8 Earth-Abundant d-Block Metal Nanocatalysis for Coupling …
253
O
O
O
O
or
[NiNPs/PEG]
(0.06 mol%)
EG
r.t., 5-20 min
CN
CN
Ar
O
+
+
O
O
O
O
Ar
CN
NH 2
CN
NH 2
Ar
or
Isolated Yield: 86-96%
O
O
O
O
NH 2
CN
+
+
CN
CN
O
Scheme 8.1 Synthesis of spiropyrans by a multicomponent reaction catalyzed by NiNPs and
stabilized by PEG in ethylene glycol [73]
in the diol. NiNPs were efficiently reused up to 3 times. Authors postulated that nickel
activates both carbonyl and nitrile groups.
The same authors previously reported Knoevenagel condensations of barbituric
or Meldrum acid and aromatic aldehydes in EG, catalyzed by NiNPs and stabilized
by PVP (polyvinylpyrrolidone) [71] and PEG [72], respectively (Scheme 8.2).
+
N
N
O
R
2
X
R
2
O
R
1
CHO
X = O, S
R 1 = H, F, Cl, Br, CH=CH, CH 3 , OH...
R 2 = H, CH 3 , Ph
(R 1 in different positions; also
polysubstituted aromatic groups)
[NiNPs/PVP]
(1.5 mol%)
EG, 50 °C
10-15 min
Isolated Yield: 82-97%
N
N
O
R
2
X
R
2
O
Ar
O
O
O
O
[NiNPs/PEG]
EG, r.t.
5-15 min
Isolated Yield: 78-94%
R
2
CHO
O
O
O
O
R
2
OH
R
2
CHO
[NiNPs/PEG]
EG, r.t.
5-15 min
O
R
2
COOH
O
Yield: 75-97%
R
1 = H, Cl, CH=CH, CH 3 , OCH 3 , OH...
R
2 = H, CH 3 , Ph
(R
1 and R
2 in different positions; also
polysubstituted aromatic groups)
Scheme 8.2 NiNPs stabilized by polymers catalyzed Knoevenagel condensations in ethylene
glycol [71, 72]