A practical method to stereospecifically synthesize trans-stilbene derivatives

Article abstract of DOI:10.1002/cjoc.201180279

A practical method to stereospecifically synthesize trans-stilbenes was developed via the one-pot benzylation-dehydration reaction of aromatic aldehydes with benzyltrimethylsilane (BTMS), which was driven by tetrabutylammonium fluoride (TBAF) in THF. At the same time a plausible description of the whole process was proposed and the effects of substituted groups on the reaction were investigated. Also this method was employed to synthesize three precursors of natural products with excellent yields, which demonstrated that this method is much efficient and practical in the synthesis of some natural products. A practical method to stereospecifically synthesize trans-stilbenes was developed via the one-pot benzylation-dehydration reaction of aromatic aldehydes with benzyltrimethylsilane, which was driven by tetrabutylammonium fluoride in THF. A plausible description of the whole process was proposed and the effects of substituted groups on the reaction were investigated. This method was employed to synthesize three precursors of natural products with excellent yields. Copyright

Full text of DOI:10.1002/cjoc.201180279

FULL PAPER
A Practical Method to Stereospecifically Synthesize
trans-Stilbene Derivatives
Jian, Yujuana(见玉娟)
Sun, Gaojunb(孙高军)
Li, Jiaming*,a(李家明)
Su, Danc(苏丹)
Li, Chuanruna(李传润)
Zhong, Guochena(钟国琛)
a Department of Pharmacy, Anhui University of Traditional Chinese Medicine, Hefei, Anhui 230031, China
b School of Biotechnology and Food Engineering, Hefei University of Technology, Hefei 230009, China
c Department of Pharmacy, the Affiliated Anhui Provincial Hospital, Anhui Medical University, Hefei, Anhui
230001, China
A practical method to stereospecifically synthesize trans-stilbenes was developed via the one-pot benzyla-
tion-dehydration reaction of aromatic aldehydes with benzyltrimethylsilane (BTMS), which was driven by tetrabu-
tylammonium fluoride (TBAF) in THF. At the same time a plausible description of the whole process was proposed
and the effects of substituted groups on the reaction were investigated. Also this method was employed to synthe-
size three precursors of natural products with excellent yields, which demonstrated that this method is much effi-
cient and practical in the synthesis of some natural products.
Keywords trans-stilbene, benzyltrimethylsilane, aromatic aldehydes, benzylation, natural products
Introduction
Scheme 1
The trans-stilbene family compounds play important
roles in biological,1 material2 and theoretical3 chemistry.
Their preparations have attracted much attention for
several decades.4 For instance, Heck reaction5 and Su-
zuki reaction6 have been developed for this purpose re-
cently. Over the last decade, nevertheless, Wittig olefi-
nation has still been the major method to prepare the
stilbene compounds1-3 due to its high yield and facile
starting materials. However, its relatively low stereo-
selectivity in a lot of cases compromises its efficiency
and attractiveness. During our efforts to discover more
economical and more efficient methods to prepare
trans-stilbene derivatives, the dehydration reaction of
ammonium fluoride (TBAF) in THF to give silyl ethers.
They were then hydrolyzed with aqueous acid to afford
1,2-diarylethanols,8 which were further dehydrated to
afford the corresponding stilbenes. Benzylation of the
aromatic aldehydes with BTMS is a suitable method to
prepare the 1,2-diarylethanols due to the readily avail-
able, inoffensive and stable starting materials. Also, this
reaction is moisture and oxygen tolerable and can be
carried out smoothly at relative low temperature without
expensive catalysts. To start the synthesis, the reaction
procedure of benzaldehyde (1 mmol) with BTMS re-
ported by Bennetau was followed,8d in which the moler
ratio of BTMS∶ benzaldehyde∶ TBAF was 2∶ 1∶ 0.3,
but without inert-atmosphere protection and without the
removal of the trace water in TBAF. A high yield was
1,2-diarylethanol attracted our interests. It is
a
well-documented reaction, which can stereospecifically
lead to the formation of the trans-isomers in decent
yields.4,7 However, the lack of efficient methods to pre-
pare the 1,2-diarylethanols greatly limits the application
of this dehydration method. We report herein a practical
one-pot reaction sequence to stereospecifically prepare
trans-stilbene derivatives with high yields through
1,2-diarylethanols.
Results and discussion
Our synthetic path was shown in Scheme 1.
The reactions of aromatic aldehydes with benzyl-
trimethylsilane (BTMS) were driven by tetrabutyl-
*
E-mail: jianxq1125@163.com
Received August 20, 2010; revised January 21, 2011; accepted February 20, 2011.
Project supported by the Key Natural Science Research Projects for Universities in Anhui Province (No. KJ2010A206).
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Jian et al.
FULL PAPER
obtained (87%) and no side reaction related to benzal-
dehyde was observed. The excess BTMS was decom-
posed to give volatile toluene at the end of the reaction.
After washing the reaction mixture with water and
evaporating the solvent, only one impurity, the remain-
ing benzaldehyde was found. This implied that quantita-
tive transformation of benzaldehyde could enhance both
the yield and the purity of the product. Therefore, the
reaction condition was optimized by adjusting the
amount of BTMS, TBAF and THF used. After many
trials, complete conversion of benzaldehyde was real-
ized by increasing the amount of BTMS to three
equivalents and reducing the TBAF to 0.15 equivalent
relative to benzaldehyde, in other words, the moler ratio
of BTMS∶ benzaldehyde∶ TBAF was adjusted to 3∶
1∶ 0.15. The high purity of the crude product prompted
us to carry out the dehydration in the same flask. At the
ents in the benzene ring (A ring in Scheme 1) of BTMS
also had an interesting influence on the benzylation re-
action. The benzylations of BTMS or (2-chlorobenzyl)-
trimethyl-silane with aldehydes were carried out
smoothly at room temperature with satisfactory results
(Entries 1— 8). When the (4-methoxybenzyl)trimethyl-
silane was employed, it was necessary to raise the reac-
tion temperature to the boiling point of THF to realize
the complete transformation of the aldehyde (Entry 9).
The following dehydration reaction was much more
sensitive to the substituents in the aromatic ring B.
Generally, electron-donating substituents in the aro-
matic ring B can accelerate the dehydration reaction
greatly. For example, it took only 45 min to dehydrate
the alcohol prepared from 4-methoxy-benaldehyde
while it took 7 h to dehydrate the one from 4-chloro-
benzaldehyde. Nevertheless, higher rate did not neces-
sarily lead to higher yield (Entries 2 and 5). The influ-
ential factors of yields were more complicated. The
substituents in the aromatic ring A exerted little influ-
ence on the dehydration. From Entries 1 and 8, 6 and 9,
it was obvious that there existed two possible synthetic
pathways for a certain target molecule, which not only
showed the flexibility of our method but also enhanced
the possibility of success. A case in point was the syn-
thesis of 2-nitrostilbene. The synthetic path starting
from 2-nitro-benzaldehyde and BTMS was proved to be
a failure (Entry 11). However, the benzylation of ben-
zaldehyde with (2-nitrobenzyl)-trimethylsilane gave a
much better yield (70%).8a On the other hand, those al-
dehydes bearing hydroxyl group did not react with
BTMS or its derivatives. After being suitably protected,
however, they could also be used to prepare the hy-
droxyl-substituted stilbenes in one-pot procedure, with-
out additional deprotection manipulation (Entry 10).
We devised a plausible description of the whole
end of the benzylation, 0.5 mL of 4 mol•L－ HCl was
1
added to hydrolyze the silylether. After removing the
THF and water, 10 mL of toluene and catalytic amount
of 85% H3PO4 were sequentially added.9 The mixture
was refluxed for 5 h with continuous removal of the
newly generated water. The trans-stilbene was isolated
as the sole product in 90% yield. A one-pot reaction to
synthesize trans-stilbene was successfully developed.
To probe the applicable scope of this one-pot sequence,
other aldehydes and BTMS derivatives10 were also
tested (Table 1). In the benzylation step, those alde-
hydes with aromatic rings (B-ring in Scheme 1) bearing
electron-donating or weak electron-withdrawing sub-
stituents were quantitatively transformed to the corre-
1
sponding alcohols in all the cases (estimated from H
NMR data of the reaction mixture and by TLC), regard-
less of the substitution patterns (Entries 1— 10). Sur-
prisingly, the benzylation of 2-nitro-benzaldehyde with
BTMS proceeded sluggishly (Entry 11). The substitu-
Table 1 Synthesis of trans-stilbene derivatives by the one-pot benzylation-dehydration procedure
R' Product Isolated yield/%
Entry
1
R
H
2-Cl
89
2
3
4
H
H
H
4-Cl
87
91
92
4-CH3
4-NMe2
a
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A Practical Method to Stereospecifically Synthesize trans-Stilbene Derivatives
Continued
Entry
5
R
H
R'
Product
Isolated yield/%
81
4-MeO
6
7
H
H
2-MeO
87
84
2,3-(CH)4
8
9
2-Cl
H
H
92
80
4-MeO
b
10
H
H
4-MOMO
2-NO2
72
11
—
trace
a 2 mmol of TBAF was added instead of hydrochloric acid at the end of benzylation reaction and the dehydration reaction was carried out
in DMSO11. b 1h is the 4-hydroxystilbene.
process by referencing to the TBAF-catalyzed allylation
reaction12 (Scheme 2). The whole process begins with a
catalytic cycle. TBAF cleaves the carbon-silicon bond
of the silanes, giving the trimethylsilyl fluoride and a
benzyl anion species i. i adds to the aldehydes to form ii,
accompanying the shift of the negative charge to the
oxygen. Then ii seizes the trimethylsilyl group from
trimethylsilyl fluoride. As a result, silyl ethers iii are
produced, and TBAF is regenerated to participate in the
next cycle. The addition of the hydrochloric acid after
the completion of the benzylation reaction decomposes
the silyl ethers v to alcohols iv. In the following dehy-
dration reaction, iv combines a proton and then looses a
water molecule to give cationic species v. Regeneration
of the proton from v leads to the formation of the target
moleculars. Some experimental phenomena can be ex-
plained by the description. Because the electro-with-
drawing substituents in the aromatic ring A can stabilize
the benzyl anion i and the electron-donating ones show
converse effects, it is reasonable for the (4-methoxy-
benzyl) trimethylsilane to require higher temperature to
generate the corresponding benzyl anion than BTMS or
(2-chlorobenzyl)trimethylsilane. The low yield of ben-
zylation of 2-nitrobenzaldehyde may be attributed to the
difficulty of the regeneration of TBAF. In the interme-
diate ii, substituent R' on the aromatic ring B can still
influence the charge-density of the oxygen to some ex-
tent despite the long distance. When R' is
a
chloro-substituent, the influence is insignificant. But
when R' is a nitro group, one of the strongest electron-
withdrawing groups, the reduction of the charge-density
on the oxygen stands out, which makes ii unable to
seize the trimethylsilyl group from the trimethylsilyl
fluoride. Therefore, the catalytic cycle ceased. The in-
volvement of the cationic species v in the whole process
also gives an answer to the accelerating-effect of elec-
tron-donating groups in the aromatic ring B other than
in the ring A.
More importantly, this method was applied to the
synthesis of some bioactive natural products (Scheme 3).
Starting from the commercially available methyl
3,5-dimethoxybenzoate, the (3,5-dimethoxybenzyl)-
trimethylsilane was prepared in three steps with excel-
lent yield conveniently. Following the same procedure,
three important intermediates 4a, 4b, and 4c were ob-
tained, as shown in Scheme 3. These intermediates
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Jian et al.
FULL PAPER
Scheme 2
Scheme 3
could be easily converted to piceatannol, pinosilvine
and resveratrol respectively in high yields according to
method described by Brooks.12
synthesis of some natural products.
Experimental
Synthesis of trans-stilbenes
Conclusion
1 mmol of aldehyde and 3 mmol of silane were dis-
solved in 4 mL of THF at room temperature. Then 0.15
of mmol of TBAF were added. The mixture was stirred
for 1 h at room temperature. At the end of the benzyla-
In conclusion, we devised a convenient and practical
method to prepare trans-stilbene derivatives and specu-
lated a possible reaction mechanism which can be
demonstrated by the experimental results. The facile
starting materials, the simple experimental operation,
the high overall yield and the stereospecificity feature
our method and promise its application. Moreover, the
successful application in the syntheses of three precur-
sors (4a, 4b, 4c) of the natural products demonstrated
that this method is much efficient and practical in the
tion, 0.5 mL of 4 mol•L－ HCl was added to hydrolyze
1
the silyl ether. After removing the THF and water under
reduced pressure, 10 mL of toluene and 0.1 mL of 85%
H3PO4 were sequentially added and the system was re-
fluxed with timely removal of the water by Dean-Stark
trap. The cease of formation of water indicated the end
of the reaction. Then the resulting mixture was cooled,
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Chin. J. Chem. 2011, 29, 1423— 1428

A Practical Method to Stereospecifically Synthesize trans-Stilbene Derivatives
and diluted with 70 mL of ethyl ether. The solution was
washed with 10 mL of water, 10 mL of saturated aque-
ous NaHCO3 and 5 mL brine orderly. The organic layer
was dried (MgSO4), evaporated, and purified by flash
chromatography to give the corresponding product. As
for the preparation of 4-(dimethylamino)stilbene, minor
adjustment was required. After the benzylation reaction
between BTMS and 4-(dimethylamino)benzaldehyde, 2
mmol of TBAF was added to convert the silyl ether to
the alcohol, then the THF was reclaimed. The residue
was again dissolved in 4 mL of DMSO, and the system
was heated at 160—170 ℃ for 1 h. The following
procedure was identical to the one described above. 1H
NMR (CDCl3, 300 MHz) δ: 2.98 (s, 6H), 6.73 (d, J＝
8.2 Hz), 6.91 (d, J＝1 6.3 Hz, 1H), 7.05 (d, J＝16.3 Hz,
1H), 7.19—7.25 (m, 1H), 7.29—7.32 (m, 2 H), 7.40—
7.43 (m, 4H); 13C NMR (CDCl3, 75 MHz) δ: 40.4,
112.4, 124.3, 125.7, 125.9, 126.6, 127.5, 128.5, 128.7,
138.2, 150.1; MS m/z: 223. (CAS number 838-95-9).
2-Chlorostilbene (1a) 1H NMR (CDCl3, 300 MHz)
δ: 7.69 (dd, J＝1.7, 7.7 Hz, 1H), 7.57—7.49 (m, 3H),
7.41—7.37 (m, 3H), 7.31—7.17 (m, 3H), 7.08 (d, J＝
16.3 Hz, 1H); 13C NMR (CDCl3, 75 MHz) δ: 137.3,
135.6, 133.7, 131.4, 130.0, 128.9, 128.7, 128.2, 127.0,
126.6, 125.0; MS m/z: 214. (CAS number 1657-52-9).
4-Chlorostilbene (1b) 1H NMR (CDCl3, 300 MHz)
δ: 7.51—7.06 (m, 9H), 7.05—7.06 (m, 2H). 13C NMR
(CDCl3, 75 MHz,) δ: 137.2, 136.0, 133.3, 129.5, 129.0,
128.9, 128.0, 127.8, 127.5, 126.7,214.5; MS m/z 214.
(CAS number 1657-50-7).
13C NMR (CDCl3, 75 MHz) δ: 137.8, 135.2, 133.9,
131.9, 131.6, 128.9, 128.7, 128.2, 127.9, 126.8, 126.2,
126.0, 125.8, 124.0, 123.8; MS m/z: 230. (CAS number
2840-87-1).
4-Hydroxystilbene (1h) 1H NMR (CDCl3, 300
MHz) δ: 7.51—7.24 (m, 7H), 7.06 (d, J＝13.5 Hz, 1H),
6.97 (d, J＝13.5 Hz, 1H), 6.84 (d, J＝6.5 Hz, 2H), 4.82
(br, 1H). (CAS number 6554-98-9).
References
1
(a) Dogan, Z.; Paulini, R.; Rojas Stutz, J. A.; Narayanan, S.;
Richert, C. J. Am. Chem. Soc. 2004, 126, 4762.
(b) Treadwell, E. M.; Cermak, S. C.; Wiemer, D. F. J. Org.
Chem. 1999, 64, 8718.
(c) Husemoen, G.; Olsson, R.; Andersson, C.-M.; Harvey, S.
C.; Hansen, H. C. J. Comb. Chem. 2003, 5, 606.
(d) Kim, S.; Ko, H.; Park, J. E.; Jung, S.; Lee, S. K.; Chun,
Y.-J. J. Med. Chem. 2002, 45, 160.
(e) Roberti, M.; Pizzirani, D.; Simoni, D.; Rondanin, R.;
Baruchello, R.; Bonora, C.; Buscemi, F.; Grimaudo, S.;
Tolomeo, M. J. Med. Chem. 2003, 46, 3546.
(f) Pettit, G. R.; Anderson, C. R.; Herald, D. L.; Jung, M. K.;
Lee, D. J.; Hamel, E.; Pettit, R. K. J. Med. Chem. 2003, 46,
525.
2
(a) Chen, C.-T.; Chiang, C.-L.; Lin, Y.-C.; Chan, L.-H.;
Huang, C.-H.; Tsai, Z.-W.; Chen, C.-T. Org. Lett. 2003, 5,
1261.
(b) Yang, J. S.; Lin, Y. H.; Yang, C. S. Org. Lett. 2002, 4,
777.
(c) Kim, S.; Seus, P.; Meier, H. Eur. J. Org. Chem. 2004,
1761.
(d) Stuhr-Hansen, N.; Christensen, J. B.; Harrit, N.;
Bjornholm, T. J. Org. Chem. 2003, 68, 1275.
(e) Larsen, M.; Krebs, F. C.; Jorgensen, M.; Harrit, N. J.
Org. Chem. 1998, 63, 4420.
(f) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew.
Chem., Int. Ed. 1998, 37, 402.
4-Methylstilbene (1c) 1H NMR (CDCl3, 300 MHz)
δ: 7.54—7.52 (m, 2H), 7.46—7.35 (m, 4H), 7.31—7.10
(m, 5H), 2.39 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ:
137.7, 137.6, 134.7, 129.5, 128.8, 127.9, 127.7, 127.5,
126.6, 126.5, 21.3; MS m/z: 194. (CAS number
1860-17-9).
4-(Dimethylamino)stilbene (1d) 1H NMR (CDCl3,
300 MHz) δ: 7.40—7.43 (m, 4H), 7.29—7.32 (m, 2H),
7.19—7.25 (m, 1H), 7.05 (d, J＝16.3 Hz, 1H), 6.91 (d,
J＝16.3 Hz, 1H), 6.73 (d, J＝8.2 Hz), 2.98 (s, 6H); 13C
NMR (CDCl3, 75 MHz) δ: 150.1, 138.2, 128.7, 128.5,
127.5, 126.6, 125.9, 125.7, 124.3, 112.4, 40.4; MS m/z:
223. (CAS number 838-95-9).
(g) Martin, R. E.; Diederich, F. Angew. Chem., Int. Ed. 1999,
38, 1350.
3
(a) Lewis, F. D.; Kalgutkar, R. S.; Yang, J.-S. J. Am. Chem.
Soc. 1999, 121, 12045.
(b) Rao, K. S. S. P.; Hubig, S. M.; Moorthy, J. N.; Kochi, J.
K. J. Org. Chem. 1999, 64, 8098.
2-Methoxystilbene (1e) 1H NMR (CDCl3, 300
MHz) δ: 7.50—7.44 (m, 4H), 7.36—7.31 (m, 2H), 7.25
—7.20 (m, 1H), 7.10—6.94 (m, 2H), 6.92—6.87 (m,
2H), 3.83 (s, 3H); 13C NMR (CDCl3, 75 MHz) δ: 159.5,
137.8, 130.3, 128.8, 128.4, 127.9, 127.3, 126.8, 126.4,
114.3, 55.4; MS m/z: 210. (CAS number 1694-19-5).
2-Methoxystilbene (1f) 1H NMR (CDCl3, 300
MHz) δ: 7.55—6.79 (m, 11H), 3.88 (s, 3H); 13C NMR
(CDCl3, 75 MHz) δ: 157.0, 138.1, 129.2, 128.8, 128.7,
127.7, 127.5, 126.7, 126.5, 123.7, 120.9, 111.1, 55.6;
MS m/z: 210. (CAS number 52805-92-2).
(c) Waldeck, D. H. Chem. Rev. 1991, 91, 415.
Becker, K. B. Synthesis 1983, 5, 341.
(a) Selvakumar, K.; Zapf, A.; Beller, M. Org. Lett. 2002, 4,
3031.
4
5
(b) Jeffery, T.; Ferber, B. Tetrahedron Lett. 2003, 44, 193.
(c) Mu, F.; Hamel, E.; Lee, D. J.; Pryor, D. E.; Cushman, M.
J. Org. Chem. 2003, 46, 1670.
(d) Chang, C. C.; Chen, K. J.; Yu, L. J. J. Org. Chem. 1999,
64, 5603.
(e) Saiyed, A. S.; Bedekar, A. V. Tetrahedron Lett. 2010, 51,
6227.
Styryl-naphthalene (1g) 1H NMR (CDCl3, 300
MHz) δ: 8.21 (d, J＝7.3 Hz, 1H), 7.90—7.72 (m, 4H),
7.61—7.58 (m, 2H), 7.56—7.45 (m, 3H), 7.42—7.37
(m, 2H), 7.11—7.16 (m, 1H), 7.11 (d, J＝16.0 Hz, 1H);
6
(a) Terao, J.; Tang, A.; Michels, J. J.; Krivokapic, A.;
Anderson, H. L. Chem. Commun. 2004, 56.
(b) Joucla, L.; Cusati, G.; Pinel, C.; Djakovitch, L. Adv.
Chin. J. Chem. 2011, 29, 1423— 1428
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
1427

Jian et al.
FULL PAPER
Synth. Catal. 2010, 352, 1993.
Alonso, E.; Ramon, D. J.; Yus, M. J. Org. Chem. 1997, 62,
417.
(a) Ricci, A.; Degl’Innocenti, A.; Fiorenza, M.; Taddei, M.;
Spartera, M. A.; Walton, D. R. M. Tetrahedron Lett. 1982,
23, 577.
J.; Xu, D. D.; Wang, C. C. M.; Ye, C. G.; Sung, J. J. Y.;
Cho, C. H.; Wang, M. F. Eur. J. Pharmacol. 2010, 637, 55.
(a) Traynelis, V. J.; Hergenrother, W. L.; Livingston, J. R.;
Valicenti, J. A. J. Org. Chem. 1962, 27, 2377.
(b) Traynelis, V. J.; Hergenrother, W. L.; Hanson, H. T.;
Valicenti, J. A. J. Org. Chem. 1964, 29, 123.
7
8
9
(b) Ricci, A.; Fiorenza, M.; Grifagni, M. A.; Bartolhi, G.;
Seconi, G. Tetrahedron Lett. 1982, 23, 5079.
(c) Bennetau, B.; Dunogub, J. Tetrahedron Lett. 1983, 24,
4217.
10 Henne, A. L.; Matuszak, A. H. J. Am. Chem. Soc. 1944, 66,
1649.
11 Hosomi, A.; Shirahata, A.; Sakurai, H. Tetrahedron Lett.
1978, 19, 3043.
(d) Bennetau, B.; Bordeau, M.; Dunogues, J. Bull. Soc.
Chim. Fr. 1981, 90.
(f) Li, H. T.; Wu, W. K. K.; Zheng, Z. P.; Che, C. T.; Li, Z.
12 Brooks, P. R.; Wirtz, M. C.; Vetelino, M. G.; Rescek, D. M.;
Woodworth, G. F.; Morgan, B. P.; Coe, J. W. J. Org. Chem.
1999, 64, 9719.
(E1008201 Lu, Y.; Lu, Z.)
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Chin. J. Chem. 2011, 29, 1423— 1428