Synthetic routes to campesterol and dihydrobrassicasterol: A first reported synthesis of the key phytosterol dihydrobrassicasterol

Article abstract of DOI:10.1016/j.tet.2012.04.060

Phytosterols are increasingly used as health supplements in functional foods and are associated with having both positive and negative effects on health. Given this disparity, an investigation of their full individual biological profile is imperative in order to assure food safety. This paper describes the de novo synthesis of pure phytosterols in multigram scale and we report the first synthesis of the key phytosterol dihydrobrassicasterol along with a comparison of routes to campesterol. A detailed spectroscopic analysis is included with full assignment of the ¹³C NMR spectroscopic data of both compounds, mixtures and their precursors leading to the potential use of NMR spectroscopy as a tool for analysis of these sterol mixtures.

Full text of DOI:10.1016/j.tet.2012.04.060

Tetrahedron 68 (2012) 4995e5004
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthetic routes to campesterol and dihydrobrassicasterol: a first reported
synthesis of the key phytosterol dihydrobrassicasterol
,
N.M. O’Connell a, Y.C. O’Callaghan b, N.M. O’Brien b, A.R. Maguire c, F.O. McCarthy a
*
a Department of Chemistry, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland
b School of Food and Nutritional Sciences, University College Cork, Cork, Ireland
c Department of Chemistry and School of Pharmacy, Analytical and Biological Chemistry Research Facility, University College Cork, Cork, Ireland
a r t i c l e i n f o
a b s t r a c t
Article history:
Phytosterols are increasingly used as health supplements in functional foods and are associated with
having both positive and negative effects on health. Given this disparity, an investigation of their full
individual biological profile is imperative in order to assure food safety. This paper describes the de novo
synthesis of pure phytosterols in multigram scale and we report the first synthesis of the key phytosterol
dihydrobrassicasterol along with a comparison of routes to campesterol. A detailed spectroscopic anal-
ysis is included with full assignment of the 13C NMR spectroscopic data of both compounds, mixtures and
their precursors leading to the potential use of NMR spectroscopy as a tool for analysis of these sterol
mixtures.
Received 19 October 2011
Received in revised form 2 April 2012
Accepted 16 April 2012
Available online 22 April 2012
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
Hypercholesterolaemia is a major risk factor in heart disease
and a key target for primary and secondary prevention.1 Functional
foods supplemented with phytosterols are marketed for the man-
agement of hypercholesterolaemia and are widely used worldwide
as a non-prescription approach to lowering cholesterol levels.2
Phytosterols are found naturally in plants where the most abun-
dant are
b-sitosterol, stigmasterol, campesterol and dihydro-
brassicasterol (these comprise about 90% of all phytosterols
dependent on source) and are components of vegetables and veg-
etable products, such as vegetable oil, olive oil, fruit and nuts. While
structurally similar to cholesterol (Fig. 1) they are absorbed in vivo
to a reduced effect and are assumed to reduce the absorption of
cholesterol via mixed micelle formation.3
Phytosterols therefore have an increasing importance in the
food industry as a direct result of their health benefits and are
responsible for a multi-billion dollar market. In contrast to the
heavily promoted health benefits of dietary phytosterol supple-
mentation, a number of groups have identified phytosterols with
adverse health effects: induction of endothelial dysfunction and
increased size of ischaemic stroke;4 inhibition of cell growth;5
aggressive vascular disease in sitosterolaemic patients.6 In addi-
tion, the biological effects of phytosterol oxides are significant
since phytosterols are structurally similar to cholesterol and can
Fig. 1. Structures of cholesterol and key phytosterols.
undergo oxidation during storage and cooking. Phytosterol oxide
mixtures and individual phytosterol oxides exhibit a toxicity
profile similar to that of cholesterol oxides in cultured mammalian
cells.7
A limited number of pure individual phytosterols are available
commercially in useful quantities and therefore toxicity data on
phytosterols and their oxidation products is incomplete. Phytos-
terols occur in nature as mixtures and attempts to separate these
mixtures on a limited scale through chromatographic purification
techniques are well documented in the literature.8 However, mul-
tigram quantities are required to fully elucidate the complex
mechanisms of action of this class of compounds hence requiring
chemical synthesis. Many groups have attempted the synthesis of
phytosterols but given the difficulties involved and the lack of
comprehensive NMR spectroscopic data published in the area, a full
synthetic route has proved elusive. Representative cases of the
* Corresponding author. Tel.: þ353 21 4901695; e-mail address: f.mccarthy@
ucc.ie (F.O. McCarthy).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.060

4996
N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
pitfalls involved in synthesis of phytosterols have identified sig-
nificant problems associated with hydrogenation and the key C-24
substituent.9
Our investigations in phytosterol chemistry began with the
synthesis of
b-sitosterol and its oxides followed by a panel of
stigmasterol oxides.9,10 Given that campesterol and dihydro-
brassicasterol are the two remaining most abundant phytosterols in
nature (between 10 and 30% total phytosterol content) a stereo-
specific synthesis of both campesterol and dihydrobrassicasterol is
required in order to provide authentic samples as standards.
Dihydrobrassicasterol is structurally similar to campesterol but
with opposite stereochemistry at C-24 (S in dihydrobrassicasterol
and R in campesterol, Fig. 1) and in food content analysis are often
quoted as a ‘campesterol content’, which actually contains 33%
dihydrobrassicasterol.11
Our approach as illustrated in Scheme 1, shows Wittig salt
synthons with the desired configuration at C-2, which will be-
come the C-24 stereocentre in the target molecules. The steroid
fragment 4 is common to the synthesis of both campesterol
and dihydrobrassicasterol. Exploitation of the Wittig reaction,
careful catalytic hydrogenation, followed by removal of the pro-
tecting group should allow for access to gram quantities of each
phytosterol.
Scheme 2. (i) BH3$THF, NaOH, H2O, H2O2 (83%); (ii) p-TsCl, pyridine (75%); (iii) NaI,
acetone (71%); (iv) PPh3, acetonitrile (67%).
Racemic 9 was synthesized starting with hydroboration of al-
kene 5 followed by oxidation using hydrogen peroxide to yield al-
cohol 6. Treatment of the alcohol using standard tosylation
conditions yields tosylate 7. Displacement of the tosylate
using sodium iodide in acetone affords the iodide 8.22 The con-
version of this intermediate compound to its corresponding phos-
phonium salt 9 was carried out using excess triphenylphosphine in
acetonitrile.22
2.2. Optimisation of the Wittig reaction
The Wittig reaction plays an important role in the synthesis of
dihydrobrassicasterol and campesterol (Scheme 3). The successful
outcome of this reaction was predominantly influenced by solvent,
temperature and time. Optimum conditions for formation of the
ylide involved using dry THF as the solvent, addition of n-BuLi at
0
ꢀC and allowing the phosphorus ylide to stir for 1.5 h at this
temperature and 0.5 h at rt. Several other temperatures were ex-
plored (ꢁ78 ꢀC, ꢁ20 ꢀC and rt) in tandem with different time
constraints. The Wittig salt 9 was used in excess in order to avoid
possible epimerization of aldehyde 4. The phosphorus salt 9 was
most soluble in dry THF at 0 ꢀC. The ylide formation was observed
by colour change in the reaction mixture from pale yellow to dark
red. On addition of aldehyde 4 at 0 ꢀC, the reaction solution
decolourised and the desired alkene 10 was formed. Standard hy-
drogenation conditions using 5% Pd/C as a catalyst and ethanol as
a solvent were used to form alkane 11.9 The i-sterol methyl ether
hydrolysis of 11 utilises aqueous sulfuric acid to form a mixture of
dihydrobrassicasterol and campesterol 12 in an approximate ratio
of 3:1 determined from the 13C NMR spectrum (Tables 2 and 3; see
Supporting Information)23e25 (Scheme 3).
Scheme 1. Outline of synthetic approach.
A key aspect in the synthesis of campesterol and dihydro-
brassicasterol involves the construction of the enantiopure side
chain (Wittig salt). Successful enantioselective syntheses repor-
ted in the literature involve two different strategies, either
one which creates the stereocentre in the chiral analogue12e14 or
uses a natural product as the starting material where the ster-
eocentre is already in place.15e18 The aforementioned methods
proceed with good to excellent reported enantioselectivities
(88%e99.9%).
We now report a novel route to the key phytosterol dihydro-
brassicasterol and the synthesis of a series of potentially useful
campesterol and dihydrobrassicasterol mixtures along with a rig-
orous comparison of their 13C NMR spectroscopic features.
2. Results and discussion
Our synthetic route to each individual phytosterol centres on
the Wittig reaction utilising the synthesis of a common aldehyde 4
reported in the literature and easily available from stigmasterol.19,20
Stigmasterol was converted into its corresponding tosylate, treated
with anhydrous methanol to give the i-stigmasterol methyl ether,
which was converted under ozonolysis, reductive work up and
oxidation into aldehyde 4 with no epimerisation.9,10,21
Scheme 3. (i) 9, n-BuLi, THF, 0 ꢀC (31%); (ii) Pd/C, H2, EtOH, 50 psi (88%); (iii) 2.5 M aq
H2SO4, THF, H2O (57%).
2.1. Dihydrobrassicasterol and campesterol racemic mixture
2.3. Campesterol side chain
Prior to initiating synthesis of the enantiopure phytosterols, we
opted to synthesise a mixture of campesterol and dihydro-
brassicasterol (using racemic 9) in order to optimise the Wittig
reaction conditions (Scheme 2).
Following the successful outcome of the Wittig reaction above,
the synthesis of campesterol began by initial formation of the
enantiopure side chain 2.

N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
4997
Table 1
Our strategic approach began with investigation into methods
Optical rotation of compound 15
whereby the stereocentre of the side chain was induced. Initial
attempts showed poor reproducibility and the desired products
were not always formed.13,15e18 Hence these routes were aban-
doned in favour of synthesis from the chiral pool.
T
Source
½
a D
ꢂ
20
Scheme 5
Scheme 6
Ref.15
½
½
½
½
a D
ꢂ
þ2.50ꢀ (c 1.000 in CHCl3)
20
a D
ꢂ
þ2.45ꢀ (c 1.000 in CHCl3)
þ3.00ꢀ (c 3.000 in CH2Cl2)
þ3.30ꢀ (c 1.000 in CHCl3)
21
a D
ꢂ
Starting from the known sulfone 13, the dimethylation step to
form 14 presented many difficulties (Scheme 4).15 It was delicately
temperature and time dependent with addition of base at ꢁ30 ꢀC
stirring for 15 min followed byaddition of the methylating agent and
warming to 10 ꢀC for 30 min. The yield of this particular step was
very scale dependent, with smaller batches giving the best yield.
Desulfonylation was accomplished by treatment with magnesium in
methanol with a catalytic amount of mercuric chloride. This induced
formation of a side product 16, which could be separated from 15
with careful chromatography. Employing standard hydrogenation
conditions enables recycling of 16 to the desired silyl ether 15.
Ref.32
a D
ꢂ
20
Scheme 6. (i) 1.0 M TBAF, THF (41%); (ii) p-TsCl, pyridine (74%); (iii) NaI, acetone (91%);
(iv) PPh3, acetonitrile (58%).
2.4. Campesterol synthesis
The Wittig reaction was repeated in the same manner as seen
for the synthesis of 10 using the same optimum conditions to
form the desired alkene 22. Following standard hydrogenation
conditions 23 and side product 24 was also isolated as a possible
result of trans-solvolysis.9 The i-sterol methyl/ethyl ether hy-
drolysis of 23 and 24 utilising aqueous sulfuric acid unexpectedly
formed a mixture of campesterol and dihydrobrassicasterol 25 in
an approximate ratio of 2:1 determined from 13C NMR
spectra23e25 (Scheme 7).
Scheme 4. (i) n-BuLi, THF, MeI, repeated twice (44%); (ii) Mg, HgCl2 (cat.), MeOH
(37%); (iii) Pd/C, H2, EtOH, 50 psi (94%).
The inefficient nature and the problems encountered in trans-
forming the aforementioned sequence from small scale to large
scale (especially formation of 14) led us to initiate an alternative
route (Scheme 5). This involved reaction of 17 with methyl-
magnesium bromide affording the corresponding alcohol in ex-
cellent yields.26 Elimination of the alcohol functional group was
accomplished using mesyl chloride and triethylamine furnishing
the terminal alkene 16. Employing standard hydrogenation condi-
tions yields 15 as seen for the previous route.
Scheme 7. (i) 2, n-BuLi, THF, 0 ꢀC (66%); (ii) Pd/C, H2, EtOH, 50 psi (R¼OMe, 53%,
R¼OEt, 20%); (iii) 2.5 M aq H2SO4, THF, H2O (R¼OMe, 80%, R¼OEt, 57%).
Scheme 5. (i) 3 M MeMgBr, Et2O (99%); (ii) MsCl, Et2O, NEt3, 0 ꢀC (32%); (iii) Pd/C, H2,
EtOH, 50 psi (95%).
On comparison of the two routes described above (Schemes 4
and 5), the latter appeared more efficient and was scaled up. We
investigated both routes examining the optical rotation of the final
silyl ether 15 obtained from each individual route in order to de-
termine if any isomerisation had occurred during hydrogenation of
16 to 15 (Table 1). The results were consistent with literature values
for 15 and thus the latter route was the reaction pathway of choice.
Exposure of 15 to TBAF in THF produced alcohol 19 and treat-
ment using standard tosylation conditions yields tosylate 20. Dis-
placement of the tosylate using sodium iodide in acetone affords
the iodide 21, which was converted into the corresponding phos-
phonium salt 2 as before (Scheme 6).22
The overall stereochemical outcome of this synthetic pathway
produced a campesterol enriched sample of campesterol and
dihydrobrassicasterol according to analysis of the 13C NMR
spectroscopic data showing a mixture of the two isomeric phy-
tosterols. It is evident that the enantiopurity of the starting
material was not retained throughout the full synthetic sequence.
It has been reported that epimerization is possible at the hy-
drogenation stage after the Wittig reaction however epimeriza-
tion was observed before this step suggesting it occurs before the
formation of the Wittig salt.9,16 This is the topic of further
investigations.

4998
N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
On closer inspection of the 1H NMR spectrum of the Wittig re-
action product 22 (Fig. 2), the methoxy signal ( 3.33, 3H, s, OCH3)
appears to be overlapping with a second methoxy signal ( 3.32, 3H,
d
d
s, OCH3). We have concluded this second set of signals belong to the
dihydrobrassicasterol precursor 31, synthesised in its purest form
reported below. In addition the alkene protons of dihydro-
brassicasterol appear to be more deshielded than campesterol. The
same pattern of signals can also be seen in the Wittig product 10 for
the mixture of campesterol and dihydrobrassicasterol where the
opposite isomer is now in excess.
Scheme 8. (i) Ac2O, pyridine (96%); (ii) O3, CH2Cl2, MeOH, NaBH4 (83%); (iii) p-TsCl,
pyridine (63%); (iv) NaI, acetone (79%); (iv) PPh3, acetonitrile (69%).
The sequence of optimised reactions as described before was
carried out to form alkene 31 (Scheme 9). Standard hydrogenation
conditions using 5% Pd/C as a catalyst and ethanol as a solvent were
used to form alkane 32.9
Fig. 2. 1H NMR comparison of the Wittig reaction products (alkenes 10, 22 and 31) on
Scheme 9. (i) 3, n-BuLi, THF, 0 ꢀC (52%); (ii) Pd/C, H2, EtOH (85%); (iii) 2.5 M aq H2SO4,
route to dihydrobrassicasterol and campesterol.
THF, H2O (54%).
A previous study explored different hydrogenation conditions in
order to impede possible isomerisation during hydrogenation of
stigmasterol. This study concluded using ethanol as a solvent and
Pd/C as a catalyst gave excellent reproducibility of purity and yield.
Analysis of the 13C NMR spectroscopic data showed complete
agreement with that of the literature and our own data.27 Hydro-
lysis of the i-sterol ether 32 forms dihydrobrassicasterol 33 with
a trace amount of campesterol (<5%) determined from 13C NMR
spectra.23e25 Overall this optimised route provides for the first time
dihydrobrassicasterol in multigram scale in 8 steps and 7% total
yield from ergosterol using a disconnection reconnection approach.
2.4.1. NMR of dihydrobrassicasterol and campesterol. In Tables 2 and
3 and Figs. 3e8 (See supplementary information) we summarise
the 13C NMR spectroscopic data for the two isomeric phytosterols
25 and 33. The chemical shifts are similar in most cases, except for
carbons located at or near the stereocentre C-24, in particular C-21
to C-28. We can readily distinguish between campesterol and
dihydrobrassicasterol in the 13C NMR spectra using our dihydro-
brassicasterol data as a standard. We can also determine approxi-
mate ratios of each isomer in sample mixtures using C-21 to C-28
where doubling of signals is observed.
The reported data here is in agreement with literature for the
natural products but for the first time a conclusive side by side
comparison reveals key differences between these isomeric
sterols.23e25 The potential for use of 13C NMR spectroscopy in the
assessment of purity of phytosterols is obvious and will form the
basis for much future work.
3. Conclusion
Our primary aim was to develop a stereospecific route to cam-
pesterol and dihydrobrassicasterol in multigram scale with a view
to further synthesis of their corresponding oxides. We encountered
two key issues arising during the synthetic sequences: synthesis of
the enantiopure Wittig salts and optimisation of the Wittig re-
action. The initial chemistry led to synthesis of a campesterol
enriched sample (similar to the natural ratio) and a dihydro-
brassicasterol enriched sample. We have developed chemical syn-
thesis to dihydrobrassicasterol in gram quantities, which is
significant given that current analytical separation of phytosterol
mixtures does not allow gram quantities to be obtained easily. The
novelty of our disconnection/reconnection approach has obvious
potential in the field of natural product synthesis and provides
a viable alternative to standard side chain synthesis. In addition, we
provide an in-depth analysis of the 13C NMR spectral data of cam-
pesterol and dihydrobrassicasterol. This allows the identification of
the two stereoisomers using 13C NMR spectroscopy as a robust tool
and can indicate the abundance of each in the sample. The
2.5. Dihydrobrassicasterol synthesis
Despite the problems encountered with campesterol, the syn-
thesis of dihydrobrassicasterol was undertaken while omitting the
problematic hydrogenation step on route to the side chain Wittig
salt. Our disconnection reconnection approach to the enantiopure
side chain 3 was similar to that used for campesterol in use of the
chiral pool. Commercially available ergosterol 26 serves as the
starting point in the synthesis of this side chain incorporating the
required R stereochemistry. In two steps, the desired alcohol 28 is
synthesised via acetylation of ergosterol 26 followed by ozonolysis
of acetate 27.18 The Wittig salt 3 was synthesized using the same
chemistry as seen previously22 (Scheme 8).

N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
4999
chemistry shown here can be envisaged to lead to the synthesis of
other phytosterols in large quantities using the central aldehyde
and varying the chiral side chain. As a result of this work, we are
currently applying our approach to the synthesis of other signifi-
cant phytosterols and their oxides.
organic extracts were washed with 2 M aqueous HCl (4ꢃ100 mL),
water (200 mL), dried, filtered and evaporated to give a crude brown
oil 7 (39.6 g, 75%) used without further purification, nmax(film)/cmꢁ1
2963, 1598, 1495, 1466, 1360, 1177, 1097; dH (300 MHz, CDCl3)
0.77e0.85 (9H, overlapping 3ꢃd, J 6.6, 2-CH3, 3-CH3 and 4-CH3),
1.63e1.69 (2H, m, containing X part of ABX system, 2-H and 3-H),
2.45 (3H, s, Ts-CH3), 3.84 (1H, dd, A part of ABX system, 2JAB 9.5, 3JAX
6.4, 1-H), 3.95 (1H, dd, B part of ABX system, 2JAB 9.4, 3JBX 5.6, 1-H),
7.34 (2H, d, J 8.4, 3,5-ArH), 7.79 (2H, d, J 8.4, 2,6-ArH); dC (75 MHz,
CDCl3) 12.6 (2-CH3), 18.0 (CH3), 20.2 (CH3), 21.6 (Ts-CH3), 28.8 (3-
CH), 38.4 (2-CH), 73.8 (CH2), 127.9 (2,6-ArCH), 129.8 (3,5-ArCH),
133.2 (4-ArC), 144.6 (1-ArC).
4. Experimental
4.1. General procedures
Reagents were purchased from SigmaeAldrich except (2R)-3-
hydroxy-2-methylpropanoate (TCI Chemicals) and tert-butyldi-
phenylsilyl chloride (Fluorochem). Specific rotations were recorded
on a PerkineElmer 341 polarimeter at 20 ꢀC in the solvents in-
dicated. The sodium D line (589 nm) was used. Melting points were
measured on a Uni-Melt Thomas Hoover Capillary Melting Point
apparatus and are uncorrected. Low resolution mass spectra were
recorded on a Waters Micromass Quattro Micromass spectrometer
(Instrument number QAA1202) in electrospray ionization (ESI)
positive and negative modes and a Waters Micromass LCT Premier
(Instrument number KD160) was used for high resolution acquisi-
tions. Infrared (IR) spectra were recorded as potassium bromide
(KBr) discs on a PerkineElmer FTIR Paragon 1000 or a Spectrum
One FTIR spectrophotometer. 1H (300 MHz) and 13C NMR (75 MHz)
NMR were recorded on a Bruker Avance 300 NMR spectrometer
unless otherwise stated. All spectra were recorded at 20 ꢀC in
deuterated chloroform (CDCl3) with tetramethylsilane (TMS) as an
internal standard unless otherwise stated. Chemical shifts (dH and
dC) are reported in parts per million (ppm), relative to TMS and
coupling constants are expressed in Hertz (Hz). Splitting patterns in
1H NMR spectra are designated as s (singlet), br s (broad singlet),
d (doublet), dd (doublet of doublets), ddd (doublet of doublet of
doublets) dt (doublet of triplets), t (triplet), q (quartet) and m
(multiplet). Thin layer chromatography (TLC) was carried out on
precoated silica gel plates (Merck 60 PF254). Visualisation was
achieved by UV light (254 nm), vanillin or potassium permanganate
staining. Column chromatography was carried out using Kieselgel
60, 0.040e0.063 nm (Merck). Abbreviations used: mCPBA, 3-
chloroperbenzoic acid; 4-DMAP, 4-(dimethylamino)pyridine:
DMSO, dimethyl sulfoxide.
4.1.3. 1-Iodo-2,3-dimethylbutane 8.15 This procedure is adapted
from Hanekamp et al.22 The tosylate 7 (39.6 g, 0.16 mol) in acetone
(75 mL) was added to a NaI (26.2 g, 0.18 mol) solution in acetone
(220 mL) and heated at reflux for 24 h. The resulting precipitate was
filtered off, and the residue was thoroughly washed with ether. The
organic solution was washed with a saturated solution of aqueous
NH4Cl (2ꢃ50 mL), water (50 mL), dried over magnesium sulfate,
filtered and evaporated at low temperature to give the crude
compound 8 as a yellow oil (23.5 g, 71%), which was used without
further purification; nmax(film)/cmꢁ1 2960, 2873, 1654, 1458, 1426,
1386, 1377; dH (300 MHz, CDCl3) 0.85e0.98 (9H, overlapping 3ꢃd, J
6.8, 2-CH3, 3-CH3 and 4-CH3), 1.31e1.44 (1H, m, containing X part of
ABX system, 2-H), 1.62e1.73 (1H, m, 3-H), 3.16 (1H, dd, A part of
2
3
ABX system, JAB3 9.6, JAX 6.9, 1-H), 3.27 (1H, dd, B part of ABX
2
system, JAB 9.6, JBX 4.8, 1-H); dC (75 MHz, CDCl3) 16.0 (CH2), 16.9
(2-CH3), 18.1 (CH3), 20.5 (CH3), 32.1 (3-CH), 41.1 (2-CH).
4.1.4. 2,3-Dimethylbutyltriphenylphosphonium iodide22 9. 1-Iodo-
2,3-dimethylbutane 8 (9.00 g, 42.5 mmol) was added to a solution
of triphenylphosphine (33.4 g, 0.13 mol) in acetonitrile (250 mL)
and the solution was heated at reflux for 24 h. The solvent was
removed in vacuo and the resulting solid was recrystallised from
toluene to give 9 as a white solid (13.3 g, 67%); mp 145e147 ꢀC
(lit:30 150e152 ꢀC); found C 60.57, H 5.76, C24H28IP requires C 60.77,
H 5.95%; nmax(KBr)/cmꢁ1 2955, 2867, 1635, 1585, 1480, 1437, 1385,
1161, 1110; dH (300 MHz, CDCl3) 0.81 (3H, d, J 6.8, 2-CH3), 0.85e0.93
(6H, overlapping 2ꢃd, J 6.8, 3-CH3 and 4-CH3), 1.70e1.95 (2H, m, 2-
H and 3-H), 3.37e3.60 (2H, m, CH2), 7.72e7.90 (15H, m, ArH); dC
(75 MHz, CDCl3) 16.2 (d, 3JCP2 4.6, 2-CH3), 17.3 (CH3), 20.3 (CH3), 28.1
4.1.1. 2,3-Dimethylbutan-1-ol 6.28 To a stirring solution of 2,3-
3
dimethylbut-1-ene
5
(20.0 g, 196 mmol) in THF (100 mL),
(d, 1JCP 49.0, CH2), 33.6 (d, JCP 10.9, 2-CH), 34.1 (d, JCP 4.3, 3-CH),
BH3$THF (1 M, 80 mL, 80.0 mmol) was added dropwise at 0 ꢀC and
stirred for 1 h. The reaction solution was quenched with aqueous
NaOH (15%, 20 mL, 81.3 mmol). This was followed with addition of
H2O2 (30%, 28 mL, 93.6 mmol) and stirred at 0 ꢀC for 1 h. The
reaction mixture was quenched with water (100 mL) and extrac-
ted with ether (3ꢃ100 mL). The combined organic layers were
washed with 10% aq sodium sulfite (200 mL), water (200 mL),
dried over magnesium sulfate, filtered and evaporated at low
temperature to give the crude title compound 6 as a colourless oil
used without further purification (20.3 g, 83%), nmax(film)/cmꢁ1
3418, 2961, 2876, 1716, 1683, 1558, 1457, 1387; dH (300 MHz,
CDCl3) 0.82e0.91 (9H, overlapping 3ꢃd, J 7.0, 2-CH3, 3-CH3 and 4-
CH3), 1.44e1.57 (1H, m, containing X part of ABX system, 2-H),
118.5 (d, 1JCP 85.4, 3ꢃArCipso), 130.6 (d, 2JCP 12.5, 6ꢃArCHortho), 133.7
(d, 3JCP 9.9, 6ꢃArCHmeta), 135.2 (d, 4JCP 2.9, 3ꢃArCHpara); m/z (ESIþ)
347 [M]þ (100%).
4.1.5. 6b-Methoxy-3a,5-cycloergostan-22-(E)-ene 10. 2,3-Dimethyl-
butyltriphenylphosphonium iodide 9 was scrupulously dried prior
to its ylide formation. The phosphonium salt (8.33 g,17.6 mmol) was
suspended in dry THF (100 mL) under a nitrogen atmosphere in
a flame-dried round bottom flask. n-BuLi (1.5 M in hexanes, 9.00 mL,
13.5 mmol) was added dropwise to the suspension at 0 ꢀC and
stirred for 1.5 h. The solution was allowed to warm to rt and stirred
for 0.5 h (20S)-3a,5-cyclo-6b-methoxy-5a-pregnane-20-carboxyal-
dehyde 4 (4.65 g, 13.5 mmol) was dissolved in dry THF (50 ml)
and added to the suspension at 0 ꢀC and stirred overnight at rt. The
reaction was quenched with a saturated solution of saturated
aqueous NH4Cl (100 ml). The organic layer was separated and the
aqueous layer was extracted with CH2Cl2 (3ꢃ50 ml). The combined
organic extracts were dried, filtered and concentrated in vacuo to
give the crude compound. Purification by flash chromatography on
silica gel [hexane:ethyl acetate (99:1)] yielded the title compound
10 as a white solid (1.70 g, 31%); 13C NMR analysis showed this to be
a mixture of dihydrobrassicasterol (D) and campesterol (C) de-
rivatives in an approximate ratio of 3:1; mp 72e73 ꢀC, [lit.31
2
1.65e1.76 (1H, m, 3-H), 3.43 (1H, dd, A part of ABX system, JAB
10.5, 3JAX 7.1, 1-H), 3.58 (1H, dd, B part of ABX system, 2JAB 10.5, 3JBX
6.0, 1-H); dC (75 MHz, CDCl3) 12.6 (2-CH3), 18.0 (CH3), 20.6 (CH3),
28.9 (3-CH), 41.5 (2-CH), 66.6 (CH2).
4.1.2. 2,3-Dimethylbutyl-1-(4-methylbenzenesulfonate) 7.29 2,3-Di-
methylbutan-1-ol 6 (20.3 g, 0.20 mol) was dissolved in pyridine
(250 mL). Tosyl chloride (57.2 g, 0.30 mol) was added and stirred at
rt overnight. Addition of ice (100 g) resulted in a suspension, which
was thoroughly extracted with ether (3ꢃ150 mL). The combined

5000
N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
72e74 ꢀC, (D), lit.20 73e75 ꢀC (C)]; found: C, 84.04; H,11.38. Calcd for
C29H48O: C, 84.40; H,11.72%; nmax(KBr)/cmꢁ1 2956, 2868,1456,1382,
1371, 1098; dH (300 MHz, CDCl3) 0.43 (1H, dd, J 8.0, 5.1), 0.65 (1H, t, J
4.3), 0.75 (3H, s, 18-CH3), 0.81e1.99 [35H, m, containing 0.85e0.92
(9H, m, 26-CH3, 27-CH3 and 28-CH3), 0.96 (3H, d, J 6.6, 21-CH3), 1.03
(3H, s, 19-CH3)], 2.17e2.29 (1H, m), 2.37e2.49 (1H, m), 2.77 (1H, t, J
2.7, 6-H), 3.32 [3H, s, OCH3, containing 3.33 (3H, s, OCH3, C)],
4.94e5.16 (2H, m, 22-H and 23-H); dC (75 MHz, CDCl3) 12.6 (CH3),
13.1 (CH2), 19.0 (CH3), 19.4 (CH3), 20.2 (CH3), 20.4 (CH3), 21.3 (CH3),
21.6 (CH), 22.8 (CH2), 24.2 (CH2), 25.0 (CH2), 28.3 (CH2), 30.5 (CH),
33.4 (CH2), 33.5 (CH), 34.6 (CH), 35.0 (CH2), 35.4 (quaternary C), 38.3
(CH), 40.3 (CH2), 42.7 (quaternary C), 43.4 (quaternary C), 48.1 (CH),
56.6 (2ꢃCH), 56.6 (OCH3), 82.4 (CH), 131.7 (CH), 135.6 (CH); m/z
(ESIþ) 381 [MþHꢁMeOH]þ (10%), 129 (66) 104.9 (16) 87.9 (100);
HRMS calcd for C28H45 [MþHꢁMeOH]þ 381.3521, found 381.3512.
The following peaks were distinguishable for the minor component:
18.7 (CH3), 20.0 (CH3), 20.4 (CH3), 20.6 (CH3), 21.5 (CH), 24.2 (CH2),
28.5 (CH2), 35.0 (CH2), 35.3 (quaternary C), 38.3 (CH), 56.2 (CH), 56.7
(CH), 131.1 (CH), 135.3 (CH).
104.9 (16), 87.9 (100); HRMS calcd for C28H47 [MþHꢁH2O]þ
383.3678, found 383.3679. The following peaks were distinguish-
able for the minor component: 15.4 (CH3), 18.3 (CH3), 18.7 (CH3),
20.2 (CH3), 28.2 (CH2), 30.3 (CH2), 32.4 (CH), 35.9 (CH3), 38.8 (CH),
56.1 (CH).
4.1.8. (R)-tert-Butyl(2,3-dimethyl-3-(phenylsulfonyl)butoxy) diphe-
nylsilane15,16 14. A solution of n-BuLi (2.5 M in hexanes, 58.4 mL,
146 mol) was added at ꢁ30 ꢀC to a solution of the sulfone 13 (20.0 g,
44.3 mmol) in THF (400 mL). The mixture was stirred for 15 min,
after which a solution of MeI (4.93 mL, 79.7 mmol) in THF (15 mL)
was added, and the temperature was gradually increased to 10 ꢀC
over 30 min. The mixture was recooled to ꢁ30 ꢀC, and a solution of
n-BuLi (2.5 M in hexanes, 28.3 mL, 70.8 mmol) was added. The
mixture was maintained at this temperature for 15 min, and
a second portion of MeI (4.93 mL, 79.7 mmol) in THF (15 mL) was
introduced. After 15 min, the mixture was allowed to warm to rt
and stirred for 24 h. The reaction mixture was diluted with H2O
(500 mL) and extracted with EtOAc (3ꢃ500 mL). The organic layer
was dried under magnesium sulfate, filtered and evaporated under
reduced pressure. Purification by flash chromatography on silica gel
[hexane:ethyl acetate (96:4)] yielded title compound 14 as a col-
ourless oil (9.30 g, 44%); nmax(film)/cmꢁ1 3507, 3071, 3052, 2959,
2932, 2888, 2857, 1472, 1428, 1390, 1297, 1159, 1075; dH (300 MHz,
CDCl3), 1.04 (9H, s, t-Bu), 1.24 (3H, d, J 6.9, 2-CH3), 1.27 (3H, s, CH3),
1.34 (3H, s, CH3), 2.15e2.25 (1H, m, containing X part of ABX sys-
tem, 2-H), 3.67 (1H, dd, A part of ABX system, 2JAB 10.4, 3JAX 5.9, 1-
4.1.6. 6b-Methoxy-3a,5-cycloergostane 11. 6b-Methoxy-3a,5-cycl-
oergostan-22-(E)-ene 10 (1.60 g, 3.88 mmol) was dissolved in
ethanol (80 mL) and 5% Pd/C (10% wt, 0.16 g) was added. The
resulting suspension was shaken at rt at 50 psi under a hydrogen
atmosphere overnight. The reaction mixture was filtered through
Celite and concentrated down to give a colourless oil 11 (1.40 g,
88%) in an approximate ratio of D:C derivatives, 3:1 from 13C NMR
analysis and used without further purification; nmax(film)/cmꢁ1
2954, 2868, 1456, 1376, 1099; dH (300 MHz, CDCl3) 0.43 (1H, dd, J
8.0, 5.1), 0.64 (1H, t, J 4.4), 0.72 (3H, s, 18-CH3), 0.77e2.02 [41H, m,
containing 0.77e0.93 (12H, m, 21-CH3, 26-CH3, 27-CH3 and 28-
CH3), 1.02 (3H, s, 19-CH3)], 2.77 (1H, t, J 2.8, 6-H), 3.32 (3H, s
OCH3); dC20 (75 MHz, CDCl3) 12.3 (CH3), 13.1 (CH2), 15.5 (CH3), 17.6
(CH3), 18.9 (CH3), 19.3 (CH3), 20.5 (CH3), 21.5 (CH), 22.8 (CH2), 24.2
(CH2), 25.0 (CH2), 28.3 (CH2), 30.5 (CH), 30.6 (CH2), 31.5 (CH), 33.4
(CH2), 33.7 (CH2), 35.1 (CH2), 35.3 (quaternary C), 36.2 (CH), 39.1
(CH), 40.3 (CH2), 42.8 (quaternary C), 43.4 (quaternary C), 48.1 (CH),
56.2 (CH), 56.6 (CH and OCH3), 82.5 (CH); m/z (ESIþ) 383
[MþHꢁMeOH]þ (10%), 129 (66), 104.9 (16) 87.9 (100); HRMS calcd
for C28H47 [MþHꢁMeOH]þ 383.3678, found 383.3677. The follow-
ing peaks were distinguishable for the minor component: 15.4
(CH3), 18.3 (CH3), 18.7 (CH3), 20.2 (CH3), 28.3 (CH2), 30.3 (CH2), 32.4
(CH), 35.9 (CH), 38.9 (CH), 56.3 (CH).
2
3
H), 3.84 (1H, dd, B part of ABX system, JAB 10.4, JBX 3.7, 1-H),
7.35e7.64 (13H, m), 7.82 (2H, dd, J 8.4, 1.4, SO2Phortho); dC (75 MHz,
CDCl3) 13.8 (2-CH3), 19.3 (quaternary C, t-Bu), 20.0 (CH3), 20.8
(CH3), 26.9 (3ꢃCH3, t-Bu), 38.7 (2-CH), 65.9 (quaternary C), 66.0
(CH2), 127.7 (4ꢃArCH), 128.7 (3ꢃArCH), 129.7 (ArCH), 130.5
(3ꢃArCH), 133.4 (ArCH), 135.6 (2ꢃArCH), 135.7 (ArCH), 136.4
(3ꢃArC); m/z (ESIþ) 481 [MþH]þ (10%), 361 (100).
4.1.9. (S)-tert-Butyl(2,3-dimethylbutoxy)diphenylsilane15
15. Magnesium (18.8 g, 0.77 mol) was added to a vigoursly stirred
solution of (R)-tert-butyl(2,3-dimethyl-3-(phenylsulfonyl)butoxy)
diphenylsilane 14 (43.6 g, 90.8 mmol) in MeOH (1 L) and a catalytic
amount of HgCl2 (tip of spatula) was added to the mixture and
stirred for 72 h at rt. The reaction mixture was filtered through
a bed of Celite and the filtrate was evaporated under reduced
pressure to give a white solid. This was partitioned between CH2Cl2
(1 L) and 10% aqueous HCl (2 L). The aqueous layer was extracted
with CH2Cl2 (3ꢃ500 mL) and the combined organic extracts were
washed with H2O (1 L), dried under magnesium sulfate, filtered and
evaporated under reduced pressure. Purification by flash chroma-
tography on silica gel [hexane:ethyl acetate (95:5)] yielded a mix-
ture of the title compound 15 and (S)-tert-butyl(2,3-dimethylbut-3-
enyloxy)diphenylsilane 16 (11.5 g, 37%) in an approx. ratio of 1.5:1
from 1H NMR analysis (dH 1.71e1.81, 1H, m, 2-H, 15 and dH
2.32e2.42, 1H, m, 2-H, 16). This mixture was hydrogenated under
4.1.7. Dihydrobrassicasterol and campesterol 12. 6b-Methoxy-3a,5-
cycloergostane 11 (1.20 g, 2.90 mmol) was dissolved in THF/H2O
(9:1, 50 mL) and 2.5 M aqueous H2SO4 (5 mL) was added. The
resulting mixture was stirred overnight. The reaction mixture was
evaporated under reduced pressure and ether (60 mL) was added.
The organic layer was washed with H2O (3ꢃ50 mL) and then was
dried over magnesium sulfate, filtered and evaporated to give
a white solid. Purification by flash chromatography on silica gel
[hexane:ethyl acetate (85:15)] yielded dihydrobrassicasterol (D)
and campesterol (C) 12 as a white solid (0.65 g, 57%) in an ap-
proximate ratio of D:C 3:1, from 13C NMR analysis; mp 152e154 ꢀC,
(lit.16,17 158e159 ꢀC); nmax(KBr)/cmꢁ1 3420, 2960, 2868, 1464, 1376,
1058; dH (300 MHz, CDCl3)24 0.68 (3H, s, 18-CH3), 0.77e1.59 [36H,
m, containing 0.77e0.93 (12H, m, 21-CH3, 26-CH3, 27-CH3 and 28-
CH3), 1.01 (3H, s, 19-CH3)], 1.81e1.87 (3H, m), 1.95e2.03 (2H, m),
standard conditions (as described earlier) to yield the desired
20
compound 15 as a colourless oil (10.82 g, 94%); ½a D þ2.50 (c 1.00 in
32
20
ꢂ
CHCl3), [lit.:15
1.00 in CHCl3)].
½
a D
ꢂ
þ3.00 (c 3.00 in CH2Cl2)], [lit.:
½
a D
ꢂ
þ3.30 (c
21
4.1.10. (R)-(tert-Butyldiphenylsilyloxy)-2,3-dimethylbutan-3-ol26
18. A solution of (R)-methyl-3-(tert-butyldiphenylsilyloxy)-2-
methylpropanoate 17 (310 g, 0.87 mol) in dry Et2O (2.4 L) was
added dropwise over 30 min to a solution of 3 M MeMgBr in THF
(639 mL, 1.92 mol) at rt. After complete addition, stirring was
continued for 24 h at rt. The reaction was quenched by slowly
pouring onto ice (1 L) and acidified using 2 M aqueous HCl. The
layers were separated and the aqueous layer was extracted with
Et2O (2ꢃ300 mL). The combined extracts were washed with brine
2.19e2.33 (2H, m), 3.47e3.56 (1H, m, 3a-H), 5.35 (1H, bd, J 5.1, H-6);
dC16e18 (75 MHz, CDCl3) 11.9 (CH3), 15.5 (CH3), 17.6 (CH3), 18.9 (CH3),
19.4 (CH3), 20.5 (CH3), 21.1 (CH2), 24.3 (CH2), 28.2 (CH2), 30.6 (CH2),
31.5 (CH), 31.7 (CH2), 31.9 (CH and CH2), 33.7 (CH2), 36.2 (CH), 36.5
(quaternary C), 37.3 (CH2), 39.1 (CH), 39.8 (CH2), 42.3 (CH2 and
quaternary C), 50.1 (CH), 56.0 (CH), 56.8 (CH), 71.8 (CH), 121.7 (CH),
140.8 (quaternary C); m/z (ESIþ) 383 [MþHꢁH2O]þ (10%), 129 (80),

N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
5001
(500 mL) and dried under magnesium sulfate. Filtration and con-
centration of the filtrate in vacuo afforded (R)-(tert-butyldiphe-
nylsilyloxy)-2,3-dimethylbutan-3-ol 18 as a yellow oil (314 g, 99%),
which was used without further purification; nmax(film)/cmꢁ1 3437,
2964, 2932, 2887, 2858, 1472, 1428; dH (400 MHz, CDCl3) 0.80 (3H,
d, J 7.1, 3-CH3), 1.06 (9H, s, t-Bu), 1.19 (3H, s, CH3), 1.23 (3H, s, CH3),
1.85e1.91 (1H, m, containing X part of ABX system, 3-H), 3.67 (1H,
dd, A part of ABX system, 2JAB 10.4, 3JAX 8.4, 4-H), 3.73 (1H, dd, B part
of ABX system, 2JAB 10.5, 3JBX 4.7, 4-H), 4.24 (1H, bs, OH), 7.39e7.47
(6H, m, 3,4,5-ArH), 7.67e7.71 (4H, m, 2,6-ArH); dC (75 MHz, CDCl3)
12.9 (3-CH3), 19.1 (quaternary C, t-Bu), 24.6 (CH3), 26.8 (3ꢃCH3, t-
Bu), 29.2 (CH3), 43.9 (3-CH), 67.9 (CH2), 73.5 (quaternary 2-C), 127.9
(4ꢃArCH), 129.95 (ArCH), 129.99 (ArCH), 132.6 (2ꢃArC), 134.9
(ArCH), 135.6 (ArCH), 135.7 (2ꢃArCH); m/z (ESIþ) 357 [MþH]þ
(30%), 281 (26), 280 (100); HRMS calcd for C22H33O2Si [MþH]þ
357.2250, found 357.2242.
4.1.13. (S)-2,3-Dimethylbutan-1-ol15 19. TBAF (1.0
M
in THF,
47.6 mL, 47.7 mmol) was added to a solution of (S)-tert-butyl(2,3-
dimethylbutoxy)diphenylsilane 15 (10.8 g, 31.8 mmol) in THF
(100 mL) and stirred for 3 h at rt. The solution was acidified with
2 M aqueous HCl and the aqueous layer was extracted with Et2O
(2ꢃ100 mL). The combined organic layers were washed with brine
(100 mL), water (100 mL), dried under magnesium sulfate, filtered
and evaporated at low temperature to give the crude title com-
pound. The residue was then purified by vacuum distillation to give
19 as a colourless oil (1.32 g, 41%); bp (50 ꢀC/3 mmHg), [lit.:33
(64 ꢀC/25.5 ꢀmmHg)]; nmax(film)/cmꢁ1 3428, 2960, 1642, 1463,
1387; dH (300 MHz, CDCl3) 0.83e0.93 (9H, overlapping 3ꢃd, J 7.0, 2-
CH3, 3-CH3 and 4-CH3), 1.47e1.57 (1H, m, containing X part of ABX
system, 2-H), 1.64e1.76 (1H, m, 3-H), 3.43 (1H, dd, A part of ABX
system, 2JAB 10.6, 3JAX 6.9, 1-H), 3.58 (1H, dd, B part of ABX system,
2JAB 10.6, 3JBX 5.9, 1-H); dC (75 MHz, CDCl3) 12.6 (2-CH3), 18.0 (CH3),
20.6 (CH3), 28.9 (3-CH), 41.5 (2-CH), 66.4 (CH2).
4.1.11. (S)-tert-Butyl(2,3-dimethylbut-3-enyloxy)diphenylsilane26
16. Mesyl chloride (201.6 g, 1.76 mol) was added dropwise to
4.1.14. (S)-2,3-Dimethylbutyl-1-(4-methylbenzenesulfonate) 20. (S)-
2,3-Dimethylbutan-1-ol 19 (7.73 g, 75.8 mmol) was dissolved in
pyridine (80 mL). Tosyl chloride (21.6 g, 113.7 mmol) was added and
stirred at rt overnight. Addition of ice (80 g) resulted in a suspen-
sion, which was thoroughly extracted with ether (3ꢃ75 mL). The
combined organic extracts were washed with 2 M aqueous HCl
(2ꢃ100 mL), water (100 mL), dried under magnesium sulfate, fil-
tered and evaporated to give a crude brown oil 20 (12.6 g, 74%),
which was used without further purification; nmax(film)/cmꢁ1
2963, 2877, 1649, 1599, 1466, 1360, 1189, 1177; dH (300 MHz, CDCl3)
0.75e0.85 (9H, overlapping 3ꢃd, J 6.6, 2-CH3, 3-CH3 and 4-CH3),
1.62e1.70 (2H, m, containing X part of ABX system, 2-H and 3-H),
2.45 (3H, s, Ts-CH3), 3.85 (1H, dd, A part of ABX system, 2JAB 9.4, 3JAX
6.5, 1-H), 3.95 (1H, dd, B part of ABX system, 2JAB 9.4, 3JBX 5.7, 1-H),
7.35 (2H, d, J 7.9, 3,5-Ar-H), 7.79 (2H, d, J 8.3, 2,6-ArH); dC (75 MHz,
CDCl3) 12.5 (2-CH3), 18.0 (CH3), 20.2 (CH3), 21.7 (Ts-CH3), 28.7 (3-
CH), 38.3 (2-CH), 73.8 (CH2), 127.9 (2,6-ArCH), 129.8 (3,5-ArCH),
133.1 (4-ArC), 144.7 (1-ArC).
a
solution
of
crude
(R)-(tert-butyldiphenylsilyloxy)-2,3-
dimethylbutan-3-ol 18 (314 g, 0.88 mol) in Et2O (2.5 L), then the
mixture was cooled to 0 ꢀC and NEt3 (1.85 L, 13.2 mol) was added
dropwise over 1 h. After complete addition, the solution was stirred
for 16 h while warming to rt. The reaction mixture was quenched
with ice-cold solution of 25% aqueous HCl (2 L). The layers were
separated and the aqueous layer was extracted with Et2O (2ꢃ1 L).
The combined extracts were washed with 1 M aqueous HCl (1 L),
saturated aqueous NaHCO3 (2ꢃ500 mL), brine (1 L) and dried over
magnesium sulfate. Filtration and concentration of the filtrate in
vacuo afforded the crude material as a dark brown oil. Purification
by flash chromatography on silica gel [hexane:ethyl acetate (99:1)]
yielded (S)-tert-butyl(2,3-dimethylbut-3-enyloxy)diphenylsilane
16 as a yellow oil (96.7 g, 32%); nmax(film)/cmꢁ1 3435, 2961, 2932,
2858, 1646, 1472, 1462, 1428; dH (400 MHz, CDCl3) 1.05e1.06 (12H,
overlapping s and d, t-Bu and 2-CH3), 1.64 (3H, s, 3-CH3), 2.32e2.42
(1H, m, containing X part of ABX system, 2-H), 3.50 (1H, dd, A part
2
3
of ABX system, JAB 9.8, JAX 7.0, 1-H), 3.64 (1H, dd, B part of ABX
system, 2JAB 9.8, 3JBX 6.2, 1-H), 4.71 (1H, s, one of ]CH2), 4.73 (1H, s,
one of ]CH2), 7.35e7.42 (6H, m, 3,4,5-ArH), 7.65e7.68 (4H, m, 2,6-
ArH); dC (75 MHz, CDCl3) 16.1 (2-CH3), 19.3 (3-CH3), 20.6 (quater-
nary C, t-Bu), 26.9 (3ꢃCH3, t-Bu), 43.4 (2-CH), 67.7 (1-CH2), 110.4 (4-
CH2), 127.6 (4ꢃArCH), 129.5 (2ꢃArCH), 134.1 (2ꢃArC), 135.7
(4ꢃArCH), 147.8 (quaternary 3-C); m/z (ESIþ) 339 [MþH]þ (8%), 281
(26), 280 (100); HRMS calcd for C22H31OSi [MþH]þ 339.2144, found
339.2149.
4.1.15. (S)-1-Iodo-2,3-dimethylbutane
21. This
procedure
is
adapted from Hanekamp et al.22 (S)-2,3-dimethylbutyl-1-(4-
methylbenzenesulfonate) 20 (12.5 g, 48.6 mmol) in acetone
(25 mL) was added to a NaI (8.75 g, 58.4 mmol) solution in acetone
(100 mL) and heated at reflux for 24 h. The resulting precipitate was
filtered off, and the residue was thoroughly washed with ether. The
organic solution was washed with a saturated aqueous solution of
NH4Cl (2ꢃ20 mL), water (20 mL), dried under magnesium sulfate,
filtered and evaporated at low temperature to give the crude
compound as a yellow oil 21 (9.08 g, 91%), which was used without
further purification; nmax(film)/cmꢁ1 2961, 1643; dH (300 MHz,
CDCl3) 0.85e0.97 (9H, overlapping 3ꢃd, J 6.6, 2-CH3, 3-CH3 and 4-
CH3), 1.30e1.41 (1H, m, X part of ABX system, 2-H), 1.57e1.73 (1H,
4.1.12. (S)-tert-Butyl(2,3-dimethylbutoxy)diphenylsilane26 15. (S)-te-
rt-Butyl(2,3-dimethylbut-3-enyloxy)diphenylsilane 16 (65.8 g,
0.19 mol) was dissolved in ethanol (400 mL) and 5% Pd/C (10% wt,
6.58 g) was added. The resulting suspension was shaken at rt at
50 psi under a hydrogen atmosphere for 3 days. The reaction mix-
ture was filtered through Celite and concentrated down to give 15 as
a colourless oil (61.5 g, 95%), which was used without further pu-
m, 3-H), 3.16 (1H, dd, A part of ABX system, 2JAB 9.6, JAX 7.0, 1-H),
3.27 (1H, dd, B part of ABX system, JAB 9.6, JBX 4.9, 1-H); dC
(75 MHz, CDCl3) 16.2 (CH2), 16.9 (2-CH3), 18.1 (CH3), 20.5 (CH3), 32.1
(3-CH), 41.1 (2-CH).
3
2
3
15
20
21
rification; ½a D
ꢂ
þ2.45 (c 1.00 in CHCl3), [lit.:
½
a D
ꢂ
þ3.00 (c 3.00 in
CH2Cl2)], [lit.:32
½
a D
ꢂ
þ3.30 (c 1.00 in CHCl3)]; nmax(film)/cmꢁ1 2959,
20
2931, 2858, 1472, 1428; dH (300 MHz, CDCl3) 0.78e0.87 (9H, over-
lapping 3ꢃd, J 6.8, 2-CH3, 3-CH3 and 4-CH3), 1.05 (9H, s, t-Bu),
1.49e1.60 (1H, m, 3-H), 1.71e1.81 (1H, m, containing X part of ABX
system, 2-H), 3.47 (1H, dd, A part of ABX system, 2JAB 9.9, 3JAX 6.6, 1-
4.1.16. (S)-(þ)-(2,3-Dimethylbutyl)triphenylphosphonium iodide22
2. (S)-1-Iodo-2,3-dimethylbutane 21 (9.08 g, 42.8 mmol) was
added to a solution of triphenylphosphine (92.2 g, 0.35 mol) in
acetonitrile (200 mL) and the solution was heated at reflux for 24 h.
The solvent was removed in vacuo and the resulting solid was
recrystallised from toluene to give a white solid 2 (11.6 g, 58%); mp
2
3
H), 3.57 (1H, dd, B part of ABX system, JAB 9.9, JBX 6.1, 1-H),
7.34e7.44 (6H, m, 3,4,5-ArH), 7.65e7.68 (4H, m, 2,6-ArH); dC
(75 MHz, CDCl3) 12.8 (2-CH3), 18.1 (CH3), 20.8 (quaternary C, t-Bu),
20.8 (CH3), 26.9 (3ꢃCH3, t-Bu), 28.7 (3-CH), 41.4 (2-CH), 67.3 (CH2),
127.6 (4ꢃArCH),129.5 (2ꢃArCH),134.2 (2ꢃArC),135.6 (4ꢃArCH); m/
z (ESIþ) 341 [MþH]þ (30%), 298 (34), 280 (100); HRMS calcd for
C22H33OSi [MþH]þ 341.2301, found 341.2295.
138e140 ꢀC, (lit:30 150e152 ꢀC); found: C, 60.83; H, 5.86. Calcd for
20
C24H28IP: C, 60.77; H, 5.95%; ½a D þ 6.70 (c 1.00 in CHCl3);
ꢂ
nmax(KBr)/cmꢁ1 2953, 1618, 1161, 1109; dH (600 MHz, CDCl3) 0.82
(3H, d, J 6.8, 2-CH3), 0.86e0.92 (6H, overlapping 2ꢃd, J 6.8, 3-CH3
and 4-CH3), 1.70e1.79 (1H, m, 2-H), 1.80e1.88 (1H, m, 3-H), 3.49

5002
N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
(1H, m, 1-CH), 3.59e3.65 (1H, m, 1-CH), 7.66e7.91 (15H, m ArH); dC
1.15 (3H, t, J 7.0, OCH2CH3)], 2.87 (1H, t, J 2.7, 6-H), 3.33e3.43 (1H, m,
OCH2), 3.56e3.66 (1H, m, OCH2); dC (75 MHz, CDCl3) 12.3 (CH3),
13.3 (CH2), 15.4 (CH3), 15.8 (CH3), 18.3 (CH3), 18.7 (CH3), 19.2 (CH3),
20.2 (CH3), 21.5 (CH), 22.8 (CH2), 24.2 (CH2), 25.0 (CH2), 28.2 (CH2),
30.3 (CH2), 30.5 (CH), 32.4 (CH), 33.4 (CH2), 33.7 (CH2), 35.3 (qua-
ternary C), 35.7 (CH2), 36.0 (CH), 38.9 (CH), 40.4 (CH2), 42.8 (qua-
ternary C), 43.3 (quaternary C), 48.1 (CH), 56.7 (2ꢃCH), 63.2 (CH2),
79.9 (CH); m/z (ESIþ) 383 [MþHꢁEtOH]þ (10%),129 (44), 87.9 (100);
HRMS calcd for C28H47 [MþHꢁEtOH]þ 383.3678, found 383.3667.
The following peaks were distinguishable for the minor compo-
nent: 12.3 (CH3), 15.5 (CH3), 17.6 (CH3), 18.9 (CH3), 20.5 (CH3), 20.8
(CH2), 22.8 (CH2), 26.9 (CH2), 28.2 (CH2), 29.1 (CH2), 30.6 (CH2), 31.5
(CH), 32.2 (CH2), 35.6 (CH), 35.7 (quaternary C), 36.3 (CH), 38.7
(CH), 39.1 (CH), 40.2 (CH2), 42.6 (quaternary C), 47.1 (CH), 54.8 (CH),
56.2 (CH), 56.3 (CH).
3
(150 MHz, CDCl3) 16.2 (d, JCP 4.5, 2-CH3), 17.3 (CH3), 20.4 (CH3),
28.1 (d, 1JCP 48.0, CH2), 33.6 (d, 2JCP 10.5, 2-CH), 34.2 (d, 3JCP 4.5, 3-
CH), 118.8 (d, 1JCP 85.5, 3ꢃArCipso), 130.6 (d, 2JCP 13.5, 6ꢃArCHortho),
3
4
133.8 (d, JCP 10.5, 6ꢃArCHmeta), 135.1 (d, JCP 3.1, 3ꢃArCHpara); dP
(161 MHz, CDCl3) 24.31; m/z (ESIþ) 347 [M]þ (100%), 348 (30);
HRMS calcd for C24H48P [M]þ 347.1929, found 347.1921.
4.1.17. (24S)-6
b
-Methoxy-3
a
,5-cycloergostane 23. (S)-(þ)-2,3-Dim-
ethylbutyltriphenylphosphonium iodide 2 was scrupulously dried
prior to its ylide formation. The phosphonium salt 2 (4.65 g,
9.80 mmol) was suspended in dry THF (250 mL) under a nitrogen
atmosphere in a flame-dried round bottom flask. n-BuLi (1.3 M in
hexanes, 7.00 mL, 9.10 mmol) was added dropwise to the suspen-
sion at 0 ꢀC and stirred for 1.5 h. The solution was allowed to warm
to rt and stirred for 0.5 h (20S)-3a,5-cyclo-6b-methoxy-5a-preg-
nane-20-carboxyaldehyde 4 (2.41 g, 7.00 mmol) was dissolved in
dry THF (25 mL) and added to the suspension at 0 ꢀC and stirred
overnight at rt. The reaction was quenched with a saturated solu-
tion of aqueous NH4Cl (100 mL). The organic layer was extracted
and the aqueous layer was washed with CH2Cl2 (3ꢃ50 mL). The
combined organic extracts were dried, filtered and concentrated in
vacuo to give the crude compound. Purification by flash chroma-
tography on silica gel [hexane:diethyl ether (99:1)] yielded the title
compound 22 as a white solid (1.90 g, 66%); 1H NMR analysis (dH
3.32, 3H, s, D and dH 3.33, 3H, s, OCH3, C) showed this to be a mix-
ture of campesterol (C) and dihydrobrassicasterol (D) derivatives in
an approximate ratio of 2:1. 13C NMR analysis showed unidentifi-
able residual peaks and the alkene 22 was used without any further
purification. The following peaks were distinguishable for cam-
4.1.18. Campesterol 25. (24S)-6b-Methoxy-3a,5-cycloergostane 23
(0.782 g, 1.88 mmol) was dissolved in THF/H2O (9:1, 28.2 mL) and
2.5 M aqueous H2SO4 (3.9 mL) was added. The resulting mixture
was heated at 50 ꢀC for 3 h. The reaction mixture was evaporated
under reduced pressure and ether (60 mL) was added. The organic
layer was extracted with H2O (3ꢃ50 mL) and the organic layer was
dried under magnesium sulfate, filtered and evaporated to give
a white solid. Purification by flash chromatography on silica gel
[hexane:ethyl acetate (90:10)] yielded campesterol 25 as a white
solid (0.602 g, 80%) in an approximate ratio of C:D 2:1, from 13C
24
NMR analysis; mp 142e144 ꢀC, (lit. 158e159 ꢀC), ½a D
ꢂ
ꢁ32.4 (c
20
0.545 in CHCl3), [lit.:24
½ ꢂ
a D
ꢁ33.0 (c 1.00 in CHCl3)]; nmax(KBr)/cmꢁ1
20
3434, 2959, 2936, 2869, 1458, 1376, 1057; dH (300 MHz, CDCl3)24
0.68 (3H, s, 18-CH3), 0.76e1.63 [36H, m, containing 0.76e0.93
(12H, m, 21-CH3, 26-CH3, 27-CH3 and 28-CH3), 1.00 (3H, s, 19-CH3)],
1.81e1.87 (3H, m), 1.94e2.03 (2H, m), 2.18e2.33 (2H, m), 3.47e3.57
13
pesterol: dC (150 MHz, CDCl3) 12.6 (CH3), 13.1 (CH2), 18.6 (CH3),
19.7 (CH3), 20.0 (CH3), 20.4 (CH3), 20.6 (CH3), 21.5 (CH), 24.2 (CH2),
28.5 (CH2), 30.5 (CH), 35.0 (CH2), 35.3 (quaternary C), 38.3 (CH),
(1H, m, 3a
-H), 5.35 (1H, bd, J 5.2, H-6); dC (75 MHz, CDCl3)23e25 11.8
40.3 (CH2), 56.6 (CH), 56.7 (CH), 131.1 (CH), 135.3 (CH). (24S)-6
b
-
(CH3), 15.3 (CH3), 18.2 (CH3), 18.7 (CH3), 19.4 (CH3), 20.2 (CH3), 21.1
(CH2), 24.3 (CH2), 28.2 (CH2), 30.2 (CH2), 31.6 (CH2), 31.86 (CH),
31.90 (CH2), 32.4 (CH), 33.7 (CH2), 35.9 (CH), 36.5 (quaternary C),
37.2 (CH2), 38.8 (CH), 39.7 (CH2), 42.26 (CH2), 42.28 (quaternary C),
50.1 (CH), 56.1 (CH), 56.7 (CH), 71.8 (CH), 121.7 (CH), 140.7 (qua-
ternary C); m/z (ESIþ) 383 [MþHꢁH2O]þ (8%), 129 (36), 87.9 (100);
HRMS calcd for C28H47 [MþHꢁH2O]þ 383.3678, found 383.3661.
The following peaks were distinguishable for the minor compo-
nent: 15.4 (CH3), 17.6 (CH3), 18.9 (CH3), 20.5 (CH3), 28.2 (CH2), 30.5
(CH2), 31.4 (CH), 36.2 (CH), 39.0 (CH), 56.0 (CH).
Methoxy-3 ,5-cycloergostan-22-(E)-ene 22 (1.70 g, 4.13 mmol) was
a
dissolved in ethanol (50 mL) and 5% Pd/C (10% wt, 0.14 g) was
added. The resulting suspension was shaken at rt at 50 psi under
a hydrogen atmosphere overnight. The reaction mixture was fil-
tered through Celite and concentrated under reduced pressure to
give a colourless oil as a mixture of the desired compound and its
ethoxy derivative. Separation of this mixture was achieved with
careful flash chromatography on silica gel [hexane:diethyl ether
(99:1)] to yield (24S)-6b-methoxy-3a,5-cycloergostane 23 (0.94 g,
53%) and (24S)-6
b
-ethoxy-3
a
,5-cycloergostane 24 (0.35 g, 20%)
(24S)-6b-Ethoxy-3a,5-cycloergostane 24 (0.290 g, 0.68 mmol)
used without further purification; 23 13C NMR analysis showed this
was dissolved in THF/H2O (9:1, 11.5 mL) and 2.5 M aqueous H2SO4
(1.5 mL) was added. The resulting mixture was heated at 50 ꢀC for
3 h. The reaction mixture was evaporated under reduced pressure
and ether (10 ml) was added. The organic layer was extracted with
H2O (3ꢃ5 mL) and the organic layer was dried under magnesium
sulfate, filtered and evaporated to give a white solid. Purification by
flash chromatography on silica gel [hexane:ethyl acetate (90:10)]
yielded campesterol 25 as a white solid (0.239 g, 57%) in an ap-
to be a mixture of campesterol (C) and dihydrobrassicasterol (D)
derivatives in an approximate ratio of 2:1; nmax(film)/cmꢁ1 2954,
20
2931, 2867, 1654, 1560, 1458, 1376; ½a D þ45.0 (c 1.45 in CHCl3); dH
ꢂ
(300 MHz, CDCl3) 0.43 (1H, dd, J 8.1, 5.1), 0.65 (1H, t, J 4.4), 0.72 (3H,
s, 18-CH3), 0.76e2.01 [41H, m, containing 0.76e0.93 (12H, m, 21-
CH3, 26-CH3, 27-CH3 and 28-CH3), 1.02 (3H, s, 19-CH3)], 2.77 (1H,
20
t, J 2.7, 6-H), 3.32 (3H, s OCH3); dC (150 MHz, CDCl3) 12.3 (CH3),
13.1 (CH2), 15.4 (CH3), 18.3 (CH3), 18.7 (CH3), 19.3 (CH3), 20.2 (CH3),
21.5 (CH), 22.8 (CH2), 24.2 (CH2), 25.0 (CH2), 28.3 (CH2), 30.3 (CH2),
30.5 (CH), 32.4 (CH), 33.4 (CH2), 33.7 (CH2), 35.1 (CH2), 35.3 (qua-
ternary C), 35.9 (CH), 38.9 (CH), 40.3 (CH2), 42.8 (quaternary C),
43.4 (quaternary C), 48.1 (CH), 56.3 (CH), 56.6 (CH and OCH3), 82.5
(CH); m/z (ESIþ) 383 [MþHꢁMeOH]þ (8%), 129 (50), 87.9 (100);
HRMS calcd for C28H47 [MþHꢁMeOH]þ 383.3678, found 383.3668.
The following peaks were distinguishable for the minor compo-
nent: 15.5 (CH3), 17.6 (CH3), 18.9 (CH3), 20.5 (CH3), 28.3 (CH2), 30.6
(CH2), 31.5 (CH), 33.7 (CH2), 36.2 (CH), 39.1 (CH), 42.8 (quaternary
proximate ratio of C:D 2:1, from 13C NMR analysis; mp 142e144 ꢀC,
(lit.24 158e159 ꢀC); ½a D
ꢁ35.1 (c 0.425 in CHCl3).
ꢂ
20
4.1.19. Ergosterol acetate 27. A solution of ergosterol 26 (100.0 g,
0.25 mol) and acetic anhydride (47.6 mL, 0.5 mol) in pyridine (1.5 L)
was stirred at room temperature for 24 h. The solution was poured
into water (1.5 L) and extracted with CH2Cl2 (2ꢃ500 mL). The
combined organic layers were washed with 50% aqueous HCl (3 L),
brine (1 L) and water (1 L), dried over magnesium sulfate, filtered to
give a yellow solid 27 (105.1 g, 96%), which was used without fur-
ther purification; mp: 138e140 ꢀC (lit.:34 150e152 ꢀC); nmax(KBr)/
cmꢁ1 2958, 2874, 1733, 1460, 1376, 1244; dH (300 MHz, CDCl3) 0.63
(3H, s, 18-CH3), 0.81e0.85 (6H, overlapping 2ꢃd, J 6.8, 26-CH3 and
27-CH3), 0.92 (3H, d, J 6.8, 28-CH3), 0.95 (3H, s,19-CH3),1.03 (3H, d, J
C), 56.2 (CH); 31 nmax(film)/cmꢁ1 2954, 2931, 2867, 1651,1455,1377;
20
½
a D
ꢂ
þ39.2 (c 1.75 in CHCl3); dH (300 MHz, CDCl3) 0.38 (1H, dd, J 8.0,
5.0), 0.60e2.01 [48H, m, containing 0.72 (3H, s, 18-CH3), 0.77e0.93
(12H, m, 21-CH3, 26-CH3, 27-CH3 and 28-CH3), 1.01 (3H, s, 19-CH3),

N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
5003
6.6, 21-CH3), 1.26e2.08 [21H, m, containing 2.05 (3H, s, COCH3)],
2.32 (1H, m, one of 20-H or 24-H), 2.50 (1H, ddd, J 14.4, 5.1, 2.1, one
of 20-H or 24-H), 4.65e4.76 (1H, m, 3-H), 5.18e5.22 (2H, m, 6-H
and 7-H), 5.38 (1H, dt, J 5.4, 2.6, one of 22-H or 23-H), 5.56 (1H,
dd, J 5.7, 2.1, one of 22-H or 23-H); m/z (ESIþ) 379 [MþHꢁAcOH]þ
(8%), 149 (20), 116 (100).
acetonitrile (600 mL) and the solution was heated at reflux for
24 h. The solvent was removed in vacuo and the resulting solid was
recrystallised from toluene to give a white solid 3 (32.7 g, 69%); mp
144e146 ꢀC (lit:30 150e152 ꢀC); found: C, 60.78; H, 5.79. Calcd for
20
C24H28IP: C, 60.77; H, 5.95%;
½
a D
ꢂ
ꢁ11.6 (c 1.00 in CHCl3);
nmax(KBr)/cmꢁ1 2955, 2867, 1584, 1437, 1161, 1109; dH (300 MHz,
CDCl3) 0.81 (3H, d, J 6.8, 2-CH3), 0.85e0.93 (6H, overlapping 2ꢃd, J
6.8, 3-CH3 and 4-CH3, 1.70e1.95 (2H, m, 2-H and 3-H), 3.37e3.60
(2H, m, CH2), 7.72e7.90 (15H, m ArH); dC (75 MHz, CDCl3) 16.3 (d,
3JCP 4.5, 2-CH3), 17.3 (CH3), 20.3 (CH3), 28.1 (d, 1JCP 48.5, CH2), 33.6
4.1.20. (R)-2,3-Dimethylbutan-1-ol18 28. A solution of ergosterol
acetate 27 (105.0 g, 0.24 mol) in CH2Cl2/methanol (2:1, 2.5 L) at
ꢁ78 ꢀC was treated with ozone for 20 h. The mixture was bubbled
with oxygen for 5 min to remove excess ozone, warmed to 0 ꢀC and
NaBH4 (88.8 g, 2.40 mol) was added slowly. The resulting mixture
was warmed to rt and stirred overnight. The solution was acidified
with 1 M aqueous HCl and the aqueous layer was extracted with
CH2Cl2 (4ꢃ500 mL). The combined organic layers were washed with
brine (500 mL), water (500 mL), dried under magnesium sulfate,
filtered and evaporated at low temperature to give the crude title
compound 28. The residue was then purified by vacuum distillation
to give a colourless oil (20.8 g, 83%); bp (60 ꢀC/24 mmHg), [lit.:33
(64 ꢀC/25.5 mmHg)]; nmax(film)/cmꢁ1 3338, 2960, 2875, 1464,
1387, 1367; dH (300 MHz, CDCl3) 0.82e0.93 (9H, overlapping 3ꢃd, J
7.0, 2-CH3, 3-CH3 and 4-CH3), 1.44e1.57 (1H, m, containing X part of
ABX system, 2-H), 1.65e1.76 (1H, m, 3-H), 2.64 (1H, brs, OH), 3.43
(1H, dd, A part of ABX system, 2JAB 10.5, 3JAX 7.1, 1-H), 3.58 (1H, dd, B
part of ABX system, 2JAB 10.5, 3JBX 6.0, 1-H); dC (75 MHz, CDCl3) 12.5
(2-CH3), 18.0 (CH3), 20.6 (CH3), 28.8 (3-CH), 41.4 (2-CH), 66.4 (CH2).
2
3
1
(d, JCP 10.8, 2-CH), 34.1 (d, JCP 4.3, 3-CH), 118.6 (d, JCP 85.0,
2
3
3ꢃArCipso), 130.6 (d, JCP 12.4, 6ꢃArCHortho), 133.7 (d, JCP 9.9,
6ꢃArCHmeta), 135.2 (d, JCP 3.1, 3ꢃArCHpara); m/z (ESIþ) 347 [M]þ
4
(100%).
4.1.24. (24R)-6
b
-Methoxy-3
a
,5-cycloergostan-22-(E)-ene
31. (R)-
was
(þ)-(2,3-Dimethylbutyl) triphenylphosphonium iodide
3
scrupulously dried prior to its ylide formation. The phosphonium
salt 3 (6.82 g, 14.4 mmol) was suspended in dry THF (100 mL) under
a nitrogen atmosphere in a flame-dried round bottom flask. n-BuLi
(1.6 M in hexanes, 8.39 mL, 13.4 mmol) was added dropwise to the
suspension at 0 ꢀC and stirred for 1.5 h. The solution was allowed to
warm to rt and stirred for 0.5 h (20S)-3a,5-cyclo-6b-methoxy-5a-
pregnane-20-carboxyaldehyde 4 (3.30 g, 9.59 mmol) was dissolved
in dry THF (40 mL) and added to the suspension at 0 ꢀC and stirred
overnight at rt. The reaction was quenched with a saturated solu-
tion of aqueous NH4Cl (100 mL). The organic layer was separated
and the aqueous layer was extracted with CH2Cl2 (3ꢃ50 mL). The
combined organic extracts were dried under magnesium sulfate,
filtered and concentrated in vacuo to give the crude compound.
Purification by flash chromatography on silica gel [hexane:ethyl
acetate (99:1)] yielded the title compound 31 as a white solid
4.1.21. (R)-2,3-Dimethylbutyl-1-(4-methylbenzenesulfonate) 29. (R)-
2,3-Dimethylbutan-1-ol 28 (20.8 g, 0.20 mol) was dissolved in
pyridine (250 mL). Tosyl chloride (58.2 g, 0.31 mol) was added and
stirred at rt overnight. Addition of ice (100 g) resulted in a sus-
pension, which was thoroughly extracted with ether (3ꢃ150 mL).
The combined organic extracts were washed with 2 M aqueous HCl
(4ꢃ100 mL), water (200 mL), dried under magnesium sulfate, fil-
tered and evaporated in vacuo to give a crude brown oil 29 (33.1 g,
63%), which was used without further purification; nmax(film)/cmꢁ1
2962, 2879, 1598, 1466, 1360, 1360, 1189, 1177; dH (300 MHz, CDCl3)
0.77e0.85 (9H, overlapping 3ꢃd, J 6.6, 2-CH3, 3-CH3 and 4-CH3),
1.63e1.69 (2H, m, containing X part of ABX system, 2-H and 3-H),
2.45 (3H, s, Ts-CH3), 3.84 (1H, dd, A part of ABX system, 2JAB 9.5, 3JAX
6.4, 1-H), 3.95 (1H, dd, B part of ABX system, 2JAB 9.4, 3JBX 5.6, 1-H),
7.34 (2H, d, J 8.4, 3,5-ArH), 7.79 (2H, d, J 8.4, 2,6-ArH); dC (75 MHz,
CDCl3) 12.6 (2-CH3), 18.0 (CH3), 20.2 (CH3), 21.7 (Ts-CH3), 28.8 (3-
CH), 38.4 (2-CH), 73.8 (CH2), 127.9 (2,6-ArCH), 129.8 (3,5-ArCH),
133.2 (4-ArC), 144.6 (1-ArC).
(2.00 g, 52%); mp 72e74 ꢀC, (lit.24 72e74 ꢀC); found: C, 84.72; H,
20
11.72. Calcd for C29H48O: C, 84.40; H, 11.72%; ½a D þ5.05 (c 1.00 in
ꢂ
CHCl3); nmax(KBr)/cmꢁ1 2960, 2870, 1457, 1385, 1100; dH (300 MHz,
CDCl3) 0.43 (1H, dd, J 8.0, 5.1), 0.65 (1H, t, J 4.4), 0.75 (3H, s, 18-CH3),
0.81e1.99 [35H, m, containing 0.85e0.92 (9H, m, 26-CH3, 27-CH3
and 28-CH3), 0.96 (3H, d, J 6.6, 21-CH3), 1.03 (3H, s, 19-CH3)],
2.17e2.29 (1H, m), 2.37e2.49 (1H, m), 2.77 (1H, t, J 2.7, 6-H), 3.32
(3H, s, OCH3), 5.03e5.16 (2H, m, 22-H and 23-H); dC (75 MHz,
CDCl3) 12.6 (CH3), 13.1 (CH2), 19.0 (CH3), 19.4 (CH3), 20.2 (CH3), 20.4
(CH3), 21.3 (CH3), 21.6 (CH), 22.8 (CH2), 24.2 (CH2), 25.0 (CH2), 28.3
(CH2), 30.5 (CH), 33.4 (CH2), 33.5 (CH), 34.6 (CH), 35.0 (CH2), 35.4
(quaternary C), 38.3 (CH), 40.3 (CH2), 42.7 (quaternary C), 43.4
(quaternary C), 48.1 (CH), 56.6 (2ꢃCH), 56.6 (OCH3), 82.4 (CH), 131.7
(CH), 135.6 (CH); m/z (ESIþ) 381 [MþHꢁMeOH]þ (100%), 255 (10),
151 (10).
4.1.22. (R)-1-Iodo-2,3-dimethylbutane 30. This procedure is adapted
from Hanekamp et al.22 (R)-2,3-Dimethylbutyl-1-(4-methyl-
benzenesulfonate) 29 (33.0 g, 0.13 mol) in acetone (50 mL) was added
to a NaI (23.2 g, 0.15 mol) solution in acetone (200 mL) and heated at
reflux for 24 h. The resulting precipitate was filtered off, and the
residue was thoroughly washed with ether. The organic solution was
washed with a saturated solution of aqueous NH4Cl solution
(2ꢃ50 mL), water (50 mL), dried under magnesium sulfate, filtered
and evaporated at low temperature to a crude compound 30 as yel-
low oil (21.63 g, 79%), which was used without further purification;
nmax(film)/cmꢁ1 2962, 1736, 1380; dH (300 MHz, CDCl3) 0.85e0.98
(9H, overlapping 3ꢃd, J 6.8, 2-CH3, 3-CH3 and 4-CH3), 1.31e1.44 (1H,
m, containing X part of ABX system, 2-H),1.62e1.73 (1H, m, 3-H), 3.16
(1H, dd, A part of ABX system, 2JAB 9.6, 3JAX 6.9, 1-H), 3.27 (1H, dd, B
4.1.25. (24R)-6b-Methoxy-3a,5-cycloergostane 32. (24R)-6b-Methoxy-
3a,5-cycloergostan-22-(E)-ene 31 (2.50 g, 6.07 mmol) was dissolved in
ethanol (250 mL) and 5% Pd/C (10% wt, 0.25 g) was added. The resulting
suspension was shaken at rt at 50 psi under a hydrogen atmosphere
overnight. The reaction mixture was filtered through Celite and con-
centrated down to give a colourless oil 32 (2.14 g, 85%), which was used
20
without further purification; ½a D
ꢂ
þ28.9 (c 0.800 in CHCl3); nmax(film)/
cmꢁ1 2930, 2868, 1457, 1376, 1099; dH (300 MHz, CDCl3) 0.43 (1H, dd, J
8.0, 5.1), 0.65 (1H, t, J 4.4), 0.71 (3H, s, 18-CH3), 0.76e2.02 [41H, m,
containing 0.76e0.92 (12H, overlapping 4ꢃd, J 6.8, 21-CH3, 26-CH3, 27-
CH3 and 28-CH3), 1.02 (3H, s, 19-CH3)], 2.77 (1H, t, J 2.8, 6-H), 3.32 (3H, s
20
OCH3); dC (75 MHz, CDCl3) 12.3 (CH3), 13.1 (CH2), 15.5 (CH3), 17.6
2
3
part of ABX system, JAB 9.6, JBX 4.8, 1-H); dC (75 MHz, CDCl3) 16.1
(CH3), 18.9 (CH3), 19.3 (CH3), 20.5 (CH3), 21.5 (CH), 22.8 (CH2), 24.2
(CH2), 25.0 (CH2), 28.3 (CH2), 30.5 (CH), 30.6 (CH2), 31.5 (CH), 33.4 (CH2),
33.7 (CH2), 35.0 (CH2), 35.3 (quaternary C), 36.2 (CH), 39.1 (CH), 40.3
(CH2), 42.8 (quaternary C), 43.4 (quaternary C), 48.1 (CH), 56.2 (CH),
56.5 (CH), 56.6 (OCH3), 82.5 (CH); m/z (ESIþ) 383 [MþHꢁMeOH]þ (6%),
347 (4), 129 (80), 104.9 (16) 87.9 (100); HRMS calcd for C28H47
(CH2), 16.9 (2-CH3), 18.1 (CH3), 20.5 (CH3), 32.1 (3-CH), 41.2 (2-CH).
4.1.23. (R)-(ꢁ)-(2,3-Dimethylbutyl)triphenylphosphonium iodide22
3. (R)-1-Iodo-2,3-dimethylbutane 30 (21.6 g, 0.10 mol) was
added to a solution of triphenylphosphine (219.9 g, 0.84 mol) in

5004
N.M. O’Connell et al. / Tetrahedron 68 (2012) 4995e5004
[MþHꢁMeOH]þ 383.3678, found 383.3671. The following peaks were
distinguishable for the minor component at a level <5% in 13C NMR
(600 MHz) spectrum assigned to campesterol (C): 15.4 (CH3), 18.3
(CH3), 18.7 (CH3), 19.3 (CH3), 20.2 (CH3), 22.7 (CH2), 30.3 (CH2), 32.4
(CH), 35.9 (CH), 38.8 (CH), 56.3 (CH).
References and notes
1. Shepherd, J.; Cobbe, S. M.; Ford, I.; Isles, G. C.; Lorimer, A. R.; MacFarlane, P. W.;
McKillop, J. H.; Packard, C. J. N. Engl. J. Med. 1995, 333, 1301e1307.
2. Brendsel, J.; Green, S. J. Atherosclerosis 2007, 192, 227e229.
3. Ostlund, R. E., jr. Curr. Opin. Gastroenterol. 2002, 18, 254e258.
4. Weingartner, O.; Lutjohann, D.; Ji, S.; Weisshoff, N.; List, F.; Sudhop, T.; von
Bergmann, K.; Gertz, K.; Konig, J.; Schafers, H. J.; Endres, M.; Bohm, M.; Laufs, U.
J. Am. Coll. Cardiol. 2008, 51, 1553e1561.
5. Bradford, P. G.; Awad, A. B. Mol. Nutr. Food Res. 2007, 51, 161e170.
6. Bhattacharyya, A. K.; Connor, W. E. J. Clin. Invest. 1974, 53, 1033e1043.
7. Ryan, E.; Chopra, J.; McCarthy, F. O.; Maguire, A. R.; O’Brien, N. M. Br. J. Nutr.
2005, 94, 443e451.
8. Lagarda, M. J.; Garcia-Llatas, G.; Farre, R. J. Pharmaceut Biomed. 2006, 41,
1486e1496.
9. (a) McCarthy, F. O.; Chopra, J.; Ford, A.; Hogan, S. A.; Kerry, J. P.; O’Brien, N. M.;
Ryan, E.; Maguire, A. R. Org. Biomol. Chem. 2005, 3, 3059e3065; (b) Hang, J.;
Dussault, P. Steroids 2010, 75, 879e883.
4.1.26. Dihydrobrassicasterol
33. (24R)-6b-Methoxy-3a,5-cyclo-
ergostane 32 (1.93 g, 4.66 mmol) was dissolved in THF/H2O (9:1,
100 mL) and 2.5 M aqueous H2SO4 (10 mL) was added. The resulting
mixture was stirred overnight. The reaction mixture was concen-
trated down under reduced pressure and ether (60 mL) was added.
The organic layer was washed with H2O (3ꢃ50 mL) and dried under
magnesium sulfate, filtered and concentrated in vacuo to give
a white solid. Purification by flash chromatography on silica gel
[hexane:ethyl acetate (85:15)] yielded the title compound 33 as
a white solid (1.00 g, 54%); mp 142e144 ꢀC, (lit.24 158e159 ꢀC);
10. (a) Foley, D. A.; O’Callaghan, Y.; O’Brien, N. M.; McCarthy, F. O.; Maguire, A. R. J.
Agric. Food Chem. 2010, 58, 1165e1173; (b) O’Callaghan, Y. C.; Foley, D. A.;
O’Connell, N. M.; McCarthy, F. O.; Maguire, A. R.; O’Brien, N. M. J. Agric. Food
Chem. 2010, 58, 10793e10798.
11. Phillips, K. M.; Ruggio, D. M.; Toivo, J. I.; Swank, M. A.; Simpkins, A. H. J. Food
Comp. Anal. 2002, 123e142.
24
20
20
½
a D
ꢂ
ꢁ43.2 (c 1.00 in CHCl3), (lit.:
½
a D
ꢂ
ꢁ46.0 (c 1.000 in CHCl3);
nmax(KBr)/cmꢁ1 3390, 2935, 2868, 1464, 1376, 1058; dH (300 MHz,
CDCl3)24 0.68 (3H, s, 18-CH3), 0.77e1.62 [36H, m, containing
0.77e0.93 (12H, overlapping 4ꢃd, J 6.8, 21-CH3, 26-CH3, 27-CH3
and 28-CH3), 1.01 (3H, s, 19-CH3)], 1.81e1.88 (3H, m), 1.94e2.02 (2H,
12. Bailey, P. L.; Clegg, W.; Jackson, R. F. W.; Methcohn, O. J. Chem. Soc., Perkin Trans.
1 1993, 1, 343e350.
13. Uemura, T.; Zhang, X. Y.; Matsumura, K.; Sayo, N.; Kumobayashi, H.; Ohta, T.;
Nozaki, K.; Takaya, H. J. Org. Chem. 1996, 61, 5510e5516.
14. Tietze, L. F.; Raith, C.; Brazel, C. C.; Holsken, S.; Magull, J. Synthesis 2008, 229e236.
15. Schmittberger, T.; Uguen, D. Tetrahedron Lett. 1997, 38, 2837e2840.
16. Khripach, V. A.; Zhabinskii, V. N.; Antonchick, A. P.; Konstantinova, O. V.;
Schneider, B. Steroids 2002, 67, 1101e1108.
17. Jackson, R. F. W.; Briggs, A. D.; Brown, P. A.; Clegg, W.; Elsegood, M. R. J.;
Frampton, C. J. Chem. Soc., Perkin Trans. 1 1996, 1, 1673e1682.
18. Hua, Z. H.; Carcache, D. A.; Tian, Y.; Li, Y. M.; Danishefsky, S. J. J. Org. Chem. 2005,
70, 9849e9856.
m), 2.19e2.33 (2H, m), 3.47e3.58 (1H, m, 3a-H), 5.35 (1H, bd, J 5.0,
H-6); dC (75 MHz, CDCl3)23e25 11.9 (CH3), 15.5 (CH3), 17.6 (CH3), 18.9
(CH3), 19.4 (CH3), 20.5 (CH3), 21.1 (CH2), 24.3 (CH2), 28.2 (CH2), 30.6
(CH2), 31.5 (CH), 31.7 (CH2), 31.9 (CH and CH2), 33.7 (CH2), 36.2 (CH),
36.5 (quaternary C), 37.3 (CH2), 39.1 (CH), 39.8 (CH2), 42.3 (CH2 and
quaternary C), 50.2 (CH), 56.0 (CH), 56.8 (CH), 71.8 (CH), 121.7 (CH),
140.8 (quaternary C); m/z (ESIþ) 383 [MþHꢁH2O]þ (10%), 129 (80),
104.9 (16), 87.9 (100); HRMS calcd for C28H47 [MþHꢁH2O]þ
383.3678, found 383.3661. The following peaks were distinguish-
able for the minor component at a level <5% in 13C NMR (600 MHz)
spectrum: 15.4 (CH3), 18.3 (CH3), 18.7 (CH3), 20.2 (CH3), 28.2 (CH2),
30.3 (CH2), 32.4 (CH), 35.9 (CH), 38.8 (CH), 56.1 (CH).
19. Spencer, T. A.; Li, D. S.; Russel, J. S.; Tomkinson, N. C. O.; Willson, T. M. J. Org.
Chem. 2000, 65, 1919e1923.
20. Marino, J. P.; deDios, A.; Anna, L. J.; delaPradilla, R. F. J. Org. Chem.1996, 61,109e117.
21. Hazra, B. G.; Joshi, P. L.; Bahule, B. B.; Argade, N. P.; Pore, V. S.; Chordia, M. D.
Tetrahedron 1994, 50, 2523e2532.
22. Hanekamp, J. C.; Rookhuizen, R. B.; Bos, H. J. T.; Brandsma, L. Tetrahedron 1992,
48, 5151e5162.
23. Seo, S.; Uomori, A.; Yoshimura, Y.; Takeda, K.; Noguchi, H.; Ebizuka, Y.; San-
kawa, U.; Seto, H. J. Chem. Soc., Perkin Trans. 1 1992, 1, 569e572.
24. Zielinski, J.; Li, H. T.; Djerassi, C. J. Org. Chem. 1982, 47, 620e625.
25. Wright, J. L. C.; Mcinnes, A. G.; Shimizu, S.; Smith, D. G.; Walter, J. A.; Idler, D.;
Khalil, W. Can. J. Chem. 1978, 56, 1898e1903.
Acknowledgements
26. Beszant, S.; Giannini, E.; Zanoni, G.; Vidari, G. Eur. J. Org. Chem. 2003,
The authors wish to acknowledge that this research was funded
under the National Development Plan, through the Food In-
stitutional Research Measure administered by the Department of
Agriculture, Fisheries and Food, Ireland.
3958e3968.
27. Khripach, V. A.; Zhabinskii, V. N.; Konstantinova, O. V.; Khripach, N. B.; An-
tonchick, A. P.; Schneider, B. Steroids 2002, 67, 597e603.
28. Brown,H.C.;Naik,R. G.;Singaram,B.;Pyun, C.Organometallics1985, 4,1925e1929.
29. Metzger, S. H.; Isbell, A. F. J. Org. Chem. 1964, 29, 623e627.
30. Kocienski, P. J.; Lythgoe, B.; Roberts, D. A. J. Chem. Soc., Perkin Trans. 1 1978, 1,
834e837.
31. Anastasia, M.; Allevi, P.; Ciuffreda, P.; Fiecchi, A.; Scala, A. J. Org. Chem. 1984, 49,
4297e4300.
Supplementary data
32. Chillous, S. E. H. D.; Hutchinson, D. K. J. Org. Chem. 1982, 47, 5418e5420.
33. Tsuda, K.; Kishida, Y.; Hayatsu, R. J. Am. Chem. Soc. 1960, 82, 3396e3399.
34. Yang, B.; Miller, P. A.; Mollmann, U.; Miller, M. J. Org. Lett. 2009, 11, 2828 28.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2012.04.060.