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Topics in Current Chemistry (2019) 377:37
the photocatalyst was firstly reduced by the excited Ir(III) complex. In order to
show the synthetic utility, a chiral benzopiperazine compound was constructed
through an operationally simple palladium-catalyzed intramolecular amination
in 77% yield with 98% ee (Scheme  20). Later in 2016, they reported the same
reaction but with a different catalytic cycle that undergoes the initial reduction
of aldimines enabled by Ir(ppy) 3 (PC-3) [23].
In 2016, the Bach group reported an stereoselective radical addition reaction of 3-alkylidene indolin-2-ones induced by visible light [24]. Because of the
defined site selectivity, a silylated amine was selected as a radical source. This
protocol uses [Ru(bpy) 3 (BArF) 2 ] (PC-9) as the photosensitizer and hydrogenbonding template organocatalyst OC-16 under low temperature condition. Thus,
a mixture of diastereoisomeric products is produced with moderate enantioselectivities (Scheme 21).
N Ar
R
OMe
OTBS
N Ar
R
MeO 2 C
PC-1 (1 mol%)
CCl 4 , MeCN, blue LEDs, 16 h
then OC-16 (20 mol%)
MTBE, 16 h, -60
o C
up tp 72% yield, 99% ee
+
N
N
N
N
N
N
Ru
PC-1
(Cl
- ) 2
N
H
N
H
S
CF 3
CF 3
tBu
N
O
S
N
H
R*
N
H
S
R*
X
R
1
N
R
2
R
3
48
49
47
OC-16
Scheme 18 Asymmetric synthesis of β-amino esters
R
N
H
N
H
Cbz
PC-3 (0.5 mol%)
OC-17 (3 mol%)
TEMPO (2 eq.),
TIPS-EBX (1.5 eq.)
0.05 M THF, blue LEDs, rt
up to 81% yield, 93% ee
Ar
O
Ar
O
P
O
O
Ar = 2,4,6-(i-Pr) 3 C 6 H 2
OC-17
R
N
H
N Cbz
O
N
H
NBu 4
TIPS
I
O
O
TIPS-EBX
N
N
H
Cbz
H O
P
O
OR'
OR'
one electron
oxidation
R
N
H
N Cbz
Nu
H
Nu
-
50
51
52
Scheme 19 Enantioselective synthesis of pyrroloindolines products
Reprinted from the journal
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