A novel consecutive three-component coupling-addition-SNAr (CASNAR) synthesis of 4H-thiochromen-4-ones

Article abstract of DOI:10.1055/s-0029-1216735

4H-Thiochromen-4-ones and 4H-thiopyrano[2,3-b]pyridin-4-ones are readily synthesized in good yields by a consecutive one-pot, three-component coupling-addition-S_NAr (CASNAR) sequence starting from aroyl chlorides, alkynes, and sodium sulfide no

Full text of DOI:10.1055/s-0029-1216735

LETTER
1255
A Novel Consecutive Three-Component Coupling–Addition–SNAr (CASNAR)
Synthesis of 4H-Thiochromen-4-ones
O
ne-Pot Couplinge–Addition N
n
–S
A
r
Synth
j
esis of
a
4
H
-Thioch
m
romen-4-ones in Willy, Thomas J. J. Müller*
Institut für Organische Chemie und Makromolekulare Chemie, Lehrstuhl für Organische Chemie, Heinrich-Heine-Universität Düsseldorf,
Universitätsstr. 1, 40225 Düsseldorf, Germany
Fax +49(211)8114324; E-mail: ThomasJJ.Mueller@uni-duesseldorf.de
Received 5 February 2009
Dedicated to Dr. Hans-Ulrich Wagner on the occasion of his 70th birthday.
tential of 4H-thiochromen-4-ones and as a part of our
Abstract: 4H-Thiochromen-4-ones and 4H-thiopyrano[2,3-b]pyri-
program to develop multicomponent synthesis of hetero-
din-4-ones are readily synthesized in good yields by a consecutive
one-pot, three-component coupling–addition–SNAr (CASNAR) se-
cycles,13 we set out to devise a rapid one-pot synthesis of
substituted 4H-thiochromen-4-ones. Here, we communi-
cate a new one-pot, three-component synthesis of 4H-
thiochromen-4-ones with a highly flexible substitution
pattern.
quence starting from aroyl chlorides, alkynes, and sodium sulfide
nonahydrate.
Key words: alkynes, catalysis, CC coupling, heterocycles, multi-
component reactions
Alkynones are accessible by Sonogashira coupling14 of
acid chlorides with terminal alkynes.15 However, by a
modified protocol with THF as a solvent and only one
stoichiometrically necessary equivalent of triethylamine
as a base has proven to be most favorable for successfully
coupling even sensitive alkynes such as trimethylsilyl
acetylene.16 In turn, the resulting alkynones are reactive to
readily react with various nucleophiles in a one-pot fash-
ion to give a plethora of heterocycles.13,17 Retrosyntheti-
cally, the formation of 4H-thiochromen-4-ones 1 in a one-
pot fashion can be perceived via a sequence of intramo-
lecular nucleophilic aromatic substitution (SNAr) and
Michael addition of hydrosulfide to alkynones 2
(Scheme 1). These alkynones are easily accessible by
Sonogashira coupling of 2-halobenzoyl chlorides 3 and
terminal alkynes 4. Only very few examples of a SNAr-
Michael addition of hydrosulfide to alkynones have been
reported so far.18 Hence, the methodological challenge re-
mains to develop a general consecutive one-pot, three-
component coupling–addition–SNAr (CASNAR) process.
Thiochromenone can be regarded as the thio homologue
of the core constituent of the natural product class of fla-
vones. In their own right, thiochromenones are as well po-
tent drug candidates and serve as key intermediates for the
synthesis of biological active compounds, and many thio-
chromenones are known to exhibit antimicrobial and anti-
fungal,1 antibacterial,2 antibiotic,3 and anticarcinogenic4
activity. Some derivatives are used as antimalaria agents,5
oxidized representatives reversibly inhibit the human
cytomegalovirus protease.6
In general, 4H-thiochromen-4-ones are synthesized either
by condensation of b-keto esters and thiophenols with
polyphosphoric acid7 or by cyclization of b-substituted
cinnamates derived from thiophenols and appropriate pro-
piolates.5,8 Condensation and subsequent acid-mediated
cyclization of lithiated intermediates derived from ace-
toacetanilides,9 C(a),N-benzoyl hydrazones or C(a),N-
carboalkoxy hydrazones10 with methyl thiosalicylates
also lead to the formation of 4H-thiochromen-4-ones. Just
recently, a synthesis via intramolecular thiolester car-
bonyl olefination using N-phenyl(triphenylphosphor-
anylidene)ethenimine as starting material has been report-
ed.11 However, most of these methods could not success-
fully be applied to the synthesis of methoxy-substituted
thioflavones.12 The described methods either require
many steps, or the starting materials are difficult to syn-
thesize. Hence, due to the interesting pharmacological po-
Therefore, upon reacting ortho-haloaroyl chlorides 3 with
ethynyl benzene (4a) under modified Sonogashira condi-
tions for 1 hour at room temperature to furnish the expect-
ed alkynones 2, and subsequently, sodium sulfide
nonahydrate (5) and ethanol were added to the reaction
mixture and heated in the microwave cavity to give 4H-
thiochromen-4-one 1a (Scheme 2, Table 1).
Mechanistically, it is likely that the rapid Michael addi-
tion of the hydrosulfide ion to the alkynone 2 to give the
S
R2
Hal
Hal
R2
HS–
+
R1
R1
R1
+
R2
Cl
O
O
O
1
2
3
4
Scheme 1 Retrosynthetic analysis of 4H-thiochromen-4-ones 1
SYNLETT 2009, No. 8, pp 1255–1260
x
x.
x
x.
2
0
0
9
Advanced online publication: 17.04.2009
DOI: 10.1055/s-0029-1216735; Art ID: G03609ST
© Georg Thieme Verlag Stuttgart · New York

1256
B. Willy, T. J. J. Müller
LETTER
1) [PdCl2(PPh3)2 (2 mol%), CuI (4 mol%)]
Et3N, THF, conditions
Hal
Cl
S
Ph
+
Ph
2) Na2S⋅9H2O (5, 1.50 equiv)
EtOH, conditions
O
O
3a–c
4a
1c
[PdII, CuI]
Et3N, THF
– Hal–
coupling
SNAr
Hal
Hal
S–
5
Ph
R1
Ph
Michael addition
O
2a–c
O
6a–c
Scheme 2 Mechanistic rationale of the coupling–addition–SNAr (CASNAR) sequence
adduct 6 proceeds the intramolecular SNAr reaction, pre- zoyl chlorides 3 with terminal alkynes 4 under modified
sumably assisted by Pd and/or Cu catalysis. Dielectric Sonogashira conditions for 1 hour at room temperature,
heating in a microwave cavity proves to be more efficient and finally, after adding sodium sulfide nonahydrate 5 and
than conductive heating in an oil bath (entry 1 vs. entry 9), ethanol, and reaction for 90 minutes at 90 °C in the micro-
but only for the addition–cyclocondensation step. The wave cavity gave rise to the formation of substituted 4H-
Sonogashira coupling proceeds smoothly at room temper- thiochromen-4-ones 1 in moderate to good yields as bright
ature and without the formation of side products.
yellow solids (Scheme 3, Table 2).19 Interestingly, 2,4-
dichlorobenzoyl chloride (3c) selectively furnished 7-
chloro-substituted products (Table 2, entries 10–12) with
out competing SNAr at the 4-chloro position.
Encouraged by these optimizations, the stage was set
for a novel three-component coupling–addition–SNAr
(CASNAR) synthesis of 4H-thiochromen-4-ones 1 in a
one-pot fashion. Therefore, after coupling of 2-haloben-
Table 1 Optimization of the Coupling–Addition–SNAr (CASNAR) Sequence of Ethynylbenzene 4a and Na2S·9H2O (5) with different ortho-
Haloaroyl Chlorides 3
Entry
3 (equiv)
3a (1.00)
3a (1.00)
3a (1.00)
3a (1.00)
3a (1.00)
3a (1.00)
3a (1.00)
3a (1.00)
3a (1.25)
3b (1.25)
4c (equiv)
1.00
5 (equiv)
1.10
1.10
1.10
1.10
1.10
1.10
1.50
1.50
1.50
1.50
Coupling (°C, min)
r.t., 60
Addition–SNAr (°C, min) Yield of 1a (%)a
1
2
90, 120b
52
34
48
41
53
58
59
61
73
40
1.00
90, 10, MW
90, 10, MW
90, 10, MW
r.t., 60
60, 20, MW
90, 20, MW
120, 20, MW
90, 20, MW
90, 90, MW
90, 90, MW
90, 90, MW
90, 90, MW
90, 90, MW
3
1.00
4
1.00
5
1.00
6
1.00
r.t., 60
7
1.00
r.t., 60
8
1.25
r.t., 60
9
1.00
r.t., 60
10
1.00
r.t., 60
a Isolated yield after column chromatography on SiO2 (EtOAc–hexanes).
b Control experiment in oil bath.
R1
Hal
R1
S
R2
1) [PdCl2(PPh3)2 (2 mol%), CuI (4 mol%)]
Et3N, THF, 1 h, r.t.
+
R2
Cl
2) Na2S⋅9H2O (5, 1.50 equiv)
EtOH, 90 min, 90 °C, MW
O
O
3a Hal = F, R1 = H
3b Hal = Cl, R1 = H
3c Hal = Cl, R1 = Cl
4
1 (39–79%,
11 examples)
Scheme 3 Coupling–addition–substitution (CAS) sequence to substituted 4H-thiochromen-4-ones 1
Synlett 2009, No. 8, 1255–1260 © Thieme Stuttgart · New York

LETTER
One-Pot Coupling–Addition–SNAr Synthesis of 4H-Thiochromen-4-ones
1257
Methodologically, this new one-pot, three-component uents give substantially lower yields. When trimethylsilyl
CASNAR synthesis of 4H-thiochromen-4-ones 1 pro- acetylene is applied (Table 2, entry 2) the TMS group is
ceeds efficiently under mild reaction conditions with a presumably lost prior to the Michael addition of the hy-
broad variety of diverse alkynes. Aliphatic, aromatic, het- drosulfide. Expectedly, free amino or hydroxy groups on
eroaromatic, even ferrocenyl- or heteroatom-substituted the alkynes interfere with the aroyl chloride and should be
alkynes can be successfully transformed in this reaction. protected.
However, alkynes with electron-poor (hetero)aryl substit-
Table 2 One-Pot, Three-Component Synthesis of Thiochromene Derivatives 1 and 8a
Entry
Aroyl chloride 3 or 7
Alkyne 4
Product (yield, %)b
S
1
3a
4a R2 = H [TMS]
O
1a (39)
S
n-Bu
2
3
3a
3a
4b R2 = n-Bu
O
1b (59)
1c (73)
S
Ph
4c R2 = Ph
O
t-Bu
S
4
5
6
3a
3a
3a
4d R2 = 4-t-BuC6H4
4e R2 = 4-MeOC6H4
4f R2 = 3,4-(MeO)2C6H3
O
1d (76)
1e (77)
1f (73)
OMe
S
O
OMe
OMe
S
O
Cl
S
7
8
3a
3a
4g R2 = 4-ClC6H4
O
S
1g (52)
1h (63)
Fe
4h R2 = ferrocenyl
O
Synlett 2009, No. 8, 1255–1260 © Thieme Stuttgart · New York

1258
B. Willy, T. J. J. Müller
LETTER
Table 2 One-Pot, Three-Component Synthesis of Thiochromene Derivatives 1 and 8a (continued)
Entry
9
Aroyl chloride 3 or 7
Alkyne 4
Product (yield, %)b
Cl
S
3c
4i R2 = 4-MeC6H4
O
1i (48)
OMe
OMe
Cl
S
10
11
3c
3c
4f R2 = 3,4-(MeO)2C6H3
O
1j (59)
F
Cl
S
4j R2 = 4-FC6H4
O
1k (47)
N
S
12
13
7
7
4k R2 = cyclopropyl
O
8a (53)
N
S
4i R2 = 4-MeC6H4
O
8b (23)
t-Bu
N
S
14
15
7
7
4d R2 = 4-t-BuC6H4
O
S
8c (15)
N
Ph
4c R2 = Ph
O
8d (55)
a Reaction conditions: aroyl chloride 3 or 7 (1.25 equiv), alkyne 4 (1.00 equiv, 0.25 M in THF), Et3N (1.05 equiv), PdCl2(PPh3)2 (0.02 equiv),
and CuI (0.04 equiv) were successively reacted for 1 h at r.t. Then, Na2S·9H2O (1.50 equiv, 5) and EtOH (1 mL) were added, and the reaction
mixture was heated for 90 min at 90 °C in the microwave.
b Yields refer to isolated yields after flash column chromatography on SiO2 gel to be 98% pure as determined by NMR spectroscopy or elemental
analysis.
To test scope and limitations we chose with 2-chloronico- chromen-4-one failed, only two examples of this hetero-
tinoyl chloride (7) as a heteroaroyl chloride leading to the cyclic system have been reported in the literature.20
formation of the highly interesting class of 4H-thiopyra-
The structures of the 4H-thiochromen-4-ones 1 and the
no[2,3-b]pyridin-4-ones 8 in modest to moderate yields
4H-thiopyrano[2,3-b]pyridin-4-ones 8 were unambigu-
(Scheme 4, Table 2, entries 13–16). To the best of our
ously supported by spectroscopic (1H NMR, 13C NMR,
knowledge, since standard syntheses for 4H-thio-
Synlett 2009, No. 8, 1255–1260 © Thieme Stuttgart · New York

LETTER
One-Pot Coupling–Addition–SNAr Synthesis of 4H-Thiochromen-4-ones
1259
1) [PdCl2(PPh3)2 (2 mol%), CuI (4 mol%)]
N
Cl
O
N
S
R2
Et3N, THF, 1 h, r.t.
+
R2
Cl
2) Na2S⋅9H2O (5, 1.50 equiv)
EtOH, 90 min, 90 °C, MW
O
7
4
8 (15–53%, 4 examples)
Scheme 4 Coupling–addition–substitution (CAS) sequence to substituted 4H-thiopyrano[2,3-b]pyridin-4-ones 7
(7) (a) Bossert, F. Justus Liebigs. Ann. Chem. 1964, 40, 680.
(b) Schneller, S. W. Adv. Heterocycl. Chem. 1975, 18, 59.
and DEPT NMR experiments, IR, UV/vis, mass spec-
trometry) and combustion analyses.
(c) Nakazumi, H.; Wanatabe, S.; Kitaguchi, T.; Kitao, T.
In comparison the existing protocols for the synthesis of
4H-thiochromen-4-one 1c generally require several steps,
sometimes harsh reaction conditions and longer reaction
times give significantly lower over all yields (Table 3).
The CASNAR sequence represents a straightforward and
rapid access to 4H-thiochromen-4-ones 1 and 4H-thiopy-
rano[2,3-b]pyridin-4-ones 8 in a one-pot fashion and with
a broad scope in the starting materials.
Bull. Chem. Soc. Jpn. 1990, 63, 847.
(8) (a) Truce, W. E.; Goldhamer, D. L. J. Am. Chem. Soc. 1959,
81, 5795. (b) Buggle, K.; Delahunty, J. J.; Philbin, E. M.;
Ryan, N. D. J. Chem. Soc. C 1971, 3168.
(9) Angel, A. J.; Finefrock, A. E.; French, K. L.; Hurst, D. R.;
Williams, A. R.; Rampey, M. E.; Studer-Martinez, S. L.;
Beam, C. F. Can. J. Chem. 1999, 77, 94.
(10) French, K. L.; Angel, A. J.; Williams, A. R.; Hurst, D. R.;
Beam, C. F. J. Heterocycl. Chem. 1998, 35, 45.
(11) (a) Kumar, P.; Rao, A. T.; Pandey, B. Chem. Commun. 1992,
21, 1580. (b) Kumar, P.; Bodas, M. S. Tetrahedron 2001,
57, 9755.
(12) Wadsworth, D. H.; Detty, M. R. J. Org. Chem. 1980, 45,
4611.
(13) For reviews, see: (a) Willy, B.; Müller, T. J. J. ARKIVOC
2008, (i), 195. (b) D’Souza, D. M.; Müller, T. J. J. Chem.
Soc. Rev. 2007, 36, 1095.
(14) For lead reviews on Sonogashira couplings, see, e.g.:
(a) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara,
N. Synthesis 1980, 627. (b) Sonogashira, K. In Metal-
Catalyzed Cross-Coupling Reactions; Diederich, F.; Stang,
P. J., Eds.; Wiley-VCH: Weinheim, 1998, 203. (c) Doucet,
H.; Hierso, J.-C. Angew. Chem. Int. Ed. 2007, 46, 834.
(d) Yin, L.; Liebscher, J. Chem. Rev. 2007, 107, 133.
(15) Toda, Y.; Sonogashira, K.; Hagihara, N. Synthesis 1977,
777.
Table 3 Comparison of Existing Protocols for the Synthesis of 1c
Route
Steps
Time
Yield (%)a
Wittig route11
PPA7
3
2
3
1
ca. 3 d
ca. 10 h
ca. 4 d
ca. 2 h
44
71
34
73
Propiolate route5
CASNAR (this work)
a Yield over all steps, starting from commercially available com-
pounds.
Methoxy groups, which proved to be unfavorable in stan-
dard syntheses, are perfectly tolerated in this sequence.
This novel one-pot procedure now opens new avenues to
an interesting class of heterocycles. Studies addressing the
biological activity and electronic properties of 4H-thio-
chromen-4-ones and 4H-thiopyrano[2,3-b]pyridin-4-ones
are currently under investigation.
(16) (a) Karpov, A. S.; Müller, T. J. J. Org. Lett. 2003, 5, 3451.
(b) D’Souza, D. M.; Müller, T. J. J. Nat. Protoc. 2008, 3,
1660.
(17) (a) Müller, T. J. J. Chimica Oggi/Chemistry Today 2007, 25,
70. (b) Müller, T. J. J. Targets Heterocycl. Syst. 2006, 10,
54. (c) Willy, B.; Müller, T. J. J. Eur. J. Org. Chem. 2008,
4157. (d) Willy, B.; Dallos, T.; Rominger, F.; Schönhaber,
J.; Müller, T. J. J. Eur. J. Org. Chem. 2008, 4796.
(e) Willy, B.; Rominger, F.; Müller, T. J. J. Synthesis 2008,
293. (f) Karpov, A. S.; Merkul, E.; Oeser, T.; Müller, T. J. J.
Chem. Commun. 2005, 2581.
Acknowledgment
The authors gratefully acknowledge the Fonds der Chemischen
Industrie, and CEM for a research corporation.
(18) (a) Shvartsberg, M. S.; Ivanchikova, I. D. ARKIVOC 2003,
(xiii), 87. (b) Ivanchikova, I. D.; Shvartsberg, M. S. Russ.
Chem. Bull. 2004, 53, 2303.
References and Notes
(19) Representative Procedure – Synthesis of 2-Phenyl-4H-
thiochromen-4-one (1c; Table 2, Entry 3)
(1) Nakazumi, H.; Ueyama, T.; Kitao, T. J. Heterocycl. Chem.
1985, 22, 1593.
(2) Nakazumi, H.; Ueyama, T.; Kitao, T. J. Heterocycl. Chem.
1984, 21, 193.
(3) Couquelet, J.; Tronche, P.; Niviere, P.; Andraud, G. Trav.
Soc. Pharm. Montpellier 1963, 23, 214.
(4) Holshouser, M. H.; Loeffler, L. J.; Hall, I. H. J. Med. Chem.
1981, 24, 853.
(5) Razdan, R. K.; Bruni, R. J.; Mehta, A. C.; Weinhardt, K. K.;
Papanastassiou, Z. B. J. Med. Chem. 1978, 21, 643.
(6) Dhanak, D.; Keenan, R. M.; Burton, G.; Kaura, A.; Darcy,
M. G.; Shah, D. H.; Ridgers, L. H.; Breen, A.; Lavery, P.;
Tew, D. G.; West, A. Bioorg. Med. Chem. Lett. 1998, 8,
3677.
In a 10 mL microwave tube PdCl2 (PPh3)2 (15 mg, 0.02
mmol) and CuI (8 mg, 0.04 mmol) were dissolved in
degassed THF (4 mL). Then, to this orange soln acid
chloride 3c (1.25 mmol), alkyne 4c (1.00 mmol), and Et3N
(1.05 mmol) were added. The reaction mixture was stirred at
r.t. for 1 h. Finally, Na2S·9H2O (5) followed by EtOH (1 mL)
were added to this suspension, and the reaction mixture was
heated at 90 °C in the microwave cavity for 90 min. After
cooling to r.t., the solvent was removed under reduced
pressure, and the crude products were purified by SiO2 flash
column chromatography (hexane–EtOAc) to afford the
analytically pure 4H-thiochromen-4-one 1c in 174 mg
(73%) yield as a yellow solid, mp 122 °C.
Synlett 2009, No. 8, 1255–1260 © Thieme Stuttgart · New York

1260
B. Willy, T. J. J. Müller
LETTER
1H NMR (500 MHz, CDCl3): d = 7.06 (s, 1 H), 7.48–7.58 (m,
4 H), 7.62–7.71 (m, 4 H), 8.54–8.57 (m, 1 H) ppm. 13C NMR
(125 MHz, CDCl3): d = 123.4 (CH), 126.5 (CH), 127.0 (2
CH), 127.8 (CH), 128.6 (CH), 129.3 (2 CH), 130.8 (CH),
130.9 (Cquat), 131.6 (CH), 136.6 (Cquat), 137.7 (Cquat), 153.1
(Cquat), 180.8 (Cquat) ppm. MS (EI, 70 eV): m/z (%) = 239
(18), 238 (100) [M]+, 211 (14), 210 (83), 165 (14), 136 (59),
108 (45), 105 (12), 92 (11), 82 (12), 69 (17). Anal. Calcd for
C20H18O3S (338.4): C, 75.60; H, 4.23. Found: C, 75.51; H,
4.41.
2-Ferrocenyl-4H-thiochromen-4-one (1h)
1H NMR (500 MHz, CDCl3): d = 4.19 (s, 5 H), 4.52 (t,
3J = 1.9 Hz, 2 H), 4.81 (t, 3J = 1.9 Hz, 2 H), 7.12 (s, 1 H),
7.49–7.53 (m, 1 H), 7.58–7.60 (m, 2 H), 8.50 (dd, 3J = 8.0
Hz, 1 H) ppm. 13C NMR (125 MHz, CDCl3): d = 67.4 (2
CH), 70.8 (5 CH), 71.1 (2 CH), 80.0 (Cquat), 119.8 (CH),
126.1 (CH), 127.4 (CH), 128.5 (CH), 131.2 (Cquat), 131.3
(CH), 137.4 (Cquat), 154.8 (Cquat), 180.2 (Cquat) ppm. Anal.
Calcd for C19H14FeOS (346.2): C, 65.91; H, 4.08. Found: C,
65.64; H, 4.04.
2-(3,4-Dimethoxyphenyl)-4H-thiochromen-4-one (1f)
1H NMR (500 MHz, CDCl3): d = 3.94 (s, 3 H), 3.96 (s, 3 H),
6.96 (d, 3J = 8.4 Hz, 1 H), 7.19 (d, 4J = 2.2 Hz, 1 H), 7.22 (s,
1 H), 7.31 (dd, 3J = 8.4 Hz, 4J = 2.2 Hz, 1 H), 7.54 (ddd,
3J = 8.2 Hz, 3J = 6.8 Hz, 4J = 1.3 Hz, 1 H), 7.61 (ddd, 3J =
8.2 Hz, 3J = 6.8 Hz, 4J = 1.3 Hz, 1 H), 7.63–7.67 (m, 1 H),
8.53 (dd, 3J = 8.0 Hz, 4J = 1.2 Hz, 1 H) ppm. 13C NMR (125
MHz, CDCl3): d = 56.05 (CH3), 56.06 (CH3), 109.6 (CH),
111.3 (CH), 120.0 (CH), 122.3 (CH), 126.4 (CH), 127.7
(CH), 128.5 (CH), 129.1 (Cquat), 130.9 (Cquat), 131.5 (CH),
137.6 (Cquat), 149.5 (Cquat), 151.4 (Cquat), 152.9 (Cquat), 180.9
(Cquat) ppm. Anal. Calcd for C17H14O3S (298.4): C, 68.44; H,
4.73. Found: C, 68.46; H, 4.57.
2-Cyclopropyl-4H-thiopyrano[2,3-b]pyridin-4-one (8a)
1H NMR (500 MHz, CDCl3): d = 1.06-1.09 (m, 2 H), 1.17–
1.21 (m, 2 H), 1.98–2.03 (m, 1 H), 6.78 (s, 1 H), 7.43 (dd,
3J = 8.1 Hz, 4J = 4.5 Hz, 1 H), 8.68 (dd, 3J = 8.1 Hz, 4J =
1.9 Hz, 1 H), 8.73 (dd, 3J = 4.5 Hz, 4J = 1.9 Hz, 1 H).
13C NMR (125 MHz, CDCl3): d = 10.6 (2 CH2), 18.0 (CH),
121.0 (CH), 122.6 (CH), 128.3 (Cquat), 136.6 (CH), 152.4
(CH), 158.6 (Cquat), 160.9 (Cquat), 180.8 (Cquat). Anal. Calcd.
for C11H9NOS (203.26): C, 65.00; H, 4.46; N, 6.89. Found:
C, 64.72; H, 4.46; N, 6.73.
(20) (a) Couture, A.; Grandclaudon, P.; Huguerre, E. Synthesis
1989, 456. (b) Becher, J.; Christensen, M. C.; Möller, M. C.;
Winckelmann, J. Sulfur Lett. 1982, 1, 43.
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