109
A similar system toward oxindole synthesis in the presence of Cu(OAc) 2 catalyst
can be also performed [12, 13]. In this reaction system, atmospheric oxygen was
used as the reoxidants without adding any bases (Scheme 4.21). The procedures are
believed to proceed by the generation of C sp3 radical intermediates which subsequently add to the aniline moiety.
N
H
O
O
73%
N
H
O
O
53%
N
H
O
O
71%
Ph
N
O
O
62%
Ph
N
H
O
O
78%
N
H
O
O
71%
N
H
O
O
76%
N
N
H
O
O
58%
F
Br
NC
Condition A: 10 mol% Ni(acac) 2 , 10 mol% Zn(OTf) 2 , 2 equiv DTBP, 120 °C, Ar.
Condition B: 10 mol% NiF 2 , 10 mol% PPh 3 , 2 equiv DTBP, 120 °C, 24h.
N
H
72%
O
O
N
51%
O
O
N
H
81%
O
O
CN
N
H
72%
O
O
Br
N
H
71%
O
O
N
H
62%
O
O
N
H
55%
O
O
N
N
H
62%
O
O
Br
+
O
O
N
H
R
N
H
R
O
O
Condition A
+
O
O
N
H
R
N
H
R
O
O
Condition B
Scheme 4.19 Nickel-catalyzed regioselective coupling of dioxane with indoles
4 Oxidative Radical Couplings