Reactions of arenediazonium o-benzenedisulfonimides with aliphatic triorganoindium compounds

Article abstract of DOI:10.1002/ejoc.200700931

The reaction of various arenediazonium o-benzenedisulfonimides with aliphatic triorganoindium compounds is described. Surprisingly, with triethyl- or tributylindium we obtained N-ethyl- or N-butylanilines, respectively. This is the first case in which, at least formally, the reactive site of a diazonium salt is the nitrogen atom directly bonded to the aromatic ring. In contrast, with trimethylindium we obtained only formaldehyde (aryl)hydrazones. In order to explain the difference between trimethyl- and triethylindium we have proposed some reaction mechanisms, supported by detailed density functional (DFT) calculations. The possible role of diazene/hydrazone tautomerism initially assumed was discarded and therefore three mechanisms for the key step (nucleophilic addition of the trialkylindium to the N=N double bond of diazene) were studied. For the favoured mechanism there is a difference in the energy barriers of 2 kcalmol^-1 between the reactions with trimethyl- and triethylindium. This difference is explained on the basis of the different C-In bond energies in the two organometallics and it is assumed to be enough to explain their different behaviour under the experimental conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200700931

FULL PAPER
DOI: 10.1002/ejoc.200700931
Reactions of Arenediazonium o-Benzenedisulfonimides with Aliphatic
Triorganoindium Compounds
Margherita Barbero,[a] Silvano Cadamuro,[a] Stefano Dughera,*[a] and Giovanni Ghigo*[a]
Keywords: Indium / Amines / Diazo compounds / Nucleophilic addition / Density functional calculations
The reaction of various arenediazonium o-benzenedisulfon-
imides with aliphatic triorganoindium compounds is de-
scribed. Surprisingly, with triethyl- or tributylindium we ob-
tained N-ethyl- or N-butylanilines, respectively. This is the
first case in which, at least formally, the reactive site of a
diazonium salt is the nitrogen atom directly bonded to the
aromatic ring. In contrast, with trimethylindium we obtained
only formaldehyde (aryl)hydrazones. In order to explain the
difference between trimethyl- and triethylindium we have
proposed some reaction mechanisms, supported by detailed
density functional (DFT) calculations. The possible role of di-
azene/hydrazone tautomerism initially assumed was dis-
carded and therefore three mechanisms for the key step (nu-
cleophilic addition of the trialkylindium to the N=N double
bond of diazene) were studied. For the favoured mechanism
there is a difference in the energy barriers of 2 kcalmol–1 be-
tween the reactions with trimethyl- and triethylindium. This
difference is explained on the basis of the different C–In
bond energies in the two organometallics and it is assumed
to be enough to explain their different behaviour under the
experimental conditions.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Introduction
Recently we reported the reactions between arenediazon-
ium o-benzenedisulfonimides and aromatic triorganoind-
ium compounds; depending on the reaction conditions, it
was possible to obtain two different products, biaryls or
diaryldiazenes.[1]
As a follow-up of previous research, in this paper we re-
port a study of the reactions of arenediazonium o-benzene-
disulfonimides 1 with aliphatic triorganoindium com-
pounds [triethyl- (2) and tributylindium (3)]. To our great
surprise, an aqueous treatment of the reaction mixtures
gave, in good yields, N-ethyl- 4 and N-butylanilines 5,
respectively, and not the expected diazenes. Furthermore,
with trimethylindium (10) we obtained formaldehyde (aryl)-
hydrazones 11 and not the expected N-methylanilines
(Scheme 1). Therefore, in order to explain these unusual
results, we have proposed some reaction mechanisms, sup-
ported by detailed density functional (DFT) calculations.
Currently, the main method of preparing indium organo-
metallics involves the reaction of indium(III) chloride with
readily available lithioorganic compounds or Grignard rea-
gents. In this way it is possible to obtain a large variety of
[a] Dipartimento di Chimica Generale ed Organica Applicata
dell’Università,
Corso M. d’Azeglio 48, 10125 Torino, Italy
Fax: +39-011-6707642
E-mail: stefano.dughera@unito.it
giovanni.ghigo@unito.it
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Scheme 1.
862
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 862–868

Reactions of Arenediazonium o-Benzenedisulfonimides
indium organometallic compounds.[2] Moreover, they have moisture (Table 1, entry 1). As has been said before, we ob-
attracted the attention of organic chemists because of the tained N-butyl-4-methoxyaniline (5c) in a poor yield
ease with which they can be prepared,[2] their remarkable (0.05 g, 6%) with weak traces by GC-MS of 1-(4-meth-
reactivity[3] and low toxicity.[4] A wide variety of indium oxyphenyl)-2-butyldiazene (13c) and 1,2-dibutyl-1-(4-meth-
organometallics have been recently used in fundamental re- oxyphenyl)hydrazine (7c).
actions in the field of organic synthesis with excellent re-
The formation of 5c was very surprising since, to the best
of our knowledge, no reactions have been reported in
sults.[5]
It must be stressed that arenediazonium o-benzenedisul- which, at least formally, the reactive site of the diazonium
fonimides 1[6] have several advantages over other diazonium salt is the nitrogen atom bonded directly to the aromatic
salts, mainly due to their high stability and easy prepara- ring.
tion, but also there are ecological and economic advantages
First of all, it must be stressed that 5c was formed only
as it is possible to recover, at the end of reactions, o- in the reaction cited above; in fact by using other common
benzenedisulfonimide (9) which can be reused to prepare organometallics, as reported in the experimental section, 1c
other salts, with.
did not react with tetrabutyltin, butylboronic acid or tri-
butylborane, even in drastic conditions (collateral proof a).
In contrast, with butyllithium or butylmagnesium chloride
we observed only the decomposition of 1c without ob-
Results and Discussion
First, we treated 4-methoxybenzenediazonium o- taining any significant product (collateral proof b).
benzenedisulfonimide (1c) with an equimolar amount of tri- On this basis, we decided to study the reaction in more
butylindium (3) at room temperature in anhydrous THF depth, first of all in order to explain the mechanism and
and under a continuous flow of N2 in order to exclude then to improve the yield of the final products 4 or 5. No
N,N-dialkylanilines were detected or isolated, even in traces.
This is very interesting since numerous procedures have
Table 1. Trial reactions between 1c and 3.
been proposed for the preparation of N-monoalkylanil-
Entry
Molar ratio
% yield
ines.[7,8] However, such procedures can have drawbacks,
mainly the formation of N,N-dialkylation products along-
side N-monoalkylation products.
1c/3
5c
7c
1
2
3
4
5
1:1
1:2
1:2.5
1:3
1:5
6[a]
Tr[b]
Tr[b]
Tr[b]
12[c]
51[c]
51[a]
95[a]
73[c]
14[c]
We made many attempts to improve the reaction yields
(Table 1). The optimal reaction conditions (entry 3) involve
a 1:2.5 molar ratio of reagents. Under these conditions, we
recovered a good yield of 5c (95%). Note that in entries 4
and 5 (Table 1), with a high excess of 3, we observed an
increased yield of 7c which could be isolated and charac-
terized.
[a] Yields refer to the product isolated by washing with pentane
and filtering through a Büchner funnel. [b] Tr = Traces. [c] Yields
refer to the pure products isolated by column chromatography. The
eluent was petroleum ether/diethyl ether (9:1).
Table 2. Synthesis of N-alkylanilines 4 and 5.
Entry
N-Alkylanilines
Ar
% yield[a,b]
N-Alkylanilines 4 and 5
4, 5
R
4, 5
m/z [M]+
M.p.[c] or b.p. [°C/Torr]
Lit. m.p. or b.p. [°C/Torr]
1
2
3
4
5
6
7
8
4a
5a
4b
5b
4c
5c
4d
5d
4e
5e
4f
Ph
Ph
Et
Bu
Et
Bu
Et
Bu
Et
Bu
Et
Bu
Et
Bu
Et
Bu
Et
82
87
89
93
86
95
71
75
69
78
75
82
84
85
79
92
71
75
121
149
135
163
151
179
201
229
166
194
166
194
166
194
179
207
149
177
57–58/0.4
60–61/0.5
63–64/0.5
70–71/0.5
67–68/0.5
80–81/0.5
77–78/0.5
95–96/0.5
70–71/0.5
81–82/0.6
52–53
87–88/0.5
69–70
95–96
140–141
104
62–63/0.5
91–92/0.5
204/760[22]
59–60/0.1[23]
96/10.2[24]
4-MeC6H4
4-MeC6H4
4-MeOC6H4
4-MeOC6H4
4-BrC6H4
74–79/0.5[25]
120–122/9[26]
142–145/6[27]
131–132/10[26a][d]
95–96/0.5[28]
93/13.5[24]
4-BrC6H4
9
2-NO2C6H4
2-NO2C6H4
3-NO2C6H4
3-NO2C6H4
4-NO2C6H4
4-NO2C6H4
4-MeOCOC6H4
4-MeOCOC6H4
2,6-Me2C6H3
2,6-Me2C6H3
10
11
12
13
14
15
16
17
18
162–164/8[29]
53–54[30]
[30][e]
5f
4g
5g
4h
5h
4i
69[31]
96–97[32]
138–139[33]
104–105[34]
51–54/0.1[35][f]
116–118/0.1[36]
Bu
Et
Bu
5i
[a] Yields refer to the pure products. [b] In all the reactions, traces of the corresponding diazenes 12 and 13 and hydrazines 6 and 7 are
always detected in the MS analysis. [c] Crystallization solvent: MeOH. [d] No NMR spectroscopic data for product 4d have been reported
in the literature. [e] Product 5f is known in the literature, but only the spectroscopic data have been reported. [f] No NMR spectroscopic
data for product 4i have been reported in the literature.
Eur. J. Org. Chem. 2008, 862–868
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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863

M. Barbero, S. Cadamuro, S. Dughera, G. Ghigo
FULL PAPER
Having found the optimal reaction conditions, numerous
We assume that the reaction can take place through the
and variously substituted arenediazonium o-benzenedisul- formation of diazene 12 or 13 by electrophilic carbon-coup-
fonimides 1 were treated with 2 or 3. All the reactions were ling between 1 and 2 or 3. Diazene 12 or 13, by nucleophilic
carried out in THF at room temperature (Scheme 1). The addition of 2 or 3 to the N=N double bond, may give rise
results are listed in Table 2. The reaction is not affected by to intermediate 14 or 15, which probably decomposes to
electronic effects. In fact, 4 and 5 were obtained in high afford 4 or 5. In order to explore in depth the mechanism
yields starting from diazonium salts bearing either electron- by which 4 or 5 form, further investigations are in progress.
donating or -withdrawing groups. Moreover, it seems that
In the same paper,[9] we reported that the reaction of (Z)-
the reaction is not drastically influenced by steric effects; (tert-butylsulfanyl)(aryl)diazenes with methyllithium led to
the hindered 4i and 5i were obtained in moderate yields N-methylanilines, but, to our great surprise, in this research
(Table 2, entries 17 and 18).
(Scheme 1) the reaction of salt 1c with trimethylindium (10)
From all the reactions we also recovered o-benzenedisul- led to only formaldehyde (4-methoxyphenyl)hydrazone
fonimide (9) (about 70%). Product 9 is probably derived (11c) in good yield; no N-methylaniline was found. Also,
from hypothetical intermediates 8 (reported in brackets in with other salts 1 we obtained the same good results, as
Scheme 1), but these were never detected in spectral analy- reported in Table 3; we recovered good amounts of 9 too.
ses. Product 9 could be recycled and used to prepare other
salts 1.
Tautomerism between diazenes and hydrazones is well
known, with the latter unable to undergo nucleophilic ad-
In our previous research,[9] we set up a general procedure dition. A theoretical study[10] has shown for methyldiazene
for the preparation of N-monoalkylanilines by reacting (Z)- and formaldehyde methylhydrazone that the most stable
(tert-butylsulfanyl)(aryl)diazenes with various alkyllithium tautomer is formaldehyde hydrazone. At the highest level of
derivatives. We proposed a reaction mechanism that can be theory, formaldehyde hydrazone is 2.0 kcal/mol more stable
used, however partly, also in this case (Scheme 2).
than methyldiazene. However, no definite and unequivocal
data have been reported for more complex diazenes and
hydrazones.[11]
In our case, with triethyl- and tributylindium we assume
that the tautomerism is shifted towards 12a or 13a which
can react with 2 or 3 to afford 4 or 5 (Scheme 3). On the
other hand, with trimethylindium the tautomerism could be
shifted towards 11a which cannot further react with 10 to
form N-methylaniline. In order to verify this hypothesis, we
performed a theoretical study on the tautomerism involving
compounds 12a and 16. The results (see the Supporting In-
formation) show that in both cases the tautomers 11a and
17 (and likely 18) are more stable than the tautomers 16
and 12a (and 13a). However, the energy barrier for the
intramolecular proton transfer is very high (almost
Scheme 2.
Scheme 3.
Table 3. Synthesis of formaldehyde (aryl)hydrazones 11.
Entry
Formaldehyde (aryl)hydrazones
% yield[a]
m/z [M]+
M.p.[b] [°C]
Lit. m.p. [°C]
11
Ar
1
2
3
4
5
6
7
8
9
11a
11b
11c
11d
11e
11f
11g
11h
11i
Ph
79
84
83
89
76
77
88
81
69
120
134
150
200
165
165
165
194
148
31–32
43–44
38–39
77–78
87–88
94–95
179–180
56–57
33–34
32[37]
[c]
4-MeC6H4
4-MeOC6H4
4-BrC6H4
2-NO2C6H4
3-NO2C6H4
4-NO2C6H4
4-MeOCOC6H4
2,6-Me2C6H3
[c]
[38][d]
85–86[39][e]
[c]
181–182[40]
[c]
[c]
[a] Yields refer to the pure products. [b] Crystallization solvent: MeOH. [c] Products 11b,c, 11f and 11h,i are unknown in the literature.
[d] Product 11d is known in the literature but only the spectroscopic data have been reported. [e] No NMR spectroscopic data have been
reported in the literature for product 11e.
864
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 862–868

Reactions of Arenediazonium o-Benzenedisulfonimides
60 kcalmol–1). Such a barrier, which we assume cannot
change significantly for 12 (and 13), should prevent taut-
omerism in both cases. Thus, we assume that this process
would take place only with the catalytic effect of water
added at the end of the reaction. The explanation for the
different behaviour of 10 must be found in the key step:
nucleophilic addition to the N=N double bond.
Three different mechanisms for the addition were studied
(see the Supporting Information). The more promising
(Scheme 4, Table 4) starts from the N–In complexes formed
during the electrophilic carbon-coupling in which the re-
maining dialkylindium cation binds to the same nitrogen
atom bonded to the alkyl group. This step, studied for tri-
methylindium only, presents an energy barrier (TS-1/19) of
less than 1 kcalmol–1 and is very exoergic and very fast. The
IRC confirmed the formation of complex 19. Complexes 19
and 21 are quite reactive towards a second trialkylindium
molecule. The energy barriers for this step are 22.7 and
20.7 kcalmol–1, respectively, for TS-19/20 (Figure 1) and
TS-21/22 and differ by 2 kcalmol–1. This difference is
enough to make the reaction of 10 25 times slower than the
reaction of 2. Owing to the decomposition of the diazenes
and 10 (see the Exp. Sect.), this delay could be enough to
prevent the addition reaction of 10. Quenching with water,
which catalyzes the tautomerism of diazene to the unreac-
tive hydrazone, would finally stop the reaction.
Figure 1. The transition-state structure for the third addition
mechanism.
We believe that the reason for the differences in the en-
ergy barriers can be found in the different C–In bond
energies in the alkylindium molecules: D0 = 55 and
47 kcalmol–1 for trimethyl- and triethylindium, respectively.
The energy of the transition-state structures involving the
methyl group are higher because the C–In bond-breaking
in 10 requires 8 kcalmol–1 more energy than that in 2.
Conclusions
In conclusion, we have developed a new procedure for
the synthesis of N-monoalkylanilines 4 or 5 or formalde-
hyde (aryl)hydrazones 11 in good yields. It must be emphas-
ized that i) among the most common aliphatic organome-
tallics, only indium organometallics 2, 3 and 10 can yield
such reactions, ii) to the best of our knowledge, no reactions
of diazonium salts have been reported in the literature in
which, at least formally, the reactive site is the nitrogen
atom directly bonded to the aromatic ring and iii) the reac-
tion with trimethylindium (10) only yields formaldehyde
(aryl)hydrazones. The different behaviour of 10 has been
explained on the basis of its stronger C–In bond in the or-
ganometallic. This different bond energy leads to a higher
energy barrier for the nucleophilic addition step and, there-
fore, to a slower reaction. Decomposition of the reactants
and quenching with water prevent the nucleophilic addition
of 10.
Scheme 4.
Table 4. Zero-point corrected energies for the addition mecha-
nism.[a]
Experimental Section
General Remarks: Column chromatography and TLC were per-
formed on Merck silica gel 60 (70–230 mesh ASTM) and GF 254,
respectively. Petroleum ether (PE) refers to the fraction boiling in
the range 40–70 °C. 1H NMR spectra were recorded with a Bruker
Avance 200 spectrometer. Mass spectra were recorded with an HP
5989B mass-selective detector connected to an HP 5890 GC, cross-
linked methylsilicone capillary column. All the reactions were per-
formed under a continuous flow of N2 in oven-dried glassware and
anhydrous THF was used as solvent. Room temperature (room
temp.) is 20–25 °C. Chromatographic solvent, yields and physical
and spectroscopic data of the pure (GC, GC-MS, TLC, 1H NMR)
Structure
E [kcalmol–1]
Phenyldiazonium+ + 2 InMe3
TS C-coupling
1 + 2 10
TS-1/19 + 10
19 + 10
TS-19/20
20
1 + 2 2
21 + 2
0.0
0.8
–48.1
–25.4
–56.4
0.0
–56.8
–36.1
–64.0
N–In+ complex + InMe3
TS addition
Adduct + InMe3
Phenyldiazonium+ + InEt3
N–In+ complex + InEt3
TS addition
TS-21/22
22
Adduct + InEt3
[a] See Scheme 4.
Eur. J. Org. Chem. 2008, 862–868
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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865

M. Barbero, S. Cadamuro, S. Dughera, G. Ghigo
FULL PAPER
isolated N-alkylanilines 4 and 5 and formaldehyde (aryl)hydrazones
11 are reported in Table 2 and Table 3. The structures and purity
of all the products obtained in this research were confirmed by
comparison of their physical (m.p. or b.p.) and spectroscopic data
with those reported in the literature.
(q, J = 7.10 Hz, 2 H), 1.03 (t, J = 7.10 Hz, 3 H) ppm. 13C NMR
(50 MHz, CDCl3, 25 °C): δ = 146.8, 132.8, 115.9, 111.3, 36.8,
16.5 ppm.
N-Ethyl-2,6-dimethylaniline (4i): 1H NMR (200 MHz, CDCl3,
25 °C): δ = 6.71–6.65 (m, 2 H), 6.40–6.33 (m, 1 H), 3.85 (br. s, 1
H), 2.98 (q, J = 7.10 Hz, 2 H), 2.29 (s, 6 H), 0.99 (t, J = 7.10 Hz,
3 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 144.8, 126.6,
125.9, 116.4, 38.1, 15.6, 15.0 ppm.
Indium chloride, 1.6  methyllithium solution in diethyl ether,
0.5  ethyllithium solution in benzene/cyclohexane, 1.6  butyllith-
ium solution in hexanes, tetrabutyltin, butylboronic acid, 1.0  tri-
butylborane in diethyl ether, 2.0  butylmagnesium chloride solu-
tion in THF and all of the amines and solvents were purchased
from Aldrich. Dowex 50X8 ion-exchange resin was purchased from
Fluka.
Formaldehyde (4-Methoxyphenyl)hydrazone (11c). Typical Pro-
cedure: Following the above procedure a solution of trimethylin-
dium (10) in THF (12.5 mmol) at room temp. was added in one
portion with vigorous stirring to 4-methoxybenzenediazonium o-
benzenedisulfonimide (1c, 5 mmol, 1.76 g). The salt dissolved at
once and the resultant solution became very dark. Stirring at room
temp. was maintained for 5 min until a test for azo-coupling with 2-
naphthol proved negative. GC, GC-MS and TLC (petroleum ether/
diethyl ether, 9:1) analyses of the reaction mixture showed formal-
dehyde (4-methoxyphenyl)hydrazone (11c) {MS (EI): m/z = 150
[M]+} as the sole product. The above work-up furnished a crude
residue that was washed with pentane and filtered through a
Büchner funnel. The obtained solid was pure 11c (0.62 g, 83%
Dry arenediazonium o-benzenedisulfonimides 1 were prepared as
described previously by us.[6c] The crude salts were virtually pure
(by 1H NMR spectroscopy) and were used in subsequent reactions
with indium organometallics 2 and 3 without further crystalli-
zation.
CAUTION! In our laboratory there was no case of sudden decom-
position during the preparation, purification or handling of salts
1. Nevertheless it must be borne in mind that all diazonium salts
in the dry state are potentially explosive. Therefore they must be
carefully stored and handled.
1
yield). H NMR (200 MHz, CDCl3, 25 °C): δ = 7.96 (br. s, 1 H),
6.83 (d, J = 11.18 Hz, 1 H), 6.75 and 6.55 (2d, 1:1, J = 9.19 Hz, 4
H), 6.40 (d, J = 11.18 Hz, 1 H) ppm. 13C NMR (50 MHz, CDCl3,
25 °C): δ = 154.8, 152.8, 135.6, 117.9, 114.9, 56.8 ppm. C8H10N2O
(150.18): calcd. C 63.98, H 6.71, N 18.65; found C 64.05, H 6.63,
N 18.72. Also, in this case, after the usual work-up, o-benzenedisul-
fonimide (9) (0.74 g, 68% yield) was recovered. We recovered 11c
in a lower yield (0.45 g, 60%) when the reaction time at room temp.
was lengthened to 2 h; we recovered only tars when reaction time
at room temp. was increased to 8 h.
Indium Organometallics. General Procedure: As reported in the lit-
erature,[2] a solution of indium chloride (1.11 g, 5 mmol) in dry
THF (20 mL) was cooled to 0 °C under N2. The appropriate alkyl-
lithium derivative (15 mmol) was added dropwise over a period of
10 min. Stirring at 0 °C was continued for 45 min until the com-
plete formation of indium organometallic derivatives. In this way,
triethyl- (2), tributyl- (3) and trimethylindium (10) were synthesized
and used directly, without isolation, in the subsequent step.
N-Butyl-4-methoxyaniline (5c). Typical Procedure: 4-Methoxyben-
zenediazonium o-benzenedisulfonimide (1c) (5 mmol, 1.76 g) was
added in one portion to a solution of tributylindium (3) in THF
(12.5 mmol), prepared as reported above, under a N2 flow with
vigorous stirring and at room temp. The salt dissolved at once and
the resultant solution became dark. Stirring at room temp. was
maintained for 5 min. The completion of the reaction was con-
firmed by the absence of azo-coupling with 2-naphthol. GC, GC-
MS and TLC (petroleum ether/diethyl ether, 9:1) analyses of the
reaction mixture showed N-butyl-4-methoxyaniline (5c) {MS (EI):
m/z = 179 [M]+} as the major product besides small traces of (E)-
2-butyl-1-(4-methoxyphenyl)diazene (13c) {MS (EI): m/z = 192
[M]+} and 1,2-dibutyl-1-(4-methoxyphenyl)hydrazine (7c) {MS
(EI): m/z = 250 [M]+} as minor products. The reaction mixture was
poured into diethyl ether/water (100 mL, 1:1). The aqueous layer
was separated and extracted with diethyl ether (2ϫ50 mL). The
combined organic extracts were washed with water (2ϫ50 mL),
dried with Na2SO4 and evaporated under reduced pressure. The
crude residue was washed with pentane and filtered through a
Büchner funnel. The obtained solid was pure 5c (0.85 g, 95%
yield). The aqueous layer and aqueous washings were collected and
the solvent evaporated under reduced pressure. The black tarry res-
idue was passed through a column of Dowex 50X8 ion-exchange
resin (1.6 g/1 g of product), eluting with water (about 50 mL). After
removal of the water under reduced pressure, virtually pure (1H
NMR) o-benzenedisulfonimide (9) was recovered (0.78 g, 72%
yield): m.p. 192–194 °C (toluene) (ref.[1] m.p. 192–194 °C). All the
N-alkylanilines 4 and 5 reported in entries 1–18 of Table 2 were
prepared according to this procedure.
All the formaldehyde (aryl)hydrazones 11 reported in entries 1–9
of Table 3 were prepared according to the above procedure.
Formaldehyde (4-Tolyl)hydrazone (11b): 1H NMR (200 MHz,
CDCl3, 25 °C): δ = 7.99 (br. s, 1 H), 6.95 (d, J = 8.25 Hz, 2 H),
6.86 (d, J = 11.18 Hz, 1 H), 6.52 (d, J = 8.25 Hz, 2 H), 6.37 (d, J
= 11.18 Hz, 1 H), 2.33 (s, 3 H) ppm. 13C NMR (50 MHz, CDCl3,
25 °C): δ = 154.5, 142.8, 129.7, 129.1, 115.9, 26.7 ppm. C8H10N2
(134.18): calcd. C 71.61, H 7.51, N 20.88; found C 71.65, H 7.58,
N 20.77.
Formaldehyde (2-Nitrophenyl)hydrazone (11e): 1H NMR (200 MHz,
CDCl3, 25 °C): δ = 8.14–8.11 (m, 1 H), 7.94 (br. s, 1 H), 7.58–7.54
(m, 1 H), 6.98–6.90 (m, 2 H), 6.85 and 6.38 (2d, 1:1, J = 11.18 Hz,
2 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 154.7, 144.2,
136.7, 135.9, 122.3, 119.9, 117.4 ppm.
Formaldehyde (3-Nitrophenyl)hydrazone (11f): 1H NMR (200 MHz,
CDCl3, 25 °C): δ = 7.98 (br. s, 1 H), 7.67–7.57 (m, 2 H), 7.48–7.43
(m, 1 H), 7.08–7.04 (m, 1 H), 6.87 and 6.41 (2d, 1:1, J = 11.18 Hz,
4 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 154.9, 149.9,
145.1, 130.9, 122.3, 111.7, 110.4 ppm. C8H10N2 (165.15): calcd. C
50.91, H 4.27, N 25.44; found C 50.65, H 4.28, N 25.47.
Methyl 4-(2-Methylidenehydrazono)benzoate (11h): 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 8.00 (br. s, 1 H), 7.91 (d, J =
8.85 Hz, 2 H), 6.86 (d, J = 11.18 Hz, 2 H), 6.80 (d, J = 8.85 Hz, 2
H), 6.40 (d, J = 11.18 Hz, 2 H), 3.89 (s, 3 H) ppm. 13C NMR
(50 MHz, CDCl3, 25 °C): δ = 166.6, 154.6, 147.5, 130.8, 121.3,
115.7, 52.5 ppm. C9H10N2O2 (178.19): calcd. C 60.66, H 5.66, N
15.72; found C 60.74, H 5.68, N 15.79.
1
N-Ethyl-4-bromoaniline (4d): H NMR (200 MHz, CDCl3, 25 °C): Formaldehyde (2,6-Dimethylphenyl)hydrazone (11i): 1H NMR
δ = 7.25 and 6.34 (2d, 1:1, J = 9.20 Hz, 4 H), 3.81 (br. s, 1 H), 3.00
(200 MHz, CDCl3, 25 °C): δ = 8.01 (br. s, 1 H), 6.86 (d, J =
866
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 862–868

Reactions of Arenediazonium o-Benzenedisulfonimides
11.18 Hz, 2 H), 6.81–6.79 (m, 2 H), 6.51–6.47 (m, 1 H), 6.36 (d, J
Supporting Information (see also the footnote on the first page of
= 11.18 Hz, 2 H), 2.29 (s, 6 H) ppm. 13C NMR (50 MHz, CDCl3, this article): Total (a.u.) and relative (kcalmol–1) electronic and
25 °C): δ = 154.8, 148.5, 128.6, 126.1, 117.9, 15.9 ppm. C9H12N2 zero-point corrected (ZPE) energies.
(148.21): calcd. C 72.94, H 8.16, N 18.90; found C 73.01, H 8.14,
N 18.85.
Trial Reactions: All the reactions reported in Table 1 (entries 1–5)
were carried out according to the general procedure described
Acknowledgments
above, treating 4-methoxybenzenediazonium o-benzenedisulfon-
This work was supported by the Ministero dell’Università e Ricerca
and by the University of Torino.
imide (1c) with tributylindium (3) (5 mmol) at room temp. with
various reagent molar ratios. In entries 1–3 the crude residues were
washed with pentane and filtered through a Büchner funnel. In
entries 4 and 5 the crude residues were purified by chromatography
on a short column, eluting with petroleum ether/diethyl ether (9:1).
The first eluted product was 1,2-dibutyl-1-(4-methoxyphenyl)hy-
drazine (7c). Details are reported in Table 1.
[1] M. Barbero, S. Cadamuro, S. Dughera, C. Giaveno, Eur. J. Org.
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Media, Wiley, New York, 1997, pp. 64–114.
1,2-Dibutyl-1-(4-methoxyphenyl)hydrazine (7c): Viscous colourless
oil. 1H NMR (200 MHz, CDCl3, 25 °C): δ = 6.73 and 6.58 (2 d,
1:1, J = 9.00 Hz, 4 H), 3.85 (s, 3 H), 3.00 (t, J = 7.00 Hz, 2 H),
2.85 (t, J = 7.00 Hz, 2 H), 1.58–1.45 (m, 4 H), 1.38–1.29 (m, 4 H),
1.01–0.95 (m, 6 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ =
149.8, 139.7, 113.9, 58.3, 55.7, 48.9, 30.2, 29.7, 20.4, 20.2,
13.5 ppm. MS (EI): m/z = 250 [M]+. C15H26N2O (250.38): calcd. C
71.96, H 10.47, N 11.19; found C 71.99, H 10.42, N 11.21.
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Collateral Proof a: 4-Methoxybenzenediazonium o-benzenedisul-
fonimide (1c) (5 mmol, 1.77 g) in THF (20 mL) was added in one
portion to a solution of tetrabutyltin, butylboronic acid or 1.0 
tributylborane in diethyl ether (15 mmol, 5.20 g, 1.53 g or 15 mL)
under vigorous stirring at room temp. The obtained suspension was
stirred at room temp. for 24 h. A test for azo-coupling with 2-naph-
thol was positive. The suspension was then refluxed for 8 h but still
a test for azo-coupling was positive. The unreacted 4-methoxyben-
zenediazonium o-benzenedisulfonimide (1c) was recovered by fil-
tration through a Buchner funnel.
Collateral Proof b: THF (20 mL) was added to a 2.0  butylmagne-
sium chloride solution in THF (15 mmol 7.5 mL) or a 1.6  butyl-
lithium solution in hexanes (15 mmol, 9.4 mL). Then, 4-methoxy-
benzenediazonium o-benzenedisulfonimide (1c, 5 mmol, 1.77 g)
was added in one portion at room temp. with vigorous stirring.
The salt dissolved at once and the resultant solution became very
dark. Stirring at room temp. was maintained for 5 min until a test
for azo-coupling with 2-naphthol proved negative. GC, GC-MS
and TLC (petroleum ether/diethyl ether, 9:1) analyses of the reac-
tion mixture showed the presence of 4-methoxybenzene as the only
product. After the usual work-up only tars were recovered.
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Eur. J. Org. Chem. 2008, 862–868
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
867

M. Barbero, S. Cadamuro, S. Dughera, G. Ghigo
FULL PAPER
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Received: October 1, 2007
Published Online: December 11, 2007
868
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 862–868