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Abstract

A ligand-promoted, palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor is developed. The chemical selectivity control is achieved based on ligand regulation. The use of triethanolamine and tetrahydrofuran at 80 °C under N₂ is found to be critical for the transfer hydrogenation of terminal alkynes. The general applicability of this procedure is highlighted by the synthesis of 27 terminal alkenes in moderate to good yields.

Keywords

ethanol hydrogen donor ligand-promoted palladium terminal alkynes

Introduction

Alkenes are a useful and important structural motif in many organic molecules including pharmaceuticals, natural products, and fragrances, such as combretastatin-A4, pinosylvin, resveratrol, and eugenol.^1–3 Hence, novel methods for the synthesis of alkenes are very desirable. The semi-hydrogenation of alkynes to alkenes is one of the most important reactions in organic synthesis, and it has been extremely used for the synthesis of pharmaceuticals, natural products, agrochemical products, and industrial materials.^4–7 Several alternative catalytic systems have been reported for the transformation of alkynes into alkenes, for example, Lindlar’s catalyst.⁸ Among all the reported transformation systems, metal-catalyzed transfer hydrogenation has attracted attention.^9–11 However, to achieve the transfer hydrogenation reaction and to obtain good product yields, these methods often require the use of explosive, flammable, expensive, or corrosive hydrogenating agents, such as ammonia borane, hydrogen, triethylsilane, and formic acid.^12–18 Therefore, it is necessary to find an economical and safe hydrogen donor for the semi-hydrogenation of alkynes to alkenes. In recent years, ethanol has attracted attention as a safer and more economical hydrogen donor, and more reactions have been reported for the semi-hydrogenation of alkynes to alkenes using ethanol as the hydrogen source.^19–24 However, the semi-hydrogenation of terminal alkynes with ethanol as the hydrogen donor is rarely reported. Very recently, Wang et al.²⁵ reported the iridium-catalyzed transfer hydrogenation of terminal alkynes with ethanol. Herein, we report a ligand-promoted, palladium-catalyzed semi-hydrogenation of terminal alkynes with ethanol as the hydrogen donor (Scheme 1).

Scheme 1.

Palladium-catalyzed semi-hydrogenation of terminal alkynes with ethanol.

Results and discussion

We commenced our studies by treating 1-chloro-4-ethynylbenzene and ethanol with 1,2-bis(diphenylphosphi-no)ethane (DPPE) as the ligand. First, various catalysts were screened to identify a suitable candidate. The use of FeI₂, CuI, MnCl₂, BrMn(CO)₅, and Co(OAc)₂ gave no catalytic activity to the reaction. However, to our delight, Pd(OAc)₂ gave good catalytic activity for the semi-hydrogenation of terminal alkynes to alkenes in the presence of ethanol (Table 1, entries 1–7). To improve the reaction efficiency, we further screened different ligands to identify a suitable ligand (Table 1, entries 8–12). GC analysis showed that 79% yield of the desired alkene was obtained when triethanolamine (TEOA) was used, and a 10% yield of the corresponding alkane was also obtained, which we speculate may be related to the reaction temperature being too high. Next, we screened various reaction temperatures (Table 1, entries 13–18), and 80 °C was found to be the optimum temperature, furnishing the corresponding product in 89% yield (Table 1, entry 16). Furthermore, we screened different reaction solvents (Table 1, entries 19–21), with tetrahydrofuran (THF) proving to be the best.

Table 1.

Optimization of the reaction conditions.


Entry	Catalyst	Ligand	Solvent	Temp (°C)	Yield of 2a (%)^a	Yield of 3a (%)^a
1	None	DPPE	THF	90	0	0
2	FeI₂	DPPE	THF	90	0	0
3	CuI	DPPE	THF	90	0	0
4	MnCl₂	DPPE	THF	90	0	0
5	BrMn(CO)₅	DPPE	THF	90	0	0
6	Co(OAc)₂	DPPE	THF	90	0	0
7	Pd(OAc)₂	DPPE	THF	90	55	0
8	Pd(OAc)₂	–	THF	90	8	0
9^b	Pd(OAc)₂	DIPAMP	THF	90	27	0
10	Pd(OAc)₂	PPh₃	THF	90	35	0
11	Pd(OAc)₂	Et₃N	THF	90	45	0
12^c	Pd(OAc)₂	TEOA	THF	90	79	10
13	Pd(OAc)₂	TEOA	THF	120	12	88
14	Pd(OAc)₂	TEOA	THF	110	49	51
15	Pd(OAc)₂	TEOA	THF	100	70	20
16	Pd(OAc)₂	TEOA	THF	80	89	trace
17	Pd(OAc)₂	TEOA	THF	70	70	0
18	Pd(OAc)₂	TEOA	THF	60	57	0
19	Pd(OAc)₂	TEOA	CH₃CN	80	43	0
20	Pd(OAc)₂	TEOA	DCE	80	12	0
21	Pd(OAc)₂	TEOA	DMF	80	trace	0

Yields were determined by GC analysis.

DIPAMP = ethylenebis(2-methoxyphenylphenylphosphine).

TEOA = triethanolamine (0.6 eq).

With the optimized reaction conditions in hand, a series of terminal alkynes was investigated to examine the substrate scope of the semi-hydrogenation reaction. As summarized in Scheme 2, this ligand-promoted, palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor exhibited good functional group tolerance to give products 2a–x. Arylethynes with electron-withdrawing groups such as chloro, fluoro, nitro, cyano, and trifluoromethyl on the aryl ring, all gave the corresponding terminal alkenes in good yields (2a–k). In addition, the reaction of an arylacetylene containing two trifluoromethyl substituents at the meta positions of the aromatic ring gave the corresponding terminal alkene(2l) in good yield. Arylacetylenes with electron-neutral or electron-donating groups on the aryl ring, such as alky, methoxy, pyridyl, naphthyl, phenyl, and anthracyl gave the corresponding arylethylenes (2m–w, 2y–z, 2aa) in moderate to good yields. To our delight, the unactivated terminal alkyne(1x) also show good compatibility.

Scheme 2.

Palladium-catalyzed transfer hydrogenation of terminal alkynes.^a

To check the synthetic utility of the current method, it was tested by performing a gram-scale (1g) palladium-catalyzed semi-hydrogenation of a terminal alkyne with ethanol under the optimized conditions. In this case, the target 2aa was obtained in 51% yield.

On the basis of previous work on the semi-hydrogenation of terminal alkynes with ethanol as the hydrogen donor,²⁵ we propose a possible catalytic cycle reaction mechanism (Scheme 3). First, TEOA coordinates with Pd(Ⅱ) to form active catalytic species A, and further forms Pd–H species B with ethanol and then terminal alkyne. The Pd–H species B then undergoes ion inserted by the Pd–H bond to form complex C. Subsequent β–H elimination affords intermediate D. Finally, intermediate D undergoes reductive elimination to give the terminal alkene and regenerates the catalytic species A.

Scheme 3.

A possible reaction mechanism.

Conclusion

In conclusion, palladium catalysts have good catalytic activity and selectivity, and have important application value in petrochemicals, pharmaceuticals, fine chemicals, organic synthesis, and other fields. We have developed a ligand-promoted palladium catalysts transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor. This process is safer and more convenient than traditional strategies, and is compatible with a range of functional groups. Further investigations of the use of cheaper metals, green hydrogenation agents, and other reaction types are underway in our laboratory.

Experimental section

General information

Unless stated otherwise, all reactions were carried out in pressure tubes under N₂. Commercially available reagents were used as received. Non-commercially available substrates were synthesized following reported protocols. Thin-layer chromatography performed on brand and samples were visualized by UV fluorescence. Silica gel (particle size 40–63 µm) was used for flash column chromatography. Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker AV 400 spectrometer at 400 MHz (¹H NMR) and 100 MHz (¹³C NMR). Proton and carbon chemical shifts are reported relative to the solvent used as an internal reference.

Typical procedure for the synthesis of terminal ethylenes

To a 15 mL pressure tube were added 1-chloro-4-ethynylbenzene 1 (0.20 mmol), Pd(OAc)₂ (0.01 mmol, 2.24 mg), and TEOA (0.08 mmol, 11.9 mg) under N₂, and then EtOH (4 mmol, 233 µL) and THF (1.5 mL) were added. The resulting solution was stirred at 80 °C for 24 h. After the reaction was complete, the solution was cooled to room temperature and diluted with ethyl acetate (10 mL). The organic phase was washed with brine, and the aqueous phase was extracted with ethyl acetate (10 mL). The combined organic phase was dried, filtered, and concentrated in vacuo. The crude product was purified by column chromatography (n-hexane or n-hexane/EtOAc = 100:1) to afford the desired product.

Gram-scale synthesis

According to the typical procedure: To a 250 mL pressure tube was charged with added 9-ethynylanthracene 1aa (4.95 mmol, 1.0 g), Pd(OAc)₂ (0.248 mmol, 55.8 mg), TEOA (1.97 mmol, 295.2 mg) and then EtOH (98.9 mmol, 5.77 mL) and THF (35 mL) were added. The resulting solution was stirred at 140 °C for 40 h. After standard work-up and column purification (n-hexane), product 2aa was obtained (0.515 g, 51% yield).

1-chloro-4-vinylbenzene (2a)²⁶: Colorless liquid (24.6 mg, 89% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.35–7.28 (m, 4H), 6.67 (dd, J = 17.6, 10.9 Hz, 1H), 5.73 (d, J = 17.6 Hz, 1H), 5.27 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 136.22, 135.86, 133.62, 128.86, 127.62, 114.64.

1-chloro-3-vinylbenzene (2b)²⁶: Colorless liquid (24.8 mg, 90% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.39 (s, 1H), 7.24 (tt, J = 2.9, 1.8 Hz, 3H), 6.65 (dd, J = 17.6, 10.9 Hz, 1H), 5.75 (d, J = 17.6 Hz, 1H), 5.29 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 139.55, 135.75, 134.64, 129.87, 127.88, 126.31, 124.59, 115.46.

1-chloro-2-vinylbenzene (2c)²⁶: Colorless liquid (24.3 mg, 88% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.58 (d, J = 7.5 Hz, 1H), 7.37 (d, J = 7.8 Hz, 1H), 7.26–7.07 (m, 3H), 5.76 (d, J = 17.5 Hz, 1H), 5.40 (d, J = 11.0 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 135.83, 133.27, 129.75, 128.92, 126.93, 126.68, 116.63.

1-fluoro-4-vinylbenzene (2d)²⁷: Colorless liquid (20.0 mg, 82% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.38 (dd, J = 8.6, 5.5 Hz, 2H), 7.01 (t, J = 8.7 Hz, 2H), 6.68 (dd, J = 17.6, 10.9 Hz, 1H), 5.67 (d, J = 17.6 Hz, 1H), 5.21 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 162.59 (d, J_C–F = 246.2 Hz), 135.82, 133.85 (d, J_C–F = 3.3 Hz), 127.87 (d, J_C–F = 8.0 Hz), 115.65, 113.66 (d, J = 2.2 Hz).

1-fluoro-3-vinylbenzene (2e)²⁸: Colorless liquid (19.0 mg, 78% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.27 (tt, J = 11.4, 5.8 Hz, 1H), 7.14 (dd, J = 18.4, 8.9 Hz, 2H), 6.95 (td, J = 8.4, 2.5 Hz, 1H), 6.68 (dd, J = 17.6, 10.9 Hz, 1H), 5.76 (d, J = 17.6 Hz, 1H), 5.28 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 163.34 (d, J_C–F = 244.0 Hz), 140.03 (d, J_C–F = 7.6 Hz), 135.94 (d, J_C–F = 2.5 Hz), 130.09 (d, J_C–F = 8.4 Hz), 122.30 (d, J_C–F = 2.7 Hz), 115.33 (d, J_C–F = 21.3 Hz), 114.7.4 (d, J_C–F = 21.0 Hz), 112.64 (d, J_C−F = 22.0 Hz).

1-fluoro-2-vinylbenzene (2f)²⁸: Colorless liquid (20.7 mg, 85% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.49 (td, J = 7.7, 1.6 Hz, 1H), 7.23–7.20 (m, 1H), 7.10–7.01 (m, 2H), 6.88 (dd, J = 17.8, 11.2 Hz, 1H), 5.83 (d, J = 17.8 Hz, 1H), 5.37 (d, J = 11.2 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 160.42 (d, J_C–F =248.0 Hz), 129.46 (d, J_C–F = 4.0 Hz), 129.22 (d, J_C–F = 8.0 Hz), 127.21 (d, J_C−F = 3.8 Hz), 125.43 (d, J_C–F = 12.1 Hz), 124.17 (d, J_C–F = 3.6 Hz), 116.56 (d, J_C–F = 4.7 Hz), 115.84 (d, J_C–F = 22.0 Hz).

1-nitro-4-vinylbenzene (2g)²⁶: Colorless liquid (23.8 mg, 80% yield); ¹H NMR (400 MHz, CDCl₃): δ = 8.16 (d, J = 7.3 Hz, 2H), 7.52 (d, J = 8.7 Hz, 2H), 6.76 (dd, J = 17.6, 10.9 Hz, 1H), 5.91 (d, J = 17.6 Hz, 1H), 5.48 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 147.21, 143.90, 135.02, 126.87, 123.98, 118.67.

1-nitro-3-vinylbenzene (2h)²⁶: Colorless liquid (25.3 mg, 85% yield); ¹H NMR (400 MHz, CDCl₃): δ = 8.26 (t, J = 1.9 Hz, 1H), 8.11 (ddd, J = 8.2, 2.2, 0.9 Hz, 1H), 7.71 (d, J = 7.7 Hz, 1H), 7.50 (t, J = 8.0 Hz, 1H), 6.77 (dd, J = 17.6, 10.9 Hz, 1H), 5.90 (d, J = 17.6 Hz, 1H), 5.45 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 139.41, 134.89, 132.21, 129.59, 122.57, 121.03, 117.23.

4-vinylbenzonitrile (2i)²⁶: Colorless liquid (21.4 mg, 83% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.61 (d, J = 8.3 Hz, 2H), 7.48 (d, J = 8.3 Hz, 2H), 6.72 (dd, J = 17.6, 10.9 Hz, 1H), 5.87 (d, J = 17.6 Hz, 1H), 5.44 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 141.99, 135.45, 132.48, 126.84, 119.01, 117.84, 111.21.

1-(trifluoromethyl)-4-vinylbenzene (2j)²⁸: Colorless liquid (28.6 mg, 83% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.55 (dd, J = 35.0, 8.3 Hz, 4H), 6.76 (dd, J = 17.6, 10.9 Hz, 1H), 5.86 (d, J = 17.6 Hz, 1H), 5.40 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 141.12 (d, J = 1.2 Hz), 135.78, 130.13 (d, J = 32.0 Hz), 129.49 (d, J = 32.0 Hz), 126.54, 125.66 (q, J_C–F = 270.0 Hz), 123.02, 116.58.

1-(trifluoromethyl)-3-vinylbenzene (2k)²⁹: Colorless liquid (27.9 mg, 81% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.64–7.42 (m, 4H), 6.74 (dd, J = 20.0, 10.9 Hz, 1H), 5.83 (d, J = 17.6 Hz, 1H), 5.36 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 138.44, 135.73, 131.29, 130.97, 129.49 (d, J_C–F = 1.1 Hz, 14H), 129.12, 125.63, 124.50 (q, J_C–F = 3.8 Hz), 123.05 (dt, J_C–F = 13.1, 6.6 Hz), 115.92.

1,3-Bis(trifluoromethyl)-5-vinylbenzene (2l)²⁹: Colorless liquid (38.4 mg, 80% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.78 (d, J = 23.1 Hz, 3H), 6.78 (dd, J = 17.6, 10.9 Hz, 1H), 5.92 (d, J = 17.6 Hz, 1H), 5.50 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 139.69, 134.45, 132.27, 131.94, 131.61, 126.27, 124.83, 122.12, 121.41, 118.07.

styrene (2m)²⁶: Colorless liquid (16.8 mg, 81% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.41 (d, J = 7.5 Hz, 2H), 7.32 (t, J = 7.5 Hz, 2H), 7.24 (dd, J = 9.7, 4.8 Hz, 1H), 6.72 (dd, J = 17.6, 10.9 Hz, 1H), 5.75 (d, J = 17.6 Hz, 1H), 5.24 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 137.71, 137.03, 128.65, 127.94, 126.35, 113.93.

1-methyl-4-vinylbenzene (2n)²⁶: Colorless liquid (15.8 mg, 60% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.32 (d, J = 7.9 Hz, 2H), 7.15 (d, J = 7.8 Hz, 2H), 6.71 (dd, J = 17.6, 10.9 Hz, 1H), 5.71 (d, J = 17.6 Hz, 1H), 5.20 (d, J = 10.9 Hz, 1H), 2.36 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): δ = 137.73, 136.85, 134.97, 129.34, 126.25, 112.87, 21.32.

1-methyl-3-vinylbenzene (2o)²⁶: Colorless liquid (19.6 mg, 83% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.22 (d, J = 4.8 Hz, 3H), 7.08 (dd, J = 5.6, 2.6 Hz, 1H), 6.70 (dd, J = 17.6, 10.9 Hz, 1H), 5.74 (d, J = 17.6 Hz, 1H), 5.23 (d, J = 10.9 Hz, 1H), 2.36 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): δ = 138.20, 137.66, 137.10, 128.64, 127.08, 123.48, 113.72, 21.52.

1-methyl-2-vinylbenzene (2p)²⁶: Colorless liquid (16.8 mg, 71% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.49 (dd, J = 4.8, 4.1 Hz, 1H), 7.18 (ddd, J = 9.3, 4.6, 2.8 Hz, 3H), 6.96 (dd, J = 17.4, 11.0 Hz, 1H), 5.65 (d, J = 17.4 Hz, 1H), 5.30 (d, J = 11.0 Hz, 1H), 2.36 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): δ = 136.97, 135.54, 134.99, 130.36, 127.80, 126.22, 125.50, 115.27, 19.83.

1-tert-butyl-4-vinylbenzene (2q)²⁷: Colorless liquid (24.6 mg, 77% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.36 (s, 4H), 6.69 (ddd, J = 13.1, 12.2, 6.6 Hz, 1H), 5.70 (d, J = 17.6 Hz, 1H), 5.20 (d, J = 10.9 Hz, 1H), 1.32 (s, 9H); ¹³C NMR (100 MHz, CDCl₃): δ = 151.01, 136.75, 134.99, 126.08, 125.57, 113.13, 34.71, 31.44.

1-methoxy-2-vinylbenzene (2r)³⁰: Colorless liquid (22.0 mg, 82% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.48 (d, J = 7.6 Hz, 1H), 7.26–7.22 (m, 1H), 7.06 (dd, J = 17.8, 11.2 Hz, 1H), 6.94 (t, J = 7.5 Hz, 1H), 6.88 (d, J = 8.3 Hz, 1H), 5.74 (d, J = 17.8 Hz, 1H), 5.27 (d, J = 11.2 Hz, 1H), 3.86 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): δ = 156.86, 131.81, 128.98, 126.91, 126.67, 120.75, 114.60, 110.97, 55.60.

1-methoxy-3-vinylbenzene (2s)³¹: Colorless liquid (23.0 mg, 86% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.25 (dd, J = 10.2, 5.6 Hz, 1H), 7.02 (d, J = 7.6 Hz, 1H), 6.95 (s, 1H), 6.82–6.80 (m, 1H), 6.68 (dd, J = 17.6, 10.9 Hz, 1H), 5.74 (dd, J = 17.6, 0.8 Hz, 1H), 5.24 (d, J = 10.8 Hz, 1H), 3.82 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): δ = 159.93, 139.15, 136.90, 129.61, 119.02, 114.22, 113.54, 111.64, 55.30.

1-methoxy-4-vinylbenzene (2t)²⁷: Colorless liquid (21.4 mg, 80% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.39–7.33 (m, 2H), 6.90–6.84 (m, 2H), 6.67 (dd, J = 17.6, 10.9 Hz, 1H), 5.62 (d, J = 17.6 Hz, 1H), 5.13 (d, J = 10.9 Hz, 1H), 3.82 (s, 3H); ¹³C NMR (100 MHz, CDCl₃): δ = 159.51, 136.36, 130.59, 127.52, 114.05, 111.71, 55.43.

3-vinylpyridine (2u)³²: Colorless liquid (15.1 mg, 72% yield); ¹H NMR (400 MHz, CDCl₃): δ = 8.57 (d, J = 4.1 Hz, 1H), 7.63 (td, J = 7.7, 1.8 Hz, 1H), 7.33 (d, J = 7.9 Hz, 1H), 7.14 (ddd, J = 7.5, 4.8, 1.0 Hz, 1H), 6.81 (dd, J = 17.5, 10.8 Hz, 1H), 6.19 (d, J = 17.5 Hz, 1H), 5.47 (d, J = 10.8 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 155.85, 149.62, 137.07, 136.56, 122.54, 121.31, 118.28.

2-vinylnaphthalene (2v)²⁷: White solid (20.0 mg, 65% yield); m.p. 65–67 °C; ¹H NMR (400 MHz, CDCl₃): δ = 7.82–7.75 (m, 4H), 7.63 (dd, J = 8.6, 1.6 Hz, 1H), 7.48–7.42 (m, 2H), 6.89 (dd, J = 17.6, 10.9 Hz, 1H), 5.88 (d, J = 17.6 Hz, 1H), 5.34 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 137.08, 135.16, 133.70, 133.30, 128.24, 127.81, 126.44, 126.06, 123.32, 114.32.

4-vinyl-1,1'-biphenyl (2w)²⁷: White solid (29.2 mg, 81% yield); m.p. 119–122 °C; ¹H NMR (400 MHz, CDCl₃): δ = 7.61–7.56 (m, 4H), 7.50–7.42 (m, 4H), 7.35 (t, J = 7.3 Hz, 1H), 6.76 (dd, J = 17.6, 10.9 Hz, 1H), 5.80 (d, J = 17.6 Hz, 1H), 5.28 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 140.82, 136.66, 128.93, 127.42, 127.11, 126.79, 114.04.

Allylbenzene (2x)³³: Colorless liquid (15.3 mg, 65% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.31 (dd, J = 10.0, 5.3 Hz, 5H), 7.22 (t, J = 7.0 Hz, 3H), 5.99 (ddt, J = 16.9, 10.1, 6.7 Hz, 1H), 5.14–5.05 (m, 2H), 3.41 (d, J = 6.7 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃): δ = 140.20, 137.60, 128.64, 126.20, 115.92, 40.38.

2-vinylpyridine (2y)³⁴: Colorless liquid (15.9 mg, 76% yield); ¹H NMR (400 MHz, CDCl₃): δ = 8.56 (d, J = 4.7 Hz, 1H), 7.63 (td, J = 7.7, 1.8 Hz, 1H), 7.33 (d, J = 7.9 Hz, 1H), 7.14 (dd, J = 7.0, 5.4 Hz, 1H), 6.81 (dd, J = 17.5, 10.8 Hz, 1H), 6.19 (dd, J = 17.5, 1.1 Hz, 1H), 5.47 (dd, J = 10.8, 1.0 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 155.77, 149.56, 137.00, 136.54, 122.52, 121.29, 118.26.

3-vinyl-1,1'-biphenyl (2z)³⁵: Colorless liquid (14.3 mg, 68% yield); ¹H NMR (400 MHz, CDCl₃): δ = 7.63–7.61 (m, 3H), 7.45 (m, 6H), 6.80 (dd, J = 17.6, 10.9 Hz, 1H), 5.84 (d, J = 17.6 Hz, 1H), 5.31 (d, J = 10.9 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 141.69, 141.23, 138.14, 136.94, 128.99, 127.41, 126.84, 125.26, 114.35.

9-vinylanthracene (2aa)³⁶: White solid (12.2 mg, 60% yield); m.p. 64–66 °C; ¹H NMR (400 MHz, CDCl₃): δ = 8.39 (s, 1H), 8.33–8.31 (m, 2H), 8.00 (dd, J = 6.3, 3.5 Hz, 2H), 7.51–7.44 (m, 5H), 6.01 (dd, J = 11.5, 2.1 Hz, 1H), 5.63 (dd, J = 17.9, 2.1 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃): δ = 133.65, 131.52, 129.34, 128.73, 126.45, 126.13, 125.49, 125.25, 123.06.

Supplemental Material

sj-rar-1-chl-10.1177_17475198221145838 – Supplemental material for Palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor

Supplemental material, sj-rar-1-chl-10.1177_17475198221145838 for Palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor by Jie Hui and Feng Wang in Journal of Chemical Research

Supplemental Material

sj-rar-2-chl-10.1177_17475198221145838 – Supplemental material for Palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor

Supplemental material, sj-rar-2-chl-10.1177_17475198221145838 for Palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor by Jie Hui and Feng Wang in Journal of Chemical Research

Footnotes

Acknowledgements

I would like to express my gratitude to my family and friends who helped me during the writing of this thesis.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This project was financially supported by project of Jiangsu United Vocational and Technical College (NO. B/2022/11/147).

ORCID iD

Jie Hui

Supplemental material

Supplemental material for this article is available online.

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