Further studies on the synthesis of 24(S),25-epoxycholesterol. A new, efficient preparation of desmosterol

Article abstract of DOI:10.1021/jo991370c

Efforts to improve the synthesis of 24(S),25-epoxycholesterol (1) from stigmasterol (3) have included identification of 6α-hydroxy-i-steroid 11 as a byproduct from the ozonolysis of 9 and an attempt to effect conversion of sulfone 14 to diol 18 via Payne rearrangement and nucleophilic trapping of epoxide 25, which led instead to 27 and 28 (97% yield). A more efficient synthesis of 1 was achieved via coupling of cuprate 21 with allylic acetate 31 to give 73% of 16, in the most efficient conversion yet of a C22 intermediate to desmosterol (5) or its acetate 6.

Full text of DOI:10.1021/jo991370c

J . Org. Chem. 2000, 65, 1919-1923
1919
F u r th er Stu d ies on th e Syn th esis of 24(S),25-Ep oxych olester ol. A
New , Efficien t P r ep a r a tion of Desm oster ol
Thomas A. Spencer,* Dansu Li, and J onathon S. Russel
Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755
Nicholas C. O. Tomkinson† and Timothy M. Willson
Department of Medicinal Chemistry, Glaxo Wellcome Research and Development,
Research Triangle Park, North Carolina 27709
Received August 30, 1999
Efforts to improve the synthesis of 24(S),25-epoxycholesterol (1) from stigmasterol (3) have included
identification of 6R-hydroxy-i-steroid 11 as a byproduct from the ozonolysis of 9 and an attempt to
effect conversion of sulfone 14 to diol 18 via Payne rearrangement and nucleophilic trapping of
epoxide 25, which led instead to 27 and 28 (97% yield). A more efficient synthesis of 1 was achieved
via coupling of cuprate 21 with allylic acetate 31 to give 73% of 16, in the most efficient conversion
yet of a C22 intermediate to desmosterol (5) or its acetate 6.
Sch em e 1
Substantial evidence has been accumulated that 24-
(S),25-epoxycholesterol (1), formed enzymatically via
squalene 2,3(S),22(S),23-dioxide,1,2 participates in the
natural regulation of cholesterol metabolism.3-6 In par-
ticular, it has recently been found that in response to 1
the nuclear LXRR receptor subtype regulates transcrip-
tion of the gene encoding cholesterol 7R-hydroxylase,7 the
enzyme that catalyzes the rate-limiting step in conversion
of cholesterol to bile acids. This increasing evidence of
the biological importance of 1 has made access to
substantial quantities of this epoxide essential and has
dictated development of stereoselective syntheses of 1.
We have described syntheses of 1 starting from cholenic
acid (2)8 and from stigmasterol (3),8 and Corey and
Grogan9 have described a synthesis of 1 from bisnor-
cholenic acid (4) (Scheme 1). Each of these approaches
relies on Sharpless asymmetric dihydroxylation10 of the
key intermediate desmosterol (5)9 or its acetate 6,8
followed by mesylation of resulting diol 79 or 88 and base-
catalyzed epoxide formation.
In this paper we describe efforts to improve our
synthesis of 1 from stigmasterol (3), the least costly of
the steroidal starting materials. These efforts include
identification of a curious byproduct from ozonolysis of
intermediate 9 and an unsuccessful attempt to achieve
in one step both addition of a prenyl moiety to a C22
intermediate such as 13 and introduction of the 24R,25-
diol functionality of 8, thus bypassing formation and
dihydroxylation of 6. We have succeeded, however, in
improving the overall yield of 1 by discovery of the best
method to date for prenylation of 13, en route to desmo-
sterol acetate (6).
† Current address: Department of Chemistry, Cardiff University,
Wales, U.K.
(1) Nelson, J . A.; Steckbeck, S. R.; Spencer, T. A. J . Biol. Chem. 1981,
256, 1067-1068.
(2) Nelson, J . A.; Steckbeck, S. R.; Spencer, T. A. J . Am. Chem. Soc.
1981, 103, 6974-6975.
(3) Spencer, T. A.; Gayen, A. K.; Phirwa, S.; Nelson, J . A.; Taylor,
F. R.; Kandutsch, A. A.; Erickson, S. K. J . Biol. Chem. 1985, 260,
13391-13394.
(4) Saucier, S. E.; Kandutsch, A. A.; Taylor, F. R.; Spencer, T. A.;
Phirwa, S.; Gayen, A. K. J . Biol. Chem. 1985, 260, 14571-14579.
(5) Spencer, T. A. Acc. Chem. Res. 1994, 27, 83-90.
(6) Sinensky, M.; Logel, J .; Phirwa, S.; Gayen, A. K.; Spencer, T. A.
Exp. Cell Res. 1987, 171, 492-497.
Our synthesis of 1 from 3 (Scheme 2)8 begins with the
sequence initially reported by Partridge,11 involving
preparation of i-steroid 9 and ozonolysis to 10. Treatment
of 9 with ozone and then NaBH4 yields up to 81% of 10,8,12
but also consistently affords another, more polar, appar-
ently previously unreported, product, which we chose to
(7) (a) Lehmann, J . M.; Kliewer, S. A.; Moore, L. B.; Smith-Oliver,
T. A.; Oliver, B. B.; Su, J .-L.; Sundseth, S. S.; Winegar, D. A.;
Blanchard, D. E.; Spencer, T. A.; Willson, T. M. J . Biol. Chem. 1997,
272, 3137-3140. (b) Peet, D. J .; Turley, S. D.; Ma, W.; J anowski, B.
A.; Lobaccaro, J . A.; Hammer, R. E.; Mangelsdorf, D. J . Cell 1998, 93,
693-704.
(8) Tomkinson, N. C. O.; Willson, T. M.; Russel, J . S.; Spencer, T.
A. J . Org. Chem. 1998, 63, 9919-9923.
(11) Partridge, J . J .; Faber, S.; Uskokovic, M. R. Helv. Chim. Acta
1974, 57, 764-770.
(12) Moriarty, R. M.; Enache, L. A.; Kinney, W. A.; Allen, C. S.;
Canary, J . W.; Tuladhar, S. M.; Guo, L. Tetrahedron Lett. 1995, 36,
5139-5142, report 85% yield of 10 from treatment of 9 with O3 and
then NaBH4.
(9) Corey, E. J .; Grogan, M. J . Tetrahedron Lett. 1998, 39, 9351-
9354.
(10) Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem.
Rev. 1994, 94, 2483-2547.
10.1021/jo991370c CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/15/2000

1920 J . Org. Chem., Vol. 65, No. 7, 2000
Spencer et al.
Sch em e 2a
cyclocholestan-6-one has previously been shown to afford
exclusively the 6R-alcohol,13,19-21 and we confirmed that
NaBH4 reduction of 12, prepared in 68% yield by Swern
oxidation of 11, likewise gave only the 6R-hydroxy
compound. If ozonolysis of 9 is allowed to proceed for 12
h, 22% of 11 (plus 69% of 10) can be obtained; ozonolysis
for the minimum time (5 min) required to consume 9
affords ca. 2% of 11.
A key step in our previous preparation of 1 from 3 is
prenylation of i-steroid sulfone 14.8 If the anion of 14
a
Reagents: (a) TsCl, py; (b) CH3OH, ∆; (c) (1) O3, CH2Cl2; (2)
NaBH4; (d) TsCl, py; (e) KI, acetone, ∆; (f) PhSO2Na, DMF, ∆; (g)
(1) BuLi; (2) 4-bromo-2-methyl-2-butene; (h) Li, NH3; (i) HOAc,
∆; (j) AD-mix-â, CH3SO2NH2; (k) CH3SO2Cl, py; (l) K2CO3,
CH3OH‚H2O; (m) Swern; (n) NaBH4.
characterize with the hope of learning how to improve
the yield of 10. This compound was determined to be 6R-
hydroxy-i-steroid 11 on the basis of its elemental com-
could be used instead to react with epoxide 17 (presum-
ably also as its anion) to give 18, both the construction
of the requisite cholestane skeleton and the stereoselec-
tive introduction of the 24R,25-diol functionality would
be accomplished in one step. Ourisson22 and Moriarty12
have used the anion of 14 in reaction with the simpler
chiral epoxide 19 to provide 20, and we have shown that
cyanocuprate 21 can be similarly used with 19 to give
56% of 22,23 so this potentially highly efficient strategy
seemed promising. Unfortunately, chiral epoxide 17 is
not readily available, because Sharpless asymmetric
epoxidation is ineffective for tertiary allylic alcohols,24,25
such as 2-methyl-3-buten-2-ol. However, it seemed that
the desired electrophile 23 might be accessible via Payne
rearrangement of anion 24 formed from the readily
prepared isomeric epoxide 25.26 If deprotonation of 25
established the equilibrium 24 a 2327 in the presence of
a suitable nucleophile, such as 21 or the anion of 14,
reaction at the least substituted epoxide carbon to give
1
position and its H and 13C NMR properties, in particular
signals at high field indicating the presence of the
cyclopropyl group and at δ 3.91 (dd, J ) 11.4, 4.2 Hz) for
the 6â-H.13 Compound 11 is presumably formed by
NaBH4 reduction of ketone 12,14 a type of product often
observed upon ozonolysis of ethers.15-17 Such ketone
formation has been rationalized by the type of mechanism
shown in eq 115-17 and tends to occur in cases, such as 9,
in which carbocation formation at the site of oxidation is
relatively favorable.15,17,18 Hydride reduction of 3R,5-
(13) Brown, H. C.; Varma, V. J . Org. Chem. 1974, 39, 1631-1636,
report the 1H NMR signal for the 6â-H in 3R,5-cyclocholestan-6R-ol at
δ 3.81 (CCl4), whereas the 6R-H in 10 appears at 2.78 (CDCl3), an
unusually high-field characteristic of this i-steroid substitution pattern.
(14) Pagani Zecchini, G.; Paglialunga Paradisi, M.; Torrini, I.
Tetrahedron 1983, 39, 2709-2713.
(19) Nagano, M.; Poyser, J . P.; Cheng, K.-P.; Luu, B.; Ourisson, G.;
Beck, J . P. J . Chem. Res., Synop. 1977, 218.
(20) Collins, D. J .; J ackson, W. R.; Timms, R. N. Aust. J . Chem. 1980,
33, 2767-2775.
(21) Kocovsky, P.; Srogl, J .; Gogoll, A.; Hanus, V.; Polasek, M. J .
Chem. Soc., Chem. Commun. 1992, 1086-1087.
(22) Koch, P.; Nakatani, Y.; Luu, B.; Ourisson, G. Bull. Soc. Chim.
Fr. 1983, 189-194.
(15) Price, C. C.; Tumolo, A. L. J . Am. Chem. Soc. 1964, 86, 4691-
4694.
(16) Erickson, R. E.; Hansen, R. T.; Harkins, J . J . Am. Chem. Soc.
1968, 90, 6777-6783.
(17) Bailey, P. S.; Lerdal, D. A. J . Am. Chem. Soc. 1978, 100, 5820-
5825.
(18) Giamalva, D. H.; Church, D. F.; Pryor, W. A. J . Am. Chem. Soc.
1986, 108, 7678-7681, discuss the possible mechanisms of reaction of
ozone with C-H bonds and conclude that either the type of mechanism
in eq 1 or initial hydride ion abstraction by ozone is most probable.
(23) Li, D.; Spencer, T. A. Unpublished.
(24) Katsuki, T.; Sharpless, K. B. J . Am. Chem. Soc. 1980, 102,
5974-5976.
(25) Pfenninger, A. Synthesis 1986, 89-116.
(26) Smith, A. B., III; Kingery-Wood, J .; Leenay, T. L.; Nolen, E.
G.; Sunazuka, T. J . Am. Chem. Soc. 1992, 114, 1438-1449.
(27) Payne, G. B. J . Org. Chem. 1962, 27, 3819-3822.

Synthesis of 24(S),25-Epoxycholesterol
J . Org. Chem., Vol. 65, No. 7, 2000 1921
18 would be expected.28 This type of Payne rearrange-
ment-nucleophilic trapping has been conducted success-
fully,28 although usually under basic aqueous conditions
that facilitate epoxide isomerization but preclude the use
of a carbon nucleophile.27 Only a few examples of such
reactions under aprotic conditions have been reported.29-31
Sutherland and co-workers30,31 have conducted a study
of solvents, Lewis acid isomerization catalysts, and
carbon nucleophiles in an effort to develop optimized
conditions for such reactions. Their study suggested that
saturated solutions of LiCl in THF offer the best pros-
pects for trapping rearranged epoxide with cyanocu-
prates.
This strategy was first tried using as nucleophile
cyanocuprate 21, which was prepared from iodide 13 via
the lithio derivative32 according to the procedure of
Acker.33 Unfortunately, treatment of 21 with the anion
formed from 25 with 1 equiv of BuLi in THF in the
presence of excess LiCl led only to formation of 26 (30%)
and alcohol 10 (53%). Although this reaction was run
under N2, adventitious O2 seems the likely source of 10.
When the more stable anion of sulfone 14 was used as
nucleophile with the anion of 25 under the same condi-
tions, carbon-carbon coupling was indeed effected, but,
disappointingly, the product was a 5:1 mixture of epimers
27 and 28, formed in 97% yield, presumably by reaction
at the less substituted end of unrearranged 24. The
turn converted by treatment with aqueous acid to 30,
which is being evaluated as a structurally novel ligand
for the LXR receptors.36
Having failed to effect direct formation of a diol such
as 18 via the Payne rearrangement strategy, we turned
to efforts to improve the prenylation of a C22 intermedi-
ate, such as iodide 13. We had previously employed
prenylation of sulfone 14 only because considerable effort
to effect efficient coupling of C22 electrophiles, such as
13, or nucleophiles, such as 21, with, respectively, prenyl
nucleophiles or electrophiles had not been rewarding.
One variation of this approach that had not been at-
tempted was the coupling of organocuprate 21 with
3-acetoxy-3-methyl-1-butene (31).37 Gratifyingly, this
reaction afforded 73% of 16 (eq 2), the same intermediate
encountered in our earlier synthesis of 6 after prenylation
of sulfone 14 to give 15 and removal of the C22 phenyl-
sulfonyl group (Scheme 2). Compound 16 has been
readily converted to either desmosterol (5)38 or its acetate
6,8 and the 73% yield of 16 obtained from the reaction of
21 with 31 effects the most efficient synthesis yet of the
desmosterol structure from C22 intermediates, bettering
the 65% yield reported for Ni(CO)4-catalyzed coupling of
13 with prenyl bromide.38 The coupling of 21 with 31 also
increases the overall yield in our conversion of stigmas-
terol (3) to 24(S),25-epoxycholesterol (1) from 16% in 12
steps8 to 21% in 10 steps.
Exp er im en ta l Section
Unless otherwise specified, NMR spectra were taken at 300
MHz in CDCl3. The 1H and 13C chemical shifts are reported
in units of δ. Tetrahydrofuran (THF) and ether were distilled
from sodium/benzophenone. Acetone was distilled from calcium
carbonate onto 3 Å molecular sieves. Pyridine was distilled
from calcium hydride onto 4 Å molecular sieves. Methanol was
distilled from magnesium and iodine onto 3 Å molecular sieves.
Acetic acid was distilled from acetic anhydride. All reactions
were magnetically stirred. Melting point determinations were
made with a Thomas-Hoover melting point apparatus and are
uncorrected.
Flash column chromatography was carried out on EM
Reagent silica gel 60 (230-400 mesh). Thin-layer chromatog-
raphy (TLC) was conducted on EM plastic sheets precoated
with silica gel 60 F-245. Visualization was obtained by
exposure to 5% phosphomolybdic acid in 2-propanol. All
solvents were dried over MgSO4. All reagents, unless otherwise
noted, were obtained from Aldrich Chemical Co.
structural assignments to 27 and 28 were based on
HRMS analysis and NMR spectra. One peak in the H
1
NMR spectra in CDCl3 at δ 3.75 for 27 and δ 3.94 for 28
was initially puzzling, but 2D NMR experiments with 27
indicated that it is probably the C22 proton geminal to
the phenylsulfonyl group appearing unexpectedly far
downfield.34 Confirmation of structure and assignment
of C22 stereochemistry was obtained by X-ray crystal
structure determination on 27.35 Reaction of either 27
or 28 with Li in NH3 afforded 29. This i-steroid was in
(28) Behrens, C. H.; Ko, S. Y.; Sharpless, K. B.; Walker, F. J . J .
Org. Chem. 1985, 50, 5687-5696.
3r,5-Cyclo-22-h ydr oxy-5r-23,24-bisn or ch olan -6â-ol 6-M-
eth yl Eth er (10) a n d 3r,5-Cyclo-22-h yd r oxy-5r-23,24-
bisn or ch ola n -6r-ol (11). A solution of 9.5 g (22.8 mmol) of 9
in 450 mL of 2:1 dry CH2Cl2/methanol at -78 °C was treated
with ozone for 12 h. The mixture was bubbled with oxygen for
5 min to remove excess ozone, warmed to 0 °C, and treated
with 100 mL of 95% ethanol, and 8.6 g (230 mmol) of NaBH4
was added slowly. The resulting mixture was warmed to room
(29) Yamaguchi, M.; Hirao, I. J . Chem. Soc., Chem. Commun. 1984,
202-203.
(30) Page, P. C. B.; Rayner, C. M.; Sutherland, I. O. J . Chem. Soc.,
Chem. Commun. 1988, 356-358.
(31) Page, P. C. B.; Rayner, C. M.; Sutherland, I. O. J . Chem. Soc.,
Perkin Trans. 1 1990, 1375-1382.
(32) Bailey, W. F.; Punzalan, E. R. J . Org. Chem. 1990, 55, 5404-
5406.
(33) Acker, R.-D. Tetrahedron Lett. 1977, 39, 3407-3410.
(34) The C22 protons in 14 are at δ 3.12 and 2.83, and the C22
protons in the epimers of 15 are at δ 3.07 and 3.05.8
(35) Atomic coordinates, bond lengths and angles, and thermal
parameters for 27 have been deposited at the Cambridge Crystal-
lographic Data Centre, with registration no. 135903.
(36) Watson, M. A.; Willson, T. M. Unpublished.
(37) Bergstrom, D. E.; Ruth, J . L.; Warwick, P. J . Org. Chem. 1981,
46, 1432-1441.
(38) Dasgupta, S. K.; Crump, D. R.; Gut, M. J . Org. Chem. 1974,
39, 1658-1661.

1922 J . Org. Chem., Vol. 65, No. 7, 2000
Spencer et al.
temperature, stirred overnight, and then poured slowly onto
100 mL of 5% HCl solution at 0 °C. The aqueous layer was
extracted five times with CH2Cl2, and the combined organic
layers were condensed to 150 mL, washed with saturated
NaHCO3 solution and brine, dried, filtered, and evaporated
to give 8.0 g of residue, which was chromatographed (3:17
EtOAc/hexane) to give 5.4 g (69%) of 10 and 1.7 g (22%) of 11
(mp 157.5-160.0 °C). Compound 10: 1H NMR 3.65 (dd, J )
10.5, 3.3 Hz, 1H), 3.38 (dd, J ) 10.5, 6.9 Hz, 1H), 3.33 (s, 3H),
2.78 (t, J ) 2.7 Hz, 1H), 1.05 (d, J ) 6.6 Hz, 3H), 1.03 (s, 3H),
0.75 (s, 3H), 0.66 (m, 1H), 0.44 (dd, J ) 8.1, 5.1 Hz, 1H); 13C
NMR 82.6, 68.3, 56.8, 56.5, 52.8, 48.2, 43.6, 43.1, 40.3, 39.0,
35.3, 33.5, 30.7, 28.0, 25.2, 24.5, 23.9, 23.0, 21.7, 19.5, 17.0,
13.3, 12.5. Compound 11: after recrystallization from CH2-
Cl2/hexane, mp 163.4-164 °C; IR νmax 3330 cm-1; 1H NMR 3.91
(dd, J ) 11.4, 4.2 Hz, 1H), 3.64 (dd, J ) 10.5, 3.0 Hz, 1H),
3.37 (dd, J ) 10.5, 6.9 Hz, 1H), 1.05 (d, J ) 6.6 Hz, 3H), 0.92
(s, 3H), 0.72 (s, 3H), 0.61 (dd, J ) 8.1, 4.5 Hz, 1H), 0.26 (m,
1H); 13C NMR 68.2, 67.4, 56.2, 52.7, 47.8, 45.2, 43.0, 40.4, 40.1,
40.0, 39.0, 35.2, 33.0, 27.9, 25.3, 24.5, 23.3, 18.9, 18.2, 16.9,
12.4, 6.83; EI-HRMS (M+) calcd for C22H36O2, 332.2715, found
332.2724.
20(S )-6-Oxo-3r,5-cyclo-5-p r e gn a n e -20-ca r b oxa ld e -
h yd e (12). According to a procedure by Swern,39 to a solution
of 0.3 mL (3.3 mmol) of oxalyl chloride in 2 mL of CH2Cl2 at
-78 °C was added 0.5 mL (6.5 mmol) of DMSO in 1 mL of
CH2Cl2. After the resulting mixture was stirred for 2 min, 99.4
mg (0.300 mmol) of 11 was added and the mixture was stirred
for 15 min before 1.8 mL (12.8 mmol) of Et3N was added. The
mixture was stirred at -78 °C for 20 min, warmed to room
temperature, stirred for 5 h, diluted with 10 mL of H2O, and
extracted thrice with CH2Cl2. The combined organic layers
were washed with 1% HCl, H2O, 5% NaHCO3, H2O, and brine,
dried, filtered, and evaporated to give 151 mg of residue, which
was chromatographed (1:4 EtOAc/hexane) to afford 66.9 mg
(68%) of 12: mp 106-107.5 °C (lit.14 105-106 °C); IR νmax 1728,
1692 cm-1; 1H NMR 9.55 (d, J ) 3.3 Hz, 1H), 1.11 (d, J ) 6.9
Hz, 3H), 0.98 (s, 3H), 0.73 (s, 3H); 13C NMR 209.4, 204.9, 56.3,
51.1, 49.5, 46.8, 46.4, 46.1, 44.7, 43.4, 39.5, 35.5, 34.8, 33.6,
27.1, 26.0, 24.5, 22.9, 19.8, 13.5, 12.5, 11.8.
Con ver sion of 12 to 11. To a solution of 86.1 mg (0.263
mmol) of 12 in 2.5 mL of CH2Cl2 and 1 mL of MeOH, and 1
mL of 90% EtOH in water at 0 °C was added 90.3 mg (2.39
mmol) of NaBH4. The resulting mixture was stirred at room
temperature for 3 h, treated with 5 mL of 1 N HCl at 0 °C,
and extracted with 4 × 10 mL of CH2Cl2. The combined organic
layers were washed with saturated NaHCO3 and brine, dried,
filtered, and evaporated to give 128.2 mg of residue in which
no 1H NMR signal for the 6R-H of the 6â-hydroxy isomer could
be detected and which crystallized from CH2Cl2/hexane to give
69.5 mg (80%) of 11: mp 163-164 °C.
3r,5-Cyclo-22(S a n d R)-p h en ylsu lfon yl-23(R)-h yd r oxy-
m eth yl-5r-26,27-bisn or er gost-6â,24-d iol 6-Meth yl Eth er
(27 a n d 28). To a solution of 262 mg (0.56 mmol) of 14 in 2
mL of THF was added dropwise 0.22 mL (0.56 mmol) of 2.5 M
nBuLi in pentane at -78 °C with stirring under N2. After being
stirred for 15 min, the yellow solution was treated dropwise
at -78 °C with a solution previously prepared by treating 157
mg (1.54 mmol) of 25, prepared according to a modification of
the procedure of Gao et al.,40 in 2 mL of THF with 0.62 mL
(1.54 mmol) of 2.5 M nBuLi in pentane at -78 °C with stirring
under nitrogen for 5 min and then allowed to warm slowly
over 10 min before being added to the anion of 14. The
resulting mixture was allowed to warm to room temperature
over 4 h, and stirring was continued for 12 h. The solvent was
evaporated, and the residue was dissolved in 20 mL of CH2-
Cl2 and washed with 20 mL of water. The aqueous layer was
extracted with EtOAc, and the combined organic layers were
dried, filtered, and evaporated to afford 398 mg of yellow
residue. Fractional recrystallization from 4:1 CH2Cl2/EtOAc
afforded 234 mg (81%) of the less polar 27 and 46 mg (16%) of
the more polar 28. Compound 27: mp 230-231 °C; H NMR
1
(4:1 CDCl3/CD3OD) 7.84-7.78 (m, 2H), 7.62-7.47 (m, 3H),
4.23-4.16 (dd, J ) 12, 6 Hz, 1H), 3.88-3.81 (dd, J ) 12, 6 Hz,
1H), 3.5 (br s, 1H), 3.18 (s, 3H), 2.65 (br, 1H), 2.48-2.42 (br,
1H), 1.27 (s, 3H), 1.24 (s, 3H), 1.23 (d, J ) 9 Hz, 3H), 0.88 (s,
3H), 0.41 (s, 3H); 13C NMR 139.3, 134.16, 129.7, 129.1, 82.9,
73.8, 68.3, 66.8, 61.5, 56.7, 56.5, 48.1, 43.6, 43.5, 40.2, 36.8,
35.5, 35.0, 33.6, 30.8, 29.3, 29.1, 28.6, 25.2, 24.2, 23.0, 22.0,
19.3, 15.8, 13.2, 11.4. Anal. Calcd for C34H52O5S‚H2O: C, 69.12;
H. 9.21. Found: C, 69.12, H. 9.21. FAB-HRMS (MH+): calcd
for C34H53O5S 573.3614, found 573.3612. X-ray analysis was
performed on a crystal grown from 4:1 CH2Cl2/EtOAc. Com-
pound 28: mp 195-197 °C; 1H NMR 8.00-7.95 (m, 2H), 7.72-
7.56 (m, 3H), 4.25-4.19 (dd, J ) 12, 6 Hz, 1H), 4.12-4.06 (dd,
J ) 12, 6 Hz, 1H), 3.94 (br s, 1H), 3.24 (s, 3H), 2.70 (t, J ) 3
Hz, 1H), 1.36 (d, J ) 6 Hz, 3H), 1.30 (s, 3H), 1.27 (s, 3H), 0.96
(s, 3H), 0.60 (s, 3H); 13C NMR 139.2, 134.2, 129.4, 128.8, 82.5,
73.7, 68.6, 61.1, 58.6, 56.6, 56.4, 48.0, 45.4, 43.6, 43.4, 40.4,
35.6, 35.2, 33.6, 30.8, 30.2, 30.1, 27.8, 25.2, 24.2, 22.9, 21.8,
19.4, 14.8, 13.2, 11.4; IR 3424, 2961, 1446, 1083, 1020, 800
cm-1; FAB-HRMS (MH+) calcd for C34H53O5S 573.3614, found
573.3612.
3r,5-Cyclo-23(R)-h ydr oxym eth yl-5r-26,27-bisn or er gost-
6â,24-d iol 6-Meth yl Eth er (29). A solution of 72 mg (10.5
mmol) of lithium in 30 mL of 3:1 ammonia/THF at -78 °C
was treated dropwise with a suspension of 211 mg (0.37 mmol)
of 27 in 10 mL of THF and 0.5 mL of ethanol. The blue solution
was stirred for 25 min at -78 °C, then quenched by dropwise
addition of acetone until the solution became colorless. The
mixture was allowed to warm slowly to room temperature over
2 h to allow the ammonia to evaporate. The residue remaining
as a suspension in THF was treated with 10 mL of EtOAc,
and this organic layer was washed with 10 mL of water. The
aqueous layer was washed with EtOAc, and the combined
EtOAc layers were washed with saturated NH4Cl solution and
brine, dried, filtered, and evaporated to afford 156 mg of
residue that was chromatographed on silica gel (1:3 EtOAc/
hexane) to afford 123 mg (77%) of colorless, oily 29: 1H NMR
3.76-3.62 (m, 2H), 3.30 (s, 3H), 2.75 (t, J ) 3 Hz, 1H), 1.28 (s,
3H), 1.17 (s, 3H), 0.99 (s, 3H), 0.93 (d, J ) 6 Hz, 3H), 0.69 (s,
3H); 13C NMR 82.6, 66.3, 57.8, 56.8, 56.6, 48.2, 43.6, 43.1, 40.5,
37.8, 35.4, 35.3, 34.9, 33.6, 30.7, 30.4, 28.8, 25.2, 24.4, 23.0,
21.7, 19.5, 13.3, 12.4; IR 3382, 2933, 1467, 1381, 1261, 1070,
1019 cm-1; EI-HRMS (M+) calcd for C28H48O3 432.3603, found
432.3601. Using the same procedure, 20 mg of 28 was
converted to 8 mg (55%) of 29.
23(R)-H yd r oxym et h yl-26,27-b isn or er gost -5-en -3â,24-
d iol (30). According to a modification of a procedure by
Partridge et al.,11 a solution of 74 mg (0.17 mmol) of 29 and
3.0 mg (0.017 mmol) of p-toluenesulfonic acid monohydrate
in 6 mL of 25% aqueous dioxane was heated (oil bath temp 75
°C) for 6 h. The mixture was cooled to room temperature and
quenched with 5 mL of water, and the colorless precipitate
was collected by suction filtration and washed four times with
water. The solid was dried under vacuum to afford 61 mg (86%)
of colorless 30: mp 222-224 °C. Recrystallization of a 26 mg
sample from 1:1 methanol/acetone gave 18 mg of 30: mp 230-
232 °C; 1H NMR (3:1 DMSO/CD3OD) 5.24 (m, 1H), 3.52-3.44
(dd, J ) 12, 6 Hz, 1H), 3.38-3.32 (dd, J ) 12, 6 Hz, 1H), 3.29-
3.17 (m, 1H), 1.07 (s, 3H), 1.03 (s, 3H), 0.91 (s, 3H), 0.89 (d, J
) 9 Hz, 3H), 0.63 (s, 3H); 13C NMR (DMSO) 141.2, 120.4, 72.6,
70.0, 63.7, 57.2, 56.2, 49.6, 48.3, 42.2, 42.0, 36.9, 36.7, 36.1,
34.4, 31.5, 31.4, 31.2, 29.0, 28.8, 27.9, 26.5, 23.9, 20.6, 19.2,
19.1, 11.7; IR 3316, 2926, 1463, 1367, 1260, 1063, 1022; FAB-
HRMS (MNa+) calcd for C27H46NaO3 441.3339, found 441.3345.
3r,5-Cyclo-5r-ch olest-24-en -6â-ol 6-Meth yl Eth er (16).
According to a procedure by Bailey32 and a modification of a
procedure by Acker,33 to a solution of 456 mg (1.00 mmol) of
13 in 1 mL of dry ether at -78 °C was added dropwise to 2.1
mL (2.247 mmol) of 1.07 M tBuLi in pentane with stirring
under N2. After 15 min, the mixture was allowed to warm
slowly and stand at room temperature for 1 h, cooled again to
-78 °C, and then added dropwise to a solution of 104 mg (1.16
mmol) of CuCN in 1 mL of dry ether at -78 °C. The resulting
(39) Mancuso, A. J .; Huang, S.-L.; Swern, D. J . Org. Chem. 1978,
43, 2480-2482.
(40) Gao, Y.; Hanson, R. M.; Klunder, J . M.; Ko, S. Y.; Masamune,
H.; Sharpless, K. B. J . Am. Chem. Soc. 1987, 109, 5765-5780.

Synthesis of 24(S),25-Epoxycholesterol
J . Org. Chem., Vol. 65, No. 7, 2000 1923
mixture was stirred for 5 min, then warmed slowly until most
of the CuCN was dissolved (∼20-30 min), and recooled to -78
°C. Then a solution of 502 mg (3.92 mmol) of 31, prepared in
48% yield from 2-methyl-3-buten-2-ol according to a procedure
by Bergstrom,37 in 1 mL of dry ether over 3 Å molecular sieves
was added dropwise. The resulting mixture was stirred at -78
°C for 3 h, warmed to room temperature, and stirred under
N2 overnight. A mixture of 10 mL of saturated NH4Cl solution
and 1 mL of NH4OH was added to the mixture, and the
aqueous layer was extracted with CH2Cl2. The combined
organic layers were dried, filtered, and evaporated to give 546
mg of yellow residue, which was chromatographed (3:20
EtOAc/hexane) to give 290 mg (73%) of colorless, oily 16. A
216 mg sample was crystallized from acetone/methanol to
afford 163 mg of colorless 16: mp 60-61 °C (lit.38 mp 64-66
J ) 6.6 Hz, 3H), 0.72 (s, 3H); 13C NMR 131.1, 125.4, 82.6, 56.7,
56.5, 48.2, 43.6, 43.0, 40.5, 36.3, 35.8, 35.5, 35.3, 33.6, 30.7,
28.5, 25.9, 25.2, 24.9, 24.4, 23.0, 21.7, 19.5, 18.8, 17.8, 13.3,
12.5.
Ack n ow led gm en t. The research at Dartmouth was
supported by NIH Grant HL52069. The X-ray structure
of 27 was determined by Peter White, University of
North Carolina, Chapel Hill.
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra of all new compounds and for 10, for which spectra
have not previously been reported. This material is available
free of charge via the Internet at http://pubs.acs.org.
1
°C); H NMR 5.09 (t, J ) 7.2 Hz, 1H), 3.33 (s, 3H), 2.77 (t, J
) 2.7 Hz, 1H), 1.69 (s, 3H), 1.60 (s, 3H), 1.03 (s, 3H), 0.93 (d,
J O991370C