Abstract
An efficient 1,4-addition of TMSCN to aromatic enones has been
achieved in excellent yields (91-99%) by CsF (1
mol%) as the catalyst and H2 O (4 equiv) as the
additive in refluxing dioxane within 2-7 hours.
Key words
1,4-addition reaction - enones - nitriles - regioselectivity - CsF
References and Notes
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Preparation of
2a
The solution of CsF (0.5 mg, 0.003 mmol,
1 mol%) and enone (1a , 62.5 mg,
0.3 mmol) in dioxane (1 mL) is added TMSCN (84 µL, 0.66
mmol, 2.2 equiv) and H2 O (22 µL, 1.2 mmol, 4
equiv) subsequently in a dry Schlenk tube equipped with cold finger
under argon. The reaction mixture is stirred at reflux temperature
until the reaction is completed (monitored by TLC). 1 M HCl (0.3
mL) is added to quench the reaction with additional 20 min stirring
at r.t. The resulting mixture is extracted with EtOAc (5 mL) (Caution! HCN
generated in the reaction mixture is highly toxic. Those operations
should be conducted in a well-ventilated hood). The extract is washed
with H2 O, brine, dried over anhyd Na2 SO4 ,
and concentrated. The crude product is purified by flash chromatography
on silica gel (PE-EtOAc, 20:1) to afford 2a as
white solid in 99% yield. Nitrile 2a :
mp 120-122 ˚C (lit.: 122-125 ˚C).¹¹ ¹ H
NMR (400 MHz, CDCl3 ): δ = 3.52 (dd, J = 6.0, 18.0
Hz, 1 H, NCCHCH
A
HB CO),
3.74 (dd, J = 8.0,
18.0 Hz, 1 H, NCCHCHA
H
B
CO), 4.57 (dd, J = 6.0,
8.0 Hz, 1 H, NCCH CHA HB CO),
7.34-7.49 (m, 7 H, ArH), 7.58-7.62 (m, 1 H, ArH),
7.92-7.94 (m, 2 H, ArH) ppm. ¹³ C
NMR (100 MHz, CDCl3 ): δ = 31.9, 44.5,
120.6, 127.5, 128.1, 128.4, 128.8, 129.3, 133.9, 135.3, 135.8, 194.6
ppm. IR (KBr): ν = 1681, 2236 cm-¹ .