72
X. Feng et al.
Table 2.32 Asymmetric synthesis of 1,2,3,4-tetrahydroquinoxalines and 3,4-dihydroquinoxalin2(1H)-ones
NH 2
NH 2
+
R
OEt
O
O
H
N
N
H
R
HB(C 6 F 5 ) 2 10
chiral diene 9f
O
Ph 2 SiH 2
(1.5 or 4.0 equiv)
72
73
74 or 75
entry product
yield (%) ee (%)
1
74a
H
N
N
H
Me
87
47
2
74d
H
N
N
H
Ph
83
76
3
74h
H
N
N
H
Bn
88
58
4
75a
H
N
N
H
Me
O
89
58
5
75b
H
N
N
H
Ph
O
85
87
6
75c
H
N
N
H
Bn
O
90
70
LB
LA
LA
H
LB
H
substrate
product
Classic FLPs
hydrogen
source
LB
LA
LA
LB
H
δ
δ
H
novel FLP
substrate
product
Fig. 2.4 Novel FLPs designed for asymmetric catalysis