1,3-Dipolar cycloadditions, 117. Reactions of thiobenzophenone S- methylide with thiocarbonyl compounds

Article abstract of DOI:10.1002/(sici)1099-0690(200005)2000:9<1695::aid-ejoc1695>3.0.co;2-4

2,5-Dihydro-2,2-diphenyl-1,3,4-thiadiazole (4) eliminates N₂ at -45 °C and generates thiobenzophenone S-methylide (5), which is intercepted by dipolarophiles. The 1,3-cycloadditions of 5 with thiones (aromatic and aliphatic thioketones, dithioesters, trithiocarbonate) furnish 1,3- dithiolanes 7, in which the substituents, even voluminous ones, appear in the proximal 4- and 5-positions. The reaction of 5 with adamant-anethione furnishes 7h and 4,4,5,5-tetraphenyl-1,3-dithiolane (7a) in a ratio of 4:1; a methylene transfer is involved, and the mechanistic pathways are discussed. The cycloadduct 7f originating from 5 and diphenyl trithiocarbonate undergoes an isomerization which consists of ionization and ring-opening leading to a ketene dithioacetal structure.

Full text of DOI:10.1002/(sici)1099-0690(200005)2000:9<1695::aid-ejoc1695>3.0.co;2-4

FULL PAPER
1,3-Dipolar Cycloadditions, 117[‡]
Reactions of Thiobenzophenone S-Methylide with Thiocarbonyl Compounds
Rolf Huisgen,*[a] Xingya Li,[a][°] Grzegorz Mloston,[a][°°] and Claudia Fulka[a]
Dedicated to Professor M. V. George, Regional Research Laboratory, Trivandrum (CSIR), India, on the occasion
of his 70th birthday
Keywords: Thiocarbonyl ylides / Cycloadditions / 1,3-Dithiolanes / Sulfur heterocycles / Thioketones
2,5-Dihydro-2,2-diphenyl-1,3,4-thiadiazole (4) eliminates N2
anethione furnishes 7h and 4,4,5,5-tetraphenyl-1,3-dithiol-
at −45 °C and generates thiobenzophenone S-methylide (5), ane (7a) in a ratio of 4:1; a methylene transfer is involved, and
which is intercepted by dipolarophiles. The 1,3-cycloaddi- the mechanistic pathways are discussed. The cycloadduct 7f
tions of 5 with thiones (aromatic and aliphatic thioketones,
dithioesters, trithiocarbonate) furnish 1,3-dithiolanes 7, in
which the substituents, even voluminous ones, appear in the
proximal 4- and 5-positions. The reaction of 5 with adamant-
originating from 5 and diphenyl trithiocarbonate undergoes
an isomerization which consists of ionization and ring-open-
ing leading to a ketene dithioacetal structure.
Introduction
Thiocarbonyl ylides are active 1,3-dipoles in cycloaddi-
tions.[1] A general synthesis consists of the thermal elimina-
tion of N2 from 2,5-dihydro-1,3,4-thiadiazoles, which, in
turn, are accessible by 1,3-cycloadditions of diazoalkanes to
CϭS double bonds. The availability of thiones constitutes a
limit; thioaldehydes cannot be prepared in substance, except
for sterically hindered types.[2] This gap is filled by the pre-
paration of thiocarbonyl ylides from silylated precursors.
Even thioformaldehyde S-methylide (2), the parent com-
pound, has been synthesized from 1 and was intercepted by
CC multiple bonds furnishing high yields of cycloadducts
(Scheme 1).[3] 1-Trimethylsilylated thioformaldehyde S-
methylides are likewise available.[4]
Scheme 1
1,3,4-Thiadiazolines, prepared from aliphatic thioketones
and diazomethane, can be isolated and have some storage
capacity. The extrusion of N2 is carried out in the presence
of a dipolarophile at controlled temperature. Recently, we
described 1,3-cycloadditions of adamantanethione S-
methylide (3).[5,6]
The rapid addition of diazomethane to thiobenzo-
phenone at Ϫ78 °C furnishes quantitatively the 2,5-dihydro-
2,2-diphenyl-1,3,4-thiadiazole (4) which is conveniently
handled in solution, as described in the preceding paper.[7]
The reaction 4 Ǟ 5 ϩ N2 proceeds in THF at Ϫ45 °C with
t1/2 ϭ 56 min; a small stationary concentration of thioben-
zophenone S-methylide (5) allows an efficient in situ cap-
turing by reaction partners.
When diazomethane is introduced into a solution of
thiobenzophenone at room temperature, the thiadiazoline 4
rapidly expels N2 and the intermediate 5 adds to a second
molecule of thiobenzophenone providing 4,4,5,5-tetra-
phenyl-1,3-dithiolane (7a) ("Schönberg reaction").[7]
Formation of "Mixed" 1,3-Dithiolanes
[‡]
Part 116: Ref.[7]
[a]
Institut für Organische Chemie der Universität München,
Thiobenzophenone (6a) fulfils a double role in the men-
tioned formation of 7a: The first molecule interacts as a
dipolarophile vs. diazomethane, whereas the second molec-
ule captures the S-ylide 5. The separation of the two roles
is the basis of a general and convenient preparation of 1,3-
Butenandtstrasse 13, D-81377 München, Germany
[°]
Present address: Avery Research Center,
Pasadena, CA 91107, USA
[°°]
Present address: Institute of Organic and Applied Chemistry,
University of Lodz, Narutowicza 68, PL-90Ϫ136 Lodz,
Poland
Eur. J. Org. Chem. 2000, 1695Ϫ1702
WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2000
1434Ϫ193X/00/0509Ϫ1695 $ 17.50ϩ.50/0
1695

R. Huisgen, X. Li, G. Mloston, C. Fulka
FULL PAPER
dithiolanes.[8] This synthesis elegantly supplements the clas-
Apart from the conversion of 7a to tetraphenylethylene,
sic reaction of 1,2-dithiols with carbonyl compounds, the 13C NMR parameters reveal the C2v symmetry of 7a
known since 1887;[9] an abundance of 2-substituted 1,3-di- and other "Schönberg products", which bear identical sub-
thiolanes originates from the protection of carbonyl groups stituents in 4- and 5-positions.[7] The symmetry is reduced
by dithioacetal formation with 1,2-dithiols.[10]
to a σ plane in 1,3-dithiolanes 7bϪ7i, and C-4 and C-5 have
The solution of 4 in THF, prepared at Ϫ78 °C, was mixed different δC values. The 13C triplets of C-2 appear in the
with the precooled solution of a second thiocarbonyl react- narrow range of δC ϭ 25.7Ϫ32.2 for 7aϪ7i, whereas the
ant 6 (usually 1.2 equiv) and kept in a cold bath at about singlets of C-4 and C-5 lie in the likewise close range of
Ϫ45 °C, until the N2 evolution ceased. The crystalline 1,3- δC ϭ 70.0Ϫ82.4. The δH singlet of 2-H2 (AB for 11) was
dithiolanes, obtained from 5 and various thiocarbonyl com- found at δ ϭ 3.27Ϫ4.26 (Table 1).
pounds are listed in Table 1; aromatic thioketones provided
Matched pairs of S-methylide A ϩ thione B and S-
high yields of cycloadducts. The procedure was adapted to methylide B ϩ thione A afforded one and the same dithiol-
other diarylthioketone S-methylides, which are analogously ane; that demands the formation of 4,5-disubstituted thiol-
amenable from the thioketones and diazomethane via the anes 7 and excludes the 2,4-regioisomers 8. E.g., the
2,5-dihydro-1,3,4-thiadiazoles (Table 2, Scheme 2).
cycloaddition of
5
with 4,4Ј-dimethoxythiobenzo-
Table 1. 1,3-Dithiolanes prepared from thiobenzophenone S-methylide (5) and thiones in THF at Ϫ45 °C
Dithiolane
Yield (%)
NMR Parameters (CDCl3)
Thione
Formula
m.p. (°C)
δ(C-2)
δ(C-4/C-5)
δH(2-H2)
Thiobenzophenone
7a
7b
95
86
82
84
95
87
47
75
27
8
202Ϫ203
181Ϫ183
Ͼ 236
30.1
30.0
31.0
31.8
30.5
30.6
31.4
32.2
28.0
77.6
3.74
3.63
4.26
4.08
4.08
4,4ЈϪDimethoxythiobenzophenone
Fluorene-9-thione
76.8, 77.4
74.1, 76.3
70.0, 80.2
78.5, 79.8
80.9, 82.4
81.3, 89.5
75.9, 79.8
76.6, 77.5
7c
Xanthione
Thioxanthione
Methyl 1-dithionaphthoate
Diphenyl trithiocarbonate
2-Thioxo-1,3-dithiolane-4,5-dione
Adamantanethione
7d
165Ϫ167
149Ϫ151
151Ϫ153
150Ϫ152
198Ϫ199
201Ϫ203
203Ϫ204
124Ϫ126
7e
11
3.25,3.81
7f
3.82
3.88
3.28
3.74
3.34
7g
7h
ϩ7a
7i
2,2,4,4-Tetramethyl-3-thioxo-cyclobutanone
62
25.7
75.3, 78.5
Table 2. 1,3-Dithiolanes from various thiocarbonyl ylides and thiobenzophenone in THF
Dipolarophilic thione
Dithiolane
Yield (%)
Formula
m.p. (°C)
a. 4,4-Dimethoxythiobenzophenone S-methylide (9b)
Thiobenzophenone
7b
7c
7e
95
98
180Ϫ182
161Ϫ162
4,4Ј-Dimethoxythiobenzophenone[7]
b. Fluorene-9-thione S-methylide (9c)
Thiobenzophenone
86
94
Ͼ 232
259Ϫ262
Fluorene-9-thione[7]
c. Thioxanthione S-methylide (9e)
Thiobenzophenone
67
149Ϫ151
168Ϫ170
Thioxanthione[12]
e. Adamantanethione S-methylide (9h)
Thiobenzophenone[7]
7h
ϩ10h
50
42
197Ϫ199
126Ϫ128
f. 2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-methylide (9i)
Thiobenzophenone[15]
7i
ϩ10i
ϩ10a
68
20
9
122Ϫ125
not isol.
202Ϫ203
The regiochemistry of the cycloaddition deserves atten- phenone (6b) gave rise to 7b (86% isolated), whereas the
tion insofar as only the 4,4,5,5-tetrasubstituted 1,3-dithiol- interaction of 4,4Ј-dimethoxythiobenzophenone S-methyl-
anes 7 were observed. Thus, the reactants combine in the ide (9b) with thione 6a produced the same 7b in 98% yield
sterically hard way by bond formation between the centers (Table 2).
bearing the voluminous substituents. Apparently, other ef-
What are the limits in the choice of the thiocarbonyl
fects are controlling. According to Aono, Terao, and Ach- compound in the role of the dipolarophile? Despite the di-
iwa, HO(5) Ϫ LU(6a) is the dominant interaction in the thioester resonance, methyl 1-dithionaphthoate accepted
concerted addition, and the atomic orbital coefficients cal- the S-methylide 5 to give 87% of 11, which is lacking sym-
culated by MNDO appear to favor the formation of 7a metry; the 13C NMR parameters reveal diastereotopicity of
over 8a.[11]
the phenyl groups. However, O-methyl thiobenzoate, thio-
1696
Eur. J. Org. Chem. 2000, 1695Ϫ1702

1,3-Dipolar Cycloadditions, 117
FULL PAPER
Scheme 3
probable. In both the MS, m/z 210 is the base peak, and
(C6H5)2CϭCϭSϩ is a likely candidate. For the (34Sϩ13C2)
isotope peak (m/z 212), 5.6% is expected; only in the case
of 7f, the intensity of m/z 212 is by 18% greater, pointing
to a second fragment C14H10Sϩ. The latter was found in
the MS of most cycloadducts of 5 and is attributed to the
radical cation of 5 (see below). The peaks m/z 110
(C6H5SHϩ) and 109 (C6H5Sϩ) are highly populated in the
MS of both 7f and 12.
Not only by acid catalysis, also by adsorption on silica
gel the isomerization 7f Ǟ 12 is accelerated. On the other
hand, 7f is stable in C6D6 at room temperature. These data
point to an ionization process, 7f Ǟ 13. The subsequent
attack of the thiophenolate on the resonance-stabilized di-
thiolanium cation is a ring-opening process.
Scheme 2
benzamide, O-ethyl thiocarbamate, and phenyl isothiocyan-
ate failed to react with 5.
Diphenyl trithiocarbonate (6f) provided dithiolane 7f in
47% yield. Besides the symmetry shown by the NMR para-
meters, the hydrogenolysis with Raney nickel in methanol
furnished 1,1-diphenylethane in accordance with structure
7f. 2-Thioxo-1,3-dithiolane-4,5-dione (6g) is a cyclic trithio-
carbonate and an active dipolarophile vs. 5; the somewhat
odd choice stems from the fact that Schönberg et al. reacted
it with diazoalkanes.[12]
The heterolysis of a CϪS bond by substitution with thiol-
ate at sulfur is unusual, but there are precedents. The acid-
catalyzed reduction of acyloins to ketones by 1,3-propane-
dithiol, described by Cram and Cordon in 1955,[13] involves
such a step with RSH as nucleophilic reagent. Methanethi-
olate is the reducing agent in the conversion of 14 to deoxy-
benzoin and dimethyl disulfide, according to Oki et al.
(Scheme 4).[14]
Many of the dithiolanes turn blue on melting, suggesting
some thiobenzophenone as dissociation product. The in-
stability of dithiolane 7f in solution has another reason. In
acid-free CDCl3 at room temp., cycloadduct 7f, δ(2-H2) ϭ
3.82, slowly isomerized to a compound with δ(CH2) ϭ 3.99;
the conversion reached 5% in 24 h, but was catalyzed by a
trace of trifluoroacetic acid. The viscous oily product gave
correct analytical data for an isomer of 7f. The methylene
protons remain equivalent, indicating a σ plane.
We first suspected a rearrangement of 7f to 8f by dissoci-
ation and recombination, but attempts of capturing the in-
termediate 5 by more active dipolarophiles failed. For both
7f and 8f, two pairs of equivalent phenyl groups are ex-
pected. The 13C NMR spectra confirm the pairwise equival-
ence for 7f. However, the new isomer shows four nonequiva-
lent phenyls, i.e., eight signals for o- and m-CH, and four
Scheme 4
Adamantanethione (6h) and 2,2,4,4-tetramethyl-3-thi-
for p-CH. Five signals appear in the δ region of quaternary oxocyclobutanone (6i) represent aliphatic thioketones in
sp2-hybridized C-atoms; at least one must be olefinic .
Table 1; both are sterically hindered. Nevertheless, both re-
Structure 12 (Scheme 3) fits the spectroscopic properties. acted with 5 furnishing the 4,5-disubstituted dithiolanes 7h
The Cq at highest frequency (δ ϭ 153.8) could well be the and 7i, albeit in lower yield.
C-3 of the ketene dithioacetal group, and the CH2 group
Some side reactions are noteworthy. The formation of 8%
between sulfur functions appears at higher frequency (δ ϭ of 4,4,5,5-tetraphenyl-1,3-dithiolane (7a) besides 27% of 7h
42.2) than in the 5-membered ring of 7f (δ ϭ 31.4). Whereas in the reaction of adamantanethione (6h) with 5 has mech-
1
many H and 13C signals of 7f are broadened, due to the anistic implications. It is conceivable that a thiophilic attack
hindered ring inversion (see below), the NMR absorptions of the 1,3-dipole 5 on 6h gives rise to a zwitterionic interme-
of the open-chain compound 12 are sharp and well-defined. diate 15; the species can also be formulated as a diradical
The mass spectra of 7f and 12 are similar; partial thermal (Scheme 5). 15 could mediate a methylene transfer equilib-
isomerization (120Ϫ160 °C) of 7f preceding ionization is rium, 5 ϩ 6h o 6a ϩ 9h. Since 6a is more reactive than 6h,
Eur. J. Org. Chem. 2000, 1695Ϫ1702
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R. Huisgen, X. Li, G. Mloston, C. Fulka
FULL PAPER
it will capture 5 with preference. Thus, 7a is formed besides
the mixed dithiolane 7h.
The cyclohexane-like chair conformations of 1,4-di-
thianes are located in pronounced energy troughs,[7]
whereas the pseudorotation circuit of the 5-membered 1,3-
dithiolanes usually involves small barriers to ring inversion.
However, the NMR signals of 1,3-dithiolanes, which con-
tain voluminous groups in 4- and 5-position, show a dis-
tinct broadening which can be ascribed to dynamic pro-
cesses at room temperature.
The tetraphenyl compound 7a was chosen as an example.
The 13C NMR spectrum (100 MHz, CDCl3) reveals at Ϫ44
°C two sets of phenyl groups, each consisting of four sharp
signals, one corresponding to pseudo-axial and the other to
pseudo-equatorial pairs of phenyl groups in a frozen 1,3-
dithiolane conformation; the CϪC6H5 rotation must still be
rapid. A pseudorotation barrier for the heteroring, ∆G϶
ϭ
Scheme 5
13.0 ± 0.2 kcal molϪ1, was evaluated from coalescence data
Is the cyclization of type 15 intermediates the normal of the ortho-C (TC ϭ 0 °C) and the quaternary phenylϪC
pathway to 1,3-dithiolanes? In the reactions of 5 with di- (TC ϭ ϩ15 °C). The same barrier height resulted from the
arylthioketones 6bϪ6g (Table 1), the formation of 7a has temperature dependence of the 1H NMR spectrum
not been observed. We favor a concerted mechanism as long (400 MHz, Cl2CDϪCDCl2). The doublet of the eight o-H
as strong steric hindrance does not give the twostep path- at 45 °C (δ ϭ 7.31) coalesces at 1 °C and splits into two
way via 15 a chance. The formula scheme above records the 4H-doublets at Ϫ44 °C (δ ϭ 7.20, 7.43).
concerted and stepwise paths giving 7h. Calculations of the
transition states for the concerted and twostep pathway
would be highly desirable.
The Mass Spectra of the 1,3-Dithiolanes
The CϭS bond of 2,2,4,4-tetramethyl-3-thioxocyclobut-
anone (6i) is screened by four methyl groups. The hindered
interaction with 5 led to 62% of 7i, and the regioisomer 8i
was not found.
When the S-ylide 5 is not intercepted, its dimer, the
2,2,3,3-tetraphenyl-1,4-dithiane, is usually formed in high
yield.[7] In the reaction with 6h, the dithiolane yields, 27%
of 7h and 8% of 7a, account for 43% of the employed 5,
and 62% of 5 was consumed in the formation of 7i from 6i.
In both reactions no dithiane, but substantial amounts of
benzophenone were observed among the products.
Some general features will be discussed using C2v-sym-
metric dithiolane 7a as an example. The stepwise degrada-
tions sketched out are formal, and the same reserve con-
cerns the structures of the fragments. Very often, molecular
formulae were confirmed by the intensities of isotope peaks
for 13C and (34Sϩ13C2), and sometimes by high resolution;
however, the structures proposed are not more than a kind
of bookkeeping on the basis of smallest structural changes
(Scheme 6).
The idea is not far-fetched that these cycloadditions of 5
could also furnish the sterically less hindered dithiolanes 8h
and 8i besides 7h and 7i. A hydrolysis of the 2,2-diphenyl-
1,3-dithiolanes 8 to give benzophenone during product sep-
aration by chromatography on silica gel would be conceiv-
able. Furthermore, the hydrolysis of an unknown interme-
diate (e.g., 15 on the path to 7) by traces of water during
the interaction with 5 would constitute another possible
source of benzophenone.
Recently we described that adamantanethione S-methyl-
ide (3), combined with thiobenzophenone affording 50% of
7h and 42% of the regioisomer 10h; the structure of the
latter was confirmed by X-ray analysis.[6] It is worth men-
tioning that 8h and 10h cannot be formed via a type 15 inter-
mediate. Similarly, the product of 2,2,4,4-tetramethyl-3-
thioxocyclobutanone S-methylide (9i) with thiobenzo-
phenone contained 68% of 7i and 20% of 10i; in addition,
9% of the tetraphenyl-1,3-dithiolane (7a) was formed.[15]
It is noteworthy that the cycloadditions of S-methylides
Scheme 6
The major splitting pathway of the radical cation 7aϩ is
9h and 9i with thiones 6h and 6i afforded only the 2,4-sub- the 1,3-cycloreversion rendering back thiocarbonyl ylide
stituted 1,3-dithiolanes;[16] here, finally, the steric interac- and thione. Each of the two fragments can accommodate
tion appears to surpass the electronic preference.
the radical cation character suggesting that the ionization
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Eur. J. Org. Chem. 2000, 1695Ϫ1702

1,3-Dipolar Cycloadditions, 117
FULL PAPER
potentials of the neutral species are not grossly different. tion of a MS peak depends on the rate ratio of formation
The radical cation of 5, present in the MS of nearly all and breakdown of a fragment, the conclusion from peak
dithiolanes of type 7, appears in 7a with a peak intensity of intensities on major or minor degradation paths is often fal-
35%. We favor a description as distonic radical ion 16a in lacious.
which charge and spin density have different centers.[17] Per-
haps 16a occurs in an equilibrium with the thiirane radical
Experimental Section
cation 17a. Species 17a is a likely candidate for the loss of
sulfur, and the peak m/z 180 (22%) corresponds to C14H1ϩ2
and could be the radical cation of 1,1-diphenylethylene,
methylfluorene, or 9,10-dihydrophenanthrene, etc.; the con-
densed systems would explain the appearance of a cascade
with m/z 179 (18%) and 178 (20%). It is worth mentioning,
that the bonded groups (C6H5)2C and CH2 of 20a were sep-
arated by sulfur in the dithiolane; they become connected
by the electrocyclic ring closure, 16a Ǟ 17a.
General:[7] CC is column chromatography on silica gel.
4,4,5,5-Tetraphenyl-1,3-dithiolane (7a).[7]
؊
(a): 1H NMR
(400 MHz, 25 °C): δ ϭ 3.74 (s, 2-H2), 7.05 (nearly tt, 8 m-H), 7.12
(tt, J ഠ 7.2, 1.2 Hz, 4 p-H), 7.34 (d, J ϭ 6.4 Hz, 8 o-H, broad,
approaching coalescence). Ϫ 13C (100 MHz, DEPT, 25 °C): δ ϭ
30.1 (C-2), 77.6 (C-4/5), 126.3, 126.5, 131.7 (the latter broadened,
2:1:2 for arom. m/p/o-CH), 143.2 (very broad, 4 arom. Cq); much
less line broadening in the 20 MHz spectrum. Ϫ MS (70 eV, 110
°C); m/z (%): 410 (1.6) [Mϩ; 13C 0.47/0.50, (34Sϩ13C2) 0.21/0.19],
332 (18) [Mϩ Ϫ CH2S2, C26H2ϩ0, 22a; 13C 5.3/5.2, no 34S peak], 255
(2.5) [C20Hϩ15, 332 Ϫ C6H5), 254 (3.2), 253 (5.9), 252 (5.5), 212 (35)
[C14H12Sϩ, 16a], 211 (28) [212ϩ Ϫ H], 198 (61) [C13H10Sϩ,
(C6H5)2CϭSϩ; 13C 8.8/9.2, (34Sϩ13C2) 3.3/3.3], 197 (21), 180 (22)
[C14Hϩ12, 20a], 179 (18) [C14H1ϩ1], 178 (20), 167 (19) [(C6H5)2CHϩ],
166 (6), 165 (100) [fluorenylϩ, 18; 13C 15/16], 152 (10) [C12H8ϩ, bi-
phenylene], 121 (56) [C6H5ϪCϵSϩ; 13C 4.3/4.8; (34Sϩ13C2) 2.6/
2.7], 77 (17) [C6H5ϩ]. Ϫ (b) 1H NMR Evidence for Dynamic Process:
The 400 MHz spectrum at 40 °C in Cl2CDϪCDCl2 shows the 8
arom. o-H as a slightly broadened d at δ ϭ 7.31. On cooling, the
signal reaches coalescence at ϩ1 °C and splits into two d at lower
temp.; at Ϫ44 °C they are still somewhat broad, δ ϭ 7.20 and 7.43,
3J ϭ 6.8 Hz. The low-frequency branch partially overlaps with the
t of the 4 p-H at δ ϭ 7.11. The ∆ν of the two d for the 2 ϫ 4 o-H
shows only a small temp. dependence and allows an extrapolation
to ∆ν ϭ 89 Hz at TC ϩ1 °C. From k ϭ 198 sϪ1, ∆GC϶ ϭ 13.1 kcal
molϪ1 at ϩ1 °C is calculated. The s of 2-H2 at δ ϭ 3.74 reveals at
Ϫ44 °C a slight broadening; due to the presence of a quasi-C2 axis,
no splitting is expected. Ϫ (c) 13C DNMR: A HETCOR experiment
connected 1H and 13C chemical shifts and confirmed the assign-
ments. The 100 MHz spectrum (CDCl3) displays at Ϫ44 °C a
double set of phenyl signals for pseudo-e and pseudo-a positions:
δ ϭ 125.73, 126.83 (2 ϫ 4 m-C), 126.20, 126.72 (2 ϫ 2 p-C), 130.75,
132.01 (2 ϫ 4 o-C). On raising the temp., the signals of p-C and m-
C merge, thwarting an evaluation. The two o-C signals coalesce at
0 °C, and those of Cq at 15 °C. The temp. dependence of v(13C)
allows a linear extrapolation of ∆ν to TC: 127 Hz for o-C and
395 Hz for Cq. k values of 283 sϪ1 at 0 °C and 877 at 15 °C lead
to ∆G϶ ϭ 12.9 and 13.0 kcal molϪ1, respectively.
Thiobenzophenone, i.e., the second fragment of 7aϩ, also
appeared as radical cation (6aϩ), m/z 198 (61%), and was
confirmed by the intensities of isotope peaks. Fragments
[Mϩ Ϫ SH] are generally found in the MS of aliphatic and
aromatic thioketones.[18] Here, as in the MS of thiobenzo-
phenone itself, C13H9ϩ is the base peak and was identified
with the 9-fluorenyl cation (18) by Schumann et al. in
1969.[19] The cation 18 and the thiobenzoyl cation 19a (m/z
121) are kind of leading fossils in the MS reported here .
The fragment m/z 332, free of sulfur, is C26Hϩ20 and com-
plies with [Mϩ Ϫ CH2S2]. More probable than a onestep
elimination of CH2S2 is a ring opening to give 21, and an
intramolecular radical substitution. Formally, 22a could be
the radical cation of tetraphenylethylene, but nonolefinic
isomers are also conceivable (Scheme 7).
Scheme 7
Matched pairs of [3ϩ2] cycloadditions afford the same
1,3-dithiolanes 7. In concordance, two cycloreversion routes
of 7ϩ are open and provide double the manifold of frag-
ments which were so far discussed. E.g., in the MS of 7b
(two 4-methoxyphenyl groups in 4 position), the distonic
ions 16b (m/z 272, 14%) and 16a (m/z 212, 15%) are found,
and so are the thione radical cations 6b (m/z 258, 19%) and
6a (m/z 198, 47%). The fluorenyl cation 18 (m/z 165, 100%)
dominates over its dimethoxy derivative (m/z 225, 16%),
and the thioacylium ions 19b (m/z 151, 16%) and 19a (m/z
121, 53%) appear side by side (Scheme 8). Since the popula-
4,4-Bis(4-methoxyphenyl)-5,5-diphenyl-1,3-dithiolane (7b). ؊ (a):
Thiobenzophenone (6a, 665 mg, 3.35 mmol) in 5 mL of THF,
cooled to Ϫ78 °C, was reacted with 1.0 equiv. of diazomethane in
about 5 mL of THF, precooled to Ϫ78 °C, until the dark-blue color
turned light-blue (see ref.[7]). 4,4Ј-Dimethoxythiobenzophenone (6b,
1.14 g, 4.42 mmol) in 8 mL of THF at Ϫ78 °C was mixed with the
above solution of 5 and kept in a Ϫ40 °C bath (thermostated) for
3 h and at Ϫ20 °C for 1 h. After the solution reached room temp.,
the solvent was removed at the rotary evaporator, and the residue
crystallized from ether/pentane; 1.35 g (86%) of 7b was obtained,
1
m.p. 181Ϫ183 °C (blue melt) after recrystallization. Ϫ H NMR:
δ ϭ 3.63 (s, 2-H2), 3.70 (s, 2 OCH3), 6.43Ϫ6.72 (m, 4 arom. H),
6.90Ϫ7.47 (m, 14 arom. H). Ϫ 13C NMR (20.2 MHz, H-decoupled
and off-resonance): Table 1; further absorptions: δ ϭ 55.1 (q, 2
OCH3), 111.5 (d, C-3Ј/5Ј of 2 p-methoxyphenyl), 126.4, 131.6,
132.8 (3 d, 14 arom. CH), 134.8, 143.5 (2 s, C-1Ј of 4 aryl), 157.9
Scheme 8
Eur. J. Org. Chem. 2000, 1695Ϫ1702
1699

R. Huisgen, X. Li, G. Mloston, C. Fulka
FULL PAPER
(s, C-4Ј of 2 p-methoxyphenyl). Ϫ MS (120 °C); m/z (%): 470 (1.5)
1.02 g of 7e as yellow crystals, m.p. 149Ϫ151 °C (dec.), were ob-
[Mϩ], 392 (63) [C28H24O2ϩ, Mϩ Ϫ CH2S2, 22b; 13C 20/19, 13C2 3.2/ tained. The mother liquor provided 292 mg of green solid, which
3.0, no S], 272 (14) [C16H16O2Sϩ, 16b], 258 (19) [C16H16O2Sϩ, 6bϩ; contained 251 mg of 7e (1H NMR analysis with weight standard),
13C 3.2/3.7, (34Sϩ13C2) 1.1/1.4], 241 (10), 240 (12) [C16H16O2ϩ, 20b], bringing the total yield to 95%. Recrystallization from CHCl3/ether
225 (16) [6bϩ Ϫ SH, 3,6-dimethoxyfluorenylϩ], 212 (15) [C14H12Sϩ,
furnished a light-yellow specimen, m.p. 149Ϫ151 °C (green black).
16a], 211 (14) [C14H11Sϩ], 198 (47) [6aϩ; 13C 6.8/7.1], 180 (82) Ϫ 1H NMR: Table 1. Ϫ 13C NMR: Table 1; δ ϭ 125.3, 126.1, 126.3,
[C14Hϩ12, 20a, 13C 13/15], 165 (100) [9-fluorenylϩ, 18], 151 (16) 127.3, 127.6, 130.9, 132.9 (7 d, 18 arom. CH), 134.7, 135.8, 136.7
[C8H7OSϩ, 19b], 121 (53) [C7H5Sϩ, 19a; 13C 4.1/4.7, (34Sϩ13C2) (3 s, 6 arom. Cq). Ϫ MS (120 °C); m/z (%): 440 (0.76) [Mϩ; 13C
2.5/2.6], 105 (42) [C8H9ϩ, no 34S peak], 77 (62) [C6H5ϩ]. Ϫ 0.23/0.22, (34Sϩ13C2) 0.13/0.11], 362 (1.7) [C26H18Sϩ, Mϩ
C29H26O2S2 (470.6): calcd. C 74.01, H 5.57, S 13.63; found C 73.90, Ϫ CH2S2, 22e; 13C 0.48/0.48, (34Sϩ13C2) 0.14/0.13], 228 (100)
H 5.54, S 13.65. Ϫ (b): 4,4Ј-Dimethoxythiobenzophenone (9b,
816 mg, 3.16 mmol) in 10 mL THF was reacted with 1 equiv. of
diazomethane in ഠ 5 mL THF affording a solution of the thiadia-
[C13H8S2ϩ, 6eϩ; (34Sϩ13C2) 9.9/9.7], 227 (42), 212 (23) [C14H12Sϩ,
16a], 211 (11) [C14H11Sϩ], 198 (10) [C13H10Sϩ, 6aϩ; 13C 1.4/1.5,
(34Sϩ13C2) 0.54/0.52], 197 (6) [C13H9Sϩ, thioxanthyliumϩ], 184 (25)
zoline 23b[7] (Ϫ78 °C, 8 h). After mixing with 805 mg (4.06 mmol) [C12H8Sϩ, 6eϩ Ϫ CS, dibenzothiophene; 13C 3.4/3.6, (34Sϩ13C2)
of 6a in 5 mL of THF, the N2 evolution took place within 5 h at 1.3/1.3], 180 (39) [C14Hϩ12, 20a; 13C 6.2/6.7], 179 (30), 178 (26), 165
Ϫ45 °C. Workup as above and trituration with ether gave 1.42 g
(95%) of 7b in two fractions. Recrystallized from CHCl3/diethyl
(44) [C13H9ϩ, 18; 13C 6.3/6.9], 152 (10) [C12H8ϩ, biphenyleneϩ], 121
(8) [19a], 105 (10) [C8H9ϩ], 77 (10) [C6H5ϩ]. Ϫ C27H20S3 (440.6):
ether, the m.p. 180Ϫ182 °C; mixed m.p., and the NMR spectra calcd. C 73.59, H 4.58, S 21.83; found C 73.50, H 4.44, S 21.82. Ϫ
confirmed the identity.
(b): Thioxanthion (6e, 571 mg, 2.50 mmol) was stirred with 1.0
equiv. of diazomethane in 15 mL of THF at Ϫ78 °C for 5 h, until
it had dissolved. 6a (3.30 mmol) was added, and the mixture was
kept at Ϫ55 °C for 5 h and at Ϫ20 °C overnight. Workup afforded
742 mg (67%) of 7e as light-green prisms, m.p. 149Ϫ151 °C (dec);
1H and 13C spectra confirmed the structure. Ϫ C27H20S3 (440.6):
found C 73.54, H 4.51, S 21.84.
5Ј5Ј-Diphenylspiro[fluorene-9,4Ј-[1,3]dithiolane] (7c). ؊ (a): The so-
lution of 3.02 mmol of thiadiazoline 4 in THF at Ϫ78 °C was
mixed with the THF solution of 4.17 mmol of 9-fluorenethione
(6c)[20] and kept for 5 h at Ϫ45 °C. 1.011 g (82%) of 7c, m.p.
230Ϫ233 °C (dec.) was isolated. Recrystallization from benzene
gave colorless needles with m.p. Ͼ 236 °C (blue black). Ϫ 1H
NMR: Table 1; δ ϭ 6.8Ϫ7.8 (m, 18 arom. H). Ϫ 13C NMR: (c) 6e (4.88 mmol) and 1.2 equiv. of diazomethane in 18 mL of
Table 1; δ ϭ 120.0, 126.3, 2 ϫ 126.8, 127.4, 128.2, 130.5 (7 d, 18
arom. CH), 139.5, 144.2, 144.9 (3 s, 6 arom. Cq). Ϫ MS (120 °C);
THF was stirred at Ϫ78 °C for 20 h, until the violet needles had
dissolved and the colorless precipitate of 23e appeared. The N2
m/z (%): 408 (25) [Mϩ], 362 (2) [Mϩ Ϫ CH2S], 330 (100) [C26H1ϩ8, evolution at Ϫ20 °C required 3 h. 652 mg of a yellow powder was
Mϩ Ϫ CH2S2, 22c; 13C 29/26; 13C2 4.1/3.6, no S], 329 (40), 328
filtered; the 1H NMR spectrum suggested a mixture of spiro[thiox-
(13), 327 (16), 326 (16), 253 (37) [330 Ϫ C6H5, C20Hϩ13; 13C 8.2/7.2, anthene-9,2Ј-thiirane] (δ ϭ 3.35, s, 3Ј-H2) and 9-methylenethioxan-
13C2 0.9/0.7, no S], 252 (35) [C20Hϩ12], 212 (80) [C14H12Sϩ, 16a; 13
C
thene (δ ϭ 5.48, s, CH2). In a separate experiment, the rate of N2
extrusion from spiro[thioxanthene-9,2Ј-[1,3,4]thiadiazoline] (23e)
was measured by volumetry in THF at Ϫ44 °C: k1 ϭ 1.23 10Ϫ4
12.4/13.8, (34Sϩ13C2) 4.5/4.2], 211 (53) [C14H11Sϩ], 210 (26)
[C14H10Sϩ, 16cϩ], 198 (6) [6aϩ], 196 (6) [6cϩ], 178 (16), 165 (51)
[18], 163 (11), 121 (6) [19a], 85 (61), 77 (2) [C6H5ϩ]. Ϫ C27H20S2
(408.6): calcd. C 79.37, H 4.93, S 15.70; found C 79.64, H 4.87, S
15.65. Ϫ (b): The thiadiazoline 23c[7] was prepared from 2.76 mmol
of 9-fluorenethione (6c) and 1 equiv. of diazomethane in THF at
Ϫ78 °C and reacted with 4.16 mmol of 6a at Ϫ45 °C for 2 h.
971 mg (86%) of 7c crystallized from CHCl3/diethyl ether, m.p. Ͼ
232 °C (dec.). The 1H and 13C NMR spectra were identical with
those of the above sample. Ϫ C27H20S2 (408.6): found C 79.61, H
4.91, S 15.69.
s
Ϫ1, i.e., lower than that of 4 by a factor of 1.7.
4-Methylthio-4-(1-naphthyl)-5,5-diphenyl-1,3-dithiolane (11):
4
(3.32 mmol) and 4.09 mmol of methyl 1-dithionaphthoate[22] were
mixed in 15 mL of THF at Ϫ78 °C. Workup after 5 h at Ϫ45 °C
furnished 1.25 g (87%) of 11 as colorless crystals, m.p. 151Ϫ153 °C
(reddish melt). Ϫ 1H NMR: δ ϭ 0.83 (s, SCH3), 3.25, 3.81 (AB,
Jgem ϭ 9.3 Hz, 2-H2), 6.9Ϫ8.4 (m, 17 arom. H). Ϫ 13C NMR: δ ϭ
17.3 (q, SCH3), 30.6 (t, C-2), 80.9, 82.4 (2 s, C-4, C-5), 122.5, 124.6,
125.5, 126.1, 127.0, 127.8, 127.9, 128.6, 129.1, 129.5, 131.9, 132.7
(12 d, 17 arom. CH), 132.2, 133.8, 134.5, 141.5 (4 s, 5 arom. Cq).
Ϫ MS (120 °C); m/z (%): 430 (0.7) [Mϩ], 353 (2.3), 352 (2.5)
5Ј5Ј-Diphenylspiro[xanthene-9,4Ј-[1,3]dithiolane] (7d):[21]
mmol) was reacted with 2.12 g (10.0 mmol) of xanthione (6d) in
THF at Ϫ45 °C; 3.57 g (84%) of 7d was isolated, m.p. 160Ϫ164 °C [C25H20Sϩ, Mϩ
(dec.). The analytical specimen (CH2Cl2) showed m.p. 165Ϫ167 °C
dithionaphthoateϩ; 13C 4.1/5.3, (34Sϩ13C2) 3.0/3.1], 212 (11)
4 (10.0
Ϫ
CH2S2], 218 (31) [C12H10S2ϩ, methyl
(green melt). Ϫ 1H NMR: (Table 1). Ϫ 13C NMR: Table 1; δ ϭ [C14H12Sϩ, 16a], 180 (100) [C14Hϩ12, 20a], 179 (83) [C14H1ϩ1], 178
115.8, 121.8, 126.7, 2 ϫ 126.9, 128.9, 131.9 (7 d, 18 arom. CH),
123.4, 140.6, 152.5 (3 s, 6 arom. Cq). Ϫ MS (120 °C); m/z (%): 424
(57), 171 (76) [C10H7ϪCϵSϩ], 165 (99) [9-fluorenylϩ, 18; 13C 14/
15], 152 (20), [C12H8ϩ, biphenyleneϩ], 127 (20) [C10H7ϩ, naphthylϩ],
(2.2) [Mϩ], 346 (4.6) [Mϩ Ϫ CH2S2, 22d], 212 (69) [xanthioneϩ, 121 (5) [19a], 89 (40), 77 (32) [C6H5ϩ]. Ϫ C26H22S3 (430.6): calcd.
C13H8OS, 6dϩ, or Mϩ Ϫ xanthione, C14H12Sϩ, 16a; 13C 10 or 11/
12; (34Sϩ13C2) 3.8 or 3.9/4.5], 198 (2) [6aϩ], 180 (100) [C14H1ϩ2, 20a;
13C 16/13], 179 (50) [C14Hϩ11], 178 (12), 168 (11), 165 (57) [18; 13C
8.2/8.9], 152 (8) [C12H8ϩ, biphenyleneϩ], 89 (22), 77 (15) [C6H5ϩ]. Ϫ
C27H20OS2 (424.6): calcd. C 76.38, H 4.75, S 15.11; found C 76.25,
H 4.99, S 15.01.
C 72.51, H 5.15, S 22.34; found C 72.71, H 5.33, S 22.28.
5,5-Diphenyl-4,4-bis(phenylthio)-1,3-dithiolane (7f).
؊
(a):
4
(2.00 mmol) and 550 mg (2.10 mmol) of diphenyl trithiocarbon-
ate[23] in 12 mL of THF were reacted for 6 h at Ϫ45 °C. In the
workup, room temp. was not exceeded; after evaporation, the res-
idue was dissolved in little of acid-free CH2Cl2. Careful addition
1
5Ј5Ј-Diphenylspiro[thioxanthene-9,4Ј-[1,3]dithiolane] (7e).
؊
(a):
of hexane gave 450 mg (47%) of 7f, m.p. 150Ϫ152 °C. Ϫ H NMR
Thiadiazoline 4 (3.02 mmol) and 753 mg (3.30 mmol) of thioxan-
(400 MHz): δ ϭ 3.82 (s, 2-H2), br m 7.02Ϫ7.42 (16 arom. H), 7.76
thione (6e) in 20 mL of THF were magnetically stirred at Ϫ45 °C, (broadened s, due to beginning coalescence, 4 arom. CH); the
whereby the crystalline 6e slowly dissolved. After 5 h, the solvent
was removed at room temp., and the residue triturated with ether:
60 MHz spectrum shows dd at δ ϭ 7.7Ϫ7.9 with J ഠ 6.5 Hz as
larger coupling, probably corresponding to 4 o-H. Ϫ 13C NMR
1700
Eur. J. Org. Chem. 2000, 1695Ϫ1702

1,3-Dipolar Cycloadditions, 117
FULL PAPER
(20.2 MHz): Table 1; δ ϭ 126.9, 127.3, 128.0, 129.6, 131.5, 137.9 (6
Table 1; δ ϭ 127.8, 128.7, 129.5 (3 d, 10 arom. H), 128.3, 139 br (2
d, 20 arom. CH), 132.9 (s, 2 Cq of SC6H5), 142.7 (br s, Cq of 2 s, 2 arom. Cq), 185.9 (s, 2 CϭO). Ϫ MS (130 °C); m/z (%): 376
CϪC6H5); in the 100.6 MHz spectrum, the line broadening of the
CH signals at δ ϭ 126.9, 131.5, and 137.9 is strong; the Cq signals
(0.4) [Mϩ], 298 (1.5) [Mϩ Ϫ CH2S2, 22g], 288 (1.7) [C15H12S3ϩ, Mϩ
Ϫ S Ϫ 2 CO; (34Sϩ13C2) 0.25/0.22], 212 (76) [C14H12Sϩ, 16a], 211
at 132.9 is hardly observable and that at 142.7 has disappeared in (56), 210 (100) [C14H10Sϩ, diphenylthioketeneϩ], 198 (1.2) [6aϩ],
coalescence. Ϫ MS (160 °C); m/z (%): 474 (1.1) [Mϩ; 13C 0.23/0.23],
178 (20), 165 (61) [18], 164 (7) [6gϩ], 121 (6) [19a], 89 (10), 77 (10)
396 (1.8) [C26H20S2ϩ, Mϩ Ϫ CH2S2, 22f; 13C 0.52/0.47, (34Sϩ13C2) [C6H5ϩ]. Ϫ C17H12O2S4 (376.5): calcd. C 54.22, H 3.21, S 34.06;
0.23/0.20], 365 (8.4) [C21H17S3ϩ, Mϩ Ϫ SC6H5; 13C 1.9/2.4, found C 54.13, H 3.12, S 34.82.
(34Sϩ13C2) 1.3/1.3], 287 (11) [C20H14Sϩ, (C6H5)2CϭCϭSC6H5ϩ;
Reaction of 5 with Adamantanethione (6h): 6a (396 mg, 2.00 mmol;
freshly purified by chromatography and recrystallization) in abs.
THF was converted into 5 at Ϫ78 °C as usual. After addition of
4.00 mmol of 6h,[25] the temp. was adjusted to Ϫ45 °C; the N2
evolution was finished after 5 h. The solvent was removed at room
temp., the residue treated with 5 mL of CCl4, and again evaporated.
1H NMR analysis in CDCl3 with sym-tetrachloroethane as weight
standard indicated 27% of 7h (δ ϭ 3.27) and 8% of 7a (δ ϭ 3.74).
Separation was achieved by CC with petroleum ether and increas-
ing amounts of CH2Cl2; the first fraction (220 mg) was trimeric 6h,
and the second fraction (260 mg) was recrystallized from methanol/
CH2Cl2 giving 180 mg (22%) of 5Ј,5Ј-diphenylspiro[adamantane-
2,4Ј-[1,3]dithiolane] (7h), m.p. 201Ϫ203 °C [dec., 203Ϫ205 °C[6]].
The third fraction was treated with methanol, and 25 mg (6%) of
7a, m.p. 203Ϫ205 °C, was obtained; 7h and 7a were identified by
their NMR spectra. The oily last fraction, eluted by petroleum
ether/CH2Cl2 7:3, contained benzophenone (TLC and IR compar-
ison) and some unidentified side products.
13C 2.4/3.1], 256 (8.2)[C15H12S2ϩ, Mϩ
Ϫ
2
C6H5S; 13C
1.4/1.6, (34Sϩ13C2) 0.83/1.03], 255 (9), 254 (8), 253 (12), 218 (12)
[C12H10S2ϩ, diphenyl disulfide ?; 13C 1.6/1.6, (34Sϩ13C2) 1.2/1.0],
212 (23) [C14H12S2ϩ, 16a; peak contains 5.6% (34Sϩ13C2) of m/z
210], 211 (32), 210 (100) [C14H10Sϩ, (C6H5)2CϭCϭSϩ], 209 (10),
208 (12), 198 (5) [6aϩ], 178 (21), 165 (50) [C13H9ϩ, fluorenylϩ], 121
(7) [C7H5Sϩ, 19a], 110 (42) [C6H5SHϩ], 109 (19) [C6H5Sϩ], 77 (9)
[C6H5ϩ]. Ϫ C27H22S4 (474.7): calcd. C 68.31, H 4.67, S 27.02; found
C 68.35, H 4.52, S 27.03. Ϫ (b) Hydrogenolysis: 300 mg of 7f and
3 g of freshly prepared Raney nickel in 30 mL of methanol were
stirred for 4 d at 45 ± 5 °C. Workup afforded 48 mg (42%) of 1,1-
diphenylethane as a colorless oil. Ϫ 1H NMR: δ ϭ 1.63 (d, J ϭ
7.1 Hz, CH3), 4.13 (q, 1-H), 7.23 (s, 2 C6H5).
[(1-Phenylthio-2,2-diphenylvinyl)thio]methyl Phenyl Disulfide (12).
؊ (a): 7f (400 mg, 0.84 mmol) was subjected to CC with CH2Cl2/
petroleum ether (2:8) as mobile phase. The first fraction contained
6f, which solidified at room temp. and was identified by its 1H
NMR spectrum. The second, major fraction, 320 mg (80%) of 12,
was isolated as a pale-yellow viscous, resin-like oil. The crude prod-
uct turned yellow on exposure to air, but, after repeated CC, was
2,2,4,4-Tetramethyl-5Ј,5Ј-diphenylspiro[cyclobutane-3,4Ј-[1,3]di-
thiolane]-1-one (7i): 2.00 mmol of
4 interacted with 328 mg
(2.10 mmol) of 2,2,4,4-tetramethyl-3-thioxocyclobutanone (6i)[26] in
15 mL of THF 4 h at Ϫ45 °C and overnight at Ϫ27 °C. After evap-
nearly colorless and insensitive to air. Ϫ IR (neat): ν˜ ϭ 710 cmϪ1
,
755 st (arom. CH out-of-plane deform.), 1040, 1090, 1200 m; 1445,
1
oration of the solvent, the H NMR analysis with weight standard
1
1470 st; 1585 m (CϭC). Ϫ H NMR (CDCl3, 400 MHz, CDCl3):
revealed 62% of 7i (δ ϭ 3.28), but no other dithiolane. Purification
by CC (CH2Cl2/petroleum ether) gave 310 mg (42%) of 7i, m.p.
124Ϫ126 °C after recrystallization from methanol. Benzophenone
δ ϭ 3.99 (s, CH2), 7.17Ϫ7.39 (complex m of 18 arom. H), 7.51,
7.53 (2 dd, 2 arom. H); (C6D6): 3.81 (s, CH2); arom. H: 6.89 (m, 2
H), 6.93Ϫ7.06 (m, 8 H), 7.13 (tt, 2 H), 7.29Ϫ7.31 (m, 4 H),
7.37Ϫ7.41 (m, 4 H). Ϫ 13C NMR (CDCl3, 100 MHz, DEPT): δ ϭ
42.21 (CH2), 126.51, 127.04, 127.68, 127.81 (4 arom. p-CH); 127.85,
128.02, 128.13, 128.86, 128.96, 129.22, 129.27, 129.63 (m- and o-
CH of 4 different C6H5), 135.3, 136.9, 141.6, 142.1, 153.8 (5 signals
for 2 olefinic and 4 arom. Cq). Ϫ MS (70 eV, 120 °C); m/z (%): 474
1
was found in the mother liquor. Ϫ H NMR: δ ϭ 1.37 (s, 2 CH3),
1.67 (s, 2 CH3), 3.34 (s, 2-H2), 7.0Ϫ7.2 (m, 6 arom. H), 7.4Ϫ7.6
(m, 4 arom. H). Ϫ 13C NMR (CDCl3): δ ϭ 25.47 (t, C-2Ј), 25.62,
25.75 (2 q, 4 CH3), 68.1, 75.3, 78.5 (3 s, C-2/4, C-4Ј, C-5Ј), 126.8
(d, 2 arom. p-CH), 127.0, 130.6 (2 d, 4 o-CH, 4 m-CH), 144.0 (s, 2
arom. Cq), 220.1 (s, CϭO). Ϫ MS (110 °C); m/z (%): 368 (1) [Mϩ],
322 (50) [Mϩ Ϫ CH2S, C21H22OSϩ], 298 (100) [Mϩ Ϫ dimethylket-
ene, C18H18S2ϩ], 262 (30) [C20H2ϩ2], 247 (20) [C19H1ϩ9], 237 (25), 220
(100) [C17Hϩ16, (C6H5)2CϭCϭC(CH3)2 ?], 205 (25) [C16H1ϩ3], 165
(10) [18], 91 (10) [C7H7ϩ]. Ϫ C22H24OS2 (368.5): calcd. C 71.69, H
6.56, S 17.40; found C 71.92, H 6.40, S 17.42.
(0.6) [Mϩ; 13C 0.19/0.18, (34Sϩ13C2) 0.14/0.11], 365 (1.6) [Mϩ
Ϫ
SC6H5; (34Sϩ13C2) 0.25/0.33], 318 (10) [C20H14S2ϩ, 13C 2.3/2.9], 287
(7), 218 (18) [C12H10S2ϩ, diphenyl disulfideϩ; 13C 2.3/2.5,
(34Sϩ13C2) 1.5/1.5], 210 (100) [C14H10Sϩ, (C6H5)2CϭCϭSϩ], 208
(12) (C14H8Sϩ, probably biphenylenethioketeneϩ], 186 (17)
[C6H5SC6H5ϩ; 13C 2.2/2.4], 185 (10), 178 (22) [C14H1ϩ0], 165 (41)
[fluorenylϩ], 110 (78) [C6H5SH; (34Sϩ13C2) 3.6/3.5], 109 (34)
[C6H5Sϩ], 77 (15) [C6H5ϩ]. Ϫ C27H22S4 (474.7): calcd. C 68.31, H
4.67, S 27.02; found C 68.51, H 4.74, S 27.33. Ϫ (b): The 1H NMR
spectrum of the fresh solution of 7f was free of 12, but after 24 h
at room temp. the conversion reached 4.5%; it was complete after
several weeks. In a further experiment in CDCl3, a trace of trifluo-
roacetic acid accelerated the conversion into 12; after 4 h, the signal
of 7f at δ ϭ 3.82 had disappeared, and 12 was quantitatively
formed. The CH2 signal of 12 at δ ϭ 3.99 is much sharper than
that of 7f (hindered ring inversion).
Acknowledgments
Our thanks are going to the Fonds der Chemischen Industrie,
Frankfurt, for the continued support of our research program.
G.M. expresses his gratitude to the Alexander von Humboldt
Foundation for a fellowship. We are greatly indebted to Reinhard
Seidl for his competence in recording the MS, to Helmut Huber
for many of the NMR spectra, to Dr. David S. Stephenson for a
DNMR study, and to Helmut Schulz and Magdalena Schwarz for
taking care of the elemental analyses. We thank cand. chem. Chris-
5,5-Diphenyl-4,2Ј-spirobi[1,3-dithiolane]-4Ј,5Ј-dione (7g):
4 (3.11
mmol) and 547 mg (3.33 mmol) of 2-thioxo-1,3-dithiolane-4,5-dione tian Leyh and cand. chem. Wolfgang Sieß for help in the cycloaddi-
(6g)[24] interacted in THF at Ϫ45 °C; 874 mg (75%) of 7g was isol-
tion experiments. Part of the experiments (1998/99) were carried
ated as light-yellow crystals, m.p. 198Ϫ199 °C (dec.). Ϫ IR (KBr): out at the Institute of Organic and Applied Chemistry, University
ν˜ ϭ 699 cmϪ1, 720, 752 m (C6H5 out-of-plane deform.), 1026 br;
1446, 1497 m (arom. ring vibr.), 1690, 1706 st (CϭO). Ϫ 13C NMR:
of Lodz, Poland; the technical assistance by Ms. M. Celeda is grate-
fully acknowledged.
Eur. J. Org. Chem. 2000, 1695Ϫ1702
1701

R. Huisgen, X. Li, G. Mloston, C. Fulka
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