Efficient metathesis route to the B-ring of eleutherobin and other medium-sized cyclic ethers

Article abstract of DOI:10.1016/j.tet.2005.05.045

A short and efficient RCM route is reported for the synthesis of the B-ring of eleutherobin and other medium-sized cyclic ethers from readily available 1,2,5,6-diisopropylidene-d-glucose. This strategy is successfully extended to the synthesis of a few bicyclic ethers, which may find applications in the synthesis of novel bicyclic nucleosides.

Full text of DOI:10.1016/j.tet.2005.05.045

Tetrahedron 61 (2005) 7461–7469
Efficient metathesis route to the B-ring of eleutherobin
and other medium-sized cyclic ethers
*
Krishna P. Kaliappan and Nirmal Kumar
Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
Received 8 March 2005; revised 3 May 2005; accepted 19 May 2005
Available online 14 June 2005
Dedicated to Professor K. K. Balasubramanian on the occasion of his 65th birthday
Abstract—A short and efficient RCM route is reported for the synthesis of the B-ring of eleutherobin and other medium-sized cyclic ethers
from readily available 1,2,5,6-diisopropylidene-D-glucose. This strategy is successfully extended to the synthesis of a few bicyclic ethers,
which may find applications in the synthesis of novel bicyclic nucleosides.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
The success of the anti-cancer drug taxolw (paclitaxel) has
stimulated an intensive search for other drugs that operate
by the same mode of action.1 Successful examples, isolated
from natural sources, include discodermolide,2 the epo-
thilones,3 laulimalide4 and eleutherobin.5 Among them, the
latest discovery, eleutherobin 16 was isolated from a marine
soft-coral found in the Indian ocean and found to be closely
related to sarcodictyins 4, 5,7 valdivone 68 and eleuthesides
(Fig. 1).9 Later, several related congeners of eleutherobin
were isolated10 from the Caribbean soft coral Erythropo-
dium caribaeorum. Eleutherobin has been shown to possess
potent cytotoxicity with an IC50 of 10.7 nM, which is
comparable to taxol. As eleutherobin was only available in
scarce amounts from natural sources, chemical syntheses
have become important to study its biological properties
further. These prompted synthetic chemists to develop new
strategies11 to synthesize eleutherobin and their sustained
efforts have culminated in two total syntheses.12–14
A strategy for the synthesis of eleutherobin was designed
based on the retrosynthetic analysis involving metathesis
reaction as the key step and is shown in Scheme 1.
With the discovery of air stable Grubbs’ first16 and second
generation catalysts,17 the last decade has witnessed a
meteoric rise in the utility of the ring closing metathesis
reaction (RCM)18 in the formation of several types of
alkenes, carbo- and heterocycles. The reaction tolerates a
wide range of functional groups and with these reliable and
practical catalysts, the RCM reaction has been widely used
in the synthesis of a number of cyclic natural and unnatural
products. However, construction of medium-size rings by
ring closing metathesis has often been hampered by entropic
and thermodynamic instability factors.19 Nevertheless, there
are quite a few successful reports of constructing medium
size rings by ring closing metathesis reaction.20 Encouraged
by these reports, we envisaged that a RCM reaction would
be an ideal key reaction to construct these natural product
skeletons. Eleutherobin possesses three double bonds,
which could be formed as a result of a RCM reaction.
However, only disconnection of the B-ring double bond will
simplify the target molecule leading to precursor C, which
then can be further disconnected to the bicyclic enone 8 and
the epoxide 9 (Scheme 1).
In continuation of our interest in the development of simple
and efficient routes to the syntheses of tubulin binding anti-
cancer agents, we became interested in the synthesis of
eleutherobin and its congeners.15
From this retrosynthetic modus operandi, it is clear that the
success of our synthetic route to eleutherobin depends on
the construction of the B-ring with the strategically placed
double bond. Furthermore, there are several natural
products, which have nine-membered cyclic ethers as their
Keywords: Eleutherobin; Cyclic ethers; Ring closing metathesis; Grubbs’
catalyst; Bicyclic nucleosides.
*
Corresponding author. Tel.: C91 22 2576 71 77; fax: C91 22 2572 34
80; e-mail: kpk@iitb.ac.in
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.05.045

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K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
Figure 1.
Scheme 1.
key substructure. A convenient access to the fully
functionalized nine-membered B-ring of eleutherobin as
well as other related natural products in enantiomerically
enriched form still remains a challenge to synthetic
chemists. Thus, in view of the importance of these
medium-size cyclic ethers, we planned to synthesize a
highly oxygenated nine-membered cyclic ether21 starting
from the readily available 1,2,5,6-diisopropylidene-D-
glucose and the details are reported here.
Our synthesis, as depicted in Scheme 2, starts with the
classical etherification of the secondary alcohol 10 to afford
11. Under mild acidic conditions, the more exposed 5,6-O-
isopropylidene group was selectively deprotected to give a
diol which was subsequently cleaved by treating with silica
Scheme 2. Reagents & Conditions: (a) NaH, allylbromide, THF, TBAI (cat.), RT, 2 h, 93%. (b) 60% aq. AcOH, H2O, 12 h, 90%. (c) Silica gel supp. NaIO4,
CH2Cl2, 30 min, 86%. (d) 4-Bromo-1-butene, Mg, THF, 08C to RT, 12 h, 83%. (e) TBSCl, imid., DMF, 08C to RT, 10 h, 84%, 77%. (f) NaH, Mel, 08C to RT,
2 h, 77%. (g) 19 (10 mol%), CH2Cl2, 408C, 2 h, (30% for RZTBS, 33% for RZMe). (h) 19 (10 mol%), Ti(O/Pr)4 (7.5 mol%), CH2Cl2, 408C, (83% for RZ
TBS, 63% for RZMe).

K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
7463
22
gel supported NaIO4 to afford 12. Addition of the
ether 16 and the key RCM reaction was subsequently
attempted with Grubbs’ first generation catalyst 19. The
observation of a similar result with the methyl ether
suggested that the low yield could be presumably attributed
to coordination of the metal center with the oxygen of the
furanose ring as suggested by Fu¨rstner.24
Grignard reagent, derived from 4-bromo-1-butene and
magnesium, to aldehyde 12 afforded two diastereomeric
products 13 and 14 as a readily separable mixture in 3:2
ratio.23 The stereochemistry of the major Grignard addition
product was tentatively assigned as a-isomer as per the
literature report.23
In order to destabilize this chelate structure, the RCM
reaction of the dienes 15 and 16 was carried out with a
catalytic amount of 19 in the presence of a sub-
stoichiometric amount of Ti(OiPr)4 and this modified
protocol successfully led to the formation of the desired
RCM products 17 and 18, respectively, in high yields.
Moreover, the major isomer seems to be more polar than the
other and this observation is consistent with all the Grignard
reactions we have attempted on this system. All attempts to
carry out this reaction at low temperature did not improve
the ratio significantly. The major alcohol 13 was separated
and subsequently protected as its TBS ether 15, which sets
the stage for the key RCM reaction. Unfortunately, when the
RCM was carried out with Grubbs’ first generation catalyst
19 under high dilution conditions (0.003 M solution with
10 mol% catalyst), only 30% of the desired cyclized product
17 was obtained, the remainder being unreacted starting
material and presumably some cross-metathesis product.
Assuming that the bulky TBDMS group would have
provided a sterically crowed environment for the key
RCM reaction, the major alcohol was protected as its methyl
24
After successfully synthesising a model of the nine-
membered B-ring of eleutherobin, we then examined the
scope of utilizing this methodology to a diversity-oriented
synthesis of various bicyclic ethers, which may find
applications in the synthesis of novel bicyclic nucleosides
(Scheme 3). Addition of Grignard reagents having terminal
alkenes to the aldehyde 20, followed by protection of the
resultant alcohols should afford RCM precursors 21. After
the key RCM reaction, these bicyclic ethers could be used
for the synthesis of several bicyclic nucleosides 23 and 24.
Herein, we report the details of the synthesis of seven, eight
and ten-membered cyclic ethers starting from the aldehyde
12. The synthesis of five-seven fused bicyclic ether was
started with the addition of vinyl magnesium bromide to
aldehyde 12 at 0 8C in THF, and as expected, it afforded two
diastereomeric products 25 and 26 as a readily separable
mixture in 1:2 ratio. The major alcohol 26 was subsequently
converted to its methyl ether 31 and unfortunately, when the
RCM of diene 31 was carried out with Grubbs’ catalyst 19
under high dilution conditions (0.003 M solution with 10%
catalyst), in the presence of catalytic amount of Ti(OiPr)4,
only starting material was recovered. It has been reported
that the protecting group in the allylic alcohol plays an
Scheme 3.
Scheme 4.

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K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
important role in the success of the RCM reaction25 and so
we attempted the RCM of the diene 26 (allylic alcohol) with
Grubbs’ catalyst 19 under our standard conditions. We were
pleasantly surprised to see the formation of cyclised product
35 in 84% yield (Scheme 4).
carried out on 0.25 mm E. Merck silica plates (60F-254)
using UV light as visualizing agent and 7% ethanolic
phosphomolybdic acid and heat as developing agents.
Optical rotation was recorded on Jasco DIP-370 digital
polarimeter. IR spectra were recorded from Thermo Nicolet
Avater 320 FT-IR and Nicolete Impact 400 machine. Mass
spectra were obtained with Waters Micromass-Q-Tof
microe (YA105) spectrometer. Elemental analysis was
The synthesis of five, eight-membered fused bicyclic ether
was started with the addition of allyl magnesium bromide to
aldehyde 12 at 0 8C in THF, and unfortunately it afforded 28
in 20% yield and the remainder being a complex mixture.
Alternatively, a zinc mediated allylation was attempted with
12 and this protocol afforded two diastereomeric products
27 and 28 in 5:1 ratio. The alcohol 27 was subsequently
converted to its methyl ether 32, which was further
subjected to RCM with Grubbs’ catalyst 19 under our
standard condition to give the cyclized product 36 in 68%
yield. We also could successfully extend this method to
synthesize the five, ten-membered fused bicyclic ether 37.
Addition of 5-bromo-1-pentene magnesium bromide in
THF to aldehyde 12 afforded two diastereomeric products
29 and 30 in 1:1 ratio and the latter alcohol 30 was protected
as its methyl ether 33. Subsequently, RCM of the diene 33
was carried out with Grubbs’ catalyst 19 in the presence of a
catalytic amount of Ti(OiPr)4 under high dilution conditions
(0.003 M solution with 10% catalyst) to afford the desired
product 37 in 82% yield. It is also very important to note that
in this case, the RCM reaction exclusively provided the cis
isomer.
1
recorded on Thermo Finnigan Flash EA 1112. H and 13C
NMR spectra were recorded either on Varian AS 400,
Varian AS 500 or Varian ASM 300 instruments in CDCl3
solutions. 1H NMR data were reported in the order of
chemical shift (d in ppm), multiplicity (s, singlet; d, doublet;
t, triplet; q, quartet; m, multiplet), number of protons, and
coupling constant J in Hertz (Hz).
4.2. General procedure for Grignard reactions
A solution of the aldehyde (1 mmol) in dry THF (5 mL) was
cooled to 0 8C under an argon atmosphere. The Grignard
reagent (3 mmol) was added dropwise and stirred for 2 h at
0 8C then for 12 h at room temperature. The reaction
mixture was quenched with saturated NH4Cl and extracted
with ethyl acetate. The organic layer was washed with brine,
dried over anhydrous Na2SO4 and concentrated in vacuo,
and purified by silica gel chromatography (hexane/ethyl
acetate) to give two diastereomeric alcohols.
4.3. General procedure for methylation of alcohol
3. Conclusion
To a suspension of sodium hydride (3 mmol, 60%
dispersion in mineral oil) in dry THF (15 mL) was added
a solution of alcohol (1 mmol) in THF (2 mL) dropwise at
0 8C and the mixture was stirred for 30 min. To this mixture
iodomethane (2 mmol) was added dropwise and the reaction
mixture was stirred at 0 8C for 1 h and then for 1 h at room
temperature. The reaction mixture was quenched with
saturated NH4Cl and extracted with ethyl acetate. The
organic layer was washed with brine, dried over anhydrous
Na2SO4 and concentrated in vacuo, and purified by silica gel
chromatography (hexane/ethyl acetate) afforded the corre-
sponding product.
In summary, we have successfully synthesized a model of
the B-ring of eleutherobin utilizing the RCM reaction as the
key step. The key factor involved in the success of this
reaction was addition of Ti(OiPr)4 which destabilised the
possible formation of a chelated structure of ruthenium
carbene with furanose oxygen. This methodology was then
successfully extended to other medium-sized cyclic ethers
through a common intermediate. This synthetic strategy has
high potential in the synthesis of several related natural
products and novel bicyclic nucleosides. Work is in progress
in our laboratory to achieve this goal.
4.4. General procedure for ring closing metathesis
reaction
4. Experimental
4.1. General
Method A. A 1 mmol portion of diene was dissolved in
325 mL of dry dichloromethane under argon and the
solution was degassed. To this mixture, a solution of
Grubbs’ catalyst (10 mol%) in CH2Cl2 (10 mL) was added
dropwise and the reaction mixture was refluxed for 2–12 h.
The reaction mixture was cooled to room temperature,
concentrated in vacuo, and purified by a silica gel column
chromatography (hexane/ethyl acetate) to give the product.
Unless and otherwise noted, all starting materials and
reagents were obtained from commercial suppliers and used
without further purification. Tetrahydrofuran was distilled
from sodium benzophenone ketyl. Dichloromethane and
hexanes were freshly distilled from calcium hydride. DMF
was distilled over calcium hydride and stored over
˚
Molecular Sieves 4 A. Solvents for routine isolation of
Method B. A solution of diene (1 mmol) and Ti(OiPr)4
(10 mol%) in dry CH2Cl2 (325 mL) was stirred under
reflux for 1 h. To this mixture, a solution of Grubbs’ catalyst
(10 mol%) in CH2Cl2 (10 mL) was added dropwise and
the reaction mixture was refluxed for 2–12 h. The
reaction mixture was cooled to room temperature and
DMSO (50 equiv with respect to catalyst) was added and
stirred for 6 h. Evaporation of the solvent and purification
products and chromatography were reagent grade and glass
distilled. Reaction flasks were dried in oven at 100 8C for
12 h before use. Air and moisture sensitive reactions were
performed under an argon/UHP nitrogen atmosphere.
Column chromatography was performed using silica gel
(100–200 mesh, Acme) with indicated solvents. All
reactions were monitored by thin-layer chromatography

K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
7465
by column chromatography yielded the corresponding
product.
H, 9.61. Found: C, 62.59; H, 9.28; HRMS (EI) calcd for
C19H34O5SiNa m/z 421.2386, found m/z 421.2391.
4.4.3. (5S)-5-O-Methyl-1,2-O-(-1-methylethylidede)-3-O-
allyl-5-C-buteyl-a-D-xylofuranose (16). Following the
general procedure for methylation reaction, a solution of
13 (880 mg 3.08 mmol) in THF was treated with sodium
hydride (370 mg, 9.26 mmol, 60% in dispersion in oil) and
methyl iodide (0.38 mL, 6.12 mmol) in presence of catalytic
amount of TBAI. The crude product was purified by silica
gel chromatography (hexanes/ethyl acetate 20:1) to give 16
(740 mg, 80%) as a colourless oil. RfZ0.8 (33%, EtOAc/
hexane); [a]2D5K49.9 (c 1.0, CHCl3); IR (neat) nmax 3085,
1643, 1091 cmK1; dH (300 MHz, CDCl3) 5.94 (1H, d, JZ
3.9 Hz, anomeric CH), 5.89–5.72 (2H, m, 2!CH2]CH),
5.31–5.19 (2H, m, CH2]), 5.05–4.94 (2H, m, CH2]), 4.53
(1H, d, JZ3.9 Hz, CH), 4.17–4.07 (2H, m, CH2), 3.88 (1H,
dd, JZ12.6, 6.1 Hz, CH), 3.76 (1H, d, JZ3.1 Hz, CH),
3.52–3.45 (1H, m, CH), 3.48 (3H, s, OMe), 2.25–2.14 (2H,
m, CH2), 1.52–1.47 (2H, m, CH2), 1.49 (3H, s, Me), 1.30
(3H, s, Me); dC (75 MHz, CDCl3) 138.3, 133.5, 118.1,
114.7, 111.4, 104.9, 83.9, 82.1, 81.8, 79.3, 70.7, 59.3, 30.2,
29.2, 26.6, 26.2. Anal. Calcd for C16H26O5: C, 64.41; H,
8.78. Found: C, 63.99; H, 8.73.
4.4.1. (5S)-1,2-O-(-1-Methylethylidede)-3-O-allyl-5-C-
buteyl-a-D-xylofuranose (13) and (5R)-1,2-O-(-1-methyl-
ethylidede)-3-O-allyl-5-C-buteyl-a-D-xylofuranose (14).
Following the general procedure for Grignard reaction, a
solution of aldehyde 12 (880 mg, 3.08 mmol) in THF was
treated with 4-bromo-1-butenemagnesium bromide
(9.32 mmol) to afford two diastereomeric products 13
(534 mg, 53%) and 14 (330 mg, 33%) as a readily separable
mixture.
Compound 13. Viscous colourless oil; RfZ0.6 (33%,
EtOAc/hexane); [a]D25 K53.9 (c 1.0, CHCl3); IR (neat)
nmax 3443, 3075, 1641, 1077 cmK1; dH (300 MHz, CDCl3)
5.97 (1H, d, JZ3.9 Hz, anomeric CH), 5.93–5.78 (2H, m,
2!CH2]CH), 5.34–5.22 (2H, m, CH2]), 5.09–4.95 (2H,
m, CH2]), 4.58 (1H, d, JZ3.9 Hz, CH), 4.22–4.15 (1H, m,
CH), 4.05 (1H, dd, JZ5.7, 3.3 Hz, CH), 4.01–3.94 (2H, m,
CH2), 3.92 (1H, d, JZ3.3 Hz), 2.37–2.12 (2H, m, CH2),
1.75–1.52 (2H, m, CH2), 1.49 (3H, s, Me), 1.33 (3H, s, Me);
dC (100 MHz, CDCl3) 138.2, 133.2, 118.2, 114.7, 111.6,
104.7, 82.7, 82.6, 82.2, 70.7, 69.1, 32.1, 29.5, 26.7, 26.2.
Anal. Calcd for C15H24O5: C, 63.36; H, 8.51. Found: C,
63.47; H, 8.42.
4.4.4. tert-Butyl-(12,12-dimethyl-8,11,13,15-tetraoxa-tri-
cyclo[7.6.0.010,14]pentadec-5-en-2-yloxy)-dimethyl-
silane (17). Procedure A. Following the general procedure
for ring closing metathesis reaction (method A), from
200 mg (0.50 mmol) of 15 and 50 mg (0.060 mmol) of
Grubb’s catalyst, 55 mg (30%) of 17 was obtained as a
colourless oil.
Compound 14. Colourless oil; RfZ0.7 (33%, EtOAc/
hexane); [a]2D5 K36.9 (c 1.0, CHCl3); IR (neat) nmax 3467,
3076, 1641, 1077 cmK1; dH (300 MHz, CDCl3) 5.96 (1H, d,
JZ4.2 Hz, anomeric CH), 5.94–5.79 (2H, m, 2!
CH2]CH), 5.36–5.24 (2H, m, CH2]), 5.10–4.96 (2H, m,
CH2]), 4.58 (1H, d, JZ4.2 Hz, CH), 4.24–4.17 (1H, m,
CH), 4.05–3.93 (4H, m, CH2 and 2!CH), 2.38–2.12 (2H,
m, CH2), 1.90–1.53 (2H, m, CH2), 1.49 (3H, s, Me), 1.33
(3H, s, Me); dC (100 MHz, CDCl3) 138.5, 133.6, 118.6,
114.9, 111.7, 105.2, 82.5, 82.3, 82.0, 70.9, 69.3, 33.9, 29.9,
26.8, 26.4; HRMS (EI) calcd for C15H24O5Na m/z 307.1521,
found m/z 307.1510.
Procedure B. Following the general procedure for ring
closing metathesis reaction (method B), from 200 mg
(0.50 mmol) of 15, 0.015 mL (0.050 mmol) of Ti(OiPr)4
and 41 mg (0.050 mmol) of Grubb’s catalyst, 160 mg (86%)
of 17 was obtained as a colourless oil. RfZ0.8 (20%,
EtOAc/hexane); [a]D25 K39.9 (c 1.0, CHCl3); IR (neat) nmax
2947, 1650, 1255, 1091 cmK1; dH (500 MHz, CDCl3) 5.90
(1H, d, JZ3.7 Hz, anomeric CH), 5.84 (1H, q, JZ9.2 Hz,
CH]), 5.52 (1H, dt, JZ9.2, 5.1 Hz, CH]), 4.47 (1H, d,
JZ3.7 Hz, CH), 4.35 (1H, dd, JZ14.2, 3.7 Hz, CH), 4.08
(1H, d, JZ2.9 Hz, CH), 3.96–3.82 (3H, m, CH2 and CH),
2.39–2.14 (2H, m, CH2), 1.91–1.51 (2H, m, CH2), 1.47 (3H,
s, Me), 1.30 (3H, s, Me), 0.88 (9H, s, SiCMe3), 0.09 (3H, s,
SiMe) 0.08 (3H, s, SiMe); dC (125 MHz, CDCl3); d 135.9,
125.7, 111.3, 104.6, 86.4, 84.1, 81.1, 73.8, 66.2, 33.2, 29.8,
26.9, 26.5, 26.0, 18.4, K4.3, K4.8. Anal. Calcd for
C19H34O5Si: C, 61.58; H, 9.25. Found: C, 61.29; H, 9.16.
4.4.2. (5S)-5-O-tert-Butyldimethylsilyl-1,2-O-(1-methyl-
ethylidede)-3-O-allyl-5-C-buteyl-a-D-xylofuranose (15).
A solution of the alcohol 13 (400 mg, 1.40 mmol) in dry
DMF (0.8 mL) was treated with imidazole (286 mg,
4.21 mmol), TBSCl (253 mg, 1.68 mmol) and a catalytic
amount of DMAP at 0 8C and this solution was stirred for
10 h at room temperature. The reaction mixture was
extracted with ethyl acetate and washed with water and
brine, dried over anhydrous Na2SO4, concentrated in vacuo
and purified by silica gel chromatography (hexanes/ethyl
acetate 20:1) to give 15 (480 mg, 87%) as a colourless oil.
RfZ0.8 (20%, EtOAc/hexane); [a]2D5 K46.9 (c 1.0, CHCl3);
IR (neat) nmax 3085, 1643, 1255, 1097 cmK1; dH (300 MHz,
CDCl3) 5.92 (1H, d, JZ3.7 Hz, anomeric CH), 5.89–5.75
(2H, m, 2!CH2]CH), 5.31–5.18 (2H, m, CH2]), 5.06–
4.93 (2H, m, CH2]), 4.53 (1H, d, JZ3.7 Hz, CH), 4.17–
4.09 (1H, m, CH), 3.99–3.86 (3H, m, CH2 and CH), 3.76
(1H, d, JZ2.9 Hz, CH), 2.28–2.09 (2H, m, CH2), 1.58–1.51
(2H, m, CH2), 1.47 (3H, s, Me), 1.31 (3H, s, Me), 0.89 (9H,
s, SiCMe3), 0.11 (3H, s, SiMe), 0.08 (3H, s, SiMe); dC
(75 MHz, CDCl3) 138.8, 133.8, 117.9, 114.5, 111.4, 104.8,
83.9, 82.2, 82.1, 70.9, 70.8, 32.7, 29.5, 26.8, 26.5, 26.1,
18.5, K3.9, K4.7. Anal. Calcd for C19H34O5Si: C, 63.28;
4.4.5. 2-Methoxy-12,12-dimethyl-8,11,13,15-tetraoxa-
tricyclo[7.6.0.010,14]pentadec-5-ene (18). Procedure A.
Following the general procedure (method A) for ring
closing metathesis, from 170 mg (0.56 mmol) of 16 and
56 mg (0.080 mmol) of Grubb’s catalyst, 52 mg (33%) of 18
was obtained as a colourless oil.
Procedure B. Following the general procedure B, from
150 mg (0.50 mmol) of 16, 0.015 mL (0.050 mmol) of
Ti(OiPr)4 and 41 mg (0.050 mmol) of Grubb’s catalyst,
90 mg (66%) of 18 was obtained as a colourless oil. RfZ0.4
(20%, EtOAc/hexane); [a]2D5 K63.9 (c 1.0, CHCl3); IR

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K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
(neat) nmax 2940, 1657, 1466 cmK1; dH (300 MHz, CDCl3)
5.89 (1H, d, JZ3.8 Hz, anomeric CH), 5.83 (1H, q, JZ
9.2 Hz, CH]), 5.48 (1H, dt, JZ9.2, 4.2 Hz, CH]), 4.43
(1H, d, JZ3.8 Hz, CH), 4.31 (1H, dd, JZ14.1, 3.8 Hz, CH),
4.06 (1H, d, JZ3.1 Hz, CH), 4.01–3.51 (2H, m, CH2), 3.37
(3H, s, OMe), 3.37–3.32 (1H, m, CH), 2.34–2.13 (2H, m,
CH2), 1.94–1.83 (1H, m, CH) 1.41 (3H, s, Me), 1.40–1.31
(1H, m, CH), 1.25 (3H, s, Me); dC (75 MHz, CDCl3) 135.6,
125.6, 111.5, 104.8, 85.3, 83.4, 82.5, 80.5, 65.9, 57.5, 27.9,
26.8, 26.4, 26.0. Anal. Calcd for C14H22O5: C, 62.20; H,
8.20. Found: C, 62.30; H, 8.21.
CH), 3.98–3.84 (2H, m, CH2), 3.72 (1H, d, JZ2.9 Hz, CH),
3.36 (3H, s, OMe), 1.48 (3H, s, Me), 1.31 (3H, s, Me); dC
(75 MHz, CDCl3) 133.9, 133.8, 119.6, 117.5, 111.7, 105.3,
82.5, 81.9, 81.5, 81.0, 70.9, 56.7, 26.8, 26.3. Anal. Calcd for
C14H22O5: C, 62.20; H, 8.20. Found: C, 61.92; H, 8.17;
HRMS (EI) calcd for C14H22O5Na m/z 293.1365, found m/z
293.1354.
4.4.8. 2,2-Dimethyl-3a,3b,5,8,8a,9a-hexahydro-1,3,4,9-
tetraoxa-cyclopenta[a]azulen-8-ol (35). Following the
general procedure B, from 120 mg (0.46 mmol) of 26,
0.013 mL (0.046 mmol) of Ti(OiPr)4 and 38 mg
(0.046 mmol) of Grubb’s catalyst, 90 mg (84%) of 35 was
obtained as a colourless oil. RfZ0.3 (25%, EtOAc/hexane);
[a]2D5 K18.9 (c 1.0, CHCl3); IR (neat) nmax 3483, 2929,
1652, 1087 cmK1; dH (500 MHz, CDCl3) 5.96 (1H, d, JZ
3.6 Hz, anomeric CH), 5.59–5.56 (1H, m, CH2]CH), 5.36–
5.33 (1H, m, CH2]CH), 4.89–4.85 (1H, m, CH), 4.58
(1H, d, JZ3.6 Hz, CH), 4.51 (1H, dd, JZ17.2, 2.4 Hz, CH),
4.44 (1H, dd, JZ8.4, 4.8 Hz, CH), 4.15 (1H, dd, JZ7.2,
2.4 Hz, CH), 4.05 (1H, d, JZ3.6 Hz, CH), 2.44 (1H, br s,
OH), 1.48 (3H, s, Me), 1.32 (3H, s, Me); dC (125 MHz,
CDCl3); d 130.3, 126.0, 112.2, 105.2, 88.2, 85.9, 83.3, 72.3,
70.9, 27.3, 26.7; LRMS (EI) [MCNa]C251.0827; HRMS
(EI) calcd for C11H16O5Na m/z 251.0895, found m/z
251.0898.
4.4.6. (5R)-1,2-O-(-1-Methylethylidede)-3-O-allyl-5-C-
vinyl-a-D-xylofuranose (25) and (5S)-1,2-O-(-1-methyl-
ethylidede)-3-O-allyl-5-C-vinyl-a-D-xylofuranose (26).
Following the general procedure for Grignard reaction, a
solution of aldehyde 12 (900 mg, 3.98 mmol) in THF was
treated with vinylmagnesium bromide (12 mmol) to afford
two diastereomeric products 25 (260 mg, 25%) and 26
(520 mg, 51%) as a readily separable mixture.
Compound 25. Colourless oil; RfZ0.5 (25%, EtOAc/
hexane); [a]2D5 K43.9 (c 1.0, CHCl3); IR (neat) nmax 3489,
3083, 1644, 1079, 1024 cmK1; dH (400 MHz, CDCl3) 6.05–
5.97 (1H, m, CH]), 5.99 (1H, d, JZ3.6 Hz, anomeric CH),
5.93–5.86 (1H, m, CH]), 5.46–5.23 (4H, m, 2!CH2]),
4.57 (1H, d, JZ3.6 Hz, CH), 4.52 (1H, dd, JZ5.2, 1.6 Hz,
CH), 4.20–4.16 (1H, m, CH), 4.09 (1H, dd, JZ6.4, 3.6 Hz,
CH), 4.04 (1H, d, JZ3.6 Hz, CH), 4.02–3.99 (1H, m, CH),
2.50 (1H, br s, OH), 1.49 (3H, s, Me), 1.32 (3H, s, Me); dC
(100 MHz, CDCl3) 137.7, 133.4, 118.4, 115.9, 111.7, 105.1,
82.7, 81.9, 81.4, 71.1, 70.6, 26.7, 26.2; LRMS (EI) [MC
Na]C279.0960; HRMS (EI) calcd for C13H20O5Na m/z
279.1208, found m/z 279.1207.
4.4.9. (5R)-1,2-O-(-1-Methylethylidede)-3-O-allyl-5-C-
allyl-a-D-xylofuranose (27) and (5S)-1,2-O-(-1-methyl-
ethylidede)-3-O-allyl-5-C-allyl-a-D-xylofuranose (28). A
stirring solution of the aldehyde 12 (1.30 g, 5.75 mmol) and
allyl bromide (1.47 mL, 17.25 mmol) was added a saturated
aqueous solution of NH4Cl/THF (5:1, 25 mol). The reaction
mixture was cooled to 0 8C and zinc dust (2.25 g,
34.51 mmol) was slowly added to the reaction mixture
and stirring was continued at 0 8C for 1 h. The reaction
mixture was filtered and extracted with ethyl acetate, and
the extracts were dried over anhydrous sodium sulphate,
filtered and concentrated in vacuo, and purified in a silica
gel column chromatography afforded two diastereomeric
products 27 (931 mg, 60%) and 28 (186 mg, 12%) as a
readily separable mixture.
Compound 26. Colourless oil; RfZ0.4 (25%, EtOAc/
hexane); [a]2D5 K55.9 (c 1.0, CHCl3); IR (neat) nmax 3496,
3084, 1645, 1077, 1022 cmK1; dH (300 MHz, CDCl3) 5.97
(1H, d, JZ3.7 Hz, anomeric CH), 5.94–5.81 (2H, m, 2!
CH2]CH), 5.48–5.19 (4H, m, 2!CH2]), 4.59 (1H, d, JZ
3.7 Hz, CH), 4.50 (1H, dd, JZ7.3, 5.9 Hz, CH), 4.15 (1H,
dd, JZ12.8, 5.5 Hz, CH), 4.04 (1H, dd, JZ6.9, 3.3 Hz,
CH), 3.94 (1H, dd, JZ12.5, 5.9 Hz, 1H), 3.86 (1H, d, JZ
3.3 Hz, CH), 2.97 (1H, br s, OH), 1.48 (3H, s, Me), 1.32 (3H,
s, Me); dC (75 MHz, CDCl3) 135.9, 133.6, 117.9, 117.1,
111.8, 104.9, 83.2, 82.3, 82.2, 71.0, 70.9, 26.8, 26.3. Anal.
Calcd for C13H20O5: C, 60.92; H, 7.87. Found: C, 60.97; H,
7.97.
Compound 27. Colourless oil; RfZ0.6 (25%, EtOAc/
hexane); [a]2D5 K53.9 (c 1.0, CHCl3); IR (neat) nmax 3504,
3077, 1642, 1077, 1025 cmK1; dH (500 MHz, CDCl3) 5.96–
5.84 (2H, m, 2!CH2]CH), 5.93 (1H, d, JZ3.6 Hz,
anomeric CH), 5.35–5.12 (4H, m, 2!CH2]), 4.58 (1H,
d, JZ3.6 Hz, CH), 4.19 (1H, dd, JZ12, 4.8 Hz, CH), 4.07–
3.96 (4H, m, CH2 and 2!CH), 2.54–2.29 (3H, m, CH2 and
OH), 1.48 (3H, s, Me), 1.32 (3H, s, Me); dC (100 MHz,
CDCl3); d 134.3, 133.7, 118.0, 117.9, 111.5, 104.9, 82.1,
81.9, 81.7, 70.9, 68.2, 39.0, 26.7, 26.2. Anal. Calcd for
C14H22O5: C, 62.20; H, 8.20. Found: C, 62.67; H, 8.88;
HRMS (EI) calcd for C14H22O5Na m/z 293.1365, found m/z
293.1368.
4.4.7. (5S)-5-O-Methyl-1,2-O-(-1-methylethylidede)-3-O-
allyl-5-C-vinyl-a-D-xylofuranose (31). Following the
general procedure for methylation reaction, a solution of
26 (740 mg, 2.88 mmol) in THF was treated with sodium
hydride (460 mg, 8.66 mmol, 60% in dispersion in oil) and
methyl iodide (0.36 mL, 2.54 mmol) in the presence of a
catalytic amount of TBAI. The crude product was purified
by silica gel chromatography (hexanes/ethyl acetate 20:1) to
give 31 (680 mg, 87%) as a colourless oil. RfZ0.6 (20%,
EtOAc/hexane); [a]D25 K42.9 (c 1.0, CHCl3); IR (neat) nmax
3081, 1645, 1078 cmK1; dH (300 MHz, CDCl3) 5.97 (1H, d,
JZ3.7 Hz, anomeric CH), 5.93–5.80 (1H, m, CH2]CH),
5.75–5.63 (1H, m, CH2]CH), 5.43–5.18 (4H, m, 2!
CH2]), 4.54 (1H, d, JZ3.7 Hz, CH), 4.13–4.07 (2H, m,
Compound 28. Colourless oil; RfZ0.5 (25%, EtOAc/
hexane); [a]2D5 K63.9 (c 1.0, CHCl3); IR (neat) nmax 3510,
3076, 1642, 1077, 1018 cmK1; dH (500 MHz, CDCl3) 5.98
(1H, d, JZ3.6 Hz, anomeric CH), 5.95–5.81 (2H, m, 2!
CH2]CH), 5.34–5.09 (4H, m, 2!CH2]), 4.58 (1H, d, JZ
3.6 Hz, CH), 4.19 (1H, dd, JZ12.6, 5.1 Hz, CH), 4.09–3.95

K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
7467
(3H, m, CH2 and CH), 3.92 (1H, d, JZ3.3 Hz, CH), 2.29
(2H, t, JZ6.3 Hz, CH2), 1.49 (3H, s, Me), 1.33 (3H, s, Me);
dC (125 MHz, CDCl3) 134.5, 133.3, 118.3, 117.5, 111.8,
104.8, 82.9, 82.4, 81.8, 70.8, 69.6, 37.8, 26.8, 26.4; HRMS
(EI) Calcd for C14H22O5Na m/z 293.1365, found m/z
293.1368.
5.36–5.23 (2H, m, CH2]), 5.06–4.93 (2H, m, CH2]),
4.58 (1H, d, JZ3.9 Hz, CH), 4.24–4.17 (1H, m, CH), 4.04–
3.91 (3H, m, CH2 and CH), 3.99 (1H, d, JZ3.3 Hz, CH),
2.11–2.09 (2H, m, CH2), 1.72–1.65 (2H, m, CH2), 1.55–1.51
(2H, m, CH2), 1.49 (3H, s, Me), 1.32 (3H, s, Me); dC
(125 MHz, CDCl3) 138.7, 133.4, 118.5, 114.6, 111.5 105.0,
82.5, 82.2, 81.9, 71.8, 69.7, 34.1, 33.7, 26.8, 26.2, 24.9;
HRMS (EI) calcd for C16H26O5Na m/z 321.1678, found m/z
321.1678.
4.4.10. (5R)-5-O-Methyl-1,2-O-(-1-methylethylidede)-3-
O-allyl-5-C-allyl-a-D-xylofuranose (32). Following the
general procedure for methylation reaction, a solution of
27 (700 mg, 2.58 mmol) in THF was treated with sodium
hydride (310 mg, 7.76 mmol, 60% in dispersion in oil) and
methyl iodide (0.32 mL, 5.17 mmol) in presence of catalytic
amount of TBAI. The crude product was purified by silica
gel chromatography (hexanes/ethyl acetate 20:1) to give 32
(680 mg, 92%) as a colourless oil. RfZ0.8 (25%, EtOAc/
hexane); [a]2D5 K75.9 (c 1.0, CHCl3); IR (neat) nmax 3077,
1642, 1079, 1023 cmK1; dH (500 MHz, CDCl3) 5.96–5.86
(3H, m, anomeric CH and 2!CH2]CH), 5.33–5.10
(4H, m, 2!CH2]), 4.55 (1H, d, JZ3.6 Hz, CH), 4.15
(1H, dd, JZ12.4, 6.4 Hz, CH), 4.05–4.00 (2H m, CH2), 3.93
(1H, d, JZ2.8 Hz, CH), 3.65–3.54 (1H, m, CH), 3.39 (3H, s,
OMe), 2.64–2.60 (1H, m, CH), 2.35–2.29 (1H, m, CH), 1.46
(3H, s, Me), 1.31 (3H, s, Me); dC (125 MHz, CDCl3);
d 134.1, 133.9, 117.6, 117.4, 111.7, 104.9, 82.2, 81.4,
80.5, 76.5, 71.1, 57.4, 34.9, 26.8, 26.4. Anal. Calcd for
C15H24O5: C, 63.36; H, 8.51. Found: C, 64.04; H, 8.64;
HRMS (EI) calcd for C15H24O5Na m/z 307.1521, found m/z
307.1518.
Compound 30. Colourless oil; RfZ0.5 (33%, EtOAc/
hexane); [a]2D5 K74.9 (c 1.0, CHCl3); IR (neat) nmax 3510,
3077, 1641, 1078 cmK1; dH (500 MHz, CDCl3) 5.97 (1H, d,
JZ3.9 Hz, anomeric CH), 5.93–5.75 (2H, m, 2!
CH2]CH), 5.34–5.22 (2H, m, CH2]), 5.05–4.93 (2H, m,
CH2]), 4.58 (1H, d, JZ3.9 Hz, CH), 4.21–4.14 (1H, m,
CH), 4.05–3.92 (3H, m, CH2 and CH), 3.91 (1H, d, JZ
3.3 Hz CH), 2.44 (1H, br s, OH), 2.13–2.06 (2H, m, CH2),
1.70–1.51 (4H, m, 2!CH2), 1.49 (3H, s, Me), 1.33 (3H, s,
Me); dC (125 MHz, CDCl3) 138.7, 133.3, 118.3, 114.6,
111.8, 104.8, 82.8, 82.7, 82.4, 70.9, 69.7, 33.5, 32.4, 26.8,
26.3, 24.7; HRMS (EI) calcd for C16H26O5Na m/z 321.1678,
found m/z 321.1678.
4.4.13. (5S)-5-O-Methyl-1,2-O-(-1-methylethylidede)-3-
O-allyl-5-C-pentenyl-a-D-xylofuranose (33). Following
the general procedure for methylation reaction, a solution
of 30 (300 mg, 1.0 mmol) in THF was treated with sodium
hydride (120 mg, 3.0 mmol, 60% in dispersion in oil) and
methyl iodide (0.125 mL, 2.0 mmol) in the presence of
catalytic amount of TBAI. The crude product purified by
silica gel chromatography (hexanes/ethyl acetate 20:1) to
give 33 (270 mg, 85%) as colourless oil. RfZ0.80 (25%,
EtOAc/hexane); [a]D25 K22.9 (c 1.0, CHCl3); IR (neat)
3077, 1641, 1078, 1022 cmK1; dH (500 MHz, CDCl3) 5.96
(1H, d, JZ3.6 Hz, anomeric CH), 5.92–5.76 (2H, m, 2!
CH2]CH), 5.31–5.21 (2H, m, CH2]), 5.04–4.95 (2H, m,
CH2]), 4.54 (1H, d, JZ3.6 Hz, CH), 4.17–4.08 (2H, m,
CH2), 3.89 (1H, dd, JZ13.2, 6 Hz, CH), 3.76 (1H, d, JZ
3.6 Hz, CH), 3.54–3.44 (1H, m, CH), 3.49 (3H, s, OMe),
2.10–2.05 (2H, m, CH2), 1.64–1.35 (4H, m, 2!CH2),
1.49 (3H, s, Me), 1.32 (3H, s, Me); dC (125 MHz, CDCl3)
138.7, 133.6, 118.1, 114.6, 111.5, 105.0, 83.8, 82.2,
81.5, 79.3, 70.7, 59.2, 33.7, 30.3, 26.7, 26.3, 24.3; HRMS
(EI) calcd for C17H28O5Na m/z 335.1834, found m/z
335.1822.
4.4.11. 9-Methoxy-2,2-dimethyl-3a,5,8,9,9a,10a-hexa-
hydro-3bH-1,3,4,10-tetraoxa-cycloocta[a]pentalene
(36). Following the general procedure for ring closing
metathesis (method B), from 200 mg (0.70 mmol) of 32,
0.020 mL (0.07 mmol) of Ti(OiPr)4 and 57 mg (0.07 mmol)
of Grubb’s catalyst, 122 mg (68%) of 36 was obtained as a
colourless oil. RfZ0.40 (25%, EtOAc/hexane); [a]2D5 K81.9
(c 1.0, CHCl3); IR (neat) nmax 2929, 1656, 1138, 1097 cmK1
;
dH (300 MHz, CDCl3) 5.95 (1H, d, JZ3.9 Hz, anomeric
CH), 5.87–5.76 (1H, m, CH]), 5.43–5.37 (1H, m, CH]),
4.62–4.59 (1H, m, CH), 4.55 (1H, dd, JZ3.9, 1.5 Hz, CH),
4.34 (1H, t, JZ2.7 Hz, CH), 4.03–3.94 (1H, m, CH), 3.86–
3.85 (1H, m, CH), 3.49–3.41 (1H, m, CH), 3.41 (3H, s,
OMe), 3.40–3.16 (1H, m, CH), 2.09–2.01 (1H, m, CH), 1.51
(3H, s, Me), 1.33 (3H, s, Me); dC (125 MHz, CDCl3) 128.3,
127.7, 111.9, 104.5, 85.9, 85.1, 81.2, 72.2, 56.5, 29.7, 27.0,
26.9, 26.5; HRMS (EI) calcd for C13H20O5Na m/z 279.1208,
found m/z 279.1209.
4.4.14. 11-Methoxy-2,2-dimethyl-3a,5,8,9,10,11,11a,12a-
octahydro-3bH-1,3,4,12-tetraoxa-cyclodeca[a]pentalene
(37). Following the general procedure for ring closing
metathesis reaction (method B), from 120 mg (0.38 mmol)
of 33, 0.011 mL (0.038 mmol) of Ti(OiPr)4 and 31 mg
(0.038 mmol) of Grubb’s catalyst, 90 mg (82%) of 37 was
obtained as a colourless oil. RfZ0.70 (25%, EtOAc/
hexane); [a]2D5 K121.9 (c 1.0, CHCl3); IR (neat) 2983,
1649, 1078 cmK1; dH (500 MHz, CDCl3) 5.99 (1H, d, JZ
3.9 Hz, anomeric CH), 5.69–5.60 (2H, m, 2!CH]), 4.46
(1H, d, JZ3.9 Hz, CH), 4.39–4.32 (1H, m, CH), 4.13
(1H, dd, JZ9.3, 3.0 Hz, CH), 3.91 (1H, d, JZ3.3 Hz, CH),
3.83 (1H, dd, JZ6.0, 3.0 Hz, CH), 3.78–3.51 (1H, m, CH),
3.49 (3H, s, OMe), 2.81–2.70 (1H, m, CH), 2.02–1.98
(1H, m, CH), 1.81–1.51 (4H, m, 2!CH2), 1.48 (3H, s, Me),
1.32 (3H, s, Me); dC (125 MHz, CDCl3) 137.9, 125.9,
4.4.12. (5R)-1,2-O-(-1-Methylethylidede)-3-O-allyl-5-C-
pentenyl-a-D-xylofuranose (29) and (5S)-1,2-O-(-1-
methylethylidede)-3-O-allyl-5-C-pentenyl-a-D-xylofura-
nose (30). Following the general procedure for Grignard
reaction, a solution of aldehyde 12 (280 mg, 1.23 mmol) in
THF was treated with 5-bromo-1-pentenemagnesium bro-
mide (9.32 mmol) afforded two diastereomeric products 29
(134 mg, 38%) and 30 (138 mg, 39%) as a readily separable
mixture.
Compound 29. Semisolid; RfZ0.6 (33%, EtOAc/hexane);
[a]2D5 K33.9 (c 1.0, CHCl3); IR (neat) nmax 3497, 3077,
1641, 1077 cmK1; dH (500 MHz, CDCl3) 5.96 (1H, d, JZ
3.9 Hz, anomeric CH), 5.94–5.75 (2H, m, 2!CH2]CH),

7468
K. P. Kaliappan, N. Kumar / Tetrahedron 61 (2005) 7461–7469
(j) By, K.; Kelly, P. A.; Kurth, M. J.; Olmstead, M. M.; Nantz,
M. H. Tetrahedron 2001, 57, 1183. (k) Ceccarelli, S.; Piarulli,
U.; Telser, J.; Gennari, C. Tetrahedron Lett. 2001, 42, 7421.
(l) Ceccarelli, S.; Piarulli, U.; Gennari, C. Tetrahedron 2001,
57, 8531. (m) Xu, Q.; Weeresakare, M.; Rainier, J. D.
Tetrahedron 2001, 57, 8029. (n) Telser, J.; Beumer, R.; Bell,
A. A.; Ceccarelli, S. M.; Monti, D.; Gennari, C. Tetrahedron
Lett. 2001, 42, 9187. (o) Sandoval, C.; Redero, E.; Timoneda,
M. M. A.; Bermejo, F. A. Tetrahedron Lett. 2002, 43, 6521.
(p) Kaliappan, K. P.; Kumar, N. Tetrahedron Lett. 2003, 44,
379. (q) Winkler, J. D.; Quinn, K. J.; MacKinnon, C. H.;
Hiscok, S. D.; McLaughlin, E. C. Org. Lett. 2003, 5, 1805.
(r) Ritter, K. L.; Metz, P. Synlett 2003, 2422. (s) Castoldi, D.;
Caggiano, L.; Panigada, L.; Sharon, O.; Costa, A.; Gennari, C.
Angew. Chem., Int. Ed. Engl. 2005, 44, 588. (t) Chiang,
G. C. H.; Bond, A. D.; Ayscough, A.; Pain, G.; Ducki, S.;
Holmes, A. B. Chem. Commun. 2005, 1860.
111.6, 105.7, 83.9, 81.8, 80.4, 78.9, 77.6, 63.8, 58.6, 28.9,
27.1, 26.8, 26.4; LRMS (EI) [MCNa]C307.1321; HRMS
(EI) calcd for C15H24O5Na m/z 307.1521, found m/z
307.1512.
Acknowledgements
Financial support from IFS, Sweden and OPCW, Nether-
lands is sincerely acknowledged. N.K. thanks CSIR, New
Delhi for a fellowship. SAIF, IIT Mumbai is thanked for
providing spectral facilities.
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