10912
H. Kawaguchi et al. / Tetrahedron 62 (2006) 10907–10913
7.58–7.61 (m, 2H), 8.00–8.03 (m, 2H); IR (KBr): n¼
934 cmꢀ1
4.1.6. Hydrolysis of 2. To a suspension of 2 (46.5 mg,
0.15 mmol) in 6 mL of methanol was added 3 mL of 1 M
aqueous KOH solution. After stirring for 2 h at 60 ꢁC, the
solution was neutralized with aqueous ammonium chloride
and extracted with CHCl3. The chloroform layer was washed
with water and dried over anhydrous MgSO4, and removed
at reduced pressure to give 5-iminothianthrene 5-oxide (3,
39.2 mg, 95%) that was recrystallized from acetone–hexane
(colorless crystal). Mp 117–118 ꢁC; 1H NMR (CDCl3):
d¼7.49–7.56 (m, 4H), 7.63–7.67 (m, 2H), 8.12–8.27 (m,
2H); IR (KBr): n¼3292, 1232, 978, 755 cmꢀ1. Anal. Calcd
for C12H9NO2S2: C, 58.27; H, 3.67; N, 5.66. Found: C,
58.11; H, 3.74; N, 5.57.
.
4.1.2. 5-(N-Bromo)iminothianthrene (2). To a solution of
1 (217.2 mg, 0.939 mmol) in 25 mL of acetone, N-bromo-
succinimide (178 mg, 1.13 mmol) in 5 mL of acetone was
added at 5 ꢁC. After 15 min, into the reaction mixture suffi-
cient ice-water was added to form yellow precipitate, that
was collected by filtration, washed with water to remove
the succinimide formed, and dried at reduced pressure to
give 2 (243.4 mg, 84.5%) followed by recrystallization
from CH2Cl2–hexane (yellow crystal). Mp 121–123 ꢁC
1
(dec); H NMR (CDCl3): d¼7.48–7.53 (m, 2H), 7.57–7.66
(m, 4H), 8.00–8.08 (m, 2H); IR (KBr): n¼1437, 881,
757 cmꢀ1. Anal. Calcd for C12H8NOS2Br: C, 46.46; H,
2.60; N, 4.51. Found: C, 46.58; H, 2.60; N, 4.53.
4.1.7. Hydrolysis of cis-5. To a suspension of cis-5
(50.2 mg, 0.15 mmol) in 6 mL of methanol was added 3 mL
of 1 M aqueous KOH solution. After stirring for 1 h at 60 ꢁC,
the solution was neutralized with aqueous H2SO4 and
extracted with CHCl3. The chloroform layer was washed
with water and dried over anhydrous MgSO4, and removed
at reduced pressure to give E-6 (39.2 mg, 97%) that was
recrystallized from EtOAc–hexane (colorless crystal). Mp
225–227 ꢁC; 1H NMR (CDCl3): d¼3.52 (s, 1H), 7.64–7.68
(m, 2H), 7.70–7.75 (m, 2H), 8.11–8.14 (m, 2H), 8.18–8.20
(m, 2H); 13C NMR (CDCl3): d¼124.8, 125.7, 130.3,
132.3, 136.6, 147.2; IR (KBr): n¼3170, 1240, 1095, 1050,
950 cmꢀ1. Anal. Calcd for C12H9NO2S2: C, 54.73; H,
3.44; N, 5.31. Found: C, 54.42; H, 3.26; N, 5.34.
4.1.3. cis-5-(N-Bromo)iminothianthrene 10-oxide (cis-5).
To a solution of cis-410 (203.0 mg, 0.82 mmol) in 34 mL
of CH2Cl2 was added N-bromosuccinimide (173.6 mg,
0.98 mmol) in 17 mL of CH2Cl2 at rt. After 30 min the sol-
vent was removed, and the residue was washed with water.
Yellow crystalline material was dissolved again in CH2Cl2
and dried over anhydrous MgSO4. The solvent was removed
at reduced pressure to give cis-5 (261.0 mg, 97%) that was
recrystallized from CH2Cl2–hexane (yellow crystal). Mp
154–176 ꢁC (dec); 1H NMR (CDCl3): d¼7.80–7.86 (m,
4H), 8.12–8.15 (m, 4H); 13C NMR (CDCl3): d¼125.0,
127.4, 129.4, 130.8, 131.6, 138.7; IR (KBr): n¼1075,
890 cmꢀ1. Anal. Calcd for C12H8NOS2Br: C, 44.18; H,
2.47; N, 4.29. Found: C, 44.14; H, 2.42; N, 4.27.
4.1.8. Hydrolysis of trans-5. To a suspension of cis-5
(50.3 mg, 0.15 mmol) in 20 mL of methanol was added
10 mL of 1 M aqueous KOH solution. After stirring for 4 h
at 60 ꢁC, the solution was neutralized with aqueous H2SO4
and extracted with CHCl3. The chloroform layer was washed
with 3% aqueous H2SO4 and water, and dried over anhy-
drous MgSO4, and removed at reduced pressure and then
the residue was purified by preparative layer chromato-
graphy (silica gel; EtOAc–CHCl3¼1:20) to give E-6
(7.5 mg, 18%), (Z)-5-iminothianthrene 5,10-dioxide (Z-6,
3.0 mg, 7%), and thianthrene 5-oxide (3.5 mg, 10%). Neu-
tralization of aqueous H2SO4 layer gave trans-4 (17.4 mg,
46%). Compound Z-6 (colorless crystal): mp 239–241 ꢁC
(recrystallization from EtOAc–hexane); 1H NMR (CDCl3):
d¼7.66–7.70 (m, 2H), 7.73–7.77 (m, 2H), 8.11–8.15 (m,
4H); 13C NMR (CDCl3): d¼125.1, 126.1, 130.4, 132.5,
136.5, 146.8; IR (KBr): n¼3190, 1240, 1095, 1070,
980 cmꢀ1. Anal. Calcd for C12H9NO2S2: C, 54.73; H,
3.44; N, 5.31. Found: C, 54.34; H, 3.48; N, 5.27.
4.1.4. trans-5-(N-Bromo)iminothianthrene 10-oxide
(trans-5). To a solution of trans-410 (501.1 mg, 2.03 mmol)
in 34 mL of CH2Cl2 was added N-bromosuccinimide
(432.8 mg, 2.43 mmol) in 23 mL of CH2Cl2 at rt. After
30 min the solvent was removed, and the residue was washed
with water. Yellow crystalline material was dissolved again
in CH2Cl2 and dried over anhydrous MgSO4. The solvent
was removed at reduced pressure to give trans-5 (591 mg,
89%) that was recrystallized from CH2Cl2–hexane (yellow
crystal). Mp 168–177 ꢁC (dec); 1H NMR (CDCl3): d¼
7.71–7.75 (m, 2H), 7.81–7.86 (m, 2H), 8.04–8.06 (m, 2H),
8.24–8.26 (m, 2H); 13C NMR (CDCl3): d¼129.8, 130.1,
131.4, 132.4, 136.2, 140.7; IR (KBr): n¼1025, 885 cmꢀ1
.
Anal. Calcd for C12H8NOS2Br: C, 44.18; H, 2.47; N, 4.29.
Found: C, 44.16; H, 2.16; N, 4.40.
4.1.5. 5-(N-Bromo)iminothianthrene 10,10-dioxide (8).
To a solution of 711 (150.7 mg, 0.57 mmol) in 5 mL
of CH2Cl2 was added N-bromosuccinimide (123.4 mg,
0.69 mmol) in 14 mL of CH2Cl2 at rt. After 30 min the sol-
vent was removed, and the residue was washed with water.
Yellow crystalline material was dissolved again in CH2Cl2
and dried over anhydrous MgSO4. The solvent was removed
at reduced pressure to give 8 (182.0 mg, 93%) that was
recrystallized from CH2Cl2–hexane (yellow crystal). Mp
180–190 ꢁC (dec); 1H NMR (CDCl3): d¼7.79–7.83 (m,
2H), 7.87–7.91 (m, 2H), 8.17–8.19 (m, 2H), 8.24–8.27 (m,
2H); 13C NMR (CDCl3): d¼126.2, 128.3, 131.4, 133.0,
136.1, 139.4; IR (KBr): n¼1320, 1165, 890 cmꢀ1. Anal.
Calcd for C12H8NO2S2Br: C, 42.11; H, 2.35; N, 4.09. Found:
C, 42.17; H, 2.06; N, 4.14.
4.1.9. Hydrolysis of 8. To a suspension of 8 (50.8 mg,
0.15 mmol) in 14 mL of methanol was added 7 mL of 1 M
aqueous KOH solution. After stirring for 4.3 h at 60 ꢁC,
the solution was neutralized with aqueous sulfuric acid
and extracted with CHCl3. The chloroform layer was washed
with 3% aqueous H2SO4 and water and dried over anhydrous
MgSO4, and removed at reduced pressure and then the resi-
due was purified by preparative layer chromatography (silica
gel; EtOAc–Hexane¼1:1) to give 9 (13.0 mg, 31%) and
thianthrene 5,5-dioxide (3.6 mg, 10%). Neutralization of
aqueous H2SO4 layer gave 7 (18.9 mg, 48%). Compound 9
(colorless crystal): mp 262–266 ꢁC (dec); 1H NMR
(CDCl3): d¼7.77–7.84 (m, 4H), 8.24–8.27 (m, 2H), 8.28–
8.30 (m, 2H); 13C NMR (CDCl3): d¼125.7, 125.8, 133.0,