Morita et al.
TABLE 4. Photolysis of 3a-d in the Presence of Several Olefins
in the photolyses, and the relatively high yields for the desired
trans-iminated product under photolytic conditions, diben-
zohiophene sulfilimines were found to be very useful and
versatile photolytic nitrene precursors.
We are now further continuing the study of the scope and
limitations and the application for the introduction of an
imino group to a variety of organic compounds under
photolyses. Particularly, we are interested in introducing an
imino group into fullerene molecules.
yield (%)a
entry
R1
Ts
Ts
Ts
Ts
Ts
COPh
COBn
COtBu
R2
R3
product
1
10
9
1
2
3
4
5
6
7
8
-(CH2)3-
-(CH2)4-
-(CH2)6-
10a
10b
10c
10d18
10e
10g
10h
10i
85
94
93
98
88
94
85
93
57
60
66
34
31
60
57
66
13
22
10
30
0
22
13
10
4. Experimental Section
nBu
H
-(CH2)3-C(O)-
N-(2-Phenylacetyl)iminodibenzothiophene (3c). To a solution
of dibenzothiophen-S-oxide (1) (100 mg, 0.5 mmol) in aceto-
nitrile (3.0 mL) was added trifluoroacetic anhydride (315 mg,
1.5 mmol) then the reaction was stirred for 10 min at -30 °C
and 2-phenylacetamide (202 mg, 1.5 mmol) was added. NaOH
(0.1 N, aq) was poured into this mixture, then the mixture was
evaporated in vacuo. The reaction mixture was extracted with
CH2Cl2 (2 × 20 mL) and NaOH aq, then the organic layer was
dried over MgSO4, filtered, and evaporated in vacuo. Compound
3c was purified by chromatography on silica with EtOAc/hexane.
Yield 128 mg, 80%; mp 133-135 °C (from CH2Cl2-hexane),
-(CH2)4-
-(CH2)4-
-(CH2)4-
a Isolated yields; not optimized.
TABLE 5. Photolysis of 3a-d in the Presence of Trivalent
Phosphorus Compound
ν
max (KBr)/cm-1 751, 1131, 1291, 1307, 1333, 1426, 1491, 1556,
1599, 2927, 3030; 1H NMR (400 MHz) δ 3.73 (2H, s),
7.20-7.39 (5H, m), 7.50 (2H, dt, J ) 7.6, 0.8 Hz), 7.63 (2H,
dt, J ) 7.6, 0.8 Hz), 7.88 (2H, d, J ) 8.0 Hz), 8.12 (2H, d, J )
8.0 Hz); 13C NMR (100 MHz) δ 43.8, 122.2, 126.2, 128.2, 128.6,
129.2, 129.8, 132.3, 137.1, 137.7, 138.2, 183.9. Anal. Calcd for
C20H15NOS: C, 75.68; H,4.76; N, 4.41. Found: C, 75.93; H, 4.78;
N, 4.40. LR-MS (M - 91) 226.
N-(Pivaloyl)iminodibenzothiophene (3d). To a solution of
dibenzothiophen-S-oxide (1) (100 mg, 0.5 mmol) in acetonitrile
(3.0 mL) was added trifluoroacetic anhydride (210 mg, 1.0 mmol)
then the reaction was stirred for 10 min at -30 °C and
pivalamide (75 mg, 0.75mmol) was added. NaOH (0.1 N) was
poured into this mixture, which was then evaporated in vacuo.
The reaction mixture was extracted with CH2Cl2 (2 × 20 mL)
and NaOH aq, then the organic layer was dried over MgSO4,
filtered, and evaporated in vacuo. Compound 3d was purified
by chromatography on silica gel with EtOAc/hexane. Yield 33.6
mg, 24%; mp 142-144 °C (from EtOAc-hexane), νmax (KBr)/
cm-1 735, 757, 1195, 1308, 1447, 1476, 1536, 2859, 2922, 2947;
1H NMR (400 MHz) δ 1.24 (9H, s), 7.51 (2H, t, J ) 7.2 Hz),
7.63 (2H, t, J ) 7.6 Hz), 7.90 (2H, d, J ) 8.0 Hz), 8.12 (2H, d,
J ) 8.0 Hz); 13C NMR (100 MHz) δ 28.7, 40.1, 122.1, 128.4,
129.6, 132.0, 138.1, 138.5, 192.1. Anal. Calcd for C17H17NOS:
C, 72.06; H, 6.05; N, 4.94. Found: C, 72.34; H, 6.09; N, 5.06.
LR-MS (M+ - 57) 226.
yield (%)a
11
entry
R1
R2
Ph
EtO
PhO
Ph
product 11
2a
9
1
2
3
4
5
6
Ts
Ts
Ts
11a
11b
11c
11d
11e
11f
>99
94
>99
95
90
86
77
64
60
64
24
53
8
4
9
0
0
0
PhC(O)
BnC(O)
tBuC(O)
Ph
Ph
a Isolated yields; not optimized.
In the photolyses of 3a in the presence of triphenyl phosphine,
iminophosphorane 11a was formed in 77% yield as a sole
product besides dibenzothiophene and 9 (entry 1). In the
presence of triphenyl phosphite or triethyl phosphite, the
photolyses of 3a gave 11b,c25 and dibenzothiophene 2a in
almost the sameyields (entries 2 and 3). The photolysis of 3b
and 3d in the presence of triphenyl phosophine gave 11d,25 11f
in slightly low yields compared with those of tosyl sulfilimine
3a (entry 1). In the case of N-phenylacetylsulfilimine 3c, the
reaction gave a complex mixture and the yield of 11e was low
(entry 5).
4-Methyl-5-N-(p-toluenesulfonyl)iminodibenzothiophene (6a). To
a solution of (N-tosyl)iminophenyliodinane (1160 mg, 3.11
mmol) in CH3CN was added compound 2b (560 mg, 2.82 mmol)
and tetrakis(acetonitrile)copper(I) hexafluorophosphate (105.2
mg, 0.282 mmol). This reaction mixture was allowed to stand
for 75 min at 0 °C under N2 atmosphere. Compound 6a was
purified by chromatography on silica with EtOAc/hexane (2/1).
Yield 52%, mp 185-186 °C; νmax (KBr)/cm-1 930, 1141, 1300,
2923, 3016, 3058; 1H NMR (400 MHz) δ 2.38 (3H, s), 2.41
(3H, s), 7.19-7.23 (3H, m), 7.41 (1H, dt, J ) 7.2, 1.2 Hz),
7.53 (1H, t, J ) 8.0 Hz), 7.59-7.63 (2H, m), 7.70 (1H, t, J )
3. Conclusion
We have presented the syntheses of dibenzothiophene
N-substituted sulfilimines and demonstrated that their pho-
tolysis proceeded smoothly in DCE in the presence of
trapping reagents, such as sulfides, olefins, and phosphorus
compounds, to afford the corresponding imino-transfer
products, namely sulfilimines, aziridines, and iminophospho-
ranes, in good yields. It is suggested that the driving force
of preferential S-N bond cleavage is due to the regaining
of resonance energy by releasing imino substituents on sulfur,
as mentioned earlier. In conclusion, in view of the easy
preparation of the precursors, the recyclable use of 3 formed
7.6 Hz), 7.74 (2H, d, J ) 8.4 Hz), 7.83 (2H, d, J ) 8.4 Hz); 13
C
NMR (100 MHz) δ 18.8, 21.5, 120.1, 122.4, 126.7, 127.4, 129.2,
129.9, 130.1, 131.5, 132.8, 133.3, 137.6, 137.8, 137.9, 139.7,
140.9, 142.0. Anal. Calcd for C20H17NO2S2: C, 65.37; H, 4.66;
N, 3.81. Found: C, 64.91; H, 4.67; N, 3.81.
4-Phenyl-5-N-(p-toluenesulfonyl)iminodibenzothiophene (6b). To
a solution of (N-tosyl)iminophenyliodinane (473 mg, 1.27 mmol)
in CH3CN was added compound 2c (300 mg, 1.15 mmol) and
(25) Laszlo, P.; Polla, E. Tetrahedron Lett. 1984, 25, 4651–4654.
(26) Gentle, C. A.; Bugg, T. D. H. J. Chem. Soc., Perkin Trans. 1 1999, 10,
1279–1286.
7162 J. Org. Chem. Vol. 73, No. 18, 2008