Formation of 1,2,5-oxadiazole, isoxazole, isothiazole, 1,2,3-triazole, and pyrrole rings from N-(5,5-dimethyl-3-oxocyclohexenyl)-S,S-diphenylsulfilimine

Article abstract of DOI:10.1080/00397910600636436

Reactions of N -(5,5-dimethyl-3-oxocyclohexenyl)- S,S -diphenylsulfilimine, a kind of enaminone, with isopentyl nitrite, isocyanates, isothocyanates, benzenediazonium chloride, and 1,1,1-trifluoro-4-ethoxy-3-buten-2-one gave 1,2,5-oxadiazole, isoxazole, i

Full text of DOI:10.1080/00397910600636436

Synthetic Communicationsw, 36: 2087–2095, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600636436
Formation of 1,2,5-Oxadiazole, Isoxazole,
Isothiazole, 1,2,3-Triazole, and Pyrrole
Rings from N-(5,5-Dimethyl-3-
oxocyclohexenyl)-S,S-diphenylsulfilimine
Masahiko Takahashi, Shinji Onda, and Nobuaki Matsumoto
Department of Materials Science, Faculty of Engineering,
Ibaraki University, Hitachi, Ibaraki, Japan
Abstract: Reactions of N-(5,5-dimethyl-3-oxocyclohexenyl)-S,S-diphenylsulfilimine,
a kind of enaminone, with isopentyl nitrite, isocyanates, isothocyanates, benzenediazo-
nium chloride, and 1,1,1-trifluoro-4-ethoxy-3-buten-2-one gave 1,2,5-oxadiazole,
isoxazole, isothiazole, 1,2,3-triazole, and pyrrole derivatives condensed with cyclo-
hexane, respectively, in one pot.
Keywords: Isothiazole, isoxazole, 1,2,5-oxadiazole, pyrrole, sulfilimine, 1,2,3-triazole
N-Unsubstituted sulfilimines (e.g., 5) are useful building blocks for nitrogen
heterocycles because they have a nucleophilic nitrogen atom and a good-
leaving sulfonium atom.[1] These sulfilimine moieties could be readily intro-
duced into organic molecules by a substitution reaction with olefinic halogens
to give N-conjugated sulfilimines, which would be cyclized to heterocycles by
elongation of the conjutated system, followed by extrusion of the sulfonium
group by photolysis or thermolysis. According to this protocol, we have intro-
duced a sulfilimine group into biological important uracils (1) to construct
a,b,g,d-unsaturated sulfilimine systems (2) by the reaction with electrophiles
and then cyclized them by photolysis or thermolysis to give uracils (3)
condensed with 1,2,5-oxadiazole, isoxazole, isothiazole,[2] 1,2,3-triazole,[3]
Received in Japan October 7, 2005
Address correspondence to Masahiko Takahashi, Department of Materials Science,
Faculty of Engineering, Ibaraki University, Hitachi, Ibaraki 316-8511, Japan.
Fax: þ81-294-38-5078; E-mail: takamasa@mx.ibaraki.ac.jp
2087

2088
M. Takahashi, S. Onda, and N. Matsumoto
and pyrrole rings[4] (Scheme 1). In these reactions, a modified enaminone
structure, –CO–C55C–N55SPh2, in the molecule (1) plays an important
role. Therefore, we have studied similar reactions using a simpler
enaminone system[5] and compared the reactivities.
As an enaminone system simpler than 1, we chose a cyclohexenone ring
(6), which was readily prepared in 70% yield from 3-chloro-5,5-dimethylcy-
clohexen-3-one (4)[6] and S,S-diphenylsulfilimine (5)[7] using a method
similar to the one reported.[8] At first, nitrosation by isopentyl nitrite was
carried out. Refluxing a mixture of 6 and isopentyl nitrite in toluene gave
1,2,5-oxadiazole (furazan) (8) in 53% yield. The structures of 8 and the
1
following compounds were determined on the basis of IR, H NMR, 13C
NMR, and mass spectra and the elemental analysis. Although the nitroso
intermediate (2a) was isolated in the case of the uracil derivatives (1),[2] the
corresponding intermediate (7) was not obtained.
Scheme 1.

Heterocycles from Sulfilimine
2089
The reaction of 6 with phenyl isocyanate and p-tolyl isocyanate in
refluxing toluene directly gave isoxazole rings (10a, 52%) and (10b, 46%).
This is in marked contrast to the reaction of 1, where the intermediate 2b
was isolated and converted into 3-substituted isoxazolo[3,4-d]pyrimidines
(3) only by photolysis.[2] On the other hand, similar treatment of 6 with
phenyl isothiocyanate and benzoyl isothiocyanate afforded condensed isothia-
zoles (10c, 21%) and (10d, 27%) in one step as observed in the reaction of 1.
The 1,2,3-triazole ring (12) was also prepared directly in 20% yield without
isolation of the intermediate 11 by the reaction with benzenediazonium
chloride prepared in a mixed solvent of DMF–THF–H2O at 08C to room
temperature, and the isolation of azo compounds (2d) in high yields was
reported in a previous paper.[3] The reaction of simple enaminones, Ph–
CO–CH55C(Me)-NHR, with benzenediazonium tetrafluoroborate was
recently reported to give azo-coupled enaminones and pyridazinium salts.[9]
The reaction of 6 with electron-deficient and unsaturated compounds
appears to be a route to the pyrrole ring via the adduct (13). Indeed, the
reaction with dimethyl acetylenedicarboxylate in refluxing toluene gave two
pyrrole products (14, 28%) and (15, 27%) (Scheme 2). The structure of 14
was deduced on the basis of the spectral data; the NMR spectrum showed
one singlet methine proton at d 3.79, nonequivalent absorptions of
methylene protons of C-5 and C-7, and two methyl protons at d1.16 and
1.17. Furthermore, no NH absorption was observed in the IR spectrum.
Additional heating of 14 in toluene did not afford the product (15), indicating
that 14 would not be the intermediate to 15. No intermediate (13) was isolated
in this case. However, the reaction with 1,1,1-trifluoro-4-ethoxy-2-butenone
(16)[10] yielded an isolable intermediate (17) in 58% yield, which was
further transformed into the expected indole derivative (18) by photolysis in
ethanol using a mercury lamp. Because photolysis of 2e by sunlight to the
Scheme 2.

2090
M. Takahashi, S. Onda, and N. Matsumoto
corresponding pyrrolo[2,3-d]pyrimidine[4] was achieved in high yields, the
ethanolic solution of 17 was similarly irradiated by sunlight for 3 h to give
18 in the best yield of 98% (method A). The high yield of 18 by photolysis
using sunlight prompted us to prepare 18 from 6 without isolation of the inter-
mediate (17); a mixture of 6 and 16 in acetonitrile was stirred at room temp-
erature for 5 days and then irradiated by sunlight for 4 h to give 18 in 49%
yield after column chromatography (method B).
In conclusion, the elongation of the enaminone system (6) by electro-
philes followed by cyclization occurred thermally in one pot without
isolation of the intermediates 7, 9, 11, and 13, showing that the reactivity of
these intermediates is higher than 2. The rather low yields in some cases are
attributable to the thermal unstability of the starting 6, which caused decompo-
sition during refluxing in the solvents. Cyclization of 17 to 18 in high yield by
sunlight was also observed as in the case of 2e, suggesting that the system of
C55C–C55C–N55SR2 is a very useful scaffold for the construction of pyrrole.
EXPERIMENTAL
Melting points were determined with MRK Mel-Temp II and are uncorrected.
The IR spectra were measured on Jasco FT/IR-420 spectrophotometer. MS
and NMR spectra were taken with JEOL JMS DX-300 and JEOL GSX-400
spectrometer, respectively. Microanalyses were performed with Yanaco
CHN-Coder MT-5.
N-(5,5-Dimethyl-3-oxocyclohexenyl)-S,S-diphenylsulfilimine (6)
This compound was prepared according to the method for N-(3-oxocyclohexe-
nyl)-S,S-diphenylsulfilimine.[8]A mixture of 4[6] (574mg, 3.6 mmol), 5[7]
(1.19 g, 5.4 mmol), and triethylamine (1.0 ml) in acetonitrile (5 ml) was
refluxed for 12h. After evaporation of the solvent, CHCl3 (10ml) and water
(50 ml) were added to the residue. The mixture was extracted with CHCl3 and
the CHCl3 solution was dried over MgSO4. Evaporation of the solvent gave
an oil, which was purified by column chromatography on silica gel using
CHCl3–AcOEt (1:1) to give yellow viscous oil (6) (817mg, yield 70%).
Because the product was somewhat labile to heat, it was used for the next
step without further purification. IR (KBr): 2956, 1736, 1601, 1520, 1475,
1444, 1362, 1240, 1142cm21. 1H NMR (CDCl3): d 1.09 (s, 6H), 2.16 (s, 2H),
2.47 (s, 2H), 5.20 (s, 1H), 7.46–7.70 (m, 10H). 13C NMR (CDCl3): d 28.33,
33.01, 47.44, 50.30, 101.05, 127.24, 129.87, 132.14, 135.37, 174.78, 196.44.
6,6-Dimethyl-4,5,6,7-tetrahydrobenzofurazan-4-one (8)
A mixture of 6 (258 mg, 0.80 mmol) and isopentyl nitrite (0.13 ml, 1.0 mmol)
in toluene (4 ml) was refluxed for 2 h. After evaporation of the solvent, the

Heterocycles from Sulfilimine
2091
residue was purified by column chromatography on silica gel using CHCl3 and
washed with hexane to give 8 (70 mg, 53%), white needles, mp 65–668C
1
(MeOH). IR (KBr): 1728, 1570, 1468, 1242 cm21. H NMR (CDCl3): d
1.16 (s, 3H), 2.65 (s, 2H), 2.99 (s, 2H). 13C NMR (CDCl3): d 28.08, 33.36,
34.91, 53.84, 148.34, 155.00, 188.38. MS m/z (%): 166 (Mþ, 31), 109 (88),
94 (100), 80 (58), 55 (96). Anal. calcd. for C8H10N2O2: C, 57.82; H, 6.07;
N, 16.86. Found: C, 57.46; H, 5.84; N, 16.94.
6,6-Dimethyl-3-phenylamino-4,5,6,7-tetrahydrobenz[c]isoxazol-4-
one (10a)
Typical Experimental Procedure
A mixture of 6 (380mg, 1.18mmol) and phenyl isocyanate (0.38 ml, 3.53mmol)
in toluene (4 ml) was refluxed for 8 h. After evaporation of the solvent, the
product was isolated by column chromatography on silica gel using CHCl3
and recrystallized from MeOH to give 10a (156mg, 52%), white needles, mp
1
156–1578C. IR (KBr): 3282, 1657, 1628, 1583, 1543, 1432, 1255cm21. H
NMR (CDCl3): d 1.14 (s, 6H), 2.32 (s, 2H), 2.67 (s, 2H), 7.14–7.46 (m, 5H),
8.75 (br s, 1H). 13C NMR (CDCl3): d 28.44, 34.75, 35.39, 51.22, 94.83,
118.68, 124.57, 129.44, 136.32, 163.17, 164.17, 192.06. MS m/z (%): 256
(Mþ, 69), 228 (20), 187 (22), 120 (51), 93 (83), 77 (100). Anal. calcd. for
C15H16O2N2: C, 70.29; H, 6.29; N, 10.93. Found: C, 70.27; H, 6.26; N, 11.00.
6,6-Dimethyl-3-(p-tolylamino)-4,5,6,7-tetrahydrobenz[c]isoxazol-4-
one (10b)
Yield 46%, white plates, mp 130–1318C (MeOH). IR (KBr): 3292, 2958,
1655, 1626, 1581, 1550, 1466, 1252 cm21 1H NMR (CDCl3): d 1.13
.
(s, 6H), 2.32 (s, 2H), 2.34 (s, 3H), 2.66 (s, 2H), 7.18 (d, J ¼ 8.6 Hz, 2H),
7.33 (d, J ¼ 8.6 Hz, 2H), 8.67 (br s, 1H). 13C NMR (CDCl3) d: 20.90,
28.48, 34.77, 35.42, 51.22, 94.66, 118.76, 129.96, 133.75, 134.42, 163.11,
164.22, 191.96. MS m/z (%): 270 (Mþ, 53), 242 (16), 200 (25), 172 (16),
144 (16), 107 (100), 77 (64). Anal. calcd. for C16H18N2O2: C, 71.09; H,
6.71; N, 10.36. Found: C, 71.20; H, 6.73; N, 10.41.
6,6-Dimethyl-3-phenylamino-4,5,6,7-tetrahydrobenz[c]isothiazol-4-
one (10c)
Yield 21%, white plates, mp 126–1278C (MeOH). IR (KBr): 3211, 2954,
1631, 1597, 1566, 1495, 1394, 1244 cm21 1H NMR (CDCl3) d: 1.12
.
(s, 6H), 2.45 (s, 2H), 2.73 (s, 2H), 7.13–7.45 (m, 5H), 10.69 (br s, 1H). 13C
NMR (CDCl3): d 28.35, 34.50, 42.76, 51.97, 113.05, 117.76, 124.00,
129.71, 139.32, 168.79, 171.32, 195.20. MS m/z (%): 272 (Mþ, 100), 257

2092
M. Takahashi, S. Onda, and N. Matsumoto
(19), 216 (20), 170 (10), 142 (12), 115 (18), 77 (95). Anal. calcd. for
C15H16N2OS: C, 66.15; H, 5.92; N, 10.29. Found: C, 66.14; H, 5.95; N, 10.27.
3-Benzoylamino-6,6-dimethyl-4,5,6,7-tetrahydrobenz[c]isothiazol-
4-one (10d)
Yield 27%, orange needles, mp 141–1428C (MeOH). IR (KBr): 3228, 2960,
1
1670, 1649, 1552, 1469, 1257 cm21. H NMR (CDCl3): d 1.13 (s, 6H), 2.52
(s, 2H), 2.83 (s, 2H), 7.55–8.05 (m, 5H), 11.92 (br s, 1H). 13C NMR
(CDCl3): d 28.36, 34.77, 42.35, 52.27, 115.89, 127.82, 129.12, 130.23,
133.56, 164.71, 165.09, 166.82, 196.55. MS m/z (%): 300 (Mþ, 14), 283
(3), 195 (3), 105 (100), 77 (71). Anal. calcd. for C16H16N2O2S: C, 63.98; H,
5.37; N, 9.33. Found: C, 63.93; H, 5.43; N, 9.32.
6,6-Dimethyl-2-phenyl-4,5,6,7-tetrahydro-2H-benzotriazol-
4-one (12)
A solution of 6 (384 mg, 1.2 mmol) in a mixed solvent of DMF (5 ml) and THF
(1 ml) was added dropwise to a solution of benzenediazonium chloride
prepared from aniline (0.14 ml, 1.5 mmol), hydrochloric acid (0.2 ml of con-
centrate hydrochloric acid in 5 ml of water), and sodium nitrite (104 mg,
1.5 mmol in 3 ml of water) below 5 8C during 20 min. After stirring for 1 h
at 5 8C, the stirring was continued for 1 h at room temperature. Water
(100 ml) was added to the mixture, and it was extracted with chloroform
(5 ml ꢀ 3). The oily residue obtained after evaporation of the solvent was
washed with diethyl ether–hexane to give a solid (12) (56 mg, 20%), white
needles, mp 113–114 8C (MeOH). IR (KBr): 1691, 1597, 1518, 1483,
1
1462, 1342, 1325 cm21. H NMR (CDCl3): d 1.18 (s, 6H), 2.59 (s, 2H),
2.92 (s, 2H), 7.39–8.17 (m, 5H). MS m/z (%): 241 (Mþ, 35), 185 (33), 105
(28), 77 (100). Anal. calcd. for C14H15N3O: C, 69.69; H, 6.27; N, 17.42.
Found: C, 69.53; H, 6.34; N, 17.41.
Dimethyl 6,6-dimethyl-4-oxo-4,5,6,7-tetrahydro-3aH-indole-2,3-
dicarboxylate (14) and Dimethyl 6,6-dimethyl-4-oxo-4,5,6,7-
tetrahydro-1H-indole-2,3-dicarboxylate (15)
A mixture of 6 (390 mg, 1.2 mmol) and dimethyl acetylenedicarboxylate
(596 mg, 4.2 mmol) in toluene (4 ml) was refluxed for 3 h. After evaporation
of the solvent, the residue was purified by column chromatography on silica
gel using CHCl3. The products (14) (94 mg, 28%) and (15) (90 mg, 27%)
were obtained as oily substances from the first and the second fractions,
respectively. They were solidified by addition of diethyl ether. The product

Heterocycles from Sulfilimine
2093
14 is white needles, mp 106–1078C (diethyl ether-hexane). IR (KBr): 2954,
1738, 1726, 1655, 1437, 1269, 1254 cm21 1H-NMR (CDCl3): d 1.16
.
(s, 3H), 1.17 (s, 3H), 2.47 (d, J ¼ 12.6 Hz, 1H), 2.86 (d, J ¼ 17.2 Hz, 1H),
2.93 (d, J ¼ 17.2 Hz, 1H), 3.23 (d, J ¼ 12.6 Hz, 1H), 3.79 (s, 3H), 3.88
(s, 3H), 6.94 (s, 1H). 13C NMR (CDCl3): d 28.38, 31.73, 32.31, 34.23,
37.29, 51.97, 53.02, 53.05, 139.06, 141.77, 161.64, 165.59, 170.18, 201.19.
MS m/z (%): 248 (Mþ-31, 4), 220 (3), 164 (9), 136 (3), 83 (100). Anal.
calcd. for C14H17NO5: C, 60.21; H, 6.13; N, 5.02. Found: C, 60.21; H, 6.10;
N, 5.01. The product (15) is white powder, mp 164–1658C (THF–hexane).
IR (KBr): 3334, 1738, 1703, 1657, 1523, 1495, 1448, 1304, 1282, 1252,
1
1203, 1169 cm21. H NMR (CDCl3): d 1.12 (s, 6H), 2.38 (s, 2H), 2.71
(s, 2H), 3.86 (s, 3H), 3.94 (s, 3H), 9.95 (br s, 1H). 13C NMR (CDCl3): d
28.46, 35.53, 36.37, 51.98, 52.30, 52.81, 118.42, 119.64, 120.36, 144.30,
160.50, 165.73, 192.30. MS m/z (%): 279 (Mþ, 37), 248 (23), 223 (100),
191 (76), 165 (14), 135 (14), 107 (22), 78 (38). Anal. calcd. for
C14H17NO5: C, 60.21; H, 6.13; N, 5.02. Found: C, 60.05; H, 6.07; N, 4.99.
N-[5,5-Dimethyl-2-(4,4,4-trifluoro-3-oxo-1-butenyl)-3-
oxocyclohexenyl]-S,S-diphenylsulfilimine (17)
A mixture of 6 (311 mg, 0.96 mmol) and 16 (568 mg, 3.4 mmol) in acetonitrile
(4 ml) was stirred at room temperature for 4 days. After evaporation of the
solvent, the residue was purified by column chromatography on silica gel
using CHCl3 to give 17 (249 mg, 58%), yellow plates, mp 140 8C (dec.)
(MeOH). IR (KBr): 2952, 1668, 1631, 1545, 1396, 1329, 1267, 1236, 1186,
1
1128, 1070, 1005 cm21. H NMR (CDCl3): d 1.01 (s, 6H), 2.30 (s, 2H),
2.68 (s, 2H), 7.56–7.80 (m, 10H), 7.83 (d, J ¼ 15.6 Hz, 1H), 8.80
(d, J ¼ 15.6 Hz, 1H). 13C NMR (CDCl3): d 28.40, 31.85, 46.50, 50.95,
111.39, 113.33, 117.43 (q, J ¼ 291 Hz), 127.13, 130.49, 133.09, 135.61,
143.96, 178.95, 181.33 (q, J ¼ 32 Hz), 194.64. MS m/z (%): 259 (Mþ-
186), 203 (68), 186 (100), 175 (45), 77 (32). Anal. calcd. for
C24H22F3NO2S: C, 64.70; H, 4.98; N, 3.14. Found: C, 64.62; H, 5.09; N, 3.17.
2-Trifluoroacetyl-6,6-dimethyl-4,5,6,7-tetrahydro-1H-indol-
4-one (18)
Method A
A solution of 17 (160 mg, 0.36 mmmol) in EtOH (30 ml) was irradiated by
sunlight at room temperature for 3 h. After evaporation of the solvent, the
residue was purified by column chromatography on silica gel using CHCl3
to give 18 (91 mg, 98%).

2094
M. Takahashi, S. Onda, and N. Matsumoto
Method B
A mixture of 6 (332 mg, 1.0 mmmol) and 16 (594 mg, 3.5 mmol) in aceto-
nitrile (4 ml) was stirred at room temperature for 5 days. Acetonitrile
(25 ml) was further added to the solution, and the mixture was irradiated by
sunlight for 4 h. After the solvent was evaporated in vacuo, the residue was
purified by column chromatography on silica gel using CHCl3 to give 18
(132 mg, 49%), white plates, mp 199–2008C (CHCl3–hexane). IR (KBr):
1
3248, 1676, 1649, 1514, 1214, 1194, 1147 cm21. H NMR (DMSO-d6): d
1.04 (s, 6H), 2.35 (s, 2H), 2.78 (s, 2H), 7.32 (s, 1H). 13C NMR (DMSO-d6):
d 27.90, 34.93, 35.82, 51.63, 116.55 (q, J ¼ 287 Hz), 117.35, 121.21,
125.22, 151.34, 169.19 (q, J ¼ 35 Hz), 192.57. MS m/z (%): 259 (Mþ, 32),
203 (100), 175 (49), 78 (39). Anal. calcd. for C12H12F3NO2: C, 55.60; H,
4.67; N, 5.40. Found: C, 55.72; H, 4.75; N, 5.41.
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