Original recyclization of S-phenacyl derivatives of 4-acylamino-2-mercapto- 1,3-oxazoles and their analogues

Article abstract of DOI:10.1002/hc.20317

Readily accessible acylamino(chloro)-acetophenones, if treated with sodium rhodanide and a-halogenocarbonyl compounds, provide 4-acylamino-5-aryl-2- mercapto-1, 3-oxazole derivatives which undergo recyclization on heating in polyphosphoric acid to give su

Full text of DOI:10.1002/hc.20317

Heteroatom Chemistry
Volume 18, Number 4, 2007
Original Recyclization of S-Phenacyl
Derivatives of 4-Acylamino-2-mercapto-
1,3-oxazoles and Their Analogues
Andrei G. Balia,1 Aleksandr G. Belyuga,1 Vladimir S. Brovarets,1
Aleksandr N. Vasylenko,1 Aleksandr V. Turov,2 Andrei A. Gakh,3
and Boris S. Drach1
1Institute of Bioorganic Chemistry and Petrochemistry, National Academy of Sciences of Ukraine,
1 Murmanskaya Str., 02660 Kiev-94, Ukraine
2Department of Chemistry, Taras Shevchenko National University, 64 Vladimirskaya Str., 01033
Kiev, Ukraine
3Oak Ridge National Laboratory Washington, P.O. Box 2008, Oak Ridge, TN 37381-6242, USA
Received 28 August 2006
a]azines [7,8], and imidazo[2,1-b]azoles [9]. In the
ABSTRACT: Readily accessible acylamino(chloro)-
present work, we have developed a new line in the
acetophenones, if treated with sodium rhodanide
synthetic use of reagents 1a–f based on the re-
and α-halogenocarbonyl compounds, provide 4-
cyclization of 3-acylaminothiazolo[2,3-b]oxazolium
acylamino-5-aryl-2-mercapto-1,3-oxazole derivatives
cations convertible into new derivatives of 1,3-
which undergo recyclization on heating in polyphos-
thiazol-2(3H)-one or 1,3-thiazolidin-2,4-dione.
phoric acid to give substituted 1,3-thiazol-2(3H)-
ones or 1,3-thiazolidin-2,4-diones containing 2-
alkyl(aryl)-5-aryl-1,3-oxazol-4-yl residues at the N3
ꢀ
C
RESULTS AND DISCUSSION
atom.
2007 Wiley Periodicals, Inc. Heteroatom Chem
18:432–437, 2007; Published online in Wiley InterScience
(www.interscience.wiley.com). DOI 10.1002/hc.20317
Treating amidophenacylating reagents 1a–f with
sodium rhodanide in tetrahydrofuran results,
already at 20–25◦C, in the formation of intermedi-
ate isothiocyanates 2a–f undergoing intramolecu-
lar cyclization that affords 4-acylamino-5-aryl-1,3-
oxazol-2(3H)-thiones 3a–f. Their tautomers 4a–f are
formed, if at all, in so minor amount that they
are undetectable during IR and 1H NMR spec-
troscopy. Nonetheless, the formation of thiol form
4 should not be neglected because the equilibrium
INTRODUCTION
Amidophenacylating reagents of the general formula
ArCOCHClNHCOR1 1a–f have already found exten-
sive application in the synthesis of functionalized
1,3-oxazoles [1–3], 1,3-thiazoles [4,5], imidazoles
[6], and condensed systems such as imidazo[1,2-
→
3←− 4, even strongly shifted toward 3, can be of
significance in some conversions. It is quite evident
that deprotonation of both tautomeric forms leads
to the same mesomeric thiolate anions that react
Correspondence to: Boris S. Drach; e-mail: Drach@bpci.kiev.ua.
2007 Wiley Periodicals, Inc.
c
ꢀ
432

Original Recyclization of S-Phenacyl Derivatives of 4-Acylamino-2-mercapto-1,3-oxazoles and Their Analogues 433
regioselectively with, for example, chloroacetone,
It should also be noted that the two-step con-
version 1→2→3, shown in Scheme 1, closely re-
sembles the formerly studied cyclocondensation of
α-ethylthio substituted α-chloroketones with potas-
sium rhodanide [10] (see Scheme 2).
Thus, the constitution of compounds 3a–f, 5a–i,
and 6a–c is determined quite unequivocally, which
enables the treatment of the further complex con-
versions, 5→7→9 and 6→8→10, occurring on heat-
ing the reaction mixture to 140◦C in polyphosphoric
acid.
phenacyl bromide, 4-halogenophenacyl bromides,
and methyl chloroacetate to give the corresponding
2-mercapto-1,3-oxazole derivatives 5a–i and 6a–c.
Structures 3, 5, 6 are supported by the IR and
1H NMR spectral data, which suggest that the con-
→
version 1−→ 3 involves the carbonyl group of the
phenacyl moiety and the proton of the methine
group is eliminated from the moiety
in
the course of the thioamide group formation. At the
same time, the spectral data summarized in Table 1
demonstrate that the conversions 3→5 and 3→6
are completely regioselective and result in the in-
troduction of the groups CH2COMe, CH2COAr, and
CH2C(O)OMe at the sulfur atom.
As was shown previously [11], substituted ox-
azoles bearing an acetonylthio- or phenacylthio
group at position 2 can be converted on heat-
ing in polyphosphoric acid into fairly stable
TABLE 1 Spectroscopic Data of Compounds 3, 5, 6, 9, and 10
IR (KBr)(cm−1
)
1H NMR (DMSO-d6/TMS)δ
3a
3b
5a
5b
5c
5g
5h
5i
1190(C S), 1670 (NC O),
3050 (NH), 3300 (NH)
1190(C S), 1670 (NC O),
3050 (NH), 3250 (NH)
1680 (NC O), 1700(C O),
3300 (NH)
1670 (NC O), 1700(C O),
3300 (NH)
1650 (NC O), 1690(C O),
3300 (NH)
1670 (NC O), 1730(C O),
3300 (NH)
1670 (NC O), 1730(C O),
3300 (NH)
1650 (NC O), 1725(C O),
3300 (NH)
2.08 (s, 3H, CH3), 7.29–7.65 (m, 5H, C6H5), 10.10 (s, 1H, NH),
13.44 (s, 1H, NH)
7.34–8.02 (m, 10H, 2C6H5), 10.57 (s, 1H, NH), 13.62 (s, 1H, NH)
2.03 (s, 3H, CH ), 4.99 (s, 2H, CH2), 7.26–8.07 (m, 10H, 2C6H5),
9.87 (s, 1H, NH3)
5.03 (s, 2H, CH2), 7.25–8.08 (m, 15H, 3C6H5), 10.39 (s, 1H, NH)
2.40 (s, 3H, CH3), 5.03 (s, 2H, CH2), 7.27–8.08 (m, 14H, 2C6H5,
C6H4), 10.29 (s, 1H, NH)
2.04 (s, 3H, CH3), 2.92 (s, 3H, CH3), 4.27 (s, 2H, CH2), 7.25–7.49
(m, 5H, C6H5), 9.87 (s, 1H, NH)
2.30 (s, 3H, CH3), 4.33 (s, 2H, CH2), 7.25–8.01 (m, 10H, 2C6H5),
10.39 (s, 1H, NH)
2.29 (s, 3H, CH3), 2.41 (s, 3H, CH3), 4.32 (s, 2H, CH2), 7.27–7.89
(m, 9H, C6H5, C6H4), 10.28 (s, 1H, NH)
6a
6b
6c
1680 (NC O), 1750(C O),
3300 (NH)
1660 (NC O), 1740(C O),
3300 (NH)
1650 (NC O), 1750(C O),
3300 (NH)
2.05 (s, 3H, CH3), 3.71 (s, 3H, CH3), 4.13 (s, 2H, CH2), 7.25–7.52
(m, 5H, C6H5), 9.89 (s, 1H, NH)
3.71 (s, 3H, CH3), 4.17 (s, 2H, CH2), 7.28–8.02 (m, 10H, 2C6H5),
10.42 (s, 1H, NH)
2.41 (s, 3H,CH3), 3.71 (s, 3H, CH3), 4.17 (s, 2H, CH2), 7.31–7.89
(m, 9H, C6H5, C6H4), 10.31 (s, 1H, NH)
9a
9b
9c
9d
9e
9fa
9g
1700(C O)
1700(C O)
1700(C O)
1690(C O)
1685(C O)
1685(C O)
1690(C O)
2.46 (s, 3H, CH3), 6.75 (s, 1H, CH), 7.16–7.45 (m, 10H, 2C6H5)
6.81 (s, 1H, CH), 7.23–8.02 (m, 15H, 3C6H5)
2.40 (s, 3H, CH3), 6.80 (s, 1H, CH), 7.23–7.92 (m, 14H, 2C6H5, C6H4)
6.82 (s, 1H, CH), 7.00–8.03 (m, 13H, C6H5, 2C6H4)
2.40 (s, 3H, CH3), 6.89 (s, 1H, CH), 7.26–7.92 (m, 12H, 3C6H4)
1.89 (s, 3H, CH3), 2.55 (s, 3H, CH3), 6.32 (s, 1H, CH), 7.26–7.45
(m, 5H, C6H5)
9h
9i
1690(C O)
1680(C O)
1.97 (s, 3H, CH3), 6.40 (s, 1H, CH), 7.42–7.58 (m, 10H, 2C6H5)
1.96 (s, 3H,CH3), 2.42 (s, 3H, CH3), 6.38 (s, 1H, CH), 7.36–8.00
(m, 10H, 2C6H5)
10a
1700(C O), 1780(C O)
2.53 (s, 3H, CH3), 4.47 (s, 2H, CH2), 7.26–7.53
(m, 5H, C6H5)
10b
1700(C O), 1780(C O)
1700(C O), 1780(C O)
4.54 (s, 2H, CH2), 7.45–8.10 (m, 10H, 2C6H5)
10cb
aMS: m/z (M+) 479.
bMS: m/z (M+) 350.
Heteroatom Chemistry DOI 10.1002/hc

434 Balia et al.
R1
O
S
H
N
H
N
C
R1
Cl
O
NaSCN
N
O
O
Ar
Ar
1a–f
2a–f
R1
O
R1
O
H
N
H
N
NH
N
Ar
S
Ar
SH
O
O
3a–f
4a–f
O
O
Cl
Hlg
2
, Et N
OMe
3
, Et3N
R
R1
O
R1
O
H
N
H
N
O
S
R2
MeO
O
N
N
Ar
Ar
S
O
O
6a–c
5a–i
PPA, ∆
PPA, ∆
H
N
R1
R1
O
R2
H
N
O
+
+
.
N
N
O.
S
S
-
Ar
Ar
-
O
An
O
An
7a–i
8a–c
PPA, ∆
PPA, ∆
R2
O
S
S
N
N
N
O
N
O
O
1
R
1
R
Ar
Ar
O
9a–i
10a–c
1-10
R1
a
b
c
d
e
Ph
4-MeC6H4
Ph
f
g
Me
Ph
h
i
4-MeC6H4
Ph
Me
Ph
Ph
Ph
Ph
Ph
4-MeC6H4
4-ClC6H4
Ph
4-FC6H4
4-MeC6H4
4-ClC6H4
4-ClC6H4
Ph
Ph
Me
Ar
Ph
Ph
R2
Me
Me
SCHEME 1
EtS
R
thiazolo[2,3-b]oxazolium salts of aromatic charac-
ter. However, attempted introduction of acylamine
residues at position 3 of this condensed system by
the cyclization 5→7 resulted in unstable intermedi-
ates 7 recyclizing to products 9. The conversion 7→9
is probably facilitated by the appropriate relative
disposition of the nucleophilic center at the oxygen
atom in the acylamino residue and the electrophilic
center C2 in the substituted thiazolo[2,3-b]oxazol-4-
ium cation 7. As a result of the interaction between
the two centers, the oxazolium nucleus is cleaved to
form the thiazolo-2(3H)-one ring and a new oxazole
ring closes involving the acylamino residue; these
H
N C S
EtS
R
Cl
O
EtS
N
KSCN
S
O
R
O
R = Me, Ph, PhCH2.
SCHEME 2
1
processes can be detected by IR and H NMR spec-
troscopy (see Table 1). In a similar manner, we suc-
cessfully performed the conversion 6→8→10 which
afforded novel N-hetaryl substituted 1,3-thiazolidin-
2,4-diones.
Heteroatom Chemistry DOI 10.1002/hc

Original Recyclization of S-Phenacyl Derivatives of 4-Acylamino-2-mercapto-1,3-oxazoles and Their Analogues 435
TABLE 2 1H and 13C NMR Signal Assignments and Correlations in the NOESY, HMQC, and HMBC Spectra for Compound
10c
1H, δ
13C, δ
1H, δ
NOESY
HMQC
HMBC
2.37 (CH3)
7.38 (C3a-H)
2.37 (CH3)
21.80 (CH3)
21.80 (CH3), 142.34 (C4a), 130.59 (C4b
)
7.38 (C3a-H)
7.96 (C2a-H)
7.67 (C2c-H)
7.52 (C3c-H)
7.45 (C4c-H)
4.59 (CH2)
130.59 (C3a
126.82 (C2a
125.52 (C2c
130.09 (C3c
130.43 (C4c
35.26 (C5d
)
)
)
)
)
)
130.59 (C5a), 123.78 (C1a
126.82 (C6a), 159.61 (C2b), 142.34 C4a
125.52 (C6c), 146.39 (C5b), 130.43 (C4c
130.09 (C5c), 126.16 (C1c
125.52 (C2c
171.66 (C4d), 171.32 (C2d
)
—
—
—
—
—
)
)
)
)
)
On comparing the IR spectra for the related rep-
resentatives of structures 9 and 10, it is seen that
the former exhibits only one band of the carbonyl
valence vibrations in the region 1650–1800 cm−1,
whereas the thiazolidin-2,4-dione moiety of the lat-
ter gives rise to two such bands. Furthermore, elimi-
1,3-thiazolidin-2,4-diones, pharmaceutically impor-
tant S,N-heterocycles promising in bioregulator
design.
EXPERIMENTAL
→
nation of water or methanol in the conversion 5−→ 9
1H NMR spectra were recorded on a Varian Gemini
300 spectrometer at 300 MHz using TMS as an in-
→
or 6−→ 10, respectively, is evidenced by mass spec-
trometry (see Table 1). Moreover, the structure of
compound 10c, one of the final recyclization prod-
ucts, is consistent with the experimentally estab-
lished one bond and long-range (two or three bond)
proton-carbon connectivities derived from 1H-13C
HMQC and HMBC spectra, respectively. These spec-
tra also enable assignment of 13C resonances. A
complete list of the correlations determined is pre-
sented in Table 2. Interestingly, the atom 13C4b dis-
plays no correlation. Its NMR signal found at 130.34
ppm is further upfield than expected (about 150
ppm), which may be attributable to the effect of
two carbonyl groups in the ring “d” (see Table 2 and
Fig. 1).
1
ternal standard. H and 13C NMR spectral measure-
ments combined with NOESY, HMQC, and HMBC
experiments for 10c were performed on a Varian
mercury 400 spectrometer using TMS as an internal
standard. IR spectra were measured on a Specord
M-80 spectrometer for KBr disks. Mass spectra were
measured on a Varian MAT-311A instrument.
N-(2-Aryl-1-chloro-2-oxoethyl)carboxamides 1a–f.
These compounds were obtained by using the known
procedure [4,5].
4-Acylamino-5-aryl-1,3-oxazol-2 (3H)-thiones 3a–f.
To a stirred suspension of sodium rhodanide
(22 mmol) in anhydrous tetrahydrofuran (10 mL), a
warm solution of one of compounds 1a–f (20 mmol)
in tetrahydrofuran (20 mL) was added. The stirred
mixture was held at 20–25◦C for 72 h. On evaporat-
ing tetrahydrofuran in vacuo, the residue was mixed
with ethyl acetate (30 mL) and heated to 50–60◦C. Af-
ter filtering off sodium chloride and removing most
of solvent, compounds 3a–f were obtained and re-
crystallized from acetic acid prior to analysis (see
Table 3).
In conclusion, it is notable that recycliza-
tions of functionalized thiazolo[2,3-b]oxazolium
cations demonstrate, even at the very outset of
the applicational research on them, great prepar-
ative value, for example, in the synthesis of
some N-hetaryl substituted thiazolo-2(3H)-ones and
4-Acy1amino-2-acylmethylthio-5-aryl-1,3-oxazo-
les 5a–i. To a solution of 3a–f (2.5 mmol) in ab-
solute methanol (30 mL), triethylamine (0.35 mL)
and chloroacetone or bromoacetophenone, or
4-chloro(fluoro)acetophenone (2.5 mmol) were
successively added. After stirring the mixture at
20–25◦C for 24 h, most of methanol was removed in
vacuo and water (100 mL) was added. The resulting
precipitate was filtered off and was purified by
recrystallization from ethanol (see Table 3).
3
2
2
6
3
5
1
4
H
O
b
c
5
4
1
H
a
1
4
5
2
6
H
N
O
3
3
N
d 4
H
O
5
2
S
H
1
FIGURE 1 Atom and ring labeling for compound 10c.
Heteroatom Chemistry DOI 10.1002/hc

436 Balia et al.
TABLE 3 Physical and Analytical Data of Compounds 3, 5, 6, 9, and 10
Analysis (%) Found (Calcd.)
Molecular Formula
M.P. (◦C) Yield (%)
(Molecular Weight)
C
H
N
S
Cl
3a 196–198a
65
55
61
69
71
74
71
70
72
85
83
82
69
59
63
58
53
61
58
59
62
79
74
82
56
61
59
55
58
65
C11H10N2O2S (234.27)
C16H12N2O2S (296.34)
C17H14N2O2S (310.37)
C16H11ClN2O2S (330.79) 58.03 (58.09) 3.41 (3.35) 8.39 (8.47)
C17H14N2O2S (310.37)
56.23 (56.39) 4.31 (4.30) 11.89 (11.95) 13.64 (13.68)
64.79 (64.84) 4.11 (4.08) 9.39 (9.45) 10.81 (10.82)
65.71 (65.78) 4.51 (4.54) 8.99 (9.02) 10.21 (10.33)
9.59 (9.69) 10.65 (10.71)
65.72 (65.78) 4.53 (4.54) 8.97 (9.02) 10.26 (10.33)
–
–
–
3b 192–193a
3c 212–214a
3d 151–152a
3e 183–185a
3f 167–169a
5a 129–131b
5b 151–152b
–
C17H13ClN2O2S (344.82) 59.15 (59.21) 3.82 (3.80) 8.09 (8.12)
9.25 (9.29) 10.21 (10.28)
C19H16N2O3S (352.41)
C24H18N2O3S (414.48)
C25H20N2O3S (428.51)
C24H16FClN2O3S (466.91) 61.65 (61.73) 3.47 (3.45) 5.93 (6.00)
C25H20N2O3S (428.51) 69.98 (70.07) 4.71 (4.70) 6.47 (6.53)
C25H18Cl2N2O3S (497.40) 60.46 (60.63) 3.68 (3.78) 5.81 (5.85)
C14H14N2O3S (290.34)
C19H16N2O3S (352.41)
C20H18N2O3S (366.43)
C14H14N2O4S (306.34)
C19H16N2O4S (368.41)
C20H18N2O4S (382.43)
C19H14N2O2S (334.39)
C24H16N2O2S (396.46)
C25H18N2O2S (410.49)
C24H14FClN2O2S (484.93) 59.35 (59.44) 2.96 (2.91) 5.71 (5.77)
C25H18N2O2S (410.49) 73.11 (73.14) 4.43 (4.42) 6.75 (6.82)
C25H16Cl2N2O2S (479.38) 62.57 (62.63) 3.41 (3.36) 5.78 (5.84)
C14H12N2O2S (272.32)
C19H14N2O2S (334.39)
C20H16N2O2S (248.42)
C13H10N2O3S (274.29)
C18H12N2O3S (336.36)
C19H14N2O3S (350.39)
64.69 (64.75) 4.53 (4.57) 7.89 (7.95)
69.48 (69.54) 4.41 (4.37) 6.68 (6.75)
70.03 (70.07) 4.75 (4.70) 6.45 (6.53)
9.01 (9.09)
7.65 (7.73)
7.41 (7.48)
6.83 (6.87)
7.43 (7.48)
–
–
5c
86–88b
–
7.51 (7.59)
–
5d 200–202b
5e 158–160b
5f 223–225b
5g 154–156b
5h 173–174b
5i 165–167b
6a 156–158b
6b 135–137b
6c 134–135b
9a 186–188c
9b 146–148b
9c 180–182b
9d 148–150b
9e 143–145b
9f 223–225d
6.63 (6.68) 14.75 (14.79)
57.85 (57.91) 4.81 (4.86) 9.58 (9.64) 10.98 (11.04) –
64.66 (64.75) 4.51 (4.57) 7.86 (7.95)
65.49 (65.55) 4.91 (4.95) 8.55 (7.64)
9.01 (9.09)
8.69 (8.75)
–
–
–
–
–
–
–
54.81 (54.89) 4.53 (4.60) 9.08 (9.14) 10.39 (10.46)
61.87 (61.94) 4.41 (4.37) 7.51 (7.60)
62.75 (62.81) 4.69 (4.74) 7.25 (7.32)
68.20 (68.24) 4.15 (4.22) 8.28 (8.37)
72.65 (72.70) 4.11 (4.06) 7.01 (7.06)
73.09 (73.14) 4.39 (4.42) 6.73 (6.82)
8.64 (8.70)
8.29 (8.38)
9.43 (9.58)
8.02 (8.08)
7.73 (7.81)
6.53 (6.61)
7.76 (7.81)
–
7.25 (7.31)
–
6.61 (6.68) 14.71 (14.79)
61.68 (61.74) 4.45 (4.44) 10.21 (10.28) 11.69 (11.77) –
9g
92–94c
9h 152–154b
9i 138–139c
10a 116–117c
10b 213–215b
10c 217–219b
68.15 (68.24) 4.18 (4.22) 8.31 (8.37)
68.89 (68.94) 4.59 (4.62) 7.98 (8.04)
9.51 (9.58)
9.15 (9.20)
–
–
–
–
–
56.87 (56.92) 3.71 (3.67) 10.16 (10.21) 11.63 (11.69)
64.15 (64.27) 3.61 (3.59) 8.25 (8.33)
65.09 (65.12) 4.01 (4.02) 8.01 (7.99)
9.46 (9.53)
9.07 (9.15)
aRecrystallization from MeC (O)OH.
bRecrystallization from EtOH.
cRecrystallization from i-PrOH.
dRecrystallization from DMF.
Methyl esters of S-(4-acylamino-5-phenyl-1,3-
oxazol-2-yl)mercaptoacetic acids 6a–c. These com-
pounds were obtained like compounds 5a–i start-
ing from 3a–c (3 mmol) and methyl chloroacetate
(3 mmol).
4-Aryl(methyl)-3-[5-aryl-2-methyl(aryl)-1,3-oxazol-
4-yl]-1,3-thiazol-2(3H)-ones 9a–i. A mixture of one
of compounds 5a–i (1 mmol) and polyphosphoric
acid (3.5 g) was held at 140◦C for 6 h before
cooling and pouring onto crushed ice (20 g). The
resulting precipitate was filtered off and purified by
recrystallization from an appropriate solvent (see
Table 3).
ACKNOWLEDGMENTS
This research was supported in part by the IPP
program through the Science and Technology Cen-
ter in Ukraine (STCU). Oak Ridge National Labo-
ratory is managed by UT-Battelle, LLC, under con-
tract DE-AC05-00OR22725 for the U.S. Department
of Energy. Contribution 20, the Discovery Chemistry
Project.
REFERENCES
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thiazolidine-2,4-diones 10a–c. These compounds
were obtained like compounds 9a–i starting from
6a–c (1 mmol) (see Table 3).
Heteroatom Chemistry DOI 10.1002/hc

Original Recyclization of S-Phenacyl Derivatives of 4-Acylamino-2-mercapto-1,3-oxazoles and Their Analogues 437
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Heteroatom Chemistry DOI 10.1002/hc