Electrochemistry of 1,3-diazadihydroazulanone: Electrochemical reduction and oxidation of 1-tosyl-3-aryl-1,3-diazadihydroazulanone leading to migration and elimination of the tosyl group

Article abstract of DOI:10.3987/COM-99-8749

Electrochemical oxidations of 1-tosyl-3-aryl-1,3-diazadihydroazulanones gave 6-tosyl-3-aryl-1,3-diazadihydroazulanones via migrations of the tosyl group. On the other hand, electrochemical reductions of the 1-tosyl- azulanones afforded 3-aryl-1,3-diazadih

Full text of DOI:10.3987/COM-99-8749

HETEROCYCLES, Vol. 53, No. 3, 2000, pp. 519 - 524, Received, 10th September, 1999
ELECTROCHEMISTRY OF 1,3-DIAZADIHYDROAZULANONE:
ELECTROCHEMICAL REDUCTION AND OXIDATION OF 1-TOSYL-3-
ARYL-1,3-DIAZADIHYDROAZULANONE LEADING TO MIGRATION
AND ELIMINATION OF THE TOSYL GROUP
Katsuhiro Saito,* Takayasu Ido, Yasutaka Awadu, Takashi Kanie, and Satoru
Kondo
Department of Applied Chemistry, Nagoya Institute of Technology, Gokiso-cho,
Showa-ku, Nagoya 466-8555, Japan
Abstract - Electrochemical oxidations of 1-tosyl-3-aryl-1,3-diazadihydro-
azulanones gave 6-tosyl-3-aryl-1,3-diazadihydroazulanones via migrations of the
tosyl group. On the other hand, electrochemical reductions of the 1-tosyl-
azulanones afforded 3-aryl-1,3-diazadihydroazulanones through eliminations of
the tosyl group.
The 1,3-diazadihydroazulanone system (1) is composed from two parts, i.e., a cycloheptatriene and a
diazacyclopentanone parts. Considering the sp2 hybridization of the two nitrogen atoms, this system can
be regarded to have a 12π electrons cross conjugation system.1 As a series of our research on the
cycloaddition reactions of heterocumulenes, we have documented on the synthetic approach to this
system2 and have pointed out a good possibility of this system to be converted to organic
electroconductors.3 Recently, we reported on the electrochemistries of several heterocyclic compounds to
proceed ring opening, ring contraction, or hydrogen migration reactions.4 These facts prompted us to
investigate the electrochemistry of 1. Here the results are discussed.
A solution of 1-tosyl-3-(p-methylphenyl)-1,3-diazadihydroazulanone (1a) in anhydrous acetonitrile was
electrochemically oxidized in the presence of tetrabutylammonium perchlorate (TBAP) as a supporting
electrolyte with a platinum gauze as an anode and a platinum wire as a cathode at 1.3 V vs. Ag/Ag+ at
0 ℃ under a nitrogen stream. After evaporation of the solvent, the reaction mixture was
chromatographed on silica gel using n-hexane ethyl acetate (7:3) as a developing solvent to give 6-tosyl-
3-(p-methylphenyl)-1,3-diaza-dihydroazulanone (2a)5 in 52 % yield via a migration of the tosyl group.
The current efficiency was 27 %.
The product yield of this reaction was not effected so much by the substituent of the aryl group of 1.
Thus, 1-tosyl-3-(p-methoxyphenyl)- (1b), 1-tosyl-3-(p-chlorophenyl)- (1c), and 1-tosyl-3-(p-bromo-
phenyl)-1,3-dizadihydroazulanone (1d) were electrochemically oxidized under analogous reaction
conditions as above to give the corresponding products 2b, 2c, and 2d in 56, 59, and 44 % yields,
respectively. The current efficiencies were 40, 31, and 27 %, respectively.

1
The structure of 2a was deduced mainly on the basis of H NMR, MS and IR spectra and confirmed by
the good resemblance of these to those of the analogues compound.6 Mass spectrum indicated that the
molecular ion peak of 2a (M+, 329) was consisted with the molecular weight of the starting material (1a).
An absorption at 3420 cm-1 in IR spectrum showed a presence of an N-H bond. 1H NMR spectrum taught
an existence of a chain of five continued carbon atoms of C4-C8, in which only C6 is a saturated carbon
atom connected to a tosyl group. Considering the chemical shifts of the corresponding protons of the
analogous compounds,6 the assignment of each proton was decided to be as shown in the Figure.
X
X
4
4
5
5
3
1
N 3
N
3a
3a
N
6
-e
2
2
6
O
Ts
O
N
H
1
1a
1a
2
7
7
8
8
Ts
1
a: X=Me b: X=OMe
c: X=Cl d: X=Br
X
4
5
3
1
3a
1a
N
2
+e
6
O
N
H
7
8
3
The electrochemical reductions of 1 resulted in eliminations of the tosyl group to afford 3-aryl-1,3-
diazadihydroazulanone derivatives (3)7. The product yields were fairly influenced by the substituent on
the aryl group. Thus, the electrochemical reduction of 1, which has an electron donating substituents on
the aryl group (1a, 1b), did not proceed smoothly, and a large intractable resinous material was produced
along with the purely isolated product (3), as shown bellow.
A solution of 1a in anhydrous acetonitrile was electrochemically reduced in the presence of TBAP using
a platinum wire as an anode and a platinum gauze as a cathode at –1.2 V vs. Ag/Ag+ at 0℃ under a
nitrogen stream. A usual treatment of the reaction mixture gave a low yield (10 %) of 3a. The current
efficiency was very low (4 %).

The reduction of 1b gave 3b in 7 % yield with the current efficiency 3 %. On the other hand , the
reductions of 1 possessing an electron withdrawing substituent on the aryl group afforded the
corresponding products in proper yields: thus 1c and 1d formed 3c and 3d in 51 and 25 % yields with the
current efficiencies 41 and 14 %, respectively.
The structures of the products (3) were confirmed by a good coincidence of their spectral properties with
those of the authentic samples.2-4,8
Table 1. Redox Potentials.
X
Me
OMe
Cl
Oxidation
1.24
Reduction
-1.02
1.23
1.19
-0.85
-0.71
Br
1.21
-0.84
V vs. Ag/AgCl
On the other hand, some scattering is observed in the reduction potentials. This scattering and the large
negative value of the reduction potential of 1a (X=Me) show that the reduction potentials depend on the
substituents on the aryl group. Thus, in the case of reduction, the coming electron is considered to be
received in the diazadihydroazulanone skeleton.
The redox potentials of 1 measured with cyclic voltammetries are summarized in the Table 1.9 No
substituent effects are observed on the oxidation potentials suggesting that these potentials are
attributable to the oxidation of the tosyl group. Thus in the case of electrochemical oxidation of 1, the
initial stage is considered to be an elimination of an electron on the tosyl group.
Ar
N
Ar
N
Ar
N
-e
O
O
O
N
N
N
H
H
O S O
O S O
Tol
H
O S O
Tol
Tol
6
4
5
1
Ar
N
Ar
N
4
5
3a
3
O
O
Ts
6
2
O S O
Tol
N
H
N
H
1
1a
7
8
6
2
7

The reaction mechanism of the electrochemical oxidation is proposed as follows. One electron oxidation
occur a removal of one electron from the nitrogen atom at 1-position on 1 to form a cation radical
intermediate (4). An N-S bond fission in 4 generates a radical intermediate (5) and a tosyl cation (6). A
hydrogen migration in 5 forms a full conjugated radical intermediate (7). The neucleophilic attack at 6-
positon on the radical intermediate 7 to tosyl cation 6 followed by an electron transfer from either the
solvent or the supporting electrolyte can form the final product (2).
Ar
1.274
1.045
1.078
N
1.238
O
N
1.181
Ar
- 0.474
H
0.927
0.022
1.035
0.155
N
Free Valencies of 7
- 0.193
O
N
H
- 0.552
Ar
- 0.138
- 0.253
-0.022
0.077
- 0.067 N
Electron Densities of 11
- 0.151
O
N
- 0.168
- 0.040
H
- 0.085
Electron Densities of 7
The preferential recombination of the tosyl group on 6-position of 7 can be explained by the free
valencies calculated by PM3 method, which show the second maximum value at the 6-position and/or by
the electron densities which show the maximum value at the 6-position. 10
Ar
N
Ar
N
Ar
N
+e
O
O
O
N
N
N
H
H
S
O
O
O S O
Tol
O S O
Tol
H
Tol
9
10
1
8
Ar
N
Ar
N
O
O
N
H
N
H
H
3
11

The electrochemical reduction is considered to be proceed as follows. One electron reduction forms an
anion radical intermediate (8), which then removes a tosyl radical (10) to form an anion intermediate (9).
A hydrogen migration in 9 forms a full conjugated anion intermediate (11), which abstracts a hydrogen
from the solvent to form the final product (3). The maximum electron density of 11 at 1a-position can
explain the preferential hydrogen abstraction of 11 at this position.11
In summary, we found that the 1,3-diazadihydroazulanone derivatives (1) afforded the tosyl migration
product (2) under electrooxidation conditions and the tosyl elimination product (3) under electro-
reduction conditions. Further studies on electrochemistries of the azulanone derivatives are currently in
progress and will be reported in due course.
REFERENCES
1. W. E. Stewart and T. H. Siddall, Chem. Rev., 1970, 70, 517; T. Sato, Y. Fukazawa, Y. Fujise, and S. Ito,
Heterocycles, 1977, 7, 807.
2. K. Ito, K. Saito, and K. Takahashi, Bull. Chem. Soc. Jpn., 1992, 65, 812; M. Nitta, H. Tomioka, A.
Akaogi, K. Takahashi, K. Saito, and K. Ito, J. Chem. Soc., Perkin Trans. 1, 1994, 2625; K. Ito and K.
Saito, Bull. Chem. Soc. Jpn., 1995, 68, 3539.
3. K. Ito and K. Saito, Heterocycles, 1994, 38, 2691; idem, ibid., 1995, 41, 2307.
4. K. Saito, M. Hattori, T. Sato, and K. Takahashi, Heterocycles, 1992, 34, 129; S. Kondo, H. Suzuki, T.
Hattori, T. Ido, and K. Saito, ibid., 1998, 48, 1151.
5. The physical properties of 2a-d are as follows.
2a: HRMS m/z 392.1185. Calcd for C22H20N2O3S: 392.1178. MS m/z (rel intensity). 392 (16, M+),
278 (9), 262 (6), 237 (26), 236 (100), 235 (73). 1H-NMR (CDCl3)δppm. 2.26 (1H, dd, H6, J = 6.0 and
6.0 Hz), 2.38 (3H, s), 2.42 (3H, s), 4.30 (1H, bs, NH), 5.20 (1H, dd, H5, J = 6.0 and 9.7 Hz), 5.47 (1H,
dd, H7, J = 6.0 and 10.2 Hz), 6.18 (1H,d, H4, J = 9.7 Hz), 7.10 (1H, d, H8, J = 10.2 Hz), 7.20 (4H, m),
7.36 (2H, d, J = 7.5 Hz), 8.01 (2H,d, J = 7.5 Hz). IR (KBr): 3420, 1718, 1375, 1172 cm-1.
2b: HRMS m/z 408.1161. Calcd for C22H20N2O4S: 408.1153. MS m/z (rel intensity). 408 (14, M+), 278
1
(17), 253 (23), 252 (100), 251 (33). H-NMR (CDCl3)δppm. 2.27 (1H, dd, H6, J = 6.2 and 6.2 Hz),
2.45 (3H, s), 3.84 (3H, s), 4.30 (1H, bs, NH), 5.22 (1H, dd, H7, J = 6.2 and 10.2 Hz), 5.50 (1H, dd, H5,
J = 6.2 and 9.7 Hz), 6.15 (1H , d, H4, J = 9.7 Hz), 7.13 (1H, d, H8, J = 10.2 Hz), 7.23 (4H, m), 7.37
(2H, d, J = 7.5 Hz), 8.04 (2H, d, J = 7.5 Hz). IR (KBr): 3423, 1721, 1379, 1178 cm-1.
2c: HRMS m/z 412.0653. Calcd for C21H17N2O3SCl: 412.0647. MS m/z (rel intensity). 412 (14, M+),
1
259 (90), 257 (100), 215 (72). H-NMR (CDCl3)δppm. 2.30 (1H, dd, H6, J = 6.1 and 6.1 Hz), 2.44
(3H, s), 4.40 (1H, bs, NH), 5.24 (1H, dd, H7, J = 6.1 and 9.9 Hz), 5.47 (1H, dd, H5, J = 1.1 and 9.7 Hz),
6.18 (1H, d, H4, J = 9.7 Hz), 7.12 (1H, d, H8, J = 9.9 Hz), 7.30 (4H, m), 7.58 (2H, d, 7.5 Hz), 7.99 (2H,
d, J = 7.5 Hz). IR (KBr): 3425, 1721, 1374, 1173 cm-1.
2d: HRMS m/z 458.0096. Calcd for C21H17N2O3SBr: 458.0120. MS m/z (rel intensity). 458 (7, M+),
1
303 (95), 301 (100), 259 (61). H-NMR (CDCl3)δppm. 2.30 (1H, dd, H6, J = 6.3 and 6.3 Hz), 2.46
(3H, s), 4.32 (1H, bs, NH), 5.27 (1H, dd, H7, J = 6.3 and 10.5 Hz), 5.54 (1H, dd, H5, J = 1.3 and 10.0

Hz), 6.16 (1H, d, H4, J = 10.0 Hz), 7.13 (1H, d, H8, J = 10.5 Hz), 7.24 (4H, m), 7.58 (2H, d, J = 7.5
Hz), 8.02 (2H, d, J = 7.5 Hz). IR (KBr): 3422, 1719, 1375, 1170 cm-1.
6. The chemical shifts of Ha and Hb of the following compound are observed to be 6.12 ppm.
T. Ido, A Thesis for a Masterate, Nagoya Inst. Tech., 1998.
Ha
Ar
H
H
N
O
N
Ph
Hb
7. The 1H NMR spectral properties of 3a-d are as follows.
3a: 1H-NMR (CDCl3)δppm. 2.38 (3H, s), 4.20 (1H, bs), 5.16 (1H, dd, J = 9.6 and 3.0 Hz), 5.43 (1H,
d, J = 6.9 Hz), 6.11 (1H, dd, J = 6.0 and 9.6 Hz), 6.23 (1H, dd, J = 11.1 and 6.0 Hz), 6.43 (1H, dd, J =
6.9 and 11.1 Hz), 7.25 (4H,m).
3b: 1H-NMR (CDCl3)δppm. 3.83 (3H, s), 4.20 (1H, bs), 5.16 (1H, dd, J = 9.6 and 3.0 Hz), 5.39 (1H,
d, J = 7.0 Hz), 6.12 (1H, dd, J = 6.0 and 9.6 Hz), 6.24 (1H, dd, J = 11.3 and 6.0 Hz), 6.44 (1H, dd, J =
7.0 and 11.3 Hz), 6.98 (2H, d, J = 8.8 Hz), 7.26 (2H, d, J = 8.8 Hz).
3c: 1H-NMR (CDCl3)δppm. 4.18 (1H, bs), 5.17 (H, dd, J = 9.9 and 3.0 Hz), 5.47 (1H, d, J = 6.6 Hz),
6.14 (1H, dd, J = 6.3 and 9.9 Hz), 6.27 (1H, dd, J = 11.3 and 6.3 Hz), 6.45 (1H, dd, J = 6.6 and 11.3
Hz), 7.32 (2H, d, J = 8.5Hz), 7.43 (2H, d, J = 8.5Hz).
3d: 1H-NMR (CDCl3)δppm. 4.19 (1H, bs), 5.16 (1H, dd, J = 9.9 and 3.3 Hz), 5.59 (1H, d, J = 6.6 Hz),
6.14 (1H, dd, J = 6.3 and 9.9 Hz), 6.27 (1H, dd, J = 11.0 and 6.3 Hz), 6.45 (1H, dd, J = 6.6 and 11.0
Hz), 7.26 (2H, d, J = 8.5 Hz), 7.58 (2H, d, J = 8.5 Hz).
8. K. Sanechika, S. Kajigaeshi, and S. Kanemasa, Chem. Lett., 1977, 861; K. Ito, K. Saito, and K.
Takahashi, Heterocycles, 1991, 32, 1117; K. Ito, Y. Hara, R. Sakakibara, and K. Saito, ibid., 1995, 41,
1675.
9. The authors are indebted to Prof. Yoshiro Yamashita of the Institute for Molecular Science for his
measurements of cyclic voltammetries.
10. The maximum value of the free valencies appears at 4-position. However the attack of the tosyl1
group at the 4-position of 11 seems to be avoided because of the steric hindrance caused by the
adjacent aryl group.
11. A mechanism which affords 3 directly from 9, seems to be still possible. The researches on the
detailed reaction mechanism are now in progress.