Molecules 2020, 25, 3666
8 of 11
21.4 mmol, 4.00 eq.) were dissolved in dry and degassed DMF (40 mL) under argon atmosphere.
The mixture was stirred for 19 h at 80 ◦C. Afterwards, the reaction was quenched with water (100 mL)
and extracted with DCM (3
×
30 mL). The unified organic phases were repeatedly washed with
2M-HCl-solution (3 50 mL) and dried over MgSO4. The solvents were removed under reduced
×
pressure and the crude product was subjected to column chromatography on silica eluting with
cyclohexane/ethyl acetate 100:1 (v/v) affording 648 mg (62%, 3.31 mmol) of a faint yellow oil after
drying in oil pump vacuum.
Since a distillation was not suitable with such a small amount, high vacuum was used to remove
residual solvents from the product. However, this diminished the yield owing to the volatile nature
of the title compound. However, we gave the isolation of most pure material priority, since it was
1
employed as reference in the following NMR-experiments. H-NMR (400 MHz, 298 K, CDCl3,
δ in
ppm): 1.26 (s, 9H), 3.81 (s, 3H), 6.83–6.88 (m, 2H), 7.41–7.47 (m, 2H). 13C-NMR (100 MHz, 298 K, CDCl3,
in ppm): 30.9, 45.6, 55.4, 114.1, 123.7, 139.0, 160.3. MS (EI+, m/z, [M]+): calc. for C11H16OS, 196.0922;
found 196.0917.
1,2,4,5-Tetrakis(tert-butylthio)benzene 5: 1,2,4,5-Tetrabromobenzene (10.0 g, 25.4 mmol),
δ
S-tert-butyl isothiouronium bromide (26.0 g, 122 mmol, 4.80 eq.), potassium tert-butoxide (45.6 g,
406 mmol, 16.0 eq.), tris(dibenzylideneacetone)dipalladium(0) (0.582 g, 0.63 mmol, 2.5 mol%) and
triphenylphosphine (0.666 g, 2.54 mmol, 10 mol%) are placed in a Schlenk tube under argon atmosphere
and are subsequently dissolved in dry DMF (200 mL). The mixture is then stirred for 16 h at 100 ◦C.
After completion of the reaction the mixture is quenched with water (200 mL) and extracted with
DCM (3
×
50 mL). The organic phase is then separated, washed a few times with 2M hydrochloric
acid and dried over MgSO4. The solvent is removed under reduced pressure and the crude product is
washed with methanol. The product is obtained as an off white solid (9.63 g, 22.4 mmol, 88%). H-NMR
(400 MHz, 298 K, CDCl3,
ppm): 31.5, 48.3, 139.5, 144.9. MS (EI+, m/z, [M]+): calc. for C22H38S4, 430.1856; found 430.1855.
For measuring the conversion via quantitative H-NMR, mesitylene was used as an internal
standard. The above mentioned reaction was carried out using 100.7 mg 1,2,4,5-Tetrabromobenzene
1
δ δ in
in ppm): 1.36 (s, 36H), 7.94 (s, 2H). 13C-NMR (100 MHz, 298 K, CDCl3,
1
(255.8 µmol) with analogous stoichiometry as above and 32.2 µL mesitylene (27.9 mg, 232.5 µmol,
0.909 eq.) were added. The work-up was carried out as described and solvents were only removed
with a vacuum above 600 mbar to avoid evaporation of mesitylene. The conversion was estimated to
99.6
±
4 % based on two independent samples and integration of the 1H-NMR spectrum (Figure S6).
The error of app. 4 % accounts for weighting uncertainty and variance between both samples.
2,2,6,6-Tetramethylbenzo[1,2-d:4,5-d0]bis[1,3]dithiole 1a: 1,2,4,5-Tetrakis(tert-butylthio)benzene
(1.00 g, 2.32 mmol), scandium triflate (0.114 g, 0.23 mmol, 10 mol%), and acetone (1.72 mL, 1.34 g,
◦
23.2 mmol, 10.0 eq.) were dissolved in 10 mL dry toluene and heated to 100 C under argon for
16 h. After reaching room temperature, 10 mL 0.5 M HCl was added to the reaction mixture and
the organic phase was separated off. After washing the aqueous phase was 10 mL diethyl ether,
the unified organic phases were dried over MgSO4 and solvents were removed under reduced pressure.
1
The title compound was obtained as a pure white solid in a yield of 0.546 g (82%, 1.90 mmol). H-NMR
(400 MHz, 298 K, CDCl3,
ppm): 31.4, 65.9, 116.9, 135.9. MS (ESI+, m/z, [M]+): calc. for C12H14S4, 285.9978; found 285.9971.
General procedure for condition screening with 4-bromoanisole. 4-Bromoanisole
δ δ in
in ppm): 1.88 (s, 12H), 7.02 (s, 2H). 13C-NMR (XY MHz, 298 K, CDCl3,
(100 mg, 0.535 mmol), tert-butyl isothiouronium bromide (137mg, 0.641 mmol, 1.2 eq.),
tris(dibenzylideneacetone)dipalladium(0) (2.5 mol%), phosphine ligand (10 mol%) and base (4.0 eq.)
were dissolved in dry and degassed DMF (4 mL) under argon atmosphere. The mixture was stirred for
19 h at the given temperature. Afterwards, the reaction was quenched with water (10 mL) and extracted
with DCM (3
×
3 mL). The unified organic phases were repeatedly washed with 2M-HCl-solution (3
×
5 mL) and dried over MgSO4. The solvents were removed under reduced pressure regularly giving an
oil containing rests of DMF. Due to the volatile nature of the products, drying of the resulting oil in
high vacuum was not performed.