Oxidation of 1-(4′-substituted phenyl)-2-(4-methylphenyl)diazene - Benzylic substitution vs. C-azo bond breaking

Article abstract of DOI:10.1139/v05-044

The low oxidation potential of 1-phenyl-2-(4-methylphenyl)diazene 4′-substituted with a dimethylamino or methoxy group (10 and 11) allows the easy single electron transfer with radical cation generation in the presence of FeCl₃. At the same time, the stabilizing effect of the positive charge exerted by 4-dimethylaminophenyl > 4-methoxy groups on the intermediate carbocation favors the hydrogen atom elimination in comparison with proton loss. Whereas benzylic substitution towards di- and triarylmethane derivatives takes place starting from diazene 11, the oxidation of diazene 10 leads mainly to products of C-azo breaking. This difference is well-supported by the idea that the electron, in the first step of oxidation, is extracted from the azo and (or) from the amino nitrogen atom.

Full text of DOI:10.1139/v05-044

244
Oxidation of 1-(4′-substituted phenyl)-2-(4-
methylphenyl)diazene — Benzylic substitution vs.
C–azo bond breaking
Alexandru C. Razus, Carmen Nitu, Claudia Pavel, Crinu-Anghel Ciuculescu,
Valentin Cimpeanu, Corneliu Stanciu, and Philip P. Power
Abstract: The low oxidation potential of 1-phenyl-2-(4-methylphenyl)diazene 4′-substituted with a dimethylamino or
methoxy group (10 and 11) allows the easy single electron transfer with radical cation generation in the presence of
FeCl3. At the same time, the stabilizing effect of the positive charge exerted by 4-dimethylaminophenyl > 4-methoxy
groups on the intermediate carbocation favors the hydrogen atom elimination in comparison with proton loss. Whereas
benzylic substitution towards di- and triarylmethane derivatives takes place starting from diazene 11, the oxidation of
diazene 10 leads mainly to products of C–azo breaking. This difference is well-supported by the idea that the electron,
in the first step of oxidation, is extracted from the azo and (or) from the amino nitrogen atom.
Key words: diazenes, oxidation, single electron transfer, benzylic substitution, C–azo bond breaking.
Résumé : Le faible potentiel d’oxydation des 1-phényl-2-(4-méthylphényl)diazènes substitués en position 4′ par des
groupes diméthylamino (10) ou méthoxy (11) permet, en présence de FeCl3 le transfert facile d’un seul électron avec la
formation d’un cation radical. En même temps, l’effet stabilisant de la charge positive des groupes 4-diméthylamino-
phényle > 4-méthoxy sur le carbocation intermédiaire favorise l’élimination de l’atome d’hydrogène par rapport à une
perte de proton. Alors que la substitution benzylique vers les dérivés di- et triarylméthanes se fait à partir du diazène
11, l’oxydation du diazène 10 conduit principalement à des produits résultant d’une rupture de la liaison C–azo. Cette
différence est bien expliquée par l’idée que l’électron, dans la première étape de l’oxydation, est extrait de l’atome
d’azote de l’azo et (ou) amino.
Mots clés : diazènes, oxydation, transfert d’un seul électron, substitution benzylique, rupture d’une liaison C–azo.
[Traduit par la Rédaction] Razus et al. 250
Introduction
1+·, and on the efficient stabilization of the positive charge
on a tropylium ion moiety both in the radical cation 1+· (the
most favoured resonance structure is represented) and in the
subsequent cation 8.
We now extend these results on the azulenic diazenes to
compounds having the azulenic moiety replaced by other
groups, which lower the oxidation potential and stabilize the
positive charge, such as 4-dimethylamino- and 4-methoxyphenyl
groups (compounds 10 (2) and 11 (3), respectively).
In a previous paper (1), we investigated the oxidation of
para-methyl substituted (E)-1-azulen-1-yl-2-phenyldiazene
(1), with iron(III) chloride (Scheme 1). The reaction was
performed in benzene, with good conversion of the starting
diazene (between 60% and 80%) to afford products that are
mono- and diphenyl-substituted at the methyl group. As shown
in the scheme, the di- and triphenylmethane derivatives, the
corresponding carbinols, and compounds resulting from
hydroxyl oxidation or intramolecular water elimination were
also generated. When chlorinated diazene 1(Cl) was oxi-
dized, 3,3′-dichloro-1,1′-biazulene was also separated from
the reaction mixture.
Oxidation of diazenes 10 and 11
The previously used reaction conditions (1) were main-
tained: the ratio of diazene : ferric chloride = 1:4 in benzene
(1 mmol diazene in 25 mL benzene), without atmospheric
protection. Because of the lower reactivity of the starting
compounds and the rather high number of formed products,
a longer reaction time was necessary. The reaction was mon-
itored by TLC and when no changes in the compound ratio
were detected, the reaction mixture was worked-up, and the
products were separated by liquid chromatography on alu-
mina. Not all of the compounds could be separated and indi-
vidually characterized. Some products were identified by the
careful analysis of GC–MS and NMR spectra of the eluted
chromatographic fractions. Along with the main products,
the reaction mixtures also contained other unidentified deriv-
The proposed oxidation mechanism shown in Scheme 2
(1) is based on an initial single electron transfer (SET), 1 →
Received 15 July 2004. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 29 March 2005.
A.C. Razus,1 C. Nitu, C. Pavel, C.-A. Ciuculescu, and
V. Cimpeanu. C.D. Nenitzescu Institute of Organic
Chemistry, Romanian Academy, Spl. Independentei 202B,
sector 6, P.O. Box 15-254, 060023-Bucharest, Romania.
C. Stanciu and P.P. Power. Department of Chemistry, One
Shields Avenue, University of California, Davis, CA 95616,
USA.
1Corresponding author (e-mail: acrazus@cco.ro).
Can. J. Chem. 83: 244–250 (2005)
doi: 10.1139/V05-044
© 2005 NRC Canada

Razus et al.
245
Scheme 1.
Scheme 3.
Scheme 2.
halogenated compound 12. Unfortunately, the chlorine
position in the molecule could not be accurately assigned,
however, the para position seems to be a plausible assump-
tion. The MS of the single compound contained in fraction 2
displayed the characteristic peak of a monochlorinated de-
rivative, M+ 155/157 (76%/25%). The structure of this com-
pound (13) (6) was ascertained on the basis of the AB group
signal at δ 7.16 and 6.63 ppm (J = 9.1 Hz) for 1,4-di-
substituted benzene as well as on the singlet peak corre-
sponding to six methyl protons at 2.86 ppm. Fraction 3 con-
sisted of the unreacted diazene 10. The GC–MS of fraction 4
showed the presence of two compounds (16 and 17) with M+
at 315 and 391, in a molar ratio of 6:1 (5), with very similar
1
retention times on the chromatographic column. In the H
NMR spectrum of this fraction, the singlets at δ 4.03 and
5.60 ppm proved the presence of diaryl- and triarylmethane
protons, respectively (other signals characteristic to the pro-
posed structures (16 and 17) were also present). The dimeric
compound 15 (4, 5, 7) was isolated from fraction 5, whereas
fraction 6 contained the carbinol 18 (8).
atives in very small amounts (under 1%) as well as a small
quantity of a complex tar mixture.2
The reaction of diazene 10
The reaction mixture was stirred for 1 week and after
work-up, six fractions were chromatographically separated.
The main products obtained and their yields are given in
Scheme 3. In this case, a significant amount of tar product
was not eluted, but remained on the column.
The reaction of diazene 11
The reaction mixture was maintained at reflux for 48 h
and after work-up, seven fractions were separated chromato-
graphically. The results are described in Scheme 4.
Lower yields of the products were obtained in this case
because of the very low reactivity of 11, even under severe
reaction conditions. For this reason, the separation and iden-
tification of the products from this diazene were more diffi-
cult in comparison to those of 10. The GC–MS of fraction 1
was consistent with the presence of compounds 2, 12 (in
traces), and 14, products also obtained from the oxidation of
10, together with triphenylmethane (3) (4), in a molar ratio
2:3:14 of 12:1.6:1. The GC–MS of fraction 2 showed the
presence of two compounds in a molar ratio of 1.1:1 with
M+ at (m/z) 241 and 260/262 (36%/84%) corresponding to
the methylated and monochlorinated starting diazenes
(11(CH3) and 11(Cl)), respectively. Unfortunately, the posi-
tion of substitution could not be established. Fraction 3 was
the starting material (11). The diaryl- and triarylmethanic
compounds (21 and 22) (8) were present in an equimolar ra-
The GC–MS of fraction 1 indicated the presence of three
compounds in the molar ratio of 10:1:1.3 The first two com-
ponents had the same M+ (molecular ion) (m/z): 168 (C13H12+ ·).
For the last compound, the fragments 202/204 in abundances
of 40%/12% indicated the presence of one chlorine atom in
the molecule (C13H11Cl+·). The first compound with an M+
of 168 had the same mass spectral features as 4-methyl-
substituted biphenyl 14 (4), whereas the mass spectrum of
the second compound resembled that of diphenylmethane 2.
In the 1H NMR spectrum of fraction 1, the singlet at
δ 3.92 ppm, near the methylene protons of 2 (δ 3.96 ppm)
(5), supported the presence of the second compound that
also possessed a methylene group. On the basis of chemical
shifts and integrations in the 1H NMR spectrum, the
diphenylmethane type of structure was attributed to the
2 The search for eventually formed products soluble in aqueous solution at work-up (as, for instance, phenols) was unsuccessful.
1
3 The ratio between the integral of singlets in the H NMR spectrum is in accord with the ratio from the GC–MS.
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Can. J. Chem. Vol. 83, 2005
Scheme 4.
The most unexpected difference among the reactivities of
the diazenes is the nature and ratio of the oxidation products.
The products obtained can be classified by: (a) compounds
formed by C–azo bond breaking, and (b) benzylic substi-
tuted compounds (in some cases the substitution was fol-
lowed by C–azo bond breaking as for 2, 3, and 12).
For the oxidation of the diazene 10, the major products 13
and 15 belong to group (a) and preserve 4-dimethylamino-
phenyl moiety. A moderate amount of compound 14 with a
4-tolyl moiety is also formed. When diazene 11 was reacted,
such products were not generated except for a small amount
of compound 14, which formed in only 1% yield.
The products of benzylic substitution, i.e., 3, 12, and 20–
22, were obtained by the oxidation of diazene 11 in about
46% yield. In contrast, for the diazene 10, the compounds of
the type (b), 2, 12, and 16–20, result only in 17% yield.
In the reaction mixture of diazene 11, the interesting bis-
diazene 19 and a very small amount of compounds 11(CH3)
and 11(Cl) were also present. However, the assignment of
the structures of the last two products as methyl- or chlorine-
substituted starting diazene 11 was based only on their mass
spectra.
tio in fraction 4 as can be concluded from both MS (M+ 302
and 378) and H NMR spectra (δ 4.06 and 5.62 ppm for
1
methylene and methyne protons). The value of M+ = 344 for
compound 19, eluted in fraction 5, corresponded to the
structure of starting diazene 11 substituted by the 4-
methylphenylazo group. In the 1H NMR spectrum of 19, two
phenyl moieties were present, both with para positions sub-
stituted by N=N and CH3 (the AB group signal at δ 7.28–
7.34 ppm corresponding to 4H, and at δ 7.81 and 7.87 ppm
each accounting for 2H). The two singlets very closely
placed (at δ 2.43 and 2.44 ppm each making for 3H) and the
singlet at δ 4.11 ppm accounting for 3H corresponded to two
benzylic and one methoxy methyl groups, respectively. The
chemical shifts and the coupling values for other signals of
19 are consistent with methoxybenzene 2,4-di-substituted by
4-methylphenylazo groups. Unfortunately, the elemental
analysis of compound 19 failed because of the presence of a
very small amount of an unidentified compound, present in
fraction 5, which could not be eliminated by chromatogra-
phy. Fraction 6 contained some unidentified compounds in
traces (as shown by GC–MS), and in fraction 7, the carbinol
22 (8) was separated and characterized.
Accordingly, the benzylic substitution without C–azo
bond breaking represents the major oxidation route for the
diazenes 1 and 11 (Schemes 1 and 4). The main compounds
formed in the reaction mixture of 10 were, however, gener-
ated by C–azo breaking followed by subsequent stabilization
of the fragments 13–15 (Scheme 3). Another feature of the
reactivity of diazene 10 is the higher amount of the product
conserving the 4-dimethylaminophenyl moiety in compari-
son with those with a 4-tolyl group. This illustrates the dif-
ference between the two types of C–azo bond breaking in
10, which involves the =N-dimethylaminophenyl and =N-
tolyl moieties.
As for all oxidations with FeCl3 that we studied, the first
reaction step consists of a SET with radical cation genera-
tion. Based on the results of EPR and theoretical investiga-
tions of the diphenyldiazene radical cation, Rhodes and co-
workers (10) suggested the structure [–:N=N+·– ↔ –+·N=N:–]
for the azo group, with the possibility of spin delocalization
on the phenyl ring. A good electron donor group, such as the
methoxy at one of the phenyl moieties, as in compound 11
or azulene, as in the diazene 1, enhances the spin delocal-
ization. Some resonance structures for the radical cation 11+·
are presented in Scheme 5.5 If the structure 11+· (B) is the
most favoured (11), the intermediates formed during the
most important oxidation route, namely benzylic substitu-
tion, would resemble those for the azulenic diazene 1
(Scheme 2). The presence of a significant amount of
bisdiazene 19 in the oxidation mixture of 11 can be consid-
ered a surprising result. Thus, the electrophilic substitution
of diazene 11 by the diazonium cation, formed in a
homolytic breaking of the C–azo bond (12),6 is prevented by
the presence of the deactivating azo double bond (in spite of
the existence of the electron donor methoxy substituent).7
Discussion
The experimental and spectroscopic data described previ-
ously support the following conclusions.
The increase in the amount of unreacted diazenes along
the series 1(CH3) = 1(Cl) > 10 > 11 (Schemes 1, 3, and 4)
reflects the decrease in their reactivity. This trend follows
their oxidation potentials (9).4 The high oxidation potential
of the diazenes that have no activating groups, for example
1-(4-methylphenyl)-2-phenyldiazene, prevents the reaction
(90% of starting material remains unreacted after 2 weeks
and an amount of tar is formed).
4 The overall yield of all products is almost the same for each of the oxidized diazenes.
5 Other structures could also be written as, for instance, a structure with one electron transferred from the oxygen atom; however, the obtained
products seem to infringe on this possibility.
6 The similar C–azo breaking in structure 11+· (A), if it takes place, leads to the formation of a low reactive diazonium salt. Possibly, at the
work-up of the reaction mixture, the small amount of stabilization products formed from diazonium salts was lost.
7 The coupling at the anisole succeeds only with very reactive diazonium salts.
© 2005 NRC Canada

Razus et al.
247
Scheme 5.
Scheme 6.
The radicalic route for generation of 19 seems to be more re-
alistic. Thus, the attack of the nitrogen spin of the radical
cation 11+· (C) on the ortho-CH3O position in 11 gives a
new radical cation. The subsequent proton elimination and
anisyl radical cleavage results in the formation of compound
19. An alternative route that can be also considered starts
from the above-mentioned diazonium salt. The diazonium
radical obtained by reduction of this salt with FeCl2, present
in the medium, substitutes the radical cation 11+· (D) or,
more probably, the compound 11. Incertitude remains, how-
ever, in connection with the aryl diazonium radical lifetime.
Some results obtained in the thermic decomposition of such
intermediates (13) indicate a rate constant for loss of nitro-
gen between 107 and 109 s–1; therefore, it is difficult to
imagine another faster reaction even if the reaction is diffu-
sion controlled (14).
At the oxidation of diazene 10, the di- and triarylmethane
derivatives originate in a radical cation similar to 11+·. How-
ever, it is difficult to say whether this intermediate is
formed, namely, by single electron transfer from the azo ni-
trogen (Scheme 5) or from the amino nitrogen (Scheme 6) or
by both ways.
One further question remains to be answered: what is the
reaction route by which diazene 10 can generate significant
amounts of the products 13 and 15, which have the 4-
dimethylaminophenyl moiety, but no azo bond? The best fit
to the experimental data involves, as the first reaction step,
the SET from the amino nitrogen atom. This interpretation is
supported by the reported structure of the radical cation that
was obtained by the anodic oxidation of dimethylaniline (15).
This intermediate possesses both the charge and the spin at
the nitrogen atom with the possibility of spin delocalization
to the para position followed by spin coupling. In contrast
with our chemical oxidation, the electrochemical oxidation
of 10 did not allow the separation of products and only for-
mation of a thin film was reported (16). The key intermedi-
ate for the generation of the product 15 seems to be the
radical cation 10+· with a charge distribution depicted by
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248
Can. J. Chem. Vol. 83, 2005
structure (B) (Scheme 6). The dimerization of 10+· (B) by
spin-spin coupling to 23 and the diazonium salt elimination
gives the biphenyl 15 (the same reaction route explains the
presence of the azulene dimer coupled at the 1,1′ positions
during the oxidation of 1(Cl)). The generation of 15 from
the free 4-dimethylaminophenyl radical can be excluded be-
cause no products of cross coupling were found in the reac-
tion mixture. The chlorine (atom or anion) attack on 10+· (B)
provides the compound 13. It seems possible that the 4-
methylbiphenyl 14 is a result of the radical arylation of ben-
zene (17). The 4-tolyl radical is formed by the reduction of
the diazonium salt obtained at the decomposition of 23 and
the subsequent nitrogen elimination.
3′-, 5′-H), 7.79 (2H, d, J = 8.3 Hz, 2′-, 6′-H), 7.90 (2H, d,
J = 9.2 Hz, 2-, 6-H). 13C NMR (CDCl3) δC: 21.44 (CH3),
55.54 (OCH3), 114.15 (C-3, -5), 122.52 (C-2′, -6′), 124.55
(C-2, -6), 129.67 (C-3′, -5′), 140.79 (C-4′), 147.03 (C-1),
150.81 (C-1′), 161.80 (C-4).
Oxidation with ferric chloride — General procedure
In a round-bottomed flask to a magnetically stirred solu-
tion of diazene 10 or 11 in benzene (1 mmol diazene for
25 cm3), anhydrous ferric chloride was added at room tem-
perature (the oxidation of diazene 11 occurred at reflux of
the solvent) without air protection (ratio between FeCl3 and
diazene is 4:1). From time to time the separated viscous oily
product was mechanically removed from the flask wall for a
better contact between the reactants. The reaction was moni-
tored by TLC (homogenous samples were collected, washed
with a saturated sodium bicarbonate solution, and dried),
and it was stopped when the spot of the starting compound
vanished or maintained a stationary intensity (the reaction
time will be indicated for each diazene). The reaction mix-
ture was quenched with a saturated sodium bicarbonate solu-
tion and the major amount of the benzene was evaporated in
vacuum. The suspension was extracted three times with
200 cm3 DCM, the organic extracts were washed once with
water, dried (Na2SO4), and the solvent was evaporated in
vacuum. The residue was fractionated by column chroma-
tography under conditions described in the following. To es-
tablish the ratio between the compounds in the eluted
Conclusion
In conclusion, the low oxidation potentials of the diazenes
10 and 11, as well as of 1, result in an easy single electron
transfer with radical cation generation. At the same time, the
stabilizing effects exerted by the azulene > 4-dimethyl-
aminophenyl > 4-methoxyphenyl groups on the carbocations
favour hydrogen atom elimination over proton loss (1).
Therefore, the superacidic behaviour of the radical cation in-
termediates proposed earlier (18) must be carefully consid-
ered. Factors such as the type of substituent or the polarity
of reaction medium can favour either the homolytic or the
heterolytic breaking of the C—H bond. The differences in
the nature and the product ratios for diazenes oxidation are
complex. Whereas di- and triarylmethane derivatives are the
major products starting from 1 and 11, diazene 10 leads
mainly to products of C–azo breaking. This difference can
be satisfactorily explained by the different position from
which the electron is lost in the first step of the oxidation
process to generate the radical cation intermediate.
1
fractions, GC–MS and H NMR signal integrals were con-
sidered and the product yields were calculated towards the
reacted diazene. For some of the obtained compounds, mass
1
spectra and (or) H NMR spectra, available in the spectra li-
braries, were used for identification.
Reaction of 10
After 7 days at room temperature, the reaction mixture
was worked-up and from 1.5 mmol of 10, an amount of
367 mg of the rough product was separated on an alumina
column (d = 3 cm; l = 13 cm) in six fractions, the first five
with n-pentane:DCM (4:1), the last one with ethyl acetate.
Fraction 1: (the ratio between the compounds was calculated
on the basis of GC–MS and 1H NMR spectra of the fraction)
4-methyl-1,1′-biphenyl (14, 17 mg, 0.102 mmol, 11%),
benzylbenzene (2, ~2 mg, 0.010 mmol, ~1%), 1-benzyl-
chlorobenzene (12, ~2 mg, 0.010 mmol, ~1%). Fraction 2:
N-(4-chlorophenyl)-N,N-dimethylamine (13, 16 mg,
0.100 mmol, 10.7%). Fraction 3: unreacted 10 (135 mg,
0.564 mmol, conversion 62.4%). Fraction 4: 17 mg, N,N-
dimethyl-N-{4-[(E)-(4-(phenylmethyl)phenyl)diazenyl]phe-
nyl}amine (16) and N,N-dimethyl-N-{4-[(E)-(4-(diphenyl-
methyl)phenyl)diazenyl]phenyl}amine (17) with a molar
Experimental
1H and 13CNMR: Bruker Avance DRX4 (1H: 400 MHz,
13C: 100.62 MHz) and Varian Gemini 300BB (1H: 300 MHz,
13C: 75.47 MHz) spectrometers; chemical shifts (δ) are ex-
pressed in ppm, and J values are given in Hz; TMS was used
as internal standard in CDCl3 as solvent; in a few cases the
signals were assigned on the basis of COSY and HETCOR
experiments. IR: Beckmann IR 5A. Mass spectra were re-
corded on a JEOL JMS-DX303 spectrometer coupled to a
Shimadzu GC-14B gas chromatograph with a DB-1 capillary
column and a C-R6A integrator. Column chromatography:
basic alumina (activity BII-III (Merck)). Dichloromethane
(DCM) was distilled over CaH2 and ethyl acetate was dis-
tilled over Na2CO3. The numbering of the positions in the
compounds is reported in Schemes 3 and 4.
1
ratio (determined by GC–MS and H NMR) of 5.8:1 (4.7%
Starting diazenes
and ~1%, respectively). Fraction 5: N,N,N′,N′-tetrametyl-
1,1′-biphenyl-4,4′-diamine (15, 15 mg, 0.063 mmol, 13.4%).
Fraction 6: N,N-dimethyl-N-{4-[(E)-(4-(diphenylhydroxi-
methyl)phenyl)diazenyl]phenyl}amine (18, 36 mg, 0.088 mmol,
9.4%).
N,N-Dimethyl-N-{4-[(E)-(4′-methylphenyl)diazenyl]phe-
nyl}amine (10) was obtained as described in literature (2).
(E)-1-(4-Methoxyphenyl)-2-(4-methylphenyl)diazene (11)
was obtained by coupling of the 4-tolyldiazonium salt with
phenol (18) and reacting the diazene with diazomethane.
1
Spectra of resultant fractions or compounds
Mixture of 16 and 17 in fraction 4: yellow powder. H
Compound 11 shows the H NMR spectrum as described
(18): δH (CDCl3): 2.42 (3H, s, CH3), 3.89 (3H, s, OCH3),
7.00 (2H, d, J = 9.2 Hz, 3-, 5-H), 7.29 (2H, d, J = 8.1 Hz,
1
NMR (CDCl3) δH: 3.07 (40.8H, s, N(CH3)2), 4.03 (11.6H, s,
© 2005 NRC Canada

Razus et al.
249
1
CH2), 5.60 (1H, s, CH), 6.75 (13.6H, d, J = 9.3 Hz, 3-, 5-H),
7.12–7.31 (52.6H, m, 3′-, 5′-H, and phenyl protons), 7.77
(13.6H, d, J = 9.2 Hz, 2-, 6-H), 7.86 (13.6H, d, J = 9.2 Hz,
2-, 6-H). GC–MS, m/z (70 eV): 317 (M(16)+ + 2, 2%), 316
(M+ + 1, 13), 315 (M+, 71), 165 (13), 157 (15), 152 (18),
148 (10), 121 (6), 120 (100), 118 (8), 105 (15), 104 (20), 91
(23), 77 (22); 392 (M(17)+ + 1, 16%), 391 (M+, 68), 167
(17), 165 (55), 120 (100), 105 (18), 104 (20), 91 (19), 77
(26).
Compound 19: H NMR (CDCl3) δH: 2.43 and 2.44 (two
singlets, 3H + 3H, two CH3), 4.11 (3H, s, OCH3), 7.21 (1H,
d, J = 8.9 Hz, 5′-H), 7.28–7.34 (4H, m, 2-, 2′′ -H), 7.81 (2H,
d, J = 8.2 Hz, 3- or 3′′ -H), 7.87 (2H, d, J = 8.2 Hz, 3′′ - or
3-H), 8.05 (1H, dd, J = 8.8 and 2.4 Hz, 6′-H), 8.22 (1H, d,
J = 2.4 Hz, 2′-H). GC–MS m/z (70 eV): 344 (M+, 1.5%),
255 (2), 119 (45), 91 (100), 76 (16), 65 (65).
1
Mixture of 20 and 21 (8) in fraction 4: yellow powder. H
NMR (CDCl3) δH: 3.87 (6H, s, OCH3), 4.06 (2H, s, CH2),
5.61 (1H, s, CH), 7.00 (4H, d, J = 8.9 Hz, 3-, 5-H), 7.05–
7.40 (19H, m, 3′-, 5′-H, and phenyl protons), 7.80 (4H, d,
J = 8.3 Hz, 2′-, 6′-H), 7.85 (4H, d, J = 9.2 Hz, 2-, 6-H).
GC–MS m/z (70 eV): 302 (M(20)+, 71%), 239 (1), 228 (3),
215 (6), 180 (6), 168 (9), 165 (100), 163 (19), 152 (66), 139
(25), 135 (44), 115 (37), 107 (77), 91 (92), 89 (45), 77 (99),
63 (99); 378 (M(21)+, 15%), 334 (2), 310 (1), 189 (3), 162
(5), 134 (20), 106 (12), 104 (20), 91 (100), 90 (22), 77 (10),
65 (60).
Because only the melting point, elemental analysis, and
1H NMR spectrum for compound 18 were reported in the lit-
erature (8) without the proton assignments, we now report
the complete characterization of this compound: yellow
crystals with mp 210 °C (lit. value (8) mp 209 °C). νmax
1
(CH2Cl2) cm–1: 3580 weak (OH). H NMR (CDCl3) δH: 3.07
(6H, s, N(CH3)2), 6.74 (2H, d, J = 9.3 Hz, 3-, 5-H), 7.30–
7.32 (10H, m, phenyl protons), 7.39 (2H, d, J = 8.7 Hz, 3′-,
5′-H), 7.76 (2H, d, J = 8.7 Hz, 2-, 6-H), 7.86 (2H, d, J =
9.2 Hz, 2′-, 6′-H). 13C NMR (CDCl3) δC: 40.23 (N(CH3)2),
81.91 (C-OH), 111.43 (t), 121.59 (t), 124.94 (t), 127.29 (t),
127.89 (t), 127.94 (t), 128.55 (t), 143.67 (q), 146.66 (q),
147.86 (q), 152.21 (q), 152.38 (q). GC–MS m/z (70 eV): 409
(M+ + 2, 1%), 408 (M+ + 1, 5), 407 (M+, 15), 121 (13), 120
(69), 105 (34), 95 (15), 93 (17), 91 (11), 81 (46), 77 (23), 69
(100), 67 (11).
Because only the melting point, elemental analysis, and
1H NMR spectrum were reported for compound 22 (8),
without the proton position assignments, the compound was
now completely characterized by us: yellow crystals with
mp 181 to 182 °C (lit. value (8) mp 182 °C). νmax
(CH2Cl2) cm–1: 3590 weak (OH). H NMR (CDCl3) δH: 3.87
1
(3H, s, OCH3), 6.99 (2H, d, J = 8.9 Hz, 3-, 5-H), 7.29–7.31
(10H, m, phenyl protons), 7.43 (2H, d, J = 8.6 Hz, 3′-, 5′-
H), 7.80 (2H, d, J = 8.3 Hz, 2′-, 6′-H), 7.90 (2H, d, J =
9.2 Hz, 2-, 6-H). GC–MS m/z (70 eV): 396 (M+ + 2, 2%),
395 (M+ + 1, 11), 394 (M+, 42), 318 (2), 317 (10), 289 (10),
259 (5), 242 (4), 241 (22), 239 (13), 183 (8), 135 (47), 107
(100), 105 (55), 92 (22), 77 (52).
Reaction of 11
After 2 days at reflux, the reaction mixture was worked-
up and from 3.54 mmol of 11, an amount of 826 mg of the
rough product was separated on an alumina column (d =
4 cm, l = 15 cm) in seven fractions, the first two with n-
pentane:DCM (4:1), the next fractions with increasing ratios
of ethyl acetate : n-pentane from 1:10 to pure ester for the
last fraction. Fraction 1: (the molar ratio between the com-
Acknowledgments
1
Authors A.C.R. and C.E.N. thank the Alexander von
Humboldt Foundation for fellowships and Professor Klaus
Hafner from the Technical University of Darmstadt, Institute
of Organic and Bioorganic Chemistry, for hosting during
their fellowships and for his full support, both material and
scientific.
pounds resulted from the GC–MS and H NMR spectra of
the fraction) compound 2 (4 mg, 0.022 mmol, 2%), com-
pound 14 (~2 mg, 0.012 mmol, ~1%), benzhydrylbenzene
(3, 4 mg, 0.018 mmol, 1.6%), and in traces, chlorinated
compound 12. Fraction 2: (the ratio between the compounds
resulted from the GC–MS of the fraction): 11(CH3) (4 mg,
0.017 mmol, 1.5%) and 11(Cl) (4 mg, 0.016 mmol, 1.4%).
Fraction 3: unreacted 11 (558 mg, 2.46 mmol, conversion
30%). Fraction 4: (the molar ratio was determined by GC–
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1
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MS and H NMR): (E)-1-(4-methoxyphenyl)-2-(4-(phenyl-
methyl)phenyl)diazene (20, 12 mg, 0.038 mmol, 3.6%), (E)-
1-(4-methoxyphenyl)-2-(4-(diphenylmethyl)phenyl)diazene
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Compound 11(Cl) m/z (70 eV): 262/260 (M+, 36%/84%),
261 (83), 153 (17), 135 (96), 125 (93), 107 (91), 92 (90), 77
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(M+, 80), 149 (47%), 122 (20), 121 (99), 119 (17), 92 (30),
91 (100), 77 (57), 65 (97).
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© 2005 NRC Canada