PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
7
General procedure for the asymmetric allylic alkylation
To a flame-dried Schlenk tube under an argon atmosphere,
NHC Pd-catalysts (2.5 mol%) and toluene (3 mL) were
added. The solution was stirred at room temperature for
0.5 h, before (E)-1,3-diarylallyl acetates 4 (1.0 mmol) was
added, followed by addition of malonate 5 (2.5 mmol) and
NaH (2.5 mmol). The mixture was then heated to 50 ꢀC and
kept for 12 h. TLC showed the full conversion of the sub-
strates. Water (10 mL) was added and the mixture was
extracted with CH2Cl2 (2 ꢁ 10 mL). The organic layer was
combined, dried over anhydrous Na2SO4, filtered and con-
centrated under vacuum. The residue was purified by col-
umn chromatography (silica gel, petroleum ether/ethyl
acetate = 20:1, v/v) to afford the desired product 6, which
Scheme 2. Proposed mechanism for the formation of enantioselectivity.
1
were characterized by H NMR. The ee of 6ab was deter-
CH(CH3)2) ppm. 13C NMR (DMSO, 100 MHz): d 137.4,
128.5, 118.1, 65.0, 57.8, 24.5, 23.5, 22.0 ppm. MS Calcd. for
C8H14N2O, 154.11. Found: ESI-MS (m/z): 155.12 [M þ H]þ.
Synthesis of pyridine hydroxyalkyl di-functionalized imi-
dazolium bromides (2): A Schlenk tube containing imidazole
alcohol 1 (0.77 g, 5.0 mmol) and 2-bromopyridine (3.0 mL)
was heated at 150 ꢀC for 72 h. The mixture was then cooled
to room temperature and added to diethyl ether (30 mL)
dropwise. The deep yellow precipitate formed was then col-
lected and purified by flash chromatography (silica, CH2Cl2/
EtOH, gradient elution, 15/1–8/1, v/v) to obtain the pure
product as a viscous oil (1.29 g, yield 83%). 1H NMR
(400 MHz, DMSO): d 10.23 (s, 1H, CH in imidazole),
8.67–8.64 (m, 2H, CH in pyridine, CH in imidazole),
8.25–8.15 (m, 3H, CH in pyridine, CH in imidazole),
7.67–7.64 (m, 1H, CH in pyridine), 5.25 (bs, 1H, CH2OH),
4.34–4.28 (m, 1H, NCH), 3.95–3.86 (m, 2H, CH2OH),
2.34–2.25 (m, 1H, CH(CH3)2), 1.03 (d, 3H, J ¼ 6.80 Hz,
CH(CH3)2), 0.79 (d, 3H, J ¼ 6.80 Hz, CH(CH3)2) ppm. 13C
NMR (100 MHz, DMSO): d 149.6, 146.9, 141.0, 135.1, 125.7,
123.4, 119.8, 114.9, 69.8, 60.9, 29.1, 19.6, 19.4 ppm. MS
Calcd. For C13H18BrN3O, 311.06. Found: ESI-MS (m/z):
232.15 [M-Br]þ.
mined by HPLC using a Chiralcel OD-H column (n-hexane/
2-propanol =100:1; 0.6 mL/min) and detected at a UV wave
length of 254 nm. The ee of other products were determined
by HPLC using a Chiralcel AD-H column (n-hexane/2-pro-
panol =90:10; 1.0 mL/min) and detected at a UV wave
length of 254 nm. The yields and the ee of each case were
listed in Table 3.
Funding
This work was supported by the National Natural Science Foundation
of China under the grant 21172055, the Natural Science Foundation of
Henan Province Department of Education under the grant 18A150004,
the Program for Innovative Research Team from Zhengzhou under the
grant 131PCXTD605, and the Fundamental Research Funds for the
Henan Provincial Colleges and Universities in Henan University of
Technology under the grant 2017RCJH08.
ORCID
Liangru Yang
Jinwei Yuan
Synthesis of palladium complex (3i): A mixture of imida-
zolium salt 2 (0.31 g, 1.0 mmol), Pd(OAc)2 (0.22 g, 1.0 mmol)
in CH2Cl2 (10 mL) was stirred at room temperature for 12 h.
The solvent was then evaporated and the residue was puri-
fied by column chromatography (silica, CH2Cl2/acetone, gra-
dient elution, 15/1–4/1, v/v). NHC palladium complex 3i
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was obtained as yellow solids (0.15 g, yield 30%). H NMR
(DMSO, 400 MHz): d 9.46 (s, 1H, CH in pyridine), 8.47 (d,
1H, J ¼ 2.24 Hz, CH in imidazole), 8.40–8.36 (m, 1H, CH in
pyridine), 8.18 (d, 1H, J ¼ 8.0 Hz, CH in pyridine), 7.76 (d,
1H, J ¼ 2.3 Hz, CH in imidazole), 7.62 (t, 1H, J ¼ 6.6 Hz, CH
in pyridine), 6.02 (bs, 1H, NCH), 5.00 (t, 1H, J ¼ 5.0 Hz,
CH2OH), 3.84–3.75 (m, 2H, CH2OH), 2.25–2.19 (m, 1H,
CH(CH3)2), 1.05 (d, 3H, J ¼ 6.6 Hz, CH(CH3)2), 0.81 (d, 3H,
J ¼ 6.8 Hz, CH(CH3)2). 13C NMR (DMSO, 100 MHz): d
151.9, 150.8, 143.4, 123.6, 122.4, 117.7, 112.8, 66.1, 61.3,
29.0, 19.6, 19.5 ppm. Anal Cald. for C13H17Br2N3OPd
(497.53): C, 31.38; H, 3.44; N, 8.45. Found: C, 31.30; H,
3.39; N, 8.48.
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