Preparation of diazenes by electrophile C-coupling reactions of dry arenediazonium o-benzenedisulfonimides with Grignard reagents

Article abstract of DOI:10.1055/s-1998-6102

The diaryldiazenes (19 examples) and aryl(tertbutyl)diazenes (3 examples) 3 were prepared by electrophilic C-coupling reactions of dry arenediazonium o-benzenedisulfonimides 1 with Grignard reagents. The reactions were carried out in anhyd THF at -78°C un

Full text of DOI:10.1055/s-1998-6102

SHORT PAPERS
1235
Preparation of Diazenes by Electrophilic C-Coupling Reactions of Dry
Arenediazonium o-Benzenedisulfonimides with Grignard Reagents
Margherita Barbero, Iacopo Degani,* Stefano Dughera, Rita Fochi,* Paolo Perracino
Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, C.so M. D’Azeglio 48, I-10125 Torino, Italy
Fax +39(11)6707642; E-mail: fochi@silver.ch.unito.it
Received 1 February 1998; revised 9 March 1998
Abstract: The diaryldiazenes (19 examples) and aryl(tert-
butyl)diazenes (3 examples) 3 were prepared by electrophilic
C-coupling reactions of dry arenediazonium o-benzenedisulfon-
imides 1 with Grignard reagents. The reactions were carried out in
anhyd THF at –78°C under nitrogen and gave diazenes in 66–91%
yield with few exceptions. In all cases the anion precursor of salts
1, i.e. the o-benzenedisulfonimide, was recovered easily, in
In a wide-ranging investigation of the possible synthetic
uses of salts 1, we aimed to prepare azo compounds 3 [di-
aryldiazenes and aryl(tert-butyl)diazenes] by electrophilic
C-coupling reactions of dry salts 1 with Grignard reagents 2.
The reactions were performed by adding equimolar amounts
of Grignard reagents to suspensions of salts 1 in anhyd THF
at –78°C, under stirring and under nitrogen; complete reac-
tion took ca. 1 hour. Two isomers were noted in all the reac-
tions. In the case of (4-methoxyphenyl)phenyldiazene, the
reaction mixture was worked up at 30°C maximum (Proce-
dure A). By column chromatography, both E and Z isomers
were isolated in 70 and 23% yield, respectively. When the
crude mixture containing both isomers was heated to 70°C
for about 1 hour (Procedure B), the Z isomer isomerized into
E isomer, which was obtained in 91% yield. Examples and
yields are given in the Table. Using the standard Procedure
B we obtained diazenes 3a–w in 61–91% yield, with few
exceptions. In all cases the o-benzenedisulfonimide was re-
covered in greater than 90% yield.
greater than 90% yield.
Key words: diazenes, dry arenediazonium salts, Grignard
reagents, o-benzenedisulfonimide
It is known1 that most dry-state arenediazonium salts are
a high risk from the point of view of storage and handling,
as many physical stimuli such as heat, light, shock, static
electricity etc. can lead to their rapid decomposition, oc-
casionally explosively. Such instability has certainly lim-
ited the use of these salts in synthetic applications, both on
a laboratory scale and, even more so, on an industrial
scale. Despite this, three classes of dry-state arenediazoni-
um salts, viz., most tetrafluoroborates and some zinc dou-
ble chlorides and sulfonates, are considered low risk re-
agents and are used, though with great caution, both in the
laboratory and industrially. From a synthetic point of view
one of the advantageous features of dry arenediazonium
salts is certainly that of being able to realize reactions in
aprotic solvents with various reagents, for example car-
banions incompatible with protic solvents. On this sub-
ject, among the methods used in the past to prepare azo
compounds, various reactions were studied, though not
in-depth, using different combinations of dry arenedi-
azonium salts and organometallic reagents, precursors of
aryl and tert-butyl carbanions. Reactions specifically
studied were those between arenediazonium tetrafluorob-
orates and Grignard reagents, or organocadmium, -mercu-
ry, -lithium, and -zinc reagents,2, 3 or also between arenedi-
azonium zinc double chlorides and Grignard reagents.4–7
The best synthetic results obtained are those related to var-
ious reactions between the arenediazonium tetrafluoro-
borates and diphenylzinc (4 examples, 40–70% yield)3 or
di-tert-butylzinc (1 example, 97% yield),3 and various re-
actions between arenediazonium zinc double chlorides
and Grignard reagents (4 examples, 72–99% yield).4 In
other cases the reactions either failed completely or gave
a maximum yield of 60%; the azo compound yield for
most of the considered examples was 1 to 10%.
With regard to what is known, the proposed procedure
presents the following advantageous characteristics: (1) it
is of general validity and gives diazenes 3 in very satisfac-
tory yields; (2) highly pure dry arenediazonium salts 1 are
readily obtained, and, as outlined above, can be stored for
extended periods without decomposition and, therefore,
are potentially commercially viable; (3) to the best of our
knowledge, dry salts 1 are the only ones, apart from the
arenediazonium zinc double chlorides, able to give di-
azenes in yields of synthetic value, for reaction with the
more common precursors of carbanions, as are the
Grignard reagents; (4) different from the other dry arenedi-
azonium salts, the o-benzenedisulfonimide from which the
anion of salts 1 derives is easily recovered, avoiding the un-
desirable pollutants that occurs with the use of arenedi-
azonium tetrafluoroborates and zinc double chlorides.
MS were recorded on an HP 5970 B mass selective detector connect-
ed to an HP 5890 GC, cross-linked methyl silicone capillary column.
Column chromatography and TLC were performed on Merck silica
gel 60 (70–230 mesh ASTM) and GF 254, respectively. Petroleum
ether bp 40–70°C is abbreviated as PE. All the reactions were per-
formed in oven-dried glassware under N2. Phenylmagnesium bro-
mide, 4-tolylmagnesium bromide, 4-chlorophenylmagnesium bro-
mide and tert-butylmagnesium chloride (1 M solutions in THF) and
anhyd THF were purchased from Aldrich.
In the course of recent research, we prepared a repre-
sentative series of dry arenediazonium salts 1, that were
stabilized to an exceptionally high degree by the anion of
o-benzenedisulfonimide. Most of these salts can be stored
without decomposition for extended periods and are ready
for use.1, 8

SYNTHESIS
Short Papers
Table. Diazenes 3a–w obtained according to Procedure B
1236
Prod-
uct
Ar
R
Chromatographic
Solvent
Yield
(%)
mp (°C) or bp (°C)/Torr
MS
m/z (M+)
Founda
Reportedb
3a
3b
3c
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
Ph
Ph
Ph
4-ClC6H4
Ph
Ph
PE/CH2Cl2 (7:3)
PE/CH2Cl2 (7:3)
PE/Et2O (9:1)
71
66
69
80
71
81
84
86
91
84
85
78
52
45
45
84
79
83
82
89
80
85
83
86
67–68
71–72
90–91
E: 6811
182
196
216
216
162
212
226
246
212
226
246
192
216
230
250
230
4-MeC6H4
4-ClC6H4
Ph
t-Bu
Ph
4-MeC6H4
4-ClC6H4
Ph
4-MeC6H4
4-ClC6H4
t-Bu
E: 71–7211
E: 90–9111
E: 90–9111
E: 56/0.7511,12
3313
PE/Et2O (9:1)
90–91
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9:1)
51–52/0.3c,d
31–32
3-MeOC6H4
3-MeOC6H4
3-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
2-ClC6H4
2-ClC6H4
2-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
3-BrC6H4
3-BrC6H4
3-BrC6H4
4-BrC6H4
4-BrC6H4
4-BrC6H4
77–79
89–90
53–54
111
120–121
61–62/0.25c
34–35
78–796
C13H11ClN2O
E: 53–549
111–111.514
PE/Et2O (9:1)
PE/CH2Cl2 (7:3)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9:1)
PE/CH2Cl2 (7:3)
PE/CH2Cl2 (7:3)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
PE/Et2O (9.8:0.2)
12115
e
Ph
E: 29–3111
45–45.514
4-MeC6H4
4-ClC6H4
4-MeC6H4
4-ClC6H4
t-Bu
44–45
111–112
154–155
188–189
57–58/0.25c
69–70
120–121
124–125
88–89
112–11311
152.5–153.514
E: 18911
250
196
e
Ph
6911
260, 262
274, 276
294, 296
260, 262
274, 276
294, 296
4-MeC6H4
4-ClC6H4
Ph
4-MeC6H4
4-ClC6H4
119.54
3t
C12H8BrClN2
E: 90–9111
15211
3u
3v
3w
151–152
192–193
193–19416
a
Crystallization solvents were: PE for 3a,b,h,m,r; CHCl3/PE for 3c,f,g,i,j,n,t,u,v; pentane for 3e,l; CHCl3 for 3o,p,w and EtOH for 3s.
Mp of compounds 3a–c,h,l,p,u are identical to those reported in the literature for diazenes in the E-form. Therefore an E-form is presumable
also for all the other diazenes.
b
c
GC analysis showed a 97–98% purity. The byproduct was 1,2-di-(tert-butyl)-1-phenylhydrazine, m/z 220 (M+), in the case of 3d, 1,2-di-(tert-
butyl)-1-(4-methoxyphenyl)hydrazine, m/z 250 (M+), in the case of 3k and 1,2-di-(tert-butyl)-1-(4-chlorophenyl)hydrazine, m/z 254 (M+), in
the case of 3q. Samples of analytical purity of 3k and 3q cannot be obtained. Moreover the elemental analyses, repeated several times also
on the same sample, did not give reproducible data. Configuration E has been assigned to compounds 3k and 3q by comparison of their 1H
NMR data (see experimental section) with those reported12 for (E)-(tert-butyl)phenyldiazene.
d
e
1H NMR spectrum was identical to that reported for the E-form;12 13C NMR (CDCl3): δ = 26.85 (q, Me), 67.56 (s, C), 121.77, 128.77 and
129.77 (d, CH), 152.35 (s, CN).
Physical and spectroscopic data are not reported in the literature17 (see experimental).
ter drying (Na2SO4) and solvent removal in vacuo by heating to 30°C
with a water bath, the crude residue was column chromatographed (PE/
Et2O 9:1) to afford two products. The product eluted first was the title
compound 3h (0.74 g, 70%); mp 53–54°C (PE) (lit.9 mp 53–54°C); m/z
212 (M+). The second eluted product was the isomer (Z)-(4-
methoxyphenyl)phenyldiazene (0.24 g, 23%); mp 24–25°C (pentane)
(lit.9 mp ≈25°C); m/z 212 (M+). The aqueous solution was concentrated
in vacuo to 4–5 mL and then passed through a column of Dowex 50 × 8
ion-exchange resin (Fluka, 15 g), eluted with water (ca. 15 mL). After
water removal in vacuo, virtually pure (NMR) o-benzenedisulfonimide
was recovered in 93% yield (1.02 g): mp 192–194°C (toluene) (lit.1 mp
192–194°C).
CAUTION! All dry diazonium salts are potentially explosive. There-
fore they must be carefully stored and handled.
Arenediazonium o-Benzenedisulfonimides 1:
Benzenediazonium o-benzenedisulfonimide (1; Ar = Ph), 3- and 4-
methoxybenzenediazonium o-benzenedisulfonimide (1; Ar = 3-
MeOC6H4, 4-MeOC6H4), 2- and 4-chlorobenzenediazonium o-ben-
zenedisulfonimide (1; Ar = 2-ClC6H4, 4-ClC6H4) and 3- and 4-bromo-
benzenediazonium o-benzenedisulfonimide (1; Ar = 3-BrC6H4, 4-
BrC6H4) were prepared as recently reported by us.1, 8
Two isomers were noted during the preparation of the other diazenes 3
according to Procedure A. No particular device was, however, adopted
for their separation.
Preparation of Diazenes 3a–w; (E)-(4-Methoxyphenyl)phenyldia-
zene (3h); Typical Procedures:
Procedure A: A suspension of 4-methoxybenzenediazonium o-benzene-
disulfonimide (1; Ar = 4-MeOC6H4; 1.77 g, 5 mmol) in anhyd THF
(15 mL) was vigorously stirred and cooled to –78°C under N2 flow. A
solution of 1 M phenylmagnesium bromide in THF (5 mL, 5 mmol) was
added dropwise using a syringe, over a period of 10 min. The solvent
immediately became dark red and a red solid substance began to precip-
itate. Stirring at –78°C was continued for 1 h until azo coupling reaction
with 2-naphthol proved negative. The mixture was poured into water (30
mL) and extracted with Et2O (2 × 30 mL). The organic extracts were
separated from the aqueous solution and washed with water (30 mL). Af-
Procedure B: The reaction was carried out as described in Procedure
A, with the only difference that the organic solvent was removed un-
der vacuo by heating to 70°C with a water bath. Heating was main-
tained for about 1 h until TLC analysis (PE/Et2O 9:1) showed the
complete disappearance of the Z isomer (always held more tenacious-
ly)10 and the presence of the E isomer only, which was successively
purified by chromatography on a short column (PE/Et2O 9:1). The
pure title compound 3h was obtained in 91% yield (0.96 g). o-Ben-
zenedisulfonimide was recovered in 93% yield (1.02 g).

SYNTHESIS
September 1998
1237
All diazenes 3a–w were prepared according to Procedure B. Yields,
chromatographic solvents and physical properties are reported in the
Table.
This work was supported by the National Research Council of Italy
(CNR), Legge 95/95 and by Ministero dell’Università e della Ricerca
Scientifica e Tecnologica (MURST).
(4-Chlorophenyl)(3-methoxyphenyl)diazene (3g):
1H NMR (CDCl3): δ = 3.92 (s, 3 H, Me), 6.95–7.20, 7.35–7.75 and
7.75–8.05 (3 m, 1:5:2, 8 H ar.).
(1) Barbero, M.; Crisma, M.; Degani, I.; Fochi, R.; Perracino, P.
Synthesis, in press; and general references cited therein.
(2) Curtin, D. Y.; Ursprung, J. A. J. Org. Chem. 1956, 21, 1221.
(3) Curtin, D. Y.; Tveten, J. L. J. Org. Chem. 1961, 26, 1764.
(4) Nomura, Y. Bull. Chem. Soc. Jpn. 1961, 34, 1648.
(5) Nomura, Y.; Anzai, H. Bull. Chem. Soc. Jpn. 1962, 35, 111.
(6) Nomura, Y.; Anzai, H.; Tarao, R.; Shiomi, K. Bull. Chem. Soc.
Jpn. 1964, 37, 967.
13C NMR (CDCl3): δ = 55.09 (q, Me), 105.58, 117.03, 117.70,
123.93, 128.98 and 129.48 (d, CH), 136.72 (s, CCl), 150.69 and
153.38 (s, CN), 160.11 (s, CO).
Anal. calcd for C13H11ClN2O: C, 63.29; H, 4.49; N, 11.36; Cl, 14.37.
Found: C, 63.34; H, 4.42; N, 11.26; Cl, 14.25.
(7) Garst, M. E.; Lukton, D. Synth. Commun. 1980, 10, 155.
(8) Barbero, M.; Degani, I.; Fochi, R.; Perracino, P. IT Patent
MI97A 000473, 1997. PCT/EP98/01145.
(3-Bromophenyl)(4-chlorophenyl)diazene (3t):
1H NMR (CDCl3): δ = 7.15–7.65 and 7.70–8.10 (2 m, 1:1, H ar.).
13C NMR (CDCl3): δ = 123.07, 124.25, 124.76, 129.47, 130.48 and
133.84 (d, CH), 129.47 (s, CBr), 137.55 (s, CCl), 150.68 and 153.37
(s, CN).
Barbero, M.; Degani, I.; Fochi, R.; Perracino, P. 2nd German-
Italian Symposium, Goslar (Germany), 29.5–1.6.1997, abstract
p 32.
(9) Le Fèvre, R. J. W.; Northcott, J. J. Chem. Soc. 1953, 867.
(10) Birnbaum, P. P.; Linford, J. H.; Style, D. W., G. Trans. Faraday
Soc. 1953, 49, 735.
Anal. calcd for C12H8BrClN2: C, 48.76; H, 2.73; N, 9.48; Br, 27.03;
Cl, 11.99. Found: C, 48.84; H, 2.81; Br, 27.23; Cl, 12.08; N, 9.35.
(11) Dictionary of Organic Compounds on CD-ROM, version 5:1;
Chapman & Hall Electronic Publishing Division: London,
1997.
(12) Ege, S. N.; Sharp, R. R. J. Chem. Soc. (B) 1971, 2014.
(13) Martynoff, M. Bull. Soc. Chim. Fr. 1951, 214.
(14) Weickhardt, B.; Siegrist, A. E. Helv. Chim. Acta 1972, 55, 138.
(15) Ayyangar, N. R.; Naik, S. N.; Srinivasan, K. V. Tetrahedron
Lett. 1989, 30, 7253.
(E)-(tert-Butyl)(4-methoxyphenyl)diazene (3k):
1H NMR (CDCl3): δ = 1.37 (s, 9 H, 3 Me), 3.86 (s, 3 H, OMe), 6.97
and 7.71 (2 d, 1:1, J = 9.15 Hz, 4 H ar.).
13C NMR (CDCl3): δ = 26.92 (q, Me), 55.29 (s, C), 113.76 and 123.49
(d, CH), 146.36 (s, CN), 161.00 (s, CO).
(16) Hartmann, H.; Schulze, M. Dyes and Pigments 1991, 15, 255.
(17) Minisci, F.; Coppa, F.; Fontana, F.; Pianese, G.; Zhao, L. J. Org.
Chem. 1992, 57, 3929.
(E)-(tert-Butyl)(4-chlorophenyl)diazene (3q):
1H NMR (CDCl3): δ = 1.32 (s, 9 H, 3 Me), 7.38 and 7.60 (2 d, 1: 1, J
= 8.9 Hz, 4 H ar.).
13C NMR (CDCl3): δ = 26.48 (q, Me), 67.54 (s, C), 122.92 and 128.81
(d, CH), 135.54 (s, CCl), 150.52 (s, CN).