Formation of Thioaldehyde Intermediates by Thermolysis of Sulfoxides Bearing Some Heteroaromatics

Article abstract of DOI:10.1021/jo9700181

Thermal reactions of phenacyl sulfoxide bearing heterocycles, such as a 2-benzothiazolyl or N-oxypyridyl group, in the presence of 2,3-dimethyl-1,3-butadiene afforded 6-benzoyl-5,6-dihydro-3,4-dimethyl-2H-thiapyran in good yield. This product is considered to be formed by the Diels-Alder reaction of a diene with thioaldehyde formed initially by the decomposition of sulfoxides.

Full text of DOI:10.1021/jo9700181

9018
J . Org. Chem. 1997, 62, 9018-9023
F or m a tion of Th ioa ld eh yd e In ter m ed ia tes by Th er m olysis of
Su lfoxid es Bea r in g Som e Heter oa r om a tics
Hiroyuki Morita,* Masahiro Takeda, Takayoshi Fujii, Toshiaki Yoshimura, and
Choichiro Shimasaki
Department of Chemical and Biochemical Engineering, Faculty of Engineering, Toyama University,
3190 Gofuku, Toyama 930, J apan
Received J anuary 2, 1997 (Revised Manuscript Received October 22, 1997X)
Thermal reactions of phenacyl sulfoxide bearing heterocycles, such as a 2-benzothiazolyl or
N-oxypyridyl group, in the presence of 2,3-dimethyl-1,3-butadiene afforded 6-benzoyl-5,6-dihydro-
3,4-dimethyl-2H-thiapyran in good yield. This product is considered to be formed by the Diels-
Alder reaction of a diene with thioaldehyde formed initially by the decomposition of sulfoxides.
In tr od u ction
molytic condition and, thus, the studies of its scope and
limitations are interesting.
The thermolysis of alkyl sulfoxides having a â-hydro-
gen is well-known to form sulfenic acid and alkene
through an Ei elimination mechanism.1 Mislow and co-
workers reported that thermolytic reactions of alkyl
sulfoxides having no â-hydrogen, such as benzyl p-tolyl
sulfoxide, afforded bibenzyl and p-tolylthiolsulfinate, and
on the thermal reaction of an optically active sulfoxide
the racemization of the sulfoxide was observed.2 They
also reported that the first step of this reaction is the
homolytic cleavage of S-C (alkyl) of benzyl p-tolyl
sulfoxide, and that no rearrangement of sulfoxide to a
sulfenate ester was observed. Recently, J enks and Guo
have reported that photolytic reaction of benzyl p-tolyl
sulfoxide afforded benzaldehyde, benzyl alcohol, mercap-
totoluene, and tolyl disulfide as major products, and from
the mechanistic study it was reported these products
were formed through a benzyl p-tolylsulfenate intermedi-
ate arising from the initial photolytic rearrangement of
the starting sulfoxide.3 Furukawa and co-workers have
also reported a similar intermediate in the photolysis of
naphtho[1,8-de]dithiin monoxide.4
Concerning the synthetic methods to generate rather
labile thioaldehydes, a recent review7 and many reports
have already been published. For example, Vedejs et al.
used a photochemical fragmentation of R-thioacetophe-
none derivatives to generate a variety of substituted
thioaldehydes which were finally trapped as adducts with
1,3-diene derivatives.8 Baldwin and Lopez studied the
thermolysis of thiolsulfinates in which thioaldehydes
were trapped as 9,10-dimethylanthracene adducts.9 In
a more convenient procedure, Kirby et al. demonstrated
that base-promoted reaction of sulfenyl compounds, such
as sulfenyl chloride,10 N-thiophthalimide,11 sodium thio-
sulfate S-ester,12 and thiolsulfonate derivatives,13 can be
widely used for the generation of thioaldehydes.
To compare with these results and to gain further
insight into this reaction, we studied the thermolytic
reaction of various sulfoxides bearing heterocycles in the
presence of dienes.
Resu lts a n d Discu ssion
Recently, we have reported that the thermolytic reac-
tion of phenacyl sulfoxide bearing heterocycles such as
benzothiazole or N-oxypyridine, in the presence of 2,3-
dimethyl-1,3-butadiene afforded 6-benzoyl-5,6-dihydro-
3,4-dimethyl-2H-thiapyran and the hydroxy-substituted
heterocycle in good yield.5 The former product is con-
sidered to be formed by the Diels-Alder reaction of
thioaldehyde formed by the 1,2-elimination of aryl phen-
acyl sulfenate generated by the rearrangement of the
starting sulfoxide, which resulted in the cleavage of the
S-C (aryl) bond and recombination of the C (aryl)-O
(sulfoxide) bond.
Th er m a l Rea ction s of P h en a cyl Su lfoxid es Ha v-
in g Heter oa r om a tics. Thermolytic reactions of phen-
acyl sulfoxides bearing aromatic or heteroaromatic groups
in dioxane at 100 °C in the presence of 2,3-dimethyl-1,3-
butadiene for 24 h were studied. The results are sum-
marized in Table 1. In the case of phenacyl sulfoxide
having an N-oxypyridyl group (1a ), 6-benzoyl-5,6-dihy-
dro-3,4-dimethyl-2H-thiapyran (7a ) was obtained in 85%
(7) Okazaki, R. In Organosulfur Chemistry; Page, P., Eds; Academic
Press: London, 1995; pp 225-258.
(8) Vedejs, E.; Eberlein, T. H.; Varie, D. L. J . Am. Chem. Soc. 1982,
104, 1445. Vedejs E., Eberlein, T. H.; Mazur, D. J .; McClure, C. K.;
Perry, D. A.; Ruggeri, R.; Schwartz, E.; Stults, J . S.; Varie, D. L.; Wilde,
R. G.; Wittenberger, S. J . Org. Chem. 1986, 51, 1556. Vedejs E. Perry,
D. A.; Houk, K. N.; Rondan, N. G. J . Am. Chem. Soc. 1983, 105, 6999.
Vedejs E.; Stults, J . S.; Wilde, R. G. J . Am. Chem. Soc. 1988, 110, 5455.
Vedejs, E.; Eberlein, T. H.; Wilde, R. G. J . Org. Chem. 1988, 53, 2220.
Vedejs, E.; Stults, J . S. J . Org Chem. 1988, 53, 2227.
(9) Baldwin, J . E.; Lopez, R. C. J . Chem. Soc., Chem. Commun. 1982,
1029.
Although a similar photolytic reaction has been re-
ported in the carbonyl methyl cyclic sulfoxide system,6
this reaction mode is the first example under a ther-
* Corresponding author: telephone: +81-764-45-6851. FAX: +81-
764-45-6703. e-mail:morita@sci.toyama-u.ac.jp.
X Abstract published in Advance ACS Abstracts, December 1, 1997.
(1) Shelton, J . R.; Davis, K. E. J . Am. Chem. Soc. 1967, 89, 718.
(2) Miller, E. G.; Rayner, D. R.; Thomas, H. T.; Mislow, K. J . Am.
Chem. Soc. 1968, 90, 4861.
(10) Bladon, C. M.; Ferguson, I. E. G.; Kirby, G, W.; Lochead, A.
W.; McDougall, D. C. J . Chem. Soc., Chem. Commun. 1983, 423. Kirby,
G. W.; Mahajan, M. P.; Rahman, M. S. J . Chem. Soc., Perkin Trans 1
1991, 2033.
(3) Guo, Y.; J enks, W. S. J . Org. Chem. 1995, 60, 5480.
(4) Furukawa, N.; Fujii, T.; Kimura, T.; Fujiwara, H. Chem. Lett.
1994, 1007.
(5) Morita, H.; Takeda, M.; Kamiyama, H.; Hashimoto, T.; Yoshimu-
ra, T.; Shimasaki, C.; Tsukurimichi, E. Tetrahedron Lett. 1996, 37,
3739.
(11) Kirby, G. W.; Lochead, A. W. J . Chem. Soc., Chem. Commun.
1982, 1325. Capozzi, G.; Menichetti, S.; Nativi, C.; Rosi, A.; Valle, G.
Tetrahedron 1992, 9023.
(12) Kirby, G. W.; Lochead, A. W.; Scheldrake, G. N. J . Chem. Soc.,
Chem. Commun. 1984, 922.
(13) Kirby, G. W.; Lochead, A. W.; Scheldrake, G. N. J . Chem. Soc.,
Chem. Commun. 1984, 1469.
(6) Kowalewski, R; Margaretha, P. Helv. Chim. Acta 1993, 76, 1251.
S0022-3263(97)00018-2 CCC: $14.00 © 1997 American Chemical Society

Thioaldehyde Intermediates by Thermolysis of Sulfoxides
J . Org. Chem., Vol. 62, No. 26, 1997 9019
Ta ble 1. Th e Rea ction of P h en a cyl Su lfoxid e Bea r in g
Heter ocycle in th e P r esen ce of Dim eth yl Bu ta d ien e
Ta ble 2. Th er m a l Rea ction of 2-Ben zoth ia zolyl
Su lfoxid e Der iva tives in th e P r esen ce of
Dim eth ylbu ta d ien e
yield, although the isolated yield of hydroxypyridine
N-oxide was extremely low (entry 1). The reason for low
yield is considered to be due to the polar nature of this
product, as the NMR analysis of the crude reaction
mixture indicated quantitative formation. In the cases
of phenacyl sulfoxides bearing a 2-pyridyl (2a ), 4-pyridyl
(3a ), and 2-pyrimidyl group (4a ), 7a was also obtained
albeit in rather lower yields of 10, 19, and 26%, respec-
tively (entries 2, 3, and 4), though other desired products,
i.e., 2-hydroxy- and 4-hydroxypyridine and 2-hydroxypy-
rimidine were hardly obtained, or not isolated.
In the reaction of phenacyl sulfoxides attached to
simple aromatics, e.g., a phenyl group, none of the desired
product was formed; only the starting material and the
corresponding sulfide in 15% yield were isolated. The
reason phenyl phenacyl sulfoxide did not afford 7a
seemed to be the lower electron-withdrawing effect of the
phenyl group compared with an N-oxypyridyl group.
Therefore, the thermolytic reactions of phenacyl sulfox-
ides having electron-withdrawing groups on the phenyl
ring such as p-nitrophenyl and 2,3,5,6-tetrafluorophenyl
were studied. However, the thermolytic reactions of both
p-nitrophenyl and 2,3,5,6-tetrafluorophenyl sulfoxides did
not proceed at all, and the complete recovery of the
starting material was observed. In contrast, the ther-
molysis of phenacyl sulfoxide having electron-rich het-
erocyclic rings, such as thiophene (5a ), was also studied,
but again resulted in complete recovery of the starting
material (entry 5).
because of the less polar nature of 8a when compared to
hydroxypyridine N-oxide. Therefore, various benzothia-
zolyl sulfoxide derivatives were prepared and used to
obtain further mechanistic details of this thermolytic
reaction.
Th er m a l Rea ction s of Ben zoth ia zolyl Su lfoxid e
Der iva tives in th e P r esen ce of Dien e a n d Ba se.
Thermal reactions of benzyl-(6b ), cyanomethyl-(6c),
(ethoxycarbonyl)methyl-(6d ), acetylmethyl-substituted
sulfoxide (6e) having a 2-benzothiazolyl group under
similar conditions in the presence of a diene were studied,
and the results are summarized in Table 2. The com-
pound 6b did not show the desired reaction, giving
complete recovery of starting material. Introduction of
acidic R-hydrogens in the benzothiazolyl substituted
sulfoxides, as in 6c-e, unexpectedly, did not effect the
thermal reaction, and hence resulted in the recovery of
the starting material. One reason the thermolytic reac-
tions of 2-benzothiazolyl sulfoxides in entries 8 and 10
did not proceed may be due to the relatively poor acidity
of R-hydrogens when compared with benzoyl-substituted
sulfoxide 6a . In the case of 6c the R-hydrogen acidity is
expected to be stronger than that of 6a ; however, 6c did
not afford the desired product at all. This result suggests
that not only the R-hydrogen acidity but also another
factor is related to effect the reaction. One possibility is
that the reaction is initiated from the enol 6a ′′ rather
than keto form 6a ′ as mentioned later.
It seems clear that not only a simple electron-
withdrawing effect but also the nitrogen-containing
heterocyclic system play an important role to afford the
product 7a in this reaction. To study the effect of
nitrogen-containing heterocycles other than pyridine, the
thermolysis of 2-benzothiazolyl phenacyl sulfoxide (6a )
was carried out under quite similar conditions (entry 6).
In this case the desired product, dihydrothiapyran 7a ,
was obtained in 73% yield together with 2-hydroxyben-
zothiazole (8a ) in good isolated yield of 83%, probably
To clarify this consideration, reactions with the diene
in the presence of triethylamine were studied, expecting
the effect of “an outer-base”. In the cases of 6b-d , the
reactions still did not proceed at all (entries 5, 7, and 9),
while, as expected, the reaction of acetylmethyl sulfoxide
6e in the presence of 1.5 equiv of triethylamine afforded
6-acetyl-5,6-dihydro-3,4-dimethyl-2H-thiapyran (7e) and

9020 J . Org. Chem., Vol. 62, No. 26, 1997
Morita et al.
Sch em e 1
Sch em e 2
studied. These results ruled out a radical mechanism
as there was no significant effect of either additive or
solvent on the product distribution.
Concerning the mechanism, the results in Tables 1 and
2 suggest the following: (i) In this reaction, a phenacyl
group is necessary to provide highly enough acidic
R-hydrogens (entries 1-4 and 6 in Table 1 and entries
1-3 in Table 2). (ii) A simple electron-withdrawing effect
is not enough for this reaction to proceed as entry 6 in
Table 2 demonstrates. (iii) An electron-rich aromatic
ring, such as a thienyl group, is not effective for this
reaction (entry 5 in Table 1). (iv) A 2-benzothiazole
moiety is useful as well as an N-oxide moiety as a
heterocyclic substituent. 2-Pyridyl and 2-pyrimidyl sul-
foxides (entries 2 and 4 in Table 1) also lead to the desired
products though the yields are rather poor. This result
seems to indicate that these nitrogen-containing het-
eroaryl groups are related in the hydrogen abstraction
step as internal bases forming a five- or six-membered
cyclic transition state. However, even 4-pyridyl sulfoxide
3a as in entry 3 in Table 1 was found to afford the desired
product; hence, an intermolecular hydrogen abstraction
mechanism is also involved. In fact, as already men-
tioned, the addition of triethylamine in the thermolysis
increased the yield of the desired product as in entries
10 and 11 in Table 2.
8a in 39% and 70% yield, respectively (entry 11).
A
possible reason the reactions of sulfoxides 6b and 6d did
not proceed is that triethylamine was not a strong enough
base to afford the intermediate 9 and/or 10′ as shown in
Scheme 1. The reaction of 6a with a diene in the
presence of the stronger base potassium tert-butoxide
was then studied; however, in dioxane at 60 °C it afforded
a complex mixture of products containing 8a and ben-
zothiazole (8b), in 38 and 20% yield, respectively.
The reaction of 6d with 10 equiv of 2,3-dimethyl-1,3-
butadiene in the presence of 1.5 equiv of triethylamine
under more forcing conditions, i.e., at 150 °C, was also
studied. (cf. eq 1 in Scheme 2.) Unexpectedly, 2-(ethoxy-
carbonyl)-2H-thiapyran (7d 1) and benzothiazole (8b) were
formed in 26 and 56% yield, respectively, and 6d was
recovered in 36% yield; however, 6c was still unreactive
under these conditions. In this reaction, a different
mechanism is obviously operating because of the com-
plete lack of the products 7d and 8a . The product 7d 1
was considered to be formed via Pummerer rearrange-
ment of the corresponding dihydrothiapyran S-oxide 7d 2
initially formed (cf. eq 2 in Scheme 2). The same
reactions with similar compounds were reported by
Zwanenburg and co-workers previously.14 The concomi-
tant formation of 8b instead of 8a also support the sulfine
formation pathway in the thermolysis of 6d under these
conditions; however, the mechanism for the sulfine
formation is not certain at present.
The above considerations suggest a possible mecha-
nism for the thermolytic reaction of phenacyl sulfoxides
attached to heterocycles as illustrated in Scheme 1 using
benzothiazole as the representative heterocycle. This
involves the abstraction of an R-hydrogen atom (path a)
or of a hydroxy-hydrogen after enolization (path b) by
the nitrogen atom of the benzothiazolyl group to afford
an intermediate 9, by ipso-attacking of the oxygen atom
of the sulfinyl group to the R-carbon of the benzothiazole
ring. Path b would be more plausible despite the
formation of seven-membered transition state 6a ′′ be-
cause of the complete recovery of the starting material
in the case of cyanomethyl sulfoxide 6c as already
mentioned. Similar ipso-substitutions on the heteroaro-
matic rings with nucleophiles are widely accepted.15 The
The reaction of 2-benzothiazolyl phenacyl sulfoxide (6a )
in the presence of 20 equiv of 2,6-di-tert-butyl-4-meth-
ylphenol (BHT) was carried out in order to test the effect
of the radical scavenger under similar conditions (entry
2). The reaction of 6a in methanol (entry 3) was also
(14) Lenz, B. G.; Regeling, H.; van Rozendaal, H. L. M.; Zwanenburg,
B. J . Org. Chem. 1985, 50, 2930.

Thioaldehyde Intermediates by Thermolysis of Sulfoxides
Sch em e 3
J . Org. Chem., Vol. 62, No. 26, 1997 9021
Ta ble 3. Th er m a l Rea ction of 2-Ben zoth ia zolyl
Su bstitu ted -P h en a cyl Su lfoxid es in th e P r esen ce of
Dien e
suggest that a rather large substituent effect rules out
the radical mechanism and the hydrogen abstraction step
in Scheme 1 is rather important as already mentioned.
Cr ossover Exp er im en t Usin g Su lfoxid e (12) a n d
18O Labeled-Su lfoxide (6a-18O). In considering Scheme
1 as depicted, it is important to clarify the existence of
equilibrium between the sulfenate intermediate 10′ and
the starting sulfoxide and also to define the origin of the
oxygen in the hydroxy heterocycles, such as 8a , formed
in this reaction. Therefore, the crossover reaction be-
tween methoxy-substituted benzothiazolyl phenacyl sul-
foxide (12) and 2-benzothiazolyl phenacyl 18O-sulfoxide
(6a -18O) was studied. 6a -18O was prepared by the reac-
tion of the corresponding sulfide and tert-butyl hypochlo-
rite in the presence of excess H218O (97 atom %).17 The
estimation of 18O-content in this sulfoxide was not
performed directly by mass spectrometry, because of the
absence of the molecular ion peak of this sulfoxide in
mass analysis. However, in the IR spectrum of this 18O-
labeled sulfoxide, the absorption band of S-O stretching
vibration shifted completely to a lower wavenumber by
40 cm-1 than that of 16O sulfoxide at 1020 cm-1. From
this difference of absorption band, the content of the 18O
atom of (6a -18O) prepared was sufficiently high for the
18O tracer experiment. The thermolytic reaction of a 1:1
mixture of 12 and 6a -18O under the usual conditions was
carried out. The results are shown in Scheme 3. Dihy-
drothiapyran derivative 7a and 2-hydroxybenzothiazole-
18O (8a -18O) and 2-hydroxy-5-methoxybenzothiazole (13)
were isolated using PLC eluting with ethyl acetate/
hexane (1:5) in 80, 98, and 77% yield, respectively. The
18O content of 8a and 13 was found to be 83 and 0% by
comparing the mass spectrum with those of products
obtained in the reaction of unlabeled phenacyl sulfoxide.
These results indicate clearly that the rearrangement of
the corresponding sulfoxide to sulfenate intermediate 10′
takes place intramolecularly.
cleavage between the S-O bond of sulfenate intermediate
10′ affords thioaldehyde 11 which is subsequently trapped
as the cycloadduct, 6-benzoyl-5,6-dihydro-3,4-dimethyl-
2H-thiapyran (7a ), with 2,3-dimethyl-1,3-butadiene by
the hetero Diels-Alder reaction.16 The direct detection
of a sulfenate ester intermediate in the case of 6a was
unsuccessfully attempted by 1H NMR spectrometry,
suggesting the rapid decomposition of the sulfenate ester
intermediate 10′ to products.
Th e Effect of Su bstitu en ts on th e P h en yl Rin g in
th e 2-Ben zoth ia zolyl 4′-Su bstitu ted P h en a cyl Su l-
foxid e. The effect of several substituents on the isolated
yield was examined in the 2-benzothiazolyl sulfoxide
system because of the difficulty of the determination of
substituent effects by direct kinetic measurements. The
results are summarized in Table 3. In the reaction of
p-methoxy-substituted phenacyl sulfoxide (6f, entry 1) in
dioxane at 100 °C for 3.5 h, conversion of the starting
sulfoxide 6f was observed as 31% with the recovery of
the starting material, and methoxy-substituted products
7f and 8a were obtained in 28 and 27% yield, respec-
tively, by NMR analysis. Under the same conditions,
changing the phenyl substituent, to methyl (6g) and then
hydrogen (6a ) and further to chloro (6h ) and nitro (6i)
increased the conversion % of the thermolysis gradually
to 64, 76, 94, and 100%, respectively. These results also
Exp er im en ta l Section
All melting points were uncorrected. 1H NMR (400 MHz)
and 13C NMR (100 MHz) spectra were recorded in CDCl3 using
TMS as internal standard. Mass spectra were recorded using
EI (Ea ) 70 eV) ionization. The elemental analyses were
performed by the Microanalytical Laboratory of the Depart-
ment of Chemical and Biochemical Engineering of Toyama
University. All the reactions were monitored by TLC using
Silica Gel 60 F254 TLC plates, and products were separated
by column chromatography using Silica Gel 60 and also by
preparative layer chromatography using 60 PF254 with UV
detection. All reagents were of highest quality and were
further purified by distillation or recrystallization. Solvents
were further purified by general methods.
Gen er a l P r oced u r e for P r ep a r a tion of Su lfoxid es 1a -
5a , 6a -i, 12. To a stirred solution of sulfide in CHCl3 or
CH2Cl2 was added m-CPBA (>70%) in CHCl3 or CH2Cl2 at 0
°C. Addition of an equimolar amount of peracid calculated
from the activity of the used m-CPBA resulted in the formation
of sulfone; therefore, a ca. 30% less amount of the peracid was
(15) Okamura, H.; Miura, M.; Takei, H. Tetrahedron Lett. 1979, 43.
Okamura, H.; Miura, M.; Takei, H. Tetrahedron Lett. 1979, 3425.
Takei, H.; Miura, M.; Sugiura, H.; Okamura, H. Chem. Lett. 1979,
1447. Furukawa, N.; Konno, Y.; Tsuruoka, M.; Fujiwara, H.; Ogawa,
S. Chem. Lett. 1989, 1501.
(16) Hetero Diels-Alder Methodology in Organic Synthesis; Boger,
D. L., Weinreb, S. M., Eds.; Academic Press: London, 1987.
(17) Kobayashi, M.; Ohkubo, H.; Shimizu, T. Bull. Chem. Soc. J pn.
1986, 59, 503.

9022 J . Org. Chem., Vol. 62, No. 26, 1997
Morita et al.
used, and the reaction mixture was stirred at 0 °C until the
starting sulfide had disappeared by TLC monitoring. The
reaction mixture was washed with saturated aqueous NaH-
CO3. The aqueous layer was extracted with CHCl3. The
combined organic layer was washed with brine and dried over
MgSO4. After evaporation of the solvent, the crude product
was obtained. Purification of the sulfoxide was done by
chromatography on silica gel and/or recrystallization.
CH2Cl2-hexane). 1H NMR (CDCl3) δ 1.25 (t, J ) 7.2 Hz, 3H),
4.12 (d, J ) 14.4 Hz, 1H), 4.24 (d, J ) 14.4 Hz, 1H), 4.26 (q, J
) 7.2 Hz, 2H), 7.49-7.60 (m, 4H), 8.00-8.03 (m, 2H), 8.06-
8.08 (m, 2H). 13C NMR (CDCl3) δ 14.0, 60.6, 62.5, 122.3, 124.1,
126.5, 127.1, 136.2, 153.6, 164.0, 175.9. IR (KBr) 1720, 1060
cm-1
. Anal. Calcd for C11H11NO3S2: C, 49.05; H, 4.12; N,
5.20%. Found: C, 48.79; H, 3.99; N, 5.01%.
2-Ben zoth ia zolyl Acetylm eth yl Su lfoxid e (6e). Spectral
data: yield 76%: mp 127 °C (white crystals from EtOAc-
hexane). 1H NMR (CDCl3) δ 2.34 (s, 3H), 4.21 (d, J ) 14.8
Hz, 1H), 4.36 (d, J ) 14.8 Hz, 1H) 7.50-7.61 (m, 2H), 8.00-
8.02 (m, 1H), 8.06-8.09 (m, 1H). 13C NMR (CDCl3) δ 31.7,
67.7, 122.3, 124.1, 126.5, 127.1, 136.2, 153.7, 175.9, 198.0. IR
(KBr) 1710, 1050 cm-1. Anal. Calcd for C10H9NO2S2: C, 50.19;
H, 3.79; N, 5.85%. Found: C, 50.36; H, 3.80; N, 5.85%.
2-Ben zoth ia zolyl 4′-Meth oxyp h en a cyl Su lfoxid e (6f).
Spectral data: yield 64%: mp 143 °C (white crystals from
EtOAc-hexane). 1H NMR (CDCl3) δ 3.87 (s, 3H), 4.75 (d, J )
15.2 Hz, 1H), 4.84 (d, J ) 15.2 Hz, 1H), 6.91-6.94 (m, 2H),
7.50 (dt, J ) 1.2, 8.0 Hz, 1H), 7.57 (dt, J ) 1.6, 7.6 Hz, 1H),
N-Oxyp yr id yl P h en a cyl Su lfoxid e (1a ). Spectral data:
yield 27%: mp 126 °C (white crystals from EtOAc-hexane).
1H NMR (CDCl3) δ 4.56 (d, J ) 14.0 Hz, 1H), 5.24 (d, J ) 14
Hz, 1H), 7.44-7.61 (m, 5H), 7.81 (dd, J ) 2.0, 8.0 Hz, 1H),
7.94-7.97 (m, 2H), 8.22-8.24 (m, 1H). 13C NMR (CDCl3) 57.8,
124.6, 126.9, 127.2, 128.7, 128.7, 134.0, 136.2, 139.1, 153.0,
190.9. IR (KBr) 1670, 1050 cm-1
. Anal. Calcd for C13H11-
NO3S: C, 59.76; H, 4.24; N, 5.36%. Found: C, 59.56; H, 4.26;
N, 5.18%.
2-P yr id yl P h en a cyl Su lfoxid e (2a ). Spectral data: yield
66%: mp 92 °C (white crystals from EtOAc-hexane). 1H NMR
(CDCl3) δ 4.44 (d, J ) 14 Hz, 1H), 4.78 (d, J ) 14 Hz, 1H),
7.36-7.47 (m, 3H), 7.55-7.61 (m, 1H), 7.89-8.00 (m, 4H),
8.60-8.63 (m, 1H). 13C NMR (CDCl3) δ 62.6, 120.4, 124.9,
128.6, 133.9, 136.0, 138.0, 149.5, 163.6, 191.2. IR (neat) 1680,
1050 cm-1. Anal. Calcd for C13H11NO2S: C, 63.66; H, 4.52;
N, 5.71%. Found: C, 64.02; H, 4.48; N, 5.67%.
7.90-7.94 (m, 2H), 7.99-8.02 (m, 1H), 8.06-8.08 (m, 1H). 13
C
NMR (CDCl3) δ 55.61, 65.24, 114.1, 122.3, 124.1, 126.3, 127.0,
128.7, 131.3, 136.3, 153.7, 164.6, 176.7, 188.8. IR (KBr) 1650,
1580, 1050 cm-1. Anal. Calcd for C16H13NO3S2: C, 57.99; H,
3.95; N, 4.23%. Found: C, 57.97; H, 4.00; N, 4.11%.
4-P yr id yl P h en a cyl Su lfoxid e (3a ). Spectral data: yield
41%: mp 114-118 °C (white crystals from EtOAc-hexane)
dec. 1H NMR (CDCl3) δ 4.39 (dd, J ) 0.8, 14.8 Hz, 1H), 4.60
(dd, J ) 0.8, 14.8 Hz, 1H), 7.47-7.50 (m, 2H), 7.61-7.65 (m,
2H), 7.87-7.99 (m, 3H), 8.78-8.79 (m,2H). 13C NMR (CDCl3)
δ 65.5, 118.5, 128.7, 128.9, 134.5, 135.5, 150.5, 153.8, 190.9.
IR (neat) 1660, 1040 cm-1. Anal. Calcd for C13H11NO2S: C,
63.66; H, 4.52; N, 5.71%. Found: C, 63.70; H, 4.52; N, 5.70%.
2-P yr im id yl P h en a cyl Su lfoxid e (4a ). Spectral data:
44%: mp 114-119 °C (white crystals from EtOAc-hexane)
dec. 1H NMR (CDCl3) δ 4.67 (d, J ) 15.0 Hz, 1H), 4.88 (d, J
) 15.0 Hz, 1H), 7.28-7.58 (m, 3H), 7.59-7.60 (m, 1H), 7.93-
7.95 (m, 2H), 8.89 (d, J ) 4.8 Hz, 2H). 13C NMR (CDCl3) δ
61.5, 121.9, 128.7, 134.0, 135.9, 158.5, 172.6, 191.2. IR (KBr)
1680, 1070 cm-1. Anal. Calcd for C12H10N2O2S: C, 58.52; H,
4.09; N, 11.37%. Found: C, 58.65; H, 4.10; N, 11.19%.
2-Th ien yl P h en a cyl Su lfoxid e (5a ). Spectral data: yield
49%: mp 87 °C (white crystals from EtOAc-hexane). 1H
NMR(CDCl3) δ 4.53 (dd, J ) 0.8, 14.8 Hz, 1H), 4.83 (dd, J )
0.8, 14.8 Hz, 1H), 7.08-7.10 (m, 1H), 7.47-7.50 (m, 3H), 7.59-
7.66 (m, 2H), 7.90-7.92 (m, 2H). 13C NMR (CDCl3) δ 66.9,
127.5, 128.7, 128.9, 130.0, 131.5, 134.3, 135.7, 145.2, 191.2.
2-Ben zoth ia zolyl 4′-Meth ylp h en a cyl Su lfoxid e (6g).
Spectral data: yield 57%: mp 147.5-153.3 °C (white crystals
from EtOAc-hexane) dec. 1H NMR (CDCl3) δ 2.17 (s, 3H),
4.77 (d, J ) 15.1 Hz, 1H), 4.87 (d, J ) 15.1 Hz, 1H), 7.27 (d,
J ) 8.4 Hz, 2H), 7.50 (dt, J ) 0.8, 8.4 Hz, 1H), 7.58 (dt, J )
1.2, 7.2 Hz, 1H), 7.84 (d, J ) 8.4 Hz, 2H), 7.99-8.02 (m, 1H),
8.06-8.08 (m, 1H), 7.99-8.02 (m, 1H), 8.06-8.08 (m, 1H). 13
C
NMR (CDCl3) δ 21.8, 65.4, 122.3, 124.1, 126.3, 127.0, 128.9,
129.6, 133.2, 136.3, 145.7, 153.7, 190.1. IR (KBr) 1650, 1290,
1050 cm-1. Anal. Calcd for C16H13NO2S2: C, 60.93; H, 4.15;
N, 4.44%. Found: C, 60.47; H, 4.15; N, 4.20%.
2-Ben zoth ia zolyl 4′-Ch lor op h en a cyl Su lfoxid e (6h ).
Spectral data: yield 70%: mp 152-158 °C (white crystals from
EtOAc-hexane) dec. 1H NMR (CDCl3) δ 4.76 (d, J ) 14.9 Hz,
1H), 4.86 (d, J ) 14.9 Hz, 1H), 7.42-7.46 (m, 2H), 7.51 (dt, J
) 1.2, 8.0 Hz, 1H), 7.58 (dt, J ) 0.8, 7.2 Hz, 1H), 7.87-7.90
(m, 2H), 7.99-8.02 (m, 1H), 8.05-8.07 (m, 1H). 13C NMR
(CDCl3) δ 64.9, 122.3, 124.1, 126.5, 127.1, 129.3, 130.2, 134.0,
136.2, 141.1, 153.6, 176.1, 189.4. IR (KBr) 1660, 1060 cm-1
.
Anal. Calcd for C15H10ClNO2S2: C, 53.64; H, 3.00; N, 4.17%.
Found: C, 53.02; H, 3.03; N, 3.95%.
2-Ben zoth iazolyl 4′-Nitr oph en acyl Su lfoxide (6i). Spec-
tral data: yield 57%: mp 177-181 °C (white crystals from
EtOAc-hexane) dec. 1H NMR (CDCl3) δ 4.83 (d, J ) 14.8 Hz,
1H), 4.94 (d, J ) 14.8 Hz, 1H), 7.05-7.40 (m, 2H), 7.46-7.71
(m, 1H) 8.00-8.12 (m, 3H), 8.18-8.38 (m, 2H). 13C NMR
(CDCl3) δ 64.6, 122.4, 124.0, 124.1, 126.7, 127.3, 129.9, 136.2,
140.6, 150.8, 153.6, 175.4, 189.3. IR (KBr) 1680, 1520, 1350,
1050 cm-1. Anal. Calcd for C15H10N2O4S2: C, 52.04; H, 2.91;
N, 8.08%. Found: C, 52.07; H, 2.92; N, 7.95%.
IR (KBr) 1670, 1040 cm-1
. Anal. Calcd for C12H10O2S2: C,
57.58; H, 4.03%. Found: C, 57.78; H, 4.02%.
2-Ben zoth ia zolyl P h en a cyl Su lfoxid e (6a ). Spectral
data: yield 33%: mp 117-120 °C (white crystals from EtOAc-
hexane) dec. 1H NMR (CDCl3) δ 4.80 (d, J ) 14.8 Hz, 1H),
4.90 (d, J ) 14.8 Hz, 1H), 7.26-7.63 (m, 5H), 7.94-7.96 (m,
2H), 8.00-8.02 (m, 1H), 8.05-8.08 (m, 1H). 13C NMR (CDCl3)
δ 65.3, 122.3, 124.1, 126.4, 127.0, 128.8, 128.9, 134.4, 135.6,
136.3, 153.7 176.5, 190.5. IR (KBr) 1670, 1060 cm-1. Anal.
Calcd for C15H11NO2S2: C, 59.78; H, 3.68; N, 4.65%. Found:
C, 59.98; H, 3.68; N, 4.54%.
2-Ben zoth ia zolyl Ben zyl Su lfoxid e (6b). Spectral data:
yield 57%: mp 123 °C (white crystals from EtOAc-hexane).
1H NMR (CDCl3) δ 4.34 (d, J ) 13 Hz, 1H), 4.52 (d, J ) 13 Hz,
1H), 7.16-7.31 (m, 5H), 7.46-7.60 (m, 2H), 7.93-7.95 (m, 1H),
8.09-8.11 (m, 1H). 13C NMR (CDCl3) δ 62.8, 122.2, 123.9,
126.1, 126.9, 128.3, 128.7, 130.4, 133.7, 136.0, 153.7. IR (KBr)
1050 cm-1. Anal. Calcd for C14H11NOS2: C, 61.51; H, 4.06;
N, 5.12%. Found: C, 61.89; H, 4.19; N, 5.04%.
5-Meth oxy-2-ben zoth ia zolyl P h en a cyl Su lfoxid e (12).
Spectral data: yield 90%: mp 143 °C (white crystals from
EtOAc-hexane). 1H NMR(CDCl3) δ 3.91 (s, 3H), 4.78 (d, J )
15.2 Hz, 1H), 4.71 (d, J ) 15.2 Hz, 1H), 7.15 (dd, J ) 2.4, 8.8
Hz, 1H), 7.46-7.51 (m, 3H), 7.62 (t, J ) 7.6 Hz, 1H), 7.84 (d,
J ) 9.0 Hz, 1H), 7.94-7.96 (m, 2H).
13C NMR (CDCl3) δ 55.7,
65.3, 105.8, 117.1, 122.5, 128.3, 128.8, 128.9, 134.4, 135.6,
155.1, 159.5, 190.6. IR (KBr) 1670, 1050 cm-1. Anal. Calcd
for C16H13NO3S2: C, 57.99; H, 3.95; N, 4.23%. Found: C,
58.05; H, 4.03; N, 4.26%.
2-Ben zoth ia zolyl P h en a cyl 18O-Su lfoxid e (6a -18O). To
a stirred solution of 100 mg of 2-benzothiazolyl phenacyl
sulfoxide (0.33 mmol) and 0.12 mL (6.6 mmol) of H2O-18O (97%)
in 3 mL of CH3CN was added 0.043 mL of tert-BuOCl (0.38
mmol) at 0 °C. After stirring for 10 min at 0 °C, this mixture
was evaporated, and the residual product was rinsed with
ether to afford a white product. This product was recrystal-
lized from CH2Cl2-hexane to afford 35 mg of the pure 6a -18O
in 33% yield as white crystals: 1H NMR (CDCl3) δ 4.80 (d, J
) 14.8, 1H), 4.90 (d, J ) 14.8, 1H), 7.26-7.63 (m, 5H), 7.94-
7.96 (m, 2H), 8.00-8.02 (m, 1H), 8.05-8.08 (m, 1H). 13C NMR
2-Ben zoth ia zolyl Cya n om eth yl Su lfoxid e (6c). Spectral
data: yield 77%: mp 138 °C (white crystals from EtOAc-
hexane). 1H NMR (CDCl3) δ 4.11 (d, J ) 16.4 Hz, 1H), 4.31
(d, J ) 16.4 Hz, 1H), 7.53-7.64 (m, 2H), 8.03-8.05 (m,1H),
8.10-8.12 (m,1H). 13C NMR (CDCl3) δ 44.2, 110.3, 122.5,
124.4, 126.9, 127.4, 136.3, 153.5, 173.4. IR (KBr) 2225, 1060
cm-1
. Anal. Calcd for C9H6NOS2: C, 48.63; H, 2.72; N,
12.60%. Found: C, 48.58; H, 2.67; N, 12.43%.
2-Ben zoth ia zolyl (Eth oxyca r bon yl)m eth yl Su lfoxid e
(6d ). Spectral data: yield 77%: mp 59 °C (white crystals from

Thioaldehyde Intermediates by Thermolysis of Sulfoxides
J . Org. Chem., Vol. 62, No. 26, 1997 9023
(CDCl3) δ 65.3, 122.3, 124.1, 126.4, 127.1, 128.8, 128.9, 134.4,
Th er m olysis of 2-Ben zoth ia zolyl P h en a cyl Su lfoxid e
(6a ) in th e P r esen ce of Dien e a n d BHT. To 3 mL of 1,4-
dioxane was added 100 mg of 6a (0.335 mmol), and into this
solution were added freshly distilled 2,3-dimethyl-1,3-butadi-
ene (10 equiv) and 2,6-di-tert-butyl-4-methylphenol (20 equiv).
This mixture in a 10-mL Pyrex tube was degassed thoroughly
in vacuo at dry ice-acetone temperature, and the glass tube
was sealed. Then the mixture was heated at 100 °C for 24 h.
The reaction mixture was chromatographed on silica gel
preparative plate using EtOAc-hexane (1:5) as eluent to afford
53 mg of 7a (69%) and 48 mg of 8a (97%).
135.6, 136.3, 153.7, 176.5, 190.48. IR (KBr) 1670, 1020 cm-1
.
Gen er a l P r oced u r e of Th er m olytic Rea ction of Su l-
foxid e 1a -6a in th e P r esen ce of 2,3-Dim eth yl-1,3-bu ta -
d ien e. A 100 mg amount of the starting sulfoxide was
dissolved in 3 mL of dioxane, and into this solution was added
freshly distilled 2,3-dimethyl-1,3-butadiene. This mixture in
a 10-mL Pyrex tube was degassed thoroughly in vacuo at dry
ice-acetone temperature, and the glass tube was sealed. The
mixture was heated at 100 °C for 24 h and was chromato-
graphed on a silica gel preparative plate using EtOAc-hexane
as eluent.
Th e Effect of Su bstitu en ts on th e P h en yl Rin g in th e
2-Ben zoth ia zolyl 4′-Su bstitu ted P h en a cyl Su lfoxid e. To
1 mL of 1,4-dioxane was added 20 mg of 2-benzothiazolyl 4′-
substituted-phenacyl sulfoxide, and into this solution was
added 2,3-dimethyl-1,3-butadiene (10 equiv) freshly distilled.
This mixture in a 10-mL Pyrex tube was degassed thoroughly
in vacuo at dry ice-acetone temperature, and the glass tube
was sealed. Then the mixture was heated at 100 °C for 3.5 h.
The solvent of this reaction mixture was evaporated and dried
thoroughly in vacuo. The yields of products and recovery of
the starting sulfoxide were found from the NMR spectrometry
of this residue. The assignment of cycloadduct 7f-i was easily
performed by the comparison of the spectra of 7a .
Th er m olysis of N-Oxyp yr id yl P h en a cyl Su lfoxid e (1a )
in th e P r esen ce of Dien e. The reaction mixture was purified
on silica gel preparative plate using EtOAc-hexane (1:1) as
eluent to afford 75.8 mg of 7a (85%). Spectral data of 7a : 1H
NMR (CDCl3) δ 1.74 (s, 6H), 2.41-2.57 (m, 2H), 2.99 (s, 2H),
4.49 (m, 1H), 7.43-7.47 (m, 2H), 7.53-7.57 (m, 1H), 7.98-
8.01 (m, 2H). 13C NMR (CDCl3) δ 19.5, 20.1, 29.8, 32.7, 41.8,
122.6, 126.3, 128.5, 128.6, 133.0, 135.2, 195.6. IR (neat) 2900,
1670 cm-1
. Anal. Calcd for C14H16OS: C, 72.37; H, 6.94%.
Found: C, 72.28; H, 7.14%.
Th er m olysis of 2a . The reaction mixture was chromato-
graphed on silica gel preparative plate using EtOAc-hexane
(1:1) as eluent to afford 10 mg of 7a (10%) and 23 mg of
2-pyridyl phenacyl sulfide (24%).
Th er m olysis of 3a . The reaction mixture was chromato-
graphed on silica gel preparative plate using EtOAc-hexane
(1:1) as eluent to afford 13 mg of 7a (19%) and 39 mg of
4-pyridyl phenacyl sulfide (58%).
Spectral data of 7f: yield 28%. 1H NMR (CDCl3) δ 1.75 (s,
6H), 2.39-2.59 (m, 2H), 2.99 (d, J ) 15.6 Hz, 1H), 3.07 (d, J
) 15.6 Hz, 1H), 3.87 (s, 3H), 2.46 (dd, J ) 5.2, 6.0 Hz, 1H),
6.94 (d, J ) 8.9 Hz, 2H), 7.99 (d, J ) 8.9 Hz, 2H). 13C NMR
(CDCl3) δ 19.6, 20.2, 30.3, 33.1, 41.9, 55.5, 113.7, 122.7, 126.6,
128.1, 131.0, 163.5, 194.7. IR (neat) 3000-2900, 1670, 1600
Th er m olysis of 4a . The reaction mixture was chromato-
graphed on silica gel preparative plate using EtOAc-hexane
(1:5) as eluent to afford 20 mg of 7a and 23 mg of 2-pyrimidyl
phenacyl sulfide in 26% and 14% yield, respectively.
Th er m olysis of 6a . The reaction mixture was chromato-
graphed on silica gel preparative plate using EtOAc-hexane
(1:5) as eluent to afford 57 mg of 7a (73%) and 42 mg of
2-hydroxybenzothiazole (8a ) (83%). Spectral data of 8a : 1H
NMR (CDCl3): δ 7.14-7.18 (m, 2H), 7.26-7.31 (m, 1H), 7.40-
7.42 (m, 1H). 13C NMR (CDCl3): δ 111.7, 122.5, 123.3, 123.9,
cm-1
.
Spectral data of 7g: yield 63%. 1H NMR (CDCl3) δ 1.74 (s,
6H), 2.35-2.08 (m, 5H), 2.74-3.08 (m, 2H), 4.55 (t, J ) 5.5
Hz, 1H),7.22 (d, J ) 8.0 Hz, 2H), 7.89 (d, J ) 8.0 Hz, 2H). 13C
NMR (CDCl3) δ 19.6, 20.1, 21.6, 30.1, 32.9, 42.1, 122.7, 126.5,
128.8, 129.3, 132.7, 143.9, 195.6. IR (neat) 3000-2900, 1670,
1600, 1030 cm-1
.
Spectral data of 7h : yield 85%. 1H NMR (CDCl3) δ 1.75 (s,
6H), 2.41-2.56 (m, 2H), 3.00 (bs, 2H), 4.26 (t, J ) 5.4 Hz,
1H),7.43 (d, J ) 8.9 Hz, 2H), 7.94 (d, J ) 8.8 Hz, 2H). 13C
NMR (CDCl3) δ 19.6, 20.1, 29.8, 32.4, 41.7, 122.6, 126.2, 128.8,
130.1, 133.5, 139.4, 194.4. IR (neat) 3000-2950, 1680, 1090
126.5, 135.3, 172.9. IR (KBr) 3300-2400, 1640 cm-1
.
Th er m olysis of 6e in th e P r esen ce of Dien e a n d NEt3.
To 1.5 mL of 1,4-dioxane was added 100 mg of 6e (0.418 mmol),
and into this solution were added freshly distilled 2,3-di-
methyl-1,3-butadiene (471 µL, 10 equiv) and 87 µL of trieth-
ylamine (1.5 equiv). This mixture in a 10-mL Pyrex tube was
degassed thoroughly in vacuo at dry ice-acetone temperature,
and the glass tube was sealed. Then the mixture was heated
at 100 °C for 24 h. The reaction mixture was chromatographed
on silica gel preparative plate using EtOAc-hexane (1:5) as
eluent to afford 28 mg of 6-acetyl-5,6-dihydro-3,4-dimethyl-
2H-thiapyran (7e) (39%), 40 mg of 8a (70%), and 22 mg of
2-benzothiazolyl acetylmethyl sulfide (23%). Spectral data of
7e: 1H NMR (CDCl3) δ 1.70 (s, 6H), 2.28-2.43 (m, 5H), 2.94
(s, 2H), 3.59 (t, J ) 6.0 Hz, 1H). IR (neat) 3300-2400, 1640
cm-1. HRMS Calcd for C9H14OS: 170.0765. Found: 170.0761.
Th er m olysis of 2-Ben zoth ia zolyl (Eth oxyca r bon yl)-
m eth yl Su lfoxid e (6d ) in th e P r esen ce of Dien e a n d Ba se
a t 150 °C. To 3 mL of 1,4-dioxane was added 100 mg of 6d
(0.37 mmol), and into this solution were added freshly distilled
2,3-dimethyl-1,3-butadiene (0.42 mL, 10 equiv) and 77 µL of
triethylamine (0.556 mmol). This mixture in a 10-mL Pyrex
tube was degassed thoroughly in vacuo at dry ice-acetone
temperature, and the glass tube was sealed. Then the mixture
was heated at 150 °C for 24 h. The reaction mixture was
chromatographed on silica gel preparative plate using EtOAc-
hexane (1:5) as eluent to afford 19 mg of 7d 1 (26%), 28 mg of
7b (56%) and 36% recovery of the starting material.
cm-1
.
Spectral data of 7i: yield 89%. 1H NMR (CDCl3) δ 1.76 (s,
3H), 1.78 (s, 3H), 2.52 (bs, 2H), 2.94 (s, 2H), 4.46 (t, J ) 5.4
Hz, 1H), 8.14 (d, J ) 8.8 Hz, 2H), 8.31 (d, J ) 8.8 Hz, 2H). 13
C
NMR (CDCl3) δ 19.6, 20.1, 29.3, 31.8, 41.7, 122.4, 123.7, 125.9,
129.7, 140.1, 150.1, 193.3. IR (neat) 2950-3000, 1690, 1350
cm-1
.
Cr ossover Exp er im en t betw een 5-Meth oxy-Su bstitu -
ted -Ben zoth ia zolyl P h en a cyl Su lfoxid e (12) a n d 2-Ben -
zoth ia zolyl P h en a cyl 18O-Su lfoxid e (6a -18O) in th e P r es-
en ce of Dien e. To 1.8 mL of 1,4-dioxane were added 33 mg
of 12 (0.1 mmol) and 29 mg of 6a -18O (0.095 mmol), and into
this solution was added freshly distilled 2,3-dimethyl-1,3-
butadiene (10 equiv). This mixture in a 10-mL Pyrex tube was
degassed thoroughly in vacuo at dry ice-acetone temperature,
and the glass tube was sealed. Then the mixture was heated
at 100 °C for 1 h. The reaction mixture was chromatographed
on silica gel preparative plate using EtOAc-hexane (1:5) as
eluent to afford 35 mg of 7a (76%) and 14 mg of 8a -18O (98%)
and 13 (77%). The ratio of the parent peak and parent peak
plus 2 of 8a -18O (M ) 151) and 13 (M ) 165) in mass spectra
is 0.19 and 14.8. On the other hand, in the control experiments
using the unlabeled sulfoxide 6a and 12 the ratio of M+ and
M+ + 2 of both 8a and 13 is 14.8. Therefore, 18O content of
13 obtained in the crossover experiment was found to be 0%,
and for 8a -18O it was calculated to be 83%.
Spectral data of 7d 1: 1H NMR (CDCl3) δ 1.32 (t, J ) 7.0
Hz, 3H), 1.84 (s, 3H), 1.92 (s, 3H), 3.22 (s, 2H), 4.27 (q, J )
7.0 Hz, 2H), 7.09 (s, 1H). 13C NMR (CDCl3) δ 14.2, 17.3, 19.9,
31.6, 61.2, 124.1, 125.9, 127.6, 135.4, 164.9. IR (neat) 1730
Ack n ow led gm en t. We thank Toyo Kasei Kogyo Co.
and Takeda Chemical Industries Ltd. for gifts of het-
erocyclic thiols.
cm-1
.
Spectral data of 8b: 1H NMR (CDCl3): δ 7.20-7.53 (m, 2H),
7.67,-8.10 (m, 2H), 8.80 (s, CH, 1H). IR (neat) 1450, 1420,
870 cm-1
.
J O9700181