C O M M U N I C A T I O N S
Scheme 4. Synthesis of 2-Ethyl-1,2,3,4-tetrahydroquinoxaline
Scheme 5. Proposed Mechanism of Regioselective Cycloaddition
Table 1. 3,4-Dihydroquinoxalin-2-one Productsa
entry
R1
R2
R3
% ee
% yield
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
4r
4s
Cl
Cl
Cl
Cl
Cl
Cl
H
H
Cl
Cl
Cl
Cl
Cl
Cl
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Et
i-Pr
CH2SMe
(CH2)3Cl
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
>99
82
79
84
81
85
93
76
71
73
83
81
79
83
77
78
84
84
84
92
87
86
90
69
72
In conclusion, we have demonstrated a highly enantioselective
bifunctional catalyst system for the cycloaddition of quinoxalinones
from o-benzoquinone diimides and acid chlorides. The highly
biologically active cycloadducts will be useful scaffolds for drug
development and are useful synthetic intermediates as well.
Bn
CH2phthalimide
Et
i-Pr
i-Bu
Bn
Et
i-Pr
i-Bu
Bn
p-Br-Bn
Et
i-Pr
i-Bu
CH2SMe
(CH2)3Cl
Bn
CH2phthalimide
p-Br-Bn
p-Br-Bn
9
H
H
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24*
CF3
CF3
CF3
CF3
CF3
COPh
COPh
COPh
COPh
COPh
COPh
COPh
COPh
COPh
Acknowledgment. T.L. thanks the NIH (Grant GM064559),
the Sloan and Dreyfus Foundations, and Merck & Co. for support.
Supporting Information Available: Procedures and compound
characterization. This material is available free of charge via the Internet
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4t
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