Versatile route to functionalized 1H-2-benzothiopyrans and 1H-2- naphthothiopyrans by electrophilic cyclization of Bis(arylmethylthio)acetylenes: 2-Benzo- and 2-naphthothiopyrylium salts

Article abstract of DOI:10.1021/jo972334l

Substituted 1H-2-benzothiopyrans find applications as pharmaceutically active compounds or synthons for more complex sulfur heterocycles. However, restricted variability in their synthesis limits the application for research or industrial purposes. To develop a direct and fast route to substituted and functionalized 1H-2-benzothiopyrans, we investigated the ring closure of symmetrical bis(arylmethylthio)acetylenes with iodine monochloride or bromine. This facile reaction yielded 1H-3-halo-4-arylmethylthio-2-benzo- and 2-naphthothiopyrans via postulated vinyl cations in yields of 47-86%. Substituted 2-benzo- and 2-naphthothiopyrylium salts were prepared by hydride abstraction with triphenylcarbenium tetrafluoroborate from the products, further enhancing the synthetic potential of the found cyclization reaction.

Full text of DOI:10.1021/jo972334l

4626
J . Org. Chem. 1998, 63, 4626-4631
Ver sa tile Rou te to F u n ction a lized 1H-2-Ben zoth iop yr a n s a n d
1H-2-Na p h th oth iop yr a n s by Electr op h ilic Cycliza tion of
Bis(a r ylm eth ylth io)a cetylen es: 2-Ben zo- a n d
2-Na p h th oth iop yr yliu m Sa lts
Thomas R. Klein, Marco Bergemann, Nasser A. M. Yehia, and Egon Fangha¨nel*,†
Department of Chemistry, Martin-Luther-University, Halle-Wittenberg, D-06099 Halle, Germany
Received December 31, 1997
Substituted 1H-2-benzothiopyrans find applications as pharmaceutically active compounds or
synthons for more complex sulfur heterocycles. However, restricted variability in their synthesis
limits the application for research or industrial purposes. To develop a direct and fast route to
substituted and functionalized 1H-2-benzothiopyrans, we investigated the ring closure of sym-
metrical bis(arylmethylthio)acetylenes with iodine monochloride or bromine. This facile reaction
yielded 1H-3-halo-4-arylmethylthio-2-benzo- and 2-naphthothiopyrans via postulated vinyl cations
in yields of 47-86%. Substituted 2-benzo- and 2-naphthothiopyrylium salts were prepared by
hydride abstraction with triphenylcarbenium tetrafluoroborate from the products, further enhancing
the synthetic potential of the found cyclization reaction.
In tr od u ction
pharmacological (antitussive, sedative, muscle relaxating,
neuroleptic) activity,5 as well.
1H-2-Benzothiopyrans both show and promise inter-
esting biological properties.1 They represent a more or
less rigid and polarizable ring system,2 which should be
capable of interacting with receptor proteins like, but
different from, the isomeric 2H-1-benzothiopyrans. The
latter have already been tested and applied as drugs.3
1H-2-Benzothiopyrans can be easily converted into isothio-
chromans in high yields by catalytic reduction.4 Certain
1-substituted and 1,1-disubstituted isothiochromans show
The value of 1H-2-benzothiopyrans as synthons is
given by the formation of highly reactive 2-benzothiopy-
rylium salts with trityl tetrafluoroborate (TrBF4).6
A
wide variety of substituted and fused heterocyclic sys-
tems can be formed from the 2-benzothiopyrylium salts,
for example, by using them as dienophiles in hetero
Diels-Alder reactions.7
In contrast to the high synthetic and pharmacologic
potential of 1H-2-benzothiopyrans, a very limited vari-
ability exists for preparation of these compounds.8 Our
aim was to develop a fast and efficient synthesis that
allows a specific substitution pattern of the product by
selecting appropriate educts. Symmetric bis(arylmeth-
ylthioacetylenes) 2 were chosen as starting material for
cyclization due to the ease of preparation and high
variability. Electrophilic attack of iodine monochloride
and to a limited extent bromine gave 1H-3-halo-4-
arylmethylthio-2-benzothiopyrans 3 in good yields (47-
† Address correspondence to this author at Institute of Organic
Chemistry; Martin-Luther-University Halle-Wittenberg; D-06099 Halle.
Tel: 0049-3461-462086. Fax: 0049-3461-462080. E-mail: Fanghaenel@
chemie.uni-halle.de.
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R.; Graneto, M. J .; Rogier, D. J . WO 9609304; Chem. Abstr. 1971, 75,
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Org. Chem. 1975, 40, 1142. (c) 3,4-Substituted; from 2-iodobenzyl
chloride, tert-butyl-SH, base, Pd(dba)2, asymmetric substituted acety-
lenes, AgBF4, PhCl reflux; 5 steps, 47-54% yield: see ref 6a. (d)
1-Phenyl-3,4-substituted; from thiobenzophenone, activated acetylenes,
61-97% yield: Rapp, J .; Huisgen, R. Tetrahedron 1997, 53, 961. See
also: Ingall, A. H. Compr. Heterocycl. Chem 1994, 3, 885. Ingall, A.
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S0022-3263(97)02334-7 CCC: $15.00 © 1998 American Chemical Society
Published on Web 06/20/1998

2-Benzo- and 2-Naphthothiopyrylium Salts
J . Org. Chem., Vol. 63, No. 14, 1998 4627
Ta ble 1. Sym m etr ica l Bis(a r ylm eth ylth io)a cetylen es 2
fr om Ar ylm eth yl Th iocya n a tes 1
Ta ble 2. Syn th esis of 1H-2-Ben zoth iop yr a n s 3 fr om 2
a n d Iod in e Mon och lor id e or Br om in e
86% isolated). The simple addition of halogen onto the
triple bond played no role under the appropriate reaction
conditions.
A preliminary description of this new reaction has been
given for the unsubstituted starting compound.9
Compounds 2a -d have been chosen to study the
electronic effect of a donor (2b,c) or an acceptor (2d ) in
the aryl group and of the type of the aromatic system
(2a ,e,f) on the electrophilic cyclization reaction.
Resu lts
Ch oice a n d P r ep a r a tion of Sta r tin g Com p ou n d s.
To test the influence of substituents on the electrophilic
ring closure reaction, several symmetric bis(arylmeth-
ylthio)acetylenes 2 have been prepared via arylmethyl
thiocyanates 1 and sodium acetylide. Commercially
available arylmethyl halides yielded thiocyanates 1
nearly quantitatively using the SiO2-supported, solvent-
free technique of Kodomari et al.10 The reaction of the
thiocyanates with sodium acetylide in liquid ammonia11
gave acetylenes 2 in 60-90% yields (Table 1). 1H NMR
signals (singlets) of the methylene groups were at 3.79-
3.89 ppm in chloroform-d as expected, with the exception
of 2d and 2e (4.19 ppm; 4.25 ppm). Compounds 2b-f
have not yet been described in the literature and are
therefore characterized in detail.
Electr op h ilic Cycliza tion of 2a -f w ith Iod in e
Mon och lor id e or Br om in e. The acetylenes 2 were
rapidly converted into 1H-2-benzothiopyrans 3, via a
vinyl cation as postulated intermediate, by reaction with
equimolar amounts of iodine monochloride or bromine
at -70 °C in methanol or methanol/chloroform (Table 2).
The products precipitated from the cold reaction mixture.
A second fraction could be obtained after neutralization
of the filtrate with solid sodium bicarbonate, filtration,
removal of the solvent, and recrystallization from ethanol.
In general iodine monochloride gave higher yields than
bromine. Some acetylenes (2c,e,f) could only be cyclized
with iodine monochloride. The structure of the reaction
products has been confirmed spectroscopically and by
X-ray crystal structure analysis of 3a . The ORTEP plot
of 3a is shown in Figure 1.
(9) Bergemann, M.; Fangha¨nel, E. 16th International Symposium
on the Organic Chemistry of Sulfur (ISOCS), abstract book, R. 318,
poster, Martin-Luther-Universita¨t Halle-Wittenberg 1994, ISBN
3-924763-46-1.
(10) Kodomari, M.; Kuzuoka, T.; Yoshitomi, S. Synthesis 1983, 141.
(11) Brandsma, L. Preparative Acetylenic Chemistry, reprint of the
2nd ed.; Elsevier: Amsterdam-Oxford-New York-Tokyo, 1992.
Two 1H NMR signals (singlets) for the methylene
groups of 3 were found: for the 4-substituents almost
unchanged at 3.66-3.92 ppm in chloroform-d (4.28 ppm

4628 J . Org. Chem., Vol. 63, No. 14, 1998
Klein et al.
Sch em e 2
F igu r e 1. ORTEP plot of 3a .
Sch em e 1
Con ver sion of 3 in to Th iop yr yliu m Sa lts 4. To
extend the synthetic variability of the ring closure
products, 3a -g were treated with TrBF4 in dry CH2Cl2
(or CH2Cl2/CH3NO2). TrBF4 acts as hydride extractor,13
forming triphenylmethane and the desired 2-benzothio-
pyrylium salts 4. All compounds 3 investigated except
3g provided the salts 4 in yields between 37% and 85%
yields (Table 3). In the case of 3g the starting material
was recovered unchanged, possibly by sterical hindrance
of the hydride abstraction by the bulky tritylium cation.
The salts 4 were deeply colored (λmax in CH3CN, 422-
450 nm; ꢀ ) 1300-8800 l/mol cm) hydrolysis-sensitive
crystals, which were stored in a desiccator. The 1H NMR
signal (singlet) of the methylene group of the substituent
was shifted downfield to 4.26 ppm (4a , CDCl3) and 4.19-
4.72 ppm (4b,c,e,f, CD3CN). The disappearance of the
singlet of the ring-methylene group and a new resonance
at 10.08-10.93 ppm (singlet) confirmed the formation of
the thiopyrylium salt.
for 3f) and the ring-methylene group shifted about 0.3
ppm upfield (with the exception of 3g, where an upfield
shift of 0.94 ppm was recorded).
From 2f two different cyclization products may be
formed (Scheme 1). The 1H NMR spectra of the resulting
substance from the reaction of 1f with iodine monochlo-
ride showed 11 signals, which can be predicted for each
of the possible isomers alone but not for a mixture of both.
Due to the existence of only one singlet in the aromatic
Discu ssion
1H-2-Benzothiopyrans 3, which are important for their
use as synthons and pharmacologically active compounds,
could be obtained in good yields in a flexible and easy
reaction from bis(arylmethylthio)acetylenes 2. The prepa-
ration of the acetylenes was achieved by modifying
standard reactions using commercial arylmethyl halides
as starting material and proceeded without difficulties.
The electrophilic addition of halogens to acetylenes is
normally catalyzed by Lewis acids and yields (E)-1,2-
dihaloalkenes stereoselectively.12 In polar solvents the
stabilization of polar intermediates and transition states
could also be expected in the absence of catalysts. In this
way the preformed cations (X ) iodonium, bromonium)
attack the electron rich triple bond of 2 by forming a vinyl
1
region, structure 3g is likely. The H-1H COSY spectra
of 3g and the interpretation of all cross-peaks proved the
postulated formula (Figure 2, Supporting Information).
Limitations of the new cyclization reaction were seen
in the attempt to generate the 1H-2-benzothiopyran ring
from 2d , which failed (Scheme 2). Instead of ring closure
to 3i halogen addition to 5 was observed with bromine.
Iodine monochloride yielded a complex reaction mixture
from which no cyclization product could be isolated. The
electronic effect of the ortho Br substituent made the
stabilization of the postulated vinyl cation by intramo-
lecular substitution less favorable and the intermolecular
addition of a nucleophile more so. The isolated addition
product 5 showed high selectivity toward one of the
possible E/ Z isomers as deduced from the 1H NMR signal
of the methylene group (4.19 ppm, 95%; 4.08 ppm, 5%).
Most probably the E isomer was formed in excess,
because bromine is known to prefer anti over syn addition
if an ionic mechanism is involved.12
(12) (a) Houben-Weyl Methoden der organischen Chemie, 4th ed.;
Georg Thieme Verlag: Stuttgart, 1960; Vol. V/4, pp 92-95. (b)
Al-Hassan, M. I. J . Organomet. Chem. 1989, 372, 183. (c) Ko¨nig, J .;
Wolf, V. Tetrahedron Lett. 1970, 19, 1629. (d) Schmid, G. H.; Modro,
A.; Yates, K. J . Org. Chem. 1980, 45, 665.
(13) (a) Dauben, H. J .; Gadecki, F. A.; Harmon, K. M.; Pearson, D.
L. J . Am. Chem. Soc. 1957, 79, 4558. (b) Bonthrone, W. Reid, D. H. J .
Chem. Soc. 1959, 2773.

2-Benzo- and 2-Naphthothiopyrylium Salts
J . Org. Chem., Vol. 63, No. 14, 1998 4629
Ta ble 3. Con ver sion of 3 in to 2-Ben zo- a n d
2-Na p h th oth iop yr yliu m Sa lts 4
Sch em e 3
Br substitution of the benzene ring blocked one of two
ortho positions (statistical factor) and deactivated the
aromatic ring for electrophilic substitution. Therefore,
the addition of bromide is favored in comparison to
intramolecular cyclization.
The potential of the ring closure reaction previously
described has not been exploited totally with the use of
iodine monochloride or bromine as electrophiles and the
symmetric bis(arylmethylthio)acetylenes as educts. Both
directions, that is, other electrophiles and different
substitution patterns of the educts (especially unsym-
metrical acetylenes 2 and bis(arylmethylseleno)acety-
lenes) will be followed by the authors. The halogen in
the 3-position of the 2-benzothiopyran ring in 3 opens
the way to further derivatization and intramolecular
cyclization to fused sulfur heterocycles.
cation which can react with nucleophiles/anions to equili-
brate its charge. Because of the reduced nucleophilicity
of the halogen anions (Y ) chloride, bromide) in metha-
nol, which is due to strong hydrogen bonding, the vinyl
cation attacks intramolecularly the aromatic π-system
forming a σ-complex and finally the 1H-2-benzothiopyran
ring. This reaction corresponds to the intramolecular
formation of indenes via a benzyl vinyl cation14 as an
intermediate. It is furthermore plausible that vinyl
cations 6 were stabilized by electronic interaction with
the nucleophilic, easily polarizable sulfur (Scheme 3).
The bridged structure 6c is expected to be the most
stable.15 Low concentration of the acetylene, low tem-
peratures, and slow addition of the halogen favored the
intramolecular course of reaction. Higher reactivity and
larger yields were observed with iodine monochloride as
compared to bromine due to the strongly polarized bond
between the two halogens in iodine monochloride. Some
acetylenes (2c,e,f) reacted only with this reagent. The
proposed mechanism (Table 2) is in agreement with the
superiority of iodine monochloride over bromine in the
reaction described.
Con clu sion
We have shown that substituted 1H-2-benzothiopyrans
3 with a new substitution pattern were readily accessible
by electrophilically induced ring closure of acetylenes 2.
The synthetic versatility of 3 was demonstrated by their
conversion into 2-benzo- and 2-naphthothiopyrylium salts
4 with TrBF4. Compounds 3 and 4 open routes for
synthesizing fused heterocycles and for potential applica-
tions in medicine and in material science.
Exp er im en ta l Section
Melting points were determined on a micro melting point
apparatus and are corrected. NMR spectra at 300 MHz (1H)
and 75 MHz (13C) were obtained in CDCl3 (1, 2, 3, 4a ) and in
CD3CN (4b,c,e,f), respectively (ppm; 13C off-resonance), with
TMS as internal standard unless stated otherwise. UV-vis
absorptions are given as [λ in nm (ꢀ in L/mol cm)]. All
elemental analyses reported were averaged from two inde-
pendent determinations. HPLC analysis was performed with
CH3CN (no gradient) on an RP-18 column connected to a UV
array detector. The peak area for accumulated absorption in
the range of 210-370 nm was utilized as a purity criterion.
For the described compounds of type 1, 2, and 3, a purity of
more than 98% was determined.
From the two possible cyclization products of 2f, only
3g was found. This high selectivity of ring closure toward
the 1- and not the 3-position of the 2-substituted naph-
thalene ring corresponds to the favored electrophilic
substitution of the 1-position of naphthalene under
kinetic control.
No ring closure but trans addition of halogen onto the
triple bond was found in case of acetylene 2d . The ortho
Arylmethyl halides, potassium thiocyanate, and iodine
monochloride and bromine used were obtained from com-
mercial sources. Ammonia and acetylene of highest com-
mercial purity from gas cylinders were purified/washed as
described in the individual experiments.
(14) (a) Maroni, R.; Melloni, G. Tetrahedron Lett. 1972, 2869. (b)
Marcuzzi, F.; Melloni, G. Tetrahedron Lett. 1975, 2771.
(15) Hanack, M. Angew. Chem. 1978, 90, 346; Angew. Chem., Int.
Ed. Engl. 1978, 17, 333.

4630 J . Org. Chem., Vol. 63, No. 14, 1998
Klein et al.
Gen er a l P r oced u r e: Ar ylm eth yl Th iocya n a tes 1 fr om
Ar ylm eth yl Halides. SiO2-supported active KSCN (75 mmol),
prepared as described by Kodomari,10 was placed in a 100 mL
Erlenmeyer flask and the arylmethyl halide (25 mmol) was
added. If the latter was a solid at room temperature, the flask
was immersed into a steam bath until all arylmethyl halide
was liquified and absorbed. The flask was placed in the dark
for 16 h and shaken from time to time. The product was
extracted with toluene and filtered to remove all solids, and
the toluene was evaporated. The pure thiocyanate was
isolated in near quantitative yield.
Ben zyl th iocya n a te (1a ): 3.35 g from 3.16 g (25 mmol) of
benzyl chloride (90%); clear, odorless crystals, mp 39-40 °C
(39.4 °C16).
4-Meth ylben zyl th iocya n a te (1b): 3.84 g from 3.51 g (25
mmol) of 4-methylbenzyl chloride (93%); clear, odorless liquid,
bp 151 °C/20 mbar (110-112 °C/6 Torr,17 148-150 °C/14
Torr17).
orange plates, mp (ethanol) 81-82 °C; 1H NMR δ 3.79 (s, 6H),
3.82 (s, 4H), 6.85 (d, 4H, 8.6 Hz), 7.18 (d, 4H, 8.6 Hz); 13C NMR
δ 41.02, 55.20, 87.98, 113.90, 128.48, 130.21, 159.12; UV-vis
(CH3CN) 239 (28 900). Anal. Calcd for C18H18S2O2: C, 65.45;
H, 5.46; S, 19.39. Found: C, 64.99; H, 5.40; S, 19.76.
Bis(2-br om oben zylth io)a cetylen e (2d ): 2.35 g from 2.0
g (8.9 mmol) of 2-bromobenzyl thiocyanate 1d (62%); clear
1
crystals, mp (ethanol) 80 °C; H NMR δ 3.91 (s, 4H), 7.11 (d,
8H, 7.1 Hz), 7.18 (d, 4H, 7.3 Hz), 7.52 (d, 4H, 7.6 Hz); 13C NMR
δ 41.66, 88.25, 124.42, 127.28, 129.29, 131.42, 132.96, 135.61;
UV-vis (CH3CN) 233 (19 800). Anal. Calcd for C16H12S2Br2:
C, 44.88; H, 2.82; S, 14.97; Br, 37.22. Found: C, 44.85; H,
3.06; S, 15.03; Br, 37.35.
Bis(1-n a p h th ylm eth ylth io)a cetylen e (2e): 1.38 g from
2.39 g (12 mmol) of 1-naphthylmethyl thiocyanate 1e (62%);
yellow crystals, mp (ethanol) 76-79 °C; 1H NMR δ 4.25 (s,
4H), 7.18 (d, 2H, 6.9 Hz), 7.31 (t, 2H, 7.6 Hz), 7.52 (m, 4H),
7.78 (d, 2H, 8.1 Hz), 7.87 (d, 2H, 9.0 Hz), 8.01 (d, 2H, 7.6 Hz);
13C NMR δ 39.19, 88.87, 123.56, 125.04, 125.80, 126.20, 128.12,
128.65, 128.76, 131.10, 131.65, 133.83; UV-vis (CH3CN) 287
(17 500). Anal. Calcd for C24H18S2: C, 77.80; H, 4.90; S, 17.31.
Found: C, 77.55; H, 5.11; S, 17.58.
4-Meth oxyben zyl th iocya n a te (1c): 2.20 g from 1.96 g
(12.5 mmol) of 4-methoxybenzyl chloride (98%); slightly yellow
liquid with anise-like smell, bp 134 °C/1 mbar (135-139 °C/
0.7 Torr18).
Bis(2-n a p h th ylm eth ylth io)a cetylen e (2f): 2.39 g from
3.70 g (19 mmol) of 2-naphthylmethyl thiocyanate 1f (69%);
2-Br om oben zyl th iocya n a te (1d ): 5.40 g from 6.25 g (25
mmol) of 1-bromobenzyl bromide (96%); slightly brownish
1
liquid with pungent odor, bp 113 °C/0.1 mbar, n20 ) 1.6102;
yellow crystals, mp (ethanol) 128-129 °C; H NMR δ 3.89 (s,
D
4H), 7.32 (d, 2H), 7.47 (t, 4H), 7.55 (s, 2H), 7.77 (m, 6H); 13C
NMR δ 41.67, 88.27, 126.01, 126.20, 126.84, 127.65, 127.76,
128.04, 128.29, 132.71, 133.15, 133.70; UV-vis (CH3CN) 263
(sh) (15 600). Anal. Calcd for C24H18S2: C, 77.80; H, 4.90; S,
17.31. Found: C, 77.24; H, 5.18; S, 17.41.
1H NMR δ 4.23 (s, 2H), 7.21 (d, 1H, 7.5 Hz), 7.33 (t, 1H, 7.4
Hz), 7.41 (t, 1H, 8.6 Hz), 7.61 (d, 1H, 8.0 Hz). Anal. Calcd
for C8H6BrNS: C, 42.12; H, 2.65; S, 14.05; N, 6.14; Br, 35.03.
Found: C, 42.20; H, 2.80; S, 14.29; N, 6.48; Br, 32.11.
1-Na p h th ylm eth yl th iocya n a te (1e): 2.59 g from 2.18 g
(12.5 mmol) of 1-chloromethylnaphthalene (99%); clear, odor-
less crystals, mp 91 °C (91-91.5 °C17).
Gen er a l P r oced u r e: 1H-2-Ben zoth iop yr a n s 3 fr om
Bis(a r ylm eth ylth io)a cetylen es 2. Acetylene 2 (1 mmol) was
dissolved in 2 mL of CHCl3, and 8 mL of CH3OH was added.
The suspension was cooled to -70 °C, and by stirring, the
halogen (Br2 or ICl; 1.1 mmol) in 1 mL of CHCl3 was slowly
added. Stirring was continued for 10 min at -70 °C. After
the solution was warmed to room temperature, all solids were
dissolved. When the solution was immersed into solid CO2/
ethanol, most of the product precipitated and was filtered. A
second fraction was obtained by neutralization with solid
NaHCO3, removal of the solvents at low temperatures (35 °C),
and purification of the dark residue by precipitation from CH2-
Cl2 with cyclohexane. The products were pure after one or
two recrystallizations from ethanol.
2-Na p h th ylm eth yl th iocya n a te (1f): 2.46 g from 2.74 g
(12.5 mmol) of 2-bromomethylnaphthalene (95%); clear, odor-
less crystals, mp 101 °C (101-101.5 °C19).
Gen er a l P r oced u r e: Sym m etr ic Bis(a r ylm eth ylth io)-
a cetylen es 2 fr om Ar ylm eth yl Th iocya n a tes 1. Ammonia
(dried by passing through a KOH-filled column) was liquified
(10 mL) under an argon atmosphere using a reflux condenser
filled with solid CO2 and ethanol. After sodium (575 mg; 25
mmol) was added, acetylene gas (passed through H2SO4 and
an active carbon filter) was bubbled into the deep blue solution
until the color disappeared. Dry CH2Cl2 (2 mL) was added,
and by stirring, a concentrated solution of the thiocyanate (20
mmol) in CH2Cl2 was slowly introduced through a dropping
funnel. After stirring was continued for 30 min and the
ammonia evaporated, 3 mL of CH2Cl2 followed by 20 mL of
H2O was added to dissolve all solids. The phases were
separated, and the water layer was extracted with CH2Cl2 (3
× 12 mL). It now contained only NaCN, which was destroyed
with alkaline H2O2. The unified organic phases were washed
with water and dried and the solvent removed. The products
were pure after recrystallization from diethyl ether.
Bis(ben zylth io)a cetylen e (2a ): 12.0 g from 15.0 g (100
mmol) of benzyl thiocyanate 1a (89%); clear crystals, mp
(ethanol) 54 °C (54 °C17); 1H NMR δ 3.80 (s, 4H), 7.25 (m, 10H);
13C NMR δ 41.42, 87.95, 127.59, 128.46, 129.04, 136.46; UV-
vis (CH3CN) 228 (20 100). Anal. Calcd for C16H14S2: C, 71.07;
H, 5.22; S, 23.71. Found: C, 71.43; H, 5.55; S, 23.73.
Bis(4-m eth ylben zylth io)a cetylen e (2b): 1.96 g from 3.26
g (20 mmol) of 4-methylbenzyl thiocyanate 1b (68%); flat, clear
crystals, mp (ethanol) 78.5 °C; 1H NMR δ 2.33 (s, 6H), 3.82 (s,
4H), 7.13 (s, 8H); 13C NMR δ 21.09, 41.23, 87.93, 128.90,
129.13, 133.38, 137.25; UV-vis (CH3CN) 231 (29 300). Anal.
Calcd for C18H18S2: C, 72.48; H, 6.04; S, 21.48. Found: C,
72.15; H, 5.84; S, 21.68.
1H-3-Iod o-4-ben zylth ioben zoth iop yr a n (3a ): 279 mg
from 270 mg (1 mmol) of 2a (84%); slightly yellow needles,
mp (ethanol) 81.0 °C; 1H NMR δ 3.49 (s, 2H), 3.84 (s, 2H), 7.20
(m, 8H), 7.92 (d, 1H, 8.0 Hz); 13C NMR δ 35.78, 39.66, 97.09,
126.48, 127.01, 127.16, 127.84, 128.11, 128.47, 129.08, 130.41,
132.24, 135.06, 136.72; UV-vis (CH2Cl2) 253 (14 400), 337
(6900); (CH3CN) 250 (13 200), 337 (6580); EI-MS m/z (relative
+
intensity) 396 (M+, 100), 305 (C9H6S2I+, 22), 269 (C16H13S2
,
12), 178 (C9H6S2+, 58), 91 (C7H7+, 59). Anal. Calcd for
C16H13S2I: C, 48.49; H, 3.31; S, 16.18. Found: C, 48.74; H,
3.86; S, 16.20.
1H-3-Br om o-4-ben zylth ioben zoth iop yr a n (3b): 245 mg
from 270 mg (1 mmol) of 2a (70%); clear needles, mp (ethanol)
59.5 °C; 1H NMR δ 3.55 (s, 2H), 3.83 (s, 2H), 7.18 (m, 8H),
7.88 (d, 1H); 13C NMR δ 34.72, 39.12, 123.37, 126.38, 127.05,
127.16, 127.82, 128.17, 128.35, 129.04, 130.10, 130.18, 133.43,
136.97; UV-vis (CH2Cl2) 248 (14 000), 332 (7200); (CH3CN)
332 (5000); EI-MS m/z (relative intensity) 349 (M+, 57), 269
(C16H13S2+, 9), 258 (C9H6S2Br+, 14), 178 (C9H6S2+, 50), 91
(C7H7+, 100). Anal. Calcd for C16H13S2Br: C, 55.02; H, 3.95;
S, 18.36; Br, 22.88. Found: C, 55.20; H, 4.38; S, 18.16; Br,
22.46.
1H -3-Iod o-4-(4-m et h ylb en zylt h io)-6-m et h ylb en zot h i-
op yr a n (3c): 303 mg from 298 mg (1 mmol) of 2b (71%); clear
needles, mp (ethanol) 67.7 °C; 1H NMR δ 2.30 (s, 3H), 2.39 (s,
3H), 3.51 (s, 2H), 3.81 (s, 2H), 7.01 (m, 6H), 7,71 (s, 1H); 13C
NMR δ 21.09, 21.29, 35.61, 39.60, 96.87, 126.36, 127.66,
127.93, 128.83, 128.97, 129.07, 132.16, 133.82, 135.33, 136.64,
137.50; UV-vis (CH3CN) 250 (12 600), 335 (4300); EI-MS m/z
Bis(4-m eth oxyben zylth io)a cetylen e (2c): 1.49 g from
2.15 g (12 mmol) of 4-methoxybenzyl thiocyanate 1c (74%);
(16) Barbaglia, G. A. Ber. Dtsch. Chem. Ges. 1872, 5, 687.
(17) U.S. Patent 2,394,915, 1946; Chem. Abstr. 1946, 41, 2261-9.
(18) Tamura, Y.; Kawasaki, T.; Adachi, M.; Tanio, M.; Kita, Y.
Tetrahedron Lett. 1977, 50, 4417.
(19) Bacon, R. G. R.; Guy, R. G.; Irwin, R. S. J . Chem. Soc. 1961,
2436.
(relative intensity) 424 (M+, 53), 297 (C18H17S2+, 7), 264
(C18H16S+, 14), 192 (C10H8S2+, 16), 148 (C9H8S+, 8), 105 (C8H9
,
+

2-Benzo- and 2-Naphthothiopyrylium Salts
J . Org. Chem., Vol. 63, No. 14, 1998 4631
100). Anal. Calcd for C18H17S2I: C, 50.94; H, 4.01; S, 15.09.
Found: C, 50.69; H, 4.21; S, 15.15.
orange powder, mp >95 °C (dec); 1H NMR δ 4.28 (s, 2H), 7.06
(d, 2H, 4.7 Hz), 7.13 (d, 1H, 2.6 Hz), 7.27 (m, 2H), 8.18 (t, 1H),
8.45 (t, 1H), 8.56 (d, 1H, 8.2 Hz), 9.03 (d, 1H, 8.6 Hz), 10.58
(s, 1H); UV-vis (CH3CN) 254 (9300), 273 (7900), 320 (4200),
1H-3-Br om o-4-(4-m eth ylben zylth io)-6-m eth ylben zoth i-
op yr a n (3d ): 89 mg from 149 mg (0.5 mmol) of 2b (47%);
clear crystals, mp (ethanol) 79-80 °C; 1H NMR δ 2.30 (s, 3H),
2.39 (s, 3H), 3.59 (s, 2H), 3.81 (s, 2H), 6.99 (m, 6H), 7.66 (s,
1H); 13C NMR δ 20.96, 21.17, 34.38, 38.87, 123.17, 126.36,
127.31, 127.92, 128.92, 128.95, 128.98, 130.41, 133.28, 134.08,
136.71, 137.53; UV-vis (CH3CN) 248 (16 500), 331 (7800).
Anal. Calcd for C18H17S2Br: C, 57.29; H, 4.54; S, 16.99.
Found: C, 57.66; H, 4.78; S, 17.32.
436 (1360); IR (KBr) νmax 1061 cm-1 (BF4-). Anal. Calcd for
-
C
16H12S2Br+BF4
:
C, 44.07; H, 3.00; S, 14.70; Br, 18.30.
Found: C, 44.59; H, 3.21; S, 14.46; Br, 18.25.
1H -3-Iod o-4-(4-m et h ylb en zylt h io)-6-m et h ylb en zot h i-
op yr yliu m tetr a flu or obor a te (4c): 46 mg from 62 mg (0.15
mmol) of 3c (61%); yellow crystals, mp >148 °C (dec); 1H NMR
δ 2.19 (s, 3H), 2.68 (s, 3H), 4.19 (s, 2H), 6.88 (s, 4H), 7.98 (d,
1H, 8.3 Hz), 8.37 (d, 1H, 8.4 Hz), 8.68 (s, 1H), 10.47 (s, 1H);
UV-vis (CH3CN) 220 (24 700), 280 (18 600), 334 (5900), 434
(2700); EI-MS m/z (relative intensity) 423 (M - BF4+, 25), 297
(C18H16S2+, 5), 105 (C8H9+, 100); IR (KBr) νmax 1060 cm-1
(BF4-). Anal. Calcd for C18H16S2I+BF4-: C, 42.38; H, 3.16; S,
12.57. Found: C, 41.95; H, 3.06; S, 12.33.
1H-3-Iodo-4-(4-m eth oxyben zylth io)-6-m eth oxyben zoth i-
op yr yliu m tetr a flu or obor a te (4e): 42 mg from 60 mg (0.13
mmol) of 3e (60%); yellow crystals, mp >143 °C (dec); 1H NMR
δ 3.67 (s, 3H), 4.17 (s, 2H), 4.23 (s, 3H), 6.66 (d, 2H, 8.3 Hz),
6.94 (d, 2H, 8.3 Hz), 7.63 (d, 1H, 9.1 Hz), 8.24 (s, 1H), 8.37 (d,
1H, 9.1 Hz), 10.09 (s, 1H); UV-vis (CH3CN) 232 (22 200), 281
(24 200), 306 (14 300), 371 (7900), 421 (6800); EI-MS m/z
(relative intensity) 455 (M - BF4+, 55), 329 (C18H16S2O2+, 33),
254 (C12H12S2O2+, 60),121 (C8H9O+, 100); IR (KBr) νmax 1033
cm-1 (BF4-). Anal. Calcd for C18H16S2O2I+BF4-: C, 39.88; H,
2.97; S, 11.83. Found: C, 39.90; H, 3.36; S, 11.75.
1H-3-Iod o-4-(1-n a p h th ylm eth ylth io)n a p h th o[1,2-c]th i-
op yr yliu m tetr a flu or obor a te (4f): 41 mg from 41 mg (0.08
mmol) of 3f (85%); bright orange powder, mp >185 °C (dec);
1H NMR δ 4.72 (s, 2H), 6.81 (d, 1H, 6.9 Hz), 7.00 (t, 1H, 7.7
Hz), 7.49 (m, 2H), 7.59 (d, 1H, 8.3 Hz), 7.70 (d, 1H, 7.6 Hz),
8.08 (m, 3H), 8.21 (d, 1H, 7.5 Hz), 8.45 (d, 1H, 9.3 Hz), 8.66
(d, 1H, 9.3 Hz), 8.80 (d, 1H, 8.0 Hz), 10.93 (s, 1H); UV-vis
(CH3CN) 285 (28 900), 450 (8800); IR (KBr) νmax 1054 cm-1
(BF4-). Anal. Calcd for C24H16S2I+BF4-: C, 49.51; H, 2.77; S,
11.01. Found: C, 49.95; H, 2.33; S, 11.02.
1H-3-Iodo-4-(4-m eth oxyben zylth io)-6-m eth oxyben zoth i-
op yr a n e (3e): 1.16 g from 1.0 g (3 mmol) of 2c (84%); clear
crystals, mp (ethanol) 97.5 °C; 1H NMR δ 3.50 (s, 2H), 3.76 (s,
3H), 3.81 (s, 2H), 3.82 (s, 3H), 6.73 (d, 2H, 8.5 Hz), 6.82 (d,
1H, 8.2 Hz), 6.97 (s, 1H), 6.98 (d, 2H, 8.4 Hz), 7.49 (d, 1H, 2.5
Hz); 13C NMR δ 35.36, 39.22, 55.24, 55.47, 97.99, 113.04,
113.56, 113.88, 122.77, 127.48, 128.86, 130.18, 133.42, 135.07,
158.62, 159.35; UV-vis (CH3CN) 228 (32 800), 253 (16 600),
320 (6500), 334 (5800); EI-MS m/z (relative intensity) 455 (M+,
100), 330 (C18H17S2+, 7), 264 (C18H17S2O2+, 48), 208 (C10H8S2O+,
22), 121 (C8H9O+, 100). Anal. Calcd for C18H17S2O2I: C, 47.37;
H, 3.75; S, 14.05. Found: C, 47.52; H, 3.70; S, 14.54.
1H-3-Iod o-4-(1-n a p h th ylm eth ylth io)n a p h th o[1,2-c]th i-
op yr a n (3f): 158 mg from 185 mg (0.5 mmol) of 2e (63%);
yellow crystals, mp (ethanol) 167.5-168.5 °C; 1H NMR δ 3.92
(s, 2H), 4.28 (s, 2H), 6.90 (d, 1H), 7.17 (t, 1H), 7.45 (m, 2H),
7.54 (m, 2H), 7.68 (d, 1H), 7.80 (m, 2H), 7.87 (d, 1H), 7.96 (d,
1H), 8.10 (t, 1H), 8.19 (d, 1H); 13C NMR δ 30.56, 37.71, 97.75,
123.31, 124.09, 124.76, 125.35, 125.73, 126.01, 126.04, 126.73,
127.45, 127.54, 127.65, 128.26, 128.61, 128.66, 129.57, 130.72,
131.50, 132.14, 132.40, 133.57, 133.77; UV-vis (CH3CN) 245
(sh) (12 100), 288 (8170), 363 (2860); EI-MS m/z (relative
intensity) 496 (M+, 95), 369 (C24H17S2+, 12), 336 (C24H16S+, 33),
254 (I2+, 6), 227 (C13H7S2+, 13), 184.5 (C24H17S22+, 9), 141
(C11H9+, 100). Anal. Calcd for C24H17S2I: C, 58.07; H, 3.45;
S, 12.92. Found: C, 58.12; H, 3.63; S, 13.04.
1H-3-Iod o-4-(2-n a p h th ylm eth ylth io)n a p h th o[2,1-c]th i-
op yr a n (3g): 275 mg from 370 mg (1 mmol) of 2f (55%); yellow
crystals, mp (ethanol) 106-108 °C; 1H NMR δ 2.95 (s, 2H),
3.66 (s, 2H), 6.71 (s, 1H), 7.04 (d, 1H), 7.17 (d, 1H), 7.39 (m,
2H), 7.55 (m, 4H), 7.72 (m, 1H), 7.78 (d, 1H), 7.86 (d, 1H), 9.03
(d, 1H); 13C NMR δ 37.83, 39.95, 95.63, 124.24, 125.72, 125.98,
126.14, 126.98, 127.50, 127.74, 128.37, 129.20, 132.24, 132.59,
133.53, 133.95, 134.09, 135.43; UV-vis (CH3CN) 250 (sh)
(27 300), 363 (5890); EI-MS m/z (relative intensity) 496 (M+,
18), 369 (C24H17S2+, 5), 336 (C24H16S+, 12), 254 (I2+, 6), 227
(C13H7S2+, 8), 192 (IS2H+, 30), 141 (C11H9+, 54), 91 (C7H7+, 100).
R ea ct ion b et w een Bis(2-b r om ob en zylt h io)a cet ylen e
(2d ) a n d Ha logen s: F or m a tion of 1,2-Bis(2-br om oben -
zylth io)-1,2-d ibr om oeth ylen e (5). Following the general
procedure for the preparation of benzothiopyrans 3 (see above),
to 1 mmol of 2d (584 mg) was added an equimolar amount of
ICl or Br2. Only educt and a mixture of decomposition
products could be isolated from the reaction with ICl. With
bromine, 208 mg (28%) of a new compound was formed. The
analytical data confirm the formation of the addition product
1,2-bis(2-bromobenzylthio)-1,2-dibromoethylene 5 and not the
corresponding benzothiopyran 3i.
Anal. Calcd for
C24H17S2I: C, 58.07; H, 3.45; S, 12.92.
1
Found: C, 58.08; H, 3.67; S, 12.99.
5: clear crystals; mp (ethanol) 75-77 °C; H NMR δ 4.14
Gen er a l P r oced u r e: 2-Ben zoth iop yr yliu m Sa lts 4 by
Hyd r id e Abstr a ction w ith Tr BF 4 fr om Ben zoth iop yr a n s
3. 3 (0.5 mmol) was dissolved in 1 mL of dry CH2Cl2 and added
(s, 4H), 7.12 (t, 2H, 6.9 Hz), 7.22 (t, 2H, 7.4 Hz), 7.30 (d, 2H,
7.3 Hz), 7.54 (d, 2H, 7.8 Hz); EI-MS m/z (relative intensity)
585 (M+, 65), 426 (M - Br2+ ) C16H12S2Br2+, 7), 337 (C9H6S2-
in one portion to a solution of TrBF4 (231 mg; 0.7 mmol) in
Br2+, 71), 258 (C9H6S2Br+, 44), 170 (C7H6Br+, 100), 89 (C7H6
,
20
+
2 mL of CH2Cl2. The resulting dark liquid was stirred for 30
min and then poured into the 3-fold volume of dry diethyl ether
with vigorous stirring. The formed solid was collected, washed
twice with diethyl ether, and dried in a vacuum desiccator.
Every step was carried out under argon and with exclusion of
moisture. If necessary, recrystallization was possible in acetic
anhydride with some loss of material (incomplete precipita-
tion).
1H-3-Iod o-4-ben zylth ioben zoth iop yr yliu m tetr a flu o-
r obor a te (4a ): 135 mg from 199 mg (0.5 mmol) of 3a (47%);
orange powder, mp >155 °C (dec); 1H NMR δ 4.26 (s, 2H), 7.03
(d, 1H), 7.14 (d, 2H), 7.27 (d, 2H), 8.17 (t, 1H), 8.42 (t, 1H),
8.51 (d, 1H), 9.03 (d, 1H), 10.66 (s, 1H); UV-vis (CH3CN) 276
(14 000), 324 (sh) (5200), 436 (2600); IR (KBr) νmax 1066 cm-1
(BF4-). Anal. Calcd for C16H12S2I+BF4-: C, 39.84; H, 2.70; S,
13.28. Found: C, 39.86; H, 2.91; S, 13.23.
16). Anal. Calcd for C16H12S2Br4: C, 32.68; H, 2.68; S, 10.90;
Br, 54.36. Found: C, 33.07; H, 2.20; S, 11.03; Br, 53.91.
Ackn owledgm en t. The authors thank Dr. Baumeis-
ter and Professor Dr. Hartung, Martin-Luther-Univer-
sity Halle-Wittenberg, Institute of Physical Chemistry,
for carrying out the X-ray crystal structure analysis
shown in Figure 1. Thomas R. Klein thanks the Studi-
enstiftung des deutschen Volkes and Nasser A. M. Yehia
the Deutscher Akademischer Austauschdienst (DAAD)
for financial support.
Su p p or tin g In for m a tion Ava ila ble: 1H-1H COSY spec-
tra of 3g with interpretation of the aromatic cross-peaks
(Figure 2). Further X-ray crystal structure data for 3a (9
pages). This material is contained in libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, and can be ordered from the ACS; see any current
masthead page for ordering information.
1H-3-Br om o-4-ben zylth ioben zoth iop yr yliu m tetr a flu -
or obor a te (4b): 97 mg from 175 mg (0.5 mmol) of 3b (37%);
(20) Organic Syntheses; Wiley: New York, 1988; Collect. Vol. 6; p
997.
J O972334L