Novel heterocyclization of imidoyl chlorides with mercaptocarboxylic acids

Article abstract of DOI:10.1055/s-2006-942537

A convenient, one-step synthetic approach to fluoro-alkyl-substituted 1,3-oxathiolanones and benzoxathianones, based on readily accessible N-acyl and N-sulfonyl imidoyl chlorides, has been developed. The novel heterocyclization involves previously unknown participation of the imidoyl carbon atom as a bifunctional 1,1-electrophile. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2006-942537

PAPER
3195
Novel Heterocyclization of Imidoyl Chlorides with Mercaptocarboxylic Acids
Heterocyclization
u
of Imidoyl
C
l
hloride
i
s
withM
y
ercaptocar
a
boxylic
A
cids V. Rassukana, Evgen A. Khomenko, Petro P. Onys’ko,* Anatoly D. Sinitsa
Institute of Organic Chemistry, National Academy of Sciences, Murmans’ka St, Kiev 02094, Ukraine
Fax +380(44)5732643; E-mail: onysko@rambler.ru.
Received 25 May 2006; revised 14 June 2006
CCl3
CCl3
NH2
O
Abstract: A convenient, one-step synthetic approach to fluoro-
alkyl-substituted 1,3-oxathiolanones and benzoxathianones, based
S
S
O
on readily accessible N-acyl and N-sulfonyl imidoyl chlorides, has
been developed. The novel heterocyclization involves previously
unknown participation of the imidoyl carbon atom as a bifunctional
1,1-electrophile.
Ar
O
O
Plant growth regulator
Enzyme inhibitors
Key words: imidoyl chlorides, oxathiolanone, benzoxathianone,
fluoroalkyl, cyclization
Figure 1 Some biologically active oxathiolanones
We present a convenient preparative method for the syn-
thesis of oxathiolanones, based on accessible fluoroacet-
imidoyl chlorides, activated by N-acyl- or N-sulfonyl
substituents. Thus, heterocyclization of imidoyl chlorides
1 with a-mercaptocarboxylic acids 2, affords the corre-
sponding oxathiolanones 3 in high yields (Table 1).
Imidoyl chlorides combine the properties of both acid
chlorides and azomethines. They are reactive and versatile
chemical agents that have found wide application in or-
ganic synthesis and in the study of chemical reactivity.1
Trifluoroacetimidoyl chlorides are regarded as promising
new building blocks for the synthesis of functionalized
fluorine-containing compounds.2
Recently, we developed a syntheses of fluoro-3 and tri-
fluoroacetimidoyl chlorides,4 containing electron-with-
drawing acyl or sulfonyl groups at the nitrogen atom, that
represent a new type of highly electrophilic fluorine-con-
taining synthons.
The method can be used for synthesis of oxathiolanones
containing alkyl substituents with varying electron-with-
drawing properties (CH2F, CF3) at the C-2 atom and either
a sulfonyl, acyl or alkoxycarbonyl group at the nitrogen
atom. The latter is important as removal of the N-protec-
tive groups can be accomplished under various condi-
tions.
Previously known heterocyclizations involved participa-
tion of electrophilic (carbon atom) and nucleophilic (ni-
trogen atom) centers of C=N imine systems, interacting
with the corresponding sites of bifunctional reagents.1a,2
Indeed, common imines, on interaction with thioglycol-
ates, either form stable addition products or undergo cy-
clization, through the C=N bond, to give thiazolidones.9
Our strategy uses imidoyl chlorides as 1,1-electrophiles,
with the imine nitrogen atom not participating in hetero-
cycle formation.
We have already demonstrated the use of these com-
pounds in the synthesis of biologically important acyclic
and heterocyclic derivatives containing, simultaneously,
fragments of aminophosphonic acids and trifluoromethyl,
fluoro or difluoromethylene groups.3–5
Now we report a novel synthesis of oxathiolanones and
oxathianones, with both fluoroalkyl substituents and an
amine function at the carbon atom of the S–C–O se-
quence, based on heterocyclization of activated imidoyl
chlorides.
It is also notable that condensation of polyfluorocarbonyl
compounds with mercaptocarboxylic acids allows the
synthesis of oxathiolanones with only carbon-centered
substituents at the C-2 atom.7,10
Specifically, derivatives of 1,3-oxathiolanones have ap-
plications as fungicides, herbicides, growth regulators,
precursors of modified nucleosides possessing antiviral
properties,6 and can be used for the introduction of a-mer-
captocarboxylic acid fragments into peptides.7 Related
oxathiolanones, containing a trichloromethyl group at the
C-2 atom, have proven to be plant growth regulators6a,8
and enzyme inhibitors6a–6c (Figure 1). To the best of our
knowledge, oxathiolanes containing both fluorinated sub-
stituents and an amino group at the C-2 atom, remain un-
known.
Virtually pure oxathiolanones 3 were obtained merely on
mixing the reagents in an organic solvent at room temper-
ature or brief heating. The unusually facile transformation
of 1 to 3 most likely results from the highly electrophilic
nature of imines 1 and from a beneficial, five-membered
ring formation. The fact that interaction of 1 with b-mer-
captopropionic acid leads to non-cyclic thioimidates 4
(Scheme 1), even upon prolonged heating or acidic catal-
ysis, supports this assumption.
Since thioimidates 4 contain an activated azomethine
bond and a peripheral carboxylic function, they can serve
SYNTHESIS 2006, No. 19, pp 3195–3198
Advanced online publication: 02.08.2006
x
x.
x
x
.
2
0
0
6
DOI: 10.1055/s-2006-942537; Art ID: P06006SS
© Georg Thieme Verlag Stuttgart · New York

3196
Y. V. Rassukana et al.
PAPER
Table 1 Synthesis of Oxathiolanones 3
chloride 1 (dF = –70 to –72 ppm), whereas the formation
of heterocycles 3, 5 results in an upfield displacement.
Generation of a new chiral center upon formation of com-
pounds 3, 5 provides additional evidence that ring closure
involves the imine carbon atom. This is clearly revealed in
magnetic non-equivalence of diastereotopic hydrogen at-
oms of CH2 group in the 1H NMR spectra of compounds
3 and 5. With R = Me, oxathiolanones 3c,d are formed as
a diastereomeric mixtures (1:1) that can be partially sepa-
rated, in the case of 3c, through fractional recrystalliza-
tion.
H
Y
N
Rf
O
Cl
HSCH(R)COOH (2)
S
72–95%
Y
Rf
N
benzene, r.t., 4 h
or 80 °C, 0.5 h
O
3a–g
R
1
Compound Rf
3a
R
Y
Isolated yield (%)
CF3
H
PhSO2
Ts
95
95
92
72
76
86
78
3b
3c
3d
3e
3f
CF3
H
It is important to note that the reactions studied here are
all highly selective. Exclusively cyclic (3, 5) or acyclic (4)
compounds are formed, depending on the reagent struc-
ture. It is apparent that the transformation of 1 to 3 is a
complex process, but we were unable to detect any inter-
mediates spectroscopically. Only a decrease in intensity
of the 19F NMR signal of 1 accompanied by a correspond-
ing increase of the respective signal of 3 was observed
upon spectral monitoring of the reaction.
CF3
CF3
CF3
CF3
CH2F
CH3
CH3
H
PhSO2
Ts
COOMe
C(O)Ph
C(O)CCl3
H
3g
H
O
It is quite possible that substitution of the chlorine atom by
the thio-function is accompanied by fast intramolecular
ring closure of immonium salts of types A or B (Figure 2).
The remarkable ease of heterocyclization can be ex-
plained by the high electrophilicity of the immonium C-
atom and the geometrically favorable location of the reac-
tive centers.
S
OH
Cl
HS(CH2)2COOH
SO2Ar
N
SO2Ar
CF3
benzene, 80 °C, 0.5 h
CF3
N
4a,b
1a,b
82–93%
1a, 4a: Ar = Ph
1b, 4b: Ar = 4-MeC6H4
In summary, we have developed a simple and efficient
synthesis of 1,3-oxathiolane-5-ones and 3,1-benzoxa-
thian-4-ones, containing a protected amino function and a
fluoroalkyl group at the C-2 atom of the heterocycle. A
characteristic feature of the new heterocyclization is the
fact that the imine carbon atom acts as a 1,1-electrophile,
while the carboxylic group of the mercaptocarboxylic
acid reacts through its O-nucleophilic center.
Scheme 1
as promising building blocks for the synthesis of function-
ally substituted, fluorine-containing compounds.
The position of the reactive centers is an important factor
controlling ring closure. Thus, thiosalicylic acid, with a
fixed cis-configuration of the HS- and HO- reactive cen-
ters, in contrast to b-mercaptopropionic acid, easily un-
dergoes heterocyclization with imidoyl chlorides 1 to
form 1,3-benzoxathian-4-ones 5 (Scheme 2).
H
H
N+
Cl–
Y
Y
N+
Cl–
S
S
Rf
O
Rf
Rf
O
S
H
O
Cl
Y
o-HSC6H4COOH
H
O
N
Y
H
A
B
Rf
benzene, 80 °C, 4 h
O
N
Figure 2
O
1
5a,b
5a: Rf = CF3, Y = Ts
5b: Rf = CH2F, Y = CCl3C(O)
IR spectra were obtained with an UR-20 instrument in KBr pellets
or as thin films. 1H NMR, 19F NMR, and 13C NMR spectra were re-
corded on a Varian VXR-300 spectrometer operating at 299.95
MHz, 282.20 MHz, and 75.43 MHz, respectively. Chemical shifts
are reported relative to TMS (1H, 13C), or CFCl3 (19F) as the internal
standards. Melting points are uncorrected. Solvents were dried be-
fore use according to standard methods.
Scheme 2
Heterocyclic compounds 3,5 and thioimidates 4 are easily
identified in the reaction mixture. The most important
structural feature for identification is the fluorine chemi-
cal shift in 19F NMR spectra (dF = –81 to –84 ppm for Preparation of Compounds 3; General Procedure
To a stirred solution of the imidoyl chloride 1 (0.3 mmol) in ben-
compounds 3, 5 and –65 to –66 ppm for thioimidates 4).
The observed differences stem from the sp3- and sp2-hy-
zene (5 mL), mercaptoacetic acid 2 (0.3 mmol) was added. After re-
acting for 4 h at r.t. or heating at 80 °C for 0.5 h, the solvent was
evaporated under vacuum and the solid or oily residue was washed
with hexane.
bridization of the carbon atom attached to the CF3 group.
Thus, transformation of 1 to 4 is accompanied by a down-
field shift of the fluorine signals of the starting imidoyl
Synthesis 2006, No. 19, 3195–3198 © Thieme Stuttgart · New York

PAPER
Heterocyclization of Imidoyl Chlorides with Mercaptocarboxylic Acids
3197
3a
Anal. Calcd for C6H6F3NO4S: C, 29.39; H, 2.47; N, 5.71; S, 13.08.
Found: C, 29.76; H, 2.59; N, 5.89; S, 12.97.
White solid; mp 95–96 °C.
1H NMR (CDCl3): d = 3.82 (d, JHAHB = 16.2 Hz, 1 H, CH2), 4.03
2
3f
2
(d, JHBHA = 16.2 Hz, 1 H, CH2), 6.40 (s, 1 H, NH), 7.57 (t,
White solid; mp 124–125 °C.
IR (KBr): 1660 (C=O), 1805 (C=O), 3220 (NH) cm–1.
3
3JHH = 7.8 Hz, 2 H, Ar), 7.64 (t, JHH = 7.8 Hz, 1 H, Ar), 7.94 (d,
3JHH = 7.8 Hz, 2 H, Ar).
2
19F NMR (CDCl3): d = –83.4.
1H NMR (CDCl3): d = 3.92 (d, JHAHB = 15.6 Hz, 1 H, CH2), 4.29
2
(d, JHBHA = 15.6 Hz, 1 H, CH2), 7.19 (s, 1 H, NH), 7.49 (t,
Anal. Calcd for C10H8F3NO4S2: C, 36.70; H, 2.46; N, 4.28; S, 19.59.
Found: C, 36.74; H, 2.51; N, 4.22; S, 19.47.
3JHH = 7.5 Hz, 2 H, Ar), 7.60 (t, JHH = 7.5 Hz, 1 H, Ar), 7.77 (d,
3
3JHH = 7.5 Hz, 2 H, Ar).
3b
19F NMR (CDCl3): d = –82.7.
White solid; mp 137–139 °C.
IR (KBr): 1180, 1345 (S=O), 1820 (C=O), 3270 (NH) cm–1.
Anal. Calcd for C11H8F3NO3S: C, 45.36; H, 2.77; N, 4.81; S, 11.01.
Found: C, 45.51; H, 2.63; N, 4.92; S, 10.88.
1H NMR (CDCl3): d = 2.46 (s, 3 H, CH3), 3.81 (d, 2JHAHB = 16.2 Hz,
1 H, CH2), 4.01 (d, 2JHBHA = 16.2 Hz, 1 H, CH2), 6.19 (s, 1 H, NH),
7.35 (d, 3JHH = 8.6 Hz, 2 H, Ar), 7.81 (d, 3JHH = 8.6 Hz, 2 H, Ar).
13C NMR (CDCl3): d = 21.6 (s, CH3), 33.0 (s, CH2), 93.0 (q,
2JCF = 35.8 Hz, CNH), 121.1 (q, 1JCF = 284 Hz, CF3), 127.4, 129.8,
137.4, 144.9 (s, Ar), 168.5 (s, C=O).
3g
White solid; mp 105–106 °C.
IR (KBr): 1730 (C=O), 1795 (C=O), 3370 (NH) cm–1.
1H NMR (CDCl3): d = 3.83 (d, 2JHAHB = 16.2 Hz, 1 H, SCH2), 4.31
2
2
(d, JHBHA = 16.2 Hz, 1 H, SCH2), 4.67 (dd, JHF = 47.1 Hz,
2JHAHB = 10.8 Hz, H, FCH2), 4.77 (dd, JHF = 47.1 Hz,
2
19F NMR (CDCl3): d = –83.5.
2JHBHA = 10.8 Hz, 1 H, FCH2), 7.87 (s, 1 H, NH).
19F NMR (CDCl3): d = –215.9 (t, 2JFH = 47.1 Hz).
Anal. Calcd for C11H10F3NO4S2: C, 38.71; H, 2.95; N, 4.10; S,
18.79. Found: C, 38.68; H, 2.90; N, 4.19; S, 18.75.
Anal. Calcd for C6H5Cl3FNO3S: C, 24.30; H, 1.70; N, 4.72; Cl,
35.87; S, 10.81. Found: C, 24.42; H, 1.63; N, 4.83; Cl, 35.69; S,
10.92.
3c
Mixture of diastereomers A and B (1:2) was obtained after a single
crystallization (benzene) of the 1:1 mixture.
Preparation of Compounds 4; General Procedure
White solid; mp 92–94 °C.
IR (KBr): 1180, 1360 (S=O), 1780 (C=O), 3310 (NH) cm–1.
3-Mercaptopropionic acid 2 (0.3 mmol) was added to a stirred solu-
tion of the appropriate imidoyl chloride 1 (0.3 mmol) in benzene (5
mL). After reacting for 0.5 h at 80 °C, the solvent was evaporated
in vacuum and the solid residue was washed with hexane.
1H NMR (CDCl3): d = 1.58 (d, 3JHH = 6.7 Hz, 3 H, CH3, A), 1.61 (d,
3JHH = 7.2 Hz, 3 H, CH3, B), 4.16 (q, 3JHH = 6.7 Hz, 1 H, CH, A), 4.36
(q, 3JHH = 7.2 Hz, 1 H, CH, B), 6.43 (s, 1 H, NH, B), 6.49 (s, 1 H,
NH, A), 7.56 [t, 3JHH = 7.8 Hz, 2 H (A) + 2 H (B), Ar], 7.66 [t, 3JHH
=
4a
Yield: 93%; white solid; mp 110–112 °C.
7.8 Hz, 1 H (A) + 1 H (B), Ar], 7.92–7.96 (m, 2 H (A) + 2 H (B), Ar].
19F NMR (CDCl3): d = –84.01 (A), –83.41 (B).
IR (KBr): 1170, 1340 (S=O) 1595 (C=N), 1710 (C=O), 3200 (OH)
cm–1.
Anal. Calcd for C11H10F3NO4S2: C, 38.71; H, 2.95; N, 4.10; S,
18.79. Found: C, 38.59; H, 2.97; N, 4.15; S, 18.68.
3
1H NMR (CDCl3): d = 2.73 (t, JHH = 6.9 Hz, 2 H, CH2), 3.35 (t,
3JHH = 6.9 Hz, 2 H, CH2), 7.57 (t, 3JHH = 7.8 Hz, 2 H, Ar), 7.66 (t,
3JHH = 7.8 Hz, 1 H, Ar), 7.99 (d, 3JHH = 7.8 Hz, 2 H, Ar).
3d
19F NMR (CDCl3): d = –65.9.
Mixture of diastereomers A and B (1:1); white solid; mp 96–99 °C.
IR (KBr): 1180, 1360 (S=O), 1795 (C=O), 3310 (NH) cm–1.
Anal. Calcd for C11H10F3NO4S2: C, 38.71; H, 2.95; N, 4.10; S,
18.79. Found: C, 38.64; H, 3.07; N, 4.26; S, 18.82.
1H NMR (CDCl3): d = 1.60 (d, 3JHH = 7.0 Hz, 3 H, CH3CH, A), 1.61
(d, 3JHH = 7.0 Hz, 3 H, CH3CH, B), 2.46 (s, 3 H, CH3Ar, A), 2.48 (s,
3
4b
3 H, CH3Ar, B), 4.17 (q, JHH = 7.0 Hz, 1 H, CH, A), 4.36 (q,
3JHH = 7.0 Hz, 1 H, CH, B), 6.18 (s, 1 H, NH, B), 6.22 (s, 1 H, NH,
A), 7.35 (d, 3JHH = 8.0 Hz, 2 H, Ar, A or B), 7.40 (d, 3JHH = 8.0 Hz,
2 H, Ar, A or B), 7.80 (d, 3JHH = 8.0 Hz, 2 H, Ar, A or B), 7.82 (d,
3JHH = 8.0 Hz, 2 H, Ar, A or B).
Yield: 82%; white solid; mp 114–115 °C.
IR (KBr): 1170, 1340 (S=O) 1595 (C=N), 1720 (C=O), 3260 (OH)
cm–1.
3
1H NMR (CDCl3): d = 2.45 (s, 3 H, CH3), 2.72 (t, JHH = 6.9 Hz,
19F NMR (CDCl3): d = –84.0 (A), –83.4 (B).
2 H, CH2), 3.35 (t, 3JHH = 6.9 Hz, 2 H, CH2), 7.35 (d, 3JHH = 8.4 Hz,
2 H, Ar), 7.87 (d, 3JHH = 8.4 Hz, 2 H, Ar).
Anal. Calcd for C12H12F3NO4S2: C, 40.56; H, 3.40; N, 3.94; S,
18.05. Found: C, 40.71; H, 3.37; N, 4.05; S, 18.12.
19F NMR (CDCl3): d = –65.8.
Anal. Calcd for C12H12F3NO4S2: C, 40.56; H, 3.40; N, 3.94; S,
18.05. Found: C, 40.71; H, 3.32; N, 4.08; S, 18.13.
3e
Oil.
IR (film): 1750 (C=O), 1805 (C=O), 3340 (NH) cm–1.
Preparation of Compounds 5; General Procedure
Thiosalicylic acid (0.3 mmol) was added to a stirred solution of the
appropriate imidoyl chloride 1 (0.3 mmol) in benzene (5 mL). After
reacting for 4 h at 80 °C, the precipitate formed was filtered and
washed with hexane.
2
1H NMR (CDCl3): d = 3.77 (s, 3 H, CH3O), 3.88 (d, JHAHB = 16.2
Hz, 1 H, CH2), 4.23 (d, 2JHBHA = 16.2 Hz, 1 H, CH2), 6.37 (s, 1 H,
NH).
19F NMR (CDCl3): d = –83.0.
Synthesis 2006, No. 19, 3195–3198 © Thieme Stuttgart · New York

3198
5a
Y. V. Rassukana et al.
PAPER
(2) Uneyama, K. J. Fluorine Chem. 1999, 97, 11.
Yield: 95%; white solid; mp 180–181 °C.
IR (KBr): 1180, 1350 (S=O), 1745 (C=O), 3170 (NH) cm–1.
(3) Rassukana, Y. V.; Davydova, K. O.; Onys'ko, P. P.; Sinitsa,
A. D. J. Fluorine Chem. 2002, 117, 107.
(4) (a) Rassukana, Y. V.; Onys'ko, P. P.; Grechukha, A. G.;
Sinitsa, A. D. Eur. J. Org. Chem. 2003, 4181. (b) Onys'ko,
P. P.; Kolodka, T. V.; Kolotilo, N. V.; Kudryavtzev, A. A.;
Sinitsa, A. D. Zh. Obshch. Khim. 1994, 64, 396.
(c) Onys'ko, P. P. Zh. Obshch. Khim. 1999, 69, 158.
(5) Onys'ko, P. P.; Sinitsa, A. A.; Pirozhenko, V. V.; Chernega,
A. N. Heteroat. Chem. 2002, 13, 22.
(6) (a) Gouault, S.; Pommelet, J.-C.; Lequeux, T. Synlett 2002,
6, 996. (b) Ogawa, K.; Yamada, S.; Terada, T.; Yamazaki,
T.; Honna, T. Synthesis 1984, 595. (c) Ead, H. A.;
Abdelaziz, M. A.; Metwalli, N. H. Pol. J. Chem. 1991, 65,
1291.
(7) Schedel, H.; Dmowski, W.; Burger, K. Synthesis 2000,
1681.
(8) Krumkalns, E. V. US Pat. Appl. US 4282030, 1981; Chem.
Abstr. 1981, 95, 163901.
(9) (a) Tierney, J. J. Heterocycl. Chem. 1989, 26, 997.
(b) Onys'ko, P. P.; Kim, T. V.; Kiseleva, E. I.; Sinitsa, A. D.
Zh. Obshch. Khim. 1997, 67, 1642. (c) Levkovskaya, G. G.;
Drozdova, T. I.; Rozentsveig, I. B.; Mirskova, A. N. Russ.
Chem. Rev. 1999, 68, 581; Usp. Khim. 1999, 68, 638.
(d) Uneyama, K.; Ohkura, H.; Hao, J.; Amii, H. J. Org.
Chem. 2001, 66, 1026.
1H NMR (CDCl3): d = 2.44 (s, 3 H, CH3), 6.84 (s, 1 H, NH), 7.18
(d, 3JHH = 7.8 Hz, 1 H, Ar), 7.26 (d, 3JHH = 7.8 Hz, 2 H, Ar), 7.38 (t,
3JHH = 7.8 Hz, 1 H, Ar), 7.54 (t, JHH = 7.8 Hz, 1 H, Ar), 7.70 (d,
3
3JHH = 7.8 Hz, 2 H, Ar), 8.10 (d, 3JHH = 7.8 Hz, 1 H, Ar).
19F NMR (CDCl3): d = –83.5.
Anal. Calcd for C16H12F3NO4S2: C, 47.64; H, 3.00; N, 3.47; S,
15.90. Found: C, 47.84; H, 2.97; N, 3.51; S, 15.76.
5b
Yield: 96%; white solid; mp 169–170 °C (dec.).
IR (KBr): 1735 (C=O), 3300 (NH) cm–1.
2
1H NMR (DMSO-d6): d = 5.02 (d, JHF = 46 Hz, 1 H, FCH2), 5.03
(d, 2JHF = 46 Hz, 1 H, FCH2), 7.44 (t, 3JHH = 7.8 Hz, 1 H, Ar), 7.52
(t, 3JHH = 7.8 Hz, 1 H, Ar), 7.65 (d, 3JHH = 7.8 Hz, 1 H, Ar), 8.05 (d,
3JHH = 7.8 Hz, 1 H, Ar), 10.80 (s, 1 H, NH).
19F NMR (DMSO-d6): d = –222.1 (t, 2JFH = 46 Hz).
Anal. Calcd for C11H7Cl3FNO3S: C, 36.84; H, 1.97; Cl, 29.66; N,
3.91; S, 8.94. Found: C, 37.04; H, 2.13; Cl, 29.53; N, 4.02; S, 8.86.
References
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Nitrogen Double Bond; Patai, S. L., Ed.; John Wiley & Sons:
New York, 1970.
Synthesis 2006, No. 19, 3195–3198 © Thieme Stuttgart · New York