Angewandte Fluororganische Chemie: Synthese ... - Fluorine

Alkoxydifluorodesulfuration of sec-Alkyldithianylium Salts
Proposed Mechanism
H 11 C 5
H 11 C 5
R
R 1
R 1
R 1
R 1
R 1
R 1
S
S
+ "Br +"
S
S +
Br
+ F -
F
S
F
S +
+ "Br +"
S +
Br
+ F -
F
F
S
S
R 1
S
S
+
R 1
- H +
+ R2O- + H + + R2O- SiMe 3
S
S
- H +
SBr
SBr
SBr
O
R 1
H
S
S
+
+ "Br +"
S +
S +
Br
NEt 3 . 3HF,
DBH
R 1
+ R2O- R 1
R 1
R 1
R 1
H 11 C 5
1. CF3SO3H H11C5 2. HOPh, NEt3 3. NEt .
3 3HF
4. DBH
H +
R
R
S
S
+ "Br +"
OR 2
S
S
+
OR 2
Br
S +
OR 2
+ F -
F
S
OR 2
+ "Br +"
S + F
Br
OR 2
+ F-
F
F
OR 2
SBr
SBr
SBr
S +
S
F
F
F
F
O
S +
S
F
F
F
R CF 2 O F
R CF 2 O F
P. KIRSCH: Angewandte fluororganische Chemie: Synthese, Pharmazeutika, Flüssigkristalle 48
HO
CCl3 R CF2O CF3 R CF2O R CF 2 O F
F
HO
F
F
R
R CF 2 O
4.6. Brücken innerhalb des mesogenen Grundkörpers:
H 7 C 3
H 7 C 3
Die Tetrafluorethylenbrücke
Liquid Crystals with a CF 2 CF 2 Bridge
First Synthesis
O
OEt
F
F
O
37%
1. Na, Me 3 SiCl,
toluene; 40°C
2. NH 4 NO 3 , HOAc,
cat. Cu(OAc) 2 ;
reflux
13%
C 3 H 7
H 7 C 3
DAST (neat),
cat. ZnI 2 ; 60°C
O
H 7 C 3
O
16%
C 3 H 7
SF 4 , cat. HF, CH 2 Cl 2 ;
70°C, 2 d
F
F
F F
C 3 H 7
Merck KGaA – Liquid Crystal Research
O
F
F
F
HOCH 2CCl3
HO
HOCH 2CF3
HO
F
F
S +
S
F
F
F
F
R CF2O OCF3 F
F
F
F
HO
F
HO
CF 3 SO 3 -
CF 3
HO
OCF 3
HO
R CF 2 O OCF 3
HO
COOEt
CN
OCF 3
R CF 2 O CF 3
F
R CF 2 O CN
CF 2 O COOEt
• after addition of nucleophil:
NEt 3 •3HF, “Hal + ” (Br 2 , NBS, NIS);
-78ºC → room temp.
The Difluorooxymethylene (CF 2 O) Bridge
• Insertion of a CF 2 O bridge in liquid crystals results in
• higher clearing points (T NI )
• higher dielectric anisotropy (Δε)
• lower birefringence (Δn)
• lower rotational viscosity (γ 1 )
• improved voltage holding ratio (VHR) and specific resistivity
• In situ oxidative fluorodesulfuration of dithioorthoesters
allows fast and easy large-scale synthesis of any CF 2 O
bridged liquid crystals
• Dithianylium salts are a convenient and readily accessible
synthon for the one-pot synthesis of aromatic and aliphatic
α,α-difluoroethers
Br
1.
H C 7 3
88%
F
O
F
F
1. Mg, THF
2. O
O
O
3. cat. H2SO4 ,
toluene; -H2O F
O
F
PPh 3 +Br-
F
H 7 C 3
LDA, THF;
-10°C to room temp.
2. MePhSO 2 Na, HCl,
toluene; reflux
75%
H 7 C 3
1. DMSO, (CF 3 CO) 2 O,
CH 2 Cl 2 ; -60°C
2. NEt 3 ; -60 to 5°C
O
O
MeO
MeOCH 2 PPh 3 + Cl - , KOtBu,
THF; -10°C to room temp.
F
F
F
F
F
55%
H2 , 5% Pd-C,
THF
O
O
F
95%
F
HCOOH,
toluene
F
F
F
F
F
F
53%
F
OHC
1. HCOOH,
F
toluene
2. cat. NaOH,
MeOH
OH
65% H7C3 NMO, cat. OsO 4 ,
H 2 O, dioxane; reflux
17%
SF 4 , cat. HF, CH 2 Cl 2 ;
-196 to 120°C, 2 d
H 7 C 3
HO
F
F
F F
Merck KGaA – Liquid Crystal Research
F
F
F
• 9 steps
• 2% overall yield
F
F
F
F
F
F
F