The Journal of Organic Chemistry
Note
General Procedure for Reduction of Alkynes Using HCO2H.
Alkyne (0.20 mmol), PdCl2 (1.8 mg, 0.010 mmol), K2CO3 (5.5 mg,
0.020 mmol), and 1,4-dioxane (1.0 mL) were added to a flame-dried
Schlenk tube under an argon atmosphere. Within a minute, formic
acid (11 μL, 0.25 mmol) was added to this suspension at once. The
resulting reaction mixture containing black precipitates and white
powder (K2CO3) was stirred at 80 °C (the reaction was monitored by
GC-MS analysis). After the reaction was complete, Pd-catalyst and
K2CO3 were removed by filtration with acetone. The solvent was
concentrated at reduced pressure. The resulting crude product was
purified by silica gel column chromatography (hexane/ethyl acetate)
and/or GPC (JAI, LC-9210 II NEXT) to give the product. The
products are literature known.
MHz, CDCl3) δ 7.18−7.28 (m, 5H), 7.14 (d, J = 8.2 Hz, 2H), 7.02
(d, J = 8.2 Hz, 2H), 6.55 (s, 2H), 2.31 (s, 3H); 13C{1H} NMR (100
MHz, CDCl3) δ 137.5, 136.9, 134.3, 130.2, 129.5, 128.9, 128.8, 128.8,
128.2, 127.0, 21.2.
(Z)-1-Methoxy-4-styrylbenzene (2g).28 Eluent for column chro-
matography, hexane/ethyl acetate = 9/1; yellow oil, 35.7 mg, 85%; 1H
NMR (399 MHz, CDCl3) δ 7.17−7.28 (m, 7H), 6.74−6.77 (m, 2H),
6.48−6.55 (m, 2H), 3.79 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3)
δ 158.7, 137.6, 130.1, 129.7, 129.6, 128.8, 128.7, 128.2, 126.9, 113.6,
55.2.
(E)-2-Styrylpyridine (3h).29 Eluent for column chromatography,
hexane/ethyl acetate/Et3N = 70/30/1; off-white solid, 26.1 mg, 72%;
1H NMR (301 MHz, CDCl3) δ 8.61 (d, J = 3.8 Hz, 1H), 7.64−7.70
(m, 2H), 7.58−7.62 (m, 3H), 7.36−7.43 (m, 3H), 7.29−7.33 (m,
1H), 7.14−7.21 (m, 2H); 13C{1H} NMR (100 MHz, CDCl3) δ 155.6,
149.7, 136.6, 136.5, 132.7, 128.7, 128.3, 127.9, 127.1, 122.1.
(Z)-3-Styrylpyridine (2i).30 Eluent for column chromatography,
Representative Procedure for Semireduction of Internal
Alkynes (0.05 mol % Pd). Tolane (1a) (20 mmol), PdCl2 (1.8 mg,
0.01 mmol, 0.05 mol %), K2CO3 (276 mg, 2 mmol, 10 mol %), and
1,4-dioxane (20 mL) were added to a flame-dried Schlenk tube under
an argon atmosphere. Within a minute, formic acid (1.08 mL, 25
mmol) was added to this suspension at once. The resulting reaction
mixture containing black precipitates and white powder (K2CO3) was
stirred at 80 °C for 9 d. After the reaction was complete, Pd-catalyst
and K2CO3 were removed by filtration with acetone. The solvent was
1
hexane/ethyl acetate/Et3N = 70/30/1; yellow oil, 13.4 mg, 37%; H
NMR (399 MHz, CDCl3) δ 8.48 (s, 1H), 8.37−8.42 (m, 1H), 7.51
(d, J = 8.2 Hz, 1H), 7.20−7.27 (m, 5H), 7.10−7.15 (m, 1H), 6.75 (d,
J = 12.3 Hz, 1H), 6.55 (d, J = 12.3 Hz, 1H); 13C{1H} NMR (100
MHz, CDCl3) δ 150.0, 148.0, 136.4, 135.7, 132.8, 132.5, 128.6, 128.4,
127.5, 126.3, 122.9.
1
concentrated at reduced pressure. The yields were determined by H
(Z)-4-Styrylpyridine (2j).31 Eluent for column chromatography,
NMR analysis.
1
Preparation of Pd-Catalysts. The mixture of PdCl2 (9 mg, 0.05
mmol), K2CO3 (13.8 mg, 0.1 mmol), and HCO2H (57.5 mg, 1.25
mmol) in 5 mL of dioxane was stirred at 80 °C for 1 h under Ar. The
black precipitates with white powder obtained after filtration were
washed with acetone, MeOH, and ultrapure water. Subsequent
dryness under a vacuum gave the desired Pd-catalysts quantitatively.
Pd-catalysts should be stored under Ar in a refrigerator.
hexane/ethyl acetate/Et3N = 70/30/1; yellow oil, 18.5 mg, 51%; H
NMR (399 MHz, CDCl3) δ 8.45 (d, J = 5.5 Hz, 2H), 7.20−7.29 (m,
5H), 7.11 (d, J = 5.5 Hz, 2H), 6.80 (d, J = 12.3 Hz, 1H), 6.50 (d, J =
12.3 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ 149.8, 144.9,
136.1, 134.0, 128.7, 128.4, 127.8, 127.5, 123.5.
(Z)-2-Styrylthiophene (2k).5h Eluent for column chromatography,
hexane only; colorless oil, 25.7 mg, 69%; 1H NMR (399 MHz,
CDCl3) δ 7.27−7.37 (m, 5H), 7.08 (dd, J = 5.0, 0.9 Hz, 1H), 6.96 (d,
J = 3.7 Hz, 1H), 6.88 (dd, J = 5.2, 3.4 Hz, 1H), 6.70 (d, J = 11.9 Hz,
1H), 6.58 (d, J = 11.9 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ
137.3, 128.9, 128.8, 128.5, 128.1, 127.5, 126.4, 125.5, 123.3.
(Z)-3-Phenyl-2-propenoic Acid Ethyl Ester (2l).32 GPC was used
The Reuse of Catalyst. After the reduction reaction was
complete, the solution mixture was transferred to another vessel
using a pipet. The residue, including black precipitates, was washed
with acetone, MeOH, and water under air. After the dryness of black
precipitates under reduced pressure, the next run was conducted.
(Z)-Stilbene (2a).5h Eluent for column chromatography, hexane
1
for purification; pale yellow oil, 25.1 mg, 71%; H NMR (399 MHz,
1
CDCl3) δ 7.58 (d, J = 6.8 Hz, 2H), 7.30−7.37 (m, 3H), 6.95 (d, J =
12.3 Hz, 1H), 5.95 (d, J = 12.3 Hz, 1H), 4.17 (q, J = 7.1 Hz, 2H),
1.24 (t, J = 7.1 Hz, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ 166.2,
142.9, 134.8, 129.7, 128.9, 127.9, 119.9, 60.3, 14.1.
only; colorless oil, 33.5 mg, 93%; H NMR (399 MHz, CDCl3) δ
7.18−7.26 (m, 10H), 6.60 (s, 2H); 13C{1H} NMR (100 MHz,
CDCl3) δ 137.2, 130.2, 128.9, 128.2, 127.1.
(Z)-1-(4-Styrylphenyl)ethanone (2b).5h Eluent for column chro-
matography, hexane/ethyl acetate = 9/1; pale yellow oil, 35.1 mg,
(Z)-(2-Cyclohexylvinyl)benzene (2m).30 Eluent for column chro-
matography, hexane only; pale yellow oil, 29 mg, 78%; 1H NMR (399
MHz, CDCl3) δ 7.20−7.35 (m, 5H), 6.31 (d, J = 11.9 Hz, 1H), 5.48
(dd, J = 11.9, 11.4 Hz, 1H), 2.54−2.63 (m, 1H), 1.64−1.82 (m, 5H),
1.11−1.33 (m, 5H); 13C{1H} NMR (100 MHz, CDCl3) δ 138.9,
137.9, 128.6, 128.2, 126.8, 126.4, 36.9, 33.3, 26.0, 25.7.
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79%; H NMR (399 MHz, CDCl3) δ 7.81 (d, J = 8.2 Hz, 2H), 7.32
(d, J = 8.2 Hz, 2H), 7.23−7.26 (m, 5H), 6.72 (d, J = 12.3 Hz, 1H),
6.60 (d, J = 12.3 Hz, 1H), 2.57 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3) δ 197.6, 142.2, 136.6, 135.6, 132.4, 129.1, 129.0, 128.8, 128.3,
128.3, 127.5, 26.5.
(Z)-6-Dodecene (2n).2a Eluent for column chromatography,
hexane only; colorless oil, 26.6 mg, 79%; 1H NMR (399 MHz,
CDCl3) δ 5.31−5.39 (m, 2H), 1.97−2.06 (m, 4H), 1.24−1.38 (m,
12H), 0.89 (t, J = 6.8 Hz, 6H); 13C{1H} NMR (100 MHz, CDCl3) δ
129.9, 31.6, 29.5, 27.2, 22.6, 14.1.
(Z)-4-Styrylmethylbenzoate (2c).26 Eluent for column chromatog-
1
raphy, hexane/ethyl acetate = 9/1; colorless oil, 35.7 mg, 75%; H
NMR (399 MHz, CDCl3) δ 7.89 (d, J = 8.2 Hz, 2H), 7.30 (d, J = 8.2
Hz, 2H), 7.20−7.24 (m, 5H), 6.71 (d, J = 12.3 Hz, 1H), 6.61 (d, J =
12.3 Hz, 1H), 3.90 (s, 3H); 13C{1H} NMR (100 MHz, CDCl3) δ
166.9, 142.1, 136.6, 132.2, 129.5, 129.2, 128.8, 128.6, 128.3, 127.5,
52.0.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
■
(Z)-4-Styrylbenzaldehyde (2d).2c Eluent for column chromatog-
S
1
raphy, hexane/ethyl acetate = 9/1; pale yellow oil, 27.5 mg, 66%; H
NMR (399 MHz, CDCl3) δ 9.95 (s, 1H), 7.74 (d, J = 8.2 Hz, 2H),
7.40 (d, J = 8.2 Hz, 2H), 7.23−7.26 (m, 5H), 6.76 (d, J = 12.3 Hz,
1H), 6.62 (d, J = 12.3 Hz, 1H); 13C{1H} NMR (100 MHz, CDCl3) δ
191.7, 143.7, 136.5, 134.9, 132.9, 129.7, 129.5, 128.9, 128.8, 128.4,
127.7.
Screening of bases and reductants, TEM images, and
NMR spectra of products (PDF)
(Z)-1-Fluoro-4-styrylbenzene (2e).2d Eluent for column chroma-
tography, hexane/Et3N = 99/1; colorless oil, 31.3 mg, 79%; 1H NMR
(399 MHz, CDCl3) δ 7.18−7.24 (m, 7H), 6.90 (t, J = 8.7 Hz, 2H),
6.59 (d, J = 12.3 Hz, 1H), 6.54 (d, J = 12.3 Hz, 1H); 13C{1H} NMR
(76 MHz, CDCl3) δ 161.8 (d, J = 246 Hz), 137.0, 133.1 (d, J = 3 Hz),
130.5 (d, J = 8 Hz), 130.2, 129.0, 128.8, 128.3, 127.2, 115.1 (d, J = 22
Hz); 19F NMR (375 MHz, CDCl3) δ −117.84.
AUTHOR INFORMATION
Corresponding Author
■
ORCID
Notes
The authors declare no competing financial interest.
(Z)-1-Methyl-4-styrylbenzene (2f).27 Eluent for column chroma-
1
tography, hexane only; colorless oil, 32.2 mg, 83%; H NMR (399
D
J. Org. Chem. XXXX, XXX, XXX−XXX