ACS Catalysis
Letter
a cyano group directly into the double bond through a
carbon−carbon coupling reaction.
pyridine as the base, which might be caused by its strong
coordination ability (entry 14). Next, screening of different
solvents indicated toluene and cyclohexane to be beneficial for
the reaction (entries 18 and 19). Further experiments revealed
that the mixed solvent of toluene/cyclohexane in a ratio of 1:2
would be the proper choice, resulting in 70% yield (entries
20−22). It is worthy to note that the addition of 20 mol %
CH3COOK improved the yield to 77% (entry 23; the detailed
Lastly, a similar yield obtained under nitrogen atmosphere
instead of air indicated that an inert atmosphere was
unnecessary (entry 24).
In continuation of our work on the activation of the
carbon−carbon bond,19 herein is reported a CC bond
cleavage reaction, in which alkenyl nitrile could be obtained by
using nitrile as a cyanation reagent. This work features the
following items: (1) CC bond cleavage and regeneration
formulated as C1C2 + C3 → C1C3 + C2 occurs between
alkene and nitrile, which contributes a different formal group-
exchange reaction from normal reported alkene metathesis
(Scheme 1b); (2) cyanation of alkene is realized through C
C cleavage and the regeneration process.
Initially, 2-cinnamoyl-pyrrole 1a and acetonitrile 2a were
chosen as model substrates to optimize reaction conditions. As
shown in Table 1, metal salts and bases seemed to be essential
Having the optimized conditions in hand, the alkene
substrate scope was then evaluated. As shown in Scheme 2,
a,b
Scheme 2. Substrate Scope of Alkene
a
Table 1. Optimization of Reaction Conditions
b
entry
catalyst
none
PdCl2
PdCl2
CuCl2
NiCl2
PtCl2
CoCl2
K2PdCl6
base
solvent
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
DMSO
THF
yield
1
2
3
4
5
6
7
8
KOH
none
ND
ND
19%
11%
10%
11%
5%
ND
ND
16%
15%
28%
13%
ND
50%
31%
28%
55%
54%
63%
70%
67%
77%
74%
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
t-BuOK
Py
CsOH
CsOH
CsOH
CsOH
CsOH
CsOH
CsOH
CsOH
CsOH
CsOH
9
Pd/C
Pd(acac)2
Pd(OAc)2
10
11
12
13
14
15
16
17
18
19
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
Pd(CH3CN)2Cl2
a
PhMe
CyH
Reaction conditions: 1 (1 mmol), 2a (2 mmol), Pd(CH3CN)2Cl2
(10 mol %), CH3COOK (20 mol %), CsOH (1.2 mmol) were stirred
c
b
20
21
22
23
PhMe/CyH
PhMe/CyH
PhMe/CyH
PhMe/CyH
PhMe/CyH
in PhMe/CyH (1 mL/2 mL) at 110 °C for 24 h in air. Isolated yield
d
and E/Z > 20/1.
e
f
most of the substrates could be converted to be corresponding
products in moderate to good yields ranging from 57% to 85%.
Steric hindrance seemed to have a significant influence on the
results. For example, para- and meta-methyl substituted
cinnamonitriles could be obtained in good yields around
80%, while only 58% yield was gained in the case of ortho-
methyl substituted analogue (3b−3d). Meanwhile, electron-
donating groups (3e−3g) seemed to be more favorable for the
transformation (3h−3l), and -OMe substituted product 3e was
formed in 85% yield. Furthermore, polycyclic aromatic
substrates led to lower yields compared with phenyl substrates
(3m and 3n). Notably, the dienenitrile product could also be
obtained by this transformation in good yields around 80% (3o
and 3p), indicating the selective CC cleavage reaction.
The substrate scope of the nitrile was also probed. As
depicted in Scheme 3, the reaction was compatible with a wide
array of arylacetonitriles (4b−4n). The steric hindrance again
g
24
a
General reaction conditions: 1a (1 mmol), 2a (2 mmol), catalyst (10
mol %), base (1.2 mmol) were stirred in 3 mL of solvent at 110 °C for
b
c
d
24 h in air. Isolated yields. PhMe/CyH (1:1). PhMe/CyH (1:2).
e
f
g
PhMe/CyH (1:3). 20 mol % CH3COOK. N2 atmosphere, 20 mol
% CH3COOK.
for the reaction, and no corresponding product was obtained in
the absence of them (entries 1−3). A range of metal salts were
then screened, and Pd(CH3CN)2Cl2 exhibited higher catalytic
ability than others including PdCl2, CuCl2, NiCl2, PtCl2,
CoCl2, K2PdCl6, Pd/C, Pd(acac)2, and Pd(OAc)2, providing
3a in 28% yield (entries 3−12). Next, a series of bases were
also tested, and 50% yield was obtained in the case of CsOH,
better than others including KOH and t-BuOK (entries 12−
15). There was no product to be found in the presence of
8679
ACS Catal. 2021, 11, 8678−8683