One-pot, stereoselective synthesis of trisubstituted 1,3-dienes by hydromagnesiation-cross-coupling tandem reaction of alkylarylacetylenes with alkenyl iodides

Article abstract of DOI:10.1080/00397911.2010.520400

Trisubstituted 1,3-dienes can be stereoselectively synthesized in one pot under mild conditions, in good yields, by hydromagnesiation of alkylarylacetylenes, followed by the palladium-catalyzed cross-coupling with alkenyl iodides. Copyright Taylor & Franc

Full text of DOI:10.1080/00397911.2010.520400

Synthetic Communications1, 41: 3728–3734, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.520400
ONE-POT, STEREOSELECTIVE SYNTHESIS
OF TRISUBSTITUTED 1,3-DIENES BY
HYDROMAGNESIATION–CROSS-COUPLING
TANDEM REACTION OF ALKYLARYLACETYLENES
WITH ALKENYL IODIDES
Xinglin Ye,1,2 Pingping Wang,2 Haiyun Zhang,1 and
Mingzhong Cai1
1Department of Chemistry, Jiangxi Normal University, Nanchang, China
2Department of Chemistry, Jiujiang University, Jiujiang, China
GRAPHICAL ABSTRACT
Abstract Trisubstituted 1,3-dienes can be stereoselectively synthesized in one pot under
mild conditions, in good yields, by hydromagnesiation of alkylarylacetylenes, followed by
the palladium-catalyzed cross-coupling with alkenyl iodides.
Keywords Alkylarylacetylene; cross-coupling; 1,3-diene; hydromagnesiation; tandem
reaction
INTRODUCTION
The stereocontrolled synthesis of conjugated dienes has attracted considerable
interest in organic chemistry because of their appearance in a wide variety of biolo-
gically active molecules and their key synthetic intermediates.[1] The synthesis of
1,3-dienes for use in the Diels–Alder reaction is still an important challenge in
organic synthesis,[2] although other elegant uses of these compounds have been
developed.[3] Conjugated dienes are usually prepared by utilizing either a Wittig-type
approach[4] or through transition-metal-catalyzed coupling reactions of stereode-
fined vinyl halides with vinyl organometallic compounds.[5] Whitby et al. reported
the insertion of 1-lithio-1-halo-butadiene into organozirconocenes derived from
the hydrozirconation of alkynes, providing a stereocontrolled synthesis of (1E,3Z)-
1,3-dienes.[6] Recently, Molander and Yokoyama reported a one-pot stereoselective
Received January 30, 2010.
Address correspondence to Mingzhong Cai, Department of Chemistry, Jiangxi Normal University,
Nanchang 330022, China. E-mail: caimzhong@163.com
3728

SYNTHESIS OF TRISUBSTITUTED 1,3-DIENES
3729
synthesis of trisubstituted 1,3-dienes via sequential Suzuki–Miyaura cross-coupling
of 1,1-dibromoalkenes with alkenyl- and alkyltrifluoroborates.[7]
The transition-metal-catalyzed cross-coupling reaction is a highly versatile
method for carbon–carbon bond formation and has been widely used as a synthetic
tool.[8] Hydromagnesiation has emerged as a unique hydrometallation with some
attractive features such as the high regioselectivity and stereoselectivity observed
with alkylarylacetylenes[9] and alkynylsilanes.[10] Recently, we reported the stereose-
lective synthesis of (E)-1,2-disubstituted vinylstannanes[11] and (E)-1,2-disubstituted
vinylic selenides[12] via the hydromagnesiation of alkylarylacetylenes. Herein we
report that trisubstituted 1,3-dienes could be stereoselectively synthesized in one
pot under mild conditions, in good yields, by hydromagnesiation of alkylarylacetyl-
enes, followed by the palladium-catalyzed cross-coupling with alkenyl iodides.
RESULTS AND DISCUSSION
Alkylarylacetylenes 1 were prepared according to the literature procedure.[13] It
is well known that the hydromagnesiation of alkylarylacetylenes 1 with i-BuMgBr in
diethyl ether proceeds highly regio- and stereoselectively to generate (E)-a-arylvinyl
Grignard reagents 2, and the addition of H-Mg to alkylarylacetylenes is in pure
syn-fashion.[9] To extend the application of the hydromagnesiation reaction of alky-
larylacetylenes, considering the fact that alkenyl halides are efficient electrophiles
and can undergo cross-coupling reaction with vinyl Grignard reagents in the
presence of transition-metal catalysts, we investigated the palladium-catalyzed
cross-coupling reaction of alkenyl halides with (E)-a-arylvinyl Grignard reagents 2
obtained by hydromagnesiation of alkylarylacetylenes 1 (Scheme 1).
We found that the trisubstituted 1,3-dienes 4 were obtained in good yields after
the hydromagnesiation reaction of alkylarylacetylenes 1 with i-BuMgBr using
5 mol% Cp2TiCl2 in diethyl ether at 25 ꢀC for 1 h, solvent removal under reduced
pressure, and stirring of the residue with tetrahydrofuran (THF), alkenyl iodides
(3), and 5 mol% Pd(PPh3)4 at room temperature for 8 h. The experimental results
are summarized in Table 1. As shown in Table 1, the hydromagnesiation–
cross-coupling tandem reaction of i-BuMgBr with a variety of alkylarylacetylenes
and alkenyl iodides proceeded smoothly under very mild conditions to afford stereo-
selectively the corresponding trisubstituted 1,3-dienes 4. The cross-coupling reaction
Scheme 1. Synthesis of trisubstituted 1,3-dienes.

3730
X. YE ET AL.
Table 1. Synthesis of trisubstituted 1,3-dienes (4a–i)
Entry
R
Ar
R1
Product
Yielda (%)
1
2
3
4
5
6
7
8
9
n-C6H13
n-C6H13
n-C6H13
n-C6H13
n-C4H9
Ph
Ph
n-C4H9
Ph
4a
4b
4c
4d
4e
4f
86
82
85
88
83
80
87
84
79
Ph
4-CH3C6H4
Ph
CH3OCH2
n-C6H13
CH3OCH2
Ph
n-C4H9
n-C4H9
Ph
Ph
n-C4H9
Ph
Ph
4g
4h
4i
CH3
CH3OCH2CH2
Ph
4-ClC6H4
aIsolated yield based on alkenyl iodide 3.
of the intermediates 2 with alkenyl bromides was very slow under the same
reaction conditions, and only traces of coupled products were obtained after 24 h
of reaction time.
1
Investigation of the crude products 4 by H NMR spectroscopy (400 MHz)
showed isomeric purities of more than 97%. One olefinic proton signal of com-
pounds 4a–i except for 4h splits characteristically into one triplet at d ¼ 5.51–5.91
with coupling constant J ¼ 7.2–7.6 Hz, which indicated that the hydromagnesiation
to the alkylarylacetylenes had taken place with strong preference for the addition
of the magnesium atom at the carbon adjacent to the aryl group. It is well documen-
ted that the cross-coupling reaction of vinyl Grignard reagents with alkenyl halides
occurs with the configuration retention of both the starting vinyl Grignard reagents
and the alkenyl halides.[14] The (E)-configuration of the compounds 4a–i has been
1
proved by their H NMR spectra, which show a doublet at d ¼ 6.20–7.01 with a
coupling constant of 15.6–16.0 Hz, and this is also the evidence of the retention of
the (E)-configuration of the starting alkenyl iodides. In addition, the (Z)-configuration
of the compound 4c was confirmed by nuclear overhauser effect spectroscopy
1
(NOESY) in the H NMR spectrum (Fig. 1). An enhancement of the allylic protons
was observed as the vinylic proton (d ¼ 5.72) of 4c was irradiated. There was no cor-
relation between the vinylic proton (d ¼ 5.72) and aromatic protons. The correlation
between the allylic protons and aromatic protons was observed. The correlation
between the vinylic proton (d ¼ 5.72) and another vinylic proton (d ¼ 6.45) was also
observed. The NOE results indicate that the compound 4c has the expected
(Z)-configuration and the Pd-catalyzed cross-coupling reaction of (E)-a-arylvinyl
Grignard reagents 2 with alkenyl iodides occurs with the configuration retention of
both the starting intermediates 2 and the alkenyl iodides.
Figure 1. NOESY spectrum of compound 4c.

SYNTHESIS OF TRISUBSTITUTED 1,3-DIENES
3731
EXPERIMENTAL
1H NMR spectra were recorded on a Bruker AC-P400 (400-MHz) spectro-
meter with tetramethylsilene (TMS) as an internal standard using CDCl3 as the
solvent. 13C NMR (100-MHz) spectra were recorded on a Bruker AC-P400
(400-MHz) spectrometer using CDCl3 as the solvent. Infrared (IR) spectra were
determined on an FTS-185 instrument as neat films. Mass spectra were obtained
on a Finnigan 8239 mass spectrometer. Microanalyses were measured using a
Yanaco MT-3 CHN microelemental analyzer. All reactions were carried out in pre-
dried glassware (150 ꢀC, 4 h) and cooled under a stream of dry Ar. Diethyl ether was
treated with lithium aluminum hydride and distilled before use. Tetrahydrofuran
(THF) was freshly distilled from sodium-benzophenone prior to use.
General Procedure for the Synthesis of Trisubstituted 1,3-Dienes (4a–i)
Cp2TiCl2 (25 mg, 0.1 mmol) was added to a solution of isobutylmagnesium
bromide (2.5 mmol) in diethyl ether (4 mL) at 0 ꢀC under Ar, and the mixture was
stirred for 30 min at that temperature. Alkylarylacetylene 1 (2.0 mmol) was added
to this solution, and the mixture was stirred for 1 h at 25 ꢀC. After removal of the
ether under reduced pressure (2 h, rt=2 Torr), the residue was dissolved in THF
(4 mL) and cooled to 0 ꢀC, and Pd(PPh3)4 (0.116 g, 0.1 mmol) and alkenyl iodide 3
(1.8 mmol) were added with stirring. The reaction mixture was brought to 30 ꢀC
gradually, stirred for 8 h, quenched with saturated aqueous NH4Cl (15 mL), and
extracted with Et2O (2 ꢁ 30 mL). The organic layer was washed with saturated aque-
ous NH4Cl (20 mL) and water (2 ꢁ 20 mL) and dried (MgSO4). Removal of solvent
under reduced pressure gave an oil, which was purified by column chromatography
on silica gel using light petroleum as eluent.
Selected Data
(5E,7Z)-7-Phenyl-5,7-tetradecadiene (4a). Oil. 1H NMR (400 MHz,
CDCl3): d 7.37–7.27 (m, 3H), 7.10 (d, J ¼ 7.2 Hz, 2H), 6.23 (d, J ¼ 15.6 Hz, 1H),
5.58 (t, J ¼ 7.6 Hz, 1H), 5.10 (dt, J ¼ 15.6, 7.6 Hz, 1H), 2.05–2.00 (m, 2H),
1.90–1.85 (m, 2H), 1.34–1.16 (m, 12H), 0.89–0.84 (m, 6H); 13C NMR (100 MHz,
CDCl3): d 141.06, 138.98, 134.19, 131.59, 131.33, 129.55, 127.93, 126.48, 32.49,
31.68, 31.56, 29.82, 28.93, 28.89, 22.59, 22.28, 14.06, 13.94; IR (neat): n (cmꢂ1
)
3058, 2932, 2860, 1724, 1600, 1493, 1465, 1379, 963, 703; MS (EI, 70 eV): m=z 270
(Mþ, 1.1), 159 (24), 105 (100), 77 (41). Anal. calc. for C20H30: C, 88.82; H, 11.18.
Found: C, 88.59; H, 11.37%.
(1E,3Z)-1,3-Diphenyl-1,3-decadiene (4b). Oil. 1H NMR (400 MHz, CDCl3):
d 7.43–7.39 (m, 2H), 7.35–7.24 (m, 5H), 7.19–7.16 (m, 3H), 7.01 (d, J ¼ 16.0 Hz, 1H),
5.98 (d, J ¼ 16.0 Hz, 1H), 5.86 (t, J ¼ 7.6 Hz, 1H), 1.98–1.94 (m, 2H), 1.36–1.20
(m, 8H), 0.85 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): d 141.24, 138.23,
137.72, 135.14, 133.39, 129.62, 129.04, 128.47, 128.16, 126.97, 126.84, 126.19,
31.66, 29.69, 29.29, 28.89, 22.59, 14.08; IR (neat): n (cmꢂ1) 3059, 3027, 2927, 2854,
1708, 1598, 1494, 1456, 1377, 962, 750, 702; MS (EI, 70 eV): m=z 290 (Mþ, 12), 219

3732
X. YE ET AL.
(29), 205 (39), 105 (90), 77 (62), 57 (100). Anal. calc. for C22H26: C, 90.98; H, 9.02.
Found: C, 90.71; H, 9.25%.
(2E,4Z)-1-Methoxy-4-phenyl-2,4-undecadiene
(4c). Oil. 1H NMR
(400 MHz, CDCl3): d 7.35 (t, J ¼ 7.4 Hz, 2H), 7.27 (m, 1H), 7.12 (d, J ¼ 6.8 Hz, 2H),
6.45 (d, J ¼ 15.6 Hz, 1H), 5.72 (t, J ¼ 7.6 Hz, 1H), 5.21 (dt, J ¼ 15.6, 6.4 Hz, 1H),
3.91 (d, J ¼ 6.4 Hz, 2H), 3.30 (s, 3H), 1.94–1.88 (m, 2H), 1.34–1.16 (m, 8H), 0.84
(t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): d 140.32, 138.19, 137.09, 134.44,
129.49, 128.09, 126.75, 126.06, 73.10, 57.95, 31.66, 29.62, 29.06, 28.86, 22.60, 14.10;
IR (neat): n (cmꢂ1) 3058, 2927, 2854, 1729, 1595, 1493, 1449, 1122, 960, 703; MS
(EI, 70 eV): m=z 258 (Mþ, 1.5), 120 (35), 105 (100), 77 (57). Anal. calc. for
C18H26O: C, 83.67; H, 10.14. Found: C, 83.43; H, 9.97%.
1
(7Z,9E)-8-Tolyl-7,9-hexadecadiene (4d). Oil. H NMR (400 MHz, CDCl3):
d 7.16 (d, J ¼ 8.0 Hz, 2H), 6.97 (d, J ¼ 8.0 Hz, 2H), 6.20 (d, J ¼ 15.6 Hz, 1H), 5.51
(t, J ¼ 7.6 Hz, 1H), 5.06 (dt, J ¼ 15.6, 7.6 Hz, 1H), 2.35 (s, 3H), 2.02–1.97 (m, 2H),
1.90–1.84 (m, 2H), 1.35–1.15 (m, 16H), 0.90–0.85 (m, 6H); 13C NMR (100 MHz,
CDCl3): d 141.25, 139.38, 134.35, 132.19, 131.84, 130.23, 126.83, 125.19, 32.86,
31.74, 31.68, 29.85, 29.75, 29.36, 28.94, 28.89, 22.62, 21.56, 14.08, 14.04; IR (neat):
n (cmꢂ1) 3057, 2926, 2858, 1712, 1600, 1493, 1456, 1378, 961, 702; MS (EI, 70 eV):
m=z 312 (Mþ, 1.8), 91 (45), 57 (100). Anal. calc. for C23H36: C, 88.39; H, 11.61.
Found: C, 88.13; H, 11.84%.
(2E,4Z)-1-Methoxy-4-phenyl-2,4-nonadiene
(4e). Oil.
1H
NMR
(400 MHz, CDCl3): d 7.34–7.26 (m, 3H), 7.12–7.10 (m, 2H), 6.45 (d, J ¼ 15.6 Hz,
1H), 5.72 (t, J ¼ 7.2 Hz, 1H), 5.20 (dt, J ¼ 15.6, 6.0 Hz, 1H), 3.91 (d, J ¼ 6.0 Hz,
2H), 3.30 (s, 3H), 1.95–1.89 (m, 2H), 1.33–1.19 (m, 4H), 0.85 (t, J ¼ 7.2 Hz, 3H);
13C NMR (100 MHz, CDCl3): d 140.34, 138.18, 137.09, 134.39, 129.49, 128.10,
126.75, 126.08, 73.10, 57.93, 31.85, 28.80, 22.26, 13.95; IR (neat): n (cmꢂ1) 2957,
2926, 1597, 1464, 1379, 1122, 968, 703; MS (EI, 70 eV): m=z 230 (Mþ, 6), 105
(100), 77 (54), 57 (65). Anal. calc. for C16H22O: C, 83.43; H, 9.63. Found:
C, 83.20; H, 9.82%.
1
(1E,3Z)-1,3-Diphenyl-1,3-octadiene (4f). Oil. H NMR (400 MHz, CDCl3):
d 7.43–7.39 (m, 2H), 7.35–7.24 (m, 5H), 7.21–7.14 (m, 3H), 6.99 (d, J ¼ 16.0 Hz,
1H), 5.98 (d, J ¼ 16.0 Hz, 1H), 5.86 (t, J ¼ 7.6 Hz, 1H), 2.00–1.94 (m, 2H), 1.39–1.31
(m, 2H), 1.29–1.22 (m, 2H), 0.83 (t, J ¼ 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 141.24, 138.21, 137.71, 135.07, 133.36, 129.60, 129.05, 128.46, 128.14, 126.95,
126.83, 126.18, 31.90, 29.00, 22.27, 13.91; IR (neat): n (cmꢂ1) 3060, 3029, 2956,
2871, 1705, 1599, 1494, 1455, 1379, 965, 754, 700; MS (EI, 70 eV): m=z 262 (Mþ,
8.5), 105 (100), 77 (56), 57 (87). Anal. calc. for C20H22: C, 91.55; H, 8.45. Found:
C, 91.28; H, 8.67%.
1
(5Z,7E)-6-Phenyl-5,7-dodecadiene (4g). Oil. H NMR (400 MHz, CDCl3):
d 7.37–7.27 (m, 3H), 7.10 (d, J ¼ 7.6 Hz, 2H), 6.23 (d, J ¼ 15.6 Hz, 1H), 5.58
(t, J ¼ 7.6 Hz, 1H), 5.11 (dt, J ¼ 15.6, 7.6 Hz, 1H), 2.06–2.00 (m, 2H), 1.93–1.86
(m, 2H), 1.33–1.20 (m, 8H), 0.87–0.79 (m, 6H); 13C NMR (100 MHz, CDCl3): d
141.06, 138.97, 134.17, 131.60, 131.28, 129.54, 127.93, 126.48, 32.48, 32.05, 31.55,
28.65, 22.27, 22.26, 13.94, 13.92; IR (neat): n (cmꢂ1) 3058, 3023, 2958, 2872, 1723,

SYNTHESIS OF TRISUBSTITUTED 1,3-DIENES
3733
1600, 1494, 1466, 1379, 983, 703; MS (EI, 70 eV): m=z 242 (Mþ, 1.3), 105 (100), 77
(47). Anal. calc. for C18H26: C, 89.19; H, 10.81. Found: C, 88.97; H, 10.97%.
(1E,3Z)-1,3-Diphenyl-1,3-pentadiene (4h). Oil. 1H NMR (400 MHz,
CDCl3): d 7.44–7.14 (m, 10H), 6.99 (d, J ¼ 16.0 Hz, 1H), 6.01 (d, J ¼ 16.0 Hz, 1H),
5.95 (q, J ¼ 6.8 Hz, 1H), 1.63 (d, J ¼ 6.8 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 142.28, 142.18, 140.53, 137.96, 137.73, 129.73, 128.89, 128.48, 127.69, 126.95,
126.78, 126.19, 15.18; IR (neat): n (cmꢂ1) 3058, 3026, 1625, 1598, 1494, 962, 702;
MS (EI, 70 eV): m=z 220 (Mþ, 4.7), 105 (100), 77 (67). Anal. calc. for C17H16: C,
92.68; H, 7.32. Found: C, 92.41; H, 7.53%.
(1E,3Z)-1-Phenyl-3-(4-chlorophenyl)-6-methoxy-1,3-hexadiene (4i). Oil.
1H NMR (400 MHz, CDCl3): d 7.43–7.15 (m, 9H), 7.01 (d, J ¼ 16.0 Hz, 1H), 6.02
(d, J ¼ 16.0 Hz, 1H), 5.91 (t, J ¼ 7.6 Hz, 1H), 3.51 (t, J ¼ 6.4 Hz, 2H), 3.29 (s, 3H),
2.97–2.91 (m, 2H); 13C NMR (100 MHz, CDCl3): d 141.76, 139.05, 137.84, 135.69,
134.78, 129.75, 129.55, 128.82, 128.57, 127.25, 126.96, 126.34, 69.36, 58.13, 31.21;
IR (neat): n (cmꢂ1) 3057, 3032, 2958, 1703, 1601, 1496, 1179, 1123, 962, 753, 702;
MS (EI, 70 eV): m=z 298 (Mþ, 35Cl, 2.1), 105 (100), 77 (51). Anal. calc. for
C19H19OCl: C, 76.36; H, 6.41. Found: C, 76.11; H, 6.23%.
CONCLUSION
In summary, we have developed an efficient and stereoselective one-pot
method for the synthesis of trisubstituted 1,3-dienes via the hydromagnesiation–
cross-coupling tandem reaction of alkylarylacetylenes with i-BuMgBr and alkenyl
iodides. The present method has the advantages of readily available starting materi-
als, straightforward and simple procedures, mild reaction conditions, and good
yields. The procedure should find wide application to the synthesis of a large array
of naturally occurring substances having the trisubstituted 1,3-diene system.
ACKNOWLEDGMENTS
We thank the National Natural Science Foundation of China (Project
No. 20862008) and the Natural Science Foundation of Jiangxi Province in China
(Project No. 2007GZW0172) for financial support.
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