78
X. Feng et al.
Table 2.37 Asymmetric transfer hydrogenations of imines
Ar
Me
N
Ar'
Ar
Me
HN
Ar'
HB(C 6 F 5 ) 2 10 (10 mol %)
9h (5 mol %)
N
H
Me
Me
COOEt
EtOOC
3
5
80
entry product
yield (%) ee (%)
1
5a
Ph
Me
HN
Ph
89
38
2
5q
Me
HN
Ph
MeO
95
24
3
5u
Me
HN
Ph
F
98
37
4
5c
Me
HN
Ph
F 3 C
98
33
5
5y’
Ph
Me
HN
Me
95
16
in combination with several different bases, such as 1,2,2,6,6-pentamethyl piperidine and Barton’s base, the aminocarbonyl products were afforded in 35–98%
yields (Table 2.38). Both acyclic and cyclic ketones, esters, amides, thioesters and
thioamides could serve as suitable nucleophiles. With N-trifluoroacetyl-substituted
(1R,2R)-(+)-1,2-diphenylethylenediamine derivative 84 as chiral base, the enantioselective variant of the reaction was also efficiently processed to furnish the desired
products in 47–95% yields with up to 98% ee (Table 2.39).
The catalytic reaction may function through the following process: the boron
Lewis acid coordinated to carbonyl pro-nucleophiles to increase the acidity of the