Synthesis and properties of monocyclic selenophene 1-oxides [1]

Full text of DOI:10.1021/ja982359h

J. Am. Chem. Soc. 1998, 120, 12351-12352
12351
Communications to the Editor
of pentane at the same temperature to leave pure 2,4-di-tert-
butylselenophene 1-oxide (2)12 nearly quantitatively. No forma-
tion of the 1,1-dioxide 3 was observed. The 1-oxide 2 is highly
hygroscopic and deliquesced on exposure to moist air. It
decomposed on warming to liquefy at about 54-55 °C. NMR
data of 2 are summarized in Table 1 together with those of 1, 3,
and a range of compounds derived from 2. The 1H NMR
Synthesis and Properties of Monocyclic Selenophene
1-Oxides
Takashi Umezawa, Yoshiaki Sugihara, Akihiko Ishii, and
Juzo Nakayama*
Department of Chemistry, Faculty of Science
Saitama UniVersity, Urawa
Saitama 338-8570, Japan
ReceiVed July 6, 1998
We report here the first synthesis, isolation, and properties of
monocyclic selenophene 1-oxides. Thiophene 1,1-dioxides are
highly reactive and, hence, both synthetically and theoretically
important compounds whose chemistry has been investigated in
all of its details.1 The much more reactive thiophene 1-oxides
have eluded isolation until recently,2,3 with one exception.4 These
successful preparations of isolably stable thiophene 1-oxides have
subsequently set the stage for the development of their chemistry.
Meanwhile, dibenzoselenophene 5-oxide had been the only known
oxide of selenophenes5 when we started the study on this class
of compounds several years ago. After numerous attempts, we
have succeeded in the preparation of a series of monocyclic
selenophene 1,1-dioxides, which are stabilized electronically or
sterically, by oxidation of the corresponding selenophenes with
dimethyldioxirane (DMD).6,7 However, despite our many efforts,
selenophene 1-oxides, the intermediates leading to the former
dioxides, have never been isolated in pure form.
2,4-Di-tert-butylselenophene 1,1-dioxide (3) is the most ther-
mally stable of the synthetically available 1,1-dioxides because
of steric protection.7,8 Since this should also be true for
selenophene 1-oxides, 2,4-di-tert-butylselenophene (1)9 was cho-
sen as the substrate for our oxidation study. Thus, a solution of
DMD10 (1 equiv) in Me2CO was added to a solution of 1 in
CH2Cl2 at -50 °C. The addition resulted in rapid oxidation of
1. The mixture was evaporated under vacuum below -40 °C.11
The resulting colorless crystals were washed with a small amount
chemical shift values of 2 fall between those of 1 and 3. The
same trend is also observed with a thiophene series.3f The 77Se
NMR spectrum showed only one signal at δ 986 which is lower
than the chemical shift values of the common selenoxides.13 The
IR spectrum showed the Se-O stretching vibration at 798 cm-1.14
This assignment was supported by the Raman spectrum in which
a strong absorption appeared at 788 cm-1
.
The 1-oxide 2 is far less stable than the corresponding thiophene
1-oxide3f and selenophene 1,1-dioxide7,8 and decomposed at 20
°C with half-lives of 42 and 34 min in 0.018 and 0.036 M CDCl3
solutions, respectively.15 A 0.05 M solution of 2 in CH2Cl2
standing at 30 °C for 0.5 h gave 1 (73%), the furanone 416 (25%),
and SeO2 by an unknown process. As is expected from the
formation of 1, 2 functions as an oxidizing agent. Thus, letting
a 1:1 mixture of 2 and PhSMe stand in CH2Cl2 gave PhS(O)Me
in 30% yield along with 1 (67%) and 4 (8%). Ph3P was also
oxidized with 2 (1 equiv) to give Ph3PO in 80% yield. To our
surprise, 2 is readily soluble in water, despite the presence of
two hydrophobic tert-butyl groups, to give an acidic solution (pH
6.6 for 5.7 × 10-2 M solution) (also easily soluble in MeOH). In
addition, it is stabilized by water and persisted in D2O without
marked decomposition at least for 24 h at room temperature. These
observations indicate that the Se-O bond is higly polarized, as
supported by the foregoing deshielded 77Se chemical shift value,
and is solvated in water. The acidity of 2 indicates that an
equilibrium involving a selenurane 5, which lies to the selenoxide
(1) (a) For a review, see Nakayama, J.; Sugihara, Y. In Topics in Current
Chemistry (Organosulfur Chemistry), Page, P., Ed.; Springer-Verlag: Heidel-
berg, to appear in 1999. (b) For the parent thiophene 1,1-dioxide, see
Nakayama, J.; Nagasawa, H.; Sugihara, Y.; Ishii, A. J. Am. Chem. Soc. 1997,
119, 9077.
(2) For a review, see Nakayama, J.; Sugihara Y. Sulfur Reports 1997, 19,
349.
(3) (a) Fagan, P. J.; Nugent, W. A. J. Am. Chem. Soc. 1988, 110, 2310.
(b) Fagan, P. J.; Nugent, W. A.; Calabrese, J. C. J. Am. Chem. Soc. 1994,
116, 1880. (c) Meier-Brocks, F.; Weiss, E. J. Organomet. Chem. 1993, 33,
453. (d) Pouzet, P.; Erdelmeier, I.; Ginderow, D.; Mornon, J.-P.; Dansette,
P.; Mansuy, D. J. Chem. Soc. Chem. Commun. 1995, 473. (e) Furukawa, N.;
Zhang, S.; Sato, S.; Higaki, M. Heterocycles 1997, 44, 61. (f) Nakayama, J.;
Yu, T.; Sugihara, Y.; Ishii, A. Chem. Lett. 1997, 499.
(4) Mock, W. L. J. Am. Chem. Soc. 1970, 92, 7610.
(5) (a) McCullough, J. D.; Campbell, T. W.; Gould, E. S. J. Am. Chem.
Soc. 1950, 72, 5753. (b) Dakova, B.; Walcarius, A.; Lamberts, L.; Evers, M.
Electrochim. Acta 1992, 37, 541. (c) Kimura, T.; Ishikawa, Y.; Minoshima,
Y.; Furukawa, N. Heterocycles 1994, 37, 541.
(6) Nakayama, J.; Matsui, T.; Sato, N. Chem. Lett. 1995, 485.
(7) (a) Nakayama, J.; Matsui, T.; Sugihara, Y.; Ishii, A.; Kumakura, S.
Chem. Lett. 1996, 269. (b) Matsui, T.; Nakayama, J.; Sato, N.; Sugihara, Y.;
Ishii, A.; Kumakura, S. Phosphorus, Sulfur Silicon Relat. Elem. 1996, 118,
227.
side, exists in water.17,18
(8) Umezawa, T.; Matsui, T.; Sugihara, Y.; Ishii, A.; Nakayama, J.
Heterocycles 1998, 48, 61.
The 1-oxide 2 quantitatively forms a 1:1 adduct (6)12 with BF3
when treated with BF3‚Et2O (1 equiv) at -40 °C (Table 1).19 The
1-oxide 2 also quantitatively formed a 1:1 adduct (7)12 with
p-toluenesulfonic acid (1 equiv) at -40 °C, similar in structure
to that of the adduct reportedly formed with dibenzyl selenoxide.20
(9) Nakayama, J.; Murai, F.; Hoshino, M.; Ishii, A. Tetrahedron Lett. 1988,
29, 1399.
(10) Adam, W.; Hadjiarapoglou, L.; Smerz, A. Chem. Ber. 1991, 124, 227.
(11) Removal of the solvents and volatile materials below -40 °C is crucial
to isolate 2 in pure form.
10.1021/ja982359h CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/11/1998

12352 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Communications to the Editor
Table 1.
1H NMR,a 13C NMR,b and 77Se NMRc Data (δ) of 2 and Related Compounds
compd
1
2
2d
6.93e
6.94
2g
3h
6.57
6.75
157.6
6
7
8
9
C3-H
C5-H
C-2
C-3
C-4
6.99
7.31
164.5
123.1
153.9
118.2
552
6.67
6.83
170.1
128.1
163.1
127.3
986
6.92
6.97
170.8
130.8
166.1
128.2
6.81
6.98
6.72
7.07
168.7
128.8
164.4
125.6
959j
6.75, 6.77
7.21, 7.32
164.0, 164.3
132.4, 132.5
168.55, 168.57
124.8, 124.9
957, 959
6.72
6.79
163.8
130.9
165.7
118.0
610
171.2e
133.8
169.8
128.5
965f
169.7
132.4
164.6
121.5
953-955
121.2
155.6
119.0
C-5
77Se
1054i
a In CDCl3 with TMS as the internal standard at 233 K, unless otherwise stated (400 MHz). b In CDCl3 with CDCl3 (δ 77.0) as the internal
standard at 233 K, unless otherwise stated (100 MHz). c In CDCl3 with the parent selenophene (δ 608.6) as the external standard at 233 K, unless
otherwise stated (76 MHz). d In D2O. e DSS as the internal standard at 297 K. f At 278 K. g In CD3OD with TMS as the internal standard at 297
K. h At 297 K. i In CDCl3 with D2SeO3 (δ 1282) as the external standard. j In CD3CN at 248 K.
Since the selenium atom of 2 is chiral, optical resolution should
be possible provided the inversion on the selenium atom and the
well-known racemization process through hydration is slow.17,21
As an approach to this goal, 2 was treated with (1S)-(+)-10-
Similar oxidation of 2,4-di(1-adamantyl)-12,23 and tetraphen-
ylselenophenes24 also gave the corresponding 1-oxides 1012 and
1112 nearly quantitatively. The 1-oxide 10, which deliquesces
on exposure to air and is slightly soluble in water, quickly
decomposed at 30 °C in CH2Cl2 to give 2,4-di(1-adamantyl)-
selenophene (85%) and the furanone 1212 (12%), whereas 11 gave
tetraphenylselenophene (73%) and cis-butenedione 13 (25%)
1
camphorsulfonic acid (1 equiv). The H NMR of the resulting
1:1 adduct (8)12 showed a pair of signals of equal intensities due
to the R- and â-hydrogens, revealing the formation of a pair of
diastereomers. This conclusion was also supported by 13C- and
77Se-NMR (observations of two signals at δ 957 and 959) spectra
(Table 1), although separation of the diastereomers was impeded
by instability of the adduct. Treatment of 2 with malononitrile
(1 equiv) at -40 °C in the presence of MgSO4 gave the
selenonium ylide 912 quantitatively, thus providing a new route
under the same conditions.
Oxidation of thiophenes, including the parent thiophene, is
difficult to stop at the 1-oxide stage3 and, therefore, generally
affords the corresponding thiophene 1,1-dioxides1 since the
oxidation of thiophene 1-oxides, which are no longer aromatic,
to the 1,1-dioxides takes place much faster than that of thiophenes
to the 1-oxides. By contrast, the present results lead to the
conclusion that the oxidation of selenophenes to the 1-oxides is
much faster than that of 1-oxides to the 1,1-dioxides. This might
be explained by (1) weaker aromaticity of selenophenes compared
to thiophenes25 and (2) decreased electron density on the selenium
atom because of the highly polarized Se-O bond.
to selenophenium ylides.22
(12) Supporting spectral data were obtained for all new compounds.
(13) Resonance range of selenoxides is δ ) 812-941 except δ 1095 for
(CF3)2SeO.; Duddeck, H. Prog. Nucl. Magn. Reson. Spectrosc. 1995, 27, 1.
(14) The 18O-labeled 2, which was prepared by treatment of 2 with H218O
showed the absorption due to the Se-18O stretching vibration at 762 cm-1
.
See Shimizu, T.; Kobayashi, M.; Kamigata, N. Bull. Chem. Soc. Jpn. 1988,
61, 3761.
Acknowledgment. This work was financially supported by a Grant-
in-Aid (No. 09440213) for Scientific Research from the Ministry of
Education, Science, Sports and Culture, Japan.
(15) Kinetics of the decomposition fitted neither first- or second-order in
2.
(16) Saito, I.; Yoshimura, T.; Arai, T.; Omura, K.; Nishinaga, A.; Matsuura,
T. Tetrahedron 1972, 28, 5131.
Supporting Information Available: Characterization data for new
1
compounds 2 and 6-12 and H and 13C NMR spectra of 2 and 6-11,
(17) For hydrate formation of selenoxides, for example, see Davis, F. A.;
Billmers, J. M.; Stringer, O. D. Tetrahedron Lett. 1983, 24, 3191.
(18) The absorption due to the Se-O stretching vibration persisted even
in the wet (deliquesced) 2.
77Se spectra of 2, 10, and 11, and IR and Raman spectra of 2 (29 pages,
print/PDF). See any current masthead page for ordering information and
Web access instructions.
(19) Thiophene 1-oxides form stable 1:1 complexes with Lewis acids such
as BF3 and SbCl5: (a) Hori, M.; Kataoka, T.; Shimizu, H.; Onogi, K. Chem.
Pharm. Bull. 1978, 26, 2811. (b) Zhang, S.; Horn, E.; Sato, S.; Furukawa, N.
private communication.
(20) Procter, D. J.; Rayner, C. M. Tetrahedron Lett. 1994, 35, 1449.
(21) For a review on preparation of optically pure selenoxides and their
racemization, Kamigata, N.; Shimizu, T. J. Org. Synth. Chem. (Japan) 1990,
48, 229 and many references therein.
JA982359H
(22) Bien, S.; Gronowitz, S.; Ho¨rnfeldt, A.-B. Chem. Scr. 1984, 24, 253.
(23) This new selenophene was prepared according to ref 9.
(24) Sawada, K.; Choi, K. S.; Kuroda, M.; Taniguchi, T.; Ishii, A.; Hoshino,
M.; Nakayama, J. Sulfur Lett. 1993, 15, 273.
(25) Bird, C. W. Tetrahedron 1992, 48, 335 and references therein.