A highly selective synthesis of 1-substituted (E)-buta-1,3-dienes with 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane as building block

Article abstract of DOI:10.1002/aoc.3095

Highly selective synthesis of 1-substituted (E)-buta-1,3-dienes via palladium-catalyzed Suzuki-Miyaura cross-coupling of (E)-alkenyl iodides with 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane (1) is reported. The vinylboronate pinacol ester (1) acts as a vinyl building block to show high chemoselectivity for the Suzuki-Miyaura pathway versus Heck coupling in the presence of biphasic conditions (Pd(PPh₃)₄, aqueous K ₂CO₃, toluene and ethanol). Copyright

Full text of DOI:10.1002/aoc.3095

Full Paper
Received: 27 September 2013
Revised: 18 October 2013
Accepted: 18 October 2013
Published online in Wiley Online Library: 29 January 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3095
A highly selective synthesis of 1-substituted
E)-buta-1,3-dienes with 4,4,5,5-tetramethyl-2-
vinyl-1,3,2-dioxaborolane as building block
(
a
a
a
Justyna Szudkowska-Frątczak , Aline Ryba , Adrian Franczyk ,
b
a
a,b
Jędrzej Walkowiak , Maciej Kubicki and Piotr Pawluć *
Highly selective synthesis of 1-substituted (E)-buta-1,3-dienes via palladium-catalyzed Suzuki–Miyaura cross-coupling of (E)-alkenyl
iodides with 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane (1) is reported. The vinylboronate pinacol ester (1) acts as a vinyl
building block to show high chemoselectivity for the Suzuki–Miyaura pathway versus Heck coupling in the presence of biphasic
conditions (Pd(PPh ) , aqueous K CO , toluene and ethanol). Copyright © 2014 John Wiley & Sons, Ltd.
3
4
2
3
Additional supporting information may be found in the online version of this article at the publisher’s web site.
Keywords: cross-coupling, palladium(0); vinylboronate ester; buta-1,3-dienes; Suzuki–Miyaura coupling
Herein, we report an improved protocol for the highly chemo-
Introduction
and stereoselective synthesis of 1-substituted (E)-buta-1,3-dienes
based on catalytic coupling of (E)-alkenyl iodides with commer-
cially available 4,4,5,5-tetramethyl-2-vinyl-1,3,2-dioxaborolane 1
which applies classical biphasic Suzuki–Miyaura conditions with-
out use of any silver additive.
The palladium-catalyzed Suzuki–Miyaura reaction of aryl or
alkenyl halides with organoboronic acids represents a straightfor-
ward and highly effective method for carbon–carbon bond
[1]
formation.
The Suzuki–Miyaura reaction also provides a
versatile method for the vinylation of aryl and alkenyl halides;
however, it is plagued by a number of drawbacks. Vinylboronic
[2]
Experimental
acids are readily polymerized and cannot be isolated. Furthermore,
vinylboronic esters are not selective in cross-coupling reactions,
General Procedure for the Synthesis of (E)-Buta-1,3-dienes
[3]
yielding mixtures of Suzuki–Miyaura and Heck coupled products.
Many of the recent development efforts on the cross-coupling
reaction have been focused on the catalyst system and boronate
coupling partners that facilitate Suzuki–Miyaura cross-coupling
and expand its scope.
A mixture consisting of the following components added in order
– (E)-alkenyl iodide (1mmol) Pd(PPh
pinacol ester 1 (1.1mmol), 1 M aqueous K
3
)
4
(0.05 mmol), vinylboronate
CO (3.0ml) and ethanol
2
3
(0.88 ml) in toluene (10 ml) – was placed in a 50 ml Schlenk bomb
flask fitted with a plug valve and heated at 55 °C for 24h. After
cooling the reaction mixture to room temperature, the organic
layer was extracted with toluene. The organic layer was concen-
trated and the product was purified by column chromatography
on silica gel, eluting with n-hexane–EtOAc (98:2).
Pinacol vinylboronate ester – 4,4,5,5-tetramethyl-2-vinyl-
1
,3,2-dioxaborolane (Fig. 1, compound 1) – undergoes both
Suzuki–Miyaura and Heck cross-coupling with aryl halides to give
a mixture of styrenes and styryl boronates, depending upon the
[4]
reaction conditions. Whiting and co-workers reported that 4,4,6-
trimethyl-2-vinyl-1,3,2,-dioxaborinane (Fig. 1, compound 2) can
act as an alternative two-carbon alkenyl building block, being able
(
E)-2-(Buta-1,3-dien-1-yl)isoindoline-1,3-dione (2f)
[
5]
[6]
to react selectively via either Heck or Suzuki–Miyaura pathways.
On the other hand, there are only a few examples of the synthetic
application of commercially available vinylboronate pinacol ester 1
in the selective synthesis of buta-1,3-diene derivatives. Whiting
and co-workers reported selective coupling of (Z)-iodoacrylate with
[7]
1
in the presence of a Pd(OAc)
2 2 3
/Ag CO catalytic system. Selective
vinylation of (Z)-alkenyl iodide by 1 has also been developed during
[3a]
studies on the synthesis of herbicide phthoxazolin A. More re-
cently, vinylboronate pinacol ester 1 has been used as building
block to form a diene side chain in the synthesis of structural ana-
*
Correspondence to: Piotr Pawluć, Faculty of Chemistry, Adam Mickiewicz
University, Grunwaldzka 6, 60-780 Poznan, Poland. Email: piotrpaw@amu.edu.pl
[8]
logues of macrocyclic product (À)-exiguolide. The buta-1,3-diene
unit was introduced stereoselectively via Suzuki–Miyaura coupling
of macrocyclic (E)-alkenyl iodide with 1 in the presence of a
a Faculty of Chemistry, Adam Mickiewicz University, 60-780 Poznan, Poland
b Center of Advanced Technologies, Adam Mickiewicz University, Grunwaldzka
[
8]
[
Pd (dba) ]/Ph As/Ag O catalytic system.
660-780 Poznan, Poland
2
3
3
2
Appl. Organometal. Chem. 2014, 28, 137–139
Copyright © 2014 John Wiley & Sons, Ltd.

J. Szudkowska-Frątczak et al.
Table 1. Synthesis of 1-substituted (E)-buta-1,3-dienes
a
Entry
Product structure
E/Z
Suzuki–Miyaura/ Isolated
Heck product: yield of 2
b
2
/3
1
98/2
96:4
70
Figure
1. Vinylboronic
esters:
4,4,5,5-tetramethyl-2-vinyl-1,3,2-
dioxaborolane (1) and 4,4,6-trimethyl-2-vinyl-1,3,2,-dioxaborinane (2)
(Whiting ester).
2
2
a
1
H NMR (300 MHz, CDCl
3
): δ = 5.18 (dd, 1H, J = 10.0, 1.6 Hz, =CH
2
),
),
2
3
4
93/7
94/6
95/5
84:16
95:5
65
55
79
5
6
>
(
1
1
(
1
.36 (dd, 1H, J = 16.9, 1.6 Hz, =CH
.84–6.89 (m, 1H, >N-CH=CH-), 7.24 (d, 1H, J = 14.4 Hz,
N-CH=CH-), 7.73–7.78 (m, 2H, Ar), 7.85–7.89 (m, 2H, Ar). C NMR
CDCl
31.7(C3), 134.5 (C5), 135.0 (C8), 166.2 (C2). MS m/z = 199 (M ,
00%), 198 (25), 170 (11), 133 (53), 115 (10), 105 (59), 104 (70), 77
25), 76 (42), 50 (40). HRMS (m/z) = 199.0628, calcd for C12
99.0633.
2
), 6.32–6.44 (m, 1H, -CH=CH
2
13
b
3
, 75 MHz) δ = 120.4 (C9), 121.3 (C7), 123.6 (C4), 123.8 (C6),
+
9
H NO
2
:
2
c
90:10
Crystal data (2f). C12
a = 25.620(4) Å, b = 4.3552(9) Å, c = 18.247(3) Å, V = 2036.0(6) Å ,
H
9
NO
2
, M
r
= 199.20, orthorhombic, Pca2 ,
1
3
À3
Z = 8, d = 1.30 g cm , Mo-K radiation (λ = 0.71069 Å), μ = 0.090
x
α
À1
cm , T = 295(2) K, 24 598 reflections measured, 3534 symmetry
2d
independent (Rint = 0.083), 1421 with I > 2σ(I)), final R = 18.9%,
5
6
96/4
99/1
80:20
99:1
72
83
À3
wR2 = 37.7%, max/min Δρ = 1.25/À0.44 e Å
.
(E)-9-(Buta-1,3-dien-1-yl)-9H-carbazole (2 g)
2
2
e
f
7
92/8
90:10
65
1
H NMR (300 MHz, C D ): δ = 5.04 (dd, 1H, J = 10.1, 1.8 Hz,
6
6
=
CH ), 5.15 (dd, 1H, J = 16.4, 1.8 Hz, =CH ), 6.36 (ddd, 1H,
2
2
J = 16.4, 10.3, 10.1 Hz, -CH=CH
2
), 6.53 (dd, 1H, J = 13.9, 10.3 Hz,
>
N-CH=CH-), 6.85 (d, 1H, J = 13.9 Hz, >N-CH=CH-) 7.19–7.39
2
g
13
(
m, 6H, Cbz), 7.90–7.93 (m, 2H, Cbz). C NMR (75 MHz, C
δ = 110.9 (C11), 115.5 (C3), 120.2 (C5), 120.6 (C6), 121.1 (C9),
24.7 (C4), 126.5 (C10), 126.7 (C7) , 135.3 (C8), 139.8 (C2). MS (EI)
6 6
D ):
a
1
Measured by H NMR.
1
b
Determined by GC-MS.
+
m/z (rel. int.): 219 (M 100%), 204 (10), 192 (5), 53 (5). Anal. calcd
for C16 13N: C 87.64; H 5.98; N 6.39; found: C 87.88; H 6.18; N 5.94.
H
Results and Discussion
Classical Suzuki–Miyaura conditions have been employed for
coupling tests, i.e. using tetrakis(triphenylphosphine)palladium(0)
with nucleophilic oxygen bases. After several attempts we found
that vinylation of (E)-styryl iodides by 1 occurs efficiently when
K2CO3 is employed, whereas the use of t-BuOK or KOH led
to formation of significant amounts of by-products such as
[
6]
1
,4-diarylbut-1-en-3-yne and Heck coupling products. (Scheme 1)
thus the cross-coupling reactions of (E)-alkenyl iodides with 1
were carried out under biphasic reaction conditions (toluene
[
9]
(0.1 M), aqueous K
2 3
CO (3 equiv., 1 M) and ethanol (15 equiv.)).
We believe that the role of ethanol is to activate the vinylborane
[
10]
for transmetalation with palladium.
Suzuki–Miyaura coupling
of 1 with selected (E)-styryl iodides (Table 1, entries 1–5) and
[
11]
(
9
E)-N-(2-iodovinyl)phthalimide,
H-carbazole
as well as (E)-9-(2-iodovinyl)-
[
12]
(Table 1, entries 6 and7), proceeded smoothly
Scheme 1. Cross-coupling of (E)-alkenyl iodides with 4,4,5,5-tetramethyl-
2-vinyl-1,3,2-dioxaborolane (1).
at 55 °C in the presence of Pd(PPh
3 4
) catalyst (5 mol%) to give
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Appl. Organometal. Chem. 2014, 28, 137–139

A highly selective synthesis of 1-substituted (E)-buta-1,3-dienes
Conclusions
We have developed an improved protocol for highly
stereoselective preparation of (E)-1-arylbuta-1,3-dienes via palla-
dium-catalyzed Suzuki–Miyaura coupling of (E)-styryl iodides with
vinylboronic pinacol ester as a two-carbon building block. As
the method under the conditions established shows high
chemoselectivity for Suzuki–Miyaura coupling versus Heck
coupling, it can be applied to the synthesis of functionalized
nitrogen-containing buta-1.3-dienes, which are versatile building
blocks in organic synthesis.
Figure 2. A perspective view of one of the molecules of 2f with labeling
scheme. Relevant geometrical parameters (in square brackets, values for
molecule B): C10–C11 1.282(15) [1.336(17)], C11–C12 1.497(16) [1.493
Acknowledgments
(
[
17)], C12–C13 1.214917) [1.299(19)], C10–C11–C12–C13 176.2(16)°
À178.8(15)°]. CCDC-957172.
This research was carried out within the framework of the Polish
National Science Center project (Grant No. 2011/03/B/ST5/01034)
and as a part of the HOMING PLUS/2012-5/14 grant of the
Foundation for Polish Science.
the corresponding (E)-buta-1,3-dienes 2a–g within 24 h. Under
these conditions, (E)-alkenyl iodides bearing functional groups
such as –Me, –Br, –Cl, –MeO, N-phthalimide and N-carbazole
reacted successfully with 1 to give the corresponding (E)-buta-
References
1
,3-dienes in moderate to high yields (55–83%), irrespective of
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1
[
[
(1.1 equiv.), the formation of homo-coupling by-products – symmetrical
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3
Table 1 is high chemoselectivity for the Suzuki–Miyaura pathway
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[
3
[
[
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1
and show that the reaction conditions significantly affect the
selectivity of the process towards either Suzuki–Miyaura or Heck
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methoxystyryl iodide (Table 1, entries 2 and 5) reacted with lower
chemoselectivity to form also Heck-arylated products in 16–20%
yield; however, they can be separated by column chromatography.
The E-configuration of the carbon–carbon double bond in the
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[
[
1
buta-1,3-dienes isolated was determined on the basis of the H and
13
C NMR spectra. Moreover, compound 2f proved to be a solid and Supporting Information
yielded a crystal amenable to X-ray structure determination (Fig. 2).
More details of the crystallographic data are given in the X-ray
crystallographic files in CIF format (supporting information).
Additional supporting information may be found in the online
version of this article at the publisher’s web site.
Appl. Organometal. Chem. 2014, 28, 137–139
Copyright © 2014 John Wiley & Sons, Ltd.
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