New cyclic zwitterionic building blocks for the synthesis of piperidine-2,4-dione and pyridine-2-one compounds

Article abstract of DOI:10.1016/j.tetlet.2009.02.143

In this Letter we describe the synthesis of new chiral cyclic zwitterionic pyridin-2-one compounds 5a,b via an intramolecular ring-closure reaction of a stabilize amide sulfur ylide 4a,b derived from (R)-(-)-2-phenylglycinol and (R)-(+)-phenylethylamine i

Full text of DOI:10.1016/j.tetlet.2009.02.143

Tetrahedron Letters 50 (2009) 4208–4211
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
New cyclic zwitterionic building blocks for the synthesis of piperidine-2,4-dione
and pyridine-2-one compounds
*
Angel Palillero, Joel L. Terán , Dino Gnecco, Jorge R. Juárez, María L. Orea, Alejandro Castro
Centro de Química, Benemérita Universidad Autónoma de Puebla, Edif. 194, Complejo de Ciencias, C.U., 72570 Puebla,Pue., Mexico
a r t i c l e i n f o
a b s t r a c t
Article history:
In this Letter we describe the synthesis of new chiral cyclic zwitterionic pyridin-2-one compounds 5a,b
via an intramolecular ring-closure reaction of a stabilize amide sulfur ylide 4a,b derived from (R)-(ꢀ)-2-
phenylglycinol and (R)-(+)-phenylethylamine in a high yield. In addition, we proved the utility of 5a,b to
produce piperidine-2,4-dione 6a,b and pyridine-2-one 7a,b depending on the reaction conditions.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 21 January 2009
Revised 12 February 2009
Accepted 19 February 2009
Available online 25 February 2009
1. Introduction
methane and triethylamine at 0 °C afforded compounds 3a,b in
98% yield. Finally, compounds 3a,b were treated with dimethylsul-
Stabilized sulfonium amide ylides are well-known reagents
widely used in epoxydation1 or cyclopropanation reactions.2 Be-
cause of their relative stability, they generally react in a reversible
manner with carbonyl electrophiles, unless the equilibrating tran-
sient betaine can evolve in a non-reversible manner to a stable spe-
cies, such as an epoxide.3 For this reason, stabilized sulfonium
ylides are generally not considered as useful nucleophiles in inter-
molecular reactions. On the other hand, a special attention has
been paid to the intramolecular cyclization of keto-stabilized sul-
fur ylides. This approach has been reported to be a good method-
ology to build nitrogen-containing heterocyclic systems such as
fur in CH3CN at room temperature for 12 h, leading to the corre-
sponding sulfonium salts 4a,b (90% and 94% yields, respectively)
(Scheme 1).
Reaction conditions for the key cyclization step were then
investigated. As sulfur ylides are generally obtained by treatment
of the corresponding sulfonium salt with KOH in CH3CN,9 salts
4a,b were subject to these reaction conditions. To our delight,
the corresponding zwitterionic dihydropyridin-2-ones 5a,b could
be obtained in 85% and 87% yields, respectively (Scheme 2). These
relatively mild conditions ensured a chemoselective deprotona-
tion, avoiding a possible base-catalyzed retro-Michael degradation
of compounds 4a,b.
indolizinoquinoline,4 pyrrolizine- and indolizinediones,5 from
Proline, or - and b-(N-phthaloyl)amino acids. In these cases, the
L-
a
The structures of compounds 5a,b were confirmed by 1H and
13C NMR analysis. Both compounds showed two singlet picks
formation of cyclic compound might prevent the reversibility of
the ylide nucleophilic attack.
In this context, we present in this Letter a simple access to chiral
non racemic zwitterionic 4-alcoxy-3-sulfonium ylide pyridin-2-
ones 5a,b from (R)-(ꢀ)-2-phenylglycinol and (R)-(+)-phenylethyl-
amine using an intramolecular cyclization of sulfonium amide
ylide intermediate. Beside the synthetic potential of such scaffolds,
it is interesting to note that zwitterionic pyridin-2-one-type com-
pounds have been little studied,6,7 and might also exhibit interest-
ing biological properties.8
O
O
R
N
R
NH
OMe
Br
O
R
NH2
Br
O
O
NEt3, CH2Cl2,
0 °C, 1 min.
Methanol
Br
OMe
3a,b
OMe
2a,b
1a,b
2. Results and discussion
a R= (R)-phenyl-ethyl
b R= (R)-2-phenyl-ethanol
CH3CN, 12 h
S(CH3)2
Sulfonium salts 4a,b were prepared in three steps from 1a,b.
The secondary amines 2a,b were first quantitatively obtained by
Michael addition reaction between the primary amines 1a,b and
methyl acrylate. Acylation with bromoacetyl bromide in dichloro-
R
N
O
O
S(CH3)2
Br
OMe
4a,b
* Corresponding author. Tel.: +52 222 2295500x7277; fax: +52 222 2295551.
E-mail address: joelluisteran@hotmail.com.mx (J.L. Terán).
Scheme 1.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.02.143

A. Palillero et al. / Tetrahedron Letters 50 (2009) 4208–4211
4209
around d 2.9–3.0 ppm assigned to S(CH3)2, proving that demethyl-
ation did not occur during the cyclization step. Compounds 5a,b
displayed a benzylic proton around d 5.7–5.9 ppm, typical for a
cyclic structure. Finally, 13C NMR signals at d 187, 166 and
74 ppm revealed the presence of enol and amide functions. All
spectroscopic details are described in the experimental part and
are in accordance with the proposed zwitterionic structure.
Some preliminary chemical reactivity studies were conducted
on these remarkable compounds. Catalytic hydrogenation of the
sulfonium moiety was first attempted under various heteroge-
neous hydrogenation conditions (Table 1). Best results were ob-
tained when the hydrogenation was carried out using Pd–C as a
catalyst in acidic (HCl) EtOH under ultrasonic activation (Table 1,
entry 5 and 6), leading to 2,4-diketo piperidines 6a,b.
Later, reactivity of the zwitterions pyridin-2-one 5a,b with bro-
mine was investigated. Oxidation in acetic acid was unsuccessful,
but we were pleased to see the formation of 4-hydroxy-3-thio-
methyl pyridin-2-ones 7a,b in CCl4, in a moderate yield. A major
improvement was obtained by addition of NEt3, giving the best re-
sults (Table 2, entries 5 and 6).
R
N
R
N
O
O
KOH, CH3CN
rt, 12h
O
S(CH3)2
S(CH3)2
Br
OMe
4a,b
O
5a,b
a R= (R)-phenyl-ethyl
b R= (R)-2-phenyl-ethanol
Scheme 2.
Table 1
Reduction of compounds 5a,b
R
N
R
N
O
O
H2, catalyst
solvent, HCl, rt
S(CH3)2
O
O
5a,b
6a,b
Entry
Compound
Catalyst (10 mol %)
Conditions
Product
Yield (%)
1
2
3
4
5a,b
5a,b
5a
Ni(Raney)
Zn
PtO2
EtOH, 48 h
EtOH, 48 h
EtOH, 120 h
EtOH, 120 h
EtOH, 25 h
EtOH, 17 h
THF, 26 h
6a,b
6a,b
6a
6b
6a
6b
6a
6b
Traces
0
35
40
46
65
42
60
This transformation can be explained by the following mecha-
nism (Scheme 3). First, bromine reacts with the C–C double bond
by an electrophilic addition reaction, assisted by the electron lone
pair of oxygen giving a sulfonium salt which through nucleophilic
5b
5a
5b
5a
PtO2
5
Pd–Cb
Pd–Cb
Pd–Cb
Pd–Cb
6
attack from bromide at methyl group gave the corresponding
a-
7a
8a
bromo ketone intermediate. This intermediate began to establish
the keto–enol equilibrium. Finally, a base-catalyzed double bond
isomerization of the enol intermediates affording compounds 7a,b.
5b
THF, 22 h
a
20 mol % of catalyst was used.
Conducted under ultrasound activation.
b
3. Conclusion
In conclusion, we have reported in this Letter the first synthesis
of zwitterionic dihydropyridones based on an original ring-closure
step involving a stabilized sulfonium ylide. The overall yield of this
simple synthetic route enables a large-scale access to these inter-
esting building blocks. Some preliminary reactivity studies have
been presented, showing the good synthetic potential of these
compounds, for instance for the preparation of 2,4-diketo piperi-
dines of 4-hydroxy-3-thiomethyl pyridin-2-ones. Finally, the pres-
Table 2
Oxidation of compounds 5a,b
R
N
R
N
Br2
Br2
O
O
NEt3
degradation
Acetic
acid
CCl4
r.t.
S(CH3)2
SCH3
O
5a,b
OH
7a,b
Entry
Compound
Br2 (equiv)
Conditions
Product
Yield (%)
ence of
a
chiral appendage enables further asymmetric
transformations of the piperidine skeleton, a reactivity which is
under investigation in our laboratory.
1
2
3
5a,b
5a,b
5a,b
5a,b
5a
1.2
1.2
1.2
5.0
1.5
1.5
AcOH, 12 h
MeOH, 17 h
CCl4, 16 h
CCl4, 16 h
CCl4, 6 h
—
—
—
20
20
49
52
7a,b
7a,b
7a,b
7a
4
4. Experimental
5a
6a
5b
CCl4, 6 h
7b
1H NMR spectra were measured with
a Varian VX400
a
Et3 N (1.5 equiv) was added.
(400 MHz) and 13C NMR spectra at 100 MHz (tetramethylsilane
NEt3
R
N
R
N
R
N
R
N
H
O
O
Br
O
Br
O
Br Br
Br
CH3
CH3
CH3
H
S(CH3)2
S
S
S
O
O
OH
O
CH3
keto-enol equilibrium
NEt3
electrophilic
addition
Br
nucleophilic
attack
isomerization
step
R
N
O
SCH3
OH
7a,b
Scheme 3.

4210
A. Palillero et al. / Tetrahedron Letters 50 (2009) 4208–4211
as internal reference). IR spectra were obtained with a Nicolet FT-
IR Magna 750 spectrometer. Optical rotations were determined at
room temperature with a Perkin–Elmer 341 polarimeter, using a
1 dm cell with a total volume of 1 mL and are referenced to the
D-line of sodium. Mass spectra were recorded with a JEOL JEM-
AX505HA instrument at a voltage of 70 eV.
11.6, 1H), 5.78 (dd, J = 5.0, 11.6, 1H), 7.27–7.40 (m, 5H). 13C NMR
(CDCl3) d 26.3, 26.6, 36.8, 39.7, 57.7, 62.0, 74.6, 127.3–128.4,
137.9, 168.2, 188.1. HRMS (FAB): Calcd for C15H19NO3S:
293.1115. Found: 293.1023.
4.3. General procedure of catalytic hydrogenation of
zwitterionic compounds, 5a,b
4.1. General procedure for the synthesis of sulfonium salts, 4a,b
To a solution of 5a,b (1.70 mmol) in EtOH (5 mL) saturated with
HCl(g), was added 10% Pd/C (0.05 g) and the mixture was place un-
der hydrogen atmosphere. The mixture reaction was located in an
ultrasonic activation apparatus and stirred at room temperature
until the disappearance of starting material confirmed by thin
layer chromatography. After, the reaction was filtered and the sol-
vent was evaporated under reduced pressure to afford the corre-
sponding piperidine-2,4-dione 6(a–b).
To a solution of compounds 3a,b (1.60 mmol) in CH3CN (3 mL)
was added dimethyl sulfur (0.23 mL). The mixture reaction was
stirred for 20 h at room temperature. The excess of dimethyl sulfur
and the solvent was eliminated under reduced pressure. Finally the
crude reaction was washed with pentane affording the correspond-
ing sulfonium salts 4a,b.
4.1.1. (R)-(+)-{[(2-Methoxycarbonyl-ethyl)-(1-phenyl-ethyl)
carbamoyl]-methyl}-dimethyl-sulfonium bromide, 4a
4.3.1. (R)-(+)-1-(2-Phenyl-ethyl)-piperidine-2,4-dione, 6a
Yield 90%,
[
a]
D = +142.03 (c 2.0, EtOH). IR (KBr) 1736,
Yield 46%, Yellow oil. [
a]D = +7.1 (c 1.0, CH2Cl2). IR (KBr) 1726,
1634 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm, J Hz): 1.70 (d,
.
1647 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm, J Hz): 1.51 (d,
.
J = 6.9, 3H, Me), 2.37 (m, 2H), 3.30 (s, 3H, SMe), 3.34 (s, 3H, SMe),
3.41 (m, 2H), 3.55 (s, 3H, OMe), 5.19 (q, J = 6.9, 1H), 5.66 (d,
J = 10.8, 1H), 5.94 (d, J = 10.8,1H), 7.27–7.40 (m,5H). 13C NMR
(CDCl3) d(ppm) 17.2, 24.7, 26.8, 32.1, 38.2, 49.2, 51.3, 55.9,
126.4–138.7, 163.6, 171.2. HRMS (FAB): Calcd for C16H24BrNO3S:
390.31. Found: 391.0256, 389.1237.
J = 6.68, 3H), 2.32 (m, 2H), 3.14 (m, 2H), 3.5 (s, 2H), 6.08 (q,
J = 6.68, 1H), 7.32–7.30 (m, 5H). 13C NMR (CDCl3) d 15.7, 37.5,
38.8, 49.6, 50.40, 126.8–139.5, 165.2, 203. HRMS (FAB): Calcd for
C13H15NO2: 217.14. Found: 217.0863.
4.3.2. (R)-(ꢀ)-1-(2-Hydroxy-1-phenyl-ethyl)-piperidine-2,4-
dione, 6b
4.1.2. (R)-(ꢀ)-{[(2-Hydroxy-1-phenyl-ethyl)-(2-methoxycar
bonyl-ethyl)-carbamoyl]-methyl}-dimethyl-sulfonium
bromide, 4b
Yield 65%, yellow oil. [
a
]
D = ꢀ56.6 (c 1.0, CH2Cl2). IR (KBr) 1729,
1645 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm, J Hz): 2.34 (m, 2H),
.
2.55 (m, 2H), 3.30 (m, 1H), 3.47 (d, J = 16.2, 2H), 3.55 (m, 1H), 4.10
(dd, J = 6.68, 1H), 4.20 (dd, J = 6.68, 1H), 5.87 (dd, J = 6.68, 1H),
7.29–7.45 (m, 5H). 13C NMR (CDCl3) d 38.9, 49.5, 53.4, 57.9, 61.3,
127.5–138.5, 167.9, 203.9. HRMS (FAB): Calcd for C13H15NO3:
233.1114. Found: 233.0984.
Yield 94%,
[
a]
D = ꢀ49.29 (c 1.0, EtOH). IR (KBr) 1730,
1636 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm, J Hz): 2.07 (ddd,
.
J = 5.2, 10.2, 1H), 2.45 (ddd, J = 5.2, 10.2, 1H), 3.18 (s, 3H, SMe),
3.25 (s, 3H, SMe), 3.29 (m, 1H), 3.45 (m, 1H), 3.55 (s, 3H,
OMe), 3.94 (dd, J = 4.4, 9.6, 1H), 4.15 (dd, J = 4.4, 9.6, 1H), 4.67
(br, 1H, OH), 5.08 (dd, J = 4.4, 9.6, 1H), 5.76 (d, J = 15.6, 1H),
5.92 (d, J = 15.6, 1H), 7.27–7.4 (m, 5H). 13C NMR (CDCl3) d
(ppm) 25.1, 27.3, 32.2, 38.8, 49.2, 51.5, 59.8, 62.3, 127.9–134.8,
164.4, 171.7. HRMS (FAB): Calcd for C16H24BrNO4S: 406.03.
Found: 407.0748, 405.0123.
4.4. General procedure for the synthesis of pyridin-2-ones, 7a,b
To a stirred suspension of zwitterions 5a,b (1.7 mmol) in CCl4
(24 mL) was added a solution of Br2 (1.5 equiv, of a 1 M solution
in CCl4) and NEt3 (1.2 equiv) at room temperature. The resultant
pale orange solution was stirred for 6 h. Finally, the reaction mix-
ture was quenched with a saturate aqueous solution of sodium
thiosulfate (3 mL). The reaction was filtered and dried with anhy-
drous Na2SO4. The solvent was removed under reduced pressure
and the resulting mixture was purified through column chroma-
tography (dichloromethane/petroleum ether, on SiO2) afforded
the corresponding pyridine-2-ones 7a,b.
4.2. General procedure of the synthesis of zwitterionic
piperidine derivatives, 5a,b
To a stirred room temperature solution of the corresponding
sulfonium salts 4a,b (0.50 g, 1.23 mmol) in CH3CN (20 mL), was
added KOH (0.13 g). After 15 h, the resulting mixture was filtered
and CH3CN was removed under vacuum to give the corresponding
zwitterionic compounds 5a,b.
4.4.1. (R)-(+)-4-Hydroxy-1-(10-phenyl-ethyl)-3-methylsulfanyl-
1H-pyridin-2-one, 7a
4.2.1. (R)-(+)-[4-Alcoxy-2-oxo-1-(10-phenyl-ethyl)-1,2,5,6-
Yield 49%. [a] .
D = +21.6 (c 1.0, CH2Cl2). IR (KBr) 1656 cmꢀ1 1H
tetrahydro-pyridin-3-yl]-dimethyl-sulfonium, 5a
NMR (400 MHz, CDCl3) d (ppm, J Hz): 1.70 (d, J = 7.2, 3H), 2.31 (s,
3H), 6.05 (d, J = 8, 1H), 6.40 (q, J = 7.2, 1H), 7.05 (d, J = 7.6, 1H),
7.28–7.37 (m, 5H). 13C NMR (CDCl3) d 16.5, 18.9, 53.8, 98.7,
104.6, 127.1–139.8, 135.3, 162.0, 165.5. HRMS (FAB): Calcd for
C14H15NO3S: 277.10. Found: 277.0054.
Yield 85%, white solid, Mp 139–140 °C. [
a]D = +70.5 (c 1.1,
MeOH). IR (KBr) 1656 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm,
.
J Hz): 1.51 (d, J = 7.2, 3H, Me), 2.32 (m, 2H), 2.90 (m, 1H), 2.98 (s,
3H, SMe), 3.00 (s, 3H, SMe), 3.16 (m, 1H), 5.94 (q, J = 7.2, 1H),
7.27–7.40 (m, 5H). 13C NMR (CDCl3) d ppm 15.4, 26.0, 26.3, 36.3,
37.6, 48.9, 74.3, 126.5–141.0, 166.2, 187.5. HRMS (FAB): Calcd for
C15H19NO2S: 277.1124. Found: 277.1103.
4.4.2. (R)-(ꢀ)-4-Hydroxy-1-(20-hydroxy-10-phenyl-ethyl)-3-
methylsulfanyl-1H-pyridin-2-one, 7b
Yield 52%, white liquid. [
a
]
D = ꢀ58.0 (c 1.1, CH2Cl2). IR (KBr)
4.2.2. (R)-(ꢀ)-[4-Alcoxy-1-(20-hydroxy-10-phenyl-ethyl)-2-oxo-
3348, 1656 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm, J Hz): 2.29
.
1,2,5,6-tetrahydro-pyridin-3-yl]-dimethyl-sulfonium, 5b
(s, 3H), 4.27 (m, 2H), 6.06 (d, J = 7.6, 1H), 6.29 (dd, J = 4.8 and
Yield 87%, white solid, Mp 141–142 °C. [
a
]D = ꢀ24.7 (c 1.1,
6.8, 1H), 7.25 (d, J = 7.6, 1H), 7.31–7.39 (m, 5H). 13C NMR
MeOH). IR (KBr)1655 cmꢀ1 1H NMR (400 MHz, CDCl3) d (ppm,
.
(CDCl3) d 16.6, 60.2, 63.4, 98.6, 104.9, 126.7–141.3, 137.0,
J Hz): 2.36 (m, 2H), 2.96 (s, 3H, SMe), 2.98 (s, 3H, SMe), 3.03 (m,
1H), 3.30 (m, 1H), 4.05 (AB, J = 5.0, 11.6, 1H), 4.15 (AB, J = 5.0,
163.2, 166.0. HRMS (FAB): Calcd for C14H15NO3S: 277.10. Found:
277.0054.

A. Palillero et al. / Tetrahedron Letters 50 (2009) 4208–4211
4211
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Acknowledgements
We are grateful to CONACyT (Project 83185) and BUAP (Project
VIEP TEVJ-NAT-08-G) for financial support, A.P.C thanks CONACyT
for the scholarship (207839) and Dr. Laurent Micouin for careful
reading of the manuscript and suggestions.
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