Regioselective Reductive Cross-Coupling Reaction

R 1
3
R 1
R 2
L
Ni
L
L
Ni
R 2
4 H
R 1
O
R 3
R 2
11
OBEt 2
R 3
acetylene
oxidative
cyclization
TS1-A
Path A
R 1
5
+
R 2
R 1
L
Ni
1
H
R 2
O
R 3
+
R 1
BEt 3
H
O
2
R 2
L
Ni
6
Path B
R 3
O
R 3
R 1
ethylene
BEt 3
R 2
oxidative
cyclization
TB1-B
L
Ni
H
7
O
R 3
R 1
R 1
BEt 3
R 2
L
Ni
L
Ni
8
O
R 3
BEt 3
R 1
R OBEt
10 2
2
R3 L Et
Ni
O
R 2
9
transmetalation
(alkyl migration)
TS2
R 3
BHEt 2
β-hydrogen
elimination and
reductive
elimination
TS3
14/16