Stereoselective total synthesis of (-)-pyrenophorin

Article abstract of DOI:10.2174/1570178613666161013145238

Background: Homo and hetero dimers of macrodilacto cyclic compounds were observed frequently in nature and they were built with different types of functional groups, chemical skeletons and ring sizes. Natural products with macrodiolide frameworks are also known to exhibit a wide range of biological properties including antibiotic, antifungal, antihelmintic, phytotoxic, and antileukemic activities. The main aim of this paper was the stereoselective total synthesis of (-)-Pyrenophorin from commercially available starting material (S)-propylene oxide with high yields. Methods: Stereoselective total synthesis of (-)-Pyrenophorin was done by hydrolytic kinetic resolution, Wittig olefination followed by Mitsunobu reaction. Results: The disconnection approach analysis (retrosynthetic) of (-)-Pyrenophorin envisions that it would be synthesized through the hydroxyl-acid via cyclo dimerisation under the Mitsunobu reaction conditions and followed by deprotection of cyclic ketals. Hydroxy-acid would be achieved from alcohol, while the alcohol would be obtained from (S)-propylene oxide. Conclusion: The total synthesis of target molecules achieved from commercially available starting materials, soft reaction conditions, decrease of reaction conditions and high purities with large yields. These type of biologically potent target molecules total synthesis was very important in industrial point of view.

Full text of DOI:10.2174/1570178613666161013145238

6
93
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Letters in Organic Chemistry, 2016, 13, 693-697
RESEARCH ARTICLE
eISSN: 1 85 7 50 - 61 27 58 56
Volume 13, Number 9
IF
m
a cp t ao cr t:
0
.756
Stereoselective Total Synthesis of (-)-Pyrenophorin
BS EC N
I
ET NH AC ME
1
2
1,*
Kolluri Ramakrishna , Reddymasu Sreenivasulu , Siddaiah Vidavalur and
3
,*
Boggu Jagan Mohan Reddy
1
Department of Organic Chemistry, Food, Drugs and Water, Andhra University, Visakhapatnam - 530 003, A.P., India;
2
Department of Chemistry, University College of Engineering (Autonomous), Jawaharlal Nehru Technological Univer-
3
sity, Kakinada - 533 003, Andhra Pradesh, India; Department of Chemistry, Adikavi Nannaya University, Rajahmun-
dry-533 296, Andhra Pradesh, India
Abstract: Background: Homo and hetero dimers of macrodilacto cyclic compounds were observed fre-
quently in nature and they were built with different types of functional groups, chemical skeletons and
ring sizes. Natural products with macrodiolide frameworks are also known to exhibit a wide range of
biological properties including antibiotic, antifungal, antihelmintic, phytotoxic, and antileukemic activi-
ties. The main aim of this paper was the stereoselective total synthesis of (-)-Pyrenophorin from com-
mercially available starting material (S)-propylene oxide with high yields.
A R T I C L E H I S T O R Y
Methods: Stereoselective total synthesis of (-)-Pyrenophorin was done by hydrolytic kinetic resolution,
Wittig olefination followed by Mitsunobu reaction.
Received: December 02, 2015
Revised: September 19, 2016
Accepted: September 21, 2016
Results: The disconnection approach analysis (retrosynthetic) of (-)-Pyrenophorin envisions that it
would be synthesized through the hydroxyl-acid via cyclo dimerisation under the Mitsunobu reaction
conditions and followed by deprotection of cyclic ketals. Hydroxy-acid would be achieved from alco-
hol, while the alcohol would be obtained from (S)-propylene oxide.
DOI:
1
3
0.2174/15701786136661610131452
8
Conclusion: The total synthesis of target molecules achieved from commercially available starting
materials, soft reaction conditions, decrease of reaction conditions and high purities with large yields.
These type of biologically potent target molecules total synthesis was very important in industrial point
of view.
Keywords: (S)-propylene oxide, Jacobsen’s hydrolytic kinetic resolution, Wittig olefination, Mitsunobu reaction.
INTRODUCTION
2
Drechslera avenae [14]. This C -symmetric dilactone is de-
rived by head-to-tail dimerization of two identical C8 units.
Due to the promising biological activity and the impressive
structural features of (-)-pyrenophorin (1), appeared to be an
attractive target for total synthesis [18-23]. The structure of
Homo and hetero dimers of macrodilacto cyclic com-
pounds were observed frequently in nature and they were
built with different types of functional groups, chemical
skeletons and ring sizes. Different types of macrodiolides [1-
(
-) - Pyrenophorin is shown in Fig. (1).
3
] and macrocyclic monolactones [4-6] were synthesized by
scientists and researchers across the world due to wide range
of biological properties including antibiotic, antifungal [7-9],
antihelmintic [10-12], phytotoxic [13-15], and antileukemic
activities.
O
O
O
O
The macrolide dilactone pyrenophorin is a good antifun-
gal and herbicidal agent and has been isolated from Pyreno-
phora avenae [16], Stemphylium radicinum [17, 19], and
O
O
(
-)-Pyrenophorin (1)
Fig. (1). Structure of (-) – Pyrenophorin.
*
Address correspondence to these authors at the Department of Organic
Chemistry, Food, Drugs and Water, Andhra University, Visakhapatnam - 530
03, A.P., India; Tel: +91 9347153270; E-mail: sidduchem@gmail.com; and
Department of Chemistry, Adikavi Nannaya University, Rajahmundry-533
96, Andhra Pradesh, India; E-mail: reddybjm2002@yahoo.com
Our ongoing research mainly concentrates through the
total synthesis of biologically potent and diverse natural
products, so we reported the total synthesis of (-)-Pyrenophorin
0
2
1
875-6255/16 $58.00+.00
© 2016 Bentham Science Publishers

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94 Letters in Organic Chemistry, 2016, Vol. 13, No. 9
Ramakrishna et al.
O
O
OH
O
OTBS
O
O
O
OH
O
O
OH
O
4
O
1
3
2
Scheme (1). Retero synthetic analysis of (-) - Pyrenophorin.
(
1) utilizing the Jacobsen’s hydrolytic kinetic resolution and
THF for 5 h afforded the pyrenophorin 1 in 76% yield as a
o o
the intermolecular Mitsunobu cyclization.
white solid. m.p. 172-174 C {lit. [9] m.p. 175 C}; [α]
D
-58.6
(
c 0.11, acetone) {lit.[32] [α] -54.5 (c 0.48, acetone)}.
D
RESULTS AND DISCUSSION
EXPERIMENTAL
The retrosynthetic analysis of 1 was shown in Scheme 1
and it would be synthesized through the hydroxylacid 2 via
cyclo dimerisation under the Mitsunobu reaction conditions
and followed by deprotection of cyclic ketals. Hydroxy-acid
All the chemical reagents and solvents were supplied by
Sigma Aldrich and AVRA, India. These solvents are not
further purified by using basic purification techniques. The
progress of the chemical reactions in this scheme were moni-
2
would be achieved from alcohol 3, while the alcohol 3
would be obtained from (S)-propylene oxide 4.
1
13
tored by TLC plates supplied by Merck company. H and
C
The known epoxide 5 [24-28] was treated with allyl
magnesium chloride in ethereal solvent followed by the sub-
sequent silylation of the secondary alcohol 5 (TBSCl, imida-
NMR spectra were recorded on Bruker spectrometer with
300 MHz, 150 MHz and 75 MHz resolution. Chemical shifts
and coupling constants are reported in δ units and Hertz.
Different multiplicities singlet, doublet, double doublet, trip-
let, quartet and multiplet were indicated by s, d, dd, t, q and
m. FT – IR spectra were recorded on Brucker IR spectropho-
tometer by using KBr Pellet. Mass values are noted as ESI
zole) in CH
2 2
Cl afforded 6 in 70% yield. The compound 6
undergo ozonolysis in CH
2
2
Cl at -78 °C over a period of half
an hour yield the corresponding aldehyde, which on immedi-
ate treatment with vinylmagnesium bromide in dry THF at
-
40°C for 4 h led to a diastereomeric mixture of allylic alco-
(
MS). Digital polarimeter was used to calculate the optical
hol 3 (syn anti 1:1) in 84% yield. Oxidation of alcohol 3 un-
der Swern reaction conditions gave keto compound 7 in 88%
yield. Masking of 7 using ethyleneglycol in the presence of
PTSA in benzene at reflux for 4 h gave ketal 8 in 71% yield.
rotation values at 25°C.
(S)-tert.-Butyl (hex-5-en-2-yloxy) dimethylsilane (6) [24,
25]
2 2
Ozonolysis of 8 in CH Cl gave the particular aldehyde,
which further undergo Wittig reaction with (methoxycarbon-
ylmethylene)triphenyl phosphorane in benzene as solvent
gave ester 9 in 76% yield and shown in Scheme 2.
A suspension of Mg (3.97 g, 165.5 mmol) was dipped in
30 mL of dry ether and treated with allyl chloride (6.8 mL,
o
82.55 mmol) at 25 C. The reaction mixture allowed for stir-
ring over a period of 30 min. Further this reaction mass was
cooled to -78°C. Now a solution of 4 (4 mL, 55.17 mmol) in
dry ether (10 mL) was added very slowly dropwise to the
above mixture and the mixture was allowed for stirring at the
same temperature over a period of 2 h. Further, the reaction
Ester 9 on hydrolysis under basic conditions (LiOH in
THF:MeOH:H O-3:1:1) gave acid 10 (Scheme 3) which fur-
2
ther desilylation with TBAF in dry tetrahydro furan solvent
gave the hydroxy-acid 2 in 86% yield. Hydroxy-acid 2 on
cyclodimerisation under the Mitsunobu reaction conditions
mixture was neutralized with aq. NH Cl solution (10 mL)
4
o
[
5
30, 31] (Ph
3
P and DEAD) for 10 h at -25 C afforded 11 in
followed by extraction with ether (2 × 50 mL). The two
organic layers are combined and washed with 30 mL brine
5% yield. Finally, deprotection of ketal with 10% HCl in
OH
OTBS
OTBS
O
a
b
c
4
5
6
3
OH
O
OTBS
OTBS
OTBS
O
d
e
f
OMe
O
O
O
7
O
8
9
o
Scheme (2). Reagents and conditions: (a) i) allyl chloride, Mg, dry ether, -78 C, 2 h; b) TBSCl, Imidazole, CH
2
)
Cl
2
2
3 2 2
, rt, 4 h; (c) i) O , CH Cl ,
o
o
o
-
78 C, 30 min; ii) vinylMgBr, THF, -40 C, 4 h; (d) (COCl)
2
, DMSO, Et
3
N CH
2
Cl
2
, -78 C, 2 h; (e) HO(CH
2
OH, PTSA, benzene, reflux,
o
4
h; (f) i) O , CH Cl , -78 C, 15 min; ii) Ph P=CHCOOMe, Benzene, reflux, 2 h.
3 2 2 3

Stereoselective Total Synthesis of (-)-Pyrenophorin
OTBS
Letters in Organic Chemistry, 2016, Vol. 13, No. 9 695
OH
O
O
OTBS
O
O
a
b
OMe
OH
OH
O
O
O
O
O
O
9
1
0
2
O
O
O
O
O
c
d
O
O
O
O
O
O
O
O
1
11
o
2 3
Scheme (3). Reagents and conditions: (a) LiOH, THF:MeOH:H O (3:1:1), rt, 4 h; (b) TBAF, THF, 0 C to rt, 3 h; (c) Ph P, DEAD, toluene:
o
o
THP (10:1) -25 C, 10 h; (d) 10% aq. HCl, THF, 0 C to rt, 5 h.
solution. Finally, the organic layers were dried on Na
2
SO
4
5.2 Hz, -CH
3
), 0.84 (s, 9H, 3 × -CH
3
3
), 0.01 (s, 6H, 2 × -CH );
+
followed by concentration gave the crude alcohol 5 (5.0 g,
ESIMS: 267 (M+Na) .
9
0%) as a colorless liquid. This crude was used as same
without further purification for next reaction.
(S)-6-(tert-Butyldimethylsilyloxy)hept-1-en-3-one (7)
Imidazole (10.2 g, 150 mmol) and the above crude alco-
Dropwise addition of dry DMSO (2.63 mL, 33.78 mmol)
was done to a mixture of oxalyl chloride (1.43 mL, 16.89
2 2
hol 5 (5 g, 50 mmol) in dry CH Cl (50 mL) was reacted
o
with TBSCl (8.29 g, 55 mmol) at 0 °C under inert condi-
tions. This reaction mass was allowed for stirring at room
temperature over a period of 4 h. Now the reaction mixture
mmol) was soluble in dry CH Cl (10 mL) at -78 C and this
2
2
reaction mixture was allowed for stirring over a period of
2 2
20 min. A solution of 3 (2.5 g, 11.26 mmol) in dry CH Cl
was neutralised with aq. NH
with CH Cl (2 × 50 mL). The two organic layers were com-
bined and washed with water (30 mL) followed by brine (30
4
Cl solution (10 mL) and mixed
(10 mL) was added dropwise to the above solution and
o
stirred over a period of 2 h at -78 C. Same above work up
2
2
procedure was also followed and available crude was puri-
fied through column chromatography (60-120 Silica gel, 5%
2 4
mL) solution. Finally it was dried on Na SO followed by
concentrated. The crude residue was eludated by column
EtOAc in pet. ether) to give ketone 7 (2.14 g, 84%) as a col-
1
chromatography (60-120 Silica gel, n-Hexane) afforded 6
ourless liquid. [α]
MHz, CDCl
.03 (d, 1H, J = 15.8 Hz, olefinic), 5.78 (d, 1H, J = 9.7 Hz,
olefinic), 3.86 (m, 1H, -CH), 2.28 (m, 2H, -CH ), 1.460 (m, 2H,
), 0.98 (s, 9H, 3 × -CH ),
); C NMR (75 MHz, CDCl ): δ 201.2,
39.3, 133.6, 66.7, 38.0, 36.1, 25.9, 23.6, 18.4, -4.2, -4.7; IR
D
+20.5 (c 0.31, CHCl
3
); H NMR (300
(
7.5 g, 70%) as a colorless liquid. [α]
D
-57.4 (c 0.76, CHCl
3
).
3
): δ 6.37 (dd, 1H, J = 15.8, 9.7 Hz, olefinic),
6
(
S)-6-(tert.-Butyldimethylsilyloxy) hept-1-en-3-ol (3) [29]
The compound 6 (7.4 g, 34.57 mmol) was soluble in
2
-
CH
2
), 1.08 (d, 3H, J = 5.8 Hz, -CH
3
3
13
0
1
.03 (s, 6H, 2 × -CH
3
3
7
-
0 mL dichloro methane solution and cooled this solution to
-
1
78°C. Ozone was passed to the above solution until pale
(
KBr): 2955, 2931, 2858, 1722, 1465, 1253, 1045, 835 cm ;
+
2
blue color was appeared. 2 mL of Me S was used to remove
ESIMS: 265 (M+Na) .
the excess ozone and the reaction mixture was allowed for
o
stirring over a period of 30 min at 0 C. The reaction mass
(S)-tert-Butyldimethyl(4-(2-vinyl-1,3-dioxolan-2-
yl)butan-2-yloxy) silane (8)
was concentrated under pressure conditions afforded alde-
hyde, which was straightly used for next reaction without
further purification.
A solution of ketone 7 (2.1g, 9.54 mmol), ethylene glycol
0.88 mL, 14.31 mmol) and p-toluenesulphonic acid (10
(
To a stirred solution of above aldehyde in dry THF
mol%) in benzene (80 mL) was allowed for reflux over a
period of 4h with Dean-Stark apparatus to remove the ben-
zene. Further the residue was soluble in ether (250mL). The
etherial mixture was washed with 5% aqeous sodium hy-
droxide (3 × 20 mL), water (4 × 50mL) followed by brine
o
(
60 mL) at -40 C, a solution of vinylmagnesium bromide (2.0 N
solution in THF) (20.5 mL, 41.5 mmol) was added dropwise.
After the completion of addition, the reaction mixture was
4
stirred for 4 h and neutralized with aq. NH Cl solution (30
mL) dropwise. The residue was filtered through celite and
(
2 4
30 mL). Finally it was dried on anhydrous Na SO and con-
filtrate was diluted with ethyl acetete (2 × 50 mL). The or-
centrated. Column chromatography technique was performed
to purify the crude product by (60-120 Silica gel, 10%
2 4
ganic layers were mixed, dried on dry Na SO and evapo-
rated under pressure conditions. Finally, chromatographic
technique was applied to purify the crude product (60-120
EtOAc in pet. ether) to afford 8 (1.78 g, 71%) as a colorless
1
liquid. [α]
D
+32.3 (c 0.31, CHCl
3
); H NMR (300 MHz,
Silica gel, 10% EtOAc in pet. ether) furnished 3 (6.8 g, 84%)
CDCl
3
): δ 5.88 (m, 1H, olefinic), 5.14 (m, 2H, olefinic), 3.89
m, 4H, OCH -OCH ), 3.73 (m, 1H, -CH), 1.60-1.39 (m,
), 1.06 (d, 3H, J = 5.2 Hz, -CH ), 0.84 (s, 9H,
); C NMR (75 MHz,
1
as a colorless liquid. H NMR (300 MHz, CDCl
3
): δ 5.84 (m,
(
4
3
2
2
1
(
H, olefinic), 5.11 (m, 2H, olefinic), 4.02 (m, 1H, -CH), 3.83
m, 1H, -CH), 1.60-1.39 (m, 4H, 2 × -CH ), 1.06 (dd, 3H, J =
H, 2 × -CH
× -CH ), 0.01 (s, 6H, 2 × -CH
2
3
1
3
2
3
3

6
96 Letters in Organic Chemistry, 2016, Vol. 13, No. 9
Ramakrishna et al.
CDCl
3
): δ 139.1, 118.6, 103.0, 66.6, 64.7, 34.2, 32.3, 25.9,
(15 mL) under inert atmosphere and allowed for stirring over
a period of 3 h. Now the compound extracted in ethyl acetate
solvent (2 × 50 mL). Combined organic layers were treated
with water (2 × 10 mL) followed by brine (10 mL). The or-
2
1
3.5, 18.3, -4.1, -4.9; IR (KBr): 2963, 2931, 2858, 1465,
-
1
+
253, 1045, 835 cm ; ESIMS: 309 (M+Na) .
(
1
S,E)-Methyl3-(2-(3-(tert-butyldimethylsilyloxy)butyl)-
2 4
ganic mass was dried on dry Na SO followed by evapora-
,3-dioxolan-2-yl)acrylate (9)
tion. Finally available crude was purified by coloumn chro-
matography (60-120 Silica gel, 55% EtOAc in pet. ether) to
The compound 8 (7.4 g, 34.57 mmol) was soluble in
give 2 (1.38 g, 87%) as a liquid. [α]
D
-32.6 (c 1.0, CHCl
3
);
7
0 mL dichloro methane solution and cooled this solution to
1
H NMR (CDCl
3
, 300 MHz): δ 6.81 (d, 1H, J = 15.6 Hz,
-
78°C. Ozone was passed to the above solution until pale
olefinic), 6.11 (d, 1H, J = 15.6 Hz, olefinic), 3.93 (m, 1H,
blue color was appeared. 2 mL of Me
the excess ozone and reaction mass allowed for stirring over
2
S was used to remove
-
-
-
OCH ), 3.87-3.79 (m, 4H, OCH
2
-OCH
), 1.11 (d, 3H, J = 5.1 Hz,
3
, 75 MHz): δ 172.6, 150.2, 120.9,
2
), 1.79-1.66 (m, 2H,
CH
CH
2
), 1.55-1.44 (m, 2H, -CH
2
1
5 min at 0°C. The reaction mass was under go concentra-
13
3
); C NMR (CDCl
tion with reduced pressure afforded aldehyde, which was
straightly used for next reaction.
1
2
09.3, 68.2, 66.4, 31.2, 28.8, 23.2; IR (neat): 3451, 2929,
857, 2102, 1722, 1612, 1514, 1360, 1041, 777 cm ;
-
1
+
Solution of the above aldehyde in benzene (50 mL) was
treated with (methoxy- carbonylmethylene)triphenyl phos-
phorane (3.54 g, 10.54 mmol) at reflux temperature. After a
period of 2 h, solvent was removed from reaction mass and
concentrated under reduced pressure and available residue
was purified by column chromatography (60-120 Silica gel,
ESIMS: 239 (M+Na) .
(
[
10R,22R)-10,22-dimethyl-1,4,9,14,17,21-hexaoxadispiro
4.7.4.7] tetracosa-6,18-diene-8,20-dione (11) [33]
DEAD (0.86 mL, 16.87 mmol) was added to a solution of
0 (0.235 g, 0.93 mmol) and Ph P (1.26g, 4.67 mmol) in
3
1
0% EtOAc in pet. ether) to furnish 9 (3.12 g, 84%) as a
1
1
yellow liquid. [α]
00 MHz): δ 6.78 (d, 1H, J = 15.6 Hz, olefinic), 6.03 (d, 1H,
J = 15.6 Hz, olefinic), 3.89 (m, 4H, OCH -OCH ), 3.73 (s,
H, OCH ), 3.61 (m, 1H, -OCH), 1.68 (m, 2H, -CH ), 1.53
m, 2H, -CH ), 1.3 (d, 3H, J = 3.0 Hz, -CH ); 1.01 (s, 9H,
× -CH ), 0.06 (s, 6H, 2 × -CH ); C NMR (CDCl , 150
D
-48.6 (c 1.0, CHCl
3 3
); H NMR (CDCl ,
toluene: THF (10:1, 250 mL) at -20 °C and this reaction
mass was stirred under inert atmosphere over 10 h. Further,
reaction mass was concentrated under reduced pressure and
available residue was purified by column chromatography
3
2
2
3
(
3
2
2
3
(
(
60-120 Silica gel, 10% EtOAc in pet. ether) to afford 11
0.12 g, 56%) as a colorless oil.
1
3
3
3
3
3
MHz): δ 166.5, 147.4, 118.8, 113.5, 66.6, 55.4, 51.6, 35.4,
3
1
0.2, 25.6, 24.2, 18.2, -4.8; IR (neat): 2932, 1724, 1612,
-1 +
Pyrenophorin (1) [33]
512, 1448, 1386, 1164, 1037 cm ; ESIMS: 367 (M+Na) .
To a stirred solution of 11 (45 mg, 0.22 mmol) in THF
(2 mL) cooled to 0 °C, treated with 10% aq. HCl (1 mL) and
reaction mass allowed for stirring at room temperature for
(
S,E)-3-(2-(3-(tert-Butyldimethylsilyloxy)butyl)-1,3-
dioxolan-2-yl) acrylic acid (10)
5
h. The reaction mass was neutralized with sat. NaHCO
3
Compound 9 (2.6 g, 6.16 mmol) was soluble in THF:
MeOH: water (3:1:1, 20 mL). To this reaction mixture,
LiOH (0.45 g, 18.48 mmol) was added very slowly and al-
lowed for stirring at room temperature over a period of 4h.
The reaction mass was acidified with 1N HCl solution and
mixed with ethyl acetate (30 mL). Combined organic layers
were treated with water (15 mL) followed by brine (15 mL).
solution (10 mL) and diluted with EtOAc (2 × 20 mL). The
combined organic layers were performed with water washing
(
2 × 25 mL) followed by brine (25 mL). Now this reaction
2 4
mass was completely dried on anhydrous Na SO and evapo-
rated. Finally column chromatography technique employed
to purify the crude mass (60-120 Silica gel, 10% EtOAc in
pet. ether) to give 40 (26 mg, 78%) as a colourless liquid.
2 4
The organic mass was dried on dry Na SO followed by
evaporation. Further, reaction mass was concentrated under
reduced pressure and available residue was purified by col-
umn chromatography (60-120 Silica gel, 30% EtOAc in pet.
CONCLUSION
Briefly, the total synthesis of (-) - pyrenophorin 1 was
accomplished from commercially available starting material
ether) to give 10 (2.02 g, 80%) as a colourless oil. [α]
D
+14.6
, 300 MHz): δ 6.81 (d, 1H,
J = 15.8 Hz, olefinic), 6.01 (d, 1H, J = 15.8 Hz, olefinic),
1
(
3 3
c 0.6, CHCl ); H NMR (CDCl
(
S)-propylene oxide. Jacobsen’s hydrolytic kinetic resolution
and intermolecular Mitsunobu cyclization were key interme-
diates to construct the above macrolactone, “(-) - pyreno-
phorin”.
3
.97-3.84 (m, 5H, OCH
2
-OCH
2
& -OCH), 1.82-1.67 (m, 2H,
-
-
CH
CH
2
), 1.58-1.47 (m, 2H, -CH ), 1.03 (d, 3H, J = 3.0 Hz,
2
13
3
); 1.01 (s, 9H, 3 x -CH
3
3
), 0.09 (s, 6H, 2 x -CH ); C
NMR (75 MHz, CDCl
6
2
3
): δ 172.8, 151.1, 120.6, 109.6, 68.6,
5.6, 31.2, 29.8, 23.9, 18.2, -4.6; IR (neat): 3540, 3031,
CONFLICT OF INTEREST
-
1
+
930, 2857, 1710, 1097 cm ; ESIMS: 353 (M+Na) .
The author(s) confirm that this article content has no con-
flict of interest.
(
S,E)-3-(2-(3-Hydroxybutyl) -1,3-dioxolan-2-yl) acrylic
acid (2)
ACKNOWLEDGEMENTS
TBAF (6.5 mL, 6.5 mmol) was added dropwise to a
o
Declared none.
cooled (0 C) solution of 10 (2.20 g, 5.40 mmol) in dry THF

Stereoselective Total Synthesis of (-)-Pyrenophorin
Letters in Organic Chemistry, 2016, Vol. 13, No. 9 697
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