Full Papers
doi.org/10.1002/ejoc.202100006
31P, 202.0 MHz) and “Ascent 700” (1H, 700.1 MHz; 13C, 176.0 MHz)
spectrometer, using different solvents purchased by Deutero. The
NMR signals were referenced to residual solvents measured relative
to TMS as internal standard.
Dimethyl 3,3'-diazene oxide 1,2-diyldibenzoate 1d (13 mg, 86%,
1
2
3
4
5
6
7
8
9
°
yellow solid, mp=134.2–136.6 C): Rf =0.46 (CH2Cl2) (CH2Cl2/n-
1
°
pentane=1:3); H NMR (700 MHz, CDCl3, 24 C, δ): 8.97 (t, J=
1.8 Hz, 1 H), 8.78 (t, J=1.7 Hz, 1 H), 8.53 (ddd, J=8.2, 2.3, 1.1 Hz, 1
H), 8.43 (ddd, J=8.1,2.0, 1.2 Hz, 1 H), 8.26 (ddd, J=7.8, 1.3, 1.3 Hz, 1
H), 8.09 (ddd, J=7.8, 1.4,1.4 Hz, 1 H), 7.63 (t, J=7.9 Hz, 1 H), 7.58 (t,
J=8.9 Hz, 1 H), 3.99 (s, 3 H), 3.96 (s, 3 H). 13C NMR (176 MHz, CDCl3,
Electron impact mass spectrometry The EI-MS measurements were
done with a high-resolution sector field “DFS” mass spectrometer
from Thermo scientific.
°
24 C, δ): 166.5 (C), 165.7 (C), 148.3 (CH), 143.8 (C), 132.8 (CH), 131.4
(CH), 130.9 (CH), 130.7 (CH), 129.4 (CH), 129.1 (CH),128.9 (CH), 127.1
(CH), 126.5 (CH), 123.6 (CH), 52.6 (CH3), 52.4 (CH3). LRMS (EI-TOF):
m/z calculated for C16H14N2O5 [M]+, 314.0903; found, 314.0493.
Electrospray ionization mass spectrometry The ESI-MS measure-
ments were done with a “Synapt-G2 HDMS” mass spectrometer
from Waters. The spectrometer is used in combination with a time-
of-flight analyzer.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
1,2-Bis(3-cyanophenyl)diazene oxide 1e (11 mg, 82%, pale yellow
solid, mp=133.1–134.3 C): Rf =0.08 (EtOAc/n-hexane=1:8); 1H
°
Contact angle measurement The contact angle measurements
were performed using a “Drop Shape Analyzer-DSA25” from Krüss.
Using Diiodomethane ReagentPlus (99%) from Sigma-Aldrich and
Water Rotisolv HPLC Gradient Grade from Roth.
°
NMR (700 MHz, CDCl3, 24 C, δ): 8.65 (t, J=1.8, 1 H), 8.60–8.57 (m, 2
H), 8.32 (ddd, J=8.2, 1.7 Hz, 1.3 Hz, 1H), 7.91–7.89 (dt, J=1.5,
1.5 Hz,1H), 7.73–7.69 (m, 2H), 7.65–7.61 (m, 1H). 13C NMR (176 MHz,
°
CDCl3, 24 C, δ): 148.3 (C), 143.9 (C), 135.6 (CH), 133.4 (CH), 130.42
Melting points The melting points were determined on a Melting
(CH), 130.41 (CH), 130.1 (CH), 129.1 (CH), 126.8 (CH), 126.5 (CH),
118.2 (C), 117.4 (C), 113.8 (C), 113.5 (C). LRMS (EI-TOF): m/z
calculated for C14H8N4O [M]+, 248.0698; found, 248.0501.
°
Point B-545 (Büchi). A gradient of 1 C/min was applied.
1,2-Bis(4-chlorophenyl)diazene oxide 1f (8 mg, 66%, pale yellow
General Procedure for the Reductive Dimerization of
Nitrosobenzenes, 2 To Form Azoxybenzenes 1
solid, mp=152.0–154.1 C): Rf =0.25 (EtOAc/n-hexane=1:50); 1H
°
°
NMR (700 MHz, CDCl3, 24 C, δ): 8.25 (d, J=9.1 Hz, 2H), 8.16 (d, J=
9.0 Hz, 2H), 7.49 (d, J=9.1 Hz, 2H), 7.45 (d, J=9.0 Hz, 2H). 13C NMR
A solution of 2 in DMSO (0.05 M; 2 eq) with cyclohexanone (1 eq) in
a HamiltonTM 1000 Series GastightTM Syringe was injected via a
Legato 200 syringe pump into the MFR. After 16–44 h of running
reaction and quenching of the crude product solution using sat.
NH4Cl solution, the reaction mixture was extracted using DCM or
EtOAc. After phase separation, the solvent was evaporated by
rotavap, and 1 was isolated using column chromatography of the
crude product.
°
(176 MHz, CDCl3, 24 C, δ): 146.6 (C), 142.3 (C), 138.1 (C), 135.3 (C),
129.1 (CH×2), 129.0 (CH×2), 127.1 (CH×2), 123.7 (CH×2). LRMS (EI-
TOF): m/z calculated for C12H8Cl2N2O [M]+, 266.0014; found,
265.9744.
1,2-Bis(4-bromophenyl)diazene oxide 1g (12 mg, 67%, yellowish
solid, mp=166.5–168.4 C): Rf =0.25 (EtOAc/n-hexane=1:8); 1H
°
°
NMR (700 MHz, CDCl3, 24 C, δ): 8.18 (d, J=8.9 Hz, 2H), 8.08 (d, J=
8.8 Hz, 2H), 7.65 (d, J=8.9 Hz, 2H), 7.61 (d, J=8.8 Hz, 2H). 13C NMR
°
(176 MHz, CDCl3, 24 C, δ): 147.1 (C), 142.6 (C), 132.1 (CH×2), 132.0
General Procedure for the Reductive Dimerization of
Nitrosobenzenes, 2 To Form unsymmetric Azoxybenzenes 1
(CH×2), 127.3 (CH×2), 126.5 (C), 123.9 (CH×2), 123.6 (C). LRMS (EI-
TOF): m/z calculated for C12H8Br2N2O [M]+, 355.8983; found,
355.8945.
Two separate solutions of the nitroso compound in DMSO (0.05 M;
2 eq) with cyclohexanone (1 eq) in a HamiltonTM 1000 Series
GastightTM Syringe were injected into the MFR via two syringes
using a T-junction using a Legato 200 syringe. After 24 h of running
reaction and quenching of the crude product solution using sat.
NH4Cl solution, the reaction mixture was extracted using DCM or
EtOAc. After phase separation, the solvent was evaporated by
rotavap.
Dimethyl 4,4'-diazene oxide 1,2-diyldibenzoate 1h (9 mg, 68%,
°
yellow solid, mp=199.1–201.4 C): Rf =0.39 (CH2Cl2) (CH2Cl2/n-
1
°
hexane=1:3); H NMR (700 MHz, CDCl3, 24 C, δ): 8.39 (d, J=8.6 Hz,
2H), 8.22–8.15 (m, 6H), 3.97 (s, 3H), 3.95 (s, 3H). 13C NMR (176 MHz,
°
CDCl3, 24 C, δ): 166.2 (C), 165.8 (C), 150.9 (C), 147.0 (C), 133.3 (C),
130.7 (C), 130.4 (CH×2), 130.2 (CH×2), 125.4 (CH×2), 122.6 (CH×2),
52.6 (CH3), 52.3 (CH3). LRMS (EI-TOF): m/z calculated for C16H14N2O5
[M]+, 314.0903; found, 314.0557.
The differently substituted nitrosobenzenes used were prepared by
the oxidation of the corresponding aniline derivatives using oxone
as described by Rück-Braun and coworker.[40]
1,2-Bis(3-bromophenyl)diazene oxide 1i (15 mg, 74%, yellowish
1
°
solid, mp=107.5–109.8 C): Rf =0.5 (EtOAc/n-hexane=1:7); H NMR
1,2-Bis(4-cyanophenyl)diazene oxide 1b (15 mg, 98%; yellowish
°
(700 MHz, CDCl3, 24 C, δ): 8.47 (t, J=1.9 Hz, 1 H), 8.41 (t, J=1.9 Hz,
solid, mp=195.7–198.1 C): Rf =0.13 (EtOAc/n-hexane=1:8); 1H
°
1 H), 8.26–8.23 (m, 1H), 8.07–8.04 (m, 1 H), 7.73–7.69 (m,1 H), 7.56–
°
7.53 (m, 1 H), 7.40 (t, J=8.2 Hz, 1 H), 7.37 (t, J=8.1 Hz, 1 H). 13C
NMR (700 MHz, CDCl3, 24 C, δ): 8.46 (d, J=8.5 Hz, 2H), 8.23 (d, J=
8.5 Hz, 2H), 7.87 (d, J=8.9 Hz, 2H), 7.79 (d, J=8.7 Hz, 2H). 13C NMR
°
NMR (176 MHz, CDCl3, 24 C, δ): 149.2 (C), 145.1 (C), 135.3 (CH),
°
(176 MHz, CDCl3, 24 C, δ):150.6 (C), 146.7 (C), 133.5 (CH×2), 133.2
133.2 (CH), 130.6 (CH), 130.4 (CH), 128.7 (CH), 126.1 (CH), 124.9 (CH),
122.9 (C), 122.7 (C), 121.5 (CH). LRMS (EI-TOF): m/z calculated for
C12H8Br2N2O [M]+, 355.8983; found, 355.8794.
(CH×2), 126.4 (CH×2), 123.7 (CH×2), 118.6 (C), 117.7 (C), 116.5 (C),
113.5 (C). LRMS (EI-TOF): m/z calculated for C14H8N4O [M]+,
248.0698; found, 248.0425.
1,2-Bis(2-cyanophenyl)diazene oxide 1j (15 mg, 72%, yellowish
solid, mp=192.4–193.5 C): Rf =0.16 (EtOAc/n-hexane=1:8); 1H
1,2-Bis(3-nitrophenyl)diazene oxide 1c (13 mg, 93%, white solid,
°
mp=145.3À 146.4 C): Rf =0.15 (EtOAc/n-hexane=1:6); 1H NMR
°
°
NMR (700 MHz, CDCl3, 24 C, δ): 8.87 (d, J=8.1 Hz, 1 H), 8.47 (d, J=
°
(700 MHz, CDCl3, 24 C, δ): 9.21 (t, J=2.0 Hz, 1 H), 9.12 (t, J=2.0 Hz,
8.3 Hz, 1 H), 7.91 (dd, J=7.5, 1.4 Hz, 1H), 7.85–7.77 (m, 2H), 7.76–
7.70 (m, 2H), 7.53 (t, J=7.6 Hz, 1H). 13C NMR (176 MHz, CDCl3, 24 C,
1 H), 8.71 (ddd, J=8.2, 2.1, 0.9 Hz, 1 H), 8.49 (m, 2 H), 8.31 (ddd, J=
°
8.2, 2.1, 0.9 Hz, 1 H), 7.79 (t, J=8.3 Hz, 1 H), 7.71 (t, J=8.2 Hz, 1 H).
δ): 149.4 (C), 144.9 (C), 135.6 (CH), 134.1 (CH), 133.9 (CH), 133.7 (CH),
132.5 (CH), 130.6 (CH), 125.3 (CH), 123.7 (CH), 116.8 (C), 116.1 (C),
111.9 (C), 108.1 (C). LRMS (EI-TOF): m/z calculated for C14H8N4O
[M]+, 248.0698; found, 248.0627.
13
°
C NMR (176 MHz, CDCl3, 24 C, δ): 148.5 (C), 148.4 (C×2), 143.9 (C),
131.6 (CH), 130.3 (CH), 129.8 (CH), 128.0 (CH), 126.8 (CH), 124.6 (CH),
120.5 (CH), 118.1 (CH). LRMS (EI-TOF): m/z calculated for C12H8N4O5
[M]+, 288.0495; found, 288.0316.
Eur. J. Org. Chem. 2021, 1628–1636
1634
© 2021 The Authors. European Journal of Organic Chemistry published
by Wiley-VCH GmbH