A new facile synthetic method for the construction of 1,3-oxathiolan-2-ylidenes

Article abstract of DOI:10.1016/j.tetlet.2008.02.103

A new, convenient and efficient synthetic method for the construction of 1,3-oxathiolan-2-ylidenes via sodium borohydride reduction of the addition product of dithiocarbamic acid esters with α-bromoketones under basic conditions is reported. This method is general and applicable to a range of systems.

Full text of DOI:10.1016/j.tetlet.2008.02.103

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 2602–2606
A new facile synthetic method for the construction
of 1,3-oxathiolan-2-ylidenes
Harisadhan Ghosh, C. B. Singh, Siva Murru, Veerababurao Kavala, Bhisma K. Patel *
Department of Chemistry, Indian Institute of Technology Guwahati, 781 039 Assam, India
Received 3 December 2007; revised 7 February 2008; accepted 16 February 2008
Available online 10 March 2008
Abstract
A new, convenient and efficient synthetic method for the construction of 1,3-oxathiolan-2-ylidenes via sodium borohydride reduction
of the addition product of dithiocarbamic acid esters with a-bromoketones under basic conditions is reported. This method is general
and applicable to a range of systems.
Ó 2008 Elsevier Ltd. All rights reserved.
1,3-Oxathiolan-2-ylidenes having an exocyclic imine
group can be used in organic synthesis for the preparation
of biologically active compounds.1 These heterocycles were
initially prepared by the reaction of alkylthiocyanates or
acetyl and benzoyl isothiocyanates with epoxides,2 and
subsequently by the 1,3-cycloaddition of heterocumulenes,
such as isothiocyanates with oxiranes under various
reaction conditions.3,4 The basic skeleton of 1,3-oxathio-
lan-2-ylidenes is unstable and has been isolated as its
N-acyl or N-carbamoyl derivatives.5 Taking advantage of
the faster alkylation of the thiocyano group compared to
the intramolecular cyclisation of 2-hydroxythiocyanates,
an alternative strategy for the synthesis of N-alkyl-1,3-oxa-
thiolan-2-ylidenes has been achieved from 2-hydroxythio-
cyanates and 1-adamantyl or tertiary butylalcohols.6 In
all these cases, the N-alkyl-1,3-oxathiolan-2-ylidenes exist
as a mixture of cis/trans isomers around the imine double
bond. In another strategy, 2-methylbut-3-yn-2-ol reacts
with benzyl isothiocyanate to give the oxathiolan-2-ylidene
moiety having an exocyclic double bond obtained by intra-
molecular attack of sulfur on the terminal acetylene.7 Reac-
tions of lithiated salts of dithioalkylimines with carbonyl
compounds give the oxathiolan-2-ylidene skeleton.8 The
synthesis of 2-imino-5-chloro-1,3-oxathiolanes, 2-imino-
1,3-oxathioles and 1,3-thiazolin-2-ones from N-aryl and
N-alkyl-S-chloroisothiocarbamoyl chlorides and ketones
has been reported.9
However, the drawbacks using the above-strategies are
the requirement of expensive and specially designed sub-
strates, reagents and catalysts and elevated temperatures.
The use of polar solvents is accompanied by undesirable
reactions such as trimerization of the isocyanate. Aromatic
and aliphatic isothiocyanates usually do not give oxathio-
lan-2-ylidenes because of the facile conversion to 2-oxazo-
lidinones in the presence of oxiranes.10 Unlike in the
synthesis of N-aryl-1,3-oxathiolan-2-ylidenes the reaction
of isocyanates with oxiranes catalysed by Lewis acids can-
not be used for the preparation of N-alkyl derivatives.11
1,3-Oxathiolan-2-ylidenes are formed only by the cyclo-
addition of activated isothiocyanates such as acetyl and
benzoyl isothiocyanates with oxiranes.
During the formation of thiazolidine-2-imine, the
sulfur atom of the thiourea attacks the bromomethyl
carbon of the a-bromoketone.12 Taking cues from the reac-
tivity of thioureas,12 the leaving ability of a thiol attached
to an imine functionality13 and the a-brominating ability
of ketones using 1,10-(ethane-1,2-diyl)dipyridinium bis-
tribromide (EDPBT)14 we envisaged a retrosynthetic
scheme for the construction of 1,3-oxathiolan-2-ylidenes
(Scheme 1).
*
Corresponding author. Tel.: +91 361 2582307; fax: +91 361 2690762.
E-mail address: patel@iitg.ernet.in (B. K. Patel).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.02.103

H. Ghosh et al. / Tetrahedron Letters 49 (2008) 2602–2606
2603
S
R
OH
pared from their parent ketones using EDPBT.14 These
a-haloketones were then reacted with dithiocarbamic acid
esters 1 and 5 in the presence of triethylamine in acetoni-
trile to provide adducts 9a–12a as shown in Table 2.
Adducts 1a–12a were obtained exclusively as their Z-iso-
mer. S-Alkylation of dithiocarbamic acid esters involves
base (triethylamine)-mediated abstraction of the NH pro-
ton, hence an E2 type of reaction which will be favourable
if the NH and C@S are anti to each other. We have shown
in an analogous system having a thioimido or a thioamido
functionality, during the formation of the thiazole-2-imine,
the imine double bonds were found to have the Z-confor-
mation (eight crystal structures).12 Further no diastereo-
N
N
O
Ar
Ar
Ar
S
S
S
H
S
N
R
Ar
S
N
R
O
S
+
O
Br
Scheme 1. Retrosynthetic analysis of oxathiolan-2-ylidenes.
As expected, the dithiocarbamic acid ester 1 (Table 1,
Scheme 1) reacted with the a-bromoketone formed by the
reaction of acetone with EDPBT in the presence of tri-
ethylamine to give the addition product 1a containing a
carbonyl functionality within 0.5 h at room temperature.20
Similarly, various other adducts 2a–8a of different dithio-
carbamic acid esters 2–8 were prepared employing this
strategy in good yields as shown in Table 1.
1
meric products could be detected even in H NMR of the
crude. Adducts 9a, 11a and 12a were obtained as racemic
products since they were prepared from the corresponding
racemic bromo compounds.
Having successfully achieved the first step in our strat-
egy we then attempted to reduce the adduct 1a using
sodium borohydride in a methanolic medium. The carb-
onyl group of 1a was reduced selectively without affecting
the imine functionality. The reduced product15 was isolated
and characterised, however, it slowly cyclised to give the
1,3-oxathiolan-2-ylidene 1b with concomitant liberation
of odorous mercaptoethanol at room temperature. How-
ever, by performing the reduction of 1a in methanolic
KOH, the carbonyl reduction was faster and complete
cyclisation was achieved by carrying out the reaction at
60 °C.21 When the leaving group was changed from –SEt
to –SMe or –SCH2Ph the reaction rate and yield were
found to be similar. Keeping in mind the cost factors,
and the ease of preparation and handling, we used –SEt
as the leaving group for all the other substrates.
Haloketones, such as 3-bromo-4-methyl-pentane-2-one,
2-bromo-1-phenyl-ethanone, 2-bromo-cyclohexanone and
1-bromo-1-(4-methoxy-phenyl)-propan-2-one, were pre-
Table 1
S-Alkylationa of dithiocarbamic acid esters
Substrate
Productb
Yieldc (%)
82
H
N
S
Et
S Et
S Et
N
O
1a
2a
1
2
S
S
F
F
H
S Et
O
N
N
78
94
95
81
80
86
S
S
H
S Et
O
S Et
N
N
3a
3
S
S
Table 2
Br
Br
S-Alkylationa of dithiocarbamic acid esters
Substrate
Productb
Yieldc (%)
75
H
N
S Et
O
N
S Et
4a
4
S
Et
O
N
S
H
N
S
S
S
Et
Et
9a
S
1
1
S
H
N
S Et
O
S
Et
5
N
5a
S
S
H
S
Et
O
N
N
80
75
10a
11a
S
S
H
N
Ph
S Et
O
N
S
Et
6
6a
S
S
S
Et
O
H
N
N
S
Et
5
H
S
S
Et
S
Et
N
N
O
O
O
O
S
S
O
7a
7
S
S
S
Et
N
H
N
12a
S
Et
H
N
S
Et
O
S
60
5
S
Et
8
N
OMe
78
8a
S
S
O
a
a
b
c
Reactions were monitored by TLC.
Reactions were monitored by TLC.
b
c
Confirmed by IR, 1H and 13C NMR.22
Isolated yield.
Confirmed by IR, 1H and 13C NMR.22
Isolated yield.

2604
H. Ghosh et al. / Tetrahedron Letters 49 (2008) 2602–2606
The versatility of this synthetic method is demonstrated
with substrates 1a–12a as shown in Table 3. Although
quantitative conversion was observed by GC and from
the crude yield, the isolated product yield was much lower.
Table 3
Formationa of 1,3-oxathiolan-2-ylidene
Substrate
Productb
Time (h) Yieldc (%)
N
S
S
Et
N
O
O
O
5
3
1
3
5
2
2
2
1
1
2
67
55
67
54
55
55
56
69
45
50
45
S
S
Fig. 1. ORTEP view of 5b with the atom-numbering scheme.
1b
1a
F
F
N
Et
O
N
Compared to the aryl systems 1a–5a, the alkyl 6a, verat-
ryl 7a and benzyl 8a systems reacted faster. This observa-
tion is comparable to the cycloaddition of PhCH2NCS
and PhNCS, where the latter is more reactive than the
former towards cycloaddition with propylene oxide.4 The
presence of the 1,3-oxathiolan-2-ylidene skeleton is shown
in the single crystal X-ray structure of 5b,16–19 Figure 1.
The versatility of this methodology has been demonstrated
successfully using ketones other than acetone as shown
with substrates 9a–12a giving the corresponding 1,3-oxa-
thiolan-2-ylidenes 9b–12b in moderate yields (Table 3).
Products 1b–8b and 10b were obtained as racemic mixtures
whereas products 9b, 11b and 12b were obtained as diaste-
reomeric mixtures.
In conclusion, this Letter reports an efficient method
for the S-alkylation of dithiocarbamic acid esters with
a-bromoketones under basic conditions. Subsequently, we
developed an efficient synthetic method for the construc-
tion of 1,3-oxathiolan-2-ylidenes by reduction of the
addition product of dithiocarbamic acid esters with
a-bromoketones. This method is convenient in terms of
simplicity and general applicability.
S
S
2b
2a
N
S
Et
N
O
O
S
S
3b
3a
Br
Br
N
Et
N
S
O
O
S
S
S
4b
4a
S
Et
O
N
N
O
S
5b
5a
N
S Et
O
N
O
N
S
S
6b
6a
S
Et
O
N
O
O
O
O
O
7a
S
S
7b
S
Et
O
N
N
O
Acknowledgements
S
8a
S
8b
S
Et
B.K.P. acknowledges support of this research from DST
New Delhi (SR/S1/OC-15/2006) and CSIR 01(1946)/04/
EMR-II. H.G., S.M. and C.B.S. thanks the CSIR for
fellowships. Thanks are due to CIF IIT Guwahati
for NMR spectra and DST FIST for the XRD facility.
N
O
N
O
S
S
S
S
9a
9b
S
Et
O
N
N
Ph
O
Ph
10b
10a
Supplementary data
S
Et
O
N
N
O
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.2008.
02.103.
S
S
11b
11a
N
O
S
Et
N
References and notes
S
S
1
40
OMe
12b
12a
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Chem. Soc. 1958, 80, 6582; (b) Condreay, L. D.; Condreay, J. P.;
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O
OMe
a
Reactions were monitored by TLC.
Confirmed by IR, 1H and 13C NMR.22
Isolated yield.
b
c

H. Ghosh et al. / Tetrahedron Letters 49 (2008) 2602–2606
2605
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20. General procedure for S-alkylation: (Z)-Ethyl 2-oxopropyl phenyl-
dithioimidocarbonate (1a): 1,10-(Ethane-1,2-diyl)dipyridinium bis-
tribromide EDPBT (3 mmol) was added to acetone (5 mL) and the
mixture stirred for 10 min, during this period the bromination of
acetone was complete as judged from the disappearance of the orange
colour of EDPBT and precipitating out of the spent reagent 1,10-
(ethane-1,2-diyl)dipyridinium dibromide (EDPDB). The supernatant
containing the bromo ketone was then filtered into a solution of
phenyldithiocarbamic acid ethyl ester 1 (5 mmol) in acetone (5 mL)
and triethylamine (10 mmol) and was stirred at room temperature.
The reaction was complete within 0.5 h as judged from the TLC. After
completion of the reaction, the solvent was evaporated and ethyl
acetate (20 mL) was added. The ethyl acetate layer was washed with a
saturated solution of NaHCO3, dried over anhydrous Na2SO4,
concentrated under reduced pressure and purified over silica gel to
give an 82% yield of (Z)-ethyl 2-oxopropyl phenyldithioimido-
carbonate (1a).
21. General procedure for the reductive cyclisation of (Z)-ethyl 2-oxopropyl
phenyldithioimidocarbonate (1a) to rac-N-[(2Z)-5-methyl-1,3-oxathio-
lan-2-ylidene]aniline (1b): To a solution of (Z)-ethyl 2-oxopropyl
phenyldithioimidocarbonate (1a) (0.762 g, 3 mmol) in methanol (5 mL)
was added KOH (0.168 g, 3 mmol) followed by portion-wise addition
of sodium borohydride (0.057 g, 1.5 mmol) over a period of 5 min at
0 °C. After stirring for 0.5 h, the reaction mixture was heated at 60 °C
for 5 h. The progress of the reaction was monitored by TLC. After
completion of the reaction, methanol was evaporated and the product
was extracted with ethyl acetate (2 ꢁ 25 mL). The organic layer was
separated and dried over anhydrous sodium sulphate and concentrated.
Further purification was accomplished by column chromatography
over a short column of basic alumina using a mixture of hexane and
ethyl acetate as eluent. The product, rac-N-[(2Z)-5-methyl-1,3-oxa-
thiolan-2-ylidene]aniline (1b), was obtained in 67% yield.
2. (a) van Tamelen, E. E. J. Am. Chem. Soc. 1951, 73, 3444; (b)
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C. C.; Kirk, P. F. J. Am. Chem. Soc. 1952, 75, 2396; (e) Lukowska, E.;
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3. (a) Shibata, I.; Toyota, M.; Baba, A.; Matsuda, H. J. Org. Chem.
1990, 55, 2487; (b) Ulrich, H. Cycloaddition Reactions of Hetero-
cumulenes; Academic: New York, 1967; (c) Dyen, M. E.; Swern, D.
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4. Shibata, I.; Baba, A.; Iwasaki, H.; Matsuda, H. J. Org. Chem. 1986,
51, 2177.
5. (a) Wagnar-Jauregg, T.; Haring, M. Helv. Chem. Acta 1958, 41, 337;
(b) Hayashi, T. Bull. Chem. Soc. Jpn. 1972, 45, 1507.
6. (a) Shirayev, A. K.; Moiseev, I. K.; Karpeev, S. S. ARKIVOC 2005,
iv, 199; (b) Shirayev, A. K.; Moiseev, I. K.; Popov, V. A. Zh. Org.
Khim. 1992, 28, 418; (c) Shirayev, A. K.; Kong Thoolin, P.; Moiseev,
I. K. Synthesis 1997, 38; (d) Kambe, S.; Hayashi, T.; Yasuda, H.;
Midorikawa, H. Bull. Chem. Soc. Jpn. 1971, 44, 1357.
7. Kutschy, P.; Milan, D.; Ladislav, K.; Juraj, B.; Jan, I.; Pavol, K.;
Robert, N. Collect. Czech. Chem. Commun. 1986, 51, 1119.
8. Dieter, H.; Rainer, F. Angew. Chem. 1977, 89, 479.
9. Ottmann, G. F.; Vickers, G. D.; Hooks, H., Jr. J. Heterocycl. Chem.
1967, 4, 527.
10. Sakai, S.; Niimi, H.; Kobayashi, Y.; Ishii, Y. Bull. Chem. Soc. Jpn.
1977, 50, 3271.
11. (a) Ansari, M. H.; Ahmad, M. J. Chem. Res. (S) 1990, 199; (b) Baba,
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1986, 59, 341; (c) Yano, K.; Amishiro, N.; Baba, A.; Matsuda, H.
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Sineokov, A. P.; Razuvayev, G. A. Izv. ANUSSR Ser. Khim. 1964,
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12. (a) Singh, C. B.; Murru, S.; Kavala, V.; Patel, B. K. Org. Lett. 2006, 8,
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Tetrahedron 2008, 64, 1931.
22. Spectral data of selected compounds: (Z)-Ethyl 2-oxopropyl phenyl-
dithioimidocarbonate 1a: 1H NMR (400 MHz, CDCl3): d 1.31 (t,
3H,J = 7.6 Hz), 2.30 (s, 3H), 3.07 (q, 2H, J = 7.6 Hz), 3.90 (s, 2H),
6.83 (d, 2H, J = 7.6 Hz), 7.09 (m, 1H), 7.31 (m, 2H). 13C NMR
(100 MHz, CDCl3): d 14.8, 26.6, 29.3, 42.0, 120.4, 124.3, 129.1, 149.3,
161.1, 202.3. IR (KBr): 3058, 2968, 2927, 1718, 1577, 1354, 1208,
1151, 943, 762, 695 cmꢀ1. HRMS (ESI), MH+, found 254.3959,
C12H16NOS2 requires 254.3965. (Z)-Ethyl 2-oxopropyl 2-Fluoro-
1
phenyldithioimidocarbonate 2a: H NMR (400 MHz, CDCl3): d 1.31
13. Fujisaki, S.; Hanada, K.; Nishida, A.; Kajigaeshi, S. Yamaguchi
Daigaku Kogakubu Kenkyu Hokoku 1990, 40, 383.
(t, 3H, J = 7.2 Hz), 2.28 (s, 3H), 3.08 (q, 2H, J = 7.2 Hz), 3.91 (s, 2H),
6.84 (br s, 1H), 7.03 (m, 3H). 13C NMR (100 MHz, CDCl3): d 14.7,
26.8, 29.0, 41.9, 116.1, 122.4, 124.3, 125.4, 136.9, 151.5, 154.0, 163.7,
202.3. IR (KBr): 3061, 2971, 2930, 2873, 1715, 1574, 1485, 1451, 1355,
1239, 1151, 1102, 950, 850, 756, 727, 577 cmꢀ1. HRMS (ESI): MH+,
found 272.3865, C12H15FNOS2 requires 272.3870. rac-N-[(2Z)-5-
Methyl-1,3-oxathiolan-2-ylidene]aniline 1b: 1H NMR (400 MHz,
CDCl3): d 1.54 (d, 3H, J = 6.4 Hz), 3.05 (app. t, 1H, J = 9.2 Hz),
3.36 (dd, 1H, J1 = 10.8 Hz, J2 = 5.6 Hz), 4.75 (m, 1H), 6.96 (d, 2H,
J = 7.2 Hz), 7.10 (t, 1H, J = 7.2 Hz), 7.31 (m, 2H). 13C NMR
(100 MHz, CDCl3): d 19.1, 37.7, 78.6, 121.3, 124.1, 129.0, 149.0,
163.6. IR (KBr): 3057, 3030, 2980, 2935, 2855, 1651, 1593, 1488, 1159,
1102, 1022, 949, 770, 697, 658, 593 cmꢀ1. HRMS (ESI): MH+, found
194.2749, C10H12NOS requires 194.2757. rac-2-Fluoro-N-[(2Z)-5-
methyl-1,3-oxathiolan-2-ylidene]aniline 2b: 1H NMR (400 MHz,
CDCl3): d 1.50 (d, 3H, J = 6.0 Hz), 3.05 (app. t, 1H, J = 10.0 Hz),
3.35 (dd, 1H, J1 = 10.8 Hz, J2 = 5.6 Hz), 4.76 (m, 1H), 6.94 (m, 4H).
13C NMR (100 MHz, CDCl3): d 19.3, 38.2, 79.8, 116.2, 116.4, 123.4,
124.5, 125.4, 136.9, 153.1, 155.5, 163.3. IR (KBr): 3033, 2977, 2927,
2869, 1651, 1488, 1453, 1242, 1161, 1097, 1024, 950, 836, 755, 653,
14. (a) Kavala, V.; Naik, S.; Patel, B. K. J. Org. Chem. 2005, 70, 4267; (b)
Kavala, V.; Naik, S.; Patel, B. K. J. Org. Chem. 2005, 70, 6556.
15. (Z)-Ethyl 2-hydroxypropyl phenyldithioimidocarbonate: 1H NMR
(400 MHz, CDCl3): d 1.27 (m, 6H), 3.04 (m, 4H), 3.20 (br s, 1H), 4.11
(br s, 1H), 6.86 (d, 2H, J = 7.2 Hz), 7.09 (t, 1H, J = 7.6 Hz), 7.30 (t,
2H, J = 8.0 Hz). IR (KBr): 3364, 3059, 2970, 2927, 2870, 1651, 1574,
1485, 1448, 1261, 1207, 1165, 1107, 1071, 946, 762, 695 cmꢀ1
16. Crystallographic description of 5b: Crystal dimensions (mm):
14H13NOS, Mr = 243.31. Monoclinic, space
.
0.28 ꢁ 0.20 ꢁ 0.17.
C
˚
˚
˚
group P2(1)/n; a = 7.8987(2) A, b = 14.0972(4) A, c = 11.5295(3) A;
3
˚
a = 90.00°, b = 106.7410(10)°, c = 90.00°, V = 1229.39(6) A ; Z = 4;
q
cal = 1.315 mg/m3; l(mmꢀ1) = 0.245; F(000) = 512; Reflections
collected/unique = 3047/2281;
refinement
method = full-matrix
least-squares on F2; final R indices [I > 2rl] R1 = 0.0579, wR2 =
0.1306, R indices (all data) R1 = 0.0414, wR2 = 0.1155; goodness of
fit = 1.033. CCDC number for compound 5b is CCDC 676901. This
data can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/datarequest/cif.
17. SMART V 4.043 Software for the CCD Detector System; Siemens
Analytical Instruments Division: Madison, WI, 1995.
.
588 cmꢀ1 HRMS (ESI): MH+, found 212.2667, C10H11FNOS
requires 212.2674.rac-4-Bromo-N-[(2Z)-5-methyl-1,3-oxathiolan-2-
ylidene]aniline 3b: 1H NMR (400 MHz, CDCl3): d 1.55 (d, 3H,
J = 6.4 Hz), 3.09 (app. t, 1H, J = 10.0 Hz), 3.41 (dd, 1H,
18. SAINT V 4.035 Software for the CCD Detector System; Siemens
Analytical Instruments Division: Madison, WI, 1995.

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J1 = 10.8 Hz, J2 = 5.6 Hz), 4.77 (m, 1H), 6.85 (d, 2H, J = 8.4 Hz),
(app. t, 1H, J = 9.6 Hz), 3.38 (dd, 1H, J1 = 10.8 Hz, J2 = 5.6 Hz),
4.35 (d, 2H, J = 6.8 Hz), 4.61 (m, 1H), 7.28 (m, 5H). 13C NMR
(100 MHz, CDCl3): d 19.3, 38.0, 57.5, 80.5, 126.8, 127.7, 128.4, 139.7,
162.8. IR (KBr): 3027, 2978, 2931, 2869, 1663, 1452, 1352, 1156, 1122,
1089, 1051, 1022, 929, 735, 699, 641 cmꢀ1. HRMS (ESI): MH+, found
208.3035, C11H14NOS requires 208.3037. rac-N-[(2Z)-4-Isopropyl-5-
methyl-1,3-oxathiolan-2-ylidene]aniline (diastereomeric mixture) 9b:
7.42 (d, 2H, J = 8.4 Hz). 13C NMR (100 MHz, CDCl3): d 19.3, 38.0,
79.1, 117.3, 123.3, 132.2, 148.2, 164.3. IR (KBr): 2991, 2935, 1680,
1634, 1486, 1388, 1250, 1163, 1096, 958, 835, 605 cmꢀ1. HRMS (ESI):
MH+, found 273.1665, C10H11BrNOS requires 273.1670. rac-2,4-
Dimethyl-N-[(2Z)-5-methyl-1,3-oxathiolan-2-ylidene]aniline 4b: 1H
NMR (400 MHz, CDCl3): d 1.45 (d, 3H, J = 6.0 Hz), 2.17 (s, 3H),
2.29 (s, 3H), 3.05 (app. t, 1H, J = 10.0 Hz), 3.35 (dd, 1H,
J1 = 10.9 Hz, J2 = 5.2 Hz), 4.75 (m, 1H), 6.75 (d, 1H, J = 7.6 Hz),
6.98 (m, 2H). 13C NMR (100 MHz, CDCl3): d 17.9, 19.3, 21.0, 37.9,
79.0, 120.4, 127.3, 130.0, 131.4, 133.9, 145.6, 163.2. IR (KBr): 2979,
2923, 2865, 1651, 1497, 1454, 1382, 1239, 1162, 1092, 1024, 951, 821,
634 cmꢀ1. HRMS (ESI): MH+, found 222.3117, C12H16NOS requires
222.3113. rac-N-[(2Z)-5-Methyl-1,3-oxathiolan-2-ylidene]naphthal-
ene-1-amine 5b: Crystalline solid, mp 87–89 °C 1H NMR (400 MHz,
CDCl3): d 1.59 (d, 3H, J = 6.0 Hz), 3.05 (app. t, 1H, J = 10.0 Hz),
3.36 (dd, 1H, J1 = 10.8 Hz, J2 = 6.0 Hz), 4.83 (m, 1H), 7.00 (d, 1H,
J = 7.2 Hz), 7.43 (m, 3H), 7.61 (d, 1H, J = 8.4 Hz), 7.81 (d, 1H,
J = 7.2 Hz), 8.05 (d, 1H, J = 8.0 Hz). 13C NMR (100 MHz, CDCl3): d
19.5, 38.0, 79.3, 115.9, 123.9, 124.5, 125.7, 126.0, 126.4, 127.8, 128.0,
134.4, 146.0, 164.1. IR (KBr): 3016, 2926, 2861, 1657, 1496, 1451,
1402, 1095, 1050, 875, 824, 804, 687, 605 cmꢀ1. HRMS (ESI): MH+,
found 244.3302, C14H14NOS requires 244.3307. rac-N-[(2Z)-5-
Methyl-1,3-oxathiolan-2-ylidene] n-butylamine 6b: 1H NMR
(400 MHz, CDCl3): d 0.87 (t, 3H, J = 7.2 Hz), 1.33 (m, 2H), 1.43
(d, 3H, J = 6.0 Hz), 1.52 (m, 2H), 3.01–3.07 (m, 3H) 3.33 (dd, 1H,
J1 = 10.8 Hz, J2 = 5.2 Hz),4.53 (m, 1H). 13C NMR (100 MHz,
1H NMR (400 MHz, CDCl3):
d 0.90 (m, 6H), 1.40 (d, 3H,
J = 6.0 Hz), 1.90 (m, 1H), 3.31 (m, 1H), 4.52 (m, 1H), 6.99 (m, 2H),
7.11 (t, 1H, J = 7.2 Hz), 7.32 (t, 2H,J = 7.6 Hz). 13C NMR (100 MHz,
CDCl3): d 18.5, 20.0, 21.3, 31.3, 61.9, 80.9, 121.6, 124.2, 129.2, 149.5,
163.4. IR (KBr): 3054, 2963, 2868, 1651, 1595, 1544, 1447, 1315, 1229,
1110, 1064, 948, 769, 696, 642 cmꢀ1. HRMS (ESI): MH+, found
236.3509, C13H18NOS requires 236.3513. rac-N-[(2Z)-5-Phenyl-1,3-
oxathiolan-2-ylidene]aniline 10b: 1H NMR (400 MHz, CDCl3): d 3.29
(app. t, 1H,J = 10.8 Hz), 3.53 (dd, 1H, J1 = 10.8 Hz, J2 = 4.8 Hz),
5.53 (app. t, 1H, J = 6 Hz), 6.81 (s, 2H), 6.94-6.99 (m, 3H), 7.16–7.57
(m, 5H).13C NMR (100 MHz, CDCl3): d 38.7, 83.4, 118.9, 121.6,
123.7, 126.1, 128.9, 129.5, 138.1, 154.3, 163.9. IR (KBr): 3054, 2950,
1648, 1604, 1541, 1497, 1445, 1314, 1229, 1067, 754, 694 cmꢀ1. HRMS
(ESI): MH+, found 254.3466, C15H14NOS requires 256.3477. rac-
N-[(2Z)-Hexahydro-1,3-benzoxathiol-2-ylidene]naphthalene-1-amine
(diastereomeric mixture) 11b: 1H NMR (400 MHz, CDCl3): d 1.12–
1.55 (m, 4H), 1.79 (m, 2H), 2.30 (m, 2H), 3.39 (m, 1H), 4.56 (m, 1H),
6.91 (m, 1H), 7.20–7.84 (m, 6H). 13C NMR (100 MHz, CDCl3): d
20.1, 20.4, 23.6, 28.0, 47.1, 81.5, 115.8, 121.0, 123.5, 124.6, 126.7,
128.1, 128.6, 128.8, 134.3, 145.9, 164.4. IR (KBr): 3054, 2937, 2859,
1650, 1574, 1536, 1504, 1393, 1358, 1259, 1184, 1114, 1013, 964, 907,
CDCl3):
d 13.8, 19.1, 20.4, 32.9, 37.6, 53.5, 79.9, 161.0. IR
(KBr): 2950, 2935, 2873, 1680, 1542, 1460, 1383, 1168, 1076, 748,
636 cmꢀ1. HRMS (ESI): MH+, found 174.2859, C8H16NOS requires
174.2865. rac-2-(3,4-Dimethoxyphenyl)-N-[(2Z-5-methyl-1,3-oxathio-
lan-2-ylidene]ethanamine 7b: 1H NMR (400 MHz, CDCl3): d 1.39 (d,
3H, J = 6.4 Hz), 2.78 (t, 2H, J = 7.6 Hz), 2.94 (app. t, 1H,
J = 9.6 Hz), 3.28 (m, 3H), 3.78 (s, 3H), 3.80 (s, 3H), 4.57 (m, 1H),
6.71 (m, 3H). 13C NMR (100 MHz, CDCl3): d 19.3, 37.0, 37.8, 51.0,
55.8, 56.0, 77.6, 111.3, 112.3, 120.9, 132.9, 147.5, 148.8, 162.2. IR
774, 729, 642 cmꢀ1
.
HRMS (ESI): MH+, found 284.4013,
C17H18NOS requires 284.4013. rac-N-[{2Z}-4-(4-Methoxyphenyl)-5-
methyl-1,3-oxathiolan-2-ylidene] naphthalene-1-amine (diastereo-
meric mixture) 12b: 1H NMR (400 MHz, CDCl3): d 1.05 (m, 3H),
3.62 (s, 3H), 4.46 (d, 1H, J = 5.6 Hz), 4.86 (m, 1H), 6.71 (t, 2H,
J = 8.4), 7.00 (m, 2H), 7.13 (m, 1H), 7.30 (m, 1H), 7.38 (m, 2H), 7.50
(d, 1H, J = 8.4 Hz), 7.70 (m, 1H), 8.07 (m, 1H). 13C NMR (100 MHz,
CDCl3): d 16.5, 54.8, 55.5, 82.5, 114.2, 115.9, 123.8, 124.6, 125.7,
126.0, 126.4, 128.3, 128.4, 128.9, 129.6, 134.4, 145.9, 159.8, 164.2. IR
(KBr): 3056, 2961, 2836, 1651, 1574, 1512, 1462, 1393, 1304, 1248,
1179, 1073, 1032, 943, 802, 777, 734, 654 cmꢀ1. HRMS (ESI): MH+,
found 350.4549, C21H20NO2S requires 350.4545.
(KBr): 2935, 2832, 1696, 1675, 1516, 1460, 1271, 1020, 748 cmꢀ1
.
HRMS (ESI): MH+, found 282.3821, C14H20NO3S requires 282.3829.
rac-N-[(2Z)-5-methyl-1,3-oxathiolan-2-ylidene]phenylmethanamine
8b: 1H NMR (400 MHz, CDCl3): d 1.47 (d, 3H, J = 6.0 Hz), 3.05