9×CH),
36.7, 42.4, 66.3, 169.5 and 170.3 (5×C) MS (ES+): m/z
525 (M+Na+, 100).
8.0, CHCl3); IR: wmax 2946, 2871, 1745, 1463, 1365,
1
1236 and 1034; H NMR (CDCl3): lH 4.85 (dd, J=9.8
and 2.0 Hz, 1H, H-3), 4.52 (m, 1H, H-6), 2.92 (s, 1H,
H-4), 1.11 (s, 3H, CH3-19), 0.70 (s, 3H, CH3-18); 13C
NMR (CDCl3): lC 11.9, 18.5, 20.0, 21.0, 21.3, 22.4 and
22.7 (7×CH3), 20.9, 21.8, 23.6, 24.1, 26.6, 28.0, 35.1,
36.0, 39.3 and 39.4 (10×CH2), 27.9, 30.1, 35.6, 46.1,
55.6, 56.0, 62.1, 68.0 and 75.7 (9×CH), 36.0, 42.5, 64.2,
169.9 and 170.1 (5×C); MS (ES+): m/z 525 (M+Na+,
100).
3.17. 4a,5-Epoxy-5a-cholestane-3a,6a-diol
Obtained via recrystallisation from chloroform/hexane
as a white solid. Mp 173–174°C; [h]2D0=+64 (c 4.0,
3.13. 4a,5-Epoxy-5a-cholestane-3b,6a-diol
CHCl3); HRMS (ES+): m/z 436.3790 (M+NH4 ,
+
Obtained via hydrolysis of 3b-acetoxy-6a-benzoxy-4a,5-
epoxy-5a-cholestane as white solid. Mp 180–181°C;
[h]2D0=+49 (c 1.0, CHCl3); HRMS (ES+): m/z 436.3788
C24H50NO3 requires 436.3791); IR: wmax 3500–3300,
1
2943, 1469, 1376 and 1042; H NMR (CDCl3): lH 4.04
(m, 1H, H-3), 3.87 (m, 1H, H-6), 3.71 (d, J=4.4 Hz,
1H, H-4), 0.98 (s, 3H, CH3-19), 0.65 (s, 3H, CH3-18);
13C NMR (CDCl3): lC 11.9, 16.6, 18.5, 22.5 and 22.7
(5×CH3), 20.6, 23.8, 24.1, 26.6, 28.0, 28.1, 36.0, 38.6,
39.4 and 39.5 (10×CH2), 27.9, 34.3, 35.7, 49.8, 55.4,
56.1, 57.7, 62.5 and 64.8 (9×CH), 36.2, 42.5 and 70.5
(3×C); MS (ES+): m/z 441 (M+Na+, 100), 401 (55), 214
(71), 114 (43).
+
(M+NH4 , C24H50NO3 requires 436.3791); IR: wmax
3500–3300, 2937, 1469, 1382 and 1074; 1H NMR
(CDCl3): lH 3.95 (m, 2H, H-3, H-6), 3.39 (s, 1H, H-4),
1.07 (s, 3H, CH3-19), 0.65 (s, 3H, CH3-18); 13C NMR
(CDCl3): lC 11.9, 17.1, 18.5, 22.5 and 22.7 (5×CH3),
20.7, 23.9, 24.1, 25.7, 28.1, 29.0, 36.0, 38.1, 39.4 and
39.5 (10×CH2), 27.9, 34.3, 35.7, 49.3, 55.4, 56.2, 60.1,

K. Zhao et al. / Tetrahedron: Asymmetry 12 (2001) 1211–1217
1217
3.18. 4a,5-Epoxy-5a-cholestane-3a,6a-diol, 3,6-diacetate
67.6, 128.3 (two carbons), 129.6 (two carbons) and
133.0 (14×CH), 36.7, 42.6, 66.7, 129.8, 165.5 and 169.8
(6×C); MS (ES+): m/z 587 (M+Na+, 100).
Obtained via acetylation of the corresponding diol.
Isolated as a white solid. Mp 160–161°C; [h]2D0=+94 (c
10.0, CHCl3); HRMS (ES+): m/z 520.4000 (M+NH4 ,
+
C31H54NO5 requires 520.4002); IR: wmax 2937, 2861,
1735, 1465, 1379, 1236 and 1033; 1H NMR (CDCl3): lH
5.20 (dd, J=12.0 and 4.8 Hz, 1H, H-6), 5.12 (m, 1H,
H-3), 3.44 (d, J=4.0 Hz, 1H, H-4), 1.06 (s, 3H, CH3-
19), 0.65 (s, 3H, CH3-18); 13C NMR (CDCl3): lC 11.9,
16.7, 18.5, 20.9, 21.0, 22.4 and 22.7 (7×CH3), 20.5, 23.4,
23.7, 23.9, 28.0, 28.8, 34.2, 36.0, 39.3 and 39.4 (10×
CH2), 27.9, 34.3, 35.6, 49.7, 55.0, 55.2, 56.0, 66.1 and
66.8 (9×CH), 36.8, 42.5, 66.9, 170.3 and 170.5 (5×C);
MS (ES+): m/z 525 (M+Na+, 100).
Acknowledgements
The authors would like to thank EPSRC National
Mass Spectrometry Service Centre, University of Wales
Swansea, UK, for measurement of the high-resolution
mass spectra, and to thank Dr. Carl Schwalbe for
useful discussions on torsion angles.
References
3.19. 4b,5-Epoxy-5b-cholestane-3a,6a-diol
1. Lehmann, J. M.; Kliewer, S. A.; Moore, L. B.; Smith-
Oliver, T. A.; Oliver, B. B.; Su, J.-L.; Sundseth, S. S.;
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Obtained via hydrolysis of the 3-acetate and flash chro-
matography. Isolated as a white solid. Mp 99–100°C;
[h]2D0=+25 (c 3.0, CHCl3); HRMS (ES+): m/z 436.3793
+
(M+NH4 , C24H50NO3 requires 436.3791); IR: wmax
3500–3300, 2937, 1467, 1365 and 1078; 1H NMR
(CDCl3): lH 4.01 (m, 2H, H-3 and H-6), 3.36 (s, 1H,
H-4), 0.96 (s, 3H, CH3-19), 0.65 (s, 3H, CH3-18); 13C
NMR (CDCl3): lC 11.8, 18.5, 18.9, 22.4 and 22.7,
(5×CH3), 21.1, 23.8, 24.2, 24.6, 26.4, 28.1, 36.0, 37.7,
39.4 and 39.5 (10×CH2), 27.9, 34.0, 35.7, 45.5, 55.6,
56.2, 59.8 and 65.9 (two carbons) (9×CH), 36.0, 42.5
and 69.8 (3×C); MS (ES+): m/z 436 (M+NH4 , 62), 401
+
(100), 236 (15), 214 (18).
7. Rossoter, B. E.; Verhoeven, T. R.; Sharpless, K. B.
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3.20. 4b,5-Epoxy-5b-cholestane-3a,6a-diol, 3,6-diacetate
8. Morrison, G. A.; Wilkinson, J. B. J. Chem. Soc., Perkin
Trans. 1 1990, 345–351.
Obtained via acetylation of the correspondent diol.
9. Bartlett, P. D. Rec. Prog. Chem. 1950, 11, 47–51.
10. Henbest, H. B.; Wilson, R. A. L. J. Chem. Soc. 1957,
1958–1965.
Isolated as a white solid. Mp 63–64°C; [h]2D0=+26 (c
1.0, CHCl3); HRMS (ES+): m/z 520.4000 (M+NH4 ,
+
C31H54NO5 requires 520.4002); IR: wmax 2952, 2861,
1741, 1465, 1379, 1234 and 1033; 1H NMR (CDCl3): lH
5.21 (dd, J=12.2, 4.8 Hz, 1H and H-6), 4.88 (dd,
J=9.2 and 0.4 Hz, 1H and H-3), 3.19 (s, 1H, H-4), 1.02
(s, 3H, CH3-19), 0.63 (s, 3H, CH3-18); 13C NMR
(CDCl3): lC 11.8, 18.5, 18.8, 20.9, 21.0, 22.4 and 22.7
(7×CH3), 21.0, 21.6, 23.6, 24.0, 25.8, 27.9, 35.9, 36.0,
39.3 and 39.4 (10×CH2) 27.8, 33.9, 35.5, 45.6, 55.6,
56.0, 57.0, 67.2 and 68.1 (9×CH), 37.1, 42.5, 66.1 and
169.8 (two carbons) (5×C); MS (ES+): m/z 525 (M+Na+,
100).
11. Paquette, L. A.; Barrett, J. H. Org. Synth. Coll. 1973, 5,
467.
12. Sharpless, K. B. J. Am. Chem. Soc. 1973, 95, 6136–6137.
13. Katsuki, T.; Sharpless, K. B. J. Am. Chem. Soc. 1980,
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14. (a) Lavie, D.; Kashman, Y.; Glotter, E. Tetrahedron
1966, 22, 1103–1111; (b) Greenfield, S.; Glotter, E.;
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17. Itoh, T.; Jitsukawa, K.; Kaaaneda, K.; Teranishi, S. J.
3.21. 3b-Acetoxy-6a-benzoxy-4a,5-epoxy-5a-cholestane
Obtained via recrystallisation from acetone. Isolated as
Am. Chem. Soc. 1979, 101, 159–169.
18. Dehnel, R. B.; Whitham, G. H. J. Chem. Soc., Perkin
Trans 1 1979, 953–955.
white flakes. Mp 145–146°C; [h]2D0=+82 (c 10.0,
CHCl3); HRMS (ES+): m/z 582.4160 (M+NH4 ,
+
C36H56NO5 requires 582.4158); IR: wmax 2946, 2869,
1730, 1724, 1447, 1378, 1272, 1240, 1110, 1032 and 715;
1H NMR (CDCl3): lH 5.48 (dd, J=12.2 and 4.8 Hz, 1H
and H-6), 4.98 (m, 1H, H-3), 3.21 (s, 1H, H-4), 1.20 (s,
3H, CH3-19), 0.70 (s, 3H, CH3-18); 13C NMR (CDCl3):
lC 11.9, 17.1, 18.6, 21.0, 22.5 and 22.7 (6×CH3), 20.7,
22.9, 23.8, 24.0, 28.0, 28.6, 34.1, 36.0, 39.3 and 39.4
(10×CH2), 27.9, 34.3, 35.7, 49.3, 55.2, 56.0, 57.6, 67.3,
.
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21. Ishigura, M.; Saita, H.; Ikekawa, N. J. Chem. Soc.,
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22. Glotter, E.; Greenfield, S.; Lavie, D. J. Chem. Soc. (C)
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23. Risenheim, O.; Starling, W. W. J. Chem. Soc. 1937, 377,
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