Synthesis and spectral properties of N-aryl-5-hydroxy-1,4-naphthoquinone 4-imines

Article abstract of DOI:10.1023/B:RUJO.0000010219.20915.5f

1,5-Dihydroxynaphthalene, 2,6-dibromo-1,5-dihydroxynaphthalene, and 2,4,6,8-tetrabromo-1,5-dihydroxynaphthalene react with aromatic amines in the presence of an oxidant to afford the corresponding N-aryl-5-hydroxy-1,4- naphthoquinone 4-imines.

Full text of DOI:10.1023/B:RUJO.0000010219.20915.5f

Russian Journal of Organic Chemistry, Vol. 39, No. 9, 2003, pp. 1309 1315. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 9, 2003,
pp. 1382 1388.
Original Russian Text Copyright
2003 by Bukhtoyarova, Ektova, Alekseev, Beregovaya.
Synthesis and Spectral Properties
of N-Aryl-5-hydroxy-1,4-naphthoquinone 4-Imines
A. D. Bukhtoyarova, L. V. Ektova, S. N. Alekseev, and I. V. Beregovaya
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
Received January 8, 2003
Abstract 1,5-Dihydroxynaphthalene, 2,6-dibromo-1,5-dihydroxynaphthalene, and 2,4,6,8-tetrabromo-1,5-di-
hydroxynaphthalene react with aromatic amines in the presence of an oxidant to afford the corresponding
N-aryl-5-hydroxy-1,4-naphthoquinone 4-imines.
Derivatives of N-arylquinonemonoimines have
been proposed as dyes for optical data storage devices
[1], antioxidants [2], anticarcinogenic compounds [3],
and synthons for the preparation of dyes for liquid
crystalline materials [4]. We previously showed that
oxidative coupling of 1,5-dihydroxynaphthalene (Ia)
with some aromatic amines leads to formation of
N-aryl-5-hydroxy-1,4-naphthoquinone 4-imines whose
yield depends on the substituent in arylamine and
the nature of oxidant [5].
With the goal of extending the series of N-aryl-5-
hydroxy-1,4-naphthoquinone 4-imine derivatives, in
the present work we performed a comparative study of
the oxidative amination of 1,5-dihydroxynaphthalene
(Ia), 2,6-dibromo-1,5-dihydroxynaphthalene (Ib), and
2,4,6,8-tetrabromo-1,5-dihydroxynaphthalene (Ic) with
arylamines in the presence of K3Fe(CN)6, HIO3, and
NaIO4 (Scheme 1, Table 1) and examined the effect
of electronic and steric factors in the arylamine on
the yield and spectral properties of N-aryl-5-hydroxy-
1,4-naphthoquinone 4-imines thus obtained (com-
pounds IIa IIp and IIIa IIIc; Tables 2, 3).
We have found that compounds Ia Ic react with
aryl- amines in aqueous alcohol at 20 C in the pres-
ence of K3Fe(CN)6 (method a) [optimal reactant ratio
I:II:K3Fe(CN)6 = 1:1:4] to afford the corresponding
N-aryl-5-hydroxy-1,4-naphthoquinone 4-imines IIa
IIp and that the product yield decreases from 85 to
3% in parallel with the basicity of arylamines [6, 7].
In the presence of K3Fe(CN)6, compounds IIa IIp
are likely to be formed according to the radical cation
mechanism which requires 4 mol of the oxidant per
mole of quinone imine (Scheme 2), by analogy with
the synthesis of indophenols and indoanilines [8].
Arylamines having electron-donor substituents in the
aromatic ring stabilize intermediate radical cations;
therefore, the products are formed in a fairly high
yield (85 50%). By contrast, the yield of N-aryl-5-
Scheme 1.
I, R = R = H (a); R = Br, R = H (b); R = R = Br (c); II, R = R = H, Ar = 4-Me2NC6H4 (a); R = R = H, Ar = 4-BuOC6H4 (b);
R = R = H, Ar = 4-MeOC6H4 (c); R = R = H, Ar = Ph (d); R = R = H, Ar = 2,4,6-Me3C6H2 (e); R = R = H, Ar = 4-IC6H4 (f);
R = R = H, Ar = 3-NO2C6H4 (g); R = R = H, Ar = 4-BuOCOC6H4 (h); R = R = H, Ar = 2-MeOCOC6H4 (i); R = R = H,
Ar = 2-MeOCO-4-IC6H3 (j); R = R = H, Ar = 4-NO2C6H4 (k); R = R = H, Ar = C6F5 (l); R = Br, R = H, Ar = 4-BuOC6H4 (m);
R = Br, R = H, Ar = 2,4,6-Me3C6H2 (n); R = R = Br, Ar = 4-BuOC6H4 (o); R = R = Br, Ar = C6F5 (p); III, R = R = H,
Ar = Ar = Ph (a); R = R = H, Ar = 4-IC6H4, Ar = Ph (b); R = R = Br, Ar = Ar = 4-BuOC6H4 (c).
1070-4280/03/3909-1309$25.00 2003 MAIK Nauka/Interperiodica

1310
BUKHTOYAROVA et al.
Scheme 2.
hydroxy-1,4-naphthoquinone 4-imines with electron-
acceptor substituents in the N-aryl fragment is poor
(3 40%).
1,5-dihydroxynaphthalene (Ia) with 4-dimethylamino-
aniline and aniline and of 2,4,6,8-tetrabromo-1,5-di-
hydroxynaphthalene (Ic) with 4-butoxyaniline. In the
first case, decrease in the yield of IIa may be ex-
plained by competing oxidation of 4-dimethylamino-
aniline (cf. [9]). The low yield of N-phenyl-5-hy-
droxy-1,4-naphthoquinone 4-imine (IId) may be due
to formation of N-phenyl-5-hydroxy-2-phenylamino-
1,4-naphthoquinone 4-imine (IIIa) [10] and iodine-
containing compounds IIf and IIIb as by-products.
Taking into account published data [11], compounds
IIf and IIIb could result from iodination of aniline
with a mixture of iodine (released during the process)
and HIO3 and from the reaction of 4-iodoaniline thus
formed with initial compound Ia. This was confirmed
by independent synthesis of IIf from Ia, aniline,
and I2. In keeping with the spectral data, product IIIb
has the structure of N-(4-iodophenyl)-5-hydroxy-2-
phenylamino-1,4-naphthoquinone 4-imine. It should
It was shown previously that oxidative amination
of 1,5-dihydroxynaphthalene with arylamines using
NaIO4 as oxidant affords with a satisfactory yield
quinone imines containing both electron-donor and
electron-acceptor substituents. The reaction is likely
to follow a ionic mechanism involving electrophilic
attack by NaIO4 on the hydroxy group in 1,5-dihy-
droxynaphthalene to give a complex (cf. [9]) which
then reacts with ArNH2. The yield of the resulting
N-aryl-5-hydroxy-1,4-naphthoquinone 4-imine
depends on the reactivity of arylamine [5].
In this work we have found that the reaction of
Ia Ic with arylamines in the presence of HIO3 or
NaIO4 (methods b and c, respectively) at a reactant
ratio of 1:1:1 is characterized by greater yields of
products IIa IIp. Exceptions were the reactions of
Table 1. Oxidative amination of compounds Ia Ic
Initial
Arylamine (pKa [6])
comp. no.
Product (yield, %; method)
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ia
Ib
Ib
Ic
Ic
4-Me2NC6H4NH2 (6.59)
4-BuOC6H4NH2
4-MeOC6H4NH2 (5.31)
PhNH2 (4.60)
2,4,6-Me3C6H2NH2 [3.89 (2,6-Me2C6H3NH2)]
4-IC6H4NH2 (3.78)
3-NO2C6H4NH2 (2.50)
4-BuOCOC6H4NH2 (2.47)
2-MeOCOC6H4NH2 (2.23)
2-MeOCO-4-IC6H3NH2
4-NO2C6H4NH2 (0.99)
C6F5NH2 ( 0.28 [7])
4-BuOC6H4NH2
IIa (85; a [5]); IIa (59; b), IIa (74; c [5])
IIb (65; a); IIb (88; b)
IIc (65; a [5]); IIc (73; b); IIc (71; c [5])
IId (64; a); IId, IIf, IIIa, IIIb (41, 2, 6, 6; b)
IIe (50; a); IIe (58; b); IIe (41; c)
IIf (45; a); IIf (61; b); IIf (70; c)
IIg (40; a); IIg (68; b); IIg (69; c)
IIh (24; a); IIh (76; b)
IIi (23; a); IIi (41; b)
IIj (38; a); IIj (44; b)
IIk (38; a [5]); IIk (40; b); IIk (55; c [5])
IIl (3; a); IIl, juglone (45, 25; b)
IIm (42; a); IIm (92; b)
2,4,6-Me3C6H2NH2
4-BuOC6H4NH2
C6F5NH2
IIn (53; a); IIn (74; b)
IIo (62; a); IIo, IIIc (43, 24; b)
IIp (14; a); IIp (62; b)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 9 2003

SYNTHESIS AND SPECTRAL PROPERTIES OF N-ARYL-5-HYDROXY-.. .
1311
Table 2. Melting points, IR and electron absorption spectra, and molecular weights of N-aryl-5-hydroxy-1,4-naphtho-
quinone 4-imines IIb, IIe IIj, IIl IIp, IIIb, and IIIc
Comp.
no.
mp,
(solvent)
C
IR spectrum UV spectruma (CHCl3),
Calculated
4
(KBr),
,
max, nm ( 10 ,
Found M+
Formula
M
1
1
cm
l mol 1 cm
IIb
122 123
1657 (C O),
490 (0.85)
321.13649
C20H19NO3
321.13648
(benzene hexane, 1619 (C N)
1: 5)
IIe
IIf
145 (hexane)
1660 (C O),
1630 (C N)
1654 (C O),
423 (0.42)
453 (0.54)
291.12372
374.97595
C19H17NO2
C16H10INO4
291.12592
374.97581
210 212
(benzene heptane, 1619 (C N)
1: 3)
IIg
224 226
(benzene hexane,
1: 5)
1660 (C O),
1630 (C N),
1530 (NO2),
1370 (NO2)
430 (0.64)
294.06251
C16H10N2O4
294.06405
IIh
IIi
131 132
(CHCl3 hexane,
1: 10)
1719 (COO ),
1660 (C O),
1620 (C N)
442 (0.71)
432 (0.62)
443 (0.61)
349.13128
307.08405
432.98117
C21H19NO4
C18H13NO4
C18H12INO4
349.13140
307.08445
432.98129
161 162
1720 (COO ),
(benzene hexane, 1660 (C O),
1: 5)
114 115
1620 (C N)
1717 (COO ),
IIj
(benzene hexane, 1657 (C O),
1: 5)
1620 (C N)
IIl
168 170
(hexane)
123 124
1660 (C O),
1620 (C N)
1660 (C O),
447 (0.59)
508 (0.89)
339.03119
476.95857
C16H6F5NO2
339.03186
476.95761
IIm
C20H17Br2NO3
(benzene hexane, 1600 (C N)
1: 5)
IIn
IIo
211 213
(CHCl3 hexane,
1: 10)
136 137
(benzene hexane, 1615 (C N)
1: 5)
223 225
(benzene hexane, 1615 (C N)
1: 5)
1671 (C O),
1600 (C N)
440 (0.61)
513 (1.09)
470 (0.72)
459 (0.89)
446.94764
554.87081
572.76367
466.01817
C19H15Br2NO2
C20H16Br3NO3
C16H3Br3F5NO2
C22H15IN2O2
446.94705
554.86818
572.76356
466.01800
640.05732
1670 (C O),
IIp
IIIb
IIIc
1676 (C O),
250 251
3268 (NH),
(benzene hexane, 1656 (C O),
1: 5)
124 125
1621 (C N)
3329 (NH),
515 (1.10), 551 (1.20), 640.05639
640 (0.80);
C30H30Br2N2O4
(benzene hexane, 1658 (C O),
1: 5) 1620 (C N)
496 (1.13), 550 (0.90),
640 (0.30)b
a
In the visible region.
In CCl4.
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 9 2003

1312
BUKHTOYAROVA et al.
Table 3. 1H and 19F NMR spectra of compounds IIa IIp, IIIb, and IIIc
Comp.
no.
Chemical shifts , ppm (J, Hz)
IIa
IIb
3.02 s (6H, 2Me), 6.68 d (1H, 2-H, 10.0), 6.74 d (2H, 2 -H, 6 -H, 8.5), 7.03 d (2H, 3 -H, 5 -H, 8.5), 7.25 d.d
(1H, 6-H, 8.0, 2.0), 7.46 t (1H, 7-H, 8.0), 7.48 d (1H, 3-H, 10.0), 7.67 d.d (1H, 8-H, 8.0, 2.0), 14.60 s
(1H, OH)
0.97 t (3H, Me, 7.0), 1.49 m (2H, CH2), 1.78 m (2H, CH2), 3.98 t (2H, CH2, 7.0), 6.68 d (1H, 2-H, 10.0),
6.96 m (4H, 2 -H, 3 -H, 5 -H, 6 -H), 7.26 d (1H, 6-H, 8.0), 7.36 d (1H, 3-H, 10.0), 7.50 t (1H, 7-H, 8.0),
7.67 d (1H, 8-H, 8.0), 14.22 s (1H, OH)
IIc
IId
IIe
IIf
3.82 s (3H, Me), 6.67 d (1H, 2-H, 10.5), 6.92 7.03 m (4H, 2 -H, 3 -H, 5 -H, 6 -H), 7.26 d.d (1H, 6-H, 8.0, 2.0),
7.34 d (1H, 3-H, 10.5), 7.48 t (1H, 7-H, 8.0), 7.65 d.d (1H, 8-H, 8.0, 2.0), 14.17 s (1H, OH)
6.63 d (1H, 2-H, 10), 7.00 d (2H, 2 -H, 6 -H, 8.5), 7.21 d (1H, 3-H, 10), 7.23 d.d (1H, 6-H, 8.0, 2.0), 7.43 m
(3H, 3 -H, 4 -H, 5 -H), 7.47 m (1H, 7-H, 8.0), 7.63 d.d (1H, 8-H, 8.0, 2.0), 13.84 s (1H, OH)
2.04 s (6H, 2Me), 2.31 s (3H, Me), 6.62 d (1H, 2-H, 10.0), 6.88 d (1H, 3-H, 10.0), 6.94 s (2H, 3 -H, 5 -H),
7.39 d (1H, 6-H, 8.0), 7.54 t (1H, 7-H, 8.0), 7.70 d (1H, 8-H, 8.0), 14.12 s (1H, OH)
6.70 d (1H, 2-H, 10.0), 6.77 d (2H, 2 -H, 6 -H, 8.5), 7.20 d (1H, 3-H, 10.0), 7.29 d.d (1H, 6-H, 8.0, 2.0), 7.54 t
(1H, 7-H, 8.0), 7.69 d.d (1H, 8-H, 8.0, 2.0), 7.75 d (2H, 3 -H, 5 -H, 8.0), 13.64 s (1H, OH)
6.75 d (1H, 2-H, 10.0), 7.12 d (1H, 3-H, 10.0), 7.29 7.41 m (2H, 6-H, 6 -H), 7.50 7.69 m (2H, 7-H, 5 -H),
7.73 d.d (1H, 8-H, 8.0, 2.0), 7.89 t (1H, 2 -H, 2.0), 8.14 d.t (1H, 4 -H, 8.0, 2.0), 13.28 s (1H, OH)
0.97 t (3H, Me, 7.0), 1.48 m (2H, CH2), 1.75 m (2H, CH2), 4.33 t (2H, CH2, 7.0), 6.69 d (1H, 2-H, 10.5),
7.05 d (2H, 2 -H, 6 -H, 8.0), 7.14 d (1H, 3-H, 10.5), 7.30 d.d (1H, 6-H, 8.0, 2.0), 7.54 t (1H, 7-H, 8.0),
7.69 d.d (1H, 8-H, 8.0, 2.0), 8.11 d (2H, 3 -H, 5 -H, 8.0), 13.46 s (1H, OH)
3.80 s (3H, Me), 6.65 d (1H, 2-H, 10.5), 6.87 d.d (1H, 6 -H, 8.0, 2.0), 7.04 d (1H, 3-H, 10.5), 7.26 7.37 m
(2H, 6-H, 4 -H), 7.47 7.62 m (2H, 7-H, 5 -H), 7.68 d.d (1H, 8-H, 8.0, 2.0), 8.08 d.d (2H, 3 -H, 8.0, 2.0),
13.52 s (1H, OH)
IIg
IIh
IIi
IIj
3.82 s (3H, Me), 6.61 d (1H, 6 -H, 8.0), 6.63 d (1H, 2-H, 10.0), 7.01 d (1H, 3-H, 10.0), 7.28 d.d (1H, 6-H, 8.0,
2.0), 7.52 t (1H, 7-H, 8.0), 7.66 d.d (1H, 8-H, 8.0, 2.0), 7.84 d.d (1H, 5 -H, 8.0, 2.0), 8.37 d (1H, 3 -H, 2.0),
13.26 s (1H, OH)
IIk
IIl
6.74 d (1H, 2-H, 10.0), 7.08 d (1H, 3-H, 10.0), 7.14 d (2H, 2 -H, 6 -H, 8.0), 7.33 d (1H, 6-H, 8.0), 7.59 t (1H,
7-H, 8.0), 7.73 d (1H, 8-H, 8.0), 8.33 d (2H, 3 -H, 5 -H, 8.0), 13.09 s (1H, OH)
6.77 d (1H, 2-H, 10.0), 6.97 d.t (1H, 3-H, 10.0, 2.5), 7.32 d.d (1H, 6-H, 8.0, 1.0), 7.59 t (1H, 7-H, 8.0),
7.70 d.d (1H, 8-H, 8.0, 1.0), 12.86 s (1H, OH);
19F NMR spectrum, F, ppm: 0.50 0.77 m (2F, 3 -F, 5 -F), 4.46 t.d (1F, 4 -F, 23.1), 12.45 d.d (2F, 2 -F, 6 -F,
23.7, 2.5)
IIm
0.99 t (3H, Me, 8.0), 1.50 m (2H, CH2), 1.79 m (2H, CH2), 3.99 t (2H, CH2, 8.0), 6.97 d (2H, 2 -H, 6 -H, 8.0),
7.05 d (2H, 3 -H, 5 -H, 8.0), 7.52 d (1H, 7-H, 8.0), 7.72 d (1H, 8-H, 8.0), 7.83 s (1H, 3-H), 15.28 s
(1H, OH)
IIn
IIo
IIp
2.04 s (6H, 2Me), 2.32 s (3H, Me), 6.96 s (2H, 3 -H, 5 -H), 7.33 s (1H, 3-H), 7.63 d (1H, 7-H, 8), 7.82 d (1H,
8-H, 8.0), 15.10 s (1H, OH)
0.99 t (3H, Me, 8.0), 1.50 m (2H, CH2), 1.79 m (2H, CH2), 4.00 t (2H, CH2, 8.0), 7.00 d (2H, 2 -H, 6 -H, 8.0),
7.10 d (2H, 3 -H, 5 -H, 8.0), 7.82 s (1H, 3-H), 8.01 s (1H, 7-H), 16.53 s (1H, OH)
7.42 t (1H, 3-H, 2.5), 8.19 s (1H, 7-H), 14.55 s (1H, OH)
19F NMR spectrum, F, ppm: 1.77 2.02 m (2F, 3 -F, 5 -F), 6.77 t (1F, 4 -F, 22), 13.34 d.d (2F, 2 -F, 6 -F,
22.5, 2.5)
IIIb
IIIc
6.58 s (1H, 3-H), 6.82 d (2H, 2 -H, 6 -H, 8.0), 7.02 d (2H, 2 -H, 6 -H, 8.0), 7.13 7.62 m (8H, 3 -H, 5 -H, 3 -H,
4 -H, 5 -H, 6-H, 7-H, NH), 7.75 d.d (1H, 8-H, 8.0, 1.0), 15.05 s (1H, OH)
0.95 m (6H, 2Me), 1.48 m (4H, 2CH2), 1.73 m (4H, 2CH2), 3.94 m (4H, 2CH2), 6.47 s (1H, 3-H), 6.81
7.13 m (8H, 2 -H, 3 -H, 5 -H, 6 -H, 2 -H, 3 -H, 5 -H, 6 -H), 7.74 s (1H, NH), 8.02 s (1H, 7-H), 18.21 s
(1H, OH)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 9 2003

SYNTHESIS AND SPECTRAL PROPERTIES OF N-ARYL-5-HYDROXY-.. .
1313
be noted that no iodination of quinone imine IId
occurs under the given conditions and that compounds
IId and IIf do not give rise to arylamino-substituted
quinone imines IIIa and IIIb. The reaction of 2,4,6,8-
tetrabromo-1,5-dihydroxynaphthalene (Ic) with
4-butoxyaniline in the presence of HIO3 gave a mix-
ture of compound IIo and product of bromine replace-
ment in position 2 by the arylamine residue, 6,8-di-
bromo-N-(4-butoxyphenyl)-2-(4-butoxyphenylamino)-
5-hydroxy-1,4-naphthoquinone 4-imine (IIIc).
at the longest wavelength,
= 592 nm [5]; com-
max
pounds IIb and IIc having weaker electron-donor
groups (BuO and MeO) [5] absorb at 490 nm. Elec-
tron-acceptor substituents (compounds IIg IIk)
reduce the absorption intensity, and the long-wave
absorption maximum shifts to the blue region. The
lowest
and values were observed for sterically
hinderedmaNx -(2,4,6-trimethylphenyl) derivative IIe.
Among bromine-containing derivatives IIm IIp, the
largest red shift of
and the strongest absorption
intensity, as well as mthaxe most downfield position of
The structure of the products was determined on
the basis of their spectral data (Tables 2, 3). In the
mass spectra we observed strong molecular ion peaks
with m/z values corresponding to the assumed struc-
tures. The IR spectra of all the products contained
1
the 3-H signal in the H NMR spectrum, are typical
of compounds IIm and IIo having an electron-donor
butoxy group in the para position of the N-aryl
moiety. N-(2,4,6-Trimethylphenyl) and N-pentafluoro-
phenyl derivatives IIn and IIp are characterized by
lower values of max and and upfield shift of the 3-H
signal. The observed variation of the 3-H chemical
1
absorption bands in the region 1600 1700 cm due
to stretching vibrations of the C O and C N bonds;
compounds IIh IIj and IIg additionally showed
bands from stretching vibrations of the ester carbonyl
and nitro group, respectively. The absence of absorp-
1
shift in the H NMR spectra and of the position of
the long-wave absorption maxima in the electron
spectra may be explained by effect of the benzene ring
which is arranged syn with respect to the 2-H and 3-H
protons [14] and is turned through an angle with
respect to the plane of the naphthoquinone fragment
[15]. Quantum-chamical calculations of the angle
in molecules IIa, IIc IIe, IIh, and IIk gave values of
54.1, 56.8, 57.7, 62.7, 58.1, and 57.8 , respectively.
Donor substituents in position 4 of the N-aryl frag-
ment makes the molecule more planar; as a result, the
1
tion in the region 3400 3600 cm is explained by
low-frequency shift of the OH stretching vibrations
to the region corresponding to C H bond vibrations
1
( 3000 cm ) due to formation of strong intramole-
cular hydrogen bond between the 5-hydroxy group
and imino nitrogen atom (C4 N) in the peri position
(cf. [12]). The existence of strong intramolecular
hydrogen bond also follows from the 1H NMR spectra
of compounds IIa IIp, IIIb, and IIIc (Table 3),
where singlets from the hydroxy protons appear in
a weak field, at 12.86 18.21 ppm, as it was ob-
served in the spectra of 5-hydroxy- and 5,8-dihydroxy-
1,4-naphthoquinones [13]. Protons in positions 2 and
3 of the quinone ring in IIa IIl give rise to two
doublets, the 3-H signal being more sensitive to the
position and nature of substituent in the N-aryl
fragment. Compounds IIa IIc having electron-donor
groups (NMe2, BuO, and MeO) in the para position
of the N-aryl fragment are characterized by the most
downfield 3-H signal ( 7.48, 7.36, and 7.34 ppm,
respectively); as electron-acceptor power of the sub-
stituent in the N-aryl fragment increases, the 3-H
signal shifts upfield ( 7.12 7.01 ppm; compounds
IIg IIk). The most upfield 3-H signals are observed
for N-pentafluorophenyl derivative IIl and sterically
hindered N-(2,4,6-trimethylphenyl)-5-hydroxy-1,4-
naphthoquinone 4-imine (IIe) ( 6.97 and 6.88 ppm,
respectively).
3-H signal shifts downfield, and
angle in sterically hindered N-(2,4,6-trimethyl-
increases. The
max
phenyl) derivative IIe is larger; therefore, conjugation
between the benzene ring and the C C C O bond
sequence through the nitrogen atom is broken, and
the 3-H signal shifts upfield while the absorption
maximum shifts to the blue region.
Introduction of bromine atoms into positions 2, 6,
and 8 of the naphthoquinone moiety leads to down-
field shift of the 3-H signal, red shift of the long-wave
absorption maximum, and increase in the absorption
intensity (cf. the spectra of IIb, IIm, IIo, IIe, and IIn,
as well as of IIl and IIp). A similar effect of electron-
acceptor substituents in position 2 of the naphthalene
ring was observed previously for N-aryl-1,4-naphtho-
quinone 4-imines [16].
We previously reported that 5-hydroxy-1,4-naph-
thoquinone 4-imines in organic solvents exist as mix-
tures of para- and ana-quinoid tautomers [17, 18].
Compounds IIa IIp show only one absorption band
in the visible region of the electron spectra. As well as
previously synthesized N-aryl-5-hydroxy-1,4-naphtho-
quinone 4-imines [5], they exist in the para-quinoid
form. Compound IIIc is characterized by appreciably
The electron absorption spectra of the products are
also characterized by considerable differences in the
position of the long-wave absorption maxima, depend-
ing on the nature of substituent in the N-aryl fragment.
The absorption maximum of compound IIa is located
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1314
BUKHTOYAROVA et al.
different electron absorption spectra in solvents with
different polarities. In going from CHCl3 to CCl4,
we observed a blue shift and increase in intensity of
the band belonging to the para-quinone imine struc-
of acetone); compounds IId, IIf, IIIa, and IIIb were
isolated in the order of elution. In the reaction of Ic
with 4-butoxyaniline, the precipitate was dissolved in
CHCl3 and subjected to column chromatography on
Al2O3 using in succession CCl4 (compound IIp) and
CHCl3 as eluent (IIIc).
c. To a suspension of 1 mmol of compound Ia and
1 mmol of the corresponding arylamine in 30 ml of
EtOH we added dropwise with stirring a solution of
1 mmol of NaIO4 in 15 ml of water, and the mixture
was stirred for 2 h at 20 C. It was then treated as
described above in a.
ture (
500 nm) and decrease in intensity of the
absorption band at 640 nm. These data suggest that
compound IIIc in CHCl3 gives rise to a mixture of
para- and ana-quinoid tautomers, as was observed for
N-phenyl-6,8-dibromo-5-hydroxy-2-phenylamino-1,4-
naphthoquinone 4-imine [18].
EXPERIMENTAL
N-Phenyl-5-hydroxy-1,4-naphthoquinone
4-imine (IId) and N-(4-iodophenyl)-5-hydroxy-1,4-
naphthoquinone 4-imine (IIf). To a suspension of
2 mmol of I2 in 30 ml of EtOH and 15 ml of water
we added 1 mmol of aniline, the mixture was stirred
for 1 h, 1 mmol of compound Ia was added, the mix-
ture was stirred for an additional 1 h and poured into
water, and 5 ml of 5% hydrochloric acid and 5 g of
sodium chloride were added. The precipitate was
filtered off, washed with water, dried, and dissolved
in CHCl3. Thin-layer chromatography on silica gel
using benzene chloroform (1:1) as eluent gave (in
the order of elution) 35% of compound IIf and 12%
of compound IId.
Behavior of compounds IId, IIf, and IIo under
conditions of oxidative amination. To a suspension
of 1 mmol of compound IId or IIf in 30 ml of EtOH
or of compound IIo in 30 ml of DMF and 1 mmol of
aniline or 4-butoxyaniline we added dropwise with
stirring a solution of 1 mmol of HIO3 in 15 or 10 ml
of water, and the mixture was stirred for 2 h at 20 C.
The mixture was then treated as described above in a
to isolate unchanged initial compounds IId (95%), IIf
(90%), or IIo (90%).
The IR spectra were recorded on Vector 22 and
UR-20 instruments in KBr. The electron absorption
spectra of solutions in CHCl3 or CCl4 were measured
on Specord UV-Vis, Hewlett Packard 4853, and
1
Beckmann DU-8 spectrophotometers. The H and 19F
NMR spectra were obtained on a Bruker WP-200SY
spectrometer from solutions in CDCl3. The molecular
weights and elemental compositions of the products
were determined from the high-resolution mass
spectra which were obtained using Finnigan MAT
8200 and Finnigan AEI MS-900 instruments. The
purity of the products was checked by TLC on Silufol
plates using CHCl3 as eluent. Quantum-chemical
calculations with full geometry optimization were
performed in the AM1 approximation using MOPAC
software [19].
Reaction of 1,5-dihydroxynaphthalenes Ia Ic
with arylamines (Table 1). a. To a suspension of
1 mmol of compound Ia or Ib in 50 ml of EtOH
(for compound Ic, in 30 ml of DMF) and 1 mmol of
the corresponding arylamine we added dropwise with
stirring a solution of 4 mmol of K3Fe(CN)6 in 50 ml
of water (in the reactions with Ic, in 10 ml of water).
The mixture was stirred for 2 h at 20 C and poured
into water, and 5 ml of 5% hydrochloric acid and 10 g
of solid sodium chloride were added. The precipitate
was filtered off, washed with water, dried, and dis-
solved in CHCl3, and the solution was subjected to
column chromatography on Al2O3 using CCl4 CHCl3
mixtures (10 to 100 vol. % of the latter) as eluent.
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