Article
Reference
Expanded Chiral Surfaces for Asymmetric Anion–π Catalysis
AKAMATSU, Masaaki, MATILE, Stefan
Abstract
The insertion of a π-acidic surface of a naphthalenediimide (NDI) between a proline and a glutamate group affords trifunctional catalysts for the stereoselective addition of aldehydes to nitroolefins. In this report, phenyl sulfides are added to this central NDI surface. Oxidation of the sulfide donors into sulfoxide and sulfone acceptors increases both rate and stereoselectivity of the reaction. This dependence on π acidity provides corroborative support that anion–π interactions can contribute to asymmetric catalysis. Non-planar π surfaces around chiral sulfoxide connectors have a profound impact on stereoselectivity. Anti stereoisomers, with phenyl wings pointing in opposite directions from the central NDI surface, perform best in chloroform/methanol mixtures. With stronger anion–π interactions in more hydrophobic aromatic solvents, this trend inverts. Catalysis within π-box binding pockets between the two phenyl wings in syn architectures gives better selectivity under these conditions. The best results are obtained in toluene, whereas competitive π–π interactions with aromatic solvents of varied π [...]
AKAMATSU, Masaaki, MATILE, Stefan. Expanded Chiral Surfaces for Asymmetric Anion–π Catalysis. Synlett , 2016, vol. 27, no. 07, p. 1041-1046
DOI : 10.1055/s-0035-1561383
Available at:
http://archive-ouverte.unige.ch/unige:83528
Disclaimer: layout of this document may differ from the published version.
1 / 1
σ cation-π
interactions
anion-π interactions
asymmetric anion-π catalysis Qzz < 0
(HOMO)
Qzz > 0 (LUMO)
-
-
+
++
+
+
-
-
+
-+
-
-
+
N
N N
O O
O O
O O O H N+
O- O
Et O
Ph NO2 +
O Ph NO2
1 2 Et 3
* *
O O H N+ O- R2
O R1
S+
-O S
N
N N
O O
O O O
N H
H N O
O OH
N O- H
O R1 R2 H
+
S+ -O
N
N N
O O
O O O
N H
HN O
catalyst
TS1 TS2
6: R = C2H5 9: R = C6H5 RO2S
SO2R O
OH
HN
N N
O O
O O O
N H
HN O
5: R = C2H5 8: R = C6H5 ROS
SOR O
OH
HN
N N
O O
O O O
N H
HN O
S+O- S
S+ O- R
S+ O-
S+
-O S
O OH
HN
N N
O O
O O O
N H
HN O
R S+O-
S R
S
S
R O
OH
HN
N N
O O
O O O
N H
HN O
S+ -O S
R
S
S -O S+S
O OH
HN
N N
O O
O O O
N H
HN O
S
R O
OH
HN
N N
O O
O O O
N H
HN O
S+ -O 4: R = C2H5
7: R = C6H5 RS
SR O
OH
HN
N N
O O
O O O
N H
HN O
ox ox
(Fn)-8
syn
F2 F3
anti
F4 F1
3S 1R
2S
4S
5R/S 6S/R
∆
∆ A
δ (ppm) 8.1 8.0 7.9
B
δ (ppm) 8.1 8.0 7.9
C
δ (ppm) 8.1 8.0 7.9
λ (nm)
300 400 500
0 +25 +50
-25 -50
∆ε (M-1cm-1)
350 450 550
t (min)
36 39 42 45
B anti
syn
t (min)
40 45 50
A
Mahlau, M.; List, B. Angew. Chem. Int. Ed. 2013, 52, 518- 533. Lacour, J.; Moraleda, D. Chem. Commun
Matile, S.
Matile, S.
Matile, S.
To a solution of the Boc/tBu protected precursor of 7 (50 mg, 0.048 mmol) in CH2Cl2 (25 mL), mCPBA (23 mg, 0.11 mmol) was added at 0 oC. The mixture was stirred for 7 h at 0 oC. The resulting mixture was subjected to liquid/liquid extraction with aqueous Na2S2O3 (10%,
30 mL), brine (10 mL), dried over Na2SO4 and concentrated in vacuo.
Stereoisomers were separated by silica gel column chromatography (CH2Cl2/EtOAc 3:1; Rf (CH2Cl2/EtOAc 3:1): 0.35 (F1), 0.25 (F3), 0.15 (F2 + F4)) and then semi-preparative HPLC (CHIRALPAK ID, 250 mm x 10 mm, Daicel, CH2Cl2/isopropanol 90:10, 3 mL/min and detection at λabs = 450 nm). The retention times of four Boc/tBu protected precursors of isomers (F1)-8, (F2)-8, (F3)-8 and (F4)-8 were 5.1 min, 7.5 min, 20.2 min and 22.5 min, respectively.
Deprotection of the pure fractions in TFA (1 mL) and CH2Cl2 (1 mL, 2 h, rt) gave the corresponding (Fn)-8 (TFA salts, quantitative) as yellow solids. (F3)-8:
∆
