Synthesis of stereoisomers of cryptofolione 6′-mono- and 4′,6′-Di-o-benzyl ethers

Article abstract of DOI:10.1002/cjoc.201190015

Synthesis of stereoisomers of 6′-mono- and 4′,6′-di-O- benzyl cryptofolione is described through a key intermediate 6, which was prepared by coupling of iodobenzene 8 with chiral propargyl alcohol 9 under Cosford protocol conditions. Monobenzyl ether 4 is

Full text of DOI:10.1002/cjoc.201190015

FULL PAPER
Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and
4',6'-Di-O-benzyl Ethers
Sabitha, Gowravaram*
Bhaskar, Vangala
Siva Sankara Reddy, S.
Yadav, J. S.
Organic Division I, Indian Institute of Chemical Technology, Hyderabad 500007, India
Synthesis of stereoisomers of 6'-mono- and 4',6'-di-O-benzyl cryptofolione is described through a key interme-
diate 6, which was prepared by coupling of iodobenzene 8 with chiral propargyl alcohol 9 under Cosford protocol
conditions. Monobenzyl ether 4 is obtained via epoxide 6 opening with vinyl Grignard, followed by
cross-metathesis reaction with a vinyl lactone 11. Whereas, dibenzyl ether 5 is prepared by epoxide 6 opening with
chiral propargyl alcohol 7 followed by simple transformations and finally cis-Wittig olefination.
Keywords lactones, oxygen heterocycles, cis-Wittig olefination, mono and di-O-benzyl ethers, cryptofolione
stereoisomers
Introduction
tigote form of Leishmania spp.
Two possible stereoisomers of cryptofolione, 1 and 2
were shown in Figure 1. To determine the absolute con-
figuration of cryptofolione, compounds 1 and 3 (enan-
tiomers of 2) were synthesized by Katsuki et al. in an
enantioselective manner by using asymmetric hetero
Diels-Alder reaction as the key step.7 Comparative
The α,β-unsaturated δ-lactone core unit (or 5,6-di-
hydro-2-(2H)-pyranone moiety) is present in various
natural products.1,2 These compounds display3 important
biological activities. Some exhibit antitumoral activity,
while others are tumor promoting. One such lactone is
cryptofolione 1, a class of 6-(ω-arylalkenyl)-5,6-dihy-
dro-α-pyrones isolated from the branch and stem bark of
two Cryptocarya species indigenous to South Africa
such as Cryptocarya myrtifolia4 and C. moschata.5 The
structure was elucidated on the basis of its CD spectra
and 13C NMR spectral analysis. Later, cryptofolione 1
was also isolated from the fruits of Cryptocarya alba6
and the structure was elucidated by spectroscopic
methods. Cryptofolione showed activity towards Try-
panosoma cruzi trypomastigotes, reducing their number
1
evaluation of the H NMR, 13C NMR, CD spectra, and
specific rotation of the synthetic compounds with those
reported in the literature was performed to establish the
absolute configuration of cryptofolione to be 1
[6R,4'S,6'R].
The main structural features of cryptofolione 1 are
an anti 1,3-diol, 1'-7'-two double bonds and a
6-substituted 5,6-dihydro-α-pyrone subunit. In con-
tinuation of our interest on the synthesis of bioactive
lactones,8 we herein report the synthesis of stereoisom-
ers of cryptofolione mono and di-O-benzyl ethers (4 and
5, Figure 1).
－
1
by 77% at 250 g•mL . It also showed moderate cyto-
toxicity in both macrophages and T. cruzi amastigotes
and displayed a mild inhibitory effect on the promas-
O
O
O
OH OH
6' 4'
2, (6R,4'R,6'S)
O
6
OH OH
6' 4'
O
6
OH OH
6' 4'
O
6
3, (6S,4'S,6'R)
Cryptofolione 1, (6R,4'S,6'R)
O
O
O
OBn OBn
6' 4'
OBn OH
6' 4'
O
6
6
Stereoisomer of 4',6'-di-O-benzyl cryptofolione 5
Stereoisomer of 6'-mono-O-benzyl cryptofolione 4
Figure 1 6-Substituted styryl lactones.
*
E-mail: gowravaramsr@yahoo.com; Tel.: 0091-40-27191629; Fax: 0091-40-27160512
Received January 8, 2010; revised and accepted August 11, 2010.
Chin. J. Chem. 2010, 28, 2421— 2427
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2421

Sabitha et al.
FULL PAPER
Results and discussion
Scheme 1 Retrosynthesis of 4 and 5
O
The retrosynthetic analysis is depicted in Scheme 1.
Di-O-benzyl ether 5 could be obtained by epoxide 6
opening with chiral propargylic alcohol 7.8d Epoxide 6
in turn could be prepared by coupling of 8 with 9 using
Cosford protocol conditions. The compound 9 could be
derived from L-malic acid. Whereas mono-O-benzyl
ether 4 could be obtained by cross-metathesis reaction
of 10 with 11. The allylic RCM precurser 10 can be de-
rived from the epoxide 6 (Scheme 1).
OBn OBn
O
5
OBn
OTBS
OTHP
7
O
+
6
The synthesis began with the coupling of iodoben-
zene 8 with the known chiral propargyl alcohol 99 using
Cosford protocol conditions as reported in our earlier
communication8d,8l to afford the coupled product 12
(92%) (Scheme 2). Partial reduction of triple bond in
compound 12 was carried out using LiAlH4 in THF at 0
℃ to give compound 13 in 86% yield and the secon-
dary hydroxyl group was protected as its benyl ether 14
in 89% yield. Removal of the cyclohexylidene group in
compound 14 proceeded smoothly in PPTS/MeOH at r.t.
to afford the corresponding diol, which on selective
monotosylation (TsCl/Et3N/high dilution CH2Cl2) of the
primary hydroxyl group and treatment with base
(K2CO3/MeOH/r.t.) furnished the epoxide 6 in 78%
yield. Opening of epoxide with the propargylic alcohol
78d afforded 15 in 76% yield. Accordingly, the secon-
dary hydroxyl group in compound 15 was protected as
the corresponding benzyl ether 16 (BnBr/NaH/reflux)
(80%) and the silyl group was removed to facilitate par-
tial reduction of triple bond. Thus, LAH reduction of
compound 17 provided 18 (87%), which was converted
OH
I
O
O
+
9
8
O
OBn OH
O
4
O
O
OBn OH
+
10
11
OBn
O
6
Scheme 2
OH
O
OR
O
O
OH
O
e
O
d
I
b
a
O
+
13 R = H
14 R = Bn
12
c
9
8
OR1
OBn
OR
OBn OBn
OBn OR
O
OTHP
k
h
OR1
6
18 R = H, R1 = THP
19 R = MOM, R1 = THP
20 R = MOM, R1 = H
15 R = H, R1 = TBS
16 R = Bn, R1 = TBS
17 R = Bn, R1 = H
i
j
f
g
O
OMOM
O
OBn OBn
OBn OBn
O
I
2
OMe
5
21
Reagents and conditions: (a) 10% Pd/C (cat.), CuI (cat.), Ph3P (0.1 equiv.), K2CO3, H2O/DME (1∶3), 85 ℃, 5 h, 92%; (b) LiAlH4, THF, 0 ℃—r.t., 30
min, 86%; (c) BnBr, NaH, THF, r.t., 2 h, 89%; (d) (i) PPTS, MeOH, r.t., 2 h, 8% starting material recovery, (ii) TsCl, Et3N, cat. DMAP, CH2Cl2, 1 h, (iii)
K2CO3, MeOH, r.t, 1 h, 78% (over three steps); (e) 7, n-BuLi, BF3OEt2, THF, －78 ℃, 2 h, 76%; (f) BnBr, NaH, THF, reflux, 4 h, 80%; (g) TBAF, THF, 0
℃, 1 h, 82%; (h) LiAlH4, THF, 0 ℃—r.t., 30 min, 87%; (i) MOMCl, DIPEA, CH2Cl2, 0 ℃, 12 h, 90%; (j) PPTS, MeOH, r.t., 5 h, 84%; (k) (i) IBX, DMSO,
CH2Cl2, 0 ℃—r.t., 5 h, (ii) NaH, (CF3CH2O)2P(O)CH2COOMe, THF, －78 ℃, 30 min, 76% (over two steps); (l) CeCl3•7H2O, MeOH/CH3CN (1∶1),
reflux, 4 h, 76%.
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Chin. J. Chem. 2010, 28, 2421—2427

Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and 4',6'-Di-O-benzyl Ethers
into (Z)-olefinic ester in four steps by protection of al-
cohol 18 as MOM ether 19 (90%) using MOMCl and
DIPEA followed by deprotection of the THP group with
PPTS/MeOH resulting in primary alcohol 20 in good
yield. The hydroxyl functional group was oxidized to
aldehyde, which was subjected to Still-Gennari reaction
without isolation. Finally, smooth deprotection of the
MOM group and concomitant cyclization under neutral
conditions using CeCl3•7H2O in MeOH/CH3CN (1∶1)
at reflux for 4 h gave the required lactone 5 in 76%
yield. Several attempts to deprotect the benzyl ethers
failed to produce 2.
Finally, another strategy was planned based on olefin
cross-metathesis reaction, in this strategy, cross-me-
tathesis reaction of 10 (prepared by opening of epoxide
6 with vinyl magnesium bromide) with the known vinyl
lactone 118m in the presence of Grubbs’ second genera-
tion catalyst (3 mol%) in dichloromethane afforded a
mono benzyl ether 4 (Scheme 3). Again several attempts
to deprotect the benzyl group failed to produce
stereisomer of cryptofolione 2.
conditions at 70 eV on LC-MSD (Agilent technologies)
spectrometers. All high resolution spectra were recorded
on QSTAR XL hybrid MS/MS system (Applied Biosys-
tems/MDS Sciex, Foster City, USA), equipped with an
ESI source (IICT, Hyderabad). Column chromatography
was performed on silica gel (60—120 mesh) supplied
by Acme Chemical Co., India. TLC was performed on
Merck 60 F-254 silica gel plates. Optical rotations were
measured with JASCO DIP-370 Polarimeter at 20 ℃.
(2S)-1-[(2S)-1,4-Dioxaspiro[4.5]dec-2-yl]-4-phenyl-
3-butyn-2-ol (12) To a solution of phenyl iodide 8
(4.07 g, 19.99 mmol) in 1,2-DME (75 mL) was added
water (25 mL), K2CO3 (5.06 g, 36.66 mmol), CuI (0.146
g, 0.76 mmol), Ph3P (0.437 g, 1.66 mmol), and catalytic
amount of 10% Pd/C. The resulting mixture was stirred
at room temperature for 30 min, and then compound 9
(3.5 g, 16.66 mmol) in 1,2-DME (15 mL, plus 5 mL×2
of rinse) was added by cannula and the reaction warmed
at 85 ℃ for 5 h. The mixture was cooled to room tem-
perature and filtered on a Celite pad washing with hot
ethyl acetate (100 mL×2). The solution was diluted
with H2O (80 mL) and extracted with ethyl acetate (100
mL×3). The organic phase was washed with brine (100
mL×2), dried over Na2SO4, and concentrated under
reduced pressure. The residue was purified by column
chromatography [silica gel 60—120 mesh, V(EtOAc)∶
V(hexane)＝6∶4] to afford 12 (4.37 g, 92%) as a pale
yellow liquid. Rf＝0.49 [V(EtOAc)∶V(n-Hexane)＝
Conclusion
In conclusion, we have disclosed the synthesis of
stereoisomers of cryptofolione mono- and di-O-benzyl-
ethers 4 and 5 starting from commercially available
L-malic acid. Using this strategy, the synthesis of cryp-
tofolione 1 is under way from D-malic acid by doing
protecting group manipulations.
1
5∶5]; [α]2D5 －41.5 (c 1.0, CHCl3); H NMR (CDCl3,
200 MHz) δ: 1.35—1.69 (m, 10H), 1.94 (dd, J＝8.0,
13.9 Hz, 1H), 2.06 (dd, J＝6.6, 13.9 Hz, 1H), 3.11 (br s,
1H, OH), 3.60 (dd, J＝7.3, 8.0 Hz, 1H), 4.10 (dd, J＝
5.9, 8.0 Hz, 1H), 4.43—4.60 (m, 1H), 4.71—4.85 (m,
1H), 7.21—7.32 (m, 3H, Ar-H), 7.33—7.46 (m, 2H,
Ar-H); 13C NMR (CDCl3, 75 MHz) δ: 23.6, 23.8, 24.8,
34.9, 36.4, 41.0, 60.0, 68.8, 72.5, 84.6, 89.6, 109.5,
122.4, 128.0, 128.1, 131.4; IR (neat) ν: 3442, 2933,
2856, 1634, 1489, 1445, 1364,1281, 1101, 1035, 927,
Experimental
Reactions were conducted under N2 in anhydrous
solvents such as CH2Cl2, THF and EtOAc. All reactions
were monitored by TLC (silica-coated plates and visu-
alizing under UV light). n-Hexane (b.p. 60—80 ℃)
was used. Yields refer to chromaographically and spec-
troscopically (1H and 13C NMR) homogeneous material.
Air sensitive reagents were transferred by syringe or
double-ended needle. Evaporation of solvents was per-
formed at reduced pressure on a Buchi rotary evaporator.
1H and 13C NMR spectra of samples in CDCl3 were re-
corded on Varian FT-200MHz (Gemini) and Bruker
UXNMR FT-300MHz (Avance) spectrometers. Chemi-
cal shift δ is reported relative to TMS (δ＝0.0) as an
internal standard. Mass spectra were recorded under E1
＋
－1
756, 691 cm ; ESI-MS m/z: 309 [M＋Na] ; HRMS
(ESI) calcd for C18H22O3Na [M ＋ Na] ＋ 309.1466,
found 309.1474.
(2S,3E)-1-[(2S)-1,4-Dioxaspiro[4.5]dec-2-yl]-4-
phenyl-3-buten-2-ol (13) A solution of compound 12
(4.2 g, 14.68 mmol) in dry THF (25 mL, plus 4 mL×2
of rinse) was added to a stirred suspension of LiAlH4
Scheme 3
OBn
O
O
OBn OH
Vinyl magnesium bromide
G-II, reflux, 8 h
O
+
6
10
11
O
O
OH OH
O
OBn OH
O
2
4
Chin. J. Chem. 2010, 28, 2421—2427
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2423

Sabitha et al.
FULL PAPER
mmol), was added to the solution slowly. The mixture
was stirred at －78 ℃ for 15 min. Then a solution of
epoxy compound 6 (1.6 g, 5.71 mmol) in dry THF (8
mL, plus 3 mL×2 of rinse) was added dropwise over a
period of 15 min and the mixture was stirred at －78
℃ for another 2 h. The mixture was quenched by add-
ing aqueous NH4Cl (15 mL). Then the mixture was ex-
tracted with EtOAC (40 mL×3) and washed with H2O
(40 mL×2) and dried (Na2SO4). The evaporation of
solvent under reduced pressure afforded the crude
product which was purified by column chromatography
using silica gel (60—120 mesh) to afford pure com-
pound 15 (2.5 g, 76% yield) as a clear liquid; Rf＝0.60
[V(EtOAc)∶V(n-Hexane)＝7∶3]; [α]2D5 ＋16.77 (c
(0.446 g, 11.73 mmol) in dry THF (10 mL) at 0 ℃ un-
der N2. The mixture was stirred at r.t. for 30 min. The
mixture was cooled to 0 ℃, then diluted with THF (15
mL) and quenched by dropwise addition of sat. Na2SO4
(4 mL). The solid material was filtered and washed
thoroughly with hot EtOAC (30 mL×4). The combined
organic layers were dried (Na2SO4). The solvent was
removed in vacuo and the crude product was purified by
silica gel column chromatography to afford compound
13 as pale yellow oil (3.63 g, 86% yield). Rf＝0.42
[V(EtOAc)∶V(n-Hexane)＝2∶8]; [α]2D5 －40.0 (c
1.0, CHCl3); 1H NMR (CDCl3, 300 MHz) δ: 1.35—1.62
(m, 10H), 1.79 (dd, J＝13.5, 7.5, 4.5 Hz, 1H), 1.90 (dd,
J＝7.5, 13.5 Hz, 1H), 2.60 (br s, 1H, OH), 3.56 (dd, J＝
7.5, 8.0 Hz, 1H), 4.05 (dd, J＝6.0, 8.0 Hz, 1H), 4.23—
4.39 (m, 1H), 4.46—4.57 (m, 1H), 6.21 (dd, J＝5.3,
15.8 Hz, 1H), 6.60 (d, J＝15.8 Hz, 1H), 7.15—7.41 (m,
5H, Ar-H); 13C NMR (CDCl3, 75 MHz) δ: 23.7, 23.9, 25,
35.0, 36.5, 40.3, 69.0, 69.7, 72.9, 109.4, 126.3, 127.4,
128.4, 129.6, 131.9, 136.6; ESI-MS m/z: 311 [M＋Na]＋＋;
HRMS (ESI) calcd for C18H24O3Na [M ＋ Na]
311.1623, found 311.1615.
1
1.35, CHCl3); H NMR (CDCl3, 300 MHz) δ: 0.06 (s,
6H), 0.88 (s, 9H), 1.39—1.71 (m, 6H), 1.72—1.99 (m,
4H), 2.30—2.44 (m, 2H), 3.39—3.51 (m, 2H), 3.65—
3.85 (m, 3H), 3.94—4.10 (m, 1H), 4.27 (t, J＝3.7, 7.5
Hz 1H), 4.40 (d, J＝11.3 Hz, 1H), 4.52 (br s, 1H), 4.65
(d, J＝12.0 Hz, 1H), 6.15 (dd, J＝8.3, 15.8 Hz, 1H),
6.58 (d, J＝15.8 Hz, 1H), 7.09—7.39 (m, 10H); 13C
NMR (75 MHz) δ: －4.6, －4.1, 18.6, 19.9, 25.9, 26.2,
28.0, 31.0, 39.5, 42.0, 60.5, 60.8, 62.6, 63.8, 70.9, 77.85,
81.2, 84.6, 99.3, 127.0, 128.1, 128.2, 128.8, 129.0,
129.8, 132.9, 133.5, 136.8, 138.6; IR (neat) ν: 3453,
3028, 2930, 2857, 1602, 1493, 1457, 1355, 1253, 1068,
(2S)-2-[(2S,3E)-2-(Benzyloxy)-4-phenyl-3-buten-
yl]-1,4-dioxaspiro[4.5]decane (14) To a stirred sus-
pension of freshly activated NaH (NaH was washed
with dry hexane thoroughly) (0.66 g, 27.77 mmol) in
THF (30 mL) under N2 atmosphere, was added 6 (3.2 g,
11.11 mmol) in dry THF (10 mL) in a dropwise manner
at 0 ℃. After stirring for 45 min at 0 ℃, benzyl bro-
mide (2.84 g, 16.66 mmol) was added dropwise over a
period of 10 min. The reaction mixture was stirred for 6
h at room temperature. Then to the reaction mixture 15
mL of cold water was added cautiously. The layers were
separeated and aq. layer was extracted with ethyl acetate
(50 mL×3). The combined organic layers were washed
with water (30 mL×3), brine solution (20 mL×3) and
then dried over anhydrous Na2SO4. Solvent was re-
moved in vacuo and the residue was purified by silica
gel column chromatography to afford benzyl ether 14
(3.75 g, 89%) as clear liquid. Rf＝0.72 [V(EtOAc)∶
V(n-Hexane)＝3∶7]; [α]2D5 －41.3 (c 0.25, CHCl3);
1H NMR (CDCl3, 200 MHz) δ: 1.35—1.60 (m, 10H),
1.85 (t, J＝7.0 Hz, 2H), 3.50 (t, J＝7.8 Hz, 1H), 4.03
(dd, J＝6.2, 7.8 Hz, 1H), 4.08—4.20 (m, 1H), 4.23—
4.33 (m, 1H), 4.39 (d, J＝11.7 Hz, 1H), 4.62 (d, J＝11.3
Hz, 1H), 6.09 (dd, J＝7.8, 16.4 Hz, 1H), 6.55 (d, J＝
16.4 Hz, 1H), 7.18—7.42 (m, 10H, Ar-H); IR (neat) ν:
3028, 2936, 2859, 1600, 1495, 144－8, 1364, 1279, 1163,
－1
1030, 980, 838, 778, 744, 696 cm ; ESI-MS m/z: 601.0
[M＋Na]＋; HRMS (ESI) calcd for C35H50O5NaSi [M＋
Na]＋ 601.3325, found 601.3347.
tert-Butyl((1R,5R,7S,8E)-5,7-di(benzyloxy)-9-
phenyl-1-[2-(tetrahydro-2H-2-pyranyloxy)ethyl]-8-
nonen-2-ynyloxy)dimethylsilane (16) To a stirred
suspension of freshly activated NaH (NaH was washed
with anhyd. hexane thoroughly) (0.348 g, 14.50 mmol)
in THF (50 mL) under N2, was added 15 (2.4 g, 4.14
mmol) in THF (10 mL, plus 4 mL×2 of rinse) at 0 ℃
in a dropwise manner. The mixture was stirred at 0 ℃
for 45 min, then benzyl bromide (0.85 g, 4.97 mmol)
was added dropwise over 10 min. The mixture was
stirred for 3 h at r.t., then cold H2O (60 mL) was added
to the reaction mixture slowly. The layers were sepa-
rated and aq. layer was extracted with EtOAC (60 mL×
3). The combined organic layers were washed with H2O
(100 mL×2), brine (100 mL×2) and dried (Na2SO4).
The solvent was removed in vacuo and the crude prod-
uct was purified by silica gel column chromatography
[silica gel 60—120 mesh, V(EtOAc)∶V(n-Hexane)＝
8∶2] to afford benzyl ether 16 (2.21 g, 80%) as a clear
liquid. Rf ＝0.72 [V(EtOAc)∶V(n-Hexane)＝3∶7];
1
1101, 1067, 969, 931, 745, 695 cm ; ESI-MS m/z: 401
25
1
[M＋Na]＋; HRMS (ESI) calcd for C25H30O3Na [M＋
[α]D －69.98 (c 1.0, CHCl3); H NMR (CDCl3, 300
MHz) δ: 1.39 (br s, 2H), 1.56 (br s, 8H ), 1.96—2.23 (m,
2H), 3.57 (t, J＝7.5 Hz, 1H), 4.06 (dd, J＝6.0, 12.8 Hz,
1H), 4.31 (pent apparent, J＝6.0, 12.8 Hz, 1H), 4.46 (dd,
J＝4.5, 9.0 Hz, 1H), 4.56 (d, J＝12.0 Hz, 1H), 4.85 (d,
J＝11.0 Hz, 1H), 7.21—7.46 (m, 10H, Ar-H); 13C NMR
(CDCl3, 75 MHz) δ: 23.8, 23.9, 25.1, 35.2, 36.6, 40.5,
66.1, 69.3, 70.7, 72.3, 85.9, 87.8, 108.9, 122.5, 127.5,
127.8, 128.2, 128.2, 128.3, 131.6, 137.8; IR (neat) ν:
Na]＋ 401.2092, found 401.2110.
(E,3S,5R,9R)-3-(Benzyloxy)-9-[1-(tert-butyl)-1,1-
dimethylsilyl]oxy-1-phenyl-11-(tetrahydro-2H-2-p－y-
1
ranyloxy)-1-undecen-7-yn-5-ol (15) A 1.36 mol•L
solution of n-BuLi in hexane (6.3 mL) was added to an
acetylenic compound 7 (2.55 g, 8.55 mmol) in dry THF
at －78 ℃ under N2. The mixture was stirred for 45
min, then, boron trifluoride etherate (0.92 mL, 7.39
2424
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Chin. J. Chem. 2010, 28, 2421— 2427

Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and 4',6'-Di-O-benzyl Ethers
3380, 3030, 2935, 2859, 1599,－1490, 1448, 1365, 1279,
6.57 (d, J＝15.6 Hz, 1H), 7.13—7.42 (m, 15H); 13C
1
1102, ＋1070, 929, 754, 694 cm ; ESI-MS m/z: 399 [M
NMR (75 MHz) δ: 19.4, 25.3, 30.5, 36.6, 37.0, 41.5,
62.1, 65.5, 70.3, 71.3, 71.6, 75.0, 75.4, 98.8, 125.7,
126.5, 126.7, 127.5, 127.6, 127.8, 127.9, 128.27, 128.3,
128.5, 130.5, 131.9, 135.2, 136.6, 138.6, 138.7; IR (neat)
ν: 3442, 2940, 1601, 1494, 1451, 1352, 1068, 1029, 971,
＋Na] ; HRMS (ESI) calcd for C25H28O3Na [M＋Na]＋
399.1936, found 399.1942.
(3R,7R,9S,10E)-7,9-Di(benzyloxy)-11-phenyl-1-
(tetrahydro-2H-－2-pyranyloxy)-10-undecen-4-yn-3-ol
(17) A 1 mol•L 1 solution of TBAF in THF (3.14 mL)
was added to a solution of compound 16 (2.1 g, 3.14
mmol) in dry THF (30 mL) at 0 ℃. The mixture was
stirred at r.t. for 60 min. After completion of the reaction,
the mixture was diluted with EtOAC (15 mL). The
combined organic layers were washed with sat. NaCl,
and the mixture was extracted with ethyl acetate (40 mL
×3). The organic extracts were washed with brine (30
mL×2) and dried (Na2SO4). The evaporation of the
solvent under reduced pressure, followed by column
chromatography by using silica gel (60—120 mesh)
afforded pure compound 17 as colourless oil (1.39 g,
82% yield). Rf＝0.44 [V(EtOAc)∶V(n-Hexane)＝3∶7];
＋
－1
906, 869, 742, 696 cm ; ESI-MS m/z: 579 [M＋Na] ＋;
HRMS (ESI) calcd for C36H44O5Na [M ＋ Na]
579.3086, found 579.3093.
2-[(3R,4E,7R,9S,10E)-7,9-Di(benzyloxy)-3-(meth-
oxymethoxy)-11-phenyl-4,10-undecadienyl]oxytetra-
hydro-2H-pyran (19) MOMCl (0.54 g, 6.82 mmol),
diisopropylethylamine (1.94 g, 11.93 mmol) were added
to a stirred solution of alcohol 18 (0.95 g, 1.70 mmol) in
anhyd. CH2Cl2 (20 mL) at 0 ℃. The mixture was
stirred at r.t. for 12 h and the mixture was quenched by
adding H2O (8 mL), and extracted with CH2Cl2 (12 mL
×3). The organic extracts were washed with brine (10
mL), dried (Na2SO4). The solvent was removed under
vacuum and the crude product was purified by column
chromatography to afford the pure product 19. Yield:
0.918 g (90%); gummy oil; Rf＝0.60 [V(EtOAc)∶
V(n-Hexane)＝3∶7]; [α]2D5 ＋18.09 (c 1.25, CHCl3);
1H NMR (CDCl3, 200 MHz) δ: 1.43—1.67 (m, 6H),
1.68—1.98 (m, 4H), 2.24—2.38 (m, 2H), 3.30 (s, 3H),
3.35—3.50 (m, 2H), 3.57—3.87 (m, 4H), 4.03—4.18
(m, 1H), 4.25 (d, J＝11.7 Hz, 1H), 4.30 (d, J＝11.0 Hz,
1H), 4.41 (d, J＝6.6 Hz, 1H), 4.51 (d, J＝11.0 Hz, 1H),
4.53 (d, J＝11.7 Hz, 1H), 4.55 (br s, 1H), 4.63 (d, J＝
6.6 Hz, 1H), 5.34 (dd, J＝8.0, 15.4 Hz, 1H), 5.66 (dd,
J＝8.0, 15.4 Hz, 1H), 6.08 (dd, J＝8.0, 16.1 Hz, 1H),
6.54 (d, J＝16.1 Hz, 1H), 7.06—7.38 (m, 15H); 13C
NMR (75 MHz) δ: 19.6, 25.5, 30.7, 35.9, 37.1, 41.5,
55.3, 62.2, 63.9, 70.8, 71.3, 73.7, 74.9, 75.2, 93.4, 98.9,
125.6, 126.4, 127.4, 127.5, 127.7, 127.8, 128.18, 128.2,
128.4, 129.7, 130.3, 131.8, 132.5, 136.5, 138.5, 138.6;
IR (neat) ν: 3027, 2936, 1634, 1494, 1452, 1353, 1208,
1
[α]2D5 －37.87 (c 0.95, CHCl3); H NMR (CDCl3, 200
MHz) δ: 1.37—1.66 (m, 6H), 1.68—2.07 (m, 4H), 2.42
—2.53 (m, 2H), 3.38—3.56 (m, 2H), 3.60—3.75 (m,
1H), 3.76—3.95 (m, 3H), 4.24 (d, J＝11.7 Hz, 1H),
4.31 (d, J＝11.7 Hz, 1H), 4.47 (d, J＝11.7 Hz, 1H), 4.51
—4.59 (m, 1H), 4.60 (d, J＝11.3 Hz, 1H), 4.61 (br s,
1H), 6.11 (dd, J＝8.0, 16.1 Hz, 1H), 6.56 (d, J＝16.1
Hz, 1H), 7.07—7.39 (m, 15H, Ar-H); 13C NMR (75
MHz) δ: 19.3, 24.4, 25.3, 30.5, 37.0, 41.5, 61.2, 61.5,
62.1, 64.8, 70.2, 71.7, 73.8, 81.7, 82.6, 98.8, 125.7,
126.5, 127.5, 127.6, 127.7, 127.8, 128.3, 128.5, 129.8,
130.2, 132.1, 136.5, 138.4, 138.5; IR (neat) ν: 3408,
3305, 2921, 2852, 1634, 1460, 1383, 1070, 744, 698
＋
－1
cm ; ESI-MS m/z: 577 [＋M＋Na] ; HRMS (ESI) calcd
for C36H42O5Na [M＋Na] 577.2929, found 577.2935.
(3R,4E,7R,9S,10E)-7,9-Di(benzyloxy)-11-phenyl-1-
(tetrahydro-2H-2-pyranyloxy)-4,10-undecadien-3-ol
(18) A solution of compound 17 (1.25 g, 2.25 mmol)
in dry THF (10 mL, plus 4 mL×2 of rinse) was added
to a stirred suspension of LiAlH4 (0.30 g, 8.03 mmol) in
dry THF (30 mL) at 0 ℃ under N2. The mixture was
stirred at r.t. for 3 h and then heated under reflux for 36
h. The mixture was cooled to 0 ℃, then diluted with
THF (50 mL) and quenched by dropwise addition of sat.
Na2SO4 (4 mL). The solid material was filtered and
washed thoroughly with hot EtOAC (50 mL×4). The
combined organic layers were dried (Na2SO4). The sol-
vent was removed in vacuo and the crude product was
purified by silica gel column chromatography to afford
compound 18 as pale yellow oil (1.08 g, 87% yield). Rf
＝ 0.44 [V(EtOAc) ∶ V(n-Hexane) ＝ 3 ∶ 7]; [α]D25
＋19.44 (c 0.55, CHCl3); 1H NMR (CDCl3, 300 MHz) δ:
1.41—1.62 (m, 4H), 1.63—1.94 (m, 6H), 2.27—2.39
(m, 2H), 2.76 (br s, 1H, OH), 3.45—3.63 (m, 2H), 3.64
—3.75 (m, 1H), 3.77—3.97 (m, 3H), 4.28 (d, J＝11.3
Hz, 1H), 4.33 (d, J＝11.3 Hz, 1H), 4.50 (d, J＝11.3 Hz,
1H), 4.53—4.60 (m, 1H), 4.58 (br s, 1H), 4.61 (d, J＝
11.3 Hz, 1H), 5.57 (dd, J＝6.0, 15.6 Hz, 1H), 5.72 (dd,
J＝8.3, 15.8 Hz, 1H), 6.13 (dd, J＝7.5, 15.8 Hz, 1H),
－1
1069, 1029, 973, 916, 749, 696 cm ; ESI-MS m/z: 623
[M＋Na]＋; HRMS (ESI) calcd for C38H48O6Na [M＋
Na]＋ 623.3348, found 623.3375.
(3R,4E,7R,9S,10E)-7,9-Di(benzyloxy)-3-(methoxy-
methoxy)-11-phenyl-4,10-undecadien-1-ol (20) To a
stirred solution of compound 19 (0.85 g, 1.41 mmol) in
methanol (20 mL) was added PPTS (10 mol%) (cat.)
and the mixture was stirred at r.t. for 4 h. The methanol
was removed under reduced pressure and the crude
product was purified by silica gel column chromatogra-
phy to afford 20. Yield: 0.614 g (84%); gummy oil; Rf＝
0.35 [V(EtOAc) ∶ V(n-Hexane) ＝ 7 ∶ 3]; [α]D25
1
＋41.95 (c 0.75, CHCl3); H NMR (CDCl3, 300 MHz)
δ: 1.60—1.91 (m, 4H), 2.18 (br s, 1H, OH), 2.27—2.38
(m, 2H), 3.34 (s, 3H), 3.54—3.80 (m, 4H), 4.09—4.22
(m, 1H), 4.21 (d, J＝11.7 Hz, 1H), 4.29 (d, J＝11.7 Hz,
1H), 4.42 (d, J＝6.7 Hz, 1H), 4.51 (d, J＝11.5 Hz, 1H),
4.56 (d, J＝11.7 Hz, 1H), 4.64 (d, J＝6.7 Hz, 1H), 5.36
(dd, J＝8.1, 15.5 Hz, 1H), 5.66 (dd, J＝8.1, 15.5 Hz,
1H), 6.07 (dd, J＝8.0, 15.8 Hz, 1H), 6.53 (d, J＝15.8
Hz, 1H), 7.08—7.36 (m, 15H); 13C NMR (75 MHz) δ:
Chin. J. Chem. 2010, 28, 2421— 2427
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2425

Sabitha et al.
FULL PAPER
36.9, 37.9, 41.4, 55.5, 60.1, 70.3, 71.3, 75.0, 75.8, 76.6,
93.5, 125.7, 126.4, 127.5, 127.7, 127.8, 127.9, 128.3,
128.31, 128.5, 130.0, 130.3, 132.0, 132.2, 136.5, 138.5,
138.7; IR (neat) ν: 3449 (OH), 302－7, 2925, 1630, 1457,
CeCl3•7H2O (cat.) was added to a stirred solution of
compound 21 (0.1 g, 0.17 mmol) in a mixture of MeOH
(2 mL) and CH3CN (2 mL) at reflux temperature for 4 h.
Then the mixture was quenched with solid NaHCO3.
Stirred the reaction mixture at r.t. for 10 min and filtered.
The solvent was removed under reduced pressure and
crude product was purified by silica gel column chro-
matography to afford compound 5. Yield: 0.065 g (76%);
colorless oil; Rf＝0.3 [V(EtOAc)∶V(n-Hexane)＝6∶4];
1
1378, 1028, 973, 917, 758, 697 cm ; ESI-MS m/z: 539
[M＋Na]＋; HRMS (ESI) calcd for C33H40O5Na [M＋
Na]＋ 539.2773, found 539.2788.
Methyl(2Z,5R,6E,9R,11S,12E)-9,11-di(benzyloxy)-
5-(methoxymethoxy)-13-phenyl-2,6,12-tridecatrieno-
ate (21) A solution of compound 20 (0.4 g, 0.77 mmol)
in anhyd. CH2Cl2 (10 mL, plus 4 mL×2 of rinse) was
added to an ice-cooled solution of 2-iodoxybenzoic acid
(IBX) (0.43 g, 1.54 mmol) in DMSO (1.5 mL). The
mixture was stirred at r.t. for 3 h and then filtered
through a Celite pad and washed with CH2Cl2 (20 mL×
4). The combined organic filtrates were washed with
H2O (10 mL×2), brine (10 mL) and dried (Na2SO4),
and concentrated under vacuum to obtained a crude
product, which was used for the next stage without fur-
ther purification.
A solution of bis-2,2,2-(trifluoromethyl)(methoxy-
carbonyl methyl)phosphonate (0.185 g, 0.58 mmol) in
anhyd. THF (2 mL) was added to a stirred solution of
NaH (0.04 g, 1.66 mmol) in anhyd. THF (5 mL) at 0 ℃
under N2 slowly. The mixture was stirred at 0 ℃ for 30
min. Then the mixture was cooled to －78 ℃ and the
above aldehyde in anhyd. THF (5 mL, plus 2 mL×2 of
rinse) was added dropwise over 10 min. The resulting
mixture was stirred at －78 ℃ for 30 min. Then the
mixture was quenched with sat. NH4Cl (2 mL) and the
product was extracted into EtOAC (15 mL×3), and
dried (Na2SO4). The solvent was removed under re-
duced pressure (water bath temperature should not ex-
ceed 30 ℃) and the crude product was purified by us-
ing silica gel (60—120 mesh) column chromatography
with 18% EtOAc in hexane to afford (Z)-olefin ester 21.
1
[α]2D5 ＋70.0 (c 0.45, CHCl3); H NMR (CDCl3, 200
MHz) δ: 1.62 (t, J＝6.6 Hz, 1H), 1.73—1.88 (m, 1H),
2.23—2.37 (m, 2H), 2.59 (t, J＝6.6 Hz, 2H), 3.53—
3.70 (m, 2H), 4.20 (d, J＝11.7 Hz, 2H), 4.44 (d, J＝11.7
Hz, 2H), 4.79 (q, J＝6.6 Hz, 1H), 5.57 (dd, J＝6.6, 15.4
Hz, 1H), 5.76 (dd, J＝8.0, 15.4 Hz, 1H), 5.95 (dxt, J＝
2.2, 9.5 Hz, 1H), 6.29 (dd, J＝7.3, 16.1 Hz, 1H), 6.52 (d,
J＝16.1 Hz, 1H), 6.70—6.83 (m, J＝9.5 Hz, 1H), 7.05
—7.34 (m, 15H); IR (neat) ν: 3026, 2924, 2856, 1723,
1607, 1494, 1453, 1381, 1244, 1062, 969, 758, 698
＋
－1
cm ; ESI-MS m/z: 495.8 [M＋1] ; HRMS (ESI) calcd
for C33H35O4 [M＋1]＋ 495.1936, found 495.1938.
(4R,6S,7E)-6-(Benzyloxy)-8-phenyl-1,7-octadien-
4-ol (10) To a stirred solution of epoxide 6 (0.1 g, 0.35
mmol) in CH2Cl2 (4 mL), was added freshly prepared
vinyl magnesium bromide (0.36 mL, 2.74 mmol) at
－10 ℃. The reaction mixture was stirred at same tem-
perature for about 1 h, then quenched with saturated
NH4Cl solution (2 mL) and extracted with EtOAc (5 mL
×3). Combined organic layers were washed with brine
(8 mL×2), dried over Na2SO4 and concentrated under
reduced pressure. Purification by column chromato-
graphy afforded 10 (0.089 g, 81%) as a thick syrup.
Rf＝ 0.65 [V(EtOAc) ∶ V(n-Hexane) ＝ 2 ∶ 8]; [α]D25
－34.81 (c 1.5, CHCl3); 1H NMR (CDCl3, 300 MHz) δ:
1.62—1.89 (m, 2H), 2.10—2.25 (m, 2H), 3.86—4.02
(m, 1H), 4.20—4.29 (m, 1H), 4.40 (d, J＝12.0 Hz, 1H),
4.65 (d, J＝12.0 Hz, 1H), 5.07 (dd, J＝1.5, 12.0 Hz,
2H), 5.71—5.88 (m, 1H), 6.16 (dd, J＝7.5, 15.8 Hz,
1H), 6.57 (dd, J＝8.3, 15.8 Hz, 1H), 7.07—7.42 (m,
10H); 13C NMR (CDCl3, 100 MHz) δ: 39.2, 42.0, 67.6,
70.5, 77.5, 117.5, 126.4, 127.6, 127.7, 128.2, 128.3,
128.5, 129.4, 132.3, 134.7, 136.2, 138.0; HRMS (ESI)
calcd for C21H24O2Na 331.1673, found 331.1660
Yield: 0.2
g
(76%); colourless oil; Rf＝ 0.55
[V(EtOAc) ∶ V(n-Hexane) ＝ 7 ∶ 3]; [α]2D5 ＋4.5 (c
1
0.75, CHCl3); H NMR (CDCl3, 200 MHz) δ: 1.60—
1.92 (m, 4H), 2.32 (t, J＝7.5 Hz, 1H), 2.90 (t, J＝7.5
Hz, 1H), 3.30 (s, 3H), 3.66 (s, 3H), 3.52—3.83 (m, 2H),
4.01—4.20 (m, 1H), 4.28 (d, J＝11.3 Hz, 1H), 4.44 (d,
J＝11.3 Hz, 1H), 4.40—4.54 (m, 1H), 4.57 (d, J＝11.0
Hz, 1H), 4.62 (d, J＝11.0 Hz, 1H), 4.57—4.67 (m, 1H),
5.36 (dd, J＝7.5, 15.1 Hz, 1H), 5.67 (dd, J＝7.5, 15.1
Hz, 1H), 5.79 (dxt, J＝2.2, 11.3 Hz, 1H), 6.08 (dd,
J＝7.5, 15.9 Hz, 1H), 6.28 (dd, J＝7.5, 11.3 Hz, 1H),
6.54 (d, J＝15.9 Hz, 1H), 7.06—7.40 (m, 15H); 13C
NMR (75 MHz) δ: 34.9, 37.1, 41.4, 51.0, 55.4, 70.2,
70.8, 74.8, 75.2, 75.7, 93.5, 120.7, 125.7, 126.5, 127.5,
127.6, 127.7, 127.8, 127.9, 128.3, 128.6, 130.2, 130.3,
130.4, 131.9, 136.5, 138.6, 138.7, 146.0, 166.6; IR (neat)
ν: 3028, 2925, 1721, 1645, 1494, 1444, 1403, 1175,
－6
(－4.2273×10 error).
Mono benzyl ether of diastereoisomer of crypto-
folione (4) Grubbs' second generation catalyst (0.019
g, 0.023 mmol, 3 mol%) was dissolved in 2 mL of
CH2Cl2 and was added dropwise to a solution of the
compound 10 (0.07 g, 0.22 mmol) and compound 11
(0.031 g, 0.25mmol) in 2 mL of CH2Cl2 at 0 ℃. After
completion of addition, reaction was allowed to stir for
8 h. The solvent was removed under reduced pressure
and the crude product was purified by silica gel column
chromatography to afford the pure product 4 (Yield:
－1
1094, 1031, 972, 916, 819, 744, 696 cm ; ESI-MS m/z:
593 [M＋Na]＋; HRMS (ESI) calcd for C36H42O6Na [M
0.067 g, 74%) as a clear liquid. H NMR (CDCl3, 400
1
＋Na]＋ 593.2879, found 593.2886.
MHz) δ: 1.91—2.16 (m, 2H), 2.23—2.32 (m, 2H), 2.50
—2.56 (m, 2H), 2.92 (br s, 1H), 3.97—4.08 (m, 2H),
4.56 (d, J＝11.8 Hz, 1H), 4.60 (d, J＝11.8 Hz, 1H), 5.07
(6R)-6-[(1E,4R,6S,7E)-4,6-Di(benzyloxy)-8-phenyl-
1,7-octadienyl]-5,6-dihydro-2H-2-pyranone
(5)
2426
www.cjc.wiley-vch.de
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2421— 2427

Synthesis of Stereoisomers of Cryptofolione 6'-Mono- and 4',6'-Di-O-benzyl Ethers
(q, J＝6.78 Hz, 1H), 5.80 (dd, J＝2.5, 15.5 Hz, 1H),
5.90 (dd, J＝2.3, 15.5 Hz, 1H), 6.07 (dxt, J＝1.7, 10.17
Hz, 1H), 6.24 (dd, J＝6.78, 16.1 Hz, 1H), 6.71 (d, J＝
15.26 Hz, 1H), 6.88 (ddd, J＝4.2, 8.5, 9.3 Hz, 1H), 7.21
—7.39 (m, 10H, Ar-H); 13C NMR (75 MHz) δ: 29.71,
34.42, 35.32, 65.17, 70.2, 71.80, 77.83, 121.45, 125.52,
126.57, 126.73, 127.53, 127.54, 127.57, 128.23, 128.28,
128.55, 132.98, 135.63, 138.15, 144.62, 163.82;
ESI-MS m/z: 427 [M＋Na]＋; HRMS (ESI) calcd for
C26H28O4Na 427.2280, found 427.2273.
C.; Rojas de Arias, A.; Ferreira, M. E.; Inchaustti, A.; Yaluff,
G. J. Pharm. Pharmacol. 2001, 53, 563.
Matsuoka, Y.; Aikawa, K.; Irie, R.; Katsuki, T. Heterocycles
2005, 66, 187.
7
8
(a) Sabitha, G.; Sudhakar, K.; Reddy, N. M.; Rajkumar, M.;
Yadav, J. S. Tetrahedron Lett. 2005, 46, 6567.
(b) Sabitha, G.; Narjis, F.; Swapna, R.; Yadav, J. S. Synthesis
2006, 17, 2879.
(c) Sabitha, G.; Reddy, E. V.; Yadagiri, K.; Yadav, J. S.
Synthesis 2006, 19, 3270.
(d) Sabitha, G.; Sudhakar, K.; Yadav, J. S. Tetrahedron Lett.
2006, 47, 8599.
Acknowledgements
(e) Sabitha, G.; Bhaskar, V.; Yadav, J. S. Tetrahedron Lett.
2006, 47, 8179.
V.B thanks UGC, S.S.S.R thanks CSIR, New Delhi
for the award of fellowships.
(f) Sabitha, G.; Swapna, R.; Reddy, E. V.; Yadav, J. S.
Synthesis 2006, 24, 4242.
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Chin. J. Chem. 2010, 28, 2421— 2427
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
2427