3-Oxo-3-thia-2-azabicyclo[2.2.1]hept-5-en-2-carboxylates: The first isolation and characterization

Article abstract of DOI:10.1016/j.tetlet.2012.07.139

Methyl and benzyl 3-oxo-3-thia-2-azabicyclo[2.2.1]hept-5-en-2-carboxylate were isolated at rt and characterized for the first time. Both endo and exo-isomers were observed. Under suitable experimental conditions (stoichiometric amount of sodium acetate, -40 °C or sodium borohydride/methyl iodide) ring opening of these compounds gave the corresponding thiosulfonates or methyl sulfides, respectively. 2012 Elsevier Ltd. All rights reserved.

Full text of DOI:10.1016/j.tetlet.2012.07.139

Tetrahedron Letters 53 (2012) 5507–5510
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
3-Oxo-3-thia-2-azabicyclo[2.2.1]hept-5-en-2-carboxylates: the first isolation
and characterization
⇑
Luca Guideri, Fabio Ponticelli
Dipartimento di Chimica, Università degli Studi di Siena, Via A. Moro 2, 53100 Siena, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl and benzyl 3-oxo-3-thia-2-azabicyclo[2.2.1]hept-5-en-2-carboxylate were isolated at rt and
characterized for the first time. Both endo and exo-isomers were observed. Under suitable experimental
conditions (stoichiometric amount of sodium acetate, ꢀ40 °C or sodium borohydride/methyl iodide) ring
opening of these compounds gave the corresponding thiosulfonates or methyl sulfides, respectively.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 22 May 2012
Revised 27 July 2012
Accepted 31 July 2012
Available online 8 August 2012
Keywords:
Hetero Diels-Alder
Ring strain
Sulfinamide
Thiosulfonate
The substitution of carbon atom with sulfur atom in pharmaco-
logically active molecules has attracted large interest, for different
reasons, such as the synthesis of bioisosteres, the collection of
information on the mode of action, to enhance the pharmacological
activity, and for the elimination of the side effects. The [4 + 2]
cycloaddition reaction between dienes and N-sulfinyl dieno-
philes1,2 allowed to synthesize the sulfur homologues of compound
A (Fig. 1), versatile building blocks for the synthesis of different
pharmacologically active molecules, such as homoallylic amines,
vicinal amino alcohols,3 vicinal amines, amino sugars,4,5 and natu-
ral products.6,7
Figure 1. Compound A is commercially available; compound B was never isolated
at rt.
As a further contribution to this synthetic strategy, in a previous
work our research group prepared 4-aminocyclopent-2-ene-1-sul-
fonic acid 5, its cyclohexene homologous 9 and some sulfinamide
derivatives (6–8) (Scheme 1).8,9
Compounds 5–9 were obtained in good yields by Hetero
Diels-Alder cycloaddition/ring opening sequence using some
nucleophiles such as OHꢀ(aq), benzylamine, pyrrolidine, some
aminoacids, and a deprotonated carbamate: lithium methoxy-
carbonylamide.
It is to be noted that in spite of wide chemical interest and po-
tential applications of a bicyclic compound like 3, there is neither a
protocol so far for its isolation, nor a spectroscopic evidence of its
formation. The presence of cycloadduct 3 as an intermediate was
assumed only on the basis of the formation of derivatives. On the
other hand, the instability of a similar bicyclic system (compound
B, Fig. 1), also at low temperature, is reported.10
⇑
Corresponding author. Tel.: +39 0577 234271; fax: +39 0577 234254.
E-mail address: ponticelli@unisi.it (F. Ponticelli).
Scheme 1. Opening of the sulfinamide bond with NaOH and amines.
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.07.139

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L. Guideri, F. Ponticelli / Tetrahedron Letters 53 (2012) 5507–5510
However, taking into account the synthetic importance of this
intermediate, we tried to find a way to isolate it and to determine
the real stability.
Starting from our experience, we knew that: (1) the sulfinamide
bond can be cleaved under acidic and basic conditions; (2) a little
amount of pyridinium chloride remains in the flask during the
work-up of N-sulfinyl carbamate 2, and which is never completely
removed with the double filtration during the work-up of the first
synthetic step; (3) the homologous compound 4 can be isolated
with a simple phosphate buffer at pH = 7.11,12 Knowing all these
features we tried the use of phosphate buffer also to attempt the
isolation of compound 3, but we recovered the starting carbamate.
What we needed was something that could neutralize the solution
but it must not be a nucleophile toward compound 3. We decided
to use an aqueous solution of sodium acetate. By varying the
amount of this reagent and temperature, we found that with small
quantity of sodium acetate (0.25 equiv) at ꢀ20 °C it is possible to
isolate the cycloadduct 313 in ꢁ60% of yield (Fig. 2); while
with stoichiometric amount and a lower reaction temperature
(ꢀ40 °C) we isolated a new derivative: thiosulfonate 10 (Scheme
2).14
The explanation of the first result was attributed to the fact that
acetate in a small amount acts as a buffer together with the resid-
ual pyridinium chloride. Mass spectra (MS and MS2), mono-, and
bi-dimensional NMR experiments (1H, 13C, HSQC, COSY) were re-
corded to confirm the structure of 3. As shown in Figure 2, by
1H-NMR it is possible to see two isomers of compound 3. Signals
were assigned to the exo-adduct (red dots) and the endo-adduct
(blue dots), respectively, in analogy to homologous 4,12 and on
the basis of anisotropic cone of the sulfinyl group.
Scheme 2. Variation of the sodium acetate gives different results.
To reach a final structural confirmation of the isolated product,
compound 3 was treated with phenyl magnesium bromide to give
a
well known product, methyl 4-(phenylsulfinyl)cyclopent-2-
enylcarbamate (Scheme 2).7,8 With the NMR experiments we also
found that in few hours at rt the product disappears as the cyclo-
addition reaction is reversible; while at ꢀ18 °C in the freezer after
1 week the endo-adduct was transformed in part into the starting
materials, in part into the exo-adduct (Fig. 2).
To find the explanation of the second result (Scheme 2) we per-
formed the reaction using sodium acetate-18O. The obtained thio-
sulfonate mainly shows in ESI-MS a molecular ion at 383 m/z,
due to the incorporation of three 18O atoms. MS2 spectrometry of
this ion gives a signal at 244 m/z, due to the neutral loss of
139 amu. (Scheme 3) The same neutral loss has been observed
with 3a containing only 16O. MS3 spectrometry of 244 gives a sig-
nal at 162 m/z assigned to a neutral loss of 18OS2.
Figure 2. The signals of exo (red) and endo (blue) isomers can be distinguished by the colored spots. Spectra were recorded at rt.

L. Guideri, F. Ponticelli / Tetrahedron Letters 53 (2012) 5507–5510
5509
Scheme 3. ESI-MS spectroscopy of 18O-thiosulfonate 10.
sodium borohydride it is possible to obtain disulfides 1221 and 1322
respectively (Scheme 4). As shown in the scheme, homologous 4
needs more time and higher temperature to give the same result.
At last we transformed compounds 12a and 12b into the methyl thi-
oether derivatives 14a and 14b23 using a well know procedure24 in
order to confirm the structure of the disulfides (Scheme 5).
In conclusion this work remarks the different stability between
compounds 3 and 4. In fact, some of the reactions shown above are
possible only with compound 3 due to its angular tension, while
other reactions are possible also for compound 4, but with higher
temperature and longer time. So varying the amount of sodium
acetate we isolated for the first time pure compound 3 for some
hours at rt, otherwise it is possible to isolate new thiosulfonate
10. At last we synthesized new disulfides 12 and 13 and meth-
ylthioether 14.
Figure 3.
a-disulfoxide 11 was never isolated.
Acknowledgments
This work was financially supported by the University of Siena
as a PAR Project (quota servizi) 2008. The authors wish to thank the
‘Centro di Analisi e Determinazioni Strutturali’ of the University of
Siena for MS spectra and Dr. Sara Draghi for helpful collaborations.
Scheme 4. The sulfinamide bond can be cleaved also by NaBH4.
References and notes
1. Wald, L.; Wucherpfennig, W. Liebigs Ann. Chem. 1971, 746, 28–31.
2. Weinreb, S. M. Acc. Chem. Res. 1988, 21, 313–318.
3. Garigipati, R. S.; Freyer, A. J.; Whittle, R. R.; Weinreb, S. M. J. Am. Chem. Soc.
1984, 106, 7861–7867.
4. Garigipati, R. S.; Weinreb, S. M. J. Am. Chem. Soc. 1983, 105, 4499–4501.
5. Remiszewski, S. W.; Whittle, R. R.; Weinreb, S. M. J. Org. Chem. 1984, 49, 3243–
3244.
6. Anderson, G. T.; Chase, C. E.; Koh, Y.; Stien, D.; Weinreb, S. M. J. Org. Chem. 1998,
63, 7594–7595.
7. Stien, D.; Anderson, G. T.; Chase, C. E.; Koh, Y.; Weinreb, S. M. J. Am. Chem. Soc.
1999, 121, 9574–9579.
8. Fusi, S.; Papandrea, G.; Ponticelli, F. Tetrahedron Lett. 2006, 47, 1749–1752.
9. Papandrea, G.; Ponticelli, F. Synth. Commun. 2008, 38, 858–865.
10. Macaluso, A.; Hamer, J. J. Org. Chem. 1966, 31, 3049–3050.
11. Garigipati, R. S.; Cordova, R.; Parvez, M.; Weinreb, S. M. Tetrahedron 1986, 42,
2979–2984.
Scheme 5. Disulfides 12a,b can be easily transformed into the methyl thioether
14a,b.
12. Bayer, A.; Gautun, O. R. Tetrahedron Lett. 2000, 41, 3743–3747.
13. Melting points were determined with a Kofler hot stage and are uncorrected.
1H and 13C NMR spectra were recorded at 27 °C (CDCl3), unless otherwise
We think that acetate is involved in the reaction both in the for-
stated, with
a Bruker AC200 MHz instrument operating at 200.13 and
mation of an
the rearrangement to the compound 10. As reported in the litera-
ture,15–19 alkyl-
-disulfoxides are stable only at low temperature
a-disulfoxide 11, never isolated (Fig. 3), and maybe in
50.33 MHz respectively. Chemical shifts are reported in ppm from internal
TMS. The 1H NMR data are reported as follows: s = singlet, d = doublet,
t = triplet, m = multiplet, brs = broad singlet, coupling constants in Hz. Mass
spectra were recorded in the positive or negative ion mode with a LCQ-DECA
Thermo instrument by using electrospray ionization. All solvents were
previously dried according to standard procedures. Analytical TLC was
performed on silica gel 60 F254 plates. Flash column chromatography was
carried out on silica gel (0.040–0.063 mm). Dicyclopentadiene was freshly
distilled with a Vigreux column in order to obtain cyclopentadiene monomer
that was collected at 0 °C and rapidly added inside the reaction flask.
General preparation method for the compounds 3a and 3b In a two neck round
bottom flask carbamate (4.0 mmol) was dissolved in dry Et2O (25 mL). Rapidly
it was made vacuum and then was added N2, and it was repeated two times
again. The mixture was cooled to 0 °C with an ice bath, and, if necessary, was
added other Et2O (2 mL). SOCl2 was added first (0.30 mL, 4.2 mmol) rapidly and
then pyridine (0.66 mL, 8.2 mmol) slowly for 1.5 h. The mixture was stirred at
0 °C for 2 h. After this time, the precipitate was rapidly filtered off with a
double filtration and the solvent was evaporated first under reduced pressure
without warming and then with high vacuum pump keeping the flask at 0 °C.
a
and they rearrange to thiosulfonates by raising the temperature
to rt. Recently, Ishii et al.,20 succeeded in the isolation of some
vic-disulfoxides, but the S(O)–S(O) moiety is constrained in a
five-membered-ring system.
Trying to understand if this type of reactivity could be extended
to other dihydrothiazine derivatives, we synthesized the homolo-
gous 4b,11,12 but we found that in any case the sulfinamide does
not react with sodium acetate to give the corresponding thiosulfo-
nate, neither changing the temperature nor prolonging the time of
reaction.
After these two significant results, we have further developed the
reactivity of the sulfinamides 3 and 4. In particular, with an excess of

5510
L. Guideri, F. Ponticelli / Tetrahedron Letters 53 (2012) 5507–5510
The residue (clear yellow oil) was dissolved in a dry and previously cooled
21. General preparation method for the compounds 12a and 12b. A solution of
unisolated compound 3 (estimated about 3.2 mmol) in dry toluene (5 mL) at
0 °C, prepared as reported above, was diluted with dry THF (10 mL) previously
cooled, and the temperature was lowered to ꢀ20 °C. Slowly drop by drop for
15 min, under stirring, was added NaBH4 (0.42 g, 11.2 mmol) dissolved in the
minimum amount of dry THF, then the mixture was stirred for 1 h at 0 °C. After
this time the reaction was quenched with 1 mL of H2O and concentrated under
reduced pressure. The residue was dissolved in CHCl3 (50 mL) and washed with
H2O (3 ꢂ 15 mL). The organic phase was dried over Na2SO4, filtered and
concentrated under vacuum. The residue was purified by chromatography on
silica gel (petroleum ether/EtOAc 1:1).
toluene (5 mL) and was added freshly distilled cyclopentadiene monomer
(0.21 mL, 3.2 mmol). The mixture was stirred at 0 °C for 20 h. After this time,
the reaction was diluted with dry THF (10 mL) previously cooled, and the
temperature was lowered to ꢀ20 °C. Slowly drop by drop for 15 min, under
stirring, was slowly added CH3COONa (65 mg, 0.8 mmol) dissolved in the
minimum amount of H2O. The reaction was stirred for another 15 min at
ꢀ20 °C. After this time the solvents were removed without warming the flask.
The residue was dissolved with DCM (30 mL) and quickly washed with H2O
(3 ꢂ 10 mL). The organic phase was dried over Na2SO4, filtered and evaporated
under reduced pressure.
(endo/eso) Methyl 3-oxo-3-thia-2-azabicyclo[2.2.1]hept-5-en-2-carboxylate (3a):
yellow oil (0.43 g, 57%), that deteriorates in a few hours at room temperature.
1H-NMR: d 1.64 (dt, J = 10.5, 1.1, 1H, H5b endo), 1.78 (dt, J = 10.5, 2.4, 1H, H5a
endo), 2.08 (dt, J = 10.5, 2.4, 1H, H5b exo), 2.61 (dt, J = 10.5, 1.1, 1H, H5a exo),
3.61 (s, 6 H, COOCH3 endo+exo), 4.27 (brs, 1H, H1 exo), 4.65 (brs, 1H, H1 endo),
4.75 (brs, 1H, H4 exo), 5.02 (brs, 1H, H4 endo), 6.00–6.10 (m, 1H, H3 exo), 6.21–
6.31 (m, 1H, H3 endo), 6.72–6.79 (m, 1H, H2 exo), 6.81–6.90 (m, 1H, H2 endo).
13C-NMR: d 45.2, 53.3, 62.5, 73.0, 130.7, 145.3, 155.9. MS(ESI): m/z = 210
[M+Na]+.
(endo/eso) Benzyl 3-oxo-3-thia-2-azabicyclo[2.2.1]hept-5-en-2-carboxylate (3b):
yellow oil (0.54 g, 55%), that deteriorates in a few hours at room temperature.
1H-NMR: d 1.79 (dt, J = 10.5, 1.2, 1H, H5b endo), 1.92 (dt, J = 10.5, 2.3, 1H, H5a
endo), 2.21 (dt, J = 10.5, 2.4, 1H, H5b exo), 2.83 (dt, J = 10.5, 1.2, 1H, H5a exo),
4.42 (brs, 1H, H1 exo), 4.74 (brs, 1H, H1 endo), 4.82 (brs, 1H, H4 exo),
4.96 (brs, 1H, H4 endo), 5.21 (s, 4H, OCH2Ph endo+exo), 6.11–6.21 (m, 1H, H3
exo), 6.40–6.50 (m, 1H, H3 endo), 6.88–6.98 (m, 1H, H2 exo), 6.97–7.07
(m, 1H, H2 endo) 7.33 (s, 10H, Ph exo+endo). MS(ESI): m/z = 264 [M+H]+, 286
[M+Na]+.
Dimethyl
4,40-disulfanediylbis(cyclopent-2-ene-4,1-diyl)dicarba-mate
(12a):
white solid (0.84 g, 77%); mp: 145–146 °C; 1H-NMR: d 1.72 (tt⁄, J = 14.1, 3.3,
2H, cis H5), 2.78 (dt, J = 15.1, 6.7, 2H, trans H5), 3.68 (s, 6H, OCH3), 3.78–3.86
(m, 2H, H4), 4.67–4.85 (m, 2H, H1), 5.85 (s, 4H, H2+H3). 13C-NMR: d 39.1, 54.3,
54.9, 55.6, 133.9, 134.3, 156.0. MS(ESI): m/z = 367 [M+Na]+. C14H20N2O4S2
(344): calcd C 48.82; H 5.85; N 8.13; found C 48.93; H 5.69; N 8.36. ⁄With
400 MHz instrument this signal appears as two doublets of triplets.
Dibenzyl
4,40-disulfanediylbis(cyclopent-2-ene-4,1-diyl)dicarba-mate
(12b):
white solid (1.19 g, 75%); mp: 95–98 °C; 1H-NMR: d 1.74 (tt⁄, J = 15.4, 4.4,
2H, cis H5), 2.78 (dt, J = 15.4, 8.9, 2H, trans H5), 3.80–3.88 (m, 2H, H4), 4.72–
4.90 (m, 2H, H1), 5.13 (s, 4H, OCH2Ph), 5.86 (s, 4H, H2+H3), 7.37 (s, 10H, Ph).
13C-NMR: d 30.2, 39.0, 54.4, 66.8, 128.0, 128.1, 128.4, 134.1, 134,3, 136.4, 156.8.
MS(ESI): m/z = 497 [M+H]+, 519 [M+Na]+. C26H28N2O6S2 (496): calcd C 62.88; H
5.68; N 5.64; found C 62.97; H 5.72; N 5.51. ⁄With a 400 MHz instrument this
signal appears as two doublets of triplets.
22. Dibenzyl 4,40-disulfanediylbis(cyclohex-2-ene-4,1-diyl)dicarbamate (13):
A
solution of unisolated 4b11 (2.9 mmol) in dry toluene (5 mL) at 0 °C was
diluted with dry THF (10 mL) previously cooled, and the temperature was
lowered to ꢀ20 °C. Slowly drop by drop for 15 min, under stirring, was added
NaBH4 (0.55 g, 14.5 mmol) dissolved in the minimum amount of dry THF. The
reaction was stirred for 14 h raising the temperature from ꢀ20 °C to rt. After
this time the reaction was quenched with 1 mL of H2O and concentrated under
reduced pressure. The residue was dissolved in CHCl3 (50 mL) and washed with
H2O (3 ꢂ 15 mL). The organic phase was dried over Na2SO4, filtered and
evaporated obtaining 13 as a white solid (1.06 g, 70%). mp: 121–122 °C; 1H-
NMR: d 1.66–2.14 (m, 8H, H5+H6), 3.37–3.50 (m, 2H, H4), 4.14–4.29 (m, 2H,
H1), 5.08 (s, 4H, OCH2Ph) 5.27 (s, 4H, H2+H3), 7.30 (s, 10H, Ph). 13C-NMR: d
25.9, 26.0, 66.4, 127.7, 127.8, 128.2, 128.4, 131.7, 136.2, 155.6. MS(ESI): m/
z = 525 [M+H]+, 547 [M+Na]+. C28H32N2O4S2 (524): calcd C 64.09; H 6.15; N
5.34; found C 64.36; H 6.09; N 5.56.
14. General preparation method for the compounds 10a and 10b A solution of
unisolated compound 3 (estimated about 3.2 mmol) in dry toluene (5 mL) at
0 °C, prepared as reported above, was diluted with dry THF (10 mL) previously
cooled and the temperature was lowered to ꢀ40 °C. Slowly drop by drop for
15 min, under stirring, was added CH3COONa (0.26 g, 3.2 mmol) dissolved in
the minimum amount of H2O. The reaction was stirred for another 15 min at
ꢀ40 °C. After this time the mixture was evaporated without heating the flask.
The residue was dissolved in CHCl3 (50 mL) and washed with H2O (3 ꢂ 15 mL).
The organic phase was dried over Na2SO4, filtered and concentrated under
vacuum. The residue was purified by chromatography on silica gel (Et2O/EtOAc
1:3).
S-4-(Methoxycarbonylamino)cyclopent-2-enyl
4-(methoxycar-bonylamino)-
cyclopent-2-ene-1-sulfonothioate (10a): yellow oil (0.80 g, 68%). 1H-NMR: d
1.93 (dt, J = 15.4, 4.6, 1H, cis H5’), 2.12 (dt, J = 15.4, 3.4, 1H, cis H5), 2.67 (dt,
J = 15.4, 7.7, 1H, trans H5), 2.97 (dt, J = 15.4, 7.7, 1H, trans H5’), 3.65 (s, 6H,
OCH3), 4.31–4.46 (m, 1H, H1’), 4.66–4.83 (m, 1H, H1), 4.83–4.98 (m, 2H,
H4’+H4), 5.88–5.98 (m, H3+H3’), 6.15–6.25 (m, 2H, H2+H2’). 13C-NMR: d 29.5,
32.7, 32.9, 52.1, 53.8, 54.0, 75.5, 125.7, 131.9, 135.6, 135.7, 156.0. MS(ESI): m/
z = 377 [M+H]+, 399 [M+Na]+. C14H20N2O6S2 (376): calcd C 44.67; H 5.35; N
7.44; found C 44.81; H 5.12; N 7.53.
23. General preparation method for the compounds 14a and 14b In a solution of
compound 10 (1.2 mmol) in dry EtOH (10 mL) at rt under N2, was added NaBH4
(0.16 g, 4.32 mmol) dissolved in the minimum amount of dry EtOH, and the
reaction was stirred for 1 h. After this time was added Na2CO3 fine powder
(0.14 g, 1.3 mmol) and stirred for 30 min. Finally was added CH3I (0.90 mL,
14.4 mmol) and stirred for 4 h. At the end of the reaction, the solvent was
evaporated and the residue was dissolved in CHCl3 (50 mL) and washed with
H2O (3 ꢂ 15 mL). The organic phase was dried over Na2SO4, filtered and
concentrated. The residue was purified by chromatography on silica gel
(petroleum ether/EtOAc 3:1).
S-4-(Benzyloxycarbonylamino)cyclopent-2-enyl
4-(benzyloxycar-bonylamino)-
cyclopent-2-ene-1-sulfonothioate (10b): yellow oil (1.09 g, 65%). 1H-NMR: d
1.88 (dt, J = 15.0, 3.6, 1H, cis H5’), 2.09 (dt, J = 15.5, 3.6, 1H, cis H5), 2.62 (dt,
J = 15.5, 8.3, 1H, trans H5), 2.93 (dt, J = 15.0, 8.3, 1H, trans H5’), 4.26–4.40 (m,
1H, H1’), 4.65–4.82 (m, 1H, H1), 4.96–5.03 (m, 2H, H4+H4’), 5.03 (s, 4H,
OCH2Ph), 5.85–5.92 (m, 2H, H3+H3’), 6.14–6.21 (m, 2H, H2+H2’) 7.28 (s, 10H,
Ph). 13C-NMR: d 29.5, 32.7, 33.0, 53.8, 54.0, 66.9, 75.0, 127.1, 127.6, 128.4,
128.9, 132.3, 132.7, 132.9, 136.4, 156.6. MS(ESI): m/z = 529 [M+H]+, 551
[M+Na]+. C26H28N2O6S2 (528): calcd C 59.07; H 5.34; N 5.30; found C 59.24; H
5.18; N 5.67.
Methyl 4-(methylthio)cyclopent-2-enylcarbamate (14a): yellow oil (0.14 g, 62%).
1H-NMR: d 1.61 (dt, J = 14.5, 5.7, 1H, cis H5), 2.16 (s, 3H, SCH3), 2.71 (dt, J = 14.5,
8.6, 1H, trans H5), 3.64 (s, 3H, OCH3), 3.77–3.88 (m, 1H, H4), 4.64–4.82 (m, 1H,
H1) 5.73–5.88 (m, 2H, H2 + H3). 13C-NMR: d 13.7, 39.1, 46.8, 52.0, 53.6, 132.8,
134.8, 156.1. MS(ESI): m/z = 188 [M+H]+, 210 [M+Na]+. C8H13NO2S (187): calcd
C 51.31; H 7.00; N 7.48; found C 51.23; H 7.46; N 7.34.
Benzyl 4-(methylthio)cyclopent-2-enylcarbamate (14b): yellow oil (0.20 g, 65%).
1H-NMR: d 1.68 (dt, J = 15.6, 3.9, 1H, cis H5), 2.14 (s, 3H, SCH3), 2.78 (dt, J = 15.6,
8.4, 1H, trans H5), 3.66–3.74 (m, 1H, H4), 4.4.76–4.85 (m, 1H, H1), 5.12 (s, 2H,
OCH2Ph), 5.78–5.98 (m, 2H, H2 + H3) 7.33 (s, 5H, Ph). 13C-NMR: d 13.9, 38.9,
48.8, 56.0, 66.7, 128.1, 128.2, 128.5, 132.7, 134.8, 136.1, 156.6. MS(ESI): m/
z = 286 [M+Na]+. C14H17NO2S (263): calcd C 63.85; H 6.51; N 5.32; found C
64.03; H 6.38; N 5.41.
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