34
Recently, Duan and co-workers reported the iron-catalyzed oxidative crosscoupling of two titanate-mediated aryl Grignard or lithium reagents using O 2 as
oxidant (Scheme 2.48) [99]. Aryl Grignard reagents were first transmetalated to the
RMgX
Fe(acac) 3 (0.1-5 mol%)
or CoCl 2 (5 mol%)
or Li 2 CuCl 4 (0.2-1 mol%)
N 2 O, THF, r.t., 1-18 h
R R
R 1 MgX
+ R 2 MgX
Li 2 CuCl 4 (1 mol%)
N 2 O, THF, r.t.
R 1 R 2
R = Aryl, Alkenyl, Alkyl
X = Cl, Br
Ph n Bu
Ph n C 10 H 21
Ph
O
O
Ph
Ph
Ph
Ph
Ph
59%
61%
6 7%
83%
1 6%
87%
82%
65%
Scheme 2.46 Fe-, Co-, and Cu-catalyzed oxidative homo- and cross-coupling reactions of
Grignard reagents
Br
R
2) BPh 3 , THF, -75 o C, 1 h
1) BuLi, THF, -75 o C, 1 h
B
R
Li
O 2 , MeCN/CH 2 Cl 2
reflux, 12 h
R
VO(OEt)Cl 2 ( 20 mol%)
NaBAr 4
VO(OEt)Cl 2 ( 20 mol%)
O 2 , MeCN/CH 2 Cl 2
r.t., 20 h
Ar
Ar
Scheme 2.47 V-catalyzed oxidative ligand coupling of organoborates
H. Zhang