A convenient hydroiodination of alkynes using I2/PPh3/H2O and its application to the one-pot synthesis of trisubstituted alkenes via iodoalkenes using Pd-catalyzed cross-coupling reactions

Article abstract of DOI:10.1016/j.tetlet.2014.10.039

A facile hydroiodination of alkynes using readily-available reagents such as I₂, PPh₃, and H₂O has been developed. This is extended to the one-pot synthesis of trisubstituted alkenes from alkynes via iodoalkenes using Pd-c

Full text of DOI:10.1016/j.tetlet.2014.10.039

Tetrahedron Letters 55 (2014) 6779–6783
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Tetrahedron Letters
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A convenient hydroiodination of alkynes using I2/PPh3/H2O and its
application to the one-pot synthesis of trisubstituted alkenes via
iodoalkenes using Pd-catalyzed cross-coupling reactions
^
Shin-ichi Kawaguchi, Yuhei Gonda, Haruna Masuno, Hue Thi Vu˜, Kotaro Yamaguchi,
Hiroyuki Shinohara, Motohiro Sonoda, Akiya Ogawa
_
_
⇑
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
A facile hydroiodination of alkynes using readily-available reagents such as I2, PPh3, and H2O has been
developed. This is extended to the one-pot synthesis of trisubstituted alkenes from alkynes via iodoalk-
enes using Pd-catalyzed cross-coupling and related methods such as the Suzuki–Miyaura cross-coupling,
Sonogashira cross-coupling reaction, and Mizoroki–Heck reaction.
Received 12 July 2014
Revised 3 October 2014
Accepted 7 October 2014
Available online 23 October 2014
Ó 2014 Elsevier Ltd. All rights reserved.
Keywords:
Hydroiodination
Cross-coupling reactions
Trisubstituted alkenes
Phosphorus reagents
One-pot synthesis
The vinyl group is one of the most versatile building blocks of
organic compounds.1 In particular, trisubstituted alkenes are
important because of their prevalence in natural products and bio-
logically active molecules.2 There are several synthetic routes to
trisubstituted alkenes. In particular, routes via vinyl halides allow
access to diverse products because there are many known transi-
tion-metal-catalyzed cross-coupling reactions using vinyl halides.3
Hydrohalogenation of alkynes is one of the most straightforward
synthetic methods to vinyl halides. From the viewpoint of green
chemistry, one-pot synthetic processes4 have recently attracted
increased attention because they reduce solvent usage and save
time. Therefore, we studied the one-pot synthesis of substituted
alkenes, including trisubstituted ones, via haloalkenes derived
from alkynes (Scheme 1).
reagents such as (PhO)2P(O)H/Ph2P(O)OH.8 These phosphorus
reagents play a dual role as reductants for iodine and as hydrogen
sources for the hydroiodination. On the basis of previous studies,
we focused on the use of PPh3 in a novel hydroiodination method
because PPh3 can act as a reductant for iodine9 and is also widely
used as a ligand in cross-coupling reactions. Herein, we report a
facile hydroiodination of alkynes using PPh3/I2 and its subsequent
application to the one-pot synthesis of trisubstituted alkenes by
cross-coupling reactions.
First, we investigated the hydroiodination of alkynes using a
mixed system of PPh3 and I2 in the presence of different hydrogen
sources (Table 1). When diphenylphosphinic acid (Ph2P(O)OH) or
monophenyl phosphate (PhOP(O)(OH)2) was used as a hydrogen
source, hydroiodination of 1-octyne proceeded with quantitative
Since vinyl iodides are the most reactive of the vinyl halides,5
they were often chosen as substrates for the cross-coupling reac-
tions. Additionally, appropriate reagent choice for hydroiodination
is required in order to prevent inhibition of the subsequent cou-
pling reactions. The hydroiodination of alkynes with HI proceeds
under a limited set of conditions.6 Thus, several alternative meth-
ods have been reported.7 Recently, we reported the hydroiodin-
ation of alkynes by the combination of iodine and phosphorus
coupling
reagent
H
H
(i.e., R3M)
R1
R1
HX
R1
R2
R2
R2
R3
X
one-pot operation
⇑
Corresponding author. Tel./fax: +81 72 254 9290.
E-mail address: ogawa@chem.osakafu-u.ac.jp (A. Ogawa).
Scheme 1. One-pot synthesis of trisubstituted alkenes from alkynes via
haloalkenes.
http://dx.doi.org/10.1016/j.tetlet.2014.10.039
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

6780
S-i. Kawaguchi et al. / Tetrahedron Letters 55 (2014) 6779–6783
Table 1
with complete stereoselectivity in excellent yield (entry 8). When
unsymmetrical internal alkynes such as 1-phenyl-1-pentyne, 1-
methyl-4-(oct-1-yn-1-yl)benzene, and 1-methoxy-4-(oct-1-yn-1-
yl)benzene were used, the hydroiodination proceeded to afford Z-
isomer (1i–k) in good yields and the iodine atom was introduced
to the aryl group substituted carbon atom selectively (entries 9–
11). 1-(Oct-1-yn-1-yl)-4-(trifluoromethyl)benzene which has an
electron withdrawing group on its para position gave the corre-
sponding regioisomeric vinyl iodide (1l) preferentially (entry 12).
1-Bromo-1-octyne also gave (Z)-1-bromo-2-iodo-1-octene (1j)
exclusively in excellent yield (entry 13). To get further information
of hydroiodination of internal alkynes, t-butylmethylacetylene and
an ynone 1-phenylhept-2-yn-1-one were employed as substrates.
Hydroiodination of t-butylmethylacetylene proceeded efficiently,
but with less regioselectivity ((Z)-3-iodo-4,4-dimethylpent-2-ene:
44% yield; (Z)-2-iodo-4,4-dimethylpent-2-ene: 52% yield). A bulky
t-butyl group could not induce high regioselectivity of the hydroio-
dination. In the case of 1-phenylhept-2-yn-1-one, a stereoisomeric
mixture of 3-iodo-1-phenylhept-2-en-1-one was obtained in low
yield (23%, E/Z = 57/43).
Hydroiodination of alkynes using I2 and PPh3 in the presence of different hydrogen
sourcesa
nHex
Hydrogen
nHex
+
I2
+
PPh3
+
source
CDCl3
rt
I
1a
0.5 mmol 0.75 equiv 0.75 equiv 1.5 equiv
Entry
1
Hydrogen source
Time (h)
24
Yield of 1ab (%)
Ph2POH
99
O
PhOP(OH)2
2
24
99
O
85% H3PO4
H2O
3
24
24
4
43c
82d
(80)
4
5e
H2O
a
Reaction conditions: I2 (0.38 mmol), PPh3 (0.38 mmol), hydrogen source
(0.75 mmol).
b
Yields are determined by 1H NMR with 1,3,5-trioxane as an internal standard
and the value in parentheses is the isolated yield.
c
2-Iodooct-2-ene (40%, E/Z mixture) and 2,2-diiodooctane (17%) are obtained as
byproducts.
Additionally, when trimethyl(p-tolylethynyl)silane was used as
a substrate, the desilylated hydroiodination product (1f)8,11 was
obtained in 98% yield (Eq. 1).
d
2-Iodooct-2-ene (4%, E/Z mixture) and 2,2-diiodooctane (6%) are obtained as
byproducts.
e
Reaction conditions: I2 (0.5 mmol), PPh3 (0.5 mmol), hydrogen source
(0.5 mmol).
H2O
1 equiv 1 equiv 1 equiv
TMS
I2
PPh3 +
+
+
CDCl3
I
rt, 22 h
0.3 mmol
yield (entries 1 and 2). On the other hand, use of phosphoric acid
gave a mixture of addition products including 2-iodo-1-octene
(1a) (43%), 2-iodooct-2-ene (40%, E/Z mixture), and 2,2-diiodooc-
tane (17%) (entry 3). Interestingly, when H2O was employed as a
hydrogen source, selective hydroiodination of 1-octyne proceeded
successfully to afford 1a in 82% yield (entry 4). Moreover, a similar
result was obtained by the use of equimolar amounts of the
reagents (entry 5).
Next, the scope of the hydroiodination of alkynes using a mixed
system of I2 and PPh3 was investigated. Hydroiodination of several
alkynes, including both aliphatic and aromatic alkynes, was suc-
cessfully attained by the use of an I2/PPh3/PhOP(O)(OH)2 system,
and the corresponding vinyl iodides were obtained in good yields
(Scheme 2). In the case of the internal alkyne, 4-octyne, hydroio-
dination proceeded stereoselectively to give the (Z)-isomer.
We next examined the hydroiodination using an I2/PPh3/H2O
system (Table 2).10 When aliphatic alkynes such as 1-octyne 1-
dodecyne, 6-chloro-1-hexyne, and 3,3-dimethyl-1-butyne were
employed, the hydroiodination proceeded to give the correspond-
ing 2-iodo-1-alkenes (1a–d) in good yields (entries 1–4). When
aromatic terminal alkynes were employed, the corresponding 1-
aryl-1-iodoethenes (1e–g) were also obtained in good yields
(entries 5–7), although in some cases prolonged reaction time
was required (entries 6 and 7). In the case of an internal aliphatic
alkyne, the reaction of 4-octyne provided (Z)-4-iodooct-4-ene (1h)
1f
98%
ð1Þ
A plausible reaction pathway for the hydroiodination using I2/
PPh3/H2O is shown in Scheme 3 and proceeds as follows: (1)
PPh3 reacts with I2 to form the [Ph3PI]+[I]ꢀ species12 (Step a); (2)
the [Ph3PI]+[I]ꢀ species reacts with H2O to generate HI and
[Ph3POH]+[I]ꢀ (Step b); (3) HI adds to an alkyne to afford the
corresponding vinyl iodide (Step c); (4) the [Ph3POH]+[I]ꢀ
species may react with an alkyne to generate vinyl iodide and
Ph3P@O (Step d). When the reaction is complete, the remaining
[Ph3POH]+[I]ꢀ species is quenched by addition of MeOH to
give Ph3P@O and MeI as byproducts (Step e).
Stimulated by the fact that Ph3P@O does not inhibit the cata-
lytic activity of transition metals and that MeI, which is formed
by the quenching process, can easily be removed by evaporation,
we next investigated several one-pot reactions to trisubstituted
alkenes via the hydroiodination of alkynes using I2/PPh3/H2O. First,
the one-pot Suzuki–Miyaura cross-coupling reaction13 was investi-
gated. To a 30 mL Schlenk flask, PPh3, I2, CHCl3, H2O, and an alkyne
were added under a nitrogen atmosphere. The mixture was gently
stirred for the appropriate time and MeOH was added. The solvent
was removed, followed by addition of the arylboronic acid, K2CO3,
dioxane/H2O, and the Pd catalyst. The mixture was heated for 20 h
to afford the expected aryl alkene. The results of this one-pot syn-
thesis of arylated alkenes from alkynes are shown in Table 3.14
When 4-octyne was used as a starting alkyne, the one-pot reaction
proceeded successfully to afford the corresponding trisubstituted
alkenes (2a–d) regardless of which species of arylboronic acid
was used (entries 1–4). In the case of unsymmetrical internal
alkynes 1-phenyl-1-pentyne and 1-methyl-4-(oct-1-yn-1-yl)ben-
zene, the corresponding (Z)-arylalkenes (2e and 2f) were obtained
regioselectively in good yields (entries 5 and 6). When 1-dodecyne
was used as a terminal aliphatic alkyne, the desired coupling prod-
uct dodec-1-en-2-ylbenzene (2g), and an E/Z mixture of the corre-
sponding isomerization product dodec-2-en-2-ylbenzene were
obtained in moderate yields (entry 7). Use of the terminal arylal-
kyne p-tolylethyne gave the corresponding coupling product in
low yield (entry 8).
R
PhOP(OH)2
O
R'
R
R'
I2
PPh3 +
+
+
CDCl3, rt
43 h
I
0.3 mmol 0.75 equiv 0.75 equiv 0.75 equiv
R = nDec
Cl(CH2)4
R' =
H
H
, 74%
1b
37 h 1c , 75 (60)%
nPr
p-CH3C6H4
nPr
H
, 70 (64)%
, 84%
27 h 1h
1f
19 h
*NMR yield (isolated yield).
Scheme 2. Hydroiodination of alkynes using I2, PPh3, and PhOP(O)(OH)2.

S-i. Kawaguchi et al. / Tetrahedron Letters 55 (2014) 6779–6783
6781
Table 2
Scope of hydroiodination of alkynes using I2/PPh3/H2O
R
R
+
H2O
+
I2
+
PPh3
CDCl3, rt
I
0.3 mmol
1 equiv
1 equiv
1 equiv
1a-m
Entry
1
Alkyne
Time (h)
4
Product
Yielda (%)
nHex
nHex
80
1a
1b
I
I
nDec
nDec
Cl
2
24
4
86
Cl
3
98
1c
I
tBu
tBu
4
24
5
(95)
76
1d
1e
I
5
I
6b
7b
24
48
87
1f
I
1g
F3C
nPr
F3C
nPr
71
I
nPr
1h
8
2
22
3
nPr
90
I
nPr
nPr
9
66c
80d
61e
1i
I
nHex
nHex
10
11
1j
I
nHex
MeO
nHex
1
MeO
1k
I
I
F3C
nHex
nHex
12
13
12
28
70f
97
F3C
1l
nHex
Br
nHex
1m
Br
I
a
b
c
d
e
f
Isolated yield. The value in parentheses is 1H NMR yield with 1,3,5-trioxane as an internal standard.
Reaction conditions: I2 (0.23 mmol), PPh3 (0.23 mmol), H2O (0.23 mmol).
A regioisomer (Z)-(2-iodopent-1-enyl)benzene (13%) was also obtained.
A regioisomer (Z)-1-(2-iodooct-1-enyl)-4-methylbenzene (3%) and a stereoisomer (E)-1-(1-iodooct-1-enyl)-4-methylbenzene (16%) were also obtained.
A stereoisomer (E)-(1-iodooct-1-enyl)-4-methoxybenzene (7%) was also obtained.
A regioisomer (Z)-1-(1-iodooct-1-enyl)-4-(trifluoromethyl)benzene (29%) was also obtained.
Next, a one-pot synthesis of alkynylalkenes from alkynes, via
iodoalkenes, using the Sonogashira cross-coupling reaction15 was
examined (Table 4). When an aliphatic internal alkyne was used
under typical conditions for the Sonogashira reaction, the corre-
sponding alkynylalkenes (3a–d) were obtained in good yields
(entries 1–4). Unsymmetrical internal alkynes 1-methyl-4-(oct-1-
yn-1-yl)benzene and 1-(oct-1-yn-1-yl)-4-(trifluoromethyl)benzene
also afforded the corresponding alkynylalkenes (3e and 3f) in mod-
erate yields, respectively (entries 5 and 6). In the case of the terminal
alkyne 1-dodecyne, the cross-coupling reaction also proceeded to
give (3-methylenetridec-1-yn-1-yl)benzene (3g) as well as an
(E/Z)-mixture of (3-methyltridec-3-en-1-yn-1-yl)benzene in good
yield (entry 7). When terminal alkynes 3,3-dimethylbut-1-yne and
p-tolylethyne, which do not contain a propargylic hydrogen, were
employed, the corresponding coupling products (3h and 3i) were
obtained exclusively in moderate yields (entries 8 and 9).
-
[ Ph3PI ]+ [ I ]
PPh3
+
I2
(a)
-
[ Ph3PI ]+ [ I ]
(b)
(c)
-
+ H2O
HI
+
[ Ph3POH ]+ [ I ]
R
I
HI
+
R
R
I
R
-
[ Ph3POH ]+ [ I ]
(d)
Ph3P
MeI
O
+
quenching
[ Ph3POH ]+ [ I ]
MeOH
-
+
H2O (e)
Ph3P
O
+
Scheme 3. Suggested reaction pathway for hydroiodination of alkynes using I2/
PPh3/H2O.

6782
S-i. Kawaguchi et al. / Tetrahedron Letters 55 (2014) 6779–6783
Table 3
One-pot synthesis of arylalkenes from alkynes via iodoalkenes using the Suzuki–Miyaura cross-coupling
1) PPh3
I2
1 equiv
1 equiv
1 equiv
3)
1.2 equiv
Ar B(OH)2
H2O
Pd(PPh3)4 5 mol%
K2CO3 3 equiv
CHCl3, rt
R1
R2
R1
R2
dioxane/H2O, 70 oC, 20 h
Ar
2) MeOH 1 mL
evaporation
1 mmol
2a-h
Entry
R1
R2
Time for hydroiodination (h)
Ar
Yield of 2a (%)
1
2
3
4
5
6
7
8d
nPr
nPr
nPr
nPr
nPr
nPr
nHex
H
2
2
2
2
22
1
Ph
2a, 70
2b, 68
2c, 76
2d, 77
2e, 63b
2f, 61
nPr
4-Me-C6H4-
4-F-C6H4-
4-HCO-C6H4-
4-Me-C6H4-
Ph
nPr
nPr
Ph
4-MeO-C6H4-
nDec
24
24
Ph
Ph
2g, 11c
2h, 36
4-Me-C6H4-
H
a
b
c
Isolated yield.
A mixture of (Z)-1-methyl-4-(1-phenylpent-1-en-1-yl) benzene (2e) (63%) and (Z)-1-methyl-4-(1-phenylpent-1-en-2-yl)benzene (13%) was obtained.
A mixture of dodec-1-en-2-ylbenzene (2f) (11%) and dodec-2-en-2-ylbenzene was obtained (38%, E/Z mixture).
Reaction conditions: I2 (0.75 mmol), PPh3 (0.75 mmol), H2O (0.75 mmol).
d
Table 4
One-pot synthesis of alkynylalkenes from alkynes via iodoalkenes using the Sonogashira cross-coupling
R3
1) PPh3 1 equiv
3)
1.2 equiv
I2
Pd(PPh3)4 5 mol%
CuI 5 mol%
1 equiv
R1
H2O
1 equiv
R2
CHCl3, rt
NEt3 2 equiv
R1
1 mmol
R2
CH3CN, 70 oC, 20 h
3a-i
2) MeOH 1 mL
evaporation
R3
Entry
R1
R2
Time for hydroiodination (h)
R3
Yield of 3a (%)
1
2
nPr
nPr
2
2
2
2
3
12
24
24
24
Ph
3a, 66
3b, 65
3c, 77
3d, 55
3e, 51c
3f, 65d
3g, 50f
3h, 44
3i, (49)
nPr
nPr
4-MeO-C6H4-
3
nPr
nPr
4-CF3-C6H4-
4b
5
nPr
nPr
nHex
4-Me-C6H4-
nHex
Ph
Ph
Ph
6
nHex
4-CF3-C6H4-
7e
8b,g
9b,h
nDec
H
H
H
tBu
4-nC8H17-C6H4-
Ph
4-Me-C6H4-
a
b
c
Isolated yield. The value in parentheses is 1H NMR yield with 1,3,5-trioxane as an internal standard.
Reaction conditions: PdCl2(PPh3)2 (5 mol %), rt, 48 h.
A mixture of (Z)-1-methyl-4-(1-phenyldec-3-en-1-yn-3-yl)benzene (3e) (51%) and (E)-1-methyl-4-(1-phenyldec-3-en-1-yn-3-yl)benzene (7%) was obtained.
A mixture of (Z)-1-(2-(phenylethynyl)oct-1-en-1-yl)-4-(trifluoromethyl)benzene (3f) (65%) and (Z)-1-(1-phenyldec-3-en-1-yn-3-yl)-4-trifluoromethyl)benzene (20%)
was obtained.
Reaction conditions: PdCl2(PPh3)2 (5 mol %), rt, 24 h.
A mixture of (3-methylenetridec-1-yn-1-yl)benzene (3g) (50%) and (3-methyltridec-3-en-1-yn-1-yl)benzene (13%, E/Z mixture) was obtained.
Without evaporation after the hydroiodination.
d
e
f
g
h
Reaction conditions: I2 (0.75 mmol), PPh3 (0.75 mmol), H2O (0.75 mmol).
Table 5
One-pot synthesis of dienes from alkynes via iodoalkenes using the Mizoroki–Heck reaction
1) PPh3
I2
1 equiv
1 equiv
1 equiv
3) R3
1.2 equiv
H2O
Pd(PPh3)4 5 mol%
NEt3 2 equiv
R1
R3
CHCl3, rt
R2
R1
R2
2) MeOH 1 mL
evaporation
CH3CN, 70 oC, 20 h
1 mmol
4a-d
Entry
R1
R2
Time for hydroiodination (h)
R3
Yield of 4a (%)
E/Z ratiob
1
2
3
4
nPr
nPr
2
2
3
1
Ph
4a, 46
4b, 83
4c, 82
4d, 74
18/82
27/73
33/67
41/59
nPr
nPr
COOMe
COOMe
COOMe
4-Me-C6H4-
4-MeO-C6H4-
nHex
nHex
a
Isolated yield.
b
The ratio was determined by 1H NMR.

S-i. Kawaguchi et al. / Tetrahedron Letters 55 (2014) 6779–6783
6783
4. Ishikawa, H.; Honma, M.; Hayashi, Y. Angew. Chem., Int. Ed. 2011, 50, 2824–
2827.
5. The Mizoroki-Heck Reaction; Oestreich, M., Ed.; John Wiley & Sons Ltd: West
Sussex, UK, 2009.
Finally, we investigated the one-pot strategy for application to
the Mizoroki–Heck reaction.16 Table 5 shows the one-pot synthesis
of substituted alkenes via iodoalkenes from alkynes using the
Mizoroki–Heck reaction. When 4-octyne, as an internal alkyne,
and styrene or methyl acrylate as olefin were employed under typ-
ical conditions of the Mizoroki–Heck reaction, the corresponding
dienes (4a and 4b) were successfully obtained via the one-pot
reaction (entries 1 and 2). Unsymmetrical internal alkynes 1-
methyl-4-(oct-1-yn-1-yl)benzene and 1-methoxy-4-(oct-1-yn-1-
yl)benzene also gave the corresponding dienes (4c and 4d) in good
yields.
In conclusion, we have developed a hydroiodination of alkynes
using readily available I2, PPh3, and H2O. Moreover, a one-pot syn-
thesis of substituted alkenes from alkynes via iodoalkenes, using
Pd-catalyzed cross-coupling reactions such as the Suzuki–Miyaura
reaction, Sonogashira reaction, and Mizoroki–Heck reaction, has
been developed. This process can contribute to decreasing environ-
mental load by reducing solvent use.
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10. The general procedure for the synthesis of iodoalkenes using I2, PPh3, and H2O:
under
a
nitrogen atmosphere, PPh3 (78.6 mg, 0.3 mmol), I2 (76.1 mg,
Schlenk tube,
0.3 mmol), and H2O (5.40 mg, 0.3 mmol) were placed in
a
followed by addition of CDCl3 (0.6 mL) at room temperature. The alkyne
(0.3 mmol) was then added to the reaction mixture and the mixture was
slowly stirred for the appropriate time (see Table 2) at room temperature,
followed by quenching with MeOH (0.3 mL). The solvent and MeI were then
removed under reduced pressure. The crude product was purified by
preparative TLC (silica gel).
Acknowledgment
This work was financially supported by JSPS KAKENHI Grant
Number 25410051.
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12. (a) Barnes, N. A.; Godfrey, S. M.; Khan, R. Z.; Pierce, A.; Pritchard, R. G.
Polyhedron 2012, 35, 31–46; (b) Deplano, P.; Godfrey, S. M.; Lsaia, F.; McAuliffe,
C. A.; Mercurp, M. L.; Trogu, E. F. Chem. Ber. 1997, 130, 299–305; (c) Ruthe, F.;
Jones, P. G.; du Mont, W.-W.; Deplano, P.; Mercuri, M. L. Z. Anorg. Allg. Chem.
2000, 626, 1105–1111.
Supplementary data
Supplementary data (detailed experimental procedures and
compound characterization data) associated with this article can
be found, in the online version, at http://dx.doi.org/10.1016/
j.tetlet.2014.10.039.
13. Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457–2483.
14. The general procedure for the one-pot synthesis of arylated alkenes using the
Suzuki–Miyaura cross coupling reaction: under a nitrogen atmosphere, PPh3
(262.2 mg, 1.0 mmol), I2 (253.8 mg, 1.0 mmol), and H2O (180 mg, 1.0 mmol)
were placed in a 30 mL Schlenk flask, followed by addition of CHCl3 (2 mL) at
room temperature. The alkyne (1.0 mmol) was then added to the reaction
mixture and the mixture was slowly stirred for the appropriate time (see
Table 3) at room temperature, followed by quenching with MeOH (1 mL). The
solvent and MeI were then removed under reduced pressure. Dioxane (2 mL),
arylboronic acid (1.2 mmol), Pd(PPh3)4 (57.7 mg, 0.05 mmol) and K2CO3
(414.6 mg, 3.0 mmol) dissolved in H2O (1 mL) were added to the same
Schlenk flask. The mixture was stirred at 70 °C for 20 h, followed by addition of
water (30 mL) and the resulting mixture was extracted with diethyl ether
(3 ꢁ 30 mL). The combined organics were dried over anhydrous MgSO4, filtered
and concentrated under reduced pressure. The crude product was purified by
silica gel column chromatography.
References and notes
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