Synthesis of 7- Epi -goniodiol by proline-catalyzed diastereoselective direct aldol reaction

Article abstract of DOI:10.1055/s-0033-1341107

A simple organocatalytic approach was developed for the total synthesis of 7-epi-goniodiol. The strategy involves l-proline-catalyzed diastereoselective direct aldol reaction and Baeyer-Villiger oxidation as key steps for the construction of chiral lactone. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0033-1341107

LETTER
▌1283
lSetyternthesis of 7-epi-Goniodiol by Proline-Catalyzed Diastereoselective Direct
Aldol Reaction
Synthesis of 7-epi-Goniodiol
Bacchu Veena,* Gangavaram V. M. Sharma
D-211, Discovery Laboratory, Organic & Biomolecular Chemistry Division, CSIR-Indian Institute of Chemical Technology, Hyderabad
500007, India
Fax +91(40)27160387; E-mail: veenabachhu@gmail.com
Received: 04.01.2014; Accepted after revision: 13.03.2014
tory activity against HL-60 at a low concentration (11
Abstract: A simple organocatalytic approach was developed for
g/mL) and displayed selective activities in the trypan blue
the total synthesis of 7-epi-goniodiol. The strategy involves L-pro-
dye exclusion test.
line-catalyzed diastereoselective direct aldol reaction and Baeyer–
Villiger oxidation as key steps for the construction of chiral lactone.
In recent years, the proline-catalyzed asymmetric aldol re-
Key words: styryllactones, 7-epi-goniodiol, proline, aldol reaction, action has been extensively studied and has emerged as an
Baeyer–Villiger oxidation
impressive protocol for the synthesis of various natural
products.5 We report herein the total synthesis of 1 using
a proline-catalyzed diastereoselective direct aldol reaction
as the key step.
Styryl lactones1 are heterocyclic natural products mainly
isolated from plants of the genus Goniothalamus (An-
nonaceae)2 and possess activities including antitumor, an-
tifungal, and antibiotic properties.3 The biological
activities and interesting structural features of styryl lac-
tones have attracted attention for their synthesis.
The retrosynthetic analysis of 1 is shown in Scheme 1.
The lactone moiety in 1 was envisaged to be accessible
through Baeyer–Villiger oxidation of ketone 4, which
could be derived from L-proline-catalyzed diastereoselec-
tive direct aldol reaction between aldehyde 5 and cylopen-
tanone (6). Thus, the main points of this synthetic strategy
are the C–C bond formation between 5 and 6, ring expan-
sion of the ketone to a lactone, and introduction of the ole-
finic double bond, en route to the construction of the α,β-
unsaturated lactone of the target molecule.
7-epi-Goniodiol (1) along with leiocarpin B (2) and leio-
carpin C (3, Figure 1), was isolated by Mu and co-
workers4 from the ethanolic extract of stem barks of Go-
niothalamus leiocarpus, a tropical plant widespread in the
south of the Yunnan province in China. The structure of 1
was elucidated and its stereochemistry was defined based
on spectroscopic methods, X-ray crystallographic analy-
sis, and some chemical transformations. It contains three
stereocenters (6R,7S,8R) and an α,β-unsaturated pyrone
ring system. 7-epi-Goniodiol (1) exhibited strong inhibi-
The stereocenter at C-8 was envisaged to be derived from
(R)-mandelic acid, while, the C-6, C-7 vic-diol would be
generated through the proline-catalyzed aldol reaction.
Baeyer–Villiger oxidation was expected to permit effi-
cient expansion of the ketone to the lactone, while the un-
O
OH
O
O
O
2
O
O
O
O
OH
OH
O
6
H
10
4
OH
8
7
OH
leiocarpin C (2)
OH
OH
7-epi-goniodiol (1)
leiocarpin B (3)
Figure 1 Structures of 7-epi-goniodiol (1), leiocarpin C (2) and B (3)
O
O
O
OMOM
H
MOMO
OH
O
+
O
OMOM
OH
4
5
6
1
Scheme 1 Retrosynthetic analysis
SYNLETT 2014, 25, 1283–1286
Advanced online publication: 28.04.2014
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
DOI: 10.1055/s-0033-1341107; Art ID: ST-2013-D1136-L
© Georg Thieme Verlag Stuttgart · New York

1284
B. Veena, G. V. M. Sharma
LETTER
O
O
OMOM
MOMO
OMOM
MOMO
OH
a
H
b
+
OH
OH
O
O
7
5
8a
8b
6
O
O
OH
O
c
d
8a
OH
O
8c
9
O
O
O
O
MOMO
MOMO
MOMO
O
e
g
h
f
8a
1
OMOM
OMOM
11
OMOM
10
4
Scheme 2 Reagents and conditions: (a) IBX, DMSO, EtOAc, reflux, 2 h; (b) L-proline, 12 h, r.t., 82% (over two steps); (c) FeCl3·6H2O,
CH2Cl2, r.t., 2 h; (d) 2,2-dimethoxypropane, PPTS, CH2Cl2, r.t., 5 h, 78%; (e) MOMCl, DIPEA, CH2Cl2, 0 °C to r.t., 12 h, 85%; (f) MCPBA,
NaHCO3, CH2Cl2, 0 °C to r.t., 4 h, 88%; (g) i) PhSeBr, LiHMDS, THF, –78 °C; ii) 30% H2O2 (aq)–CH2Cl2 (2:1), 0 °C, 10 min, 72% (over two
steps); (h) FeCl3·6H2O, CH2Cl2, r.t., 2 h, 78%.
saturation would be created through a selenation– Finally, deprotection of the MOM groups in 11 was af-
deselenation protocol.
fected by reaction with FeCl3·6H2O8 in CH2Cl2 at room
25
temperature for two hours to afford 1 in 78% yield {[α]D
Thus, the synthesis of 1 began with the known alcohol 76
(Scheme 2). Accordingly, oxidation of 7 with IBX in
EtOAc and DMSO at reflux for two hours gave the corre-
sponding aldehyde 5 which was subjected to L-proline-
+107.6 (c 0.3, CHCl3); lit.4 [α]D25 +96.4 (c 0.3, CHCl3)}.
The spectroscopic and physical data of synthetic 1 were
consistent with the data reported in the literature.4
catalyzed diastereoselective direct aldol reaction with cy- Thus, in conclusion, a simple organocatalytic route, cata-
clopentanone 6 at room temperature for 12 hours to afford lyzed by L-proline, for the total synthesis of 7-epi-gonio-
a diastereomeric mixture of 8a and 8b. After purification diol (1) has been achieved. Of the three stereocenters, two
by flash column chromatography on silica gel (11% are obtained from the proline-catalyzed diastereoselective
EtOAc in PE), diastereomers 8a and 8b were obtained in direct aldol reaction, while the third stereocenter was de-
82% yield in a ratio of 88:12, respectively.
rived from (R)-mandelic acid. This strategy has signifi-
cant potential for the synthesis of a variety of other
biologically important styrylpyrones.
The major diastereomer 8a was subjected to FeCl3·6H2O
in CH2Cl2 at room temperature for two hours to give the
diol 8c, which, on subsequent treatment with 2,2-dime-
thoxypropane and PPTS in CH2Cl2 at room temperature
for five hours, afforded the acetonide 9 in 78% yield
(R)-2-[(1R,2R)-1-Hydroxy-2-(methoxymethoxy)-2-phenylehyl]-
cyclopentanone (8a) and (R)-2-[(1S,2R)-1-Hydroxy-2-(me-
thoxymethoxy)-2-phenylethyl]cyclopentanone (8b)
(Scheme 2). The absolute stereochemistry of 9 was con-
25
firmed from its specific rotation value {[α]D +97.0 (c A suspension of IBX (11.5 g, 41.1 mmol) in DMSO (5.0 mL) was
0.95, CHCl3)}, comparable with the reported7 {[α]D25 +93
cooled to 0 °C, treated with a solution of alcohol 7 (5 g, 27.4 mmol)
in EtOAc (60 mL) and stirred at r.t. for 2 h. The reaction mixture
(c 1.2, CHCl3)}.
was filtered through a Celite® pad and washed with EtOAc (4 × 20
Alcohol 8a was subjected to reaction with MOMCl and
DIPEA in CH2Cl2 at room temperature for five hours to
afford MOM ether 4 in 85% yield. Baeyer–Villiger oxida-
tion of ketone 4 with MCPBA in CH2Cl2 at room temper-
ature for four hours furnished lactone 10 in 88% yield.
After conversion of the ketone in 4 into lactone 10, intro-
duction of α,β-unsaturation was achieved in two steps
through selenation and deselenation. Accordingly, treat-
ment of 10 with LiHMDS and phenylselenenyl bromide in
THF at –78 °C followed by oxidative elimination on reac-
tion with 30% H2O2 gave compound 11 in 72% yield over
two steps.
mL). The organic layers were washed with H2O (2 × 30 mL), brine
(40 mL), dried (Na2SO4), filtered, and evaporated to give the corre-
sponding aldehyde 5, which was directly used for the next reaction.
A mixture of aldehyde 5 (4.9 g, 27.2 mmol), cyclopentanone (6, 5
mL), and L-proline (0.94 g, 8.1 mmol) were stirred at r.t. for 12 h.
The reaction mixture was quenched with H2O (10 mL) and extract-
ed with CHCl3 (4 × 20 mL). The combined extracts were dried
(Na2SO4), filtered, evaporated, and the residue purified by column
chromatography (60–120 mesh silica gel, 11% EtOAc in PE) to af-
ford 5.19 g of 8a (Rf = 0.50) and 0.71 g of 8b (Rf = 0.45) in 82%
yield.
Compound 8a: [α]D25 +40.1 (c 0.5, CHCl3). IR (neat): 3351, 2823,
2857, 1689, 1447 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.33–7.16
Synlett 2014, 25, 1283–1286
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of 7-epi-Goniodiol
1285
(m, 5 H, ArH), 4.51 (q, 2 H, J = 6.9, 13.8 Hz, OCH2), 4.36 (d, 1 H,
J = 9.3 Hz, OCH), 4.27 (dd, 1 H, J = 1.9, 8.8, 10.8 Hz, OCH), 3.31
(s, 3 H, OCH3), 2.22–1.92 (m, 5 H, 2 × CH2, CH), 1.64–1.59 (m, 2
H, CH2). 13C NMR (75 MHz, CDCl3): δ = 138.3, 128.2, 128.0,
127.9, 94.9, 79.7, 75.9, 55.9, 48.7, 39.5, 27.3, 20.8. HRMS: m/z
calcd for C15H20O4Na [M + Na]+: 287.1259; found: 287.1265.
Compound 8b: [α]D25 –102.5 (c 0.8, CHCl3). IR (neat): 3351, 2823,
2857, 1689, 1447 cm–1. 1H NMR (300 MHz, CDCl3): δ = 7.32–7.24
(m, 5 H, ArH), 4.44 (q, 2 H, J = 6.7, 9.4 Hz, OCH2), 4.30 (d, 1 H, J
= 8.8 Hz, OCH), 4.24–4.20 (m, 1 H, OCH), 3.26 (s, 3 H, OCH3),
2.17–1.86 (m, 5 H, 2 × CH2, CH), 1.60–1.51 (m, 2 H, CH2). 13C
NMR (75 MHz, CDCl3): δ = 137.6, 128.6, 128.5, 127.6, 94.5, 81.3,
73.3, 55.7, 49.7, 38.7, 22.2, 20.6. HRMS: m/z calcd for C15H20O4Na
[M + Na]+: 287.1259; found: 287.1263.
(10 mL) and brine (10 mL). The extract was dried (Na2SO4), fil-
tered, evaporated, and the residue purified by flash chromatography
(60–120 mesh silica gel, 16% EtOAc in PE) to afford 10 (0.48 g,
88%) as a pale yellow syrup; [α]D25 –68.7 (c 3.35, CHCl3). IR (neat):
2823, 2857, 1689, 1447, 1248, 1054. 1H NMR (500 MHz, CDCl3):
δ = 7.27–7.21 (m, 5 H, ArH), 4.66 (d, 1 H, J = 5.9 Hz, OCH), 4.52–
4.37 [m, 4 H, (OCH2)2], 4.12–4.05 (m, 1 H, OCH), 3.92–3.84 (m, 1
H, OCH), 3.24 [d, 6 H, J = 5.4 Hz, (OCH3)2], 2.46–2.16 (m, 2 H,
COCH2), 1.85–1.56 (m, 4 H, 2 × CH2). 13C NMR (75 MHz, CDCl3):
δ = 128.7, 128.4, 127.4, 98.3, 94.4, 82.2, 79.4, 56.3, 55.8, 29.8, 22.8,
21.1, 18.4. HRMS: m/z calcd for C17H24O6Na [M + Na]+: 347.1470;
found: 347.1472.
(R)-6-[(5R,6R)-6-Phenyl-2,4,7,9-tetraoxadecan-5-yl]-5,6-di-
hydro-2H-pyran-2-one (11)
To a stirred solution of LiHMDS (1.4 mL, 1.07 mmol) in THF (1.5
mL) at –78 °C was added, dropwise, a solution of 10 (0.25 g, 0.77
mmol) in THF (3.5 mL). After 30 min, phenylselenenyl bromide
(0.27 g, 1.06 mmol) was added and the reaction stirred for 1 h. The
mixture was then quenched with aq NH4Cl (4 mL), distilled H2O (8
mL) and extracted with Et2O (20 mL). The combined organic ex-
tracts were filtered through a pad of silica gel (eluting with Et2O)
and evaporated to give a slightly orange oil.
(R)-2-[(4R,5R)-2,2-Dimethyl-5-phenyl-1,3-dioxolan-4-yl]cyclo-
pentanone (9)
To a solution of MOM ether 8a (0.05 g, 0.18 mmol) in CH2Cl2 (1.5
mL) was added FeCl3·6H2O (10 mol%, 0.005 g) at 0 °C, and the re-
action mixture was stirred at r.t. for 2 h. It was quenched with H2O
(2 mL) and extracted with CH2Cl2 (2 × 12 mL). The combined or-
ganic layers were washed with brine (10 mL), dried (Na2SO4), fil-
tered, and evaporated to give the diol 8c, which was directly used
for the next reaction.
To a stirred solution of the above compound in CH2Cl2 (5 mL) at 0
°C, aq H2O2 (30%, 2 mL) was added, and the mixture was stirred at
r.t. for 10 min. It was extracted with CH2Cl2 (20 mL) and dried
(Na2SO4). After filtration, the solvent was evaporated, and the resi-
due purified by flash column chromatography (60–120 mesh silica
gel, 8% EtOAc in PE) to afford 11 (0.17 g, 72%) as a colorless oil;
To a solution of diol 8c (0.04 g, 0.19 mmol) in CH2Cl2 (20 mL) were
added 2,2-dimethoxypropane (0.03 mL, 0.27 mmol) and a catalytic
amount of PPTS at 0 °C. The reaction mixture was stirred at r.t. for
5 h. NaHCO3 was added to neutralize the PPTS and filtered. Re-
moval of solvent and purification of the residue by column chroma-
tography (60–120 mesh silica gel, 6% EtOAc in PE) afforded 9
(0.03 g, 78%) as a pale brown oil; [α]D25 +98.0 (c 0.95, CHCl3). 1H
NMR (500 MHz, CDCl3): δ = 7.31–7.27 (m, 5 H, ArH), 4.57 (d, 1
H, J = 9.0 Hz, OCH), 4.20–4.16 (m, 1 H, OCH), 2.31–2.04 (m, 6 H,
3 × CH2, CH), 1.88–1.70 (m, 1 H), 1.52 [br s, 3 H, C(CH3)2], 1.45
[br s, 3 H, C(CH3)2]. 13C NMR (75 MHz, CDCl3): δ = 218.1, 136.7,
128.6, 128.5, 126.6, 109.0, 81.1, 80.8, 47.3, 38.5, 27.0, 26.9, 22.7,
20.8. HRMS: m/z calcd for C17H28O5Na [M + Na]+: 333.1678;
found: 333.3751.
25
[α]D –148.0 (c 0.95, CHCl3). IR (neat): 2986, 2933, 1720, 1494,
1454, 1380, 1248, 1063, 1030 cm–1. 1H NMR (500 MHz, CDCl3): δ
= 7.40–7.31 (m, 5 H, ArH), 6.86–6.78 (m, 1 H, CH=CH), 5.95–5.91
(m, 1 H, CH=CH), 4.82 (d, 1 H, J = 5.5 Hz, OCH), 4.66–4.58 [m, 4
H, (OCH2)2], 4.38 (d, 1 H, J = 7.0 Hz, OCH), 4.04 (t, 1 H, J = 5.0
Hz, OCH), 3.33 [d, 6 H, J = 7.8 Hz (OCH3)2], 2.63–2.54 (m, 1 H,
CH), 2.28–2.19 (m, 1 H, CH). 13C NMR (75 MHz, CDCl3): δ =
145.5, 128.7, 128.3, 127.3, 120.8, 98.2, 94.4, 81.5, 76.8, 76.4, 56.3,
55.9, 31.4, 29.6, 24.9. HRMS: m/z calcd for C17H22O6Na [M + Na]+:
345.1315; found: 345.1308.
(R)-2-[(5R,6R)-6-Phenyl-2,4,7,9-tetraoxadecan-5-yl]cyclopen-
tanone (4)
7-epi-Goniodiol (1)
To a solution of 11 (0.03 g, 0.09 mmol) in CH2Cl2 (1 mL) at 0 °C,
FeCl3·6H2O (10 mol%, 0.02 g) was added, and the mixture was
stirred at r.t. for 2 h. The reaction was quenched with H2O (1 mL)
and extracted with CH2Cl2 (2 × 12 mL). The combined organic lay-
ers were washed with brine (10 mL), dried (Na2SO4), filtered, and
evaporated. The residue was purified by column chromatography
(60–120 mesh silica gel, 50% EtOAc in PE) to afford 1 (0.19 g,
To a stirred solution of alcohol 8a (1.28 g, 4.84 mmol) in CH2Cl2
(14 mL) at 0 °C, DIPEA (1.43 mL, 19.3 mmol) was added, and the
reaction mixture was stirred for 20 min. MOMCl (0.73 mL, 9.69
mmol) and a catalytic amount of DMAP were added, the mixture
stirred at r.t. for 12 h; then quenched with sat. aq NH4Cl (5 mL) and
extracted with CH2Cl2 (2 × 12 mL). The combined organic layers
were washed with H2O (10 mL), brine (10 mL), and dried (Na2SO4).
Filtration, evaporation of solvent, and purification of the residue by
column chromatography (60–120 mesh silica gel, 8% EtOAc in PE)
25
25
78%) as a viscous liquid; [α]D +107.6 (c 0.3, CHCl3); lit.4 [α]D
+96.4 (c 0.3, CHCl3). IR (neat): 3451, 2986, 1719, 1645, 1440,
1375, 1210, 1058 cm–1. 1H NMR (500 MHz, CDCl3): δ = 7.39–7.37
(m, 5 H, ArH), 6.95–6.89 (m, 1 H, CH=CH), 6.02–5.97 (m, 1 H,
CH=CH), 4.93 (d, 1 H, J = 3.9 Hz, OCH), 4.46–4.40 (m, 1 H, OCH),
4.24–4.18 (m, 1 H, OCH), 2.64–2.58 (m, 1 H, CH), 2.54–2.49 (m,
1 H, CH). 13C NMR (75 MHz, CDCl3): δ = 164.0, 145.8, 140.3,
128.7, 128.1, 126.4, 120.8, 77.4, 76.1, 29.6. HRMS: m/z calcd for
C13H14O2Na [M + Na]+: 257.0792; found: 257.0790.
25
afforded 4 (1.26 g, 85%) as a colorless syrup; [α]D –7.9 (c 0.65,
1
CHCl3). IR (neat): 3448, 2956, 2925, 2854, 1734, 1642 cm–1. H
NMR (500 MHz, CDCl3): δ = 7.35–7.26 (m, 5 H, ArH), 4.70 (q, 2
H, J = 8.4, 14.3 Hz, OCH2), 4.56–4.51 (m, 2 H, OCH2), 4.45 (d, 1
H, J = 6.4 Hz, OCH), 4.31–4.25 (m, 1 H, OCH), 3.26 [d, 6 H, J =
5.9 Hz –(OCH3)2], 2.20–1.85 (m, 5 H, 2 × CH2, CH), 1.72–1.55 (m,
2 H, CH2). 13C NMR (75 MHz, CDCl3): δ = 219.1, 138.5, 128.6,
128.2, 127.6, 98.3, 94.4, 80.6, 78.9, 56.1, 55.5, 50.5, 38.6, 23.1,
20.8. HRMS m/z calcd for C17H24O5Na [M + Na]+: 331.1521;
found: 333.1518.
Acknowledgment
One of the authors (B.V.) thanks the CSIR, New Delhi, for financial
support in the form of a fellowship and thanks to Dr. V. B. Jadhav,
SMCG, Dist.-Aurangabad, for his support and encouragement.
(R)-6-[(5R,6R)-6-Phenyl-2,4,7,9-tetraoxadecan-5-yl]tetra-
hydro-2H-pyran-2-one (10)
To a solution of 4 (0.52 g, 1.68 mmol) in anhydrous CH2Cl2 (30 mL)
at 0 °C were added MCPBA (98% activity; 1.74 g, 10.12 mmol) and
NaHCO3 (0.84 g, 10.08 mmol), and the reaction mixture was stirred
at r.t. for 4 h. It was then extracted with Et2O (12 mL), and the or-
ganic layer was washed successively with aq NaHCO3 (8 mL), H2O
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnuIpofoiprmntgirStanoIuifpog
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© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1283–1286

1286
B. Veena, G. V. M. Sharma
LETTER
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Synlett 2014, 25, 1283–1286
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