Stereoselective synthesis of a fully protected C13-C 23 fragment of tedanolide

Article abstract of DOI:10.1016/j.tet.2011.10.024

The combination of a high-yielding dienyllithium addition and a highly diastereoselective 1,2-reduction allows the preparation of the completely protected C₁₃-C₂₃ fragment 3 of the potent cytotoxic agent tedanolide 1. A convergent ap

Full text of DOI:10.1016/j.tet.2011.10.024

Tetrahedron 67 (2011) 10281e10286
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Stereoselective synthesis of a fully protected C13eC23 fragment of tedanolide
*
Michael E. Jung , Dongwon Yoo
Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 July 2011
Received in revised form 7 October 2011
Accepted 10 October 2011
Available online 18 October 2011
The combination of a high-yielding dienyllithium addition and a highly diastereoselective 1,2-reduction
allows the preparation of the completely protected C13eC23 fragment 3 of the potent cytotoxic agent
tedanolide 1. A convergent approach was used, namely a late stage coupling of the dienyllithium 16 with
the selectively protected aldehyde 5 followed by oxidationereduction and final epoxidation to give 3. The
dienylstannane 4 was prepared from the dibromide 6 in five steps, the key step being the highly regio-
and stereoselective stannylcupration of the alkyne 7. The commercially available hydroxy ester 10 was
converted in 11 steps to the aldehyde 5. The compound 3 could potentially be a key intermediate for the
synthesis of tedanolide 1.
Keywords:
Non-aldol aldol
Semipinacol rearrangement
Stannylcupration
Dienylstannane
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
fragments is shown in Fig. 1. We designed the synthetic route for
fragment 3 from the dienylstannane 4 via nucleophilic addition of
Schmitz and co-workers isolated the macrolide tedanolide 1 in
1984 from the Caribbean sponge Tedania ignis.1 This lactone epox-
ide exhibits very potent cytotoxicity, with ED50s of 250 pg/mL
against human nasopharynx carcinoma and 16 pg/mL against
in vitro lymphocytic leukemia. Because of its excellent antitumor
activity and its intriguing structural features (18-membered mac-
rocyclic lactone with a polypropionate skeleton, an internal tri-
the derived dienyllithium to the selectively protected aldehyde 5.
Although this addition would be expected to give the undesired
stereochemistry at C17 due to CrameFelkineAnh control,7 the ste-
reochemistry at C17 could be easily changed via a simple oxida-
tionereduction protocol using a bulky hydride agent, again via
CrameFelkineAnh control.
substituted
E olefin, and 13 stereocenters), tedanolide has
generated considerable synthetic interest. Three total syntheses2
have resulted as well as a significant amount of synthetic work.3
2. Background
In our attempts to synthesize this molecule, our group has
employed over the last few years the non-aldol aldol process,
a reaction that we developed for the preparation of aldol natural
products.4,5 Recently we reported two approaches for the prepa-
ration of the C1eC12 fragment of tedanolide 2 using an alke-
nyllithium addition followed by
a reductive hydroboration
methodology6a and the combination of aldol and non-aldol aldol
methodology,6b respectively. We report herein the efficient prep-
aration of the fully protected C13eC23 fragment of tedanolide 3 by
a convergent synthetic method that involves a dienyllithium ad-
dition and a highly diastereoselective reduction of an enone as the
key steps. Our proposed retrosynthesis for tedanolide 1 using these
* Corresponding author. E-mail address: jung@chem.ucla.edu (M.E. Jung).
Fig. 1. Retrosynthesis of tedanolide 1.
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.024

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M.E. Jung, D. Yoo / Tetrahedron 67 (2011) 10281e10286
3. Results and discussion
copper(I) bromideedimethyl sulfide complex13 to give the diol 14.
Selective protection of the primary alcohol of this diol as the p-
methoxybenzyl (PMB) ether proceeded in 83% yield. Final protection
of the secondary alcohol as the triethylsilyl (TES) ether afforded the
selectively protected alkene 15 in 94% yield. Finally dihydroxylation
with catalytic osmium tetroxide/NMO gave in quantitative yield the
expected diol mixture, which underwent oxidative cleavage using
sodium periodate to afford the desired aldehyde 5.
In order to prepare the fully protected C13eC23 fragment of
tedanolide 3, efficient syntheses of both the dienylstannane 4 and
the protected aldehyde 5 were required. The synthesis of the
dienylstannane with high E-selectivity was difficult to achieve. Fi-
nally we developed a method that utilized a regio- and stereo-
selective hydrostannylation of a substituted alkyne to prepare the
desired vinylstannane, which could then be converted into the
dienylstannane without any loss of the tin component. Thus the
alkyne 7 was prepared from the dibromoolefin 6, prepared by
a CoreyeFuchs reaction on the known aldehyde, in 83% yield via
lithiumehalogen exchange followed by trapping with iodo-
methane (Scheme 1). Initially we explored the palladium-catalyzed
hydrostannylation using Yamamoto’s procedure.8 However the
desired vinylstannane 8 was obtained in only 13% yield along with
a small amount of the undesired regioisomer (6:1 ratio). When
a larger amount of the palladium catalyst and tributyltin hydride
was used, the yield of the vinylstannane increased while the
regioselectivity unfortunately decreased. However, when stannyl-
cupration9 of the alkyne 7 was carried out, the desired vinyl-
stannane
8 was isolated in good yield and with superb
regioselectivity (>99:1). Desilylation of 8 with TBAF gave the pri-
mary alcohol 9. Oxidation of this alcohol using DesseMartin peri-
odinane (DMP)10 afforded in 90% yield the somewhat unstable
aldehyde, which was immediately subjected to the Wittig olefina-
tion with ethyltriphenylphosphonium bromide using potassium
hexamethyldisilazide (KHMDS) in THF to afford the desired dien-
ylstannane 4 in 85% yield. All of the vinylstannanesd4, 8, and
9dare unstable on normal silica gel chromatography. Therefore,
either adding triethylamine in the eluent or chromatography on
neutral alumina is preferred for purification of these compounds.
Scheme 2.
With both the dienylstannane 4 and the aldehyde 5 in hand, we
next explored the coupling reaction (Scheme 3). Lithiumetin ex-
change of 4 was achieved with n-butyllithium at 0 ꢀC within 10 min
to give the dienyllithium 16. Carrying out this exchange reaction at
ꢁ78 ꢀC resulted in no significant exchange of tin for lithium. Ad-
dition of the dienyllithium 16 to the aldehyde 5 afforded an ap-
proximately 2.5:1 mixture of the two diastereomeric allylic
alcohols 17 (b-OH) and 18 (a-OH) in 75% yield. To confirm the
stereochemistry at the newly generated chiral center, the major
diastereomer 17 was transformed to the corresponding acetonide
19 by removal of the silyl ether with TBAF and acetonide formation
(Fig. 2). The stereochemistry was confirmed via coupling constant
(small J values) and NOE analysis.
Scheme 1.
The coupling partner for the dienylstannane, the aldehyde 5, was
prepared from the commercially available methyl (R)-3-hydroxy-2-
methylbutanoate 10 by a short sequence (Scheme 2). Protection of
the alcohol as the 4,40-dimethoxytrityl (DMTr) ether followed by
reduction of the ester gave the known4d alcohol 11 in 94% yield.
Oxidation with tetrapropylammonium perruthenate (TPAP) and N-
methylmorpholine N-oxide (NMO)11 afforded the aldehyde, which
was immediately subjected to the Wittig reaction with (ethox-
ycarbonylmethylidene)triphenylphosphorane to give the desired E-
enoate 12 in 75% yield for the two steps. Reduction of the ester 12
with DIBAL furnished, in 83% yield, the allylic alcohol, which upon
Scheme 3.
Sharpless asymmetric epoxidation12 afforded the
b-epoxy alcohol 13
in 71% yield and >90% ee. The epoxide was opened regio- and ster-
eoselectively by treatment of vinylmagnesium chloride and
Fig. 2. NMR data of 19 for structure determination of 17.

M.E. Jung, D. Yoo / Tetrahedron 67 (2011) 10281e10286
10283
The mixture of undesired and desired isomers 17 and 18, which
were difficult to cleanly separate, could be readily converted into
only the desired isomer 18 via an oxidationereduction protocol
(Scheme 4). DesseMartin oxidation9 of the allylic alcohol afforded
the ketone 20 in 84% yield. Several reducing reagents were screened
to effect diastereoselective reduction of the enone. Small reducing
agents gave a mixture of diastereomers in which 17 predominated,
e.g., DIBAL, afforded a 2:1 mixture favoring 17. However, Super Hy-
dride reduction afforded the desired diastereomer 18 in 72% yield
with an excellent diastereomeric ratio (97:3). In an attempt to in-
crease the selectivity, we used the more sterically bulky hydride L-
Selectride, but it gave only the product of 1,4-reduction.
and the reactionwas allowed to warm to 21 ꢀCwithstirringovernight.
The reaction was quenched with satd NH4Cl solution (30 mL). The
phases were separated, and the aqueous phase was extracted with
dichloromethane (50 mL). The organic phase was combined, washed
with brine (40 mL), and dried over MgSO4. Removal of the solvent
under reduced pressure yielded crude orange oil, which was used
without further purification. A solution of the crude dimethoxytrityl
methyl ester in THF (80 mL) was cooled to 0 ꢀC and treated with LAH
(0.49 g, 12.7 mmol). The suspension was then allowed to warm to
21 ꢀC and stirred for 1 h. After being cooled to 0 ꢀC, the reaction was
quenched by the successive addition of water (0.65 mL), 15% NaOH
solution (0.65 mL), and water (1.95 mL) with vigorous stirring. The
insoluble materials were filtered off through Celite and the solute was
washed with diethyl ether (3ꢂ40 mL). The solvents were concen-
trated under reduced pressure and the residue was purified by flash
silica column chromatography (20% ethyl acetate in hexane) to yield
2.34 g (94%) of the alcohol 11 as a viscous yellowish oil. To a stirred
ꢀ
solutionofthealcohol11 (2.34 g, 5.96 mmol)and4Amolecularsieves
in dichloromethane (60 mL) was added NMO (1.05 g, 8.94 mmol)
followed by TPAP (0.21 g, 0.60 mmol) at 21 ꢀC. After 1 h, the reaction
mixture was passed through Celite, and the filtrate was concentrated.
Purification by short column chromatography on silica gel (13% ethyl
acetate in hexane) yielded the desired aldehyde. The aldehyde was
then dissolved in benzene (80 mL), treated with (ethox-
ycarbonylmethylidene)triphenylphosphorane (3.12 g, 8.94 mmol)
and stirred overnight. After evaporation of the benzene, the residue
was purifiedbyflashsilicacolumnchromatography(13%ethylacetate
in hexane) to yield 2.06 g (75%) of the conjugated ester 12 as colorless
Scheme 4.
In order to guarantee the success of the epoxidation of the allylic
alcohol moiety in a late intermediate for the synthesis of tedanolide
1, we tried the reaction on 18 (Scheme 5). Oxidation of 18 with
MCPBA in dichloromethane afforded the bottom fragment of
tedanolide 3 in 63% yield and with high regio- and stereoselectivity.
oil.1H NMR (400 MHz, CDCl3)
d: 7.40e7.43 (2H, m), 7.26e7.35 (6H, m),
7.15e7.22 (1H, m), 6.94 (1H, dd, J¼15.8, 7.3 Hz), 6.80e6.85 (4H, m),
5.82 (1H, dd, J¼15.8, 1.3 Hz), 4.19 (2H, q, J¼7.1 Hz), 3.79 (6H, s), 3.07
(1H, dd, J¼8.8, 6.7 Hz), 3.01 (1H, dd, J¼8.8, 6.4 Hz), 2.60 (1H, b septet,
Jw7 Hz), 1.29 (3H, t, J¼7.1 Hz), 1.08 (3H, d, J¼6.8 Hz). 13C NMR
(100 MHz, CDCl3) d: 166.8, 158.4, 151.7, 145.1, 136.27, 136.26, 130.1,
128.2, 127.8, 126.7, 120.9, 113.1, 85.9, 67.1, 60.2, 55.2, 37.3, 16.3,14.3. IR
(neat) vmax 1717 cmꢁ1. HRMS calcd for C29H32O5: 460.2250. Found:
460.2251.
4.2. (S,E)-5-((4,40-Dimethoxytrityl)methoxy)-4-methylpent-2-
en-1-ol 12a
Scheme 5.
A solution of 12 (1.55 g, 3.37 mmol) in dichloromethane (30 mL)
was treated with a 1 M solution of DIBAL in hexane (8.43 mL,
8.43 mmol) at 21 ꢀC. This reaction was quenched after 30 min by
addition of a satd Rochelle’s salt solution (70 mL), followed by di-
lution with diethyl ether (70 mL), and addition of water (30 mL).
The reaction was stirred at 21 ꢀC until both phases were clearly
separated and the organic layer was clear. After extraction, the
separated organic layer was dried over MgSO4, filtered, and con-
centrated under reduced pressure. The resulting mixture was pu-
rified by flash silica column chromatography (20% ethyl acetate in
hexane) to give 1.17 g (83%) of compound 12a as a colorless oil. 1H
In summary, we have achieved an efficient, straightforward
synthesis of the fully protected C13eC23 fragment of tedanolide 3,
which features the addition of the dienyllithium reagent 16, pre-
pared by lithiumetin exchange of the dienylstannane 4, to the se-
lectively protected aldehyde 5. The mixture of the undesired and
desired diastereomers 17 and 18 could be transformed nearly ex-
clusively to the desired diastereomer 18 in two steps through an
oxidationereduction protocol. Finally the allylic alcohol of 18 could
be readily converted into the desired epoxy alcohol regio- and
stereoselectively to give the desired C13eC23 fragment of tedanolide
3. Further progress toward the total synthesis of tedanolide will be
reported in due course.
NMR (400 MHz, CDCl3) d: 7.35e7.47 (2H, m), 7.24e7.35 (6H, m),
7.16e7.21 (1H, m), 6.80e6.83 (4H, m), 5.64e5.66 (2H, m), 4.09 (2H,
m), 3.79 (6H, s), 3.01 (1H, dd, J¼8.7, 6.4 Hz), 2.92 (1H, dd, J¼8.7,
6.8 Hz), 2.48 (1H, b septet, Jw7 Hz), 1.05 (3H, d, J¼6.8 Hz). 13C NMR
4. Experimental section
(100 MHz, CDCl3) d: 158.3, 145.3, 136.5, 136.0, 130.1, 130.0, 129.1,
128.5, 128.3, 127.7, 126.6, 113.0, 85.6, 67.8, 63.9, 55.2, 37.0, 17.1. IR
(neat) vmax 3373 cmꢁ1. HRMS calcd for C27H30O4: 418.2144. Found:
418.2142.
4.1. Ethyl (S,E)-5-(4,40-dimethoxytrityl)-4-methyl-2-
pentenoate 12
Methyl (R)(ꢁ)-3-hydroxy-2-methylpropionate 10 (0.75 g,
6.35 mmol) was dissolved in dichloromethane (35 mL). Collidine
(2.54 mL, 19.2 mmol) was then added to the solution, which was
stirred for 2 min at 21 ꢀC. The reaction mixture was then cooled to
0 ꢀC, treated with 4,40-dimethoxytrityl chloride (2.79 g, 8.25 mmol),
4.3. ((2R,3R)-3-((R)-1-((4,40-Dimethoxytrityl)methoxy)
propan-2-yl)oxiran-2-yl)methanol 13
ꢀ
D
(ꢁ)-Diisopropyl tartrate (99 mg, 0.21 mmol) and 4 A powdered
molecular sieves (84 mg) were suspended in dichloromethane

10284
M.E. Jung, D. Yoo / Tetrahedron 67 (2011) 10281e10286
(2 mL). The suspension was cooled to ꢁ20 ꢀC and treated with ti-
tanium (IV) isopropoxide (0.12 mL, 0.42 mmol) followed by stirring
for 20 min at ꢁ20 ꢀC. A 5.8 M solution of tert-butyl hydroperoxide
in decane (0.41 mL, 2.36 mmol) was then added and the reaction
mixture was stirred for a further 20 min at ꢁ20 ꢀC. A solution of 12a
(0.47 g, 1.12 mmol) in dichloromethane (3 mL) was then introduced
and the reaction temperature kept at ꢁ23 ꢀC for 24 h. The reaction
was then diluted with diethyl ether (10 mL) and filtered through
a mixture of Celite and silica gel. The solvent was then removed
under reduced pressure and the resulting mixture was purified by
flash silica column chromatography (13% ethyl acetate in hexane) to
give 0.35 g (71%) of compound 13 as a colorless oil. 1H NMR
NMR (100 MHz, CDCl3) d: 159.2, 158.5, 144.9, 137.6, 136.2, 136.1,
130.3, 130.10, 130.07, 129.2, 128.2, 127.8, 126.8, 116.6, 113.8, 113.1,
86.4, 77.3, 72.9, 71.7, 65.3, 55.3, 55.2, 47.7, 36.2, 15.6. IR (neat) vmax
3493 cmꢁ1
.
4.6. (3S,4R,5R)-6-((4,40-Dimethoxytrityl)methoxy)-3-((4-
methoxybenzyloxy)methyl)-5-methyl-4-triethylsilyloxyhex-1-
ene 15
To 14a (0.30 g, 0.51 mmol) in dichloromethane (20 mL) cooled
ꢀ
€
to ꢁ78 C was added Hunig’s base (0.26 mL, 1.54 mmol) followed
by dropwise addition of TESOTf (0.17 mL, 0.77 mmol). After 1 h, the
reaction was quenched with satd NaHCO3 solution (50 mL) and
extracted with dichloromethane (30 mL). The organic layer was
washed with brine (50 mL), dried over MgSO4, and concentrated
under reduced pressure. Purification by flash column chromatog-
raphy (13% ethyl acetate in hexane) provided 0.34 g (94%) of 15 as
(400 MHz, CDCl3)
d: 7.42e7.45 (2H, m), 7.27e7.35 (6H, m),
7.16e7.22 (1H, m), 6.81e6.84 (4H, m), 3.91 (1H, ddd, J¼12.4, 5.6,
2.4 Hz), 3.79 (6H, s), 3.62 (1H, ddd, J¼12.4, 7.3, 4.2 Hz), 3.11 (2H, m),
2.98 (2H, m), 1.79 (1H, b septet, Jw7 Hz), 0.99 (3H, d, J¼7.0 Hz). 13C
NMR (100 MHz, CDCl3) d: 158.4, 145.2, 136.4, 130.1, 128.2, 127.8,
126.7, 113.1, 85.8, 65.4, 62.0, 58.1, 56.9, 55.2, 36.1, 13.3. IR (neat) vmax
a clear oil. 1H NMR (400 MHz, CDCl3)
d: 7.40e7.43 (2H, m),
3440 cmꢁ1. HRMS calcd for C27H30O5: 434.2093. Found: 434.2097.
7.27e7.32 (6H, m), 7.16e7.24 (3H, m), 6.83e6.86 (2H, m), 6.78e6.81
(4H, m), 5.66 (1H, ddd, J¼18.2, 9.1, 8.9 Hz), 4.92e4.96 (2H, m), 4.40
(1H, d, J¼11.7 Hz), 4.37 (1H, d, J¼11.7 Hz), 3.79 (3H, s), 3.78 (6H, s),
3.19 (1H, dd, J¼8.8, 5.5 Hz), 2.80 (1H, t, J¼8.7 Hz), 2.41 (1H, m), 2.07
(1H, m), 0.99 (3H, d, J¼7.0 Hz), 0.84 (9H, t, J¼7.9 Hz), 0.46 (6H, q,
4.4. (2S,3R,4R)-5-((4,40-Dimethoxytrityl)methoxy)-4-methyl-
2-ethenylpentane-1,3-diol 14
To a suspension of copper(I) bromideedimethyl sulfide complex
(50 mg, 0.24 mmol) in Et2O (40 mL) was added a 1.6 M solution of
vinylmagnesium chloride in THF (1.51 mL, 2.42 mmol) and then
added a solution of epoxy alcohol 13 (0.35 g, 0.81 mmol) in Et2O
(3 mL) at ꢁ30 ꢀC. After stirring for 12 h at 0 ꢀC, the reaction was
quenched with satd NH4Cl solution (50 mL). The organic layer was
separated and the aqueous layer was extracted with ethyl acetate
(50 mL). The combined organic layers were dried over MgSO4 and
concentrated under reduced pressure. Flash silica column chro-
matography of the residue (33% ethyl acetate in hexane) yielded
J¼7.9 Hz). 13C NMR (100 MHz, CDCl3)
d: 159.1, 158.2, 145.5, 138.9,
136.8, 136.7, 130.8, 130.2, 130.1, 129.2, 128.3, 127.7, 126.5, 116.3, 113.7,
112.9, 85.7, 75.4, 72.6, 70.8, 64.9, 55.3, 55.2, 48.2, 38.5, 14.9, 7.1, 5.3.
IR (neat) vmax 1609 cmꢁ1
.
4.7. (2S,3R,4R)-5-((4,40-Dimethoxytrityl)methoxy)-2-((4-
methoxybenzyloxy)methyl)-4-methyl-3-
triethylsilyloxypentanal 5
To a solution of 15 (0.13 g, 0.19 mmol) in acetone/water (4:1,
5 mL) at 0 ꢀC, NMO (44 mg, 0.37 mmol) and OsO4 (7.1 mg,
0.028 mmol) were added and the solution was stirred overnight at
21 ꢀC. The product was extracted with ethyl acetate (30 mL) and
satd sodium sulfite solution (30 mL) and dried over MgSO4. The
solvent was removed under reduced pressure. The crude diol was
dissolved in acetone/water (4:1, 5 mL) and NaIO4 (0.12 g,
0.56 mmol) was added. The mixture was kept stirring for 1 h at
21 ꢀC. The product was extracted with Et2O (30 mL), and satd so-
dium thiosulfate solution (30 mL). The solvent was removed under
reduced pressure and the crude product was purified by flash silica
column chromatography (13% ethyl acetate in hexane) to obtain
0.29 g (78%) of the desired diol 14. 1H NMR (400 MHz, CDCl3)
d:
7.41e7.45 (2H, m), 7.29e7.34 (6H, m), 7.21e7.25 (1H, m), 6.80e6.86
(4H, m), 5.57 (1H, ddd, J¼17.2, 10.3, 9.1 Hz), 5.00 (1H, dd, J¼10.3,
1.8 Hz), 4.82 (1H, dd, J¼17.2, 1.8 Hz), 3.91 (1H, d, J¼6.4 Hz), 3.80 (6H,
s), 3.73e3.78 (1H, m), 3.61e3.67 (1H, m), 3.55e3.60 (1H, m), 3.32
(1H, dd, J¼9.4, 3.5 Hz), 3.24 (1H, dd, J¼9.4, 4.7 Hz), 3.05 (1H, m),
2.05 (1H, m), 1.88 (1H, m), 1.16 (3H, d, J¼7.1 Hz). 13C NMR (100 MHz,
CDCl3)
d: 158.6, 144.3, 136.6, 135.7, 135.5, 130.0, 129.9, 128.04,
128.00, 126.7, 117.5, 113.3, 87.0, 79.8, 65.9, 65.4, 55.3, 49.5, 35.6, 15.4.
IR (neat) vmax 3423 cmꢁ1
.
4.5. (2R,3R,4S)-1-((4,40-Dimethoxytrityl)methoxy)-4-((4-
0.12 g (95%) of the aldehyde 5. 1H NMR (400 MHz, CDCl3)
d: 9.66
methoxybenzyloxy)methyl)-2-methylhex-5-en-3-ol 14a
(1H, d, J¼1.8 Hz), 7.40e7.41 (2H, m), 7.16e7.39 (9H, m), 6.84e6.88
(2H, m), 6.79e6.83 (4H, m), 4.41 (1H, d, J¼11.7 Hz), 4.39 (1H, d,
J¼11.7 Hz), 4.20 (1H, dd, J¼5.5, 4.6 Hz), 3.82 (1H, t, J¼9.7 Hz), 3.80
(3H, s), 3.78 (6H, s), 3.68 (1H, dd, J¼9.7, 4.4 Hz), 3.12 (1H, dd, J¼9.0,
6.2 Hz), 2.85 (1H, dd, J¼9.1, 7.3 Hz), 2.67 (1H, dddd, J¼8.9, 4.4, 4.4,
1.7 Hz), 2.04 (1H, b septet, Jw7 Hz), 0.94 (3H, d, J¼6.9 Hz), 0.82 (9H,
To a suspension of 60% sodium hydride dispersion in mineral oil
(63 mg, 1.57 mmol) in THF (15 mL) at 21 ꢀC was slowly added diol
14 (0.29 g, 0.63 mmol) in THF (5 mL) via syringe. The resulting
heterogeneous mixture was stirred at 21 ꢀC for 0.5 h and freshly
prepared p-methoxybenzyl chloride (0.11 mL, 0.81 mmol) was
added. After stirring at 21 ꢀC for 12 h, the mixture was carefully
quenched by addition of 1 mL of water followed by dilution with
50 mL of diethyl ether. The resulting mixture was washed with
brine (50 mL), dried over MgSO4, filtered, and concentrated under
reduced pressure. For flash silica column chromatography, starting
eluent was 50% diethyl ether in petroleum ether mixtures to
remove some less polar material, then solvent polarity was in-
creased to 33% ethyl acetate in hexane to collect 0.30 g (83%) of the
t, J¼8.0 Hz), 0.42 (6H, q, J¼8.0 Hz). 13C NMR (100 MHz, CDCl3)
d:
204.1, 159.2, 158.4, 145.2, 136.40, 136.38, 130.14, 130.08, 129.3, 128.2,
127.7, 126.7, 116.3, 113.8, 113.0, 86.0, 73.0, 71.6, 65.9, 65.3, 55.28,
55.25, 55.19, 39.4, 14.1, 6.9, 5.0. IR (neat) vmax 1725, 1609 cmꢁ1
.
4.8. (R,E)-Tributyl(4-methyl-5-((2,3,3-trimethylbutan-2-yl)
oxy)pent-2-en-2-yl)stannane 8
To a solution of hexabutylditin (2.28 g, 3.94 mmol) in THF (3 mL)
was added 2.5 M solution of n-butyllithium in hexane (1.58 mL,
3.94 mmol) at ꢁ78 ꢀC. The solution was stirred for 30 min at
ꢁ40 ꢀC. Then the mixture was added via cannula to a suspension of
CuCN (0.18 g, 1.97 mmol) in THF (3 mL) at ꢁ78 ꢀC. The solution was
stirred at ꢁ40 ꢀC until obtention of a yellow gold solution and
recooled to ꢁ78 ꢀC. Anhydrous MeOH (1 mL) was added, then the
desired product 14a. 1H NMR (400 MHz, CDCl3)
d: 7.41e7.44 (2H,
m), 7.27e7.34 (6H, m), 7.17e7.23 (3H, m), 6.80e6.88 (6H, m), 5.67
(1H, ddd, J¼17.2,10.3, 8.9 Hz), 4.98 (1H, dd, J¼10.3,1.8 Hz), 4.83 (1H,
dd, J¼17.2, 1.8 Hz), 4.41 (2H, s), 3.79 (3H, s), 3.78 (6H, s), 3.55e3.60
(2H, m), 3.52 (2H, m), 3.20 (1H, dd, J¼9.2, 4.9 Hz), 3.19 (1H, dd,
J¼9.2, 5.2 Hz), 2.24 (1H, m), 1.92 (1H, m), 1.22 (3H, d, J¼7.0 Hz). 13C

M.E. Jung, D. Yoo / Tetrahedron 67 (2011) 10281e10286
10285
yellow solution turned to a red gel. The temperature was allowed to
4.11. (2R,3R,4R,5RS,6E,8S,9Z)-1-((4,40-Dimethoxytrityl)
warm to ꢁ10 ꢀC for 30 min, until obtention of a red solution. A
solution of the alkyne 7 (0.11 g, 0.52 mmol) in THF (1 mL) was
added at ꢁ78 ꢀC, and the temperature was allowed to warm to
ꢁ5 ꢀC overnight. The reaction mixture was poured into Et2O
(30 mL) and a satd NH4Cl/concentrated ammonia (5:1) solution
(60 mL). The mixture was extracted with Et2O (30 mL), and the
organic layer was washed with brine (40 mL), dried over MgSO4,
and filtered. The solvent was removed under reduced pressure and
the crude product was purified by flash silica column chromatog-
raphy (1% triethylamine, 6% ethyl acetate in hexane) to obtain 0.16 g
methoxy)-4-((4-methoxybenzyl-oxy)methyl)-2,6,8-trimethyl-
3-triethylsilyloxyundeca-6,9-dien-5-ol 17 and 18
To a stirred solution of a vinylstannane 4 (75 mg, 0.19 mmol)
in THF (1 mL) at 0 ꢀC was added 1.6 M solution of butyllithium in
hexane (0.14 mL, 0.23 mmol). The reaction mixture was stirred for
10 min and recooled to ꢁ78 ꢀC. A solution of aldehyde 5 (98 mg,
0.14 mmol) in THF (2 mL) was added. The reaction mixture was
stirred for 30 min at ꢁ78 ꢀC and then quenched with satd NH4Cl
solution (3 mL). The resulting mixture was extracted with ethyl
acetate (30 mL) and water (30 mL). The organic layer was washed
with brine (20 mL), dried over MgSO4, filtered, and concentrated
under reduced pressure. Flash silica column chromatography (13%
ethyl acetate in hexane) provided 85 mg (75%) of a mixture of 17
(major isomer) and 18 (minor isomer) as a colorless oil. 1H NMR
(61%) of 8. 1H NMR (400 MHz, CDCl3)
d
: 5.27 (1H, dq, J¼8.7, 1.8 Hz),
3.45 (1H, dd, J¼9.7, 6.0 Hz), 3.35 (1H, dd, J¼9.7, 7.2 Hz), 2.78 (1H,
dm), 1.85 (3H, d, J¼1.8 Hz), 1.40e1.48 (6H, m), 1.31 (6H, sextet,
J¼7.2 Hz), 0.94 (3H, d, J¼6.6 Hz), 0.83e0.90 (6H, m), 0.89 (9H, s),
0.88 (9H, t, J¼7.3 Hz), 0.04 (3H, s), 0.03 (3H, s). 13C NMR (100 MHz,
CDCl3)
d
: 143.9, 137.8, 67.9, 35.2, 29.2, 27.4, 25.9, 19.4, 18.3, 17.2, 13.7,
(400 MHz, CDCl3) d: 7.40e7.44 (2H, m), 7.17e7.34 (9H, m),
9.1, -5.28, -5.36. IR (neat) vmax 1463 cmꢁ1
.
6.79e6.90 (6H, m), 5.14e5.34 (3H, m), 4.19e4.38 (2H, m), 3.80
(3H, s), 3.78 (6H, s), 3.61 (1H, dd, J¼9.3, 4.5 Hzdmajor dia), 3.55
(1H, dd, J¼9.3, 2.5 Hzdminor dia), 3.32e3.43 (2H, m), 3.10e3.19
(2H, m), 2.87 (1H, t, J¼9.0 Hzdmajor dia), 2.78 (1H, t,
J¼8.8 Hzdminor dia), 2.16e2.22 (1H, m), 1.64 (3H, dd, J¼6.6,
1.6 Hzdmajor dia), 1.61 (3H, dd, J¼6.6, 1.6 Hzdminor dia), 1.56
(3H, d, J¼1.0 Hzdmajor dia), 1.37 (3H, d, J¼1.0 Hzdminor dia),
1.09 (3H, d, J¼6.8 Hzdmajor dia), 1.05 (3H, d, J¼6.8 Hzdminor
dia), 0.85 (9H, t, J¼8.0 Hz), 0.48 (6H, q, J¼8.0 Hz). 13C NMR
4.9. (R,E)-2-Methyl-4-(tributylstannyl)pent-3-en-1-ol 9
To a stirred solution of the vinylstannane 8 (0.16 g, 0.32 mmol)
in THF (3 mL) at 21 ꢀC was added 1.0 M solution of TBAF in THF
(0.95 mL, 0.95 mmol). The reaction mixture was stirred for 1 h and
then diluted with hexanes (10 mL). The resulting mixture was fil-
tered and the filtrate was concentrated under reduced pressure.
Purification by flash silica column chromatography (1% triethyl-
amine, 19% ethyl acetate in hexane) provided 96 mg (78%) of 9 as
(100 MHz, CDCl3) d: 159.4, 158.3, 145.3, 136.6, 135.5, 134.0, 130.1,
129.7, 128.9, 128.3, 127.7, 126.5, 121.5, 113.8, 113.6, 113.0, 85.8, 78.5,
73.8, 73.3, 55.3, 55.2, 43.5, 37.9, 30.4, 21.5, 15.7, 13.0, 12.9, 7.1, 6.9,
a colorless oil: 1H NMR (400 MHz, CDCl3)
d
: 5.24 (1H, dq, J¼9.0,
5.4, 5.0. IR (neat) vmax 3484, 1610 cmꢁ1
.
1.8 Hz), 3.48 (1H, m), 3.32 (1H, dd, J¼8.2, 3.4 Hz), 2.88 (1H, m), 1.89
(3H, d, J¼1.8 Hz), 1.44e1.53 (6H, m), 1.31 (6H, sextet, J¼7.2 Hz), 0.94
(3H, d, J¼6.6 Hz), 0.86e0.90 (6H, m), 0.89 (9H, t, J¼7.3 Hz). 13C NMR
4.12. (2R,3R,4S,6E,8S,9Z)-1-((4,40-Dimethoxytrityl)methoxy)-
4-((4-methoxybenzyloxy)-methyl)-2,6,8-trimethyl-3-
triethylsilyloxyundeca-6,9-dien-5-one 20
(100 MHz, CDCl3) d: 142.9, 141.0, 67.6, 35.2, 29.2, 27.3, 19.6, 16.8,
13.7, 9.1. IR (neat) vmax 3345, 1463 cmꢁ1
.
To a stirred solution of alcohol 17 and 18 (85 mg, 0.11 mmol) in
CH2Cl2 (5 mL) at 0 ꢀC were added NaHCO3 (8.8 mg, 0.11 mmol) and
DesseMartin periodinane (0.13 g, 0.32 mmol). The reaction mixture
was stirred for 1 h at 0 ꢀC and then quenched with satd NaHCO3
solution (5 mL) and 10% Na2S2O3 solution (5 mL). The aqueous layer
was extracted with Et2O (20 mL), and the organic layer was washed
with brine (20 mL), dried over MgSO4, filtered, and concentrated
under reduced pressure. Flash silica column chromatography (20%
ethyl acetate in hexane) provided 71 mg (84%) of 20 as colorless oil.
4.10. Tributyl((S,2E,5Z)-4-methylhepta-2,5-dien-2-yl)
stannane 4
To a stirred solution of alcohol 9 (96 mg, 0.25 mmol) in CH2Cl2
(3 mL) at 0 ꢀC were added NaHCO3 (21 mg, 0.25 mmol) and
DesseMartin periodinane (0.16 g, 0.37 mmol). The reaction mix-
ture was stirred for 0.5 h at 0 ꢀC and then quenched with satd
NaHCO3 solution (5 mL) and 10% Na2S2O3 (5 mL). The aqueous
layer was extracted with Et2O (20 mL), and the organic layer was
washed with brine (10 mL), dried over MgSO4, filtered, and con-
centrated under reduced pressure. Flash silica column chroma-
tography (1% triethylamine, 19% ethyl acetate in hexane) provided
86 mg (90%) of the desired aldehyde as a colorless oil. To a solu-
tion of ethyltriphenylphosphonium bromide (0.41 g, 1.10 mmol) in
THF (3 mL) was added 0.5 M solution of KHMDS in toluene
(2.10 mL, 1.05 mmol) at 0 ꢀC. The suspension was stirred for
30 min and then recooled to ꢁ78 ꢀC. To the reddish slurry was
added the aldehyde prepared above in THF (2 mL) at ꢁ78 ꢀC. The
reaction mixture was warmed up to 0 ꢀC then stirred for 1 h. The
reaction was quenched with satd NH4Cl solution (3 mL) and di-
luted with Et2O (30 mL). The organic layer was washed with
water (30 mL) and dried over MgSO4 and concentrated under
reduced pressure. The residue was purified by flash silica gel
column chromatography (1% triethylamine, 12% ethyl acetate in
hexane) to give 75 mg (85%) of the diene 4 as a colorless oil. 1H
1H NMR (400 MHz, CDCl3)
d: 7.35e7.45 (2H, m), 7.14e7.29 (9H, m),
6.78e6.85 (6H, m), 6.38 (1H, d, J¼9.2 Hz), 5.39 (1H, dqd, J¼10.6, 6.8,
1.0 Hz), 5.10 (1H, ddq, J¼10.6, 9.8, 1.0 Hz), 4.36 (1H, d, J¼11.6 Hz),
4.31 (1H, d, J¼11.6 Hz), 3.92 (1H, dd, J¼6.6, 4.0 Hz), 3.78 (3H, s), 3.77
(6H, s), 3.69 (2H, m), 3.46 (1H, m), 3.16 (1H, dd, J¼9.0, 5.2 Hz), 2.65
(1H, t, J¼8.8 Hz), 1.89 (1H, m), 1.68 (3H, d, J¼1.0 Hz), 1.59 (3H, dd,
J¼6.8,1.7 Hz), 0.98 (3H, d, J¼7.0 Hz), 0.96 (3H, d, J¼6.8 Hz), 0.84 (9H,
t, J¼8.0 Hz), 0.44 (6H, q, J¼8.0 Hz). 13C NMR (100 MHz, CDCl3)
d:
203.3, 158.3, 146.8, 145.3, 136.7, 136.5, 135.5, 133.0, 130.7, 130.2,
130.1, 129.1, 128.9, 128.3, 127.6, 126.5, 123.8, 113.5, 113.0, 85.9, 75.1,
72.8, 70.4, 65.4, 55.3, 55.2, 49.1, 40.1, 31.9, 20.4, 14.8, 13.1, 11.6, 6.9,
5.1. IR (neat) vmax 1659, 1609 cmꢁ1
.
4.13. (2R,3R,4R,5S,6E,8S,9Z)-1-((4,40-Dimethoxytrityl)
methoxy)-4-((4-methoxybenzyl-oxy)methyl)-2,6,8-trimethyl-
3-triethylsilyloxyundeca-6,9-dien-5-ol 18
NMR (400 MHz, CDCl3)
d
: 5.23e5.29 (3H, m), 3.54 (1H, m), 1.86
A solution of enone 20 (23 mg, 0.028 mmol) in THF (3 mL)
was cooled to ꢁ78 ꢀC, and 1.0 M solution of LiEt3BH in THF
(0.085 mL, 0.085 mmol) was added via syringe. The solution was
warmed to 0 ꢀC and the reaction mixture was cautiously
quenched with satd NH4Cl solution (1 mL). The solution was
(3H, d, J¼1.8 Hz), 1.64 (3H, dd, J¼6.4, 1.4 Hz), 1.42e1.50 (6H, m),
1.30 (6H, sextet, J¼7.3 Hz), 1.00 (3H, d, J¼6.8 Hz), 0.88 (9H, t,
J¼7.4 Hz), 0.83e0.87 (6H, m). 13C NMR (100 MHz, CDCl3)
d: 145.4,
135.7, 135.3, 121.6, 30.7, 29.1, 27.3, 21.6, 19.1, 13.7, 12.9, 9.1.

10286
M.E. Jung, D. Yoo / Tetrahedron 67 (2011) 10281e10286
diluted with CH2Cl2 (20 mL) and extracted with water (10 mL),
and the organic phase was washed with brine (10 mL), dried
over MgSO4, and concentrated under reduced pressure. Flash
silica column chromatography (33% of ethyl acetate in hexane)
gave 17 mg (72%) of 18 as a colorless oil. 1H NMR (400 MHz,
Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2011.10.024.
CDCl3)
d
: 7.43 (2H, br d, Jw8 Hz), 7.31 (4H, br d, J¼8.9 Hz),
References and notes
7.17e7.28 (5H, m), 6.85 (2H, br d, Jw8 Hz), 6.80 (4H, br d,
J¼8.9 Hz), 5.30 (1H, br dq, J¼11.7, 6.7 Hz), 5.17e5.23 (2H, m),
4.31 (1H, d, J¼11.5 Hz), 4.24 (1H, d, J¼11.5 Hz), 4.04 (1H, dd,
J¼5.6, 2.4 Hz), 3.98 (1H, dd, J¼5.6, 2.4 Hz), 3.79 (3H, s), 3.78 (6H,
s), 3.32e3.40 (3H, m), 3.26 (1H, m), 3.13 (1H, dd, J¼9.9, 5.7 Hz),
2.77 (1H, t, J¼8.8 Hz), 2.19 (1H, m), 2.02 (1H, m), 1.60 (3H, dd,
J¼6.6, 1.5 Hz), 1.56 (3H, s), 1.04 (3H, d, J¼6.8 Hz), 0.99 (3H, d,
J¼6.7 Hz), 0.85 (9H, t, J¼7.9 Hz), 0.48 (6H, m). 13C NMR
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(100 MHz, CDCl3) d: 159.0, 158.3, 145.4, 136.7, 135.3, 133.9, 130.7,
103.1, 129.1, 128.9, 128.3, 127.7, 126.6, 121.6, 113.6, 112.9, 85.9,
77.8, 74.5, 72.6, 68.6, 55.3, 55.2, 38.1, 30.4, 25.3, 21.4, 15.1, 13.0,
11.4, 6.9, 5.0. IR (neat) vmax 3476, 1609 cmꢁ1
.
4.14. (1S,2R,3R,4R)-5-((4,40-Dimethoxytrityl)methoxy)-2-((4-
methoxybenzyloxy)methyl)-4-methyl-1-((2R,3R)-2-methyl-3-
((S,Z)-pent-3-en-2-yl)oxiran-2-yl)-3-triethylsilyloxy-pentan-1-
ol 3
To a solution of allyl alcohol 18 (17 mg, 0.021 mmol) in CH2Cl2
(3 mL) was added 70% MCPBA (5.7 mg, 0.023 mmol) at ꢁ20 ꢀC.
After stirring for 10 h, satd NaHCO3 solution (5 mL) and satd
Na2S2O3 solution (5 mL) were added. The mixture was extracted
with ethyl acetate (10 mL). The organic layer was washed with
brine (10 mL), dried over MgSO4, and concentrated under reduced
pressure. The residue was purified by flash silica column chro-
matography (20% ethyl acetate in hexane) to give 11 mg (63%) of
epoxy alcohol 3. 1H NMR (400 MHz, CDCl3)
d: 7.42 (2H, br d,
Jw8 Hz), 7.16e7.36 (9H, m), 6.86 (2H, br d, Jw8 Hz), 6.79 (4H, br
d, J¼8.9 Hz), 5.43 (1H, br dq, J¼11.0, 6.7 Hz), 5.22 (1H, br dd,
J¼11.2, 9.4 Hz), 4.39 (1H, d, J¼11.6 Hz), 4.26 (1H, d, J¼11.6 Hz),
4.01 (1H, dd, J¼7.5, 1.6 Hz), 3.78 (9H, s), 3.43 (1H, dd, J¼9.8,
7.3 Hz), 3.35 (1H, dd, J¼8.6, 4.4 Hz), 3.25 (1H, dd, J¼9.8, 8.2 Hz),
3.08 (1H, dd, J¼10.4, 2.0 Hz), 2.87 (1H, br s), 2.74 (1H, t, J¼8.8 Hz),
2.52 (1H, d, J¼9.2 Hz), 2.40e2.47 (1H, m), 2.13e2.20 (1H, m),
2.00e2.09 (1H, m), 1.58 (3H, dd, J¼6.8, 1.7 Hz), 1.30 (3H, s), 1.11
(3H, d, J¼6.4 Hz), 1.02 (3H, d, J¼6.8 Hz), 0.79 (9H, t, J¼7.9 Hz), 0.38
(6H, m).
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Acknowledgements
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We thank the National Institutes of Health and the National
Science Foundation for support. We wish to dedicate this manu-
script to my wonderful mentor and very close friend, Gilbert Stork,
on the happy occasion of his 90th birthday.
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