4936
Y. Zhang et al. / Tetrahedron 69 (2013) 4933e4937
4H), 7.03 (d, J¼9.2 Hz, 4H), 3.91 (s, 6H); 19F NMR (CDCl3, 376 MHz)
(CDCl3, 400 MHz): d 1.60 (s, 9H), 2.35 (s, 3H), 3.79 (s, 3H), 6.89
d
ꢀ37.43 (s, 1F).
(t, J¼2.4 Hz, 1H), 7.01 (dt, J¼9.0, 2.4 Hz, 1H), 7.20 (d, J¼8.4 Hz, 2H),
7.25 (d, J¼8.6 Hz, 2H), 7.92 (dd, J¼9.0, 1.4 Hz, 1H); 19F NMR (CDCl3,
4.2.3. N-Fluoro-p-tert-butylbenzenesulfonimde (1d). White crystal,
376 MHz):
d
ꢀ145.35 (s, 1F); HPLC: (OD-H, hexane/i-PrOH¼99:1,
mp 149.5e150.3 ꢁC; 1H NMR (CDCl3, 400 MHz)
d
7.95 (d, J¼8.8 Hz,
0.5 mL/min, 254 nm), tR (R-isomer)¼14.5 min, tR (S-isomer)¼
4H), 7.61 (d, J¼8.8, 4H), 1.36 (s, 18H); 19F NMR (CDCl3, 376 MHz)
16.8 min.
d
ꢀ36.43 (s, 1F).
4.3.5. (S)-N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-2-oxindole
4.2.4. N-Fluoro-p-trifluoromethylbenzene
sulfonimide(1e). White
(3e). White solid; mp: 71e73 ꢁC; 1H NMR (CDCl3, 400 MHz)
d 1.62
crystal, mp 127.9e128.6 ꢁC; 1H NMR (CDCl3, 400 MHz)
d
8.17 (d,
(s, 9H), 7.27 (d, J¼6.0 Hz, 1H), 7.29e7.40 (m, 6H), 7.51e7.53 (m, 1H),
J¼8.4 Hz, 4H), 7.92 (d, J¼8.4 Hz, 4H); 19F NMR (CDCl3, 376 MHz)
8.01 (d, J¼8.4 Hz, 1H); 19F NMR (CDCl3, 376 MHz)
ꢀ145.37 (s, 1F);
d
d
ꢀ36.00 (s, 1F), ꢀ63.51 (s, 6F).
HPLC: (Lux 5u Cellulose-4, hexane/i-PrOH¼98:2, 0.7 mL/min,
25
214 nm), tR (S-isomer)¼9.2 min, tR (R-isomer)¼10.3 min; [
a]
D
25
4.2.5. N-Fluoro-p-trifluoromethoxylbenzenesulfonimide (1f). White
þ78.4 (c 0.900, CHCl3) 96% ee, S; lit.4a
87% ee, S.
[
a
]
þ82.9 (c 0.450, CHCl3)
D
crystal, mp 81.5e82.4 ꢁC; 1H NMR (CDCl3, 400 MHz)
d 7.86 (d,
J¼8.8 Hz, 4H), 7.76 (d, J¼8.8 Hz, 4H); 19F NMR (CDCl3, 376 MHz)
d
ꢀ36.23 (s, 1F), ꢀ57.65 (s, 6F).
4.3.6. (S)-N-tert-Butoxycarbonyl-3-fluoro-3-phenyl-5-methyl-2-
oxindole (3f). White solid; mp: 126e128 ꢁC; IR (KBr): 2922, 2854,
4.3. General procedure for the catalytic enantioselective
1781, 1734, 1597, 1490, 1371, 1332, 1277, 1250, 1151, 1124 cmꢀ1 1H
;
fluorination of oxindole
NMR (CDCl3, 400 MHz) d 1.61 (s, 9H), 2.36 (s, 3H), 7.17 (s, 1H), 7.30
(d, J¼8.6 Hz, 1H), 7.34e7.40 (m, 5H), 7.87 (d, J¼8.4 Hz, 1H); 13C NMR
(DHQD)2PHAL (5 mol %) and NFSI analogues (1.2 equiv) in CH3CN/
CH2Cl2 (v/v¼3:4, 1.5 mL) were stirred under argon atmosphere at
room temperature for 30 min. K2CO3 (6.0 equiv) was then added to
the solution, and the reaction mixture stirred for 30 min at ꢀ80 ꢁC. A
solution of oxindole 2aeh (0.148 mmol) in CH3CN/CH2Cl2 (v/v¼3:4,
1 mL) was added to the above solution. The solution was stirred at
the temperature for 1.5e4 days with monitoring by TLC, and it was
stopped by the addition of water. The reaction mixture was then
diluted with AcOEt, washed with 2 N HCl, saturated aqueous sodium
bicarbonate solution, brine, dried over Na2SO4, and the solvent was
evaporated under reduced pressure. The residue was purified by
column chromatography on silica gel to give 3aeh.4a The ee of the
products 3aeh was determined by chiral HPLC on CHIRALCEL OD-H
or Phenomenex Lux 5u Cellulose-1 column.
(CDCl3, 100 MHz):
d
169.4 (d, J¼24.9 Hz), 147.9, 137.5 (d, J¼5.2 Hz),
134.7 (d, J¼27.6 Hz), 134.2 (d, J¼2.7 Hz), 131.3 (d, J¼3.5 Hz), 127.6,
125.6, 125.1 (d, J¼6.0 Hz), 124.5 (d, J¼17.6 Hz), 114.4, 91.8 (d,
J¼186.5 Hz), 83.8, 28.7, 26.0, 19.9; 19F NMR (CDCl3, 376 MHz)
d
ꢀ145.64 (s, 1F); MS (EI): m/z (%) 341 (Mþ, 3), 212 (59), 241 (100).
HRMS (EI) calcd for C20H20FNO3: 341.1427, found: 341.1425; HPLC:
(Lux 5u Cellulose-4, hexane/i-PrOH¼80:20, 0.4 mL/min, 214 nm), tR
25
(S-isomer)¼13.4 min, tR (R-isomer)¼14.0; [
a
]
þ69.9 (c 0.500,
D
CHCl3) 86% ee.
4.3.7. (S)-N-tert-Butoxycarbonyl-3-fluoro-3-(4-fluorophenyl)-5-
methyl-2-oxindole (3g). Oil; 1H NMR (CDCl3, 400 MHz)
1.61
d
(s, 9H), 2.37 (s, 3H), 7.07 (d, J¼8.5 Hz, 2H), 7.17 (s, 1H), 7.30e7.37 (m,
3H), 7.87 (d, J¼8.4 Hz, 1H); 19F NMR (CDCl3, 376 MHz)
d
ꢀ111.71
(s, 1F), ꢀ143.17 (s, 1F); HPLC: (AD-H, hexane/i-PrOH¼98:2, 0.7 mL/
20
4.3.1. (S)-N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-5-
methyl-2-oxindole (3a). White solid; mp: 110e112 ꢁC; 1H NMR
min, 214 nm), tR (S-isomer)¼8.7 min, tR (R-isomer)¼9.3 min; [
a]
D
þ95.7 (c 0.750, CHCl3) 94% ee, S; lit.3g
ee, S.
[
a]
25 þ78.6 (c 0.87, CHCl3) 98%
D
(CDCl3, 400 MHz)
d
1.53 (s, 9H), 2.28 (s, 6H), 7.10 (d, J¼4.0 Hz, 2H),
7.13e7.23 (m, 4H), 7.79 (d, J¼8.8 Hz, 1H); 19F NMR (CDCl3, 376 MHz)
d
ꢀ144.9 (s, 1F); HPLC: (OD-H, hexane/i-PrOH¼99:1, 0.9 mL/min,
4.3.8. (S)-N-tert-Butoxycarbonyl-3-fluoro-3-(4-fluorophenyl)-2-ox-
indole (3h). Oil; 1H NMR (CDCl3, 400 MHz)
1.62 (s, 9H), 7.08 (d,
254 nm), tR (R-isomer)¼5.99 min, tR (S-isomer)¼7.33 min.
d
2H, J¼8.4 Hz), 7.28e7.30 (m, 1H), 7.34e7.37 (m, 3H), 7.53 (tt, 1H,
4.3.2. (S)-N-tert-butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-2-
oxindole (3b). White solid; Mp: 90e92 ꢁC; 1H NMR (CDCl3,
J¼1.8, 7.8 Hz), 8.01 (d, 1H, J¼8.4 Hz); 19F NMR (CDCl3, 376 MHz)
d
ꢀ111.53 111.54 (s, 1F), ꢀ142.95 (s, 1F); HPLC: (Phenomenex Lux 5u
400 MHz)
d
1.61 (s, 9H), 2.35 (s, 3H), 7.19 (d, J¼8.4 Hz, 2H),
Cellulose-1, hexane/i-PrOH¼96:4, 1.0 mL/min, 230 nm), tR (R-iso-
mer)¼4.23 min, tR (S-isomer)¼4.82 min.
7.26e7.28 (m, 1H), 7.25 (d, J¼7.9 Hz, 2H), 7.37 (d, J¼7.6 Hz, 1H),
7.48e7.52 (m, 1H), 8.00 (d, J¼8.2 Hz,1H); 19F NMR (CDCl3, 376 MHz)
d
ꢀ144.55 (s, 1F); HPLC: (OD-H, hexane/i-PrOH¼99:1, 0.5 mL/min,
4.4. The procedure for electrochemical measurement of the
fluorinating ability of NeF fluorinating reagents by cyclic
voltammetry
254 nm), tR (R-isomer)¼11.16 min, tR (S-isomer)¼13.16 min.
4.3.3. N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-5-fluoro-
2-oxindole (3c). White solid; mp: 132e133 ꢁC; IR (KBr): 2962, 1784,
4.4.1. Cells and electrodes. Working electrodes for cyclic voltam-
metry were a platinum disk electrodes with an area of 2 cm2
(purchased from Tianjin Aidahongsheng Technology Co. Ltd), the
auxiliary electrode was a coiled platinum wire, and the reference
electrode was a AgjAgCl reference (silver wire in contact with
AgClþsaturated KCl aqueous solution). All electrodes for voltam-
1730, 1489, 1344, 1297, 1261, 1156, 878, 810 cmꢀ1 1H NMR (CDCl3,
;
400 MHz)
d
1.60 (s, 9H), 2.36 (s, 3H), 7.08e7.10 (m, 1H), 7.21e7.26
168.9 (d,
(m, 5H), 8.01 (m, 1H); 13C NMR (CDCl3, 100 MHz):
d
J¼25.0 Hz), 160.3 (dd, J¼160.3, 31.5 Hz), 147.9, 138.9 (d, J¼1.6 Hz),
135.8 (dd, J¼5.3, 2.7 Hz), 131.2, 130.9, 126.2 (dd, J¼56.0, 8.0 Hz),
125.1 (d, J¼5.7 Hz), 117.4 (dd, J¼22.8, 2.9 Hz), 116.2 (d, J¼7.2 Hz),
112.5 (d, J¼24.6 Hz), 92.3 (dd, J¼188.3, 1.7 Hz), 84.2, 28.7, 27.0, 20.2;
metry were polished for 5 min prior to use with 50e75 mm silica gel
in acetonitrile. The cells used in these experiments were some
100 mL glass flasks.
19F NMR (CDCl3, 376 MHz)
d
ꢀ145.66 (s,1F), ꢀ116.08 (s,1F); MS (EI):
m/z (%): 359 (Mþ, 2), 230 (20), 244 (21), 258 (20), 259 (100). HRMS
(EI) calcd for C20H19F2NO3: 359.1333, found: 359.1335.
4.4.2. Experimental procedure. In a 100 mL three-neck flask was
added Bu4NF4 acetonitrile solution (0.1 M, 30 mL), a platinum disk
working electrode, a coiled platinum wire auxiliary electrode, and
a AgjAgCl reference electrode were inserted into the solution, and
4.3.4. (S)-N-tert-Butoxycarbonyl-3-fluoro-3-(4-methylphenyl)-5-
methoxy-2-oxindole (3d). White solid; mp: 128e130 ꢁC; 1H NMR