Conversion of 3-benzoyl-1-methyl-4-phenyl-γ-piperidol by arylamines and arylhydrazines. Synthesis of 3-arylamino-1-oxo-1-phenylpropanes and 1,3-diarylpyrazoles and their fragmentation under electron impact

Article abstract of DOI:10.1007/s10593-007-0192-9

It has been established that on heating, 3-benzoyl-4-hydroxy-1-methyl-4- phenylpiperidine is ring-opened in the presence of arylamines by a type of retroaldol reaction, with subsequent transamination of the intermediate Mannich base and the formation of 3-arylamino-1-oxo-1-phenylpropanes. When using arylhydrazines this γ-piperidol is recyclized with the formation of 1,3-diarylpyrazoles and their 4,5-dihydro derivatives. The mass spectral behavior of a series of 3-arylamino-substituted 1-phenylpropanones has been studied.

Full text of DOI:10.1007/s10593-007-0192-9

Chemistry of Heterocyclic Compounds, Vol. 43, No. 10, 2007
CONVERSION OF 3-BENZOYL-1-METHYL-4-PHENYL-
γ-PIPERIDOL BY ARYLAMINES AND ARYLHYDRAZINES.
SYNTHESIS OF 3-ARYLAMINO-1-OXO-1-PHENYL-
PROPANES AND 1,3-DIARYLPYRAZOLES AND THEIR
FRAGMENTATION UNDER ELECTRON IMPACT
S. V. Volkov1, S. V. Kutyakov1, A. N. Levov1, E. I. Polyakova1, Le Tuan An1,
S. A. Soldatova1, P. B. Terentiev2, and A. T. Soldatenkov1
It has been established that on heating, 3-benzoyl-4-hydroxy-1-methyl-4-phenylpiperidine is ring-opened
in the presence of arylamines by a type of retroaldol reaction, with subsequent transamination of the
intermediate Mannich base and the formation of 3-arylamino-1-oxo-1-phenylpropanes. When using
arylhydrazines this γ-piperidol is recyclized with the formation of 1,3-diarylpyrazoles and their
4,5-dihydro derivatives. The mass spectral behavior of a series of 3-arylamino-substituted
1-phenylpropanones has been studied.
Keywords: arylamines, arylhydrazines, 3-arylamino-1-oxo-1-phenylpropanes, 3-benzoyl-4-hydroxy-
1-methyl-4-phenylpiperidine, 1,3-diarylpyrazoles, mass spectra.
Previously [1], in attempting the synthesis of Schiff's bases from 3-benzoyl-4-hydroxy-1-methyl-
4-phenylpiperidine (1) [2] and o-phenylenediamine, we established an unusual direction for their interaction
under conditions standard for that type of condensation (boiling in toluene in the presence of catalytic amounts
of p-toluene-sulfonic acid). In place of the expected imine we isolated from the reaction mixture mono- and di-
N-benzoylethyl-substituted o-phenylenediamine and a benzo-annelated macrocycle, 1,4,8-triazacycloundecane.
The structure of the compounds obtained in this case indicated the occurrence of a complex cascade of reactions
the, chief of which may be: ring-opening of piperidol 1, transamination of the opened products, and
intramolecular cyclocondensation of the new Mannich bases. In the present report results are presented of a
systematic study of the reactions of piperidol 1 with p-, m-, and o-substituted anilines and arylhydrazines. In all
cases the interaction of 2 equiv. arylamine with 1 equiv. piperidol 1 under the conditions indicated above form
the expected (in agreement with the results of [1]) N-monobenzoylethylated anilines 2a-u (Tables 1 and 2). On
using unsubstituted aniline the yield of aminopropanone 2a was 49%. The introduction of electron-donating
substituents (alkyl or methoxyl groups), reducing the NH-acidity of arylamines, into the position 4 of aniline led
to a significant reduction in the yield of the corresponding aminopropanones 2b-e.
__________________________________________________________________________________________
1Peoples' Friendship University of Russia, Moscow 117198; e-mail: swelfen@mail.ru.
2M. V. Lomonosov Moscow State University, Moscow 119992, Russia; e-mail: petr_terentev@mail.ru
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1486-1495, October, 2007. Original
article submitted February 17, 2006; revision submitted June 23, 2006.
1260
0009-3122/07/4310-1260©2007 Springer Science+Business Media, Inc.

O
OH
NH2
Ph
Ph
NHCH2CH2COPh
+
–H2NMe
N
R
R
2a–u
Me
1
2 a R = H, b R = 4-Me, c R = 4-Et, d R = 4-i-Pr, e R = 4-OMe, f R = 4-Br, g R = 4-Cl,
h R = 4-I, i R = 4-COOEt, j R = 4-NO2, k R = 3-Cl, l R = 3-COMe, m R = 3-CF3, n R = 3-NO2,
o R = 2-COOMe, p R = 2-F, q R = 2-Cl, r R = 2-Br, s R = 2-NH2 [1],
t R = HNCH2CH2COPh [1], u R = 2-Cl, 4-Br
However the presence of halogen or ethoxycarbonyl groups in the para position provides an increase in
the yield of analogous products up to 63-74%. It might be assumed that such a strong electron-withdrawing
substituent as a nitro group at the C(4) atom of the aniline would increase further the yield of the expected
3-aminopropanone 2j. However this product was formed only in trace amounts and was identified only on
chromatomass-spectral analysis of the reaction mixture. The reason for the inactivity of 4-nitroaniline in this
reaction may probably be transition of the primary amino group into imine with the formation of an
iminoquinonoid tautomer which is incapable of partaking in the transamination reaction. If the nitro group is
present in the meta position of the nitroaniline then reaction occurs smoothly and compound 2n is formed in
high yield (82%).
On going to ortho-substituted anilines, the yields of 3-aminopropanones as a rule fell (compounds 2o-u),
which is probably linked with an increase in the role of steric factors.
Intense absorption bands were present in the IR spectra of the obtained 3-(N-arylamino)propanones 2 for
1
the C=O (at 1655-1686 cm-1) and NH groups (3210-3410 cm-1). The H NMR spectra of these compounds
(Table 2) were characterized by the presence of two triplet signals for the protons of the O=C–CH2–CH2–N
grouping, which were recorded in the region of 3.46-3.70 and 3.05-3.33 ppm with coupling constant 5.7-6.9 Hz.
The proton of the secondary amino group resonates at 3.8-4.8 ppm and is displayed as a broadened signal. The
aromatic protons in the positions ortho to the amino group of the aniline fragment afford diagnostic signals from
their high field disposition (at 6.6-6.8 ppm). At the same time the three groups of signals at low field (at
7.27-7.45, 7.46-7.65, and 7.93-7.97 ppm with ratio of integral intensities 2:1:2), belonging to the meta, para, and
ortho protons of the benzoyl fragment, are characteristic for the identification of all compounds 2.
A detailed analysis of the mass spectra of compounds 2a-i,k-q,t, obtained under electron ionization
conditions (Table 3), enabled assessment of the relative stability of their molecular ions and the finding of
general pathways for the fragmentation of the latter.
Analysis of the obtained mass spectra of compounds 2 (Tables 3 and 4) shows that the stability of these
molecular ions (WM) varies from 1.9 to 17.9% of the total ion current, however it was not possible to clarify the
influence of the electronic properties of the substituents in the aniline portion of the molecule on the stability of
the molecular ion.
Nonetheless the character of the fragmentation of the molecular ions of all compounds 2 has much in
general (which is evident from the scheme given below) and is determined first of all by the fission of the C–C
bond in the benzoylethyl fragment of the molecule with the formation of ion F1, the intensity of the peak of
which in the majority of cases is maximal or close to maximal (Table 4). Fission of the benzoyl fragment with
the formation of ions F4, F5, and F6 is the second decomposition pathway of significance. Finally, decomposition
of the molecular ion by the third main pathway is accompanied by transfer of a hydrogen atom from the
benzoylethyl fragment to the nitrogen atom with the formation of the rearranged odd-electron ions F2
1261

1262

1263

TABLE 2. Characteristics of the Synthesized Compounds
Found, %
——————
Calculated, %
IR spectrum, ν, cm-1
Com-
pound
Empirical
formula
mp, ºС
Yield, %
C
H
N
NH
C=O
1686
2a
2b
2c
2d
2e
2f
C15H15NO
C16H17NO
C17H19NO
C18H21NO
C16H17NO2
C15H14BrNO
C15H14ClNO
C15H14INO
C18H19NO3
79.80
80.00
6.88
6.67
6.25
6.22
109-110
110-111
94-95
3400,
3410
49
37
44
46
30
65
63
74
66
80.15
80.33
7.35
7.11
6.01
5.86
3381,
3400
1681
1678
1679
1673
1681
1677
1667
79.88
80.63
7.62
7.51
5.47
5.53
3375
3378
3361
3400
3390
3388
3366
80.30
80.90
7.43
7.87
5.12
5.24
108-109
104-105
138-140
132-133
140-141
139-140
75.41
75.29
6.55
6.67
5.62
5.49
59.14
59.21
4.39
4.61
4.50
4.61
2g
2h
2i
70.00
69.37
5.70
5.39
5.82
5.39
51.36
51.28
3.89
3.99
4.07
3.99
72.12
72.73
6.80
6.40
5.00
4.71
1670,
1678
2j
C15H14N2O3
C15H14ClNO
<1
75
2k
70.01
69.37
5.64
5.39
5.73
5.39
112-113
81-82
105-106
116-117
110-112
95-96
Oil
3371
3378
3378
3394
3353
3390
3385
3400
3392
1670
1678
1670
1673*
2l
C17H17NO2
C16H14F3NO
C15H14N2O3
C17H17NO3
C15H14FNO
C15H14ClNO
C15H14BrNO
75.90
76.40
6.53
6.37
5.63
5.24
79
84
82
60
60
23
17
35
2m
2n
2o
2p
2q
2r
2u
65.63
65.53
4.63
4.78
4.83
4.78
66.78
66.67
5.31
5.19
10.24
10.37
72.01
72.09
6.09
6.01
5.11
4.95
1680,
1673
73.61
74.10
5.48
5.76
5.51
5.76
1680
1675
1655
1687
69.94
69.37
5.76
5.39
5.02
5.39
59.45
59.21
4.26
4.61
3.57
3.84
4.85
4.61
4.43
4.14
Oil
C15H13BrClNO 53.57
53.25
Oil
_______
*IR spectrum, ν, cm-1: 1530, 1334 (NO2).
and F3. As follows from the data of Table 4, the total intensity of the peaks of the molecular ion and the six
fragment ions listed above is from 33 to 70% of the total ion current, which indicates the high selectivity of the
fragmentation process of the investigated compounds. In all probability, in the molecular ions of all compounds
2 the positive charge is localized predominantly on the aminoethylbenzoyl portion of the molecule. Confirmation
of this conclusion is the very low intensity (or even absence) of ion peaks linked with the primary fission or
breakdown of substituent R.
For example, the [M-Me]+ ion, so characteristic of acetylarenes [3], was absent in the mass spectrum of
acetyl-substituted 2l. The ions caused by loss of methyl (or ethoxcarbonyl group respectively), typical of the
mass spectra of 4-methoxy (or ethoxycarbonyl) anilines [3-5], were absent from the mass spectra of the
1264

TABLE 3. Mass Spectra of Compounds 2a-i,k-q,t
Com-
pound
m/z (Iотн, %)*
2a
2b
2c
2d
2e
2f
2g
2h
2i
225 [M] (27), 120 (5), 118 (5), 105 (100), 93 (6), 91 (6), 77 (47), 65 (10), 52 (15)
239 [M] (28), 238 (25), 120 (100), 118 (20), 105 (31), 91 (26), 77 (63), 65 (14), 51 (20)
253 [M] (100), 238 (14), 148 (13), 134 (85), 119 (15), 118 (21), 105 (48), 91 (15), 77 (70)
267 [M] (13), 252 (15), 148 (35), 136 (37), 132 (49), 120 (100), 105 (82), 91 (20), 77 (81)
255 [M] (59), 136 (100), 135 (27), 123 (24), 120 (38), 108 (36), 105 (80), 77 (59), 51 (22)
303 [M] (40)*2, 184 (100)*2, 171 (9)*2, 155 (6)*2, 118 (12), 105 (58), 91 (19), 77 (87), 51 (21)
259 [M] (34)*2, 140 (100)*2, 132 (15), 127 (17)*2, 111 (8), 105 (39), 77 (56), 65 (8), 51 (16)
351 [M] (56), 232 (88), 219 (25), 105 (100), 92 (19), 91 (23), 77 (29), 65 (23), 51 (35)
297 [M] (27), 178 (74), 165 (35), 132 (48), 120 (100), 105 (28), 77 (98), 65 (34), 51 (45)
2k
259 [M] (56)*2, 140 (72)*2, 127 (10)*2, 118 (11), 111 (13)*2, 105 (54), 99 (19)*2,
77 (100), 51 (40)
2l
2m
2n
267 [M] (27), 162 (11), 148 (100), 135 (13), 120 (17), 105 (13), 77 (55), 51 (23), 43 (40)
293 [M] (37), 274 (10), 174 (100), 161 (18), 145 (10), 120 (8), 105 (21), 77 (22), 51 (8)
270 [M] (29), 151 (53), 138 (34), 132 (18), 120 (21), 105 (100), 92 (25), 77 (84), 51 (25)
233 [M] (42), 164 (56), 151 (8), 146 (20), 132 (100), 119 (6), 105 (24), 77 (30), 51 (6)
243 [M] (26), 132 (21), 124 (100), 111 (67), 105 (69), 83 (20), 77 (98), 55 (21), 51 (42)
273 [M] (6)*2, 140 (89)*2, 134 (100), 133 (66), 127 (12)*2, 119 (15), 103 (20),
91 (14), 77 (51)
2o
2p
2q*3
2t
372 [M] (75), 240 (13), 147 (14), 133 (51), 132 (35), 119 (44), 105 (94), 92 (14), 77 (100)
_______
*[M] and the eight most abundant ion peaks are given.
*2Ions containing the 35Cl or 79Br isotopes .
*3As hydrazone.
4-methoxy (2e)- and 4-ethoxycarbonyl (2i)-substituted derivatives. Such processes however (frequently to an
insignificant extent) occur only after the formation of ions F1 and F2. Intense peaks for the F1-F4 and F6 ions are
observed even in the mass spectrum of compound 2q, but in the case of 1,2-bis(2-benzoylethylamino)benzene
.
+
H
Ph
N
O
R
.
– PhCOCH2
H
+
+
N
PhCO
+
N
H
CH2
F5
H
R
–CO
R
F1
F4
.
+
+
Ph
NH2
.
+
Ph–CO–CH=CH2
F6
F3
R
F2
1265

(2t) the molecular ion initially loses a molecule of phenyl vinyl ketone, but the resulting odd-electron (pseudo-
molecular) ion of 2-amino-substituted 2s eliminates a phenacyl radical with the formation of ion F1.
On replacing arylamines by arylhydrazines a more complex chain of sequential conversions of piperidol
1
1 occurs. In reality, analysis of the H NMR spectra of the reaction mixture and chromato-mass spectrometric
analysis of it showed that, in the case of phenylhydrazine, the final products of this interaction were
1,3-diphenyl-substituted 4,5-dihydropyrazole 3a and pyrazole 4a.
Both substances have close chromatographic mobilities and were isolated by column chromatography
only as mixtures in a total yield of 55% (in a ratio of 1:2 according to NMR data).
On oxidation of this mixture with manganese dioxide individual pyrazole 4a was obtained in high yield.
The use in place of phenylhydrazine of its 2,4-dinitro derivative led, as assumed, to complete dehydrogenation of
the intermediate dihydro-pyrazole 3b in status nascendi.
MnO2
(at Ar = Ph)
Ph
Ph
ArNHNH2
N
1
+
N
N
N
Ar
Ar
3a,b
4a,b
3,4 a Ar = Ph, b Ar = C6H3(NO2)2-2,4
Proceeding from the hypothesis that 3-benzoyl-substituted γ-piperidol 1 undergoes a retroaldol reaction
at the first stage of its conversion into 3-aminopropanones 2, we studied the interaction of 4-bromoaniline with
Mannich base 5b. The reaction proceeded in the presence of an equimolar amount of pyridine with conversion of
the Mannich salt 5a [2] into the free base 5b. As a result the expected aminopropanone 2f was isolated in 60%
yield.
H2N
Br
C5H5N
–HCl
MeN(CH2CH2COPh)2 . HCl
MeN(CH2CH2COPh)2
– MeNH2
5b
5a
Br
NHCH2CH2COPh
2f
On the basis of the results obtained in the previous [1] and the present communications it is possible to
offer a scheme for the sequential conversions of piperidol 1 under the action of arylamines and arylhydrazines in
the following form.
+
H+
2 CH2=CHCOPh
MeNH(CH2CH2COPh)2
1
5b
+
– H2NMe, – H
B
A
[O]
ArNHR
3
4
ArN(R)CH2CH2COPh
– H2O
– H2
(R = H, NH2)
2
1266

TABLE 4. Intensities of Peaks of Characteristic Ions in the Mass Spectra
of Compounds 2a-i,k-q,t (ΣI, %)
Com-
pound
WM
F1
F2
F3
F4
F5
F6
∑
M + Fi%
2a
2b
2c
2d
2e
2f
11.0
6.6
17.9
1.9
—
22.1
15.4
3.8
2.0
0.9
0.5
3.1
4.4
2.2
6.1
3.7
3.8
2.0
3.0
5.0
5.1
2.1
8.7
1.8
1.7
—
0.9
2.3
6.2
2.1
—
1.8
1.0
1.3
—
37.6
6.4
7.7
8.9
5.4
8.5
8.6
15.7
9.5
7.8
6.6
5.9
13.3
6.2
9.1
2.1
14.5
17.3
15.4
11.8
8.5
69.7
58.3
60.0
32.4
59.2
61.7
61.2
54.3
39.7
50.2
47.7
68.9
45.4
51.8
67.7
44.2
60.7
9.5
12.0
8.2
15.2
26.6
24.6
12.2
8.1
0.4
0.8
1.0
0.3
0.2
1.7
2.2
2.2
0.6
0.4
0.6
0.7
1.9
8.0
11.6
11.0
13.1
10.5
13.8
9.3
2g
2h
2i
1.7
1.0
4.3
—
8.3
3.3
2k
2l
11.6
5.3
13.6
18.8
33.0
8.1
2.5
0.8
3.7
25.8
2.6
1.7
4.7
2m
2n
2o
2p
2q
2t
13.1
5.7
6.7
8.9
11.0
4.0
14.4
14.0
18.3
6.8
7.8
12.6
8.2
1.4
12.4
7.4
The Mannich base 5b resulting from the retroaldol decomposition gives intermediate cation A after
protonation, which in its turn is decomposed to methylamine and phenyl vinyl ketone B. The latter then
undergoes a Mannich reaction with arylamines and forms new bases 2, which usually are difficult to synthesize
by the Mannich method. In the case of R=NH2 the amino ketones readily undergo heterocyclization and are
converted into dihydropyrazoles 3.
According to the predictions of the internet programs PASS [6] 3-(N-arylamino) ketones
2a-c,e,g,k,n,o,q may possess antileishmanial activity with a probability of 66-78%. Vasodilator action on heart
vessels may be displayed by compounds 2e,n,o (probability 60-71%). Antiviral activity (against herpes)
(probability 61-67%) may be expected for 2c,d,g,h,p,r,u and also amino ketone hydrazone 2q. The
trifluorophenyl amino ketone 2m is promising for testing as an inhibitor of tyrosine phosphatase (74%
probability), and N-(2-fluorophenyl)amino ketone 2p as an agonist of interferon (59%) and the GABA receptor
(61%). There is a particularly high probability of bioactivity for amino ketone 2r as an agonist of interferon
(70%) and an antagonist of interleukin (90%).
EXPERIMENTAL
1
The H NMR spectra were taken on a Bruker WP 400 (400 MHz) spectrometer in CDCl3, internal
standard was TMS. Mass spectra were obtained on a Finnigan MAT Incos 50 (70 eV) mass spectrometer. The IR
spectra were recorded on an IR 75 spectrometer in KBr disks. Silufol UV 254 plates were used for TLC
(visualization with iodine vapor). The characteristics of the synthesized compounds are given in Tables 1-4.
Preparation of 3-Aminopropanones 2 (General Method). A. A solution of piperidol 1 (2 mmol),
arylamine (4 mmol), and TsOH (10 mg) in toluene (30 ml) was boiled for 3-5 h with a Dean – Stark trap. The
solvent was evaporated to ½ volume, and cooled. The isolated crystals were separated, and recrystallized from
an appropriate solvent. Oily products 2q,r,u were isolated by column chromatography on silica gel, eluting with
hexane–chloroform, 5:1. Compound 2q was also characterized as the hydrazone, which was obtained in 36%
yield as light yellow crystals by boiling a methanolic solution of amino ketone (2.8 g; 10 mmol) with
1267

1
hydrazine hydrate (2 ml). Mp 86-88°C. IR spectrum, ν, cm-1: 1593 (C=N), 3210 (NH), 3330 (NH2). H NMR
spectrum, δ, ppm: 2.99 and 3.45 (2H each, both m, NCH2 and N=CCH2), 4.51 (1H, br. s, NH); 5.51 (2H, s,
NH2), 6.65, 7.11, and 7.25 (total 4H, all m, NC6H4Cl), 7.40-7.76 (5H, m, C6H5). Mass spectrum, see Table 3.
Amino Ketone 2a is described in [7], mp 111-112oC.
Compounds 2s,t, and also the diacetate of compound 2s were obtained previously in [1].
B. Pyridine (2 mmol), 4-bromoaniline (0.71 g, 4.1 mmol), and TsOH (10 mg) were added to a suspension
of Mannich salt 5a (0.66 g, 2 mmol) in toluene (30 ml). The mixture was boiled for 3 h, the solvent evaporated,
and the residue recrystallized from ether. Aminopropanone 2f (0.36 g, 60%) was obtained.
Preparation of 1,3-Diphenyl-4,5-dihydropyrazole (3a) and 1,3-Diphenyl-pyrazole (4a). A mixture of
piperidol 1 (1.2 g, 4 mmol), phenylhydrazine hydrochloride (0.6 g, 4 mmol), pyridine (0.32 g, 4 mmol), and
TsOH (10 mg) was boiled for 5 h. The solvent was distilled, and the residue separated on a chromatographic
column of silica gel, eluting with hexane. A mixture (0.5 g, 55%) of compounds 3a and 4a (in a ratio of 1:2
1
according to data of NMR and chromato-mass spectra) was isolated. H NMR spectrum of dihydropyrazole 3a,
δ, ppm (J, Hz) (obtained by deducting signals of the pyrazole 4a spectrum from the spectrum of a mixture of it
with dihydropyrazole 3a): 3.25 and 3.90 (2H each, both t, J = 10.5, 3-CH2 and 2-CH2 respectively); 6.85 (1H, t,
J = 7.4, H-4 NPh fragment); 7.1 (2H, d, J = 8.0, H-2,6 NPh fragment); 7.25-7.80 (7H, m, H arom.).
Oxidation of a Mixture of 3a compounds and 4a. Manganese dioxide (0.7 g, 8 mmol) was added to a
solution of the mixture (0.1 g, 0.4 mmol) of compounds 3a and 4a in toluene (30 ml) and the suspension
obtained was boiled for 3 h. The solid phase was filtered off and washed on the filter with hot toluene (10 ml),
the combined filtrates were evaporated to ¼ the initial volume, and cooled. 1,3-Diphenylpyrazole 4a (80 mg,
80%) was obtained as grayish white crystals, mp 82°C (lit. mp 84-85°C [8]).
1-(2,4-Dinitrophenyl)-3-phenylpyrazole) (4b) was obtained analogously to the synthesis of the
compounds 3a and 4a mixture from piperidol 1 (0.6 g, 2 mmol) and 2,4-dinitrophenylhydrazine (0.8 g, 4 mmol).
Following resolution of the reaction mixture by column chromatography on silica gel, compound 4b (0.45 g,
60%) was isolated as yellowish crystals; mp 159-160°C (lit. mp 162-163°C [9]).
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