A transition-metal-free cross-coupling reaction of allylic bromides with aryl- and vinylboronic acids

Article abstract of DOI:10.1055/s-0031-1290656

A cross-coupling reaction between aryl- and vinylboronic acids and various allylic bromides proceeded without the use of a transition-metal catalyst to give the corresponding allylated products in moderate to good yields. The use of an inorganic base (KF

Full text of DOI:10.1055/s-0031-1290656

LETTER
1085
A Transition-Metal-Free Cross-Coupling Reaction of Allylic Bromides with
Aryl- and Vinylboronic Acids
Transition-Metal-Free
i
Cross-
t
s
g Reactio
u
n
hiro Ueda,* Kota Nishimura, Ryo Kashima, Ilhyong Ryu*
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
Fax +81(72)2549695; E-mail: ryu@c.s.osakafu-u.ac.jp; E-mail: ueda@c.s.osakafu-u.ac.jp
Received 25 December 2011
In our first investigation, treatment of cinnamyl bromide
Abstract: A cross-coupling reaction between aryl- and vinylboron-
ic acids and various allylic bromides proceeded without the use of a
transition-metal catalyst to give the corresponding allylated prod-
ucts in moderate to good yields. The use of an inorganic base (KF
(2a) with 4-methoxyphenylboronic acid (1a; 1.3 equiv)
and KF (1.5 equiv) in THF at 80 ºC for 18 hours gave (E)-
3-(4-methoxyphenyl)-1-phenyl-1-propene (3aa) in a 49%
or Cs2CO3) and a small amount of water is crucial in obtaining good yield (Table 1, entry 1).9 Interestingly, the addition of
performance in the present transition-metal-free reaction.
H2O (THF–H2O, 10:1) remarkably improved the yield
(87%; entry 2). To improve this process, we then surveyed
the effects of the base, solvent, and leaving groups of al-
lylic substrates. The use of K2CO3 in THF–H2O (10:1)
gave 3aa in a 66% yield (entry 3). Further improvement
in the yield was achieved by using Cs2CO3 in THF–H2O
(10:1; 90%; entry 4).10 An experiment without a base re-
sulted in no reaction (entry 5). Switching the solvent from
THF–H2O to DMF–H2O and toluene–H2O at 80 °C gave
Key words: transition-metal-free, C–C bond formation, aryl- and
vinylboronic acids
The palladium-catalyzed cross-coupling reaction of allyl-
ic halides,1 esters,2 and alcohols3 with organoboronic ac-
ids provides a magnificent tool for organic synthesis.
With this method, we generally rely on the use of precious
transition metals, such as Pd complexes, as the catalyst.4
In 2005, Kabalka and co-workers reported that a cross-
coupling reaction of secondary allylic alcohols with alke-
nylboron dihalides proceeded in the absence of a transi-
tion metal, in which typically stoichiometric n-BuLi was
used as a base.5 This work suggests the possibility of a
metal-free process in the cross-coupling reaction of orga-
noboron compounds, however, to the best of our knowl-
edge, no related studies on the transition-metal-free cross-
coupling reaction of organoboron compounds with allylic
halides have not been reported.6,7
Table 1 Screening of Reaction Conditions for the Transition-Metal-
Free Cross-Coupling Reaction of 4-Methoxyphenylboronic Acid (1a)
with Cinnamyl Compounds 2a
(HO)2B
OMe
1a (1.3 equiv)
base (1.5 equiv)
Ph
+
solvent
80 °C, 18 h
OMe
Ph
X
3aa
2
Entry
1
X
Base
Solvent
THF
Yield (%)b
Herein, we wish to report a Suzuki–Miyaura-type cross-
coupling reaction of allylic bromides with aryl- and vinyl-
boronic acids that proceeded under metal-free conditions
(Scheme 1). Concurrently with our work, Scrivanti and
co-workers reported a similar metal-free cross-coupling
reaction, in which they used potassium carbonate as a
base. However, the reaction reported in this work has a
broader scope and generality than expected from their
work.8
Br
Br
Br
Br
Br
Br
Br
Br
Cl
2a
2a
2a
2a
2a
2a
2a
2a
2b
KF
49
2
KF
THF–H2O (10:1)
THF–H2O (10:1)
THF–H2O (10:1)
THF–H2O (10:1)
DMF–H2O (10:1)
toluene–H2O (10:1)
CH2Cl2–H2O (10:1)
87
3
K2CO3
Cs2CO3
none
66
4
90
5
0
6
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
92
previous work
7
95
R1B(OH)2
+
8c
9c
10c
11c
99 (95)d
Pd
R2
R2
CH2Cl2–H2O (10:1) (42)d
R3
R1
this work
R3
Br
OAc 2c
OH 2d
CH2Cl2–H2O (10:1)
CH2Cl2–H2O (10:1)
0
0
transition-metal-free
Scheme 1 A transition-metal-free cross-coupling reaction of allylic
bromides with organoboronic acids
a Reaction conditions: 1a (1.3 equiv), 2 (1.0 equiv), base (1.5 equiv),
solvent (0.3 M), 80 °C, 18 h.
b NMR yield of 3aa. Tetrachloroethane was used as an internal stan-
dard.
SYNLETT 2012, 23, 1085–1089
x
x
.
x
x
.
2
0
1
2
Advanced online publication: 28.03.2012
DOI: 10.1055/s-0031-1290656; Art ID: U80511ST
© Georg Thieme Verlag Stuttgart · New York
c The reaction was carried out at 60 ºC.
d Isolated yield of 3aa.

1086
M. Ueda et al.
LETTER
3aa in 92% and 95% yields, respectively (entries 6 and 7).
The reaction using CH2Cl2–H2O as a solvent at 60 °C af-
forded 3aa in a 95% isolated yield (entry 8). We also ex-
amined some other cinnamyl substrates. Whereas
cinnamyl chloride (2b) reacted with 1a to afford 3aa in a
moderate yield (entry 9), no reaction took place with cin-
namyl acetate (2c) and cinnamyl alcohol (2d; entries 10
and 11).
Table 2 Transition-Metal-Free Cross-Coupling Reaction of Orga-
noboronic Acids 1 with Cinnamyl Bromide (2a)a
R1B(OH)2
1 (1.3 equiv)
Cs2CO3 (1.5 equiv)
+
Ph
R1
CH2Cl2–H2O (10:1)
60 °C, 18 h
3
Ph
Br
2a
Entry R1B(OH)2 1
Product 3
Yield
(%)b
With the optimized reaction conditions, represented in en-
try 8 (Table 1), in hand, the scope of the transition-metal-
free cross-coupling reaction with respect to various orga-
noboronic acids was investigated using 2a as a coupling
partner (Table 2). 2-Methoxyphenylboronic acid (1b) and
3,4-dimethoxyphenylboronic acid (1c) showed a compa-
rable reactivity with 4-methoxyphenylboronic acid (1a;
entries 2 and 3). The reaction of 4-benzyloxyphenylbo-
ronic acid (1d) with 2a also gave the corresponding prod-
uct 3da in a 91% yield (entry 4). Nitrogen-substituted
phenylboronic acid (1e) was also applicable albeit in a
modest yield (entry 5). 4-Methylphenylboronic acid (1f)
reacted with cinnamyl bromide (2a) to give 3fa in a good
yield (77%; entry 6). The reaction of 4-fluorophenylbo-
ronic acid gave 3ga in a 56% yield (entry 7). The reaction
of unsubstituted phenylboronic acid (1h) gave 3ha in a
79% yield under the reaction conditions involving KF and
toluene–H2O at 90 ºC (entry 8).11
(HO)2B
1
95
85
74
91
OMe
OMe
3aa
3ba
3ca
3da
1a
(HO)2B
2
MeO
MeO
1b
(HO)2B
OMe
OMe
OMe
OMe
3
1c
(HO)2B
4
OBn
OBn
1d
(HO)2B
Importantly, these conditions were applicable to the cross-
coupling reaction of vinylboronic acids. For example,
trans-2-(4-methylphenyl)vinylboronic acid (1i) reacted
with 2a to give the expected 1,4-diene 3ia in a 87% yield
(Scheme 2).
5
52
77
NMe2
NMe2
3ea
3fa
1e
(HO)2B
6
Me
F
Me
F
(HO)2B
Ar
1f
(HO)2B
1i (1.3 equiv)
Cs2CO3 (1.5 equiv)
+
Ph
Ar
CH2Cl2–H2O (10:1)
60 °C, 18 h
7
56
79
3ia
Ph
Br
2a
87% yield
3ga
3ha
1g
(HO)2B
8c
Ar = 4-MeC6H4
Scheme 2 Transition-metal-free cross-coupling reaction of trans-2-
(4-methylphenyl)vinylboronic acid (1i) with cinnamyl bromide (2a)
1h
a Reaction conditions: 1 (1.3 equiv), 2a (1.0 equiv), Cs2CO3 (1.5
equiv), CH2Cl2–H2O (10:1, 0.3 M), 60 °C, 18 h.
b Isolated yield of 3.
Having examined the substrate scope of organoboronic
acids with cinnamyl bromide (2a), we next turned our at-
tention to the allylic bromides 2e–2i (Table 3). A range of
electron-withdrawing ring substituents of cinnamyl bro-
mides 2e and 2f tolerated the reaction conditions well
enough to furnish the corresponding cross-coupling prod-
uct 3 in good yields (entries 1 and 2). Straight-chain ali-
phatic allylic bromide 2g also reacted with 1a to afford
3ag in a 68% yield (entry 3). Geranyl bromide (2h) partic-
ipated in the reaction with 1a to afford the desired product
3ah in a 94% yield (entry 4). Interestingly, conjugated al-
lylic bromide 2i containing vinyl bromide reacted with 1a
to give only monosubstituted product 3ai in a 76% yield
(entry 5), since it is known that the substrate containing
both vinyl and allylic bromide react with organoboronic
acid to afford the bis-substituted cross-coupling product
c KF (1.5 equiv), toluene–H2O (10:1, 0.3 M), 90 °C, 18 h.
as a major product under palladium-catalyzed cross-cou-
pling conditions.12
The addition of radical scavengers, such as 2,2,6,6-tet-
ramethylpiperidine 1-oxyl (TEMPO) and 1,4-dinitroben-
zene (an ET scavenger),13 did not affect the yield of the
reaction of 1a with 2a (Scheme 3). Therefore, it seems un-
likely that the reaction proceeded by a radical mechanism.
Although the mechanistic details of this reaction remain to
be elucidated, an ionic substitution mechanism including
an ipso-attack of organoboronic acid is shown in
Scheme 4.14 As a first step, 1a is converted to a borate an-
Synlett 2012, 23, 1085–1089
© Thieme Stuttgart · New York

LETTER
Transition-Metal-Free Cross-Coupling Reaction
1087
Table 3 Transition-Metal-Free Cross-Coupling Reaction of 4-Methoxyphenylboronic Acid (1a) with Allylic Bromides 2a
R2
R2
(HO)2B
Cs2CO3 (1.5 equiv)
+
R3
R3
Br
CH2Cl2–H2O (10:1)
60 °C, 18 h
2
OMe
3
1a (1.3 equiv)
OMe
Entry
1
Allyl bromide 2
Product 3
Yield (%)b
68
Br
O2N
O2N
OMe
2e
3ae
Br
Br
2
3
52
68
F3C
OMe
OMe
F3C
2f
3af
Me
Me
2g
3ag
Me
Me
Me
Me
Me
4
5
94
76
Me
Br
OMe
2h
3ah
Br
Br
Br
OMe
2i
3ai
a Reaction conditions: 1a (1.3 equiv), 2 (1.0 equiv), Cs2CO3 (1.5 equiv), CH2Cl2–H2O (10:1, 0.3 M), 60 °C, 18 h.
b Isolated yield of 3.
Cs+
ion A by an hydroxide anion attack. The borate anion A
Cs2CO3
–
+
Ph
Br
could then react with cinnamyl bromide (2a) through a
transition state B to give the cross-coupling product 3aa
with the liberation of boronic acid.
B(OH)2
B(OH)3
H2O
2a
MeO
MeO
MeO
1a
A
(HO)2B
Cs+
HO
OH
O
B
Ph
OMe
1a (1.3 equiv)
–
additive (1 equiv)
Cs2CO3 (1.5 equiv)
H
OMe
B(OH)3
Ph
3aa
Ph
Br
+
+
CsBr
B
CH2Cl2–H2O (10:1)
60 °C, 18 h
OMe
Ph
Br
3aa
Additive
2a
Scheme 4 Plausible mechanism for the formation of 3aa
Yield (%)
none
95
95
77
89
none (dark)
TEMPO
1,4-dinitrobenzene
(HO)2B
Scheme 3 Effect of additives on transition-metal-free cross-cou-
pling reaction of 4-methoxyphenylboronic acid (1a) with cinnamyl
bromide (2a)
OMe
1a 1 g (1.3 equiv)
Cs2CO3 (1.5 equiv)
Ph
+
CH2Cl2–H2O (10:1)
60 °C, 18 h
OMe
Ph
Br
3aa 1.07 g (93%)
The distinction of this transition-metal-free C–C bond-
forming reaction is very easy to handle. In this reaction,
purifications of commercial solvents and reagents are not
required, and an open-air condition is tolerated. Thus, we
performed a gram-scale reaction with cinnamyl bromide
(2a; 1 g, 5.1 mmol), 4-methoxyphenylboronic acid (1a; 1
g, 6.6 mmol), and Cs2CO3 (2.5 g, 7.65 mmol) in CH2Cl2–
2a 1 g
open-air
Scheme 5 Gram-scale transition-metal-free C–C bond-forming
reaction
H2O (15.5 mL/1.5 mL) at 60 ºC, which gave 3aa in a 93%
yield (1.07 g; Scheme 5).
© Thieme Stuttgart · New York
Synlett 2012, 23, 1085–1089

1088
M. Ueda et al.
LETTER
(3) (a) Tsukamoto, H.; Sato, M.; Kondo, Y. Chem. Commun.
2004, 1200. (b) Kayaki, Y.; Koda, T.; Ikariya, T. Eur. J.
Org. Chem. 2004, 4989. (c) Tsukamoto, H.; Uchiyama, T.;
Suzuki, T.; Kondo, Y. Org. Biomol. Chem. 2008, 6, 3005.
(d) Kantam, M. L.; Kumar, K. B. S.; Sreedhar, B. J. Org.
Chem. 2008, 73, 320.
(4) Rh- and Ni-catalyzed cross-coupling reactions of allylic
acetates, allylic amines, and allylic alcohols with
arylboronic acids also have been reported, but, in these
reactions, the range of applicable substrates was very
narrow. (a) Rh: Kabalka, G. W.; Dong, G.; Venkataiah, B.
Org. Lett. 2003, 5, 893 . Ni: (b) Trost, B. M.; Spagnol, M.
D. J. Chem. Soc., Perkin Trans. 1 1995, 2083. (c) Chung,
K.-G.; Miyake, Y.; Uemura, S. J. Chem. Soc., Perkin Trans.
1 2000, 15.
(5) (a) Kabalka, G. W.; Yao, M.-L.; Borella, S.; Wu, Z. Chem.
Commun. 2005, 2492. (b) Kabalka, G. W.; Yao, M.-L.;
Borella, Z.; Wu, Z.; Ju, J.-H.; Quick, T. J. Org. Chem. 2008,
73, 2668.
(6) (a) Leadbeater, N. E.; Marco, M. Angew. Chem. Int. Ed.
2003, 42, 1407. (b) Leadbeater, N. E.; Marco, M. J. Org.
Chem. 2003, 68, 5660. (c) Yan, J.; Zhu, M.; Zhou, Z. Eur. J.
Org. Chem. 2006, 2060.
(7) Shirakawa, E.; Hayashi, Y.; Itoh, K.; Watabe, R.; Uchiyama,
N.; Konagaya, W.; Masui, S.; Hayashi, T. Angew. Chem. Int.
Ed. 2012, 51, 218.
(8) Scrivanti, A.; Beghetto, V.; Bertoldini, M.; Matteoli, U. Eur.
J. Org. Chem. 2011, 264.
(9) We also tested the reactivity of other organoboronic acid
derivatives. Potassium 4-methoxyphenyltrifluoroborate was
able to react with 1a, but the yield was low (25%). Pinacol
ester of 1a did not work as a substrate.
(10) The use of Cs2CO3 in the absence of H2O gave 3aa in a
moderate yield (60%).
(11) In the general conditions, phenylboronic acid (1h) gave the
cross-coupling product 3ha in a poor yield (7% yield), and
the reaction of 4-acetylphenylboronic acid with 2a did not
give the corresponding product.
(12) (a) Yamada, Y. M. A.; Takeda, K.; Takahashi, H.; Ikegami,
S. J. Org. Chem. 2003, 68, 7733. (b) Alacid, E.; Nájera, C.
Org. Lett. 2008, 10, 5011.
(13) (a) Huang, X.-T.; Chen, Q.-Y. J. Org. Chem. 2001, 66,
4651. (b) Loy, R. N.; Sanford, M. S. Org. Lett. 2011, 13,
2548.
(14) (a) Petasis, N. A.; Zavialov, I. A. Tetrahedron Lett. 1996, 37,
567. (b) Salzbrunn, S.; Simon, J.; Prakash, G. K. S.; Petasis,
N. A.; Olah, G. A. Synlett 2000, 1485. (c) Prakash, G. K. S.;
Panja, C.; Mathew, T.; Surampudi, V.; Petasis, N. A.; Olah,
G. A. Org. Lett. 2004, 6, 2205. (d) Lee, S.; MacMillan, D.
W. C. J. Am. Chem. Soc. 2007, 129, 15438. (e) Stefani, H.
A.; Cella, R.; Vieira, A. S. Tetrahedron 2007, 63, 3623.
(f) Vieira, A. S.; Ferreira, F. P.; Fiorante, P. F.; Guadagnin,
R. C.; Stefani, H. A. Tetrahedron 2008, 64, 3306.
(g) Vieira, A. S.; Fiorante, P. F.; Hough, T. L. S.; Ferreira, F.
P.; Ludtke, D. S.; Stefani, H. A. Org. Lett. 2008, 10, 5215.
(h) Mitchell, T. A.; Bode, J. W. J. Am. Chem. Soc. 2009, 131,
18057. (i) Zeng, J.; Vedachalam, S.; Xiang, S.; Liu, X.-W.
Org. Lett. 2011, 13, 42. (j) Molander, G. A.; Cavalcanti, L.
N. J. Org. Chem. 2011, 76, 7195. (k) Larouche-Gauthier,
R.; Elford, T. G.; Aggarwal, V. J. Am. Chem. Soc. 2011, 133,
16794.
In summary, we have developed an efficient transition-
metal-free carbon–carbon bond-forming reaction with
various allylic bromides using aryl- and vinylboronic
acids under the mild reaction conditions.15 A transition-
metal-free cross-coupling reaction has some benefits such
as low cost, environmental benignity, easy operation, and
avoidance of the need to eliminate trace metals from the
final compounds. Therefore, we believe that the present
transition-metal-free system will be a useful tool in cross-
coupling chemistry.
Acknowledgment
This work was supported by a Grant-in Aid for Scientific Research
on Innovative Areas (No. 2105) from the MEXT.
References and Notes
(1) (a) Moreno-Mañas, M.; Pajuelo, F.; Pleixats, R. J. Org.
Chem. 1995, 60, 2396. (b) Cortes, J.; Moreno-Mañas, M.;
Pleixats, R. Eur. J. Org. Chem. 2000, 239. (c) Moreno-
Mañas, M.; Pleixats, R.; Villarroya, S. Organometallics
2001, 20, 4524. (d) Botella, L.; Nájera, C. J. Organomet.
Chem. 2002, 663, 46. (e) Alonso, D. A.; Nájera, C.;
Pacheco, M. C. J. Org. Chem. 2002, 67, 5588. (f) Llobet,
A.; Masllorens, E.; Rodríguez, M.; Roglans, A.; Benet-
Buchholz, J. Eur. J. Inorg. Chem. 2004, 1601. (g) Nájera,
C.; Gil-Moltó, J.; Karlström, S. Adv. Synth. Catal. 2004, 346,
1798. (h) Singh, R.; Viciu, M. S.; Kramareva, N.; Navarro,
O.; Nolan, S. P. Org. Lett. 2005, 7, 1829. (i) Kabalka, G.
W.; Dadush, E.; Al-Masum, M. Tetrahedron Lett. 2006, 47,
7459. (j) Srimani, D.; Sarkar, A. Tetrahedron Lett. 2008, 49,
6304. (k) Gerbino, D. C.; Mandolesi, S. D.; Schmalz, H.-G.;
Podestá, J. C. Eur. J. Org. Chem. 2009, 3964. (l) Alacid,E.;
Nájera, C. J. Organomet. Chem. 2009, 694, 1658.
(m) Crociani, B.; Antonaroli, S.; Burattini, M.; Paoli, P.;
Rossi, P. Dalton. Trans. 2010, 39, 3665. (n) Ghosh, R.;
Adarsh, N. N.; Sarkar, A. J. Org. Chem. 2010, 75, 5320.
(o) Civicos, J. F.; Alonso, D. A.; Nájera, C. Adv. Synth.
Catal. 2011, 353, 1683.
(2) (a) Uozumi, Y.; Danjo, H.; Hayashi, T. J. Org. Chem. 1999,
64, 3384. (b) Badone, D.; Baron, M.; Cardamone, R.;
Ielmini, A.; Guzzi, U. J. Organomet. Chem. 1997, 62, 7170.
(c) Chen, H.; Deng, M.-Z. J. Organomet. Chem. 2000, 603,
189. (d) Bouyssi, D.; Gerusz, V.; Balme, G. Eur. J. Org.
Chem. 2002, 2445. (e) Kabalka, G. W.; Al-Masum, M. Org.
Lett. 2006, 8, 11. (f) Mino, T.; Kajiwara, K.; Shirae, Y.;
Sakamoto, M.; Fujita, T. Synlett 2008, 2711. (g) Ohmiya,
H.; Makida, Y.; Tanaka, T.; Sawamura, M. J. Am. Chem.
Soc. 2008, 130, 17276. (h) Yamada, Y. M. A.; Watanabe,
T.; Torii, K.; Uozumi, Y. Chem. Commun. 2009, 5594.
(i) Maslak, V.; Tokic-Vujosevic, Z.; Saicic, R. N.
Tetrahedron Lett. 2009, 50, 1858. (j) Nishikata, T.;
Lipshutz, B. H. J. Am. Chem. Soc. 2009, 131, 12103.
(k) Ohmiya, H.; Makida, Y.; Li, D.; Tanabe, M.; Sawamura,
M. J. Am. Chem. Soc. 2010, 132, 879. (l) Pigge, F. C.
Synthesis 2010, 1745. (m) Ohmiya, H.; Yokokawa, N.;
Sawamura, M. Org. Lett. 2010, 12, 2438. (n) Li, D.;
Tanaka, T.; Ohmiya, H.; Sawamura, M. Org. Lett. 2010, 12,
3344. (o) Makida, Y.; Ohmiya, H.; Sawamura, M. Chem.
Asian. J. 2011, 6, 410.
(15) Typical Procedure for a Transition-Metal-Free Cross-
Coupling Reaction of Allylic Bromides with Aryl- and
Vinylboronic Acids: A mixture of 4-benzyloxyphenyl
boronic acid (1d; 0.65 mmol, 1.3 equiv), cinnamyl bromide
(2a; 0.5 mmol), and Cs2CO3 (0.75 mmol, 1.5 equiv) in
CH2Cl2–H2O (1.65 mL, 10:1) was stirred at 60 °C for 18 h.
Synlett 2012, 23, 1085–1089
© Thieme Stuttgart · New York

LETTER
After the reaction was completed, the reaction mixture was
Transition-Metal-Free Cross-Coupling Reaction
1089
5.05 (s, 2 H), 6.34 (dt, J = 15.6, 6.9 Hz, 1 H), 6.43 (d, J = 15.6
Hz, 1 H), 6.93 (d, J = 8.7 Hz, 2 H), 7.16 (d, J = 8.7 Hz, 2 H),
7.20 (t, J = 7.4 Hz, 1 H), 7.27–7.39 (m, 7 H), 7.43 (d, J = 6.9
Hz, 2 H). 13C NMR (125 MHz, CDCl3): d = 38.6, 70.2,
115.0, 126.2, 127.2, 127.6, 128.0, 128.6, 128.7, 129.7 (two
peaks overlap), 130.9, 133.0, 137.3, 137.6, 157.4. IR (neat):
3031, 1454, 1231 cm–1. HRMS (EI): m/z [M]+ calcd for
C22H20O: 300.1514; found: 300.1512.
treated with aq 1 N HCl, extracted with CH2Cl2 and dried
over MgSO4. The organic layer was concentrated and the
resulting residue was purified by column chromatography
on silica gel (hexane–EtOAc, 100:1) to give (E)-3-(4-
benzyloxyphenyl)-1-phenyl-1-propene (3da) as a white
solid in 91% yield (136.6 mg, 0.455 mmol); mp 44–48 °C.
1H NMR (500 MHz, CDCl3): d = 3.49 (d, J = 6.9 Hz, 2 H),
© Thieme Stuttgart · New York
Synlett 2012, 23, 1085–1089

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