Org. Synth. 2005, 81, 54
DOI: 10.15227/orgsyn.081.0054
PLATINUM CATALYZED HYDROSILYLATION AND PALLADIUM CATALYZED CROSS-COUPLING: ONE-POT HYDROARYLATION OF 1-HEPTYNE TO (E)-1-(1-HEPTENYL)-4-METHOXYBENZENE
[Benzene, 1-(1E)-1-heptenyl-4-methoxy-]
Submitted by Scott E. Denmark and Zhigang Wang
1.
Checked by Adam I. Keller and Dennis P. Curran.
1. Procedure
(E)-1-(1-Heptenyl)-4-methoxybenzene. A solution of
2.79 mL (2.12 g, 15.6 mmol) of 1,1,3,3-tetramethyldisiloxane in
3.0 mL of tetrahydrofuran (THF) is added to a
flame-dried, three-necked, 250-mL, round-bottomed flask equipped with a
temperature probe,
addition funnel,
argon inlet, and
stirbar (Note 1).
t-Bu3P-Pt(0) complex (200 µL) (Notes
2 and
3) is added by
syringe.
1-Heptyne (3.43 mL, 2.51 g, 26.0 mmol) (Note 4) is then slowly added by syringe with external cooling in a
water bath so that the temperature of the reaction solution is not allowed to exceed 30°C
(Note 5). The mixture is stirred at room temperature for 60 min after complete addition of
1-heptyne. A solution of
tetrabutylammonium fluoride in THF (40 mL, 1.0M, 40 mmol) is then added over 10 min (Notes
6 and
7). After complete addition of
TBAF, the solution is stirred for 10 min and then
0.575 g (1.0 mmol) of Pd(dba)2 is added in one portion
(Note 8). A solution of
4-iodoanisole (Note 9) in
THF (20 mL, 1.0M, 20 mmol) is then slowly added via the addition funnel such that the temperature of the reaction solution is kept between 30-33°C (addition time 45 min). The mixture is stirred at room temperature for 30 min after the complete addition of
4-iodoanisole.
Diethyl ether (50 mL) is added and the mixture is stirred for an additional 5 min. The mixture is filtered through a short column of
silica gel (Note 10), eluting with
200 mL of diethyl ether. The filtrate is concentrated by rotary evaporation and vacuum drying to give a residue that is purified by Kugelrohr distillation, chromatography, and Kugelrohr distillation to afford
3.38-3.42 g (
83-84%) of
(E)-1-(1-heptenyl)-4-methoxybenzene as a colorless oil,
bp 90-95°C/0.1 mm (lit.
4 85-90°C/1.2 mm) (Notes
11,
12, and
13).
2. Notes
1.
1,1,3,3-Tetramethydisiloxane was purchased from Lancaster Synthesis Inc. and used as received.
THF was obtained from Mallinckrodt Inc. and freshly distilled from sodium/benzophenone ketyl.
2.
t-Bu3P-Pt(0) complex was prepared by the literature procedure:
2 t-Bu3P (32 mg, 0.158 mmol) (Strem Chemicals) was dissolved in
platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex (
1.5 mL of xylene solution obtained from Aldrich Chemical Company, Inc., catalog number 47-951-9). The mixture was stirred at 65°C (
oil bath) for 5 min and then was slowly cooled to room temperature. This solution could be stored under
N2 in the freezer indefinitely.
3.
t-Bu3P is pyrophoric and should be handled and stored under an inert atmosphere of
nitrogen or
argon.
4.
1-Heptyne was purchased from GFS Chemicals Inc. and was used without further purification.
5.
The hydrosilylation of
1-heptyne with 1,1,3,3-tetramethyldisiloxane is exothermic. If the temperature of the reaction exceeds 30°C, the amount of the undesired α-isomer will increase. However, the solution should not be cooled to below 10°C as the reaction becomes very sluggish.
6.
A solution of
tetrabutylammonium fluoride (TBAF) in THF (1.0M) was prepared from colorless, crystalline tetrabutylammonium fluoride trihydrate purchased from Fluka Chemical Corp.7.
Caution: TBAF reacts exothermally with the disiloxane mixture and the first few drops must be added very slowly and carefully.
8.
Pd(dba)2 was prepared by the literature procedure:
3 palladium chloride (1.05 g, 5.92 mmol) was added to hot (ca. 50°C)
methanol (150 mL) containing
dibenzylideneacetone (DBA) (4.60 g, 19.6 mmol) and
sodium acetate (3.90 g, 47.5 mmol). The mixture was stirred for 4 hr at 40°C to give a reddish-purple precipitate and allowed to cool to complete the precipitation. The precipitate was isolated by filtration, washed successively with water and
acetone, and dried in vacuo.
9.
4-Iodoanisole was purchased from Aldrich Chemical Company, Inc., and was purified by chromatography on
silica gel (elution with
hexane/EtOAc, 50/1) prior to use.
10.
Silica gel was purchased from VWR Scientific (230-400 mesh). A 45-mm diameter column was employed and 60 g of silica gel was loaded as a pentane slurry.
11.
The boiling point (bp) corresponds to uncorrected air-bath temperature of a Büchi GKR-50 Kugelrohr.
12.
The crude product was purified by Kugelrohr distillation (98-103°/0.2 mm) followed by column chromatography (55-mm diameter column, 200 g of silica gel, elution with
pentane/EtOAc, 50/1), and another Kugelrohr distillation.
13.
The analytical data are as follows:
1H NMR
pdf(500 MHz, CDCl
3) δ: 0.91 (t,
J = 7.1, 3 H), 1.33 (m, 4 H), 1.46 (m, 2 H), 2.18 (qd,
J = 7.1, 1.5, 2 H), 3.80 (s, 3 H), 6.09 (dt,
J = 15.9, 6.9, 1 H), 6.33 (d,
J = 15.9, 1 H), 6.84 (d,
J = 8.8, 2 H), 7.28 (d,
J = 8.8, 2 H);
13C NMR (100.6 MHz, CDCl
3) δ: 14.1, 22.6, 29.2, 31.4, 33.0, 55.2, 113.8, 126.9, 128.9, 129.1, 130.8, 158.5; IR (NaCl) cm
−1: 2956, 2927, 2855, 1608, 1511, 1464, 1291, 1248, 1175, 1037, 964, 833; Anal. calcd for C
14H
20O: C, 82.30; H, 9.87; Found: C, 82.10; H, 10.07; GC analysis: t
R(
Z) = 6.07 min (1.6%), t
R(
E) = 6.56 min (95.3%), tR(α) = 5.91 min (3.1%) (HP-5, 250 °C, 15 psi).
Handling and Disposal of Hazardous Chemicals
The procedures in this article are intended for use only by persons with prior training in experimental organic chemistry. All hazardous materials should be handled using the standard procedures for work with chemicals described in references such as "Prudent Practices in the Laboratory" (The National Academies Press, Washington, D.C., 2011 www.nap.edu). All chemical waste should be disposed of in accordance with local regulations. For general guidelines for the management of chemical waste, see Chapter 8 of Prudent Practices.
These procedures must be conducted at one's own risk. Organic Syntheses, Inc., its Editors, and its Board of Directors do not warrant or guarantee the safety of individuals using these procedures and hereby disclaim any liability for any injuries or damages claimed to have resulted from or related in any way to the procedures herein.
3. Discussion
One-pot coupling reactions of organoboron- and organotin reagents with aryl or alkenyl halides and their applications in organic synthesis have been well documented.
5,6 There were only a few examples of hydrosilylation/cross-coupling applied to specific synthetic target molecules.
7,8 The procedures presented here provide a general route to (
E)-olefins by
palladium-catalyzed cross-coupling of alkenyl disiloxanes with aryl or alkenyl iodides.
9Tetramethyldisiloxane is an inexpensive, commercially available reagent. It reacts with alkynes to generate the alkenyldisiloxanes in situ, which can then react with a variety of iodides bearing different substituent patterns. The processes display very good functional group compatibility and afford products in high yield and with excellent regio- and stereoselectivity (Table 1). A notable characteristic of this protocol is the extremely mild reaction conditions employed. The hydrosilylation was complete at room temperature after 30 min. Most coupling reactions proceeded in 10 min to a few hours at room temperature.
Table 1. One-Pot Hydrosilyation/Cross-Coupling of 1-Heptyne with Aryl Iodides
|
|
Entry
|
Iodide, R1
|
Time, min
|
Product, R1
|
Yield, %
|
|
|
1
|
1-napthyl
|
10
|
1-napthyl
|
82
|
|
2
|
4-(CH3CO)C6H4
|
10
|
4-(CH3CO)C6H4
|
94
|
|
3
|
4-(CH3O)C6H4
|
10
|
4-(CH3O)C6H4
|
89
|
|
4
|
3-(NO2)C6H4
|
10
|
3-(NO2)C6H4
|
85
|
|
5
|
3-(NO2)C6H4
|
60 (1 mol% Pd)
|
3-(NO2)C6H4
|
89
|
|
6
|
3-(CH3)C6H4
|
10
|
3-(CH3)C6H4
|
78
|
|
7
|
2-(CH3OCO)C6H4
|
20 h (10 mol% Ph3As)
|
2-(CH3OCO)C6H4
|
88
|
|
8
|
2-(CH3O)C6H4
|
10
|
2-(CH3O)C6H4
|
82
|
|
The generality and functional group compatibility were also excellent with regard to the alkynes (Table 2). Free hydroxyl groups and even a remote double bond were compatible and give very good yields and purities.
Table 2. One-Pot Hydrosilyation/Cross-Coupling of 1-Alkynes with Aryl Iodides
|
|
Entry
|
Alkyne, R2
|
Iodide, R1
|
Time, min
|
Product
|
Yield, %
|
|
|
1
|
C6H5
|
4-(CH3CO)C6H4
|
10
|
1a
|
89
|
|
2
|
C6H5
|
4-(CH3O)C6H4
|
10
|
1b
|
74
|
|
3
|
HO(CH2)3
|
4-(CH3CO)C6H4
|
30
|
2a
|
82
|
|
4
|
HO(CH2)3
|
4-(CH3O)C6H4
|
60
|
2b
|
89
|
|
5
|
C6H5C(OH)(CH3)
|
4-(CH3CO)C6H4
|
24 h
|
3a
|
72
|
|
6
|
C6H5C(OH)(CH3)
|
4-(CH3O)C6H4
|
24 h
|
3b
|
79
|
|
7
|
CH2=CHCH2O(CH2)3
|
4-(CH3CO)C6H4
|
10
|
4a
|
78
|
|
8
|
CH2=CHCH2O(CH2)3
|
4-(CH3O)C6H4
|
10
|
4b
|
76
|
|
The couplings of reactive iodides (with electron-withdrawing groups) were exothermic. However, the reaction temperature can be modulated by the slow addition of iodides last. These protocols are suitable for larger scale applications as well.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
1-Heptyne:
1-Heptyne; (628-71-7)
(E)-1-Heptenyl-4-methoxybenzene:
Benzene, 1-(1E)-1-heptenyl-4-methoxy-; (135987-61-0)
4-Iodoanisole:
Benzene, 1-iodo-4-methoxy-; (696-62-8)
1,1,3,3-Tetramethyldisiloxane:
Disiloxane, 1,1,3,3-tetramethyl-; (3277-26-7)
Tri-(tert-butyl)phosphine:
Phosphine, tris(1,1-dimethylethyl)-; (13716-12-6)
Platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex:
Platinum, 1,3-diethenyl- 1,1,3,3-tetramethyldisiloxane complex; (68478-92-2)
Tetrabutylammonium fluoride trihydrate:
1-Butanaminium, N, N, N-tributyl, fluoride, trihydrate; (87749-50-6)
Pd(dba)2: Palladium, bis[(1,2,4,5-η)-1,5-diphenyl-1,4-pentadien-3-one]-; (32005-36-0)
Palladium chloride;
Palladium chloride (PdCl2); (7647-10-1)
Dibenzylideneacetone (DBA):
1,4-Pentadien-3-one, 1,5-diphenyl-; (538-58-9)
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