Reaction of 3-benzoyl-1-methyl-4-phenyl-γ-piperidol with 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/s10593-007-0064-3

Upon heating in the presence of arylamines 3-benzoyl-4-hydroxy-1-methyl-4- phenylpiperidine decyclizes via a retroaldol type reaction with subsequent transamination of the intermediate Mannich base to give 3-arylamino-1-oxo-1- phenylpropanes. In the case of the use of arylhydrazines this γ-piperidol recyclizes to give 1,3-diarylpyrazoles and their 4,5-dihydro derivatives. The mass spectroscopic behavior of a series of 3-arylamino-substituted 1-phenylpropanones has been studied.

Full text of DOI:10.1007/s10593-007-0064-3

Chemistry of Heterocyclic Compounds, Vol. 43, No. 4, 2007
REACTION OF 3-BENZOYL-1-METHYL-4-PHENYL-γ-PIPERIDOL
WITH ARYLAMINES AND ARYLHYDRAZINES. SYNTHESIS
OF 3-ARYLAMINO-1-OXO-1-PHENYLPROPANES AND 1,3-DIARYL-
PYRAZOLES AND THEIR FRAGMENTATION UNDER ELECTRON IMPACT
S. V. Volkov1, S. V. Kutyakov1, A. N. Levov1, E. I. Polyakova1, Le Tuan Anh1,
S. A. Soldatova1, P. B. Terentiev2, and A. T. Soldatenkov1
Upon heating in the presence of arylamines 3-benzoyl-4-hydroxy-1-methyl-4-phenylpiperidine decyclizes
via a retroaldol type reaction with subsequent transamination of the intermediate Mannich base to give
3-arylamino-1-oxo-1-phenylpropanes. In the case of the use of arylhydrazines this γ-piperidol recyclizes
to give 1,3-diarylpyrazoles and their 4,5-dihydro derivatives. The mass spectroscopic behavior of a
series of 3-arylamino-substituted 1-phenylpropanones has been studied.
Keywords: 3-arylamino-1-oxo-1-phenylpropanes, arylamines, arylhydrazines, 3-benzoyl-4-hydroxy-
1-methyl-4-phenylpiperidine, 1,3-diarylpyrazoles, mass spectra.
In previous [1] attempts to synthesize a Schiff base from 3-benzoyl-4-hydroxy-1-methyl-
4-phenylpiperidine (1) [2] and 1,2-diaminobenzene we identified an unusual route for their condensation under
standard type conditions (refluxing in toluene in the presence of a catalytic amount of para-toluenesulfonic
acid). In place of the expected imine the mono- and di-N-(benzoylethyl)-substituted ortho-phenylenediamines
and benzo derivative of the macrocycle 1,4,8-triazacycloundecane were separated from the reaction mixture. The
structure of the compounds obtained in this case pointed to a complex reaction cascade, of which the principal
might be decyclization of piperidol 1, transamination of the decyclization products and intramolecular
cyclocondensation of the novel Mannich bases. We now present the results of a systematic study of the reaction
of piperidol 1 with para-, meta-, and ortho-substituted anilines and arylhydrazines. In all cases the reaction of
two equivalents of the arylamines with one equivalent of the piperidol 1 under the conditions indicated above
gave the expected N-monobenzoylethyl aniline derivatives 2a-u (in agreement with the results of [1]), the
charcteristics of which are given in Table 1. For the unsubstituted aniline the yield of the aminopropanone 2a
was 49%. Introduction of electron-donor substituents into the para-position of the aniline lowers the NH-acidity
of the arylamines leading to a marked decrease in the yield of the corresponding aminopropanones 2b-e.
__________________________________________________________________________________________
1Russian People's Friendship University, Moscow 117198; e-mail: swelfen@mail.ru. 2M. V. Lomonosov
State University, Moscow 119899, Russia; e-mail: petr_terentev@mail.ru. Translated from Khimiya
Geterotsiklicheskikh Soedinenii, No. 4, pp. 544-554, April, 2007. Original article submitted February 17, 2006.
0009-3122/07/4304-0445©2007 Springer Science+Business Media, Inc.
445

TABLE 1. Characteristics of the Synthesized Compounds
IR spectrum,
ν, cm-1
Found, %
Calculated, %
——————
Com-
pound
Empirical
formula
mp, °C
Yield, %
С
Н
N
NH
C=O
2a
2b
C15H15NO
C16H17NO
79.80
80.00
6.88
6.67
6.25
6.22
109-110
110-111
3400,
3410
1686
1681
49
37
80.15
80.33
7.35
7.11
6.01
5.86
3381,
3400
2c
2d
2e
2f
C17H19NO
C18H21NO
C16H17NO2
79.88
80.63
80.30
80.90
75.41
75.29
7.62
7.51
7.43
7.87
6.55
6.67
4.39
4.61
5.70
5.39
3.89
3.99
6.80
6.40
5.47
5.53
5.12
5.24
5.62
5.49
4.50
4.61
5.82
5.39
4.07
3.99
5.00
4.71
94-95
3375
3378
3361
3400
3390
3388
3366
1678
1679
44
46
30
65
63
74
66
<1
75
79
84
82
108-109
104-105
138-140
132-133
140-141
139-140
1673
C15H14BrNO 59.14
59.21
C15H14ClNO 70.10
69.37
C15H14INO
C18H19NO3
C15H14N2O3
1681
2g
2h
2i
1677
51.36
51.28
72.12
72.73
1667
1670, 1678
2j
2k
2l
C15H14ClNO 70.11
69.37
C17H17NO2
5.64
5.39
6.53
6.37
4.63
—
5.31
5.19
5.73
5.39
5.63
5.24
4.83
—
10.24 116-117
10.37
112-113
81-82
3371
3378
3378
3394
1670
1678
1670
75.90
76.40
2m
2n
C16H14F3NO 65.63
—
C15H14N2O3
105-106
66.78
66.67
1673 (1530,
1334, NO2)
2o
2p
2q
2r
2u
C17H17NO3
C15H14FNO
72.01
72.09
73.61
74.10
6.09
6.01
5.48
5.76
5.76
5.39
4.26
4.61
5.11
4.95
5.51
5.76
5.02
5.39
4.85
4.61
110-112
3353
3390
1680, 1673
60
60
23
17
35
95-96
1680
C15H14ClNO 69.94
69.37
C15H14BrNO 59.45
59.21
C15H13BrClNO 3.57
3.25
3400
1655
3.57
3.84
4.43
4.14
The presence of halogens or carbethoxy groups in the para position leads to an increase in the yield of the
analogous products to 63-74%. It might be expected that such a strong electron-acceptor substituent as the nitro
group on the C(4) position of the aniline would increase the yield of the expected 3-aminopropanone 2j even
O
NH2
OH
Ph
Ph
NHCH2CH2COPh
+
–H2NMe
N
R
R
2 a–u
Me
1
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,
u R = 2-Cl + 4-Br
446

further. However this product is formed only in trace amounts and was identified only by chromatomass-
spectrometric analysis of the reaction mixture. The reason for the unreactivity of the 4-nitroaniline in this
reaction can evidently derive from a change of the primary amine to an imino group with formation of an
iminoquinoid tautomer structure which cannot then take part in the transamination reaction. If the nitro group is
present in the meta position of the nitroaniline the reaction occurs smoothly with a high yield (82%) of the
compound 2n.
OH
+
N
HN
–
O
The yields of the 3-aminopropanones formed on going to the ortho-substituted anilines generally fall
(compounds 2o-u) and this is evidently associated with the increased steric factor.
The IR spectra of the 3-(N-aryl)propanones 2 obtained show strong absorption bands for the C=O groups
(at 1655-1686 cm-1) and NH group (3210-3410 cm-1). The 1H NMR spectra of these compounds (Table 2) show
the characteristic presence of two triplet signals for the protons of the O=C–CH2–CH2–N– group in the regions
3.46-3.7 and 3.05-3.33 ppm with a spin-spin coupling of 5.7-6.9 Hz. The secondary amino group proton absorbs
at 3.8-4.8 ppm as a broadened signal. The aromatic protons ortho to the amino group of the aniline fragment give
a typically high field positioned signal (6.6-6.8 ppm). An identifier for these compounds 2 is the presence of
three groups of signals to low field (7.27-7.45, 7.46-7.65, and 7.93-7.97 ppm) in the integrated ratio 2 : 1: 2 for
the meta, para, and ortho protons of the benzoyl fragment.
A detailed analysis of the mass spectra of compounds 2a-i,k-q,t recorded under electron ionization
conditions (Table 3) allowed us to assign the relative stability of their molecular ions and to find an overall route
for the fragmentation of the latter.
Analysis of the mass spectra of compounds 2 shows that the stability values of their molecular ions (WM)
occurs in the range form 1.9 to 17.9% of the total ion current but explaining the effect of the electronic
properties of the substituent in the aniline part of the molecule to the molecular ion stability value did not prove
possible, probably because the mass spectra were recorded over an extended time and often under differ
conditions. None the less, the nature of the fragmentation of the molecular ions of all of the compounds 2 have
much in common (as evident in the Scheme) and are determined mostly by cleavage of the C–C bond in the
benzoylethyl fragment of the molecule to give the ion F1, the intensity of whose peak is maximal or close to in
most cases (Table 4).
The second most important route for decomposition is cleavage of the benzoyl fragment to form the ions
F4, F5, and F6. Finally, the third basic cleavage route for the molecular ion involves transfer of a hydrogen atom
from the benzoylethyl fragment to the nitrogen atom with formation of the rearranged, odd electron ions F2
and F3.
As seen in Table 4, the overall peak intensity of the molecular ion peaks and the six fragmentation ions
listed above from 33 to 70% of the total ion current point to a high selectivity of the process in the fragmentation
of the compounds investigated. In all probability, the positive charge in the molecular ions of all of the
compounds 2 are localized principally in the aminoethylbenzoyl part of the molecule. The conclusion is
confirmed by the very low intensity (or even absence) of ion peaks associated with primary cleavage or cleavage
of the R substituent. Hence in the mass spectrum of the acetyl-substituted 2l the [M–Me]+ ion (so characteristic
of acetylarenes [3]) is absent. In the mass spectra of the 4-methoxy (2e) and 4-carbethoxy (2i) derivatives the
ions for primary loss of methyl (correspondingly carbethoxy) which are so typical of the mass spectra of
4-methoxy(carbethoxy)anilines [3-5] are absent. Such processes (often to a minor degree) occur only after
formation of the ions F1 or F2. The strong peaks for the F1-F4 and F6 ions are even observed in the mass
447

448

449

TABLE 3. Mass Spectra of Compounds 2a-i, k-q,t
Com-
pound
m/z (Ireal %)*
2a
2b
2c
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)
2d
2e
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)
2f
259 [M] (34)*2, 140 (100)*2, 132 (15), 127 (17)*2, 111 (8), 105 (39), 77 (56), 65 (8), 51 (16)
303 [M] (40)*2, 184 (100)*2, 171 (9)*2, 155 (6)*2, 118 (12), 105 (58), 91 (19), 77 (87), 51 (21)
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)
259 [M] (56)*2, 140 (72)*2, 127 (10)*2, 118 (11), 111 (13)*2, 105 (54), 99 (19)*2,
77 (100), 51 (40)
2g
2h
2i
2k
2l
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)
2m
2n
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 strongest ion peaks given.
*2 Ions containing the 35Cl and 79Br isotopes.
*3 As the hydrazone.
H
N
.
+
Ph
O
R
.
– PhCOCH2
H
+
N
+
CH2
PhCO
F5
+
N
H
R
H
F1
R
–CO
+
F4
Ph
F6
.
.
+
+
NH2
Ph–CO–CH=CH2
F3
R
F2
450

spectrum of compound 2q but in the case of the 1,2-bis(2-benzoylethylamino)benzene (2t) the molecular ion
initially loses a molecule of phenyl vinyl ketone and the odd electron (pseudomolecular) ion formed of 2-amino-
substituted 2s eliminates a phenacyl radical to give ion F1.
When changing from arylamines to arylhydrazines a more complex chain of consecutive reactions of
piperidol 1 takes place. In fact, the 1H NMR and mass spectrometric analysis of the reaction mixture showed that
for phenylhydrazine the final products of the reaction discussed are the 1,3-diphenyl-substituted
4,5-dihydropyrazole 3a and pyrazole 4a.
MnO2
(Ar = Ph)
O
OH
Ph
Ph
Ph
Ph
ArNHNH2
N
N
+
N
N
N
Me
Ar
Ar
4a,b
3a,b
1
3,4 a Ar = Ph, b Ar = C6H3(NO2)2-2,4
Both substances have similar chromatographic mobility and are separated chromatographically only as a
mixture with overall yield 55% (in the ratio 1 : 2 according to the 1H NMR data). Oxidation of this mixture with
manganese dioxide gave a high yield of the individual pyrazole 4a. The use of the 2,4-dinitrophenyl derivative
in place of phenylhydrazine led, as expected, to complete dehydrogenation of the intermediate dihydropyrazole
3b in status nascendi.
Starting from the basis that the 3-benzoyl-substituted γ-piperidol 1 undergoes a retroaldol reaction in the
first stage of conversion to the 3-aminopropanones 2 we have studied the reaction of 4-bromoaniline with the
Mannich base 5b. The reaction was carried out in the presence of an equivalent amount of pyridine for
conversion of the Mannich salt 5a to the free base 5b. As a result the expected aminopropanone 2f was formed
in 60% yield.
TABLE 4. Peak Intensities for the Characteristic Ions in the Mass Spectra
of Compounds 2a-i, k-q,t
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
37.6
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
—
—
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
451

H2N
Br
C5H5N
–HCl
MeN(CH2CH2COPh)2 . HCl
MeN(CH2CH2COPh)2
– MeNH2
5b
5a
Br
NHCH2CH2COPh
2f
On the basis of the results obtained before [1] and in this work the results can be rationalized by the
following scheme of successive reactions for piperidol 1 in the presence of arylamines and arylhydrazines:
H+
+
MeNH(CH2CH2COPh)2
2CH2=CHCOPh
1
5b
ArNHR
R = H, NH2
+
–H2NMe, – H
B
A
[O]
– H2
3
4
ArN(R)CH2CH2COPh
– H2O
2
The Mannich base 5b formed as a result of the retroaldol cleavage gives the intermediate cation A after
protonation and, in turn, this decomposes to methylamine and the phenyl vinyl ketone B. The latter then takes
part in a Michael reaction with arylamines to give the new bases 2 which are usually hard to synthesize by direct
condensation using the Michael method. In the case of R = NH2 the amino ketones readily undergo
heterocyclization and convert to the dihydropyrazoles 3.
According to the predictive PASS program [6] the 3-(N-arylamino ketones 2a-c,e,g,k,n,o,q may possess
a 66 to 78% probability of antileishmanial activity. Compounds 2e,n,o may show vasodilator activity on heart
vessels (probability 60-71%). The amino ketones 2c,d,g,h,p,r,u and the hydrazone of amino ketone 2q should be
tested for antiviral (Herpes virus) activity, a probability of possessing such activity is 61-67%.
The trifluorophenyl-substituted amino ketone 2m is promising for testing as a tyrosine phosphatase
inhibitor (74% probability) and the N-(2-fluorophenyl)amino ketone 2p as an interferon (59%) and GABA
receptor (61%) agonist. There is also a high probability for the bioactivity of amino ketone 2r as interferon
(70%) and interleukin (90%) antagonist.
EXPERIMENTAL
1H NMR spectra were taken on a Bruker WP-400 spectrometer using CDCl3 with TMS as internal
standard and mass spectra on a Finnigan MAT Incos 50 instrument (70 eV). IR spectra were recorded on an
IR-75 instrument for KBr tablets. TLC was carried out on Silufol UV-254 plates and spots were revealed using
iodine vapour. The characteristics of the compounds synthesized are given in Tables 1-4.
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 refluxed for 3-5 h in a Dean and Stark apparatus. The solvent
was evaporated to half volume and cooled. The precipitated crystals were separated and recrystallized from the
corresponding solvent. The oily products 2q,r,u were separated by column chromatography on silica gel eluting
with a mixture of hexane and chloroform (5 : 1). Compound 2q was also characterized as the hydrazone in 36%
yield as light-yellow crystals by refluxing a methanol solution of the amino ketone (2.8 g, 10 mmol) with
452

1
hydrazine hydrate (2 ml). Mp 86-88ºC. 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, d, 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 has been reported in [7], mp 111-112ºC.
Compounds 2s,t,u and also the diacetate of compound 2s have been prepared before [1].
B. Pyridine (0.16 g, 2 mmol), 4-bromoaniline (0.71 g, 4.1 mmol), and TsOH (10 mg) were added to a suspension
of the Mannich salt 5a (0.66 g, 2 mmol) in toluene (30 ml). The mixture was refluxed for 3 h, solvent evaporated
off, and the residue was recrystallized from ether to give the aminopropanone 2f (0.36 g, 60%).
1,3-Diphenyl-4,5-dihydropyrazole (3a) and 1,3-Diphenylpyrazole (4a). A mixture of the 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 refluxed for 5 h. Solvent was distilled off and the residue was separated on a silica gel chromatography
column with hexane as eluent to give the mixture of compounds 3a and 4a (0.5 g, 55%) (in the ratio 1 : 2 according
1
1
to the H NMR spectrum and mass spectrometry). H NMR spectrum of dihydropyrazole 3a (obtained by
subtracting the spectrum of pyrazole 4a from its mixture with 3a), δ, ppm (J, Hz): 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, N–C6H5 fragment); 7.1 (2H, d, J = 8.0, H-
2,6 N–C6H5 fragment); 7.25-7.80 (7H, m, Harom.).
Oxidation of the Mixture of 3a and 4a. MnO2 (0.7 g, 8 mmol) was added to a solution of a mixture of
compounds 3a and 4a (0.1 g, 0.4 mmol) in toluene (30 ml) and the suspension obtained was refluxed for 3 h.
The solid phase was filtered and washed on the filter with hot toluene (10 ml). The combined filtrates were
evaporated to one quarter initial volume and cooled to give the 1,3-diphenylpyrazole 4a (80 mg, 80%) as
grayish-white crystals with mp 82ºC (mp 84-85ºC [8]).
1-(2,4-Dinitrophenyl)-3-phenylpyrazole (4b) was prepared similarly to the mixture of 3a and 4a from
the piperidol 1 (0.6 g, 2 mmol) and 2,4-dinitrophenylhydrazine (0.8 g, 4 mmol). The reaction mixture was
separated by column chromatography on silica gel to give compound 4b (0.45 g, 60%) as yellowish crystals with
mp 159-160ºC (mp 162-163ºC [9]).
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