Stereoselective synthesis of dendrodolide-L

Article abstract of DOI:10.1016/j.tetasy.2016.02.007

An efficient stereoselective total synthesis of 12-membered macrolide dendrodolide L has been achieved. The key reactions involved are Keck asymmetric allylation, Jacobsen's hydrolytic kinetic resolution, Sharpless asymmetric epoxidation, Mitsunobu reaction and ring-closing metathesis reaction.

Full text of DOI:10.1016/j.tetasy.2016.02.007

Tetrahedron: Asymmetry xxx (2016) xxx–xxx
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Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Stereoselective synthesis of dendrodolide-L
⇑
Sheshurao Bujaranipalli, Saibal Das
Natural Products Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient stereoselective total synthesis of 12-membered macrolide dendrodolide L has been achieved.
The key reactions involved are Keck asymmetric allylation, Jacobsen’s hydrolytic kinetic resolution,
Sharpless asymmetric epoxidation, Mitsunobu reaction and ring-closing metathesis reaction.
Ó 2016 Elsevier Ltd. All rights reserved.
Received 23 January 2016
Accepted 16 February 2016
Available online xxxx
1. Introduction
R2
R2
R1
R1
O
Marine fungi, a potential source of biologically active secondary
metabolites, are a topic of growing interest. Dendrodolide L is a sec-
ondary metabolite, which was isolated by Zhang et al. from den-
drochium sp.,1 (a fungus associated with the sea cucumber
Holothuria nobilis Selenka, which was collected from the South China
Sea) along with twelve other dendrodolides (Fig. 1). The structure of
dendrodolide L 12 was elucidated by means of a detailed spectro-
scopic analysis and X-ray single crystal diffraction studies. Further-
more, it was shown to exhibit in vitro cytotoxicity against the
O
O
O
OH
O
OH
1 dendrodolide A, R1 = OMe, R2 = H
2 dendrodolide B, R1 = H, R2 = OMe
3 dendrodolide C, R1 = OH, R2 = H
4 dendrodolide D, R1 = H, R2 = OH
5 dendrodolide E, R1, R2 = O
6 dendrodolide F, R1 = OH, R2 = H
7 dendrodolide G, R1 = H, R2 = OH
R3
O
R2
R1
OH
H
O
tumour cell line HCT-116 with an IC50 value of 26.5 lg/mL. Over last
H
two years, the synthesis of a few dendrodolides has been reported
using various protocols.2 In continuation of our interests in the syn-
thesis of bioactive natural products,3 we herein report the stereose-
lective total synthesis of dendrodolide L 12 using Keck asymmetric
allylation, Jacobsen’s hydrolytic kinetic resolution, Sharpless asym-
metric epoxidation, Mitsunobu reaction and ring closing metathesis
(RCM) reaction as the key steps.
O
O
OH
O
OH
8 dendrodolide H
9 dendrodolide I, R1 = OH; R2, R3 = H
10 dendrodolide J, R1, R3 = H, R2 = OH
11 dendrodolide K, R1 = H; R2, R3 = OH
O
O
2. Results and discussion
O
O
OMe
As outlined below, the retrosynthetic approach (Scheme 1) sug-
gests that the construction of the 12-membered macrolide could
be obtained using an RCM approach of compound 14. Compound
14 was envisaged from esterification of compound 15 and 16,
which may possibly be prepared from easily available butane-
1,4-diol 17 (route 1)/5-hexene-1-ol 18 (route 2) and propane-1,3-
diol 19, respectively.
To begin the synthesis, the proposed acid subunit 16 was pro-
duced (Scheme 2) from propane-1,3-diol 19, which was selectively
mono-protected as its PMB ether using a literature procedure.4
O
OH
O
OH
12 dendrodolide L
13 dendrodolide M
Figure 1. Structures of dendrodolides A–M.
Oxidation of the free hydroxyl group of 20 under PCC oxidation
conditions afforded the desired aldehyde, which was then
subjected to Keck asymmetric allylation5 conditions [(R)-BINOL,
Ti(OiPr4), allyl tributyltin, 4 Å MS, dry CH2Cl2, À78 °C to À20 °C]
to produce homoallylic alcohol 21 in 84% yield and with good
enantioselectivity (>96% ee, by HPLC).
⇑
The chiral secondary alcohol functionality in alcohol 21 was
protected as its TBS ether by treatment with imidazole/TBSCl in
Corresponding author. Tel.: +91 40 2719 1887; fax: +91 40 2716 0512.
E-mail address: saibal@iict.res.in (S. Das).
http://dx.doi.org/10.1016/j.tetasy.2016.02.007
0957-4166/Ó 2016 Elsevier Ltd. All rights reserved.
Please cite this article in press as: Bujaranipalli, S.; Das, S. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.007

2
S. Bujaranipalli, S. Das / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
OMOM
b
a
O
OH
OH
HO
BnO
24
17
25
O
O
OEt
c
d
f
OH
O
OTBS
BnO
BnO
O
OH
OH
14
O
26
28
12
O
O
e
OH
OTs
BnO
BnO
O
OTBS
OMOM
27
+
HO
OH
OH
OH
15
16
TsO
+
+
g
OBn
OBn
O
OTs
Route 1
Route 2
29
29a
29b
OH
OH
HO
OH
HO
Scheme 3. Reagents and conditions: (a) NaH, BnBr, THF, 0 °C–rt, 1 h, 80.%, (b) (1)
(COCl)2, DMSO, TEA, CH2Cl2, À78 °C (2) Ph3P = CHCO2Et, benzene, reflux, 4 h, 91%
from two steps; (c) DIBAL-H, CH2Cl2, 0 °C–rt, 1 h, 92%; (d) (+)-DET, Ti(OiPr)4,
Cumene hydroperoxide, 4 Å MS, CH2Cl2, À20 °C, 12 h, 89%; (e) TsCl, TEA, CH2Cl2,
0 °C–rt, 3 h, 94%; (f) see Table 1; (g) LiAlH4, THF, 0 °C–rt, 30 min, 86%.
17
18
19
Scheme 1. Retrosynthetic analysis of dendrodolide 12.
b
a
OH
OH
OH
HO
PMBO
TEA in CH2Cl2. Regioselective reduction of epoxide 28 using
DIBAL-H7 in CH2Cl2 at À20 °C to room temperature gave a mixture
of fully reduced compound 29 in 22% yield, partially reduced com-
pound 29a in 16% yield and the undesired substituted tetrahydro-
furan (THF) derivative 29b in 40% yield instead of giving 23 as
reported. Compound 29a was then further reduced with LiAlH4
in THF to obtain 29 in 86% yield.
20
19
OTBS
c
PMBO
PMBO
22
21
The formation of the undesired furan compound 29b can be
attributed to the chelation of the aluminium, thus leading to the
thermodynamically more stable and more favored 5-exo-tet
cyclization which resulted in the cleavage of the benzyl ether after
forming the THF ring (Scheme 4). The cleavage of the epoxide can
be explained by Baldwin rules,8 in which 5-exo-tet is favored
where as 6-endo-tet is disfavored. Several attempts were made to
minimize the formation of compound 29b and to improve the yield
of the compound 29/29a (Table 1).
OTBS
O
OTBS
d
e
HO
HO
23
16
Scheme 2. Reagents and conditions: (a) PMBOH, Amberlyst-15 (cat.), CH2Cl2, 6 h,
75%; (b) (1) PCC, Celite, CH2Cl2, 0 °C–rt, 1 h; (2) (R)-BINOL, Ti(OiPr4), 4 Å molecular
sieves, allyl tributyltin, CH2Cl2, À78 °C then À20 °C, 6 h, 77% from two steps; (c)
TBSCl, imidazole, CH2Cl2, 0 °C–rt, 3 h, 96%; (d) DDQ, CH2Cl2: pH 7 buffer (9:1), 0 °C–
rt, 30 min, 82%; (e) TEMPO, BAIB, CH2Cl2/H2O (1:1), 0 °C–rt, 1 h, 76%.
δ+
O
Al
OTs
OTs
O
dichloromethane to give compound 22 in 96% yield. Removal of the
PMB group in compound 22 was successfully achieved using DDQ
in CH2Cl2/pH 7 buffer (9:1) to provide compound 23 in 82% yield.
The primary alcohol 23 was then oxidized to its acid under BAIB/
TEMPO in CH2Cl2/H2O (1:1) conditions to yield the expected acid
16 in 76% yield.
BnO
O
Al
5-exo-tet
favoured
Scheme 4. Proposed mechanism for tetrahydrofuran derivative formation.
Alcohol fragment 15 was synthesised via two different
approaches. In route 1 (Scheme 3), the butane-1,4-diol 17 was
selectively mono-protected as its benzyl ether using BnBr and
NaH in THF to afford 24 in 80% yield. Oxidation of the alcohol
was achieved under Swern oxidation conditions [(COCl)2, DMSO,
TEA, CH2Cl2, À78 °C] to afford the corresponding aldehyde, which
was further treated with (ethoxycarbonylmethylene)triph-
enylphosphorane for two carbon homologation in benzene under
reflux conditions to provide (E)-allyl ester 25 in 91% yield over
two steps. The E-geometry of the double bond was confirmed by
the coupling constant between the respective olefin protons
(J = 15.6 Hz).
Compound 25 was then treated with DIBAL-H in CH2Cl2 to pro-
vide allyl alcohol 26 in 92% yield. Exposure of compound 26 to
Sharpless asymmetric epoxidation conditions6 [(+)-DET, cumene
hydroperoxide, Ti(OiPr)4, CH2Cl2] afforded the desired epoxyalco-
hol 27 in 89% yield. The epoxy alcohol was then converted into
its corresponding, 2,3-epoxytosylate 28 in 94% yield using TsCl,
When the reaction was carried out at 0 °C–rt in hexane, only
16% of 29 was formed, whereas 29b was formed in 73% (entry 1,
Table 1) but when the reaction was carried out at lower tempera-
tures, only trace amounts of 29a and 29b were formed (entries 2
and 3) thus indicating the role of temperature. In THF, when the
reaction was carried out at 0 °C–rt, almost exclusive formation of
undesired 29b was observed (entry 4) whereas at lower tempera-
tures, only trace amounts of 29a and 29b were formed (entries 5
and 6). In CH2Cl2, at 0 °C–rt under a longer reaction time, 18% of
desired 29 and 77% of undesired 29b were obtained (entry 7). At
a lower temperature, a partially reduced compound 29a and the
undesired tetrahydrofuran compound 29b were formed in 68%
and 12% yields respectively (entry 8). However, when less equiva-
lents of DIBAL-H were used, a mixture of 29a and 29b was formed.
Increasing the equivalents of DIBALH from 1 to 2, an improvement
in the yield for the desired compound 29a was observed (entries 9
and 10).
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S. Bujaranipalli, S. Das / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
3
Table 1
Entry
Solvent
DIBAL-Ha
Temp (°C)
Time (h)
Yield, 29 (%)b
Yield, 29a (%)b
Yield, 29b (%)b
1
2
3
4
5
6
7
8
Hexane
Hexane
Hexane
THF
THF
THF
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
3
3
3
3
3
3
3
3
1
2
3
0–rt
À20
4
4
4
4
4
16
—
—
—
—
—
18
—
—
—
Trace
Trace
Trace
Trace
—
—
Trace
68
73
Trace
Trace
86
Trace
Trace
77
12
26
18
40
À78
0–rt
À20
À78
4
0–rt
12
1.5
4
4
12
À78
9
10
11
À20
43
76
16
À20
À20–rt
22
a
Molar equivalents of DIBAL-H used relative to 28.
Isolated yields after column chromatography.
b
a
OH
OTBS
OH
OBn
a
b
34
OBn
OBn
18
29
30
e
15
29
36
b
OTBS
OTBS
OH
d
d
c
O
OH
OBn
+
O
32
31
c
OBn
35
OTBS
OMOM
OH
OMOM
OH
OH
e
f
TBSO
HO
OBn
OBn
33
15
37
36a
Scheme 5. Reagents and conditions: (a) TBSCl, imidazole, CH2Cl2, 0 °C–rt, 3 h, 97%;
(b) H2, 10% Pd/C, EtOAc, 4 h, 94%; (c) (1) (COCl)2, DMSO, TEA, CH2Cl2, À78 °C; (2)
vinyl magnesium bromide, THF, 0 °C–rt, 30 min, 79% over two steps; (d) MOMCl,
DIPEA, CH2Cl2, 0 °C–rt, 10 h, 89%; (e) TBAF, THF, 0 °C–rt, 3 h, 90%.
g
36
Scheme 6. Reagents and conditions: (a) NaH, BnBr, THF, 0 °C–rt, 3 h, 95.%; (b) m-
CPBA, CH2Cl2, 0 °C–rt, 1 h, 96%; (c) (R,R)-Salen-CoIIIOAc (0.5 mol %), dist. H2O
(0.55 equiv), 0 °C–rt, 14 h, 43% for 36, 47% for 36a; (d) LiAlH4, THF, 0 °C–rt, 3 h, 89%;
(e) see Scheme 5; (f) TBSCl, imidazole, CH2Cl2, 0 °C–rt, 3 h, 91%; (g) (1) TsCl, TEA,
CH2Cl2, 0 °C–rt, 10 h; (2) TBAF, THF, 0 °C–rt, 6 h, 72% over two steps.
At this stage, alcohol 29 was protected as its TBS ether using
TBSCl/imidazole in CH2Cl2 to afford compound 30 in 97% yield.
The benzyl group was deprotected using Pd/C in EtOAc in the pres-
ence of hydrogen to afford primary alcohol 31 in 94% yield
(Scheme 5). This alcohol was oxidized under Swern conditions to
afford the corresponding aldehyde, which was subjected to
Grignard reaction with vinyl magnesium bromide to furnish the
desired diastereomeric alcohol 32 in 79% yield over two steps.
Compound 32 would be converted into keto functionality in a later
stage. The secondary alcohol present in olefinic compound 32 was
then protected as its MOM ether using MOMCl (50% in methyl
acetate)9 in the presence of Hunig’s base in CH2Cl2 to provide com-
pound 33 in 89% yield and subsequent removal of the silyl ether
with TBAF afforded the secondary alcohol 15 in 90% yield.
With both fragments 15 and 16 in hand, the coupling was
achieved using classical Mitsunobu conditions12 to obtain the cor-
responding desired ester 14 in 82% yield (Scheme 7). Treatment of
the ester with Grubbs second generation catalyst (5 mol %) under
dilute conditions in degassed CH2Cl2 under reflux conditions
OMOM
OMOM
Another route was explored for the synthesis of intermediate 15
(Scheme 6). Compound 5-hexene-1-ol 18 was protected as its ben-
zyl ether using BnBr, NaH in THF to afford 34 in 95% yield. It was
then subjected to epoxidation using m-CPBA in CH2Cl2 to furnish
epoxide 35 in 96% yield. Racemic epoxide 35 was resolved using
(R,R)-Salen-CoIIIOAc catalyst to provide the enantioenriched
(>96% ee, based on HPLC) epoxide 3610 in 43% yield along with diol
36a in 47%. Diol 36a was then converted into the required epoxide
36 in 3 steps by regioselective protection of the primary alcohol in
36a as its TBS ether using TBSCl/imidazole in CH2Cl2 followed by
conversion of the secondary alcohol to its tosyl derivative and
finally desilylation using TBAF to furnish the desired epoxide 36
in 78% over two steps. Reductive opening of epoxide 36 using
LiAlH4 in THF furnished the secondary alcohol 29 in 89% yield.11
Target compound 15 was prepared from compound 29 as dis-
cussed earlier in Scheme 5.
a
b
15 + 16
O
O
O
14
OTBS
O
O
OTBS
38
OH
c
d
O
O
O
OH
O
OH
39
12
Scheme 7. Reagents and conditions: (a) TPP, DIAD, toluene, 30 min, 82%; (b)
Grubbs II generation catalyst (5 mol %), CH2Cl2, reflux, 4 h, 79%; (c) 4 M HCl/THF
(1:1), 5 h, 78%; (d) (1) MnO2, CH2Cl2, rt, 3 h; (2) Pd/C, H2, EtOAc, 1 h, 76% over two
steps.
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S. Bujaranipalli, S. Das / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
furnished the desired lactone 38 in 79% yield as a mixture of
diastereomers. Acid catalyzed removal of MOM as well as TBS
groups using 4 M HCl in THF afforded 39 in 78% yield. The
secondary allylic alcohol in compound 39 was then oxidized to a
ketone with MnO2 in CH2Cl2, which was then subjected to hydro-
genation with Pd/C in the presence of hydrogen in EtOAc to furnish
the target molecule dendrodolide L in 76% over two steps. The
spectroscopic and analytical data of the synthesized target compound
were in agreement with the natural product. The specific rotation
[a]
27 = +4.6 (c 0.60, CHCl3; IR (neat): 3439, 3075, 2927, 1613,
D
1513, 1248, 1089, 1034, 819, 793 cmÀ1; (1H, 500 MHz): d 7.24 (d,
J = 8.6 Hz, 2H), 6.87 (d, J = 8.6 Hz, 2H), 5.87–5.78 (m, 1H), 5.12–
5.07 (m, 2H), 4.45 (s, 2H), 3.88–3.82 (m, 1H), 3.80 (s, 3H), 3.71–
3.66 (m, 1H), 3.63–3.58 (m, 1H), 2.89 (br s, 1H), 2.25–2.21 (m,
2H), 1.76–1.72 (m, 2H); (13C, 100 MHz): d 158.9, 134.6, 129.0,
117.2, 113.5, 72.6, 69.9, 68.1, 54.9, 41.6, 35.5; MS (ESI): m/z = 259
(M+Na)+; HRMS (ESI): calcd for C14H20O3Na (M+Na)+, 259.1304,
found 259.1300.
of compound 12 [a]
27 = +8.6 (c 0.2, CHCl3) was in agreement with
D
the reported value [
a]
27 = +10.7 (c 0.065, CHCl3).1
4.1.2. (R)-tert-Butyl((1-((4-methoxybenzyl)oxy)hex-5-en-3-yl)
oxy)dimethylsilane 22
D
To a solution of homoallylic compound 21 (1.27 g, 5.38 mmol)
in CH2Cl2 (15 mL) was added imidazole (1.1 g, 16.14 mmol) fol-
lowed by TBSCl (0.89 g, 5.91 mmol) at 0 °C and the reaction mix-
ture was stirred for 3 h. After completion of the reaction, it was
diluted with CH2Cl2, washed with H2O (20 mL), brine (20 mL),
dried over Na2SO4, filtered and concentrated. The residue was puri-
fied by silica gel column chromatography (Hexanes/EtOAc) to give
3. Conclusion
In conclusion, we have accomplished the stereoselective total
synthesis of dendrodolide L 12 by employing Keck asymmetric
allylation, Jacobsen’s hydrolytic kinetic resolution, Sharpless asym-
metric epoxidation, Mitsunobu reaction and RCM reaction as the
key steps with an overall yield of 19.7% starting from enantiopure
epoxide 36.
22 as a colourless liquid (1.8 g, 96%). [
a]
27 = À17.4 (c 1.9, CHCl3); IR
D
(neat): 2953, 2931, 2857, 1613, 1513, 1465, 1363, 1249, 1094,
1040, 912, 836, 774 cmÀ1; (1H, 500 MHz): d 7.27–7.24 (m, 2H),
6.89–6.86 (m, 2H), 5.85–5.75 (m, 1H), 5.05–5.00 (m, 2H), 4.44 (d,
J = 11.4 Hz, 1H), 4.38 (d, J = 11.4 Hz, 1H), 3.91–3.86 (m, 1H), 3.80
(s, 3H), 3.51 (t, J = 6.7 Hz, 2H), 2.27–2.18 (m, 2H), 1.81–1.74 (m,
1H), 1.72–1.65 (m, 1H), 1.60–1.57 (m, 1H), 0.88 (s, 9H), 0.04 (d,
J = 5.4 Hz, 6H); (13C, 100 MHz): d 159.0, 134.9, 130.6, 129.2,
116.9, 113.7, 72.5, 68.9, 66.7, 55.2, 42.2, 36.6, 25.8, 18.0, À4.3,
À4.7; MS (ESI): m/z = 373 (M+Na)+. HRMS (ESI): calcd for
4. Experimental
4.1. General
Reactions were conducted under N2 in anhydrous solvents such
as CH2Cl2, DMSO, and THF. Evaporation of the solvents was per-
formed at a reduced pressure on a Buchi rotary evaporator. 1H
and 13C NMR spectra of samples in CDCl3 were recorded on Varian
FT-400 MHz, Varian FT-500 MHz and Bruker UXNMR FT-300 MHz
(Avance) spectrometers at ambient temperature. Chemical shifts
d are reported relative to TMS (d = 0.0) as an internal standard. FTIR
spectra were recorded on a Perkin–Elmer 683 infrared spectrome-
ter; neat or as thin films in KBr. Optical rotations were measured
on an Anton Paar MLP 200 modular circular digital polarimeter
using a 2 mL cell with a path length of 1 dm. Mass spectra were
recorded EI conditions at 70 eV on ES-MSD (Agilent technologies)
spectrometers. Column chromatography was performed on silica
gel (60–120 mesh) packed in glass columns.
C
20H34O3NaSi (M+Na)+, 373.2169, found 373.2168.
4.1.3. (R)-3-((tert-Butyldimethylsilyl)oxy)hex-5-en-1-ol 23
Compound 22 (1.67 g, 4.77 mmol) was taken up in CH2Cl2 after
which pH 7 buffer (20 mL, 9:1) was added. Next, DDQ (1.3 g,
5.72 mmol) was added in one portion at 0 °C. After being stirred
for 30 min at room temperature, the reaction mixture was
quenched with solid NaHCO3 and stirring was continued for
30 min and then filtered. The filtrate was washed with H2O
(10 mL), brine (10 mL), dried over Na2SO4, filtered and concen-
trated. The residue was purified by silica gel column chromatogra-
phy (Hexanes/EtOAc) to give 23 as a colourless liquid (0.9 g, 82%).
4.1.1. (R)-1-((4-Methoxybenzyl)oxy)hex-5-en-3-ol 21
[
a
]
27 = À28.8 (c 1.24, CHCl3); IR (neat): 3356, 2932, 2858, 1469,
D
To a mixture of 20 (3 g, 15.31 mmol) and Celite in CH2Cl2
(40 mL) was added pyridinium chlorochromate (4.45 g,
22.96 mmol) portionwise at 0 °C and after being stirred for 1 h,
the crude reaction mixture was filtered through a small plug of sil-
ica and the residue was washed with CH2Cl2. The filtrate was con-
centrated under reduced pressure to afford the aldehyde (2.73 g)
which was used directly in the next step.
1363, 1255, 1074, 912, 836, 775 cmÀ1; (1H, 500 MHz): d 5.82–
5.72 (m, 1H), 5.11–5.04 (m, 2H), 4.00–3.95 (m, 1H), 3.86–3.80
(m, 1H), 3.75–3.69 (m, 1H), 2.34 (br s, 1H), 2.32–2.29 (m, 2H),
1.85–1.78 (m, 1H), 1.70–1.63 (m, 1H), 0.9 (s, 9H), 0.1 (d,
J = 4.7 Hz, 6H); (13C, 100 MHz): d 134.4, 117.2, 71.1, 60.0, 41.6,
37.6, 25.7, 17.9, À4.4, À4.8; MS (ESI): m/z = 253 (M+Na)+, 231 (M
+H)+; HRMS (ESI): calcd for C12H27O2Si (M+H)+, 231.1774, found
231.1772.
A dry two neck round bottomed flask was charged with (R)-
BINOL (0.4 g, 1.4 mmol) and vacuum-flame-dried powdered
molecular sieves (4 Å). One neck was fitted with a reflux condenser
and the other was closed with a rubber septum. Dry CH2Cl2
(10 mL) was added followed by titanium (IV) isopropoxide
(0.29 mL, 1.4 mmol) by syringe, resulting in an immediate colour
change to deep red, then refluxed for approximately 1 h. The reac-
tion mixture was cooled to room temperature and then the alde-
hyde (2.73 g, 14.07 mmol) in CH2Cl2 (30 mL) was added dropwise
and stirred for 5 min. The reaction mixture was then cooled to
À78 °C, and allyltributylstannane (4.75 mL, 15.48 mmol) was
added by syringe. The resulting mixture was stirred for 30 min
and then transferred to a freezer at À20 °C and allowed to stand
for 6 h. The reaction mixture was filtered over a small pad of Celite
and concentrated. The residue was purified by silica gel column
chromatography (Hexanes/EtOAc) to give 21 as a light yellow oil
4.1.4. (R)-3-((tert-Butyldimethylsilyl)oxy)hex-5-enoic acid 16
Compound 23 (0.76 g, 3.3 mmol) was taken up in CH2Cl2/H2O
(8 mL, 1:1) and the reaction mixture was cooled to 0 °C, then
TEMPO (144 mg, 0.92 mmol), BAIB (3.19 g, 9.91 mmol) was added
sequentially. After being stirred for 1 h, the reaction mixture was
diluted with CH2Cl2, and quenched with a saturated solution of
hypo. The mixture was extracted with CH2Cl2 (2 Â 15 mL). The
combined organic extracts were washed with H2O (10 mL), brine
(10 mL), dried over Na2SO4, and concentrated under reduced pres-
sure. The residue was purified by silica gel column chromatogra-
phy (Hexanes/EtOAc) to give 16 as a colourless oil (0.61 g, 76%).
[a]
27 = À23.4 (c 2.0, CHCl3); IR (neat): 2928, 2876, 1713, 1460,
D
1255, 1092, 835, 773 cmÀ1; (1H, 400 MHz): d 5.87–5.73 (m, 1H),
(2.79 g, 77% over two steps). [a]
27 = +3.6 (c 1.6, CHCl3), lit.5b
D
5.13–5.05 (m, 2H), 4.23–4.16 (m, 1H), 2.55–2.43 (m, 2H),
Please cite this article in press as: Bujaranipalli, S.; Das, S. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.007

S. Bujaranipalli, S. Das / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
5
2.32–2.28 (m, 2H), 0.88 (s, 9H), 0.08 (d, J = 8.3 Hz, 6H); (13C, 100 MHz):
d 177.3, 133.6, 117.9, 68.7, 41.8, 41.7, 25.6, 17.8, À4.6, À5.0;
MS (ESI): m/z = 267 (M+Na)+; HRMS (ESI): calcd for C12H24O3NaSi
(M+Na)+, 267.1386, found 267.1381.
4.1.8. (R)-6-(Benzyloxy)-2-hydroxyhexyl 4-methylbenzene
sulfonate 29a
27 = +9.5 (c 0.64, CHCl3); IR (neat): 3421, 2923, 2854, 1727,
[a]
D
1598, 1456, 1358, 1175, 1091, 973, 772 cmÀ1; (1H, 500 MHz): d
7.72 (d, J = 8.3 Hz, 2H), 7.31–7.20 (m, 7H), 4.41 (s, 2H), 3.95 (dd,
J = 9.5, 2.6 Hz, 1H), 3.83–3.78 (m, 1H), 3.77–3.70 (m, 1H), 3.38 (t,
J = 6.2 Hz, 2H), 2.38 (s, 3H), 1.57–1.49 (m, 3H), 1.40–1.34 (m,
3H); (13C, 100 MHz): d 145.0, 138.4, 132.6, 129.9, 128.3, 127.9,
127.6, 127.5, 73.8, 72.9, 69.9, 69.3, 32.3, 31.9, 22.6, 21.6; MS
(ESI): m/z = 401 (M+Na)+; HRMS (ESI): calcd for C20H27O5S (M
+H)+, 379.1574, found 379.1580.
4.1.5. ((2S,3S)-3-(3-(Benzyloxy)propyl)oxiran-2-yl) methanol 27
To a suspension of flame dried 4 Å molecular sieves in dry
CH2Cl2 (50 mL) at À20 °C, was added (+)-DET (1.26 mL, 6.79 mmol)
followed by Ti(OiPr)4 (1.21 mL, 4.07 mmol). After stirring for
30 min, cumene hydroperoxide (9.68 mL, 80% solution,
50.97 mmol) was added dropwise. The reaction mixture was stir-
red for a further 30 min at the same temperature before the addi-
tion of 26 (7.0 g, 33.98 mmol) in CH2Cl2 (50 mL). The reaction
mixture was stirred at À20 °C for 12 h, then warmed up to 0 °C,
and quenched with an aq. basic solution (0.695 g of NaOH in
6.95 mL of brine). The reaction mixture was stirred for 1 h before
being filtered through a small bed of Celite and washed with CH2-
Cl2. The filtrate was concentrated under reduced pressure. The resi-
due was purified by column chromatography to afford 27 (6.71 g,
4.1.9. (S)-2-Hydroxy-2-((R)-tetrahydrofuran-2-yl)ethyl
4-methylbenzenesulfonate 29b
[
a
]
27 = À12.1 (c 1.4, CHCl3); IR (neat): 3446, 2924, 1633, 1357,
D
1302, 1174, 1082, 772 cmÀ1; (1H, 500 MHz): d 7.80 (d, J = 8.3 Hz,
2H), 7.35 (d, J = 8.0 Hz, 2H), 4.20 (dd, J = 10.3, 3.0 Hz, 1H), 4.02
(dd, J = 10.3, 6.7 Hz, 1H), 3.83–3.75 (m, 3H), 3.74–3.68 (m, 1H),
2.45 (s, 3H), 1.98–1.78 (m, 4H); (13C, 100 MHz): d 144.9, 132.5,
129.8, 127.9, 78.4, 71.7, 71.1, 68.5, 27.1, 25.5, 21.6; MS (ESI):
m/z = 309 (M+Na)+, 304 (M+NH4)+; HRMS (ESI): calcd for
89%) as a light yellow liquid. [
a
]
27 = À27.0 (c 1.8, CHCl3), lit.6b[-
D
a]
D = À29, CHCl3; IR (neat): 3330, 2961, 2857, 1470, 1427, 1378,
1219, 1107, 1007, 703 cmÀ1; (1H, 500 MHz): d 7.37–7.26 (m, 5H),
4.50 (s, 2H), 3.85 (dd, J = 12.5, 2.7 Hz, 1H), 3.59 (dd, J = 12.5,
4.4 Hz, 1H), 3.54–3.48 (m, 2H), 2.98–2.95 (m, 1H), 2.92–2.89 (m,
1H), 1.81–1.61 (m, 4H); (13C, 125 MHz): d 138.2, 128.3, 127.6,
127.5, 72.8, 69.5, 61.6, 58.4, 55.6, 28.3, 26.0; MS (ESI): m/z = 245
(M+Na)+; HRMS (ESI): calcd for C13H18O3Na (M+Na)+, 245.1148,
found 245.1159.
C
13H18O5SNa (M+Na)+, 309.0751, found 309.0767.
4.1.10. (7S)-7-((tert-Butyldimethylsilyl)oxy)oct-1-en-3-ol 32
At first, DMSO (1.04 mL, 14.65 mmol) was added at À78 °C to a
solution of oxalyl chloride (0.96 mL, 10.99 mmol) in CH2Cl2
(20 mL), and the resulting solution was stirred for 15 min. A solu-
tion of the alcohol 31 (1.7 g, 7.32 mmol) in CH2Cl2 (15 mL), was
then added dropwise at À78 °C over 15 min. After the solution
had been stirred for an additional 30 min, Et3N (6.12 mL,
43.96 mmol) was added and the reaction mixture was allowed to
warm to room temperature and stirred for 1 h. The reaction mix-
ture was poured into ice cooled water and extracted with CH2Cl2.
The organic layer was washed with brine, dried over Na2SO4, and
concentrated under reduced pressure to give a crude aldehyde
(1.52 g) which was directly used for next step without further
purification.
4.1.6. ((2S,3S)-3-(3-(Benzyloxy)propyl)oxiran-2-yl)methyl
4-methylbenzenesulfonate 28
To a solution of compound 27 (3 g, 13.51 mmol) in anhydrous
CH2Cl2 (30 mL) was added Et3N (5.6 mL, 40.54 mmol) at 0 °C fol-
lowed by tosyl chloride (2.83 g, 14.86 mmol). After the solution
had been stirred for 3 h at room temperature, volatiles were
removed under vacuo. The residue was purified by silica gel col-
umn chromatography (Hexanes/EtOAc) to give 28 (4.77 g, 94%) as
a light yellow liquid. [
a]
27 = À23.8 (c 1.3, CHCl3); IR (neat): 2931,
To a solution of the aldehyde (1.52 g, 6.6 mmol) in anhydrous
THF (10 mL) was added vinyl magnesium bromide (0.7 M in THF,
10.35 mL, 7.27 mmol) at 0 °C. The reaction mixture was stirred
for 30 min at room temperature, then quenched with saturated
solution of NH4Cl at 0 °C and extracted with EtOAc (2 Â 15 mL).
The combined organic extracts were washed with brine and dried
over Na2SO4, filtered and concentrated under reduced pressure.
The residue was purified by silica gel column chromatography
(Hexanes/EtOAc) to give 32 as a slightly yellow colour liquid
D
1598, 1453, 1364, 1177, 1098, 962, 817, 772 cmÀ1
;
(1H,
500 MHz): d 7.81–7.77 (m, 2H), 7.36–7.28 (m, 7H), 4.48 (s, 2H),
4.15 (dd, J = 11.4, 3.8 Hz, 1H), 3.95 (dd, J = 11.4, 5.4 Hz, 1H), 3.52–
3.40 (m, 2H), 2.98–2.93 (m, 1H), 2.83–2.80 (m, 1H), 2.44 (s, 3H),
1.76–1.60 (m, 4H); (13C, 100 MHz): d 145.0, 138.2, 132.6, 129.8,
128.3, 127.8, 127.5, 72.8, 70.0, 69.3, 56.4, 54.5, 28.1, 25.9, 21.6;
MS (ESI): m/z = 399 (M+Na)+; HRMS (ESI): calcd for C20H24O5S (M
+H)+, 377.1417, found 377.1408.
(1.49 g, 79% over two steps). [a]
27 = +6.5 (c 1.5, CHCl3); IR (neat):
D
4.1.7. (S)-6-(Benzyloxy)hexan-2-ol 29
3419, 2936, 2880, 1461, 1378, 1248, 1039 cmÀ1; (1H, 500 MHz):
d 5.90–5.82 (m, 1H), 5.22 (dt, J = 17.2, 1.3 Hz, 1H), 5.10 (dt,
J = 10.5, 1.2 Hz, 1H), 4.13–4.07 (m, 1H), 3.82–3.75 (m, 1H), 1.59–
1.30 (m, 6H), 1.12 (d, J = 5.9 Hz, 3H), 0.88 (s, 9H), 0.05 (s, 6H);
To a solution of compound 28 (2.61 g, 6.94 mmol) in anhydrous
CH2Cl2 (25 mL) was added DIBAL-H (25% in toluene, 11.8 mL,
20.84 mmol) dropwise at À20 °C. After the solution had been stir-
red for 12 h at room temperature, it was cooled to 0 °C, and then
treated with a saturated solution of sodium potassium tartarate
and allowed to stir for 2 h. The organic layer was separated and
the aqueous layer was extracted with CH2Cl2 (3 Â 20 mL). The
combined organic layers were dried over anhydrous Na2SO4 and
the solvent was removed in vacuo. The residue was purified by sil-
ica gel column chromatography (Hexanes/EtOAc) to afford 29
(
13C, 100 MHz): d 141.1, 114.6, 114.5, 73.2, 73.1, 68.5, 68.4, 39.5,
39.4, 37.0, 36.9, 25.8, 23.7, 21.6, 21.4, 18.1, À4.4, À4.7; MS (ESI):
m/z = 281 (M+Na)+, 259 (M+H)+; HRMS (ESI): calcd for C14H31O2Si
(M+H)+, 259.2087, found 233.2083.
4.1.11. (9S)-9,11,11,12,12-Pentamethyl-5-vinyl-2,4,10-trioxa-
11-silatridecane 33
(317 mg, 22%), 29a (410 mg, 16%), 29b (800 mg, 40%). [
a]
27 = +7.9
To a stirred solution of 32 (0.9 g, 3.48 mmol) in anhydrous
CH2Cl2 (10 mL) was added diisopropylethylamine (3.0 mL,
17.44 mmol) at 0 °C followed by MOMCl (50% solution in methyl
acetate, 0.61 mL, 3.83 mmol). Stirring was continued for 10 h at
room temperature, and then quenched with water (5 mL). The
organic layer was separated and the aqueous layer was extracted
with CH2Cl2 (2 Â 10 mL). The combined organic layers were dried
over anhydrous Na2SO4 and the solvent was removed in vacuo.
D
(c 2.0, CHCl3); IR (neat): 3356, 2940, 1657, 1466, 1416, 1375,
1300 cmÀ1; (1H, 500 MHz): d 7.39–7.27 (m, 5H), 4.51 (s, 2H),
3.83–3.77 (m, 1H), 3.48 (t, J = 6.5 Hz, 2H), 1.68–1.58 (m, 2H),
1.52–1.40 (m, 4H), 1.18 (d, J = 6.2 Hz, 3H); (13C, 100 MHz): d
138.4, 128.2, 127.5, 127.4, 72.8, 70.1, 67.7, 38.9, 29.5, 23.3, 22.3;
MS (ESI): m/z = 231 (M+Na)+; HRMS (ESI): calcd for C13H21O2 (M
+H)+, 209.1536, found 209.1533.
Please cite this article in press as: Bujaranipalli, S.; Das, S. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.007

6
S. Bujaranipalli, S. Das / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
The residue was purified by silica gel column chromatography
(m, 1H), 5.08–4.84 (m, 1H), 4.71–4.63 (m, 1H), 4.53–4.45 (m,
1H), 4.16–3.94 (m, 2H), 3.35–3.31 (m, 3H), 2.68–2.55 (m, 1H),
2.50–2.33 (m, 3H), 1.58–1.27 (m, 6H), 1.23–1.14 (m, 3H), 0.91–
0.87 (m, 9H), 0.11–0.05 (m, 6H); (13C, 100 MHz): d 170.2, 170.1,
133.5, 131.6, 130.5, 129.7, 93.8, 93.58, 93.51, 76.4, 75.7, 72.3,
70.6, 69.9, 68.7, 55.2, 45.7, 42.7, 42.6, 32.8, 30.9, 30.8, 29.1,
25.77, 25.73, 20.2, 19.4, 18.1, 18.0, 17.2, 16.8, À4.7, À4.8, À4.9.;
MS (ESI): m/z = 409 (M+Na)+; HRMS (ESI): calcd for C20H39O5Si
(M+H)+, 387.2561, found 387.2545.
(Hexanes/EtOAc) to afford 33 (0.93 g, 89%) as a colourless liquid.
[a]
27 = +8.9 (c 1.0, CHCl3); IR (neat): 2932, 2858, 1466, 1375,
D
1254, 1152, 1099, 1039, 922, 835, 774 cmÀ1; (1H, 300 MHz): d
5.73–5.59 (m, 1H), 5.23–5.15 (m, 2H), 4.71 (d, J = 6.7 Hz, 1H),
4.53 (dd, J = 6.7, 1.1 Hz, 1H), 4.02–3.93 (m, 1H), 3.83–3.72 (m,
1H), 3.38 (s, 3H), 1.60–1.36 (m, 6H), 1.12 (d, J = 6.0 Hz, 3H), 0.88
(s, 9H), 0.04 (s, 6H); (13C, 100 MHz): d 138.3, 117.1, 117.0, 96.3,
93.6, 93.5, 68.4, 55.3, 39.5, 35.45, 35.43, 29.7, 29.6, 25.8, 23.8,
21.8, 21.7, 18.1, À4.4, À4.7; MS (ESI): m/z = 325 (M+Na)+;
HRMS (ESI): calcd for C16H35O3Si Na (M+Na)+, 325.2169, found
325.2162.
4.1.15. (4R,12R)-4,8-Dihydroxy-12-methyloxacyclododec-6-en-
2-one 39
A solution of compound 38 (100 mg, 0.259 mmol) in THF (5 mL)
was treated with 4 M HCl (5 mL) and allowed to stir for 5 h, after
which EtOAc (5 mL) and H2O (5 mL) were added. The layers were
separated and the aqueous phase was extracted with EtOAc
(2 Â 5 mL). The combined organic portion was washed with satu-
rated sodium bicarbonate solution (10 mL) followed by brine solu-
tion (10 mL), dried over Na2SO4, and then concentrated under
reduced pressure. The residue was purified by silica gel column
chromatography (Hexanes/EtOAc) to give 39 (46 mg, 78%) as a
4.1.12. (2S)-6-(Methoxymethoxy)oct-7-en-2-ol 15
To a stirred solution of 33 (0.8 g, 2.64 mmol) in THF (10 mL) was
added TBAF (2.91 mL, 1 M in THF, 2.91 mmol) and stirred for 3 h at
room temperature. It was then quenched with water (10 mL). The
organic layer was separated and the aqueous layer was extracted
with ethyl acetate (3 Â 20 mL). The combined organic layers were
dried over anhydrous Na2SO4 and the solvent was removed in
vacuo. The residue was purified by silica gel column chromatogra-
phy (Hexanes/EtOAc) to afford 15 (0.44 g, 90%) as a colourless liq-
colourless liquid. [
a]
27 = À8.2 (c 0.96, CHCl3); IR (neat): 3400,
D
uid. [
a]
27 = +4.6 (c 0.4, CHCl3); IR (neat): 3424, 2937, 1218, 1152,
2925, 2853, 1722, 1451, 1377, 1268, 1038, 722 cmÀ1
;
(1H,
D
1099, 1036, 924, 772 cmÀ1; (1H, 300 MHz): d 5.74–5.60 (m, 1H),
5.25–5.16 (m, 2H), 4.71 (d, J = 6.7 Hz, 1H), 4.54 (d, J = 6.7 Hz, 1H),
4.04–3.95 (m, 1H), 3.85–3.76 (m, 1H), 3.38 (s, 3H), 1.66–1.38 (m,
6H), 1.19 (d, J = 6.0 Hz, 3H); (13C, 100 MHz): d 138.2, 117.1, 93.6,
77.2, 67.8, 55.3, 39.0, 35.2, 23.4, 21.4; MS (ESI): m/z = 211 (M
+Na)+; HRMS (ESI): calcd for C10H20O3Na (M+Na)+, 211.1304, found
211.1301.
500 MHz): d 5.78–5.60 (m, 1H), 5.56–5.38 (m, 1H), 5.08–4.86 (m,
1H), 4.21–4.01 (m, 2H), 2.63–2.15 (m, 4H), 1.78–1.37 (m, 6H),
1.16–1.10 (m, 1H); (13C, 125 MHz): d 172.9, 172.3, 172.2, 135.7,
135.1, 134.6, 128.3, 127.7, 127.2, 126.9, 126.3, 126.0, 78.0, 73.7,
72.0, 71.8, 70.9, 70.2, 69.7, 68.7, 68.5, 65.3, 61.8, 42.4, 41.4, 41.0,
34.6, 34.8, 33.7, 32.9, 31.8, 31.2, 30.9, 23.3, 22.5, 22.0, 19.4, 18.2,
17.8, 17.5, 17.4, 16.6, 15.2, 14.0; MS (ESI): m/z = 229 (M+H)+; HRMS
(ESI): calcd for C12H21O4 (M+H)+, 229.1199, found 229.1197.
4.1.13. (3R)-(2R)-6-(Methoxymethoxy)oct-7-en-2-yl 3-((tert-
butyldimethylsilyl)oxy)hex-5-enoate 14
4.1.16. Dendrodolide L 12
Triphenyl phosphine (0.28 g, 4.24 mmol) and DIAD (0.84 mL,
4.24 mmol) were added sequentially to a stirred solution of acid
16 (0.52 g, 2.12 mmol) and alcohol 15 (0.4 g, 2.12 mmol) in dry
toluene (5 mL). After 30 min, EtOAc (5 mL) and H2O (5 mL) were
added. The layers were separated and the aqueous phase extracted
with EtOAc (. 10 mL). The combined organic portions were washed
with brine solution (20 mL), dried over Na2SO4 and concentrated
under reduced pressure. The residue was purified by silica gel col-
umn chromatography (Hexanes/EtOAc) to afford diene compound
At first, MnO2 (76 mg, 0.877 mmol) was added to a stirred solu-
tion of 39 (40 mg, 0.17 mmol) in CH2Cl2 at room temperature. After
the mixture had been stirred for 3 h, the solvent was evaporated
and the crude reaction mixture was filtered through a small pad
of silica gel and concentrated to give a keto compound (33 mg)
as a pale yellow liquid, which was used for the next step without
further characterization.
To a stirred solution of ketone (33 mg, 0.146 mmol) in EtOAc
(2 mL) was added a catalytic amount of 10% Pd/C and the reaction
mixture was stirred for 1 h under a hydrogen atmosphere. The
reaction mixture was filtered through a small plug of Celite and
washed with EtOAc (2 Â 5 mL). The combined organic layers were
concentrated under reduced pressure and the residue was purified
by silica gel column chromatography (Hexanes/EtOAc) to give the
title compound dendrodolide L (12) (30 mg, 76% over two steps).
14 (0.72 g, 82%) as a light yellow liquid. [
a]
27 = À20.1 (c 0.74,
D
CHCl3); IR (neat): 2933, 2858, 1733, 1464, 1379, 1254, 1175,
1096, 1040, 920, 836, 776 cmÀ1; (1H, 500 MHz): d 5.86–5.75 (m,
1H), 5.71–5.60 (m, 1H), 5.22–5.16 (m, 2H), 5.09–5.04 (m, 2H),
4.91–4.84 (m, 1H), 4.7 (d, J = 6.7 Hz, 1H), 4.53 (d, J = 6.5 Hz, 1H),
4.22–4.16 (m, 1H), 4.00–3.94 (m, 1H), 3.37 (s, 2H), 2.45–2.40 (m,
2H), 2.32–2.24 (m, 2H), 1.64–1.58 (m, 2H), 1.54–1.36 (m, 4H),
1.21 (d, J = 6.1 Hz, 3H), 0.87 (s, 9H), 0.06 (d, J = 11.4 Hz, 6H); (13C,
75 MHz): d 171.2, 138.1, 134.2, 117.5, 117.2, 93.6, 70.8, 68.7,
55.3, 42.3, 41.9, 35.6, 35.1, 25.7, 21.1, 19.7, 17.9, À4.5, À4.8; MS
(ESI): m/z = 437 (M+Na)+; HRMS (ESI): calcd for C22H43O5Si (M
+H)+, 415.2874, found 415.2858.
[a]
27 = +8.6 (c 0.2, CHCl3); IR (KBr): 3380, 2952, 2872, 1716,
D
1251, 1169, 1062, 980 cmÀ1; (1H, 500 MHz): d 5.23–5.17 (m, 1H),
4.04–3.98 (m, 1H), 2.90 (ddd, J = 16.1, 8.8, 3.5 Hz, 1H), 2.78 (ddd,
J = 12.8, 9.1, 3.3 Hz, 1H), 2.73 (dd, J = 14.0, 3.5 Hz, 1H), 2.49 (dd,
J = 14.0, 7.4 Hz, 1H), 2.25–2.18 (m, 2H), 1.95–1.86 (m, 2H), 1.81–
1.75 (m, 1H), 1.73–1.51 (m, 4H), 1.33–1.27 (m, 1H), 1.23 (d,
J = 6.5 Hz, 3H); (13C, 125 MHz): d 211.3, 170.5, 70.9, 67.3, 41.9,
40.5, 39.8, 34.1, 31.4, 29.6, 20.1, 18.1, 17.5; MS (ESI): m/z = 251
(M+Na)+; HRMS (ESI): calcd for C12H20O4Na (M+Na)+, 251.1254,
found 251.1247.
4.1.14. (4R,12R)-4-((tert-Butyldimethylsilyl)oxy)-8-
(methoxymethoxy)-12-methyloxacyclododec-6-en-2-one 38
A solution of compound 14 (100 mg, 0.24 mmol) in degassed
CH2Cl2 (81 mL) was treated with 5% mol of Grubbs 2nd generation
catalyst and stirred at reflux for 4 h. The reaction mixture was fil-
tered through a pad of SiO2, washed with CH2Cl2 and concentrated
under reduced pressure. Purification by silica gel column chro-
Acknowledgements
S.B. thanks UGC, New Delhi for the award of fellowship. All the
authors thank CSIR, New Delhi, India for financial support as part of
XII Five Year plan programme under title ORIGIN (CSC-0108).
matography (Hexanes/EtOAc) gave 38 (73 mg, 79%). [
a]
27 = À1.3
D
(c 0.48, CHCl3); (1H, 500 MHz): d 5.64 À5.53 (m, 1H), 5.31–5.18
Please cite this article in press as: Bujaranipalli, S.; Das, S. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.007

S. Bujaranipalli, S. Das / Tetrahedron: Asymmetry xxx (2016) xxx–xxx
7
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(d) HPLC Method: CHIRAL PAK IC 250 Â 4.6 mm 5
l (column), 3% IPA in hexane
(mobile phase), flow rate 1 mL/min, tR: 10.0 min (major enantiomer) and
10.6 min (minor enantiomer).
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(c) HPLC method: CHIRAL PAK IC 250 Â 4.6 mm 5
l (column), 5% IPA in hexane
(mobile phase), flow rate 1 mL/min, tR: 13.1 min (major enantiomer) and
11.4 min (minor enantiomer).
Please cite this article in press as: Bujaranipalli, S.; Das, S. Tetrahedron: Asymmetry (2016), http://dx.doi.org/10.1016/j.tetasy.2016.02.007