Photochemical reactions of N-acylbenzoxazole-2-thiones

Article abstract of DOI:10.1039/b002548h

The photochemical reactions of N-acylbenzoxazole-Z-thiones 1 are examined. Irradiation of N-acylbenzoxazole-2-thiones 1 in the presence of a variety of alkenes 2 yields 2-substituted benzoxazoles 3-20 and/or the unexpected products, iminothietanes 21-29 by intramolecular trapping of the acyl group by thiolate anion of the zwitterionic intermediate I and by the phenolate anion of the zwitterionic intermediate II, respectively, derived from the spirocyclic aminothietanes AT which are formed by regioselective [2+2] cycloaddition of the carbon-sulfur double bond of 1 to the alkene double bond. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b002548h

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Photochemical reactions of N-acylbenzoxazole-2-thiones
Takehiko Nishio,*a Ikuo Iidaa and Kunio Sugiyamab
a Department of Chemistry, University of Tsukuba, Tsukuba-shi, Ibaraki, 305-8571 Japan
b Department of Industrial Chemistry, College of Industrial Technology, Nihon University,
Narashino-shi, Chiba, 275-8575 Japan
1
Received (in Cambridge, UK) 30th March 2000, Accepted 30th June 2000
Published on the Web 22nd August 2000
The photochemical reactions of N-acylbenzoxazole-2-thiones 1 are examined. Irradiation of N-acylbenzoxazole-2-
thiones 1 in the presence of a variety of alkenes 2 yields 2-substituted benzoxazoles 3–20 and/or the unexpected
products, iminothietanes 21–29 by intramolecular trapping of the acyl group by thiolate anion of the zwitterionic
intermediate I and by the phenolate anion of the zwitterionic intermediate II, respectively, derived from the
spirocyclic aminothietanes AT which are formed by regioselective [2ϩ2] cycloaddition of the carbon–sulfur
double bond of 1 to the alkene double bond.
Introduction
The photochemistry of thiocarbonyl compounds such as
thioketones1 and thioimides1,2 has been of considerable syn-
thetic and mechanistic interest and these compounds behave
like carbonyl compounds in many respects. Thioamides are,
however, photochemically much less reactive than these com-
pounds and few reports have been published on their photo-
chemical reactions.1b,2b,3 In the course of our studies on the
photochemistry of cyclic conjugated nitrogen-thiocarbonyl
systems,3,4 we have reported the photochemical behavior of
the benzoxazole-2-thiones.4b,e, f For example, irradiation of the
benzoxazole-2-thiones in the presence of alkenes gave 2-alkyl-
ated benzoxazoles, 2-alkylidenebenzoxazoles and the ring-
opened products, amide derivatives, depending on the nature of
substituents both on the N-atom of the benzoxazole and those
present in the alkene. In these reactions, aminothietanes (AT)
are believed to be intermediates. However, they are usually
unstable, probably because the nitrogen lone pair electron-
assisted cleavage of the C–S bond of the thietane ring facilitates
the formation of a zwitterion (Scheme 1). We are interested
in exploring the effect of substituents on the N-atom of
benzoxazole-2-thiones 1 upon [2 ϩ 2] photocycloaddition of
species 1 with alkenes 2. We now report the results of photo-
addition reactions of N-acylbenzoxazole-2-thiones 1, substi-
tuted with an electron-withdrawing group on the N-atom,
and alkenes 2 yielding 2-substituted benzoxazoles 3–20 and/
Scheme 1
or the unexpected products, iminothietane derivatives 21–29
(Scheme 2).4e
Results and discussion
When a benzene solution of N-acetyl- and N-isobutyrylbenz-
oxazole-2-thione 1a and 1b was irradiated with a high-pressure
mercury lamp through a Pyrex filter under argon, the starting
material was recovered quantitatively. However, irradiation of
N-acetylbenzoxazole-2-thione 1a in benzene in the presence
of 1,1-disubstituted alkenes such as 2-methylpropene 2a and
methacrylonitrile 2h under the same conditions as described
above gave 2-substituted benzoxazoles 3 and 6, exclusively,
which were 1:1-adducts of the reactants, in 59 and 63% isolated
yield, respectively. Irradiation of 1a in the presence of a 1,1,2-
trisubstituted alkene, 2-methylbut-2-ene 2b, and a 1,1,2,2-tetra-
substituted alkene, 2,3-dimethylbut-2-ene 2c, gave 2-substituted
benzoxazoles 4 and 5 and the unexpected products, imino-
Scheme 2
DOI: 10.1039/b002548h
J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046
3039
This journal is © The Royal Society of Chemistry 2000

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Fig. 2 ORTEP perspective view of o-acetoxy-N-(3,3,4,4-tetramethyl-
Fig. 1 ORTEP perspective view of S-2-(1,3-benzoxazol-2-yl)-2,2-
diphenylethyl 2-methylpropanethioate 10 with crystallographic num-
bering scheme. Non-H-atoms are drawn at 50% probability level.
thietan-2-ylidene)aniline 22 with crystallographic numbering scheme.
Non-H-atoms are drawn at the 50% probability level.
thietanes 21 and 22. Photoreaction of 1a and a diene such
as 2,5-dimethylhexa-2,4-diene 2l also proceeded smoothly to
yield both products, the 2-substituted benzoxazole 7 and the
iminothietane 23. On the other hand, irradiation of 1a in the
presence of 1,2-disubstituted alkenes such as stilbene and 1,2-
dicyanoethylene resulted in recovery of unchanged 1a, while
that of 1a and but-2-ene 2d gave the (2-mercaptoalkyl)benz-
oxazole 30 as the only isolable product. In contrast, irradiation
of N-isobutyryl-, N-(3-methylbutanoyl)-, N-phenylacetyl-, and
N-(2-phenylpropanoyl)-benzoxazole-2-thione 1b–1e in benzene
in the presence of alkenes 2 gave 2-substituted benzoxazoles
8–14, 17–20 or iminothietanes 24, 25, 28, 29, exclusively,
depending on the substitution pattern of the alkenes. Similar
results were obtained when the benzoxazole-2-thiones 1 and
alkenes 2 were irradiated in methanol and acetonitrile. In the
cases of 1b and 2e,f, and 1d and 2c, the formation of 2-(2-
mercaptoalkyl)benzoxazoles 31–33 was observed. Furthermore,
irradiation of 1b and 2,5-dimethylhexa-2,4-diene 2l, and of
1b and 2,3-dimethylbuta-1,3-diene 2m, yielded both products,
2-substituted benzoxazoles 15 and 16, and iminothietanes 26
and 27. The structures of all new photoproducts 3–31 were
elucidated on the basis of spectral data, analytical results and
chemical evidence, and those of 32 and 33 were confirmed by
direct comparison of their spectral properties with those of the
known compounds.4b The IR spectra of 2-substituted benz-
oxazoles 3–20 showed the characteristic absorption of thioester
carbonyls (1665–1700 cmϪ1), while those of iminothietanes 21–
29 showed absorptions characteristic of an ester group (1750–
1775 cmϪ1) and an imino group (1650–1675 cmϪ1). The 13C
NMR spectra of 2-substituted benzoxazoles 3–20 exhibited the
presence of a thioester carbonyl carbon (δC 185.1–204.8) and an
imino carbon (δC 157.3–171.5) of the benzoxazole ring. Those
of iminothietanes 21–29 exhibited the corresponding signals at
δC 168.8–174.8 and δC 166.3–173.1, which were assigned to ester
carbonyl and imino carbons, respectively. Finally, the structures
of S-2-(1,3-benzoxazol-2-yl)-2,2-diphenylethyl 2-methylprop-
anethioate 10 and N-(3,3,4,4-tetramethylthietan-2-ylidene)-o-
acetoxyaniline 22 were confirmed by X-ray structural analysis
(Figs. 1 and 2). The photoproduct, 2-(1,3-benzoxazol-2-yl)-2-
cyanopropyl 2-methylpropanethioate 11, was hydrolyzed with
sodium hydroxide in methanol to yield 2-(1,3-benzoxazol-2-yl)-
2-cyanopropane-1-thiol 34, whose structure was confirmed by
spectral comparison with authentic material which was
independently prepared by the photoaddition of benzoxazole-
2-thione with methacrylonitrile,4b in 56% yield. Treatment of
11 with sodium ethoxide in ethanol also gave 34, in quantitative
Fig. 3 ORTEP perspective view of o-hydroxy-N-(3,3,4-trimethyl-
thietan-2-ylidene)aniline 37 with crystallographic numbering scheme.
Non-H-atoms are drawn at the 50% probability level.
yield. The iminothietanes 22, 24, 25 and 29 were treated with
sodium methoxide in methanol to yield o-hydroxy-N-(thietan-
2-ylidene)anilines 36 and 37 in high yields. Methyl 3-phenyl-
propionate was isolated in 43% yield as a by-product when 29
was treated with sodium methoxide. The structures of 36 and
37 were elucidated on the basis of spectral properties and ele-
mental analysis, and finally the structure of o-hydroxy-N-(3,3,4-
trimethylthietan-2-ylidene)aniline 37 was confirmed by X-ray
structural analysis (Fig. 3). o-Hydroxy-N-(tetramethylthietan-2-
ylidene)aniline 36 thus obtained was heated to reflux in toluene
to yield the 2-(mercaptoalkyl)benzoxazole 33 quantitatively.
The o-hydroxythietanylideneaniline 37 also gave a 2-(mer-
captoalkyl)benzoxazole, 35, when heated to reflux in toluene.
Treatment of the o-acetoxy-N-(thietan-2-ylidene)aniline 22
with hydrochloric acid yielded 33 and 36. The latter gave 33 by
further treatment with hydrochloric acid. Reduction of the
o-isobutyryloxy-N-(thietan-2-ylidene)aniline 25 with sodium
borohydride in methanol gave 2-(mercaptoalkyl)benzoxazole 33
and the o-hydroxy-N-(thietan-2-ylidene)aniline 36, while that
of 25 with lithium aluminium hydride in diethyl ether gave 36.
The 2-(mercaptoalkyl)benzoxazole 36 was refluxed in acetic
anhydride to yield two acetylated products, 22 and 5. The
o-acetoxy-N-(thietan-2-ylidene)aniline 22 was treated with
m-chloroperbenzoic acid (MCPBA) to give a complex mixture
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J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046

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Fig. 4 ORTEP perspective view of 3-(o-acetoxyphenylimino)-4,4,5,5-
tetramethyl-1,2-dithiolane 1-oxide 38 with crystallographic numbering
scheme. Non-H-atoms are drawn at the 50% probability level.
Scheme 3
formed is unstable and undergoes C–S bond cleavage of the
thietane ring or C–O bond cleavage of the oxazole ring assisted
by the lone-pair electrons on nitrogen to yield the respective
zwitterion I or II. Intramolecular nucleophilic attack of the
thiolate anion of the zwitterion I (path a) and of the phenolate
anion of the zwitterion II on the acyl group (path b) yielded the
2-substituted benzoxazoles 3–20 and the iminothietanes 21–29,
respectively. Irradiation of N-acylbenzoxazole-2-thiones 1 and
alkenes 2 in methanol was carried out in the hope of trapping a
zwitterion intermediate AT; however, this attempt was unsuc-
cessful, and similar results were obtained as when the photo-
reaction of 1 and 2 was run in benzene (see Table 1). The two
modes of cleavage in this proposed reaction intermediate,
aminothietane AT, could be explained in terms of the stability
of aminothietanes AT and zwitterions I and II: MO calculation
suggests that the heat of formation of thietanes having sub-
stituents at C-2 adjacent to the S-atom is lower than that of
thietanes having no substituents at C-2 by about 4 kcal molϪ1.†
The zwitterion II substituted at the carbon adjacent to sulfur is
more stable than the other zwitterion II having no substituents
adjacent to sulfur by 10–15 kcal molϪ1, although there is only a
small difference in the heat of formation of identically substi-
tuted zwitterions I (Table 2). The formation of 2-(mercapto-
alkyl)benzoxazoles 30–33 can be interpreted in terms of the
photoaddition of N-unsubstituted benzoxazole-2-thione,
which was produced by hydrogen abstraction by the excited
thiocarbonyl group of N-acylbenzoxazole-2-thiones 1,5 with
alkenes.4b
Chart 1
of products from which the 3-(o-acetoxyphenylimino)-4,4,5,5-
tetramethyl-1,2-dithiolane 1-oxide 38 was isolated in low yield
(14%) when the reaction mixture was purified through silica
gel column chromatography (Chart 1). The structure of 38 was
confirmed by X-ray structural analysis (Fig. 4).
The formation of 2-substituted benzoxazoles 3–20 and imino-
thietanes 21–29 in the photocycloaddition of N-acylbenz-
oxazole-2-thiones 1 and alkenes 2 can be rationalized by the
mechanism shown in Scheme 3. The aminothietane AT was
initially formed through the regioselective [2 ϩ 2] photo-
The photoaddition reaction of N-acylbenzoxazole-2-thiones
1 to a variety of alkenes (electron-rich and -poor) proceeds
smoothly to yield 2-substituted benzoxazoles 3–20 and/or
iminothietanes 21–29, depending on the nature of substituents
present in the alkenes. Although a few syntheses of imino-
thietanes have been reported,6 the photoreaction described here
would be an efficient and novel method for their synthesis.
cycloaddition of the C᎐S double bond of 1 and the alkene
᎐
double bond. The regiochemistry is in accord with the form-
ation of the more stable diradical intermediate in the [2 ϩ 2]
photocycloaddition process.1b,2b,3a The aminothietane AT thus
† 1 cal = 4.184 J.
J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046
3041

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Table 1 Yields of photoproducts 3–33
Thione
Alkene
R
R1
R2
R3
R4
Yield (%)a
1a
1a
1a
1a
1a
1a
1ab
1b
1bc
1b
1b
1b
1b
1bb
1b
1bb
1bc
1b
1b
1b
1b
1bb
1b
1c
Me
2a
2b
2c
2d
2h
2l
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
CN
Me
H
H
H
Me
H
H
3 (59)
4 (61)
5 (7)
Me
Me
Me
H
21 (tr)
22 (52)
30 (25)
6 (63)
7 (28)
7 (26)
H
CH᎐CMe2
23 (31)
23 (38)
24 (53)
24 (76)
25 (51)
᎐
2l
Me2CH
2b
2b
2c
2e
2f
Me
Me
Me
H
Me
Ph
Ph
Ph
Me
H
Me
Ph
Me
H
H
Me
H
H
8 (25)
9 (38)
31 (18)
32 (tr)
2g
2g
2h
2h
2h
2i
H
H
10 (55)
10 (94)
11 (54)
11 (77)
11 (59)
12 (26)
13 (56)
14 (53)
15 (5)
Me
CN
H
H
CN
Me
EtO
Me
H
CO2Me
H
H
H
H
H
H
H
H
2j
2k
2l
Me
CH᎐CMe2
26 (48)
26 (33)
27 (20)
᎐
2l
15 (21)
16 (50)
17 (64)
2m
2h
2c
2h
2c
2h
2j
Me
Me
Me
Me
Me
Me
Me
C(Me)᎐CH2
CN
Me
CN
Me
CN
CO2Me
H
H
Me
H
Me
H
H
H
Me
H
Me
H
᎐
Me2CHCH2
PhCH2
1d
1d
1e
1e
1e
28 (11)
29 (63)
33 (55)
18 (58)
PhCH2CH2
19 (63)
20 (63)
H
H
a Isolated yield. b In MeOH. c In CH3CN.
(2.07 × 104). 1b λmax(EtOH)/nm (ε) 211.5 (1.97 × 104), 259
(1.49 × 104) and 300 (4.26 × 104). 1c λmax(EtOH)/nm (ε)
259 (9.4 × 103), 300 (2.80 × 104) and 303.5 (2.81 × 104). 1d
λmax(EtOH)/nm (ε) 259 (1.28 × 104), 300 (3.63 × 104) and 303.5
(3.64 × 104). 1e 259 (6.0 × 103) and 304 (1.96 × 104).
Table 2 Heat of formation of aminothietanes (AT) and zwitterions
(I and II)a
Heat of formation
R
R1
R2
R3
R4
(kcal molϪ1
)
A solution of 1 (1 mmol) and 2 (≈1 cm3 or 2 equiv. for the
alkenes 2f and 2g) in benzene (70 cm3) was irradiated in a Pyrex
vessel with the high-pressure mercury lamp (500 W) under
argon for 10–20 h at room temperature. After removal of the
solvent, the residual oil was chromatographed on a silica gel
column with benzene (or toluene)–ethyl acetate (9:1–50:1) as
eluent to yield the corresponding photoproducts (3–33). The
structure of the photoproducts 32 and 33 was determined on
the basis of our previous work.4b
AT
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
H
Me
H
H
Me
H
H
H
H
H
Me
H
Me
H
Me
H
Me
H
Me
H
Me
Ϫ21.3749
Ϫ27.9568
Ϫ31.6509
Ϫ31.0276
Ϫ31.7902
Ϫ28.0839
Ϫ27.2179
Ϫ29.1132
Ϫ28.2083
Ϫ26.6756
Ϫ33.1855
Ϫ36.4227
Ϫ41.9096
Me
Me
Me
H
Me
Me
Me
H
Me
Me
Me
H
Me
Me
Me
H
Me
Me
Me
H
Me
Me
Me
H
I
II
Me
Me
Me
S-2-(1,3-Benzoxazol-2-yl)-2-methylpropyl thioacetate 3. Bp
180 ЊC/2 mmHg (Found: C, 62.5; H, 6.05; N, 5.6. C13H15NO2S
requires C, 62.65; H, 6.05; N, 5.6%); νmax(film)/cmϪ1 1685;
δH 1.53 (6H, s), 2.30 (3H, s), 3.44 (2H, s), 7.28–7.32 (2H, m),
7.48–7.52 (1H, m) and 7.68–7.73 (1H, m); δC 25.5 (q), 30.6 (q),
38.4 (s), 39.0 (t), 110.4 (d), 119.9 (d), 124.2 (d), 124.7 (d), 140.9
(s), 150.8 (s), 170.7 (s) and 194.8 (s).
Me
Me
Me
Me
a Calculated by PM3 (HyperChem) method.
Experimental
Mps and bps were measured on a Yanako micro melting
point apparatus (MP-3J) and a Shibata tube oven distillation
apparatus (GTO-350D), respectively and are uncorrected. IR
spectra were recorded on a Hitachi 260-30 or JASCO FT/IR-
S-3-(1,3-Benzoxazol-2-yl)-3-methylbutan-2-yl thioacetate 4.
Bp 170 ЊC/2 mmHg (Found: C, 63.55; H, 6.45; N, 5.35.
C14H17NO2S requires C, 63.85; H, 6.5; N, 5.3%); νmax(film)/cmϪ1
1685; δH 1.27 (3H, d, J 6.9), 1.52 (3H, s), 1.54 (3H, s), 2.31 (3H,
s), 4.19 (1H, q, J 6.9), 7.29–7.34 (2H, m), 7.49–7.54 (1H, m) and
7.69–7.74 (1H, m); δC 18.0 (q), 23.2 (q), 25.0 (q), 30.7 (q), 41.5
(s), 47.2 (d), 110.5 (d), 124.1 (d), 124.7 (d), 140.8 (s), 150.7 (s),
170.6 (s) and 194.6 (s).
300 spectrophotometer. H and 13C NMR spectra were run on
1
JEOL FX 90Q (90 MHz) and JEOL JMN-EX-270 (270 MHz)
spectrometers with CDCl3 as solvent and tetramethylsilane as
internal standard. J-Values are given in Hz. UV spectra were
measured with a Shimadzu UV-3100PC spectrophotometer. An
Eikosha HALos (500 W) high-pressure mercury lamp was used
as the irradiation source.
S-3-(1,3-Benzoxazol-2-yl)-2,3-dimethylbutan-2-yl thioacetate
5. Bp 180 ЊC/2 mmHg; mp 55–56 ЊC (Found: C, 65.05; H, 6.9;
N, 5.05. C15H19NO2S requires C, 64.95; H, 6.9; N, 5.05%);
λmax(EtOH)/nm (ε) 235 (1.42 × 104), 272 (4.9 × 104) and 279
(4.2 × 104); νmax(film)/cmϪ1 1685; δH 1.61 (6H, s), 1.68 (6H, s),
General procedure for the photochemical reactions of the N-acyl-
benzoxazole-2-thiones 1 with the alkenes 2
UV spectra: 1a λmax(EtOH)/nm (ε) 258 (6.2 × 103) and 304
3042
J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046

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2.21 (3H, s), 7.30–7.34 (2H, m), 7.50–7.55 (1H, m) and 7.72–
7.76 (1H, m); δC 22.9 (q), 23.7 (q), 31.8 (q), 45.4 (s), 58.4 (s),
110.5 (d), 119.9 (d), 124.1 (d), 124.7 (d), 140.8 (s), 150.5 (s),
169.6 (s) and 185.1 (s).
for 15 min at room temperature. Usual work-up gave 34
quantitatively.
S-2-(1,3-Benzoxazol-2-yl)-2-cyanoethyl
2-methylpropane-
thioate 12. Mp 73–74 ЊC (Found: C, 61.0; H, 5.1; N, 10.25.
C14H14N2O2S requires C, 61.3; H, 5.15; N, 10.2%); νmax(KBr)/
cmϪ1 2200 and 1690; δH 1.20 (6H, d, J 6.9), 2.71–2.80 (1H, m),
3.53–3.63 (1H, A of ABX), 3.67–3.76 (1H, B of ABX), 4.52
(1H, X of ABX, J 6.6, 7.6), 7.23–7.44 (2H, m), 7.54–7.59 (1H,
m) and 7.72–7.77 (1H, m); δC 19.1 (q), 29.2 (t), 32.8 (d), 43.2 (d),
110.0 (d), 115.2 (s), 120.6 (d), 125.1 (d), 126.1 (d), 140.5 (s),
151.1 (s), 157.3 (s) and 202.2 (s).
S-2-(1,3-Benzoxazol-2-yl)-2-cyanopropyl thioacetate 6. Mp
67–68 ЊC (Found: C, 60.35; H, 4.7; N, 10.8. C13H12N2O2S
requires C, 60.0; H, 4.6; N, 10.75%); νmax(KBr)/cmϪ1 2240 and
1700; δH 1.94 (3H, s), 2.37 (3H, s), 3.74 (2H, dd, J 12.9, 15.5),
7.37–7.42 (2H, m), 7.56–7.60 (1H, m) and 7.74–7.78 (1H, m);
δC 23.4 (q), 30.4 (q), 36.1 (t), 39.8 (s), 110.0 (d), 118.4 (s), 120.6
(d), 125.0 (d), 126.1 (d), 140.4 (s), 151.1 (s), 161.5 (s) and
192.8 (s).
S-2-(1,3-Benzoxazol-2-yl)-2-(methoxycarbonyl)propyl
2-
S-2-(1,3-Benzoxazol-2-yl)-2,5-dimethylhex-4-en-3-yl thioacet-
ate 7. Bp 185 ЊC/2 mmHg (Found: C, 67.45; H, 7.0; N, 4.65.
C17H21NO2S requires C, 67.3; H, 7.0; N, 4.6%); νmax(film)/cmϪ1
1680; δH 1.56 (3H, s), 1.62 (3H, s), 1.75 (3H, d, J 1.0), 1.79 (3H,
d, J 1.3), 2.29 (3H, s), 4.85 (1H, d, J 10.6), 5.59 (1H, br d,
J 10.6), 7.26–7.32 (2H, m), 7.48–7.52 (1H, m) and 7.69–7.73
(1H, m); δC 18.5 (q), 24.9 (q), 25.2 (q), 26.1 (q), 31.4 (q), 45.8
(d), 54.4 (s), 110.5 (d), 119.0 (d), 119.9 (d), 124.1 (d), 124.6 (d),
137.9 (s), 141.2 (s), 150.2 (s), 166.4 (s) and 196.6 (s).
methylpropanethioate 13. Bp 210 ЊC/1 mmHg (Found: C, 60.1;
H, 5.9; N, 4.35. C16H19NO4S requires C, 59.8; H, 5.95; N,
4.35%); νmax(film)/cmϪ1 1740 and 1690; δH 1.12 (3H, d, J 6.9),
1.13 (3H, d, J 6.9), 1.78 (3H, s), 2.62–2.76 (1H, m), 3.73 (3H, s),
3.77 (2H, s), 7.29–7.37 (2H, m), 7.48–7.53 (1H, m) and 7.71–
7.76 (1H, m); δC 19.3 (q), 20.5 (q), 34.2 (t), 43.1 (d), 49.6 (s), 53.1
(q), 110.7 (d), 120.3 (d), 124.5 (d), 125.3 (d), 128.3 (d), 140.7 (s),
150.9 (s), 165.2 (s), 171.5 (s) and 202.4 (s); MS 321 (Mϩ) and
250 (Mϩ Ϫ Me2CHCHO).
S-2-(1,3-Benzoxazol-2-yl)-2-phenylethyl
2-methylpropane-
S-2-(1,3-Benzoxazol-2-yl)-2-ethoxyethyl
2-methylpropane-
thioate 8. Bp 190 ЊC/2 mmHg (Found: C, 70.45; H, 5.8; N, 4.6.
C19H19NO2S requires C, 70.15; H, 5.9; N, 4.3%); νmax(film)/cmϪ1
1680; δH 1.13 (3H, d, J 6.9), 1.14 (3H, d, J 6.9), 2.68 (1H, sep,
J 6.9), 3.62 (1H, A of ABX, J 6.3, 13.5), 3.73 (1H, B of ABX,
J 9.2, 13.5), 4.47 (1H, X of ABX, J 6.3, 9.2), 7.20–7.47 (8H, m)
and 7.72–7.76 (1H, m); δC 19.2 (q), 19.3 (q), 32.6 (t), 43.0 (d),
46.3 (d), 110.6 (d), 120.0 (d), 124.2 (d), 124.9 (d), 127.9 (d),
128.9 (d), 138.4 (s), 141.0 (s), 150.8 (s), 166.3 (s) and 203.4 (s).
thioate 14. Bp 200 ЊC/1 mmHg (Found: C, 61.15; H, 6.45; N,
4.7. C15H19NO3S requires C, 61.4; H, 6.55; N, 4.8%); νmax(film)/
cmϪ1 1685; δH 1.16 (6H, d, J 6.9), 1.24 (3H, t, J 6.9), 2.72 (1H,
sep, J 6.9), 3.51 (2H, d, J 6.9), 3.67 (2H, q, J 6.9), 4.68 (1H, t,
J 6.9), 7.29–7.40 (2H, m), 7.52–7.59 (1H, m) and 7.71–7.77 (1H,
m); δC 15.1 (q), 19.2 (q), 31.3 (t), 43.0 (d), 66.2 (t), 74.4 (d), 110.9
(d), 120.4 (d), 124.5 (d), 125.5 (d), 140.7 (s), 150.8 (s), 163.9 (s)
and 203.0 (s).
S-2-(1,3-Benzoxazol-2-yl)-2-phenylpropyl 2-methylpropane-
thioate 9. Bp 190 ЊC/2 mmHg (Found: C, 71.05; H, 6.3; N, 4.1.
C20H21NO2S requires C, 70.8; H, 6.25; N, 4.15%); νmax(film)/
cmϪ1 1680; δH 1.09 (3H, d, J 6.9), 1.11 (3H, d, J 6.9), 1.90 (3H,
s), 2.68 (1H, sep, J 6.9), 3.86 (2H, s), 7.20–7.40 (8H, m) and
7.75–7.79 (1H, m); δC 19.3 (q), 23.1 (q), 38.1 (t), 43.1 (d), 46.3
(s), 110.7 (d), 120.1 (d), 124.3 (d), 124.9 (d), 126.2 (d), 127.4 (d),
128.6 (d), 169.5 (s) and 203.0 (s); MS 339 (Mϩ) and 268
(Mϩ Ϫ Me2CHCHO).
S-2-(1,3-Benzoxazol-2-yl)-2,5-dimethylhex-4-en-3-yl
2-
methylpropanethioate 15. Bp 200 ЊC/2 mmHg (Found: C, 68.75;
H, 7.4; N, 4.3. C19H25NO2S requires C, 68.85; H, 7.6; N, 4.25%);
νmax(film)/cmϪ1 1665; δH 1.13 (6H, d, J 6.9), 1.55 (3H, s), 1.63
(3H, s), 1.76 (3H, s), 1.78 (3H, s), 2.60 (1H, sep, J 6.9), 4.98 (1H,
q, J 10.6), 5.63 (1H, d, J 10.6), 7.27–7.33 (2H, m), 7.45–7.49
(1H, m) and 7.68–7.72 (1H, m); δC 18.6 (q), 19.2 (q), 19.6 (q),
24.8 (q), 25.6 (q), 26.0 (q), 43.4 (d), 53.8 (s), 110.4 (d), 119.2 (d),
119.8 (d), 124.1 (d), 124.5 (d), 137.6 (s), 137.6 (s), 141.2 (s),
150.1 (s), 166.7 (s) and 204.8 (s).
S-2-(1,3-Benzoxazol-2-yl)-2,2-diphenylethyl 2-methylpropane-
thioate 10. Mp 93–94 ЊC (Found: C, 74.8; H, 5.85; N, 3.45.
C25H23NO2S requires C, 74.8; H, 5.75; N, 3.5%); νmax(KBr)/
cmϪ1 1685; δH 0.93 (6H, d, J 6.9), 2.53 (1H, sep, J 6.9), 4.34 (2H,
s), 7.02–7.45 (13H, m) and 7.74–7.78 (1H, m); δC 19.2 (q), 37.2
(t), 42.8 (d), 55.8 (s), 110.8 (d), 120.4 (d), 124.3 (d), 125.0 (d),
126.9 (d), 127.4 (d), 128.0 (d), 128.5 (d), 128.9 (d), 140.7 (s),
141.7 (s), 151.0 (s), 168.3 (s) and 202.3 (s).
S-2-(1,3-Benzoxazol-2-yl)-2,3-dimethylbut-3-enyl 2-methyl-
propanethioate 16. Bp 230 ЊC/1 mmHg (Found: C, 67.3; H, 6.9;
N, 4.7. C17H21NO2S requires C, 67.3; H, 7.0; N, 4.6%);
νmax(film)/cmϪ1 1685 and 1640; δH 1.13 (3H, d, J 6.9), 1.15 (3H,
d, J 6.9), 1.63 (3H, s), 1.74 (3H, s), 2.72 (1H, sep, J 6.9), 3.67
(2H, dd, J 3.5, 7.2), 4.92 (1H, s), 5.05 (1H, s), 7.27–7.35 (2H,
m), 7.46–7.52 (1H, m) and 7.71–7.77 (1H, m); δC 19.4 (q), 20.0
(q), 21.7 (q), 35.5 (t), 43.1 (d), 47.1 (s), 110.6 (d), 113.4 (t), 120.1
(d), 124.2 (d), 124.9 (d), 140.8 (s), 145.9 (s), 150.8 (s), 169.0 (s)
and 203.1 (s); MS 303 (Mϩ), 232 (Mϩ Ϫ Me2CHCO), 200
(Mϩ Ϫ Me2CHCOS) and 186 (Mϩ Ϫ Me2CHCOSCH2).
S-2-(1,3-Benzoxazol-2-yl)-2-cyanopropyl 2-methylpropane-
thioate 11. Mp 60–61 ЊC (Found: C, 62.3; H, 5.65; N, 9.55.
C15H16N2O2S requires C, 62.5; H, 5.6; N, 9.7%); νmax(KBr)/cmϪ1
2225 and 1680; δH 1.16 (3H, d, J 6.9), 1.17 (3H, d, J 6.9), 1.95
(3H, s), 2.66–2.83 (1H, m), 3.72 (2H, dd, J 13.8, 16.5), 7.34–7.44
(2H, m), 7.56–7.60 (1H, m) and 7.74–7.78 (1H, m); δC 19.1 (q),
19.2 (q), 23.4 (q), 35.4 (t), 40.0 (s), 43.2 (d), 110.0 (d), 118.5 (s),
120.6 (d), 125.0 (d), 126.1 (d), 140.4 (s), 151.1 (s), 161.6 (s) and
201.1 (s); MS 288 (Mϩ) and 217 (Mϩ Ϫ Me2CHCHO).
A solution of 11 (0.5 mmol) and NaOH powder (25 mg) in
methanol (10 cm3) was stirred under argon for 2 h at room
temperature. Usual work-up gave 2-(benzoxazol-2-yl)-2-
cyanopropane-1-thiol 34 (56%) whose structure was confirmed
by direct comparison of IR and NMR spectra with those of an
authentic sample.4b To a solution of sodium (15 mg) in EtOH
(5 cm3) was added dropwise a solution of 11 (0.5 mmol) in
EtOH (10 cm3) under argon and the mixture was then stirred
S-2-(1,3-Benzoxazol-2-yl)-2-cyanopropyl
3-methylbutane-
thioate 17. Bp 235 ЊC/1 mmHg (Found: C, 63.5; H, 5.95; N, 9.5.
C16H18N2O2S requires C, 63.55; H, 6.0; N, 9.25%); νmax(film)/
cmϪ1 1695; δH 0.92 (6H, d, J 6.6), 1.95 (3H, s), 2.02–2.18 (1H,
m), 2.46 (2H, d, J 6.8), 3.74 (2H, dd, J 13.9, 15.8), 7.36–7.42
(2H, m), 7.55–7.60 (1H, m) and 7.72–7.78 (1H, m); δC 22.2 (q),
23.4 (q), 26.4 (d), 35.9 (t), 39.9 (s), 52.7 (t), 110.0 (d), 118.5 (s),
120.6 (d), 125.0 (d), 126.1 (d), 140.5 (s), 151.1 (s), 161.6 (s) and
195.9 (s).
S-2-(1,3-Benzoxazol-2-yl)-2-cyanopropyl phenyl(thioacetate)
18. Bp 230 ЊC/1 mmHg (Found: C, 68.05; H, 5.0; N, 8.45.
C19H16N2O2S requires C, 67.85; H, 4.8; N, 8.35%); νmax(film)/
J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046
3043

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cmϪ1 2240 and 1695; δH 1.87 (3H, s), 3.70 (2H, dd, J 13.9, 15.8),
3.83 (2H, s), 7.17–7.39 (7H, m), 7.49–7.54 (1H, m) and 7.70–
7.75 (1H, m); δC 23.3 (q), 36.0 (t), 39.7 (s), 50.2 (t), 110.0 (d),
118.3 (s), 120.6 (d), 125.0 (d), 126.1 (d), 127.6 (d), 128.7 (d),
129.5 (d), 132.6 (s), 140.3 (s), 151.0 (s), 161.4 (s) and 194.5 (s).
νmax(film)/cmϪ1 1760 and 1665; δH 1.32 (6H, d, J 6.9), 1.41 (6H,
s), 1.60 (6H, s), 2.81 (1H, sep, J 6.9) and 6.95–7.19 (4H, m);
δC 19.0 (q), 23.0 (q), 27.7 (q), 33.9 (d), 52.0 (s), 62.5 (s), 120.5
(d), 122.7 (d), 125.5 (d), 126.2 (d), 140.4 (s), 143.0 (s), 172.8 (s)
and 174.6 (s); MS 305 (Mϩ).
S-2-(1,3-Benzoxazol-2-yl)-2-cyanopropyl
2-phenylpropane-
N-[3,3-Dimethyl-4-(2-methylprop-1-enyl)thietan-2-ylidene]-o-
(2-methylpropanoyl)aniline 26. Bp 180 ЊC/1 mmHg (Found: C,
68.9; H, 7.55; N, 4.45. C19H25NO2S requires C, 68.85; H, 7.6; N,
4.25%); νmax(film)/cmϪ1 1760 and 1660; δH 1.33 (6H, d, J 6.9),
1.54 (3H, s), 1.68 (3H, s), 1.73 (3H, s), 1.78 (3H, s), 2.81
(1H, sep, J 6.9), 4.61 (1H, d, J 9.2), 5.42 (1H, d, J 9.2) and 6.98–
7.36 (4H, m); δC 18.6 (q), 19.0 (q), 25.7 (q), 27.9 (q), 32.4 (q),
34.0 (d), 51.2 (s), 66.3 (d), 119.4 (d), 120.5 (d), 122.7 (d),
125.6 (d), 126.2 (d), 137.3 (s), 140.5 (s), 143.1 (s), 166.3 (s) and
174.7 (s).
thioate 19. Bp 250 ЊC/1 mmHg (Found: C, 68.85; H, 5.4; N, 8.1.
C20H18N2O2S requires C, 68.55; H, 5.2; N, 8.0%); νmax(film)/
cmϪ1 2240 and 1700; δH 1.89 (3H, s), 2.86–2.96 (4H, m), 3.73
(2H, t, J 14.5), 7.12–7.43 (7H, m), 7.54–7.58 (1H, m) and 7.73–
7.77 (1H, m); δC 23.3 (q), 31.2 (t), 35.8 (t), 39.8 (s), 45.3 (t),
110.0 (d), 118.4 (s), 120.6 (d), 125.0 (d), 126.4 (d), 126.6 (d),
128.2 (d), 128.6 (d), 139.5 (s), 140.4 (s), 151.0 (s), 161.5 (s) and
195.6 (s).
S-2-(1,3-Benzoxazol-2-yl)-2-(methoxycarbonyl)propyl
2-
phenylpropanethioate 20. Bp 230 ЊC/1 mmHg (Found: C, 65.75;
H, 5.6; N, 3.8. C21H21NO4S requires C, 65.8; H, 5.5; N, 3.65%);
νmax(film)/cmϪ1 1730 and 1685; δH 1.74 (3H, s), 2.79–2.95 (4H,
m), 3.71 (3H, s), 3.77 (2H, s), 7.11–7.36 (7H, m), 7.49–7.55 (1H,
m) and 7.73–7.78 (1H, m); δC 20.4 (q), 31.4 (t), 34.6 (t), 45.3 (t),
49.5 (s), 53.1 (q), 110.7 (d), 120.3 (d), 124.5 (d), 126.4 (d), 128.2
(d), 128.5 (d), 139.7 (s), 140.7 (s), 150.9 (s), 165.1 (s), 171.4 (s)
and 197.0 (s).
N-[3-Isopropenyl-3-methylthietan-2-ylidene]-o-(2-methyl-
propanoyl)aniline 27. Bp 220 ЊC/1 mmHg (Found: C, 67.1; H,
6.95; N, 4.5. C17H21NO2S requires C, 67.3; H, 7.0; N, 4.6%);
νmax(film)/cmϪ1 1750 and 1650; δH 1.30 (6H, d, J 6.9), 1.63 (3H,
s), 1.93 (3H, s), 2.78 (1H, sep, J 6.9), 2.90 (1H, d, J 8.6), 3.24
(1H, d, J 8.6), 4.91 (1H, s), 5.12 (1H, s) and 7.04–7.26 (4H, m);
δC 19.0 (q), 19.1 (q), 24.1 (q), 32.8 (t), 33.9 (d), 68.2 (s), 111.4 (t),
120.2 (d), 123.0 (d), 125.2 (d), 126.3 (d), 139.9 (s), 143.0 (s),
144.3 (s), 170.8 (s) and 174.8 (s); MS 303 (Mϩ).
o-Acetoxy-N-(3,3,4-trimethylthietan-2-ylidene)aniline
21.
Oil; νmax(film)/cmϪ1 1775 and 1665; δH 1.35 (3H, s), 1.46 (3H, s),
1.47 (3H, d, J 6.9), 2.28 (3H, s), 3.50 (1H, q, J 6.9) and 6.99–
7.27 (4H, m).
o-Phenylacetoxy-N-(3,3,4,4-tetramethylthietan-2-ylidene)-
aniline 28. Bp 220 ЊC/1 mmHg (Found: C, 71.15; H, 6.65;
N, 4.1. C21H23NO2S requires C, 71.35; H, 6.55; N, 3.95%);
νmax(film)/cmϪ1 1760 and 1660; δH 1.33 (6H, s), 1.56 (6H, s), 3.87
(2H, s) and 6.95–7.42 (9H, m); δC 22.8 (q), 27.6 (q), 40.8 (t), 52.0
(s), 62.4 (s), 120.5 (d), 122.5 (d), 125.4 (d), 126.4 (d), 127.1 (d),
128.5 (d), 129.5 (d), 133.5 (s), 140.4 (s), 142.8 (s), 169.0 (s) and
173.0 (s); MS 353 (Mϩ).
o-Acetoxy-N-(3,3,4,4-tetramethylthietan-2-ylidene)aniline
22. Mp 63–64 ЊC (Found: C, 64.8; H, 6.85; N, 5.1. C15H19NO2S
requires C, 64.95; H, 6.9; N, 5.05%); λmax(EtOH)/nm (ε) 246
(1.17 × 104) and 286 (6.4 × 104); νmax(KBr)/cmϪ1 1760 and 1665;
δH 1.43 (6H, s), 1.61 (6H, s), 2.28 (3H, s), 6.95–6.99 (1H, m) and
7.06–7.18 (3H, m); δC 20.7 (q), 22.8 (q), 27.7 (q), 52.1 (s), 62.4
(s), 120.5 (d), 122.5 (d), 125.5 (d), 126.4 (d), 140.4 (s), 142.8 (s),
168.9 (s) and 173.2 (s).
A solution of 22 (0.5 mmol) in methanol in the presence of
a few drops of hydrochloric acid was stirred for 5 h at room
temperature. Usual work-up gave the 2-substituted benzoxazole
33 (18%) and the o-hydroxy-N-thietanylideneaniline 36 (59%).
A solution of 36 (0.5 mmol) thus produced, containing a
few drops of hydrochloric acid, was kept for 15 h at room
temperature and then usual work-up gave 33 quantitatively.
o-(2-Phenylpropanoyl)-N-(3,3,4,4-tetramethylthietan-2-ylid-
ene)aniline 29. Bp 230 ЊC/1 mmHg (Found: C, 72.1; H, 6.85; N,
3.75. C22H25NO2S requires C, 71.9; H, 6.85; N, 3.8%); νmax(film)/
cmϪ1 1760 and 1660; δH 1.39 (6H, s), 1.58 (6H, s), 2.83–2.90
(2H, m), 3.04–3.10 (2H, m) and 6.95–7.36 (9H, m); δC 22.9 (q),
27.7 (q), 30.9 (t), 35.7 (t), 52.1 (s), 62.4 (s), 120.5 (d), 122.6 (d),
125.5 (d), 126.3 (d), 128.4 (d), 128.5 (d), 140.3 (s), 142.8 (s),
170.4 (s) and 173.1 (s).
2-(3-Mercaptobutan-2-yl)benzoxazole 30. Bp 190 ЊC/2 mmHg
(Found: C, 63.75; H, 6.3; N, 6.65. C11H13NOS requires C, 63.75;
H, 6.3; N, 6.75%); νmax(film)/cmϪ1 2560; δH 1.41 (3H, d, J 6.9),
1.53 (3H, d, J 6.9), 1.72 (1H, d, J 7.6), 3.22–3.36 (1H, m),
3.42–3.56 (1H, m), 7.29–7.35 (2H, m), 7.47–7.57 (1H, m)
and 7.67–7.75 (1H, m); δC 14.7 (q), 21.8 (q), 38.3 (d), 42.7 (d),
110.3 (d), 119.7 (d), 124.1 (d), 124.5 (d), 140.9 (s), 150.4 (s) and
168.0 (s).
o-Acetoxy-N-[3,3-dimethyl-4-(2-methylprop-1-enyl)thietan-2-
ylidene]aniline 23. Bp 205 ЊC/2 mmHg (Found: C, 67.15; H,
7.1; N, 4.75. C17H21NO2S requires C, 67.3; H, 7.0; N, 4.6%);
νmax(film)/cmϪ1 1760 and 1660; δH 1.54 (3H, s), 1.69 (3H, s), 1.75
(3H, s), 1.80 (3H, s), 2.29 (3H, s), 4.63 (1H, d, J 9.2), 5.45 (1H,
br d, J 9.2) and 6.98–7.27 (4H, m); δC 18.7 (q), 20.8 (q), 25.8 (q),
27.7 (q), 32.4 (q), 51.4 (d), 66.2 (s), 119.3 (d), 120.5 (d), 122.6
(d), 125.6 (d), 126.4 (d), 137.4 (s), 140.4 (s), 142.9 (s), 166.9 (s)
and 168.8 (s).
2-(2-Mercapto-1-phenylethyl)benzoxazole 31. Mp 61–62 ЊC
(Found: C, 70.85; H, 5.3; N, 5.45. C15H13NOS requires C, 70.6;
H, 5.15; N, 5.5%); νmax(KBr)/cmϪ1 2560 and 1670; δH 1.68 (1H,
t, J 8.6), 3.09–3.20 (1H, m), 3.43–3.56 (1H, m), 4.41 (1H, dd,
J 6.9, 8.6), 7.13–7.46 (8H, m) and 7.71–7.75 (1H, m); δC 28.6 (t),
50.2 (d), 110.5 (d), 119.9 (d), 124.2 (d), 124.8 (d), 127.9 (d),
128.3 (d), 128.9 (d), 138.1 (s), 141.0 (s), 150.7 (s) and 166.1 (s).
o-(2-Methylpropanoyl)-N-(3,3,4-trimethylthietan-2-ylidene)-
aniline 24. Bp 190 ЊC/1 mmHg (Found: C, 65.65; H, 7.3;
N, 4.95. C16H21NO2S requires C, 65.95; H, 7.25; N, 4.8%);
νmax(film)/cmϪ1 1755 and 1675; δH 1.32 (6H, d, J 6.9), 1.34 (3H,
s), 1.45 (3H, s), 1.47 (3H, d, J 6.9), 2.81 (1H, sep, J 6.9), 3.50
(1H, q, J 6.9) and 6.90–7.20 (4H, m); δC 17.7 (q), 19.0 (q), 20.6
(q), 26.7 (q), 33.9 (d), 44.2 (d), 61.4 (s), 120.5 (d), 122.8 (d),
125.6 (d), 126.2 (d), 140.0 (s), 143.0 (s), 173.1 (s) and 174.6 (s);
MS 291 (Mϩ).
Reaction of the o-acyloxythietan-2-ylideneanilines 22, 24, 25
and 29 with sodium methoxide
To a solution of sodium methoxide [Na (15 mg) in MeOH (5
cm3)] was added dropwise a solution of an o-acyloxythietan-2-
ylideneaniline (0.5 mmol) in methanol (10 cm3) under argon
with stirring. The mixture was stirred for 15 min at room tem-
perature. Usual work-up yielded the corresponding o-hydroxy-
o-(2-Methylpropanoyl)-N-(3,3,4,4-tetramethylthietan-2-yl-
idene)aniline 25. Bp 200 ЊC/1 mmHg (Found: C, 65.65; H,
7.6; N, 4.65. C17H23NO2S requires C, 65.85; H, 7.6; N, 4.6%);
3044
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thietan-2-ylideneaniline 36 or 37. A solution of 36 (or 37) (0.5
mmol) in toluene (15 cm3) was refluxed under argon for 5 h,
then usual work-up gave the 2-substituted benzoxazole 33 (or
354b) in quantitative yield.
Data collection, structure solution and refinement. The
intensity data were collected on an Enraf-Nonius CAD4
diffractometer with graphite-monochromated Mo-Kα radi-
ation (λ 0.709 30 Å) using the ω–2θ scan technique in the
range of 2θ < 50.0Њ. Out of 4221 total reflections, 2934
having intensities greater than 3.0 σ(I) were used in the refine-
ments. The data were corrected for Lorentz-polarization
factors but no absorption corrections were made. The struc-
ture was solved by direct methods using the SPD/VAX
(Enraf-Nonius & B. A. Frenz and Associates). Least-squares
refinement including anisotropic thermal parameters for non-
hydrogen atoms and isotropic refinement of hydrogen atoms
located in difference Fourier Synthesis terminated at 0.044 (Rw
0.040).
o-Hydroxy-N-(3,3,4,4-tetramethylthietan-2-ylidene)aniline
36. Bp 165 ЊC/2 mmHg (Found: C, 66.4; H, 7.25; N, 5.9.
C13H17NOS requires C, 66.35; H, 7.3; N, 5.95%); νmax(film)/cmϪ1
3410 and 1645; δH 1.43 (6H, s), 1.64 (6H, s) and 6.81–7.07 (4H,
m); δC 23.3 (q), 27.7 (q), 54.4 (s), 63.7 (s), 114.3 (d), 118.8 (d),
119.5 (d), 127.0 (d), 133.0 (s), 151.1 (s) and 170.7 (s).
o-Hydroxy-N-(3,3,4-trimethylthietan-2-ylidene)aniline
37.
Mp 78–79 ЊC (Found: C, 65.05; H, 6.85; N, 6.25. C12H15NOS
requires C, 65.15; H, 6.85; N, 6.3%); νmax(KBr)/cmϪ1 1630;
δH 1.35 (3H, s), 1.45 (3H, s), 1.50 (3H, d, J 6.9), 3.62 (1H, q,
J 6.9), 6.77–6.87 (2H, m) and 6.93–7.10 (2H, m); δC 17.7 (q),
20.8 (q), 27.0 (q), 46.4 (d), 62.5 (s), 114.3 (d), 118.8 (d), 119.5
(d), 127.0 (d), 132.9 (s), 151.1 (s) and 170.7 (s).
X-Ray crystal structure determination of o-acetoxy-N-(3,3,4,4-
tetramethylthietan-2-ylidene)aniline 22
A crystal of 22 from chloroform–hexane, with approximate
dimensions of 0.30 × 0.30 × 0.40 mm, was used for the X-ray
study.
Oxidation of the o-acyloxythietan-2-ylideneaniline 22 with
MCPBA
Crystal data. C15H19NO2S, M = 277.39. Orthorhombic, space
group P212121, a = 6.577(2), b = 12.604(1), c = 18.742(3) Å, V =
1553.6 Å3, Z = 4, Dc = 1.19 g cmϪ3. Colorless rods. F(000) = 592.
To a solution of 22 (1 mmol) in methylene dichloride (15 cm3)
was added a solution of MCPBA (1.2 equiv.) in methylene
dichloride (15 cm3) under argon at 0 ЊC (ice-bath) and then the
mixture was stirred for 5 h at room temperature. Usual work-
up yielded 3-(acetoxyphenylimino)-4,4,5,5-tetramethyl-1,2-
dithiolane 1-oxide 38 (14%). With use of 3 equiv. of MCPBA,
the oxide 38 was obtained in 10% yield.
µ(Mo-Kα) 1.6 cmϪ1
.
Data collection, structure solution and refinement. Out of
1297 total reflections, 1176 having intensities greater than 3.0
σ(I) were used in the refinements. Least-squares refinement
terminated at 0.056 (Rw 0.054).
3-(o-Acetoxyphenylimino)-4,4,5,5-tetramethyl-1,2-dithiolane
1-oxide 38. Mp 120–121 ЊC (Found: C, 55.4; H, 5.9; N, 4.25.
C15H19NO3S2 requires C, 55.4; H, 5.9; N, 4.3%); νmax(KBr)/cmϪ1
1750, 1630, 1480, 1365, 1205, 1180, 1080, 985, 840 and 765;
δH 1.18 (3H, s), 1.34 (3H, s), 1.57 (3H, s), 1.59 (3H, s), 2.20 (3H,
s), 6.91–6.96 (1H, m) and 7.08–7.25 (3H, m); δC 17.7 (q), 20.5
(q), 20.6 (q), 23.6 (q), 25.3 (q), 55.5 (s), 71.0 (s), 120.3 (d), 122.9
(d), 126.4 (d), 126.6 (d), 140.9 (s), 142.0 (s), 168.3 (s) and 177.8
(s); MS 325 (Mϩ).
X-Ray crystal structure determination of o-hydroxy-N-(3,3,4-
trimethylthietan-2-ylidene)aniline 37
A crystal of 37 from chloroform–hexane, with approximate
dimensions of 0.30 × 0.40 × 0.20 mm, was used for the X-ray
study.
Crystal data. C12H15NOS, M = 221.22. Orthorhombic, space
group Ccc2, a = 16.400(1), b = 20.779(3), c = 6.931(2) Å, V =
2361.9 Å3, Z = 8, Dc = 1.14 g cmϪ3. Colorless rods. F(000) = 468.
Reduction of the o-acyloxythietan-2-ylideneaniline 25
The mixture of 25 (0.5 mmol) and NaBH4 (1 mmol) in MeOH
(20 cm3) was stirred under argon for 30 min at room temper-
ature and then usual work-up gave 2-substituted benzoxazole
33 (95%) and the o-hydroxythietan-2-ylideneaniline 36 (trace).
A mixture of 25 (0.5 mmol) and LiAlH4 (1 mmol) in diethyl
ether (30 cm3) was stirred under argon for 1.5 h at room
temperature. Usual work-up gave 36 (90%).
µ(Mo-Kα) 1.2 cmϪ1
.
Data collection, structure solution and refinement. Out of
4352 total reflections, 3959 having intensities greater than 3.0
σ(I) were used in the refinements. Least-squares refinement
terminated at 0.036 (Rw 0.037).
Acetylation of the o-hydroxythietan-2-ylideneaniline 36
X-Ray crystal structure determination of 3-(o-acetoxyphenyl-
imino)-4,4,5,5-tetramethyl-1,2-dithiolane 1-oxide 38
A solution of 36 (0.5 mmol) in acetic anhydride (10 cm3)
was refluxed under argon for 1 h and then usual work-up
gave the o-acetoxythietan-2-ylideneaniline 22 (48%) and the
2-substituted benzoxazole 5 (52%).
A crystal of 38 from chloroform–hexane, with approximate
dimensions of 0.40 × 0.30 × 0.60 mm, was used for the X-ray
study.
X-Ray crystal structure determination of S-2-(1,3-benzoxazol-2-
yl)-2,2-diphenylethyl 2-methylpropanethioate 10‡
Crystal data. C15H19NO3S2, M = 325.44. Monoclinic, space
group P21, a = 6.375(2), b = 11.908(2), c = 10.866(2) Å, β =
98.39(1), V = 816.0 Å3, Z = 2, Dc = 1.32 g cmϪ3. Colorless rods.
A crystal of 10 from chloroform–hexane, with approximate
dimensions of 0.70 × 0.40 × 0.40 mm, was mounted on a glass
fiber and used for the X-ray study.
F(000) = 344. µ(Mo-Kα) 2.1 cmϪ1
.
Data collection, structure solution and refinement. Out of
1594 total reflections, 1474 having intensities greater than 3.0
σ(I) were used in the refinements. Least-squares refinement
terminated at 0.031 (Rw 0.039).
Atomic coordinates, bond lengths and angles and thermal
parameters of X-ray crystal structures of 10, 22, 37 and 38
have been deposited with the Cambridge Crystallographic Data
Centre.‡
Crystal data. C25H23NO2S, M = 401.52. Monoclinic, space
group P21/c, a = 11.060(5), b = 10.059(3), c = 19.726(10) Å,
β = 92.26(3)Њ, V = 2192.9 Å3, Z = 4, Dc = 1.22 g cmϪ3. Colorless
rods. F(000) = 816. µ(Mo-Kα) 1.6 cmϪ1
.
‡ Tables of crystal data are available as supplementary data. For direct
electronic access see http://www.rsc.org/suppdata/p1/b0/b002548h/
J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046
3045

View Article Online
Y. Mori, I. Iida and A. Hosomi, J. Chem. Soc., Perkin Trans. 1,
1996, 921; (c) T. Nishio, J. Chem. Soc., Perkin Trans. 1, 1997, 889;
(d) T. Nishio and M. Oka, Helv. Chim. Acta, 1997, 80, 388; (e) Part of
this work was reported in preliminary form: T. Nishio, J. Chem. Soc.,
Perkin Trans. 1, 1998, 1007; ( f ) T. Nishio, J. Chem. Soc., Perkin
Trans. 1, 1999, 1151.
References
1 (a) A. Ohno, Int. J. Sulfur Chem., Part B, 1971, 6, 183; (b) J. D. Coyle,
Chem. Soc. Rev., 1975, 4, 523; J. D. Coyle, Tetrahedron, 1985, 41,
5395; (c) P. de Mayo, Acc. Chem. Res., 1976, 9, 52; (d) N. J. Turro,
V. Ramamurthy, W. Cherry and W. Farneth, Chem. Rev., 1978, 78,
125; (e) V. Ramamurthy, in Organic Photochemistry, ed. A. Padwa,
Marcel Dekker, New York, 1985, vol. 7, p. 231.
2 (a) M. Machida, K. Oda, E. Sato and Y. Kanaoka, Yuki Gosei
Kagaku Kyokaishi, 1986, 44, 1071; (b) M. Sakamoto, T. Fujita,
S. Watanabe and T. Nishio, Yuki Gosei Kagaku Kyokaishi, 1994, 52,
658; (c) M. Sakamoto and T. Nishio, Rev. Heteroat. Chem., 12, 53;
(d) J. D. Coyle and P. A. Rapley, J. Chem. Soc., Perkin Trans. 1, 1986,
2273 and references cited therein.
5 T. Nishio and K. Shiwa, unpublished results.
6 (a) A. Dondoni, A. Battagilia and P. Giorgianni, J. Chem. Soc.,
Chem. Commun., 1977, 43; A. Dondoni, A. Battagilia and P.
Giorgianni, J. Org. Chem., 1980, 45, 3766; (b) J. Mulzur and T.
Kerkmann, Angew. Chem., Int. Ed. Engl., 1980, 19, 466; (c) E.
Schaumann, H. G. Bauch and G. Adwidjaja, Angew. Chem., Int. Ed.
Engl., 1981, 20, 613; (d) M. Sakamoto, T. Ishida, T. Fujita and S.
Watanabe, J. Org. Chem., 1992, 57, 2422.
3 (a) T. Nishio and M. Sakamoto, Rev. Heteroat. Chem., 12, 23;
(b) K. Oda, M. Sakai and M. Machida, Chem. Pharm. Bull., 1997, 45,
584 and references cited therein.
7 (a) O. Ivanciuc, J. Chem. Inf. Comput., 1996, 36, 612; (b) G. Mock,
J. McClarin and D. Smith, Sci. Comput. Autom., 1992, 8, 29; (c)
W. R. Winchester and M. P. Doyle, J. Am. Chem. Soc., 1992, 114,
9243.
4 (a) T. Nishio, J. Chem. Soc., Perkin Trans. 1, 1995, 561; (b) T. Nishio,
3046
J. Chem. Soc., Perkin Trans. 1, 2000, 3039–3046