Oxidation of sterically-crowded selones using chloramine-T: Generation and skeletal rearrangement of selone Se-imides

Article abstract of DOI:10.1016/S0040-4039(00)01155-2

Treatment of sterically-crowded bornane-2-selones possessing substituted bornane skeletons with chloramine-T afforded several products originated from intermediary selone Se-imides, and the direct observation of the intermediates was performed by NMR monitoring at low temperature. (C) 2000 Elsevier Science Ltd.

Full text of DOI:10.1016/S0040-4039(00)01155-2

Tetrahedron Letters 41 (2000) 6833±6837
Oxidation of sterically-crowded selones using chloramine-T:
generation and skeletal rearrangement of selone Se-imides
Kazuaki Shimada,a,* Keiichi Kodaki,a Takashi Nanae,a Shigenobu Aoyagi,a
Yuji Takikawaa and Chizuko Kabutob
aDepartment of Chemical Engineering, Faculty of Engineering, Iwate University, Morioka, Iwate 020-8551, Japan
bInstrumental Analysis Center for Chemistry, Faculty of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan
Received 7 June 2000; revised 5 July 2000; accepted 7 July 2000
Abstract
Treatment of sterically-crowded bornane-2-selones possessing substituted bornane skeletons with
chloramine-T a€orded several products originated from intermediary selone Se-imides, and the direct
observation of the intermediates was performed by NMR monitoring at low temperature. # 2000 Elsevier
Science Ltd. All rights reserved.
Keywords: thione S-imide; selone Se-imide; skeletal rearrangement; sulfenamide; selenenamide.
Much interest has been concentrated on the oxidized variants of thiones A in the light of their
heterocumulene-like structures and novel reactivities, and recently, the synthetic methods,
reactivities, and synthetic uses of thione S-imides C have been widely studied. However, in spite
of their potentiality as new reactive intermediates and building blocks for various heterocyclic
compounds, studies on selone Se-imides D have been limited due to the diculties incurred in
* Corresponding author. Tel: +00-81-19-621-6324; fax: +00-81-19-621-6347; e-mail: shimada@iwate-u.ac.jp
0040-4039/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(00)01155-2

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preparation and treatment.1 Especially, no studies on the isolation or detection of D have been
reported to date. In the course of our current work on the generation of highly reactive
chalcogenocarbonyl species, we attempted the chloramine-T oxidation of selones B possessing
substituted bornane skeletons according to the kinetic protection methodology. In this paper, we
would like to describe the generation, direct NMR observation, and thermal skeletal rearrangement
of selone Se-imides D.
Ketones 1a,b bearing substituents at the C-3 position of the bornane skeleton were at ®rst
prepared from d-camphor (1c),2 and 1a,b were then converted into selones 2a,b or thiones 3a,b by
using bis(1,5-cyclooctanediylboryl) selenide or Lawesson's reagent, respectively.3,4
When a methanolic solution of sterically-crowded selone 2a or 2b was treated with chloramine-T
(2.2 mol amt.) at ^78ꢀC, the original deep-blue color of the solution of 3 immediately turned
colorless, and selenenamides 6 (6a: 44% from 2a, 6b: 35% from 2b) were obtained along with
trace amounts of ketones 1a,b and diselenide 8a or triselenide 8b, respectively, after usual
workup.5 In all cases, neither selenaziridines nor p-toluenesulfonylimines were found in the crude
reaction mixture. The structure of 6b was determined by X-ray crystallographic analysis, and the
ORTEP drawing of 6b is shown in Fig. 1.6
Figure 1. ORTEP drawing of 6b
Furthermore, when a CDCl3 solution of selone 2b was treated with a CD3OD solution of
chloramine-T (2.2 mol amt.) at ^78ꢀC in an NMR tube and the reaction was monitored by NMR
measurements, the NMR signals of 2b (13C NMR: ꢀ=298 ppm, 77Se NMR: ꢀ=1644 ppm) were
quickly extinguished and a new signal assigned to the selenocarbonyl carbon of 4b was just
observed at ꢀ=273 ppm in the 13C NMR spectrum and at ꢀ=1204 ppm in the 77Se NMR
spectrum at ^78ꢀto ^50ꢀꢀC range. Subsequently, when the temperature of the reaction mixture was
raised from ^50 C to 0 C, the signals of 4b completely disappeared and a new set of sp2 carbon
signals of the exo-methylene group of selenenamide 6b appeared at ꢀ=163 and 102 ppm in the
13C NMR spectrum and a new sole selenium signal at ꢀ=723 ppm in the 77Se NMR spectrum.7
In addition, the signals of byproducts, such as 1b or 8b, were not observed throughout the NMR
monitoring experiments. These results strongly indicated that selone Se-imide 4b possessing a
single geometry was generated in the reaction mixture at low temperature and that 4b caused
skeletal rearrangement to give 6b exclusively.

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When a methanolic solution of thione 3b was treated with chloramine-T (2.2 mol amt.) at 40ꢀC
for 1 h in a similar manner as shown above, sulfenamide 7b (35%) was obtained along with an
epimeric mixture of thione S-oxides 10b (23%, combined yield),3 trisul®de 9b (trace), p-toluene-
sulfonamide, and an epimeric mixture of sul®nylimides 11b (trace, 1:1). It was noteworthy that
neither thione S-imide 5b, thiaziridine, nor p-toluenesulfonylimine was found at all in the crude
reaction mixture.1 Treatment of 7b with silica gel (excess) in hexane at rt gave 9b in low yield
along with the recovery of 7b, and further treatment of a methanolic solution of 7b with chloramine-T
(1.1 mol amt.) at rt gave an epimeric mixture of 11b (35%, about 1:1). An epimer of 11b was
puri®ed by repeated recrystallization, and the structure of the crystalline epimer of 11b was ®nally
determined by X-ray crystallographic analysis. The ORTEP drawing of 11b is shown in Fig. 2.8
Thus, it was clari®ed that 7b, 9b, and 11b possessed the same skeleton as those of 6 and 8 in the
selenium series. A similar treatment of an ethanolic solution of 3a with chloramine-T gave thione
S-imide 5a (86%),9 and the signal of the thiocarbonyl carbon of 5a in 13C NMR was revealed at
much higher ®eld region (ꢀ=220 ppm) than that of the selenocarbonyl carbon of 4b. Heating a
toluene solution of 5a at re¯uxing temperature for 24 h also gave sulfenamide 7a (63%) along
with a trace amount of p-toluenesulfonamide. It was assumed that the lower thermal stability of
5b than that of 5a might be attributed to the preferred E-geometry of the CˆS moiety of 5b due
to the steric repulsion between the p-toluenesulfonyl group and the neighboring spiro-2-indanyl
substituent, and the E-isomers of 5 were presumed to cause thermal skeletal rearrangement
exclusively to give 7 through abstraction of the C-1 methyl proton. It was suggested that the
selective formation of 6 from 4 even at about 0ꢀC, in contrast with the requirement of high
temperature for the same skeletal rearrangement from 5a to 7a, might be attributed to facile
equilibration of the Se±N bond of 4 under mild reaction conditions.10
Figure 2. ORTEP drawing of 11b
All the results clearly showed evidence of the in situ generation of selone Se-imides 4 at the
primary stage of the reaction of selones 2 with chloramine-T at low temperature. Furthermore, 4

6836
caused thermal skeletal rearrangement to give selenenamides 6 through a similar reaction course
to that from thione S-imides 5 to sulfenamides 7. Formation of diselenide 8a or triselenide 8b was
also explained by hydrolytic cleavage of 6 and the subsequent condensation of the resulting
selenenic acids in a similar manner as mentioned in the case of the formation of trisul®de 9b. In
addition, the formation of p-toluenesulfonylimines through generation of the intermediary
selenaziridines or thiaziridines, respectively, and subsequent thermal selenium or sulfur extrusion
might also be sterically suppressed in these cases (Scheme 1).1,9b,11
Scheme 1.
In conclusion, we have established the generation and direct observation of selone Se-imides 4
possessing sterically-crowded bornane skeletons. Further attempts for chemical conversion of 4
into the syntheses of various heterocycles are in progress in our laboratory.
References
1. (a) Tamagaki, S.; Oae, S. Tetrahedron Lett. 1972, 1159±1162. (b) Tamagaki, S.; Sakaki, K.; Oae, S. Tetrahedron
Lett. 1974, 1059±1062.
2. (a) Krapcho, A. Synthesis 1974, 383±419, and references cited therein. (b) Helmchen, G.; Selim, A.; Dorsch, D.;
Taufer, I. Tetrahedron Lett. 1983, 31, 3213±3216.
3. (a) Koster, R.; Seidel, G.; Yalpani, M. Chem. Ber. 1989, 122, 1815±1824. (b) Shimada, K.; Jin, N.; Fujimura, M.;
Nagano, Y.; Kudoh, E.; Takikawa, Y. Chem. Lett. 1992, 1843±1846. (c) Shimada, K.; Jin, N.; Kawaguchi, M.;
Dobashi, K.; Nagano, Y.; Fujimura, M.; Kudoh, E.; Kai, T.; Saito, N.; Masuda, J.; Iwaya, M.; Fujisawa, H.;
Aoyagi, S.; Takikawa, Y. Bull. Chem. Soc. Jpn. 1997, 70, 197±206.
4. Shimada, K.; Kodaki, K.; Aoyagi, S.; Takikawa, Y.; Kabuto, C. Chem. Lett. 1999, 695±696.
5. Treatment of 6b with an excess amount of silica gel at rt overnight a€orded 8b (17%) and p-toluenesulfonamide
along with the recovery of 6b.
6. X-Ray crystallographic data for 6b: C25H29NO2SSe, FW=486.53, colorless prism, orthorhombic, P212121 (#19),
a=14.522(3), b=15.754(3), c=10.205(4) A, V=2334.8(9) A3, Dcalc=1.384 g/cm3, ꢁ(CuKa)=31.71 cm^1, R
=0.042, Rw=0.051.
7. (a) Reich, H. J.; Hoeger, C. A.; Willis, W. W. J. Am. Chem. Soc. 1982, 104, 2936±2937. (b) Reich, H. J.; Hoeger,
C. A.; Willis, W. W. Tetrahedron 1985, 41, 4771±4779. (c) Paulmier, C.; Lerouge, P.; Outurquin, F.; Chapelle, S.;
Granger, P. Magn. Reson. Chem. 1987, 25, 955±959. (d) Hosay, Th.; Christiaens, L.; Anthoine, G.; Moniotte, Ph.
Tetrahedron Lett. 1990, 31, 873±876. (e) Back, T. G.; Dyck, B. P. J. Am. Chem. Soc. 1997, 119, 2079±2083.

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8. X-Ray crystallographic data for 11b: C26H31NO3S, FW=437.60, colorless prism, orthorhombic, P212121 (#19),
a=17.853(2), b=18.248(2), c=7.427(3) A, V=2419.6(9) A3, Z=4, Dcalc=1.201 g/cm3, ꢁ(MoKa)=1.60 cm^1,
R=0.056, Rw=0.060.
9. (a) Campbell, M. M.; Evgenios, D. M. J. Chem. Soc., Chem. Commun. 1971, 179±180. (b) Campbell, M. M.;
Evgenios, D. M. J. Chem. Soc., Perkin Trans. 1 1973, 2866±2869.
10. Taka, H.; Shimizu, T.; Iwasaki, F.; Yasui, M.; Kamigata, N. J. Org. Chem. 1999, 64, 7433±7438.
11. (a) Saito, T.; Motoki, S. J. Org. Chem. 1977, 42, 3922±3925. (b) Boberg, F.; Puttins, U.; Wentrup, G.-J. Liebigs
Ann. Chem. 1979, 689±700. (c) Motoki, S.; Toba, Y.; Karakasa, T.; Saito, T. Chem. Lett. 1988, 319±322.