Androsterone-based gels enable diastereospecific reductions and diastereoselective epoxidations of gelators

Article abstract of DOI:10.1039/c8ob01505h

Eleven new androsterone-based gelators were synthesized, and their gelation properties and gel-mediated reactions were investigated. The relationships between the structures, gelation and self-assembly processes of the gelators are discussed. By using granular PTFE (polytetrafluoroethylene) as costirrers, quantitative and diastereospecific reductions of the gelator carbonyl groups mediated by water were achieved in the gels of seven gelators. This reduction did not occur in the control experiment which used organic solvent-mediated conventional conditions. The diastereospecific and quantitative reductions possibly occur via a hydrogen-bonded-activated carbonyl mechanism. Five of the gelators underwent gel-mediated epoxidation and the products were more diastereoselective than those obtained using conventional epoxidation reactions. This can be attributed to the ordered arrangements in the gels.

Full text of DOI:10.1039/c8ob01505h

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COMMUNICATION
Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
rsc.li/obc

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DOI: 10.1039/C8OB01505H
Journal Name
ARTICLE
Androsterone-based Gels Enable Diastereospecific Reductions and
Diastereoselective Epoxidations of Gelators
Received 00th January 20xx,
Accepted 00th January 20xx
‡
a
‡b
a
Tao Li, Yu Chen and Chunbao Li*
DOI: 10.1039/x0xx00000x
Eleven new androsterone-based gelators were synthesized, and their gelation properties and gel-mediated reactions were
investigated. The relationships between the structures, gelation and self-assembly processes of the gelators are discussed.
By using granular PTFE (polytetrafluoroethylene) as costirrers, quantitative and diastereospecific reductions of the gelator
carbonyl groups mediated by water were achieved in the gels of seven gelators. This reduction did not occur in the control
experiment which used organic solvent-mediated conventional conditions. The diastereospecific and quantitative
reductions possibly occur via a hydrogen-bonded-activated carbonyl mechanism. Five of the gelators underwent gel-
mediated epoxidation and the products were more diastereoselective than those obtained using conventional epoxidation
reactions. This can be attributed to the ordered arrangements in the gels.
www.rsc.org/
27
based derivatives.
Dehydroepiandrosterone, especially
Introduction
epoxy-functionalized dehydroepiandrosterone has never been
investigated as a gelator.
In recent decades, the interest in low-molecular-mass organic
gelators (LMOGs), which are capable of self-assembly leading
to gelation, has increased greatly. Their unique properties
have given rise to numerous potential applications in materials
Recently, some surprising gel-mediated reactions such as
cycloaddition, photopolymerization, light-induced redox,
nucleophilic substitution and asymmetric catalytic reaction
2
8-38
1
-9
have been reported.
Most of these gel-mediated reactions
science, nanoelectronics, drug delivery and biomedicine.
A
have better reaction rates or diastereoselectivities compared
to conventional methods. However, to the best of our
knowledge, there have been no reports on using gel reactions
to realize reactions that can not be achieved by conventional
methods.
great deal of effort has been made to design and synthesize
new types of LMOGs and to better understand the gelation
10-14
mechanisms.
The driving forces for the self-assembly
processes are usually combinations of hydrogen bonding,
hydrophobic effects, π-π stacking, van der Waals interactions
or other noncovalent interactions.
As ubiquitous natural products, steroids are a versatile and
1
5-18
Herein, eleven new androsterone-based gelators were
synthesized. The relationship between their structures and
gelation properties was studied. Ketone reduction and olefin
epoxidation reactions were then carried out on the gelators.
The former is not achievable via non-gel methods, and the
24 latter gives better diastereoselectivities than non-gel methods.
5
well-known class of LMOGs. The two most reported types of
steroidal gelators are cholesterol-based and bile acid-based
19-22
gelators.
There are only a few examples of other steroidal
2
3
gelators which include pregnane-based, estradiol-based,
diosgenin-based,
25
26
stigmasterol-based,
and androstanol-
Results and discussion
a.
Gelation performance of compounds 1-11
Department of Chemistry, College of Science, Tianjin University, Tianjin, 300072,
P. R. of China.
Tianjin Key Laboratory of Organic Solar Cells and Photochemical Conversion,
School of Chemistry & Chemical Engineering, Tianjin University of Technology,
Tianjin, 300384, P.R. of China.
b.
*
Corresponding Author, E-mail: lichunbao@tju.edu.cn; Tel: +86-022-27892351;
Fax: +862227403475.
Electronic Supplementary Information (ESI) available: [Synthesis of the
androsterone-based gelators; XRD patterns for xerogels (2% w/v) from 1/benzene
4
and 11/CCl ; Procedure for the more than 1 g scaled reduction of carbonyl group
of gelator 1; Control experiment for the reduction of carbonyl group in methanol;
Control experiment for the reduction of carbonyl group on water; Control
+
+
+
experiment for the effects of metal ions (Li /Na /K ) on the reduction; Control
experiment for the function of granular PTFE in the reduction: 2 reductions in the
absence of granular PTFE; Control experiments for the epoxidations of double
bond in gelation solvent and CH Cl solution; Control experiment for the function
2 2
1 13
of granular PTFE in the epoxidation; References; H NMR, C NMR and NOE
spectra for new products]. See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
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obtained. Most of the gelating solvents were aromatic ones
View Article Online
DOI: 10.1039/C8OB01505H
such as benzene, toluene, m-, o-, and p-xylene, and mesitylene.
The non-aromatic gelating solvents were ethanol, carbon
tetrachloride and triethylamine. Some of the gels formed at
room temperature (
treatment ( /toluene,
of gelation ability at 1% (w/v) concentration was
10 11 The following structure-gelation
relationships are seen: (1) Compound (with an unsubstituted
3
/benzene and
4/CCl ) or with ultrasonic
4
1
1
/p-xylene and
2/o-xylene). The order
1
＞4＞2≈5
≈
9
＞
3
＞
＞
.
1
phenyl group β-orientated to the epoxy group) has the
strongest gelation tendency. (2) The gelation tendency of
compounds
electron-withdrawing substituent, is stronger than that of
compound , where the phenyl ring bears an electron-
2, 4 and 5, where the phenyl rings bear an
3
Scheme 1. The synthetic routes and chemical structures of potential donating substituent. (3) Compounds
androsterone-based gelators
1 and 3 with C5-C6
double bonds are more efficient gelators than compounds
9
and 10 without C5-C6 double bonds. (4) Compound 11 without
an epoxy group only formed a gel in carbon tetrachloride and
Gelators
1-11 were synthesized from haloketones or a ketone
and aldehydes in the presence of a base promoted and
granular PTFE (Scheme 1).
compounds 11 were examined in 23 solvents at a
concentration of 1% (w/v), and the results are presented in
Table 1. Out of the 253 combinations formed by the 11
compounds and the 23 different solvents, 34 gel systems were
compound
group did not form a gel in any of the tested solvents. (5)
Compounds with a blocked 3β-hydroxyl group ( ) and without
an aryl group ( ) did not form gels in the tested solvents.
7 with a phenyl group α-orientated to the epoxy
39, 40
The gelation properties of
1
-
6
8
a
Table 1. Gelation behaviors of compounds 1-11 in various solvents
Solvent
methanol
ethanol
1
2
P
P
P
P
P
3
4
P
P
P
P
P
5
P
P
P
P
S
6
I
7
S
S
S
S
S
S
S
I
8
S
S
S
S
S
S
P
I
9
PG
P
P
P
S
10
P
P
S
11
P
S
P
P
S
S
P
P
G
0.36)
TG (0.80)
I
(
ethyl acetate
acetone
P
S
S
S
P
I
P
S
P
P
I
S
CH Cl
S
S
P
I
S
2
2
CHCl3
CCl4
P
S
S
S
S
S
*
TG
G
TG
TG
G
(0.13)
TG
(0.91)
P
I
(
0.06) (0.20) (0.80) (0.50)
b
petroleum ether
n-heptane
THF
I
I
I
I
I
I
I
I
I
I
I
I
I
P
S
I
I
P
S
S
P
S
P
S
S
S
P
S
2
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View Article Online
DOI: 10.1039/C8OB01505H
dioxane
P
P
P
P
P
S
P
P
P
P
P
P
P
P
I
S
S
S
S
S
S
S
S
S
S
S
S
I
S
S
S
P
S
S
S
S
S
S
S
S
I
P
P
S
S
acetonitrile
triethylamine
benzene
toluene
P
P
P
P
S
P
P
P
P
P
P
S
S
S
I
G
0.36)
P
P
P
(
*
G
G
G
TG
G
G (0.92)
S
P
P
P
P
P
P
P
S
I
(
0.40) (0.36) (0.90)
(0.40) (0.80)
*
*
G
0.57)
G
G
G (0.50)
G (0.33)
G (0.28)
P
P
P
P
P
P
S
S
I
PG
PG
PG
S
(
(0.83) (0.91)
*
*
G
G
(0.67)
o-xylene
m-xylene
p-xylene
mesitylene
DMSO
PG
(
0.50)
G
TG
G
G
(1.00)
S
(
0.31)
P
(1.00) (0.90)
*
*
TG
0.36)
TG
PG
G
(0.67)
PG
S
(
(0.50)
TG
0.80)
G
(0.91)
G
(0.40)
TG (0.57)
PG
(
P
P
S
I
S
S
S
S
I
S
S
S
I
S
S
S
I
S
DMF
S
S
I
S
pyridine
water
S
I
a
Concentration of gelator = 1%, w/v; G = turbid gel; PG = partial gel; TG = transparent gel; P = precipitate; I = insoluble; S = solution; G* = gel forming at
b
room temperature; G** = gel forming by ultrasound; the number in the parentheses is the CGC of the system (%, w/v); bp = 60-90 °C .
phenyl groups of gelator
The kinetics of the gel formation processes depend on the gelator
solvent and the structure of the gelator. The gel formations for The thermostability of the gel systems was further investigated.
/benzene, 10/benzene and 11/CCl took more than 20 min. Figure 1 shows plots of the sol-gel transition temperatures (Tgel)
2, which may hinder aggregation of
2
.
3
4
The other gel systems only took less than 5 min.
The numbers in the parentheses in Table 1 are the CGCs Tgel is proportional to the concentration of gelator. In benzene,
critical gelator concentrations) of the gelators in the various the Tgel of gelators and are approximately 30 °C higher
solvents. Except for /m-xylene and /m-xylene, the CGC than those for and 10 (Figure 1a). This indicates that the gel
values were all below 1% (w/v), which indicates that these systems of gelators and are more thermostable than
and 10, which is consistent with the gelation order
CCl is only 0.06% (w/v), which is the lowest value in these given above. In addition, the gel systems of gelators and
bp of
benzene) which demonstrates that the driving forces for gel
with an electron-withdrawing substituted phenyl group. This is formation are very strong (Figure 1a).
for the gel systems as a function of gelator concentration. The
(
1
,
4
,
5
9
4
9
3
1
,
4
,
5
9
5
compounds are super-gelators. Particularly, the CGC of
2
in those for
3
1, 4, 5
4
systems. In aromatic solvents, the CGCs of gelator
1
with an 9 have extraordinarily high Tgel values in benzene(＞
unsubstituted phenyl group are lower than those of gelator
2
41
due to π-π stacking interactions between the electron-rich Figure 1b shows that the Tgel order of gelator
aromatic solvents and the electron-withdrawing substituted solvents is mesitylene m-xylene ethanol
1
＞
in different
o-xylene ＞
＞
≈
toluene. The differences of Tgel between a polar solvent
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ARTICLE
Journal Name
(
ethanol) and apolar solvents (the aromatic solvents) are not
very large. Above a concentration of 1.7 wt% (w/v) the Tgel of
/p-xylene increased dramatically (Figure 1b), which may be
attributed to the heat caused by the cross linking between the
View Article Online
DOI: 10.1039/C8OB01505H
1
42
gelator molecules.
Table 2. FTIR data for reference gelators and the corresponding xerogels in different solvents
Epoxy group
Δνsy
ν C=O
Δν C=O
ν OH
Δν OH
-1
Sample
νsy
νas
-1
Δνas
-
1
-1
-1
(
cm )
(
cm )
(cm )
(cm )
-
1
-1
-1
(
cm )
(cm )
(cm )
920
920
925
924
920
920
921
(cm )
Reference
1746
1744
1749
1748
1745
1742
1744
1744
1744
1743
1747
1744
1743
1743
1715
3394
3251
1247
1247
1249
1248
1250
1249
1243
1242
1243
1246
1260
1260
1248
1251
1
2
1
143
55
0
0
a
Xerogel
Reference
3392
3337
3468
3470
3478
3475
3471
3237
3382
3242
3251
2
3
4
5
9
1
1
1
0
1
b
Xerogel
Reference
3
0
1
2
a
Xerogel
Reference
3
1
c
Xerogel
920
921
Reference
234
140
32
3
0
3
1
d
Xerogel
922
914
Reference
3
0
1
0
3
a
Xerogel
914
Reference
908
911
10
a
Xerogel
3219
3417
3209
Reference
11
208
-
e
Xerogel
1714
a
b
c
d
e
Xerogels from 1, 3, 9 and 10 in benzene. Xerogel from 2 in mesitylene. Xerogel from 4 in m-xylene. Xerogel from 5 in p-xylene. Xerogel from 11 in CCl
4
.
2
/mesitylene xerogel (Figure 2
that are 100-800 nm in diameter. The
/benzene xerogels (Figure 2, e and f) contain fibers that are
much smaller and they are highly entangled. The /benzene
,
b) contains bundles of fibers
5
/p-xylene and
9
3
xerogel (Figure 2, c) contains plate-like aggregates which are
comprised of many fibers. Surprisingly, the 11/CCl xerogel
4
(Figure 2, h) has an entangled network of closely packed tiny
fibers. These different xerogel structures demonstrated that
the aggregation of the gelator molecules depends on both the
structure of the gelators and the gelation solvents.
Figure 1. Gel-to-sol transition temperature (Tgel) as a function of gelator
concentration: (a)
1
,
■;
●
3
,
●
;
4,
＋;
▲
5
,
◆
;
9
,
▲;
▼
10
,
▼
in benzene; (b)
1 in
toluene, ■; o-xylene,
; m-xylene,
; p-xylene,
; mesitylene,
◆
; ethanol, ＋
Morphology studies
Scanning electron microscope (SEM) was used to observe the
morphologies of the gelators in different solvents and the
results are shown in Figure 2. The
1/benzene xerogel (Figure 2,
a) contains entangled fibers with diameters of approximately
3
1
0-260 nm. Similar structures are seen in the
/benzene xerogels (Figure 2, d and g). The fiber diameters
/m-xylene and are 50-170 nm for
/benzene. There are fewer fibers in /m-xylene (Figure 2, d)
and the thick fibers are composed of many thin ones. The
4/m-xylene and
Figure 2. SEM images of xerogels (2% w/v): (a)
mesitylene (bar = 5 um); (c) in benzene (bar = 5 um); (d)
um); (e) in p-xylene (bar = 1 um); (f) in benzene (bar = 2 um); (g) 10 in
benzene (bar = 2 um); (h) 11 in CCl (bar = 2 um)
1
in benzene (bar = 2 um); (b)
2 in
3
4
in m-xylene (bar = 2
0
5
9
are 40-340 nm for
1
4
4
0
4
4
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FTIR spectroscopy studies
ARTICLE
-
1
(cm )
View Article Online
DOI: 10.1039/C8OB01505H
FTIR spectroscopy was used to gain insight into the driving
forces of the gel formation and the results are shown in Figure
Reference
1454
1455
1
2
1
a
Xerogel
3
. The
representative systems and gelators
reference compounds. For reference gelator
and carbonyl group stretching vibrations are at 3394 and 1746
1
/benzene and 10/benzene samples were chosen as
and 10 were used as the
, the hydroxyl
Reference
1604, 1518, 1455
1
0, 3, 3
b
Xerogel
1604, 1515, 1452
1
Reference
1614, 1515, 1455
-
1
3
1, 2, 2
a
cm respectively (Figure 3, (I) b). After gelation, these bands
Xerogel
1613, 1513, 1457
-
1
shifted to 3251 and 1744 cm (Figure 3, (I) a). In contrast, the
epoxy group stretching band for gelator
did not significantly change after gelation (Figure 3, (I)). This
indicates that the epoxy group has only a weak contribution to
the hydrogen bonding interactions or does not participate in
the hydrogen bonding interactions.
Reference
1451
-1
1
(1247 and 920 cm )
4
5
3
c
Xerogel
1454
Reference
1451
2
d
Xerogel
1453
Reference
1449
In contrast, in gelator 10 the hydroxyl and epoxy group bands
9
10
11
3
0, 0, 1
3
a
-
1
Xerogel
1452
shifted from 3251, 1248 and 908 cm (Figure 3, (II) b) to 3219,
-1
1
251 and 911 cm (Figure 3, (II) a) respectively upon gelation.
Reference
1614, 1515, 1452
-1
b
The carbonyl group band (1743 cm ) did not change
significantly after gelation (Figure 3, (II)). This demonstrates
that the carbonyl group has a weak contribution to the
hydrogen bonding interactions or does not participate in the
hydrogen bonding interactions. In summary, these data
Xerogel
1614, 1515, 1453
Reference
1448
1445
b
a
Xerogel
a
c
Xerogels from 1, 3, 9 and 10 in benzene. Xerogel from 2 in mesitylene.
d
e
indicate that for gelator
1
, the hydroxyl and carbonyl groups
Xerogel from 4 in m-xylene. Xerogel from 5 in p-xylene. Xerogel from 11
in CCl
participate in the gelator hydrogen bonding interactions and
for gelator 10, the hydroxyl and epoxy groups participate in
hydrogen bonding interactions. These are the main driving
4
.
4
3, 44
X-ray diffraction (XRD) studies
forces for gel formations.
XRD was employed to investigate the structures of the
xerogels. The 1/benzene and 11/CCl xerogels were used as
4
the representative xerogels and the major peaks observed are
presented in Table 4. The spectra are shown in the supporting
information (Figure S1). Both xerogels have six refection peaks
3
：1
7：1
and the corresponding d-spacing ratios are 1:1,
, 2:1,
indicating hexagonal columnar lattice
structures. The long spacing distances of the assemblies are
.78 ( /benzene) and 1.67 nm (11/CCl ) respectively. The
molecular length of gelator
model in Chem3D software). Since the long spacing distance of
/benzene (1.78 nm) is longer than one molecular length of
but shorter than two molecular lengths, the xerogel from
,
12：1
3
:1 and
47
Figure 3. FTIR spectra of (I) (a) xerogel from
1/benzene and (b) reference gelator
1
1
4
1
, (II) (a) xerogel from 10/benzene and (b) reference gelator 10
1
is 1.00 nm (by ball-and-stick
Similar results were observed in the other gel systems and the
results are shown in Table 2. For samples and 11, the
hydroxyl and carbonyl groups participated in the gelator
hydrogen bonding interactions. However, for samples and 10
the hydroxyl and epoxy groups participated in the gelator
hydrogen bonding interactions. For samples , and , the
hydroxyl, epoxy and carbonyl groups all participated in the
gelator hydrogen bonding interactions.
The skeletal vibrations of the aromatic groups also shifted
upon gelation. These results are presented in Table 3. For
1
1
1, 9
1
1
/benzene adopts a hexagonal structure with a thickness of
.78 nm. The molecular length of gelator 11 is 1.29 nm (by
4
,
ball-and-stick model in Chem3D software) and the long spacing
distance of 11/CCl (1.67 nm) is also between one and two
times the molecular length of 11. Thus a similar structure (a
hexagonal structure with a thickness of 1.67 nm) was formed
2
,
3
5
4
in 11/CCl system.
4
sample
515 and 1455 cm to 1613, 1513, and 1457 cm respectively
after gelation. Shifts in the aryl skeletal vibrational bands were
also seen for samples and 11. This is an evidence of
the existence of π-π stacking interactions.
3, the aryl skeletal vibrational bands shifted from 1614,
Table 4. XRD data for 1/benzene and 11/CCl
4
xerogels
-
1
-1
1
Gelator
1
Peak
2θ (deg)
4.96
d (nm)
1.78
1
,
2
,
4
,
5
9
-
1
4
5, 46
2
3
4
5
8.54
1.03
Table 3. FTIR aryl skeletal vibrational data for the reference gelators and their
corresponding xerogels in different solvents
9.96
0.89
0.67
0.59
13.16
-
1
Sample
ν aryl (cm )
Δν aryl
14.86
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1
17.86
5.28
0.50
1.67
the reduction was complete in 11.5 h. The yield of product 1gr
was quantitative and the reaction was diastereoselective. To
the best of our knowledge, this is the first time that a gel
medium has facilitated a reaction which could not be achieved
by conventional methods.
View Article Online
DOI: 10.1039/C8OB01505H
2
3
4
5
6
8.99
10.42
13.88
15.70
18.20
0.98
0.85
0.64
0.56
0.49
11
To reduce the amount of volatile organic solvent, the xerogel
of
1/toluene (4 wt%) was next subjected to the reduction
reaction conditions. The xerogel reduction gave the same
result as the gel reaction, but the reaction required 36 h.
Adding a small amount of water (0.12 mL) to the system,
shortened the reaction time to 13 h. The function of the water
Possible gelation mechanism
Based on the above experiments, the possible driving forces is to dissolve the NaBH
for the self-assembly of the gelators are van der Waals Next the reduction scope was expanded to six other xerogels
interactions from the steroidal skeletons, π-π stacking
and 10). All were quantitatively and diastereospecificly
.
4
(2-5, 9
interactions between the aryl groups and hydrogen bonding reduced (Table 5, entries 2-7). The epoxy group in each of the
interactions with the hydroxyl groups. Steroids with a rigid xerogels remained intact (Table 5, entries 1-7). Increasing the
tetracyclic ring can provide strong van der Waals interactions scale of gelator
during gel formations. Although van der Waals interactions produced the same quantitative and diastereospecific results
are weaker than the other non-covalent interactions; they play but had the added benefit of making the recovery of the
1 from 100 mg to more than 1000 mg,
1
6
important roles in the process of self-assembly.
A possible gel formation process for
/benzene is shown in small amount of water at the end of the reduction followed by
Figure 4. First, gelator
with a hydroxyl group on ring A and a filtration. No organic solvents were needed for extraction or
carbonyl group on ring D are connected head to tail by purification of the product.
products greener. The product, 1gr, was collected by adding a
1
1
hydrogen bonding interactions (I). This then forms a hexagonal
a
Table 5. Quantitative, diastereospecific and green reductions of gelators using xerogels
structure (II). Subsequently, the hexagonal structures pile up
into elemental fibers via π-π stacking and van der Waals
interactions. These elemental fibers further combine with each
other via π-π stacking and van der Waals interactions, which
leads to larger fibers and eventually three-dimensional
networks are formed (Figure 2, a).
R
R
OH
O
(R)
NaBH4, H2O,
(R)
O
granular PTFE, rt
O
HO
HO
(R)
O
O
Ar
Conc.
(wt %
)
Time
h)
O
Entry
Xerogel
Product
(
R)
(
O
Ar
H
O
HO
O
Gelator 1
(R)
O
O
OH
(
R)
b
(R)
HO
1
4.0
O
13.0
12.5
O
I
Ar
Ar
HO
HO
1
gr
1
Ar
Ar
Ar
NO2
NO2
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
Ar
O
OH
b
Ar
(R)
2
3
2.0
(R)
O
O
Ar
Ar
Ar
HO
HO
II
1/benzene
2
2
gr
OMe
OMe
Figure 4. Schematic representation of the gel formation process of
Gel-mediated reduction of the gelator carbonyl group
O
OH
c
(R)
1.0
6.0
(R)
48
O
O
First a conventional method using NaBH /MeOH was used in
4
an attempt to reduce the carbonyl group of gelator
reaction did not occur. Increasing the amount of NaBH to 8
1
. The
HO
HO
3
3gr
4
equiv and raising the temperature to reflux, still gave no
reaction even after 12 h. However, when the reduction was
performed with 1/ toluene gel (4 wt%), NaBH , and granular
4
3
9, 40, 49-53
PTFE
at room temperature with mechanical stirring,
6
| J. Name., 2012, 00, 1-3
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Page 7 of 11
O rP gl ea na is ce &d Bo i on mo to al e dc juu l sa tr mC haer mg i ins ts ry
Journal Name
ARTICLE
Cl
Cl
hydrogen bonding in the xerogel is essential for the reduction
of the carbonyl group (Figure 5).
View Article Online
DOI: 10.1039/C8OB01505H
O
OH
b
4
5
6
7
(R)
2.0
(R)
17.0
5.5
O
O
O
HO
HO
4
5
4
gr
Br
Br
steric crowded
NaBH4 + MeOH
NaBH OMe + H2
3
R
O
OH
R
R
b
(
R)
2.0
(R)
O
O
O
H
HO
HO
O
5gr
(R)
O
O
O
(R)
(R)
O
O
O
OH
(
R)
face attack
face attack
(R)
O
d
O
BH OMe- Na+
2.2
13.0
6.5
BH4- Na+
BH - Na+
3
4
HO
HO
(
I)
conversion 100%
gel)
(III)
(II)
9
gr
conversion 0%
(methanol solution)
Figure 5. Proposed mechanisms for the reduction of the carbonyl group in a gel,
in a methanol solution and on water
conversion 26%
(on water)
9
(
OMe
OMe
O
OH
c
(R)
1.0
(R)
Gel-mediated epoxidation of the gelators
O
O
HO
HO
To test if the advantage of the gel constrained environment in
gel medium could be further exploited for other
10
10gr
diastereoselective syntheses, the epoxidation of gelator
1 was
a
b
All conversions were 100%. All isolated yields were >99%. The gelation solvent
carried out in a gel medium (toluene, 4 wt %) with m-
chloroperbenzoic acid (m-CPBA) and granular PTFE at 0-5 °C .
The epoxidation was highly diastereoselective (epoxy
configuration ratio α/β = 15/1, Table 6, entry 1). Two
comparison experiments were conducted using m-CPBA to
c
d
4
was toluene. The gelation solvent was CCl . The gelation solvent was benzene.
Reaction conditions: xerogel (100 mg, 1.0 equiv), NaBH
mL) and granular PTFE (5.0 g) at rt.
4 2
(8.0 equiv), H O (0.12
The proposed mechanism for the gel mediated reduction is
shown in Figure 5. Since the carbonyl groups in gelators 1-5, 9
oxidize the double bond of gelator
1
in toluene (0.1 wt%) and
56
CH Cl (2 wt%) solution. In toluene solution, the α/β ratio
2
2
and 10 are each connected to two quaternary carbons and the
aryl groups are positioned above the epoxy groups, there is a
very large steric effect. In methanol (SI, S4), this steric effect
means that the carbonyl group is not accessible to the bulky
sodium methoxyboron hydride (Figure 5, II). In contrary, in the
gel or xerogel, both the intermolecular hydrogen bonds
between the carbonyl and C3-hydroxyl groups and the
associations between the sodium ions and the carbonyl groups
activate the carbonyl double bond. In addition, sodium boron
hydride is smaller than sodium methoxyboron hydride, which
allows the hydride to attack the β-face of the dually activated
carbonyl group; thus an α-hydroxyl group is formed (Figure 5,
I).
was 2/1 and the conversion was only 61% and in CH Cl2
solution, the α/β ratio was 2.8/1 and the conversion was 100%.
2
The epoxidation of gelator
2 yielded similar results: α/β ratios
were 20/1, 2.8/1 and 2.3/1, and conversions were 100%, 46%
and 100% in toluene gel (Table 6, entry 2), in toluene (0.25
wt%) and CH Cl (1 wt%) solution respectively (SI, S6-S8).
2
2
Next a lower reaction temperature (-10 to -15 °C ) for the
/toluene gel was tested and both the reaction rates (8 vs. 4 h)
and diastereoselectivities (α/β = 4/1 vs. 15/1) decreased
significantly. Reacting /toluene xerogel (4 wt %) with m-CPBA
1
1
produced worse results (11 h, α/β = 6/1). Therefore, the best
results were obtained with the gelator gel, m-CPBA and
granular PTFE at 0-5 °C .
Gelators 1-2, 4-5 and 11 were then subjected to the optimized
reaction conditions and all gave excellent diastereoselectivities
and yields (Table 6, entries 1-5). The gelators with smaller
To verify the effects of the metal ion on the reduction, a set of
comparison experiments were conducted using NaBH4,
LiCl/KBH and KBH . The order of the reduction rates was
4
4
LiCl/KBH > NaBH > KBH . Since the order of hardness for the
4
4
4
molecular weights tended to react faster (gelator 11
< 1 < 2 < 5)
+
+
+
three metals is Li >Na >K and oxygen atom is a hard Lewis
(Table 6, entries 5, 1, 2 and 4 respectively). This reaction
5
4, 55
base,
this suggests that the metal ions participate in the
system is compatible with epoxy, hydroxyl, electron-poor C=C
and carbonyl groups. The better diastereoselectivties of the gel
mediated epoxidation reactions can be attributed to the
ordered spacial arrangements of the gelator molecules, which
makes an attack on the α-face by the peroxyacid favorable.
activation of the carbonyl group and in hydrogen bonding (SI,
S5). In another control experiment, the same reaction
conditions were used to reduce gelator
1 on water and a yield
of only 26% was obtained (SI, S4-S5). This indicates that
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O rP gl ea na is ce &d Bo i on mo to al e dc juu l sa tr mC haer mg i ins ts ry
Page 8 of 11
ARTICLE
Journal Name
a
Table 6. Diastereoselective gel-mediated epoxidations of the gelators
gel) was performed without granular PTFE, the conversion and
View Article Online
α/β ratio at 4 h were 65% and 6/1 respectively (SI, S8),
DOI: 10.1039/C8OB01505H
whereas with granular PTFE, the conversion and α/β ratio
were 100% and 15/1 respectively (Table 6, entry 1). Again this
demonstrates that the granular PTFE has a large promoting
effect on both the reaction rate and the diastereoselectivity.
The granular PTFE functions as co-stirrers which smash and
disperse the gel (or xerogel), and enhances the agitation
8
5% m-CPBA, gelation solvent,
granular PTFE, 0-5 o
C
HO
HO
O
b
α/β
rati- me
o
Ti-
Yi-
eld
Entr
y
Gel
Product
39, 40, 49-53
efficiency.
(h) (%)
O
O
Conclusions
(
R)
(R)
c
e
1
O
O
15/1
4.0
5.5
87
In conclusion, the gelation properties of a series of
androsterone-based gelators, some of which are super-
gelators, were studied. These gels and xerogels were
HO
HO
HO
HO
O
1
1
ge
NO2
NO2
successfully subjected to reductions using NaBH and to
4
oxidations using peroxyacids. Using conventional organic-
solvent mediated methods these reactions either did not occur
or gave poor diastereoselectivities. This is the first time that
gel-mediated reactions have been reported to facilitate
reactions that are unavailable using conventional methods.
The promotion effect of granular PTFE in these gel-mediated
reactions has also been demonstrated. This work represents a
new green synthetic method that uses a combination of
granular PTFE and gels or xerogels.
O
O
c
e
(
R)
(R)
2
20/1
7/1
92
O
O
HO
O
2
2
ge
Cl
Cl
O
O
c
(R)
e
(
R)
3
6.5
82
O
O
HO
O
Experimental
Materials and methods
4
4
ge
Br
Br
NMR spectra were recorded on a Bruker AM-400 spectrometer
(
400 MHz), a VARIAN INOVA 500 MHz spectrometer (500 MHz)
O
O
c
(R)
e
(
R)
4
9/1
8/1
9.5
1.5
84 or a Bruker Avance III spectrometer (600 MHz), using
O
O
tetramethylsilane (TMS) as the internal standard (=0). FTIR
spectra were obtained using a Bruker ALPHA spectrometer,
using potassium bromide disks and the spectra were scanned
HO
HO
O
5
5
ge
O
O
-1
from 400-4000 cm . Melting points were obtained using an X-
d
f
4 Micro-melting Point Apparatus. A xerogel is a solid formed
from a gel by drying with unhindered shrinkage. SEM images of
the xerogel were taken on a Hitachi S-4800 scanning electron
microscope after coating the samples with gold. XRD spectra
of the xerogels were collected with a Rigaku D/max-2500 X-ray
powder diffractometer using Cu-Kα radiation. Samples were
5
81
HO
HO
O
11
11ge
a
b
All conversions were 100% and all yields were crystallization yields. Determined
by H NMR, ref. [57]. The gelation solvent was toluene, the concentrations for
gelator 1, 2, 4 and 5 were 4.0, 2.5, 2.5 and 2.0 wt %, respectively. The gelation
1
c
d
e
solvent was CCl
4
, the concentration was 1.3 wt %. The crystallization solvent was tested from 2° to 20° at a scanning rate of 5°/min. Xerogels for
ethanol. The crystallization solvent was methanol. Reaction conditions: gel (gelator SEM were prepared by slowly evaporating the solvents in the
f
1
00 mg, 1.0 equiv, gelation solvent), m-CPBA (85%, 1.2 equiv) and granular PTFE (5.0
atmosphere for seven days and for reactions were prepared by
the slow evaporation of the solvents under reduced pressure.
The granular PTFE was 70 pieces/g.
g) at 0-5 °C.
Synthesis of the androsterone-based gelators
Function of the granular PTFE
All of the chemicals were obtained from commercial sources
or prepared according to standard methods. The
androsterone-based gelators were synthesized by the methods
When the carbonyl groups of 1/toluene xerogel and 1/toluene
gel were reduced in the absence of granular PTFE the
conversions were only 14% (13 h), and 2% (11.5 h) respectively
39, 40
previously reported by us.
Gelators 1-11 are all known
(SI, S5-S6). With granular PTFE, both of these reductions were
39, 40
compounds.
Gelation tests of the potential gelators (1-11)
diastereospecific and quantitative (Table 5, entry 1). This
indicates that the granular PTFE greatly promotes the
reduction reaction. When the epoxidation of gelator 1 (toluene
8
| J. Name., 2012, 00, 1-3
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Page 9 of 11
O rP gl ea na is ce &d Bo i on mo to al e dc juu l sa tr mC haer mg i ins ts ry
Journal Name
ARTICLE
1
Gelation tests were conducted by dissolving different amounts 2gr: white solid; mp 218-220 °C ; H NMR (600 MHz, CDCl ) δ
View Article Online
3
of the potential gelator in a measured volume of a selected 8.20 (2H, d, J = 8.0 Hz, Ar-H), 7.56 (2H, d,DJO=I: 180..110H39z/,CA8rO-HB0),1550.35H7
solvent under a heating-cooling cycle. All the gels were (1H, s, 6-H), 4.06 (1H, s, epoxy-H), 4.00 (1H, s, 17β-H), 3.58 –
prepared in sealed glass tubes (10 mm i.d.). Finally, the test 3.49 (1H, m, 3α-H), 1.03 (3H, s, 19-CH ), 0.85 (3H, s, 18-CH );
3
3
13
tube was turned upside down to observe whether the solution
C NMR (101 MHz, CDCl ) δ 147.17, 144.67, 141.01, 126.59,
3
flowed or not. The critical gelation concentration is defined as 123.38, 120.95, 83.68, 72.94, 71.62, 63.06, 49.99, 47.71, 44.11,
the minimum amount of gelator needed for the formation of a 42.19, 37.08, 36.62, 36.27, 34.37, 31.54, 31.41, 31.24, 20.35,
-1
gel.
19.45, 12.19; IR (KBr, cm ) ν: 3365, 2933, 2894, 2853, 1645,
The gel-to-sol transition temperature was determined by a 1602, 1513, 1438, 1405, 1343, 1089, 1048, 1012, 842, 792, 739,
58
+
conventional “falling ball” method. In the test, a small glass 696; HRMS calcd. for C H NO Na [M + Na] : 462.2251, found:
26
33
5
ball (diameter~3 mm) was carefully placed on top of the gel in 462.2256.
the test tube. The tube was then slowly heated (2 °C /min) in a 3gr: white solid; mp 206-208 °C ; H NMR (600 MHz, CDCl ) δ
1
3
thermostated oil bath until the ball fell to the bottom of the 7.33 (2H, d, J = 7.7 Hz, Ar-H), 6.90 (2H, d, J = 7.9 Hz, Ar-H), 5.37
tube. The temperature corresponding to the end of the falling (1H, s, 6-H), 4.01 (2H, s, epoxy & 17β-H), 3.79 (3H, s, OCH3),
process is the Tgel of the system.
General procedure for the gel mediated reductions of carbonyl
groups using the synthesis of 1gr as an example
3.58 – 3.49 (1H, m, 3α-H), 1.03 (3H, s, 19-CH ), 0.85 (3H, s, 18-
3
13
CH3); C NMR (101 MHz, CDCl ) δ 159.32, 140.98, 127.97,
3
126.66, 121.07, 114.24, 84.17, 71.61, 71.42, 63.08, 55.28,
5
3
2
1
0.03, 47.74, 44.32, 42.22, 37.10, 36.62, 36.57, 34.68, 31.56,
Gelator
1
(100 mg, 1.0 equiv) and toluene (2.5 mL) were added
was
-
1
1.52, 31.18, 20.45, 19.45, 12.33; IR (KBr, cm ) ν: 3583, 3453,
938, 2904, 2858, 1613, 1514, 1444, 1400, 1376, 1302, 1252,
171, 1083, 1038, 946, 838, 799; HRMS calcd. for C H O Na
to a 50-mL flask. The mixture was heated until gelator
1
completely dissolved. The solution was then cooled to room
temperature to form a gel. The xerogel was prepared by the
slow evaporation of the toluene under reduced pressure. Then
NaBH (77 mg, 8.0 equiv), H O (0.12 mL) and granular PTFE
2
7 36 4
+
[
M + Na] : 447.2506, found: 447.2512.
1
4
7
1
gr：white solid; mp 214-216 °C ; H NMR (600 MHz, CDCl ) δ
3
4
2
.38 – 7.30 (4H, m, Ar-H), 5.37 (1H, s, 6-H), 4.00 (2H, s, epoxy &
(5.0 g) were added to the prepared xerogel. The reaction
7β-H), 3.59 – 3.48 (1H, m, 3α-H), 1.03 (3H, s, 19-CH ), 0.84
3
mixture was mechanically stirred for 13 h at room
temperature. TLC (thin layer chromatography) was used to
determine the reaction completion. The reaction mixture was
extracted with ethyl acetate (5 mL×3) followed by washing
with water (10 mL×2). Ethyl acetate was evaporated to give
product 1gr in a quantitative yield.
13
(3H, s, 18-CH3); C NMR (101 MHz, CDCl ) δ 140.99, 135.09,
3
1
5
3
2
8
4
5
7
33.49, 128.68, 126.98, 121.02, 83.96, 71.98, 71.61, 63.00,
0.02, 47.71, 44.20, 42.20, 37.10, 36.62, 36.44, 34.57, 31.54,
-
1
1.47, 31.20, 20.41, 19.45, 12.25; IR (KBr, cm ) ν: 3365, 2966,
934, 2853, 1643, 1492, 1440, 1399, 1134, 1085, 1035, 947,
+
56, 834, 778; HRMS calcd. for C H ClO Na [M + Na] :
26
33
3
Procedure for the reduction of carbonyl groups using more than 1
g of gelator 1 and no organic solvents in the workup
51.2010, found: 451.2010.
1
gr: white solid; mp 223-225 °C ; H NMR (400 MHz, CDCl3) δ
.50 (2H, d, J = 8.4 Hz, Ar-H), 7.30 (2H, d, J = 8.3 Hz, Ar-H), 5.38
Gelator
1
(1.10 g, 1.0 equiv) and toluene (27.5 mL) were added
was
to a 100-mL flask. The mixture was heated until gelator
1
(1H, d, J = 5.0 Hz, 6-H), 4.01 (1H, s, epoxy-H), 4.00 (1H, s, 17β-
completely dissolved. The solution was then cooled to room
temperature to form a gel. The xerogel was prepared by the
slow evaporation of the toluene under reduced pressure. Then
NaBH (0.85 g, 8.0 equiv), H O (1.32 mL) and granular PTFE (5.0
H), 3.68 – 3.47 (1H, m, 3α-H), 1.05 (3H, s, 19-CH ), 0.86 (3H, s,
1
CDCl ) δ 141.01, 135.67, 131.61, 127.30, 121.60, 121.02, 83.97,
7
3
cm ) ν: 3441, 2935, 2901, 2851, 1488, 1435, 1332, 1296, 1133,
1
for C H BrO Na [M + Na] : 495.1505, found: 495.1506.
3
13
8-CH ), 0.58 (1H, d, J = 5.5 Hz, 12β-H); C NMR (101 MHz,
3
3
4
2
1.95, 71.62, 63.02, 50.03, 47.72, 44.21, 42.23, 37.11, 36.63,
g) were then added to the prepared xerogel. The reaction
mixture was mechanically stirred for 11 h at room
temperature. TLC was used to determine the reaction
completion. A small amount of water (10 mL×3) was added to
the reaction mixture followed by filtration to give product 1gr
6.46, 34.58, 31.57, 31.47, 31.21, 20.41, 19.44, 12.24; IR (KBr,
-1
068, 1043, 1009, 946, 907, 860, 832, 775, 731; HRMS calcd.
+
26
33
3
1
9
gr: white solid; mp 193-195 °C ; H NMR (600 MHz, CDCl ) δ
3
(1.12 g) in a quantitative yield.
7
.41 (2H, d, J = 7.3 Hz, Ar-H), 7.36 (2H, t, J = 7.5 Hz, Ar-H), 7.29
1
1
gr: white solid; mp 209-211 °C ; H NMR (600 MHz, CDCl ) δ
3
(1H, d, J = 7.3 Hz, Ar-H), 4.04 (1H, s, epoxy-H), 3.99 (1H, s, 17β-
7
.42 (2H, d, J = 7.5 Hz, Ar-H), 7.37 (2H, t, J = 7.5 Hz, Ar-H), 7.30
13
H), 3.68 – 3.53 (1H, m, 3α-H), 0.82 (6H, s, 18 & 19-CH3);
NMR (101 MHz, CDCl ) δ 136.37, 128.68, 127.83, 125.44, 84.17,
7
3
1
1
7
C
(1H, d, J = 7.2 Hz, Ar-H), 5.37 (1H, s, 6-H), 4.06 (1H, s, epoxy-H),
3
4
.01 (1H, s, 17β-H), 3.59 – 3.45 (1H, m, 3α-H), 1.03 (3H, s, 19-
1.77, 71.18, 63.36, 54.28, 47.49, 44.84, 44.59, 38.09, 36.84,
6.75, 35.62, 34.75, 34.72, 31.72, 31.42, 28.49, 20.62, 12.46,
1
3
CH ), 0.85 (3H, s, 18-CH ), 0.66 (1H, d, J = 11.6 Hz, 12β-H);
C
3
3
NMR (101 MHz, CDCl ) δ 140.99, 136.32, 128.72, 127.88,
-1
3
2.33; IR (KBr, cm ) ν: 3416, 3357, 2974, 2935, 2852, 1637,
1
4
1
1
25.45, 121.08, 84.10, 71.78, 71.61, 63.32, 50.02, 47.77, 44.29,
2.20, 37.10, 36.62, 36.55, 34.76, 31.52, 31.17, 20.44, 19.46,
2.32; IR (KBr, cm ) ν: 3356, 2970, 2937, 2908, 2850, 1635,
460, 1388, 1245, 1213, 1156, 1071, 1037, 947, 913, 796, 756,
+
35, 697; HRMS calcd. for C H O Na [M + Na] : 419.2557,
2
6 36 3
-
1
found: 419.2558.
461, 1379, 1356, 1296, 1133, 1078, 1039, 756, 696; HRMS
1
1
7
–
0gr: white solid; mp 213-215 °C ; H NMR (600 MHz, CDCl ) δ
3
+
calcd. for C H O Na [M + Na] : 417.2400, found: 417.2397.
26 34 3
.33 (2H, d, J = 8.0 Hz, Ar-H), 6.90 (2H, d, J = 7.9 Hz, Ar-H), 4.08
3.92 (2H, m, epoxy & 17β-H), 3.79 (3H, s, OCH ), 3.64 – 3.56
3
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O rP gl ea na is ce &d Bo i on mo to al e dc juu l sa tr mC haer mg i ins ts ry
Page 10 of 11
ARTICLE
Journal Name
1
3
1
(
1H, m, 3α-H), 0.82 (6H, s, 18 & 19-CH3); C NMR (101 MHz, 5ge: white solid; mp 254-256 °C ; H NMR (400 MHz, CDCl ) δ
View Article Online
3
DOI: 10.1039/C8OB01505H
CDCl ) δ 159.30, 128.01, 126.65, 114.21, 84.24, 71.42, 71.17, 7.47 (2H, d, J = 8.4 Hz, Ar-H), 7.34 (2H, d, J = 8.4 Hz, Ar-H), 4.16
3
6
3
3.12, 55.28, 54.28, 47.44, 44.83, 44.61, 38.10, 36.84, 36.76, (1H, s, epoxy-H), 4.00 – 3.86 (1H, m, 3α-H), 2.97 (1H, d, J = 4.3
13
5.61, 34.75, 34.64, 31.72, 31.43, 28.49, 20.63, 12.48, 12.33; IR Hz, 6β-H), 1.11 (3H, s, 19-CH ), 0.85 (3H, s, 18-CH ); C NMR
3
3
-
1
(KBr, cm ) ν: 3511, 2927, 2851, 1616, 1516, 1445, 1383, 1298, (101 MHz, DMSO-d ) δ 211.61, 133.58, 130.96, 129.15, 121.56,
6
1
250, 1173, 1133, 1074, 1034, 833, 791, 741; HRMS calcd. for 67.39, 66.55, 65.53, 64.16, 58.19, 48.46, 47.97, 42.72, 40.12,
+
C H O Na [M + Na] : 449.2662, found: 449.2671.
General procedure for the gel mediated epoxidation reactions of
double bonds using the synthesis of 1ge as an example
35.11, 32.66, 31.40, 30.78, 29.22, 28.75, 27.31, 19.63, 16.08,
13.06; IR (KBr, cm ) ν: 3278, 2943, 2867, 1743, 1450, 1378,
27
38
4
-
1
1334, 1251, 1217, 1199, 1147, 1105, 1064, 1044, 991, 924, 858,
+
8
5
1
7
4
33, 786, 729; HRMS calcd. for C H BrO Na [M + Na] :
26
31
4
Gelator
1
(100 mg, 1.0 equiv) and toluene (2.5 mL) were added
was
09.1298, found: 509.1296.
to a 50-mL flask. The mixture was heated until gelator
1
1
1ge: white solid; mp 207-209 °C ; H NMR (400 MHz, CDCl ) δ
.55 (2H, d, J = 7.2 Hz, Ar-H), 7.48 – 7.38 (4H, m, Ar-H & ArCH),
.03 – 3.85 (1H, m, 3α-H), 2.98 (1H, d, J = 4.3 Hz, 6β-H), 1.15
3
completely dissolved. The solution was then cool to room
temperature to form a gel. Next m-CPBA (85%, 62 mg, 1.2
equiv) and granular PTFE (5.0 g) were added to the prepared
gel. The reaction mixture was mechanically stirred for 4.0 h at
13
(
3H, s, 19-CH ), 0.94 (3H, s, 18-CH ); C NMR (101 MHz, CDCl3)
3
3
δ 209.23, 135.58, 135.52, 133.29, 130.32, 129.30, 128.70,
0
-5 °C. TLC was used to determine the reaction completion.
6
3
8.46, 65.76, 58.38, 49.93, 47.40, 42.85, 39.75, 35.12, 32.38,
1.19, 31.02, 29.21, 29.11, 27.86, 20.04, 15.97, 14.26; IR (KBr,
Saturated Na CO solution (10 mL) and ethyl acetate (20 mL)
were added to the reaction mixture at 0-5 °C followed by
stirring for 10 min. The mixture was then washed with water
2
3
-
1
cm ) ν: 3173, 3091, 2971, 2925, 2852, 1708, 1626, 1466, 1443,
1
6
4
372, 1338, 1249, 1101, 1065, 1041, 986, 932, 869, 771, 736,
(10 mL×2) and dried using anhydrous Na SO . After
2 4
+
94; HRMS calcd. for C H O Na [M + Na] : 415.2244, found:
26 32 3
evaporation of the ethyl acetate, the product was crystallized
with ethanol to give α-epoxide product 1ge in an 87% yield.
15.2246.
1
1
ge: white solid; mp 253-255 °C ; H NMR (400 MHz, CDCl ) δ
3
7
.45 (2H, d, J = 7.0 Hz, Ar-H), 7.37 – 7.30 (3H, m, Ar-H), 4.22
Conflicts of interest
There are no conflicts to declare.
(1H, s, epoxy-H), 4.01 – 3.87 (1H, m, 3α-H), 2.98 (1H, d, J = 4.3
13
Hz, 6β-H), 1.11 (3H, s, 19-CH ), 0.87 (3H, s, 18-CH ); C NMR
3
3
(
101 MHz, CDCl ) δ 211.12, 133.14, 128.25, 127.80, 126.49,
3
6
3
1
1
8.46, 66.06, 65.60, 65.38, 58.53, 48.63, 48.00, 42.55, 39.71,
5.05, 32.26, 30.99, 30.64, 29.42, 29.37, 27.44, 19.61, 15.93,
2.98; IR (KBr, cm ) ν: 3283, 2936, 2859, 1743, 1452, 1376, ‡ T. Li and Y. Chen contributed equally.
Notes and references
-
1
1
2
J. W. Steed, Chem. Commun., 2011, 47, 1379.
338, 1250, 1198, 1148, 1067, 1045, 990, 926, 865, 748, 698;
+
E. K. Johnson, D. J. Adams, P. J. Cameron, J. Mater. Chem.,
HRMS calcd. for C H O Na [M + Na] : 431.2193, found:
26 32 4
2
011, 21, 2024.
4
2
8
31.2193.
3
4
5
P. Terech, R. G. Weiss, Chem. Rev., 1997, 97, 3133.
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ge: white solid; mp 272-274 °C ; H NMR (400 MHz, CDCl ) δ
3
D. J. Abdallah, R. G. Weiss, Adv. Mater., 2000, 12, 1237.
H. Svobodová, V. Noponen, E. Kolehmainen, E. Sievänen, RSC
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13
6
7
8
9
A. R. Hirst, B. Escuder, J. F. Miravet, D. K. Smith, Angew.
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Hz, 6β-H), 1.11 (3H, s, 19-CH ), 0.85 (3H, s, 18-CH ); C NMR
3
3
(101 MHz, CDCl ) δ 210.81, 147.81, 140.34, 127.54, 123.08,
3
S. Banerjee, R. K. Das, U. Maitra, J. Mater. Chem., 2009, 19
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,
6
3
1
1
8
4
4
7
8.47, 66.21, 65.56, 63.92, 58.43, 48.60, 48.11, 42.52, 39.68,
5.05, 32.25, 30.99, 30.57, 29.41, 29.31, 27.44, 19.58, 15.92,
6
-
1
6
3.01; IR (KBr, cm ) ν: 3233, 2948, 2920, 2868, 1744, 1603,
522, 1450, 1345, 1201, 1149, 1105, 1066, 1045, 989, 926, 866,
+
6
44, 745, 694; HRMS calcd. for C H NO Na [M + Na] :
26
31
6
1
1
0 Y. Lin, R. G. Weiss, Macromolecules, 1987, 20, 414.
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76.2044, found: 476.2038.
,
1
ge: white solid; mp 262-264 °C ; H NMR (400 MHz, CDCl ) δ
3
1
2 M. George, G. Tan, V. T. John, R. G. Weiss, Chem. -Eur. J.,
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2
005, 11, 3243.
(1H, s, epoxy-H), 3.99 – 3.87 (1H, m, 3α-H), 2.97 (1H, d, J = 4.3
13
13 A. R. Hirst, D. K. Smith, Chem. -Eur. J., 2005, 11, 5496.
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Hz, 6β-H), 1.11 (3H, s, 19-CH ), 0.85 (3H, s, 18-CH ); C NMR
3
3
4 W. Weng, J. B. Beck, A. M. Jamieson, S. J. Rowan, J. Am.
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(101 MHz, CDCl ) δ 211.03, 134.15, 131.65, 128.06, 127.92,
3
6
3
1
1
8
4
8.50, 66.05, 65.54, 64.66, 58.47, 48.61, 48.03, 42.54, 39.71, 15 T. Wang, Y. Li, M. Liu, Soft Matter, 2009,
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1
5.05, 32.26, 31.01, 30.62, 29.42, 29.30, 27.44, 19.60, 15.93,
-
1
7
2.97; IR (KBr, cm ) ν: 3277, 2944, 2869, 1744, 1492, 1450,
1
378, 1333, 1252, 1199, 1147, 1087, 1063, 1044, 991, 926, 859,
+
35, 805, 788; HRMS calcd. for C H ClO Na [M + Na] :
26
31
4
18 T. Tu, W. Fang, X. Bao, X. Li, K. H. Dötz, Angew. Chem. Int. Ed.,
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9 M. Žinić, F. Vögtle, F. Fages, Top. Curr. Chem., 2005, 256, 39.
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0 | J. Name., 2012, 00, 1-3
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