Aliphatic thiocarbonyl ylides and thiobenzophenone: Experimental study of regiochemistry and methylene transfer in cycloadditions

Article abstract of DOI:10.1002/ejoc.200400765

1,3-Dipolar cycloadditions of aliphatic or alicyclic thiocarbonyl ylides 3A-D - sterically hindered at least at one terminus - with thiobenzophenone produce both regioisomeric 1,3-dithiolanes 4 and 5. According to quantum-chemical calculations (preceding paper), a concerted cycloaddition furnishing 2,4-substituted dithiolanes 4 competes with the formation of an intermediate C,C-biradical 9 which cyclizes to the more crowded 4,5-substituted dithiolanes 5. When steric hindrance of 3 increases, the cycloaddition is superseded by 'methylene transfer', i.e., the transfer of the less hindered terminus of 3E-J to the S-atom of thiobenzophenone. The thiobenzophenone S-alkylide 11, thus formed, rapidly reacts with a second molecule ofthiobenzophenone to generate the 4,4,5,5-tetraphenyl-1,3-dithiolane 12 via the highly stabilized C,C-biradical 10. Methylene transfer occurs when the cyclization of the mixed C,C-biradical 9 requires a higher activation barrier than its dissociation to aliphatic thioketone + 11; the threshold is surprisingly well reproduced by calculations. The structural assignment of sixteen 1,3-dithiolanes is based on their formation from corresponding reactant pairs as well as on ¹H and ¹³C chemical shifts. X-ray diffraction analyses of three spiro-1,3-dithiolanes reveal the van der Waals strain in non-bonded interactions, folding angles, shearing forces, and bond lengths. Comparison of the mass spectra of many 1,3-dithiolanes allows the reconstruction of major fragmentation pathways. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejoc.200400765

FULL PAPER
Aliphatic Thiocarbonyl Ylides and Thiobenzophenone: Experimental Study of
Regiochemistry and Methylene Transfer in Cycloadditions[‡]
Rolf Huisgen,*[a] Grzegorz Mloston,[a,c] Henry Giera,[a,d] Elke Langhals,[a,e] Kurt Polborn,[a]
and Reiner Sustmann[b]
Dedicated to Gottfried Märkl, Regensburg, on the occasion of his 75th birthday
Keywords: Thiocarbonyl ylides / Cycloadditions / 1,3-Dithiolanes / Methylene transfer / Heterocycles
1,3-Dipolar cycloadditions of aliphatic or alicyclic thiocar-
bonyl ylides 3A-D – sterically hindered at least at one ter-
minus – with thiobenzophenone produce both regioisomeric
1,3-dithiolanes 4 and 5. According to quantum-chemical cal-
C,C-biradical 10. Methylene transfer occurs when the cycli-
zation of the mixed C,C-biradical 9 requires a higher acti-
vation barrier than its dissociation to aliphatic thioketone +
11; the threshold is surprisingly well reproduced by calcula-
culations (preceding paper), a concerted cycloaddition fur- tions. The structural assignment of sixteen 1,3-dithiolanes is
nishing 2,4-substituted dithiolanes 4 competes with the for- based on their formation from corresponding reactant pairs
mation of an intermediate C,C-biradical 9 which cyclizes to
the more crowded 4,5-substituted dithiolanes 5. When steric
hindrance of 3 increases, the cycloaddition is superseded by
‘methylene transfer’, i.e., the transfer of the less hindered ter-
minus of 3E-J to the S-atom of thiobenzophenone. The thio-
benzophenone S-alkylide 11, thus formed, rapidly reacts
with a second molecule ofthiobenzophenone to generate the
4,4,5,5-tetraphenyl-1,3-dithiolane 12 via the highly stabilized
as well as on 1H and 13C chemical shifts. X-ray diffraction
analyses of three spiro-1,3-dithiolanes reveal the van der
Waals strain in non-bonded interactions, folding angles,
shearing forces, and bond lengths. Comparison of the mass
spectra of many 1,3-dithiolanes allows the reconstruction of
major fragmentation pathways.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
same when the aromatic substituents of 1,3-dipole and di-
polarophile were varied.[5,6]
Introduction
The 1,3-cycloaddition of thiocarbonyl ylides to thiones
affords 1,3-dithiolanes. The first example was inadvertently
discovered in 1930 and 1931 when thiobenzophenone was
treated with diazomethane to give 4,4,5,5-tetraphenyl-1,3-
dithiolane as a 2:1 product in high yield.[1,2] Fifty years
later, the intermediacy of 2,2-diphenyl-2,5-dihydro-1,3,4-
thiadiazole and thiobenzophenone S-methylide was estab-
lished (Scheme 1).[3,4] The regiochemistry remained the
[‡] 1,3-Dipolar Cycloadditions, Part 130. Part 129: E. Langhals, R.
Huisgen, K. Polborn, Chem. Eur. J. 2004, 10, 4353.
[a] Department
München,
Chemie,
Ludwig-Maximilians-Universität
Scheme 1. Formation of 4,4,5,5-tetraphenyl-1,3-dithiolane by
cycloaddition of thiobenzophenone S-methylide to thiobenzo-
phenone.
Butenandt-Str. 5–13, 81377 München, Germany
E-mail: Rolf.Huisgen@cup.uni-muenchen.de
[b] Institut für Organische Chemie der Universität Duisburg-Essen,
Universitätsstr. 5, 45117 Essen, Germany
On the other hand, it was observed that thiocarbonyl
ylides and thiones containing cycloaliphatic or aliphatic
substituents furnished 2,4-substituted 1,3-dithiolanes exclu-
sively;[7–10] an example is shown in Scheme 2. 2,4-Substi-
tuted 1,3-dithiolanes suffer much less from the van der
Waals strain created by sterically demanding substituents
than the 4,5-substituted regioisomers.
E-mail: reiner.sustmann@uni-essen.de
[c] Present address: Section of Heteroorganic Compounds, Univer-
sity of Lodz,
Narutowicza 68, 90–136 Lodz, Poland
[d] Present address: Fachhochschule München, Fachbereich 05,
Lothstr. 34, 80535 München, Germany
[e] Present address: Consortium für Elektrochemische Industrie,
Wacker Chemie GmbH,
Zielstattstraße 20, 81379 München, Germany
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DOI: 10.1002/ejoc.200400765
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FULL PAPER
Scheme 2. Conversion of 2,2,4,4-tetramethyl-3-thioxocyclobut-
anone S-methylide and adamantanethione to a 2,4-substituted dis-
piro-1,3-dithiolane.
The suspected mechanistic dichotomy was confirmed by
quantum-chemical calculations (restricted and unrestricted
B3LYP/6-31G*). For the reaction of thioacetone S-meth-
ylide with thioacetone, the concerted formation of the
2,2,4,4-tetramethyl-1,3-dithiolane resulted as the preferred
course; pathways via C,S- or C,C-biradicals had higher acti-
vation energies.[11] For the reaction of thiobenzophenone S-
methylide with thiobenzophenone, the calculation (UB3-
LYP/6-31G*//UHF/3-21G*) indicated a moderate barrier
to the concerted process which leads to 2,2,4,4-tetraphenyl-
1,3-dithiolane. However, this pathway had no chance be-
cause a C,C-biradical 10 (Scheme 4), stabilized by four
phenyl groups and two thioether functions is exothermally
formed with virtually no activation energy. The cyclization
of this intermediate is geared to the 4,4,5,5-tetraphenyl-1,3-
dithiolane which is in bond energy by 16.8 kcalmol–1 less
favorable than the 2,4-substituted isomer.[12]
The calculations of the preceding paper deal with cyclo-
additions of aliphatic and cycloaliphatic thiocarbonyl ylides
to thiobenzophenone. Here a C,C-biradical as intermediate
can only profit from one benzhydryl-type stabilization. Acti-
vation barriers of comparable magnitude resulted for the
concerted pathway which leads to the 2,4-substituted 1,3-
dithiolanes, and for the two-step process to give the more
hindered 4,5-substituted regioisomers.[13] Furthermore, the
calculations provided the clue to the understanding of the
‘methylene transfer’ reaction and the nonequivalence of
corresponding pairs of reactants. Theory and experiment
will be compared here.
Scheme 3. Preparation of thiocarbonyl ylides and formation of re-
gioisomeric 1,3-dithiolanes by cycloaddition with thiobenzo-
phenone; position numbering of monocyclic dithiolanes.
How will methyl substitution at the second terminus of
3 influence the reactivity? Analogous cycloadditions of 1
with diazoethane or 2-diazopropane provided the methyl-
ated 2,5-dihydro-1,3,4-thiadiazoles 2b and 2c which, in
turn, furnish the tri- and tetra-substituted thiocarbonyl
ylides 3b and 3c on thermal N2 extrusion. The two mani-
folds of R2 and RЈ2 in Scheme 3 require double indices of
formula numbers, e.g., 5Bb is 5,5-diisopropyl-2-methyl-4,4-
diphenyl-1,3-dithiolane.
When the adamantanethione S-methylide (3Aa) was gen-
erated in the presence of 1.1 equivalents of thiobenzo-
1
phenone (6), quantitative H NMR analysis with weights-
tandard revealed the regioisomeric 1,3-dithiolanes 4Aa and
5Aa in 42% and 50% yield, respectively.[8] Analogous ex-
periments with the S-ethylide 3Ab and S-isopropylide 3Ac
pointed to a modest shift towards the 2,4-substituted 1,3-
dithiolanes 5Ab/5Ac in the mixture of regioisomers. The N2
elimination from the methylated precursors, 2Ab and 2Ac,
proceeded somewhat slower than that of 2Aa; the experi-
mental conditions and products are listed in Table 1. The
properties of the isolated cycloadducts and their structural
assignment will be described in the next chapter.
Results and Discussion
Competing Formation of Regioisomeric 1,3-Dithiolanes and
the Methylene Transfer Reaction
The additional introduction of methyl groups into the
second terminus of the thiocarbonyl ylide was not subject
The addition of diazomethane to thioketones 1 at 0 °C to calculations, and its effect on the competing pathways is
in pentane afforded the 2,5-dihydro-1,3,4-thiadiazoles 2a as interpreted with reserve. The dimethylated terminus of 3Ac
major or exclusive products; their thermolysis at 40–50 °C which is still less hindered than the one with the adamantyl-
was the method of choice for the generation and in situ idene group, will attack the S-atom of 6, and the formation
reaction of thiocarbonyl S-methylides 3a (Scheme 3). On of biradical 9c will be sterically retarded; the methyl groups
systematically varying the bulky residues R2, the sequence will not contribute to the radical stabilization (Scheme 4).
A–J goes along with increasing steric hindrance in the inter- The shifting of the regioselectivity towards 2,4-substitution
action with thiobenzophenone (6).
suggests that the early TS 8c of the concerted addition suf-
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Aliphatic Thiocarbonyl Ylides and Thiobenzophenone
FULL PAPER
Table 1. In situ reactions of thiocarbonyl ylides 3 with thiobenzo- fers less from methyl substitution than the TS of biradical
phenone (6); for R2 and formula numbers see Scheme 3.
formation.
The reactions of thiocarbonyl S-methylides 3Ba, 3Ca,
and 3Da with 6 reveal increasing shares of 4,5-substituted
dithiolanes 5 (Table 1). It is a sequence of growing steric
demand of R2. In cycloadditions to dimethyl 2,3-dicyanofu-
marate and dimethyl 2,3-dicyanomaleate, a high violation
of stereoretention was observed for 3Ca and 3Da as a con-
sequence of rotation in a zwitterionic intermediate;[14,15] on
the other hand, the loss of stereochemical integrity was only
modest for cycloadditions of 3Aa.[16]
The emergence of a by-product in the reactions of 3Ca
and 3Da with thiobenzophenone was most remarkable: 3–
13% of 4,4,5,5-tetraphenyl-1,3-dithiolane (12a). Two mole-
cules of thiobenzophenone are linked by a methylene group
which is provided by the thiocarbonyl ylide 3. By-product
12a gained dominance, when the S-methylides of the in-
creasingly hindered thioketones were reacted with thioben-
zophenone (Table 1). The ‘methylene transfer’ reaction was
first observed, when thiofenchone S-methylide (3Ea) was
reacted with 6 and furnished 86% of 12a; interestingly, the
reaction with thioxanthione instead of 6 still provided some
4,5-substituted 1,3-dithiolane of type 5 besides the methyl-
ene transfer product.[17,18]
The methyl groups in the tetramethylcyclobutane ring are
‘bent back’ as a consequence of the intracyclic bond angle,
thus reducing the van der Waals pressure in the spirodithi-
olanes 4C/5C and 4D/5D and diminishing the strain in the
preceding TSs. This alleviation is no longer offered by the
tetramethyl five-membered and six-membered rings of F, G,
and J in the role of R2 (Scheme 3). The reaction of tet-
ramethylcyclopentanethione S-methylide (3Fa) with two
equivalents of 6 (40 °C, 15 h) afforded 95% of the 1:2 pro-
duct 12a and 98% of thioketone 1F. Thus, steric hindrance
prevents the formation of cycloadducts. Finally, in the reac-
tion of tetramethylcyclohexanethione S-methylide (3Ja)
and 6, the electrocyclization yielding thiirane 7Ja (18%) be-
gan to compete with the methylene transfer (73% 12a). The
interaction of di-tert-butyl thioketone S-methylide (3Ha)
with 6 met similar hindrance: methylene transfer and thiir-
ane formation occurred side by side.
In the plausible mechanistic Scheme 4, the thiocarbonyl
ylide 3 attacks 6 at the S-atom and forms the ‘mixed’ biradi-
cal 9. The cyclization barrier of 9 on the way to the 4,5-
substituted dithiolane 5 will rise with increasing volume of
R2. A competing dissociation to thione 1 and thiobenzo-
phenone S-alkylide 11 takes control. The latter avidly picks
up a second molecule of thiobenzophenone to produce the
favored stabilized biradical 10. In a subsequent step, 10 cy-
clizes to 12, i.e., in the case of 12a, the product of the
‘Schönberg reaction’.[4,12] In summa: thiocarbonyl ylide 3
combines with two molecules of thiobenzophenone to give
thione 1 + dithiolane 12. In the most crowded ylides like
3Gc and 3Jb, electrocyclization leading to thiiranes 7 com-
petes with alkylidene transfer.
The data perfectly harmonize with the calculations.[13]
The ‘mixed’ biradical 9Aa, containing the adamantyl radi-
cal, cyclizes exothermally to 1,3-dithiolane 5Aa via a barrier
Scheme 4. Thiocarbonyl ylides and thiobenzophenone: competition
of cycloaddition and methylene transfer reaction.
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R. Huisgen, G. Mloston, H. Giera, E. Langhals, K. Polborn, R. Sustmann
FULL PAPER
of 6.6 kcalmol–1 whereas the dissociation to adamantane- the S-methylide 11a occurring in the equilibrium at 140 °C
thione (1A) + 11A requires an activation energy of 11.1 enters the irreversible electrocyclization to give thiirane 14a;
kcalmol–1. On the other hand, the mixed biradical 9Fa subsequent sulfur loss leads to 13a (Scheme 5).
which is formed from tetramethylcyclopentanethione S-
The 2,2-dimethyl-4,4,5,5-tetraphenyl-1,3-dithiolane (12c)
methylide (3Fa) and 6 will not pass the cyclization barrier of is more thermolabile than 12a. After heating at 100 °C in
23.9 kcalmol–1 leading to 5Fa, but prefers the dissociation CDCl3 for 110 h, the conversion to 1,1-diphenylisobutene
leading to thione 1F + 11a (barrier 8.3 kcalmol–1) with sub- (13c) reached 99%. By-the-way, a sulfur atom is not in-
sequent interception of 11a by 6 (Scheme 4).
volved in the desulfurization of thiiranes 14. A kinetic study
Compared with the S-methylide 3Ca of the tetramethyl- carried out in the Munich laboratory established the nucle-
3-thioxocyclobutanone series, the S-ethylide 3Cb and the S- ophilic catalysis of such sulfur extrusions, and phenylated
isoproylide 3Cc furnished slightly higher shares of dithiol- thiiranes served as models.[21]
anes 4Cb/4Cc, and the products of ethylidene and isopro-
pylidene transfer, 12b (9%) and 12c (10%), respectively,
Regiochemical Assignments of 1,3-Dithiolanes
were likewise observed (Table 1). The occurrence of thiir-
anes (11% 7Cb, 18% 7Cc) indicated increasing steric hin-
drance in the interaction with 6. Several examples of Table 1
suggest that, with rising temperature, the regioisomer ratio
4/5 shifts vs. 5, and the share of 12, the product ofmethylene
transfer, is increased. That makes sense because a lower
temperature coefficient is expected for the concerted cyclo-
addition (via TS 8) than for the formation of inter-mediate
9 (Scheme 4). The thiocarbonyl ylides 3F and 3G, i.e., those
derived from tetramethylcyclopentanethione and tetrameth-
ylindan-2-thione, ran parallel in their behavior: the S-eth-
ylides furnished 12b + thione 1 in virtuallyquantitative
yields whereas the S-isopropylides no longer interacted with
6, but rather furnished thiiranes 7Fc and 7Gc.
The 1,3-dithiolanes 5 suffer from van der Waals pressure
caused by spiroanellation and the front strain of substitu-
ents in positions 4 and 5. The cycloaddition of thioformal-
dehyde S-methylide + H2C=S to afford the parent 1,3-dithi-
olane was calculated by (U)B3LYP/6-31G* to be exother-
mic with –76.0 kcalmol–1.[11] This reaction heat shrinks for
3Aa + 6 to –25.1 kcalmol–1 and for 3Fa + 6 to a mere –4.8
kcalmol–1.[13]
These data suggest another test for the mechanism of the
methylene transfer reaction (Scheme 4). When dithiolane
5Da – R2 is the spiro-tetramethylcyclobutane residue – was
heated with 6 in benzonitrile at 140 °C for 5 h, the 1H NMR
spectrum showed the emergence of tetraphenyldithiolane
12a, thione 1D, and 1,1-diphenylethylene (13a). This indi-
cates equilibration of 5Da with C,C-biradical 9Da, dissoci-
ation of the latter into 1D + thiobenzophenone S-methylide
(11a), and capturing of 11a by the added 6. However, the
cycloaddition which affords 12a is likewise reversible, and
Corresponding pairs of thiocarbonyl ylide + thioketone
give rise to one and the same 4,5-substituted 1,3-dithiolane.
Thus, the reactant pairs 3Ca + 6 and 11a + 1C contain
thiobenzophenone and tetramethyl-3-thioxocyclobutanone
(1C) in exchanged functions. The common product must be
5Ca whereas the 2,4-substituted regioisomers are different
in the two systems. Similarly, it was shown that dithiolane
5Aa resulted from corresponding reactant pairs.[6,8]
Reliable NMR criteria are based on the CH2 group in
the heterocycle and were recently employed to regioisomeric
dithiolanes with aliphatic and cycloaliphatic substituents.[10]
In the 13C NMR spectra, the triplet for C-5 of 4a (RЈ2 =
H,H) occurs at higher frequencies than that of C-2 in 5a.
The neighboring diphenyl-substituted C-4 deshields C-5 in
4a to a higher extent than the second thioether function
does on C-2 of 5a; Δδ = 18.7–24.2 ppm was observed for
four pertinent pairs (Table 2). The same criterion holds for
the 13C doublets in 4b and 5b (RЈ2 = Me,H), and even for
the singlets in dithiolanes 4c and 5c (RЈ2 = Me,Me), albeit
with smaller values of Δδ. Since the multiplicities do not
help in the recognition of C-5 in 4c and of C-2 in 5c, the
assignment of 4Cc was confirmed by an X-ray analysis (see
below).
Table 2. 1,3-Dithiolanes prepared by cycloaddition of thiocarbonyl
ylides to thiobenzophenone (see Scheme 3 for formula numbers).
Formula
M.p. [°C]
δ(1H)
δ(13C)
Ref.
[8]
4Aa
5Aa
4Ab
5Ab
4Ac
5Ac
4Ba
5Ba
4Ca
5Ca
4Cb
5Cb
4Cc
5Cc
4Da
5Da
12a
126–128
203–205
115–117
195–196
153–155
(not pure)
93–94
3.95 (5-H2)
3.28 (2-H2)
4.55 (5-H)
3.57 (2-H)
48.3 (C-5)
28.0 (C-2)
52.8 (C-5)
35.9 (C-2)
62.4 (C-5)
50.8 (C-2)
49.0 (C-5)
30.3 (C-2)
49.7 (C-5)
25.5 (C-2)
54.0 (C-5)
38.9 (C-2)
62.8 (C-5)
51.1 (C-2)
49.6 (C-5)
25.4 (C-2)
30.1 (C-2)
42.7 (C-2)
54.2 (C-2)
[8]
[19]
[19]
3.72 (5-H2)
3.63 (2-H2)
3.83 (5-H2)
3.34 (2-H2)
4.35 (5-H)
3.87 (2-H)
138–140
85–86
[20]
[6,20]
124–126
170–171
126–128
136–138
148–149
51–52
106–107
203–204
172–174
161–163
3.69 (5-H2)
3.26 (2-H2)
3.66 (2-H2)
4.09 (2-H)
[1,2,4]
[4]
12b
12c
Scheme 5. Thermolysis of 4,4,5,5-tetraphenyl-1,3-dithiolanes.
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Aliphatic Thiocarbonyl Ylides and Thiobenzophenone
FULL PAPER
The 1H NMR shifts corroborate the structural attri-
butions: the δ(5-H2) of 4a and the δ(5-H) of 4b have higher
values than the δ(2-H2) of 5a and the δ(2-H) of 5b, respec-
tively, although ΔδH (0.09–0.98) varies more. Furthermore,
the δH of the methyl pairs at C-2Ј and C-4Ј of the tetrameth-
ylcyclobutane (and, 1Ј-one) residues reveal stronger de-
shielding by the CPh2 in 4-position of 5 than by the neigh-
boring S-3 in 4. E. g., the δ(Me4) of 5Ca at δ = 1.35 and
1.65 ppm are higher than 1.22 and 1.28 ppm observed for
4Ca. This rule pertains to all 4/5 regioisomers of Table 2
(see Experimental).
The 1,3-dithiolanes with RЈ2 = H,H (a) and Me,Me (c)
display a σ-plane in their NMR spectra, i.e., a ‘dynamic Cs
symmetry’ which results from the equilibrium of nonplanar
enantiomeric conformations. The ratios of 13C signals for
CH and CH2 groups in the adamantane systems of 4Aa/
5Aa and 4Ac/5Ac mirror the σ–plane, as well as the methyl
pairs do in 4Ca/5Ca and 4Cc/5Cc. The diisopropyl-1,3-di-
thiolanes 4Ba/5Ba exhibit two 13C signals for pairs of dia-
stereotopic Me groups. On the other hand, dithiolanes with
RЈ2 = Me,H (b) are chiral and show the anticipated higher
Figure 1. X-ray structure of 1,1,3,3,7,7-hexamethyl-6,6-diphenyl-
5,8-dithiaspiro[3,4]octane-2-one (4Cc). ZORTEP plot (thermal el-
lipsoids at 30% probability level; position numbering of monocyclic
dithiolanes).
1
numbers of H and 13C signals.
Table 3. X-ray structures of some 1,3-dithiolanes; selected bond
lengths and angles.
It is only in the NMR spectra at 100 °C that the hexasub-
stituted dithiolanes 4Cc and 5Cc display sharp signals in
accordance with the point group Cs. In the spectra at 32 °C,
4Cc
5Ca
5Da
1
selected H and 13C signals of methyl and phenyl groups
Bond lengths [Å]
reveal beginning coalescence by line broadening (see Exper-
imental). We suppose that hindered phenyl rotation is re-
sponsible, the more so, as we described such 13C DNMR
phenomena for 4,4,5,5-tetraphenyl-1,3-dithiolane (12a): co-
alescences of two o-CH (0 °C) and two aromatic Cq (15 °C)
revealed a rate process with ΔG϶ = 12.9 kcalmol–1.[6]
S1–C2
C2–S3
S3–C4
C4–C5
C5–S1
1.827(3)
1.818(3)
1.847(2)
1.577(4)
1.840(3)
1.808 (3)
1.798(2)
1.847(2)
1.594(3)
1.835(2)
1.805(2)
1.790(2)
1.854(2)
1.601(2)
1.841(2)
Bond angles [°]
S1–C2–S3
107.0(2)
109.8(1)
109.1(2)
94.7(2)
100.1(2)
102.4(1)
96.7(2)
C2–S3–C4
S3–C4–C5
C4–C5–S1
C5–S1–C2
98.1(1)
104.0(2)
106.5(2)
100.8(2)
94.1(1)
101.1(1)
103.5(1)
98.7(1)
Structure Analyses of Three 1,3-Dithiolanes
Single crystal X-ray analyses of 4Cc, 5Ca, and 5Da sup-
plement those of 4Aa and 5Aa published previously.[8] The
spiroadamantane system of 4Aa and 5Aa is replaced by the
sterically more demanding spiro-annulated tetramethylcy-
clobutanone in 4Cc and 5Ca, and by tetramethylcyclobu-
tane in 5Da. The compromise between the various steric
constraints looks different in each examples.
Intracyclic torsion angles [°]
S1–C2–S3–S4
C2–S3–C4–C5
S3–C4–C5–S1
C4–C5–S1–C2
C5–S1–C2–S3
27.0(2)
–24.8(2)
52.4(2)
–61.0(1)
41.9(2)
–6.5(2)
–32.6(2)
54.5(2)
–56.0(1)
32.7(2)
3.8(2)
–46.7(2)
48.0(2)
–28.7(2)
–2.4(2)
In contrast to 4Aa and 5Aa, the three new structures
contain the 1,3-dithiolane ring in an envelope conformation
with the diphenyl-substituted C4 as the flap. The spiro-C-
atom is C2 in 4Cc, and C5 in 5Ca and 5Da. Would the
envelope be regular, the intracyclic torsion angle at S1–C2
should be zero. The hexasubstituted dithiolane 4Cc (Fig-
Folding angle [°]
Dithiolane
Cyclobutane
132.4
174.8
122.0
157.2
123.4
158.3
Closely connected is the folding angle, which varies from
ure 1) comes close with a deviation of only 2.4°, vs. 6.5° 122.0° to 132.3° in the three dithiolanes. The puckering of
and 3.8° in the tetra-substituted 5Ca and 5Da, respectively cyclopentane reduces the Pitzer strain of a planar five-mem-
(Table 3).
bered ring. The non-bonded interactions should be lower
In a regular envelope, the two bonds at the flap have the in thiolanes and 1,3-dithiolanes than in the carbocycle.
same torsion angle (opposite sign), e.g., 40.3° for cyclopen- Characteristically, the torsion angle at C4–C5, the only C–
tane.[22] The dithiolane 4Cc (Figure 1) shows with 48.0° at C bond of the ring, has the highest value (Table 3).
C4–C5 and 46.7° at S3–C4 the best approximation, whereas
Cyclobutane (gas phase) exhibits a puckering angle φ of
5Ca with 61.0° and 52.4° is farer progressed towards the 28°[24] and an inversion barrier of ca. 1.4 kcalmol–1;[25] in
half-chair on the pseudorotational circuit.[23]
cyclobutanone the barrier is even lower, and φ is
Eur. J. Org. Chem. 2005, 1519–1531
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R. Huisgen, G. Mloston, H. Giera, E. Langhals, K. Polborn, R. Sustmann
FULL PAPER
10.4 2.7°.[26] According to a survey, 20° Ͻ φ Ͻ 35° was Mass Spectra of 1,3-Dithiolanes
observed for most substituted cyclobutanes, and crystal
The assignment of molecular formulae to mass peaks
packing forces were made responsible for values of φ close
to 0° which were found in a substantial number of crystal
structures.[27]
The shallow puckering function of the four-membered
ring is modified by various steric restraints in our examples,
as suggested by folding angles of 174.8° (4Cc) and 157.2°
(5Ca) for the two tetramethylcyclobutanones, and 158.3°
for the tetramethylcyclobutane ring in 5Da. In another di-
thiolane structure reported recently, the cyclobutanone ring
was virtually planar.[10]
was supported by the intensities of 13C and 34S peaks and,
in some examples, by high resolution. Many common fea-
tures in the MSs of the dithiolanes (Table 2) invite to recon-
structing sequences of fragmentation, although the struc-
tures in Schemes 6 and 7 remain speculative.
Both hexasubstituted dithiolanes, 4Cc and 5Cc, display
hindered phenyl rotation in the NMR spectra at 32 °C (see
above). Figure 1 illustrates the curbing of phenyl rotation
by the methyl groups at C5 in 4Cc: the closest distance of
a methyl-H at C19 and the aromatic 13-H is 1.93 Å which
is significantly below the sum of the van der Waals radii.
The 4,5-tetrasubstituted dithiolanes 5Ca and 5Da likewise
suffer from front strain, and the methyl groups at the cyclo-
butane ring interfere with phenyl rotation; one H,H dis-
tance of 1.96 Å in 5Da (Figure 2) establishes the proximity.
On the NMR time scale, however, phenyls in 5Ca and 5Da
rotate still unrestricted at 32 °C.
Scheme 6. Mass spectrum of the spiro[adamantane-2,2Ј-[1,3]dithi-
olane] 4Ab: Supposed fragmentation pathways.
Figure 2. X-ray structure of 1,1,3,3-tetramethyl-8,8-diphenyl-5,7-
dithiaspiro[3.4]octane (5Da); ZORTEP plot.
The bulky substituents exert shearing forces in our 1,3-
dithiolanes, as exemplified with 4Cc (Figure 1): C2Ј and C4Ј
of the four-membered ring have different distances from the
plane defined by S1–C2–S3, –1.08 and +1.17 Å, respec-
tively. Similarly, the aromatic C-atoms C6 and C12 are lo-
cated by +1.29 Å above and –1.19 Å below the plane S3–
C4–C5.
The bond lengths likewise demonstrate the van der Waals
strain: 4Cc shows 1.82–1.85 Å for all four C–S bonds,
whereas the bonds S–CH2 in 5Ca and 5Da are markedly
Scheme 7. Mass spectra of spiro-1,3-dithiolanes 5C and 5D: Sec-
tion of fragmentation pathways.
The fragmentation process is dominated by 3+2 cyclore-
shorter: 1.79–1.81 Å. The distances in the cyclobutane ring versions in concordance with previous discussions,[6,8] and
of 5Da (Figure 2) differ even more: 1.53 Å for C2Ј–C3Ј(H2) the dithiolane 4Ab may serve as a prototype. Whether its
and C4Ј–C3Ј(H2) vs. 1.61 and 1.62 Å for the bonds C2Ј–C5 radical cation 19 preserves the heterocycle or consists of a
and C4Ј–C5.
mixture of open-chain species 18 and 20, is uncertain. The
1524
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 1519–1531

Aliphatic Thiocarbonyl Ylides and Thiobenzophenone
FULL PAPER
formulation as distonic species (separate centers of charge ions m/z 237 and m/z 205 among which are the base peaks
and spin density),[28]18 and 20, allows the substituents to in the MS of 5Ca, 5Cc and 5Da. Formula 31 for m/z 237
contribute to cation and radical stabilization. The ionized illustrates the smallest structural change, but the fluorene-
thiocarbonyl ylides are allyl-type radicals with a sulfonium 9-sulfonium structure 29 or the 2-thionianaphthalene deriv-
+
center in the middle. In calculations of related species, they ative 30 appear more likely. For the cation C16H13 (m/z
rank in energy below the corresponding three-membered 205), the sulfur-free analogues of 29–31 can be considered:
rings.[29]
9-(1-propenyl)fluorenyl+, 1-phenyl-3-methylindenyl+, or
The fragmentation pathways a and b of 18, ring-opened propynyl-diphenylmethyl+ among others.
at the bond C4–C5, mirror the 1,3-dipolar cycloadditions
A closer study of the MSs of dithiolanes 4 and 5 (see
which start from two reactant pairs. In addition to 15 and Experimental) brings to light many more common features
21, also the mass peaks of the thioketones were observed. which reveal fragmentation sequences, but little structural
Ring-opening of 19 at the bond S3–C4 likewise retains evidence.
the superior benzhydryl-type stabilization. Intramolecular
substitutions in 20 by paths c and d give rise to dithiirane
17 and thiirane 23 which, in turn, produce the distonic spe- Experimental Section
cies 16 and 22. Adamantanethione S-sulfide is a known 1,3-
General Remarks: 1H NMR spectra were recorded on a Bruker
dipole,[30] and 16, its radical cation, has been observed be-
fore.[8]
WP80CW (80 MHz) for 1H and WP80DS (20.15 MHz) for 13C;
some spectra were run on Varian XR400S. Solvent was acid-free
CDCl3, stored over dry K2CO3, if not stated otherwise. As weight
standard for quantitative 1H NMR analysis (usually 5%, relative),
The base peak in the MS of 4Ab, m/z 226, fits the radical
cation 22 of thiobenzophenone S-ethylide. Generally, the
radical cations of thiobenzophenone S-alkylides showed sym-tetrachloroethane (δ = 5.92 ppm), the as-isomer (δ = 4.28 ppm)
or trichloroethylene (δ = 6.70 ppm) were used; 3–5 machine inte-
grals of each signal were averaged. The multiplicities of the 13C
NMR signals were determined by comparison of H-decoupled with
off-resonance spectra. The MS are EI spectra with 70 eV, recorded
on a AET 909 or a Finnegan MAT90 instrument; intensities of
isotope peaks are reported as, e.g., 13C% calcd./% found, and in
the same way for HR = high resolution. CC = column chromatog-
raphy; PLC = preparative layer chromatography on 20×20 cm
high intensities in the MS of 1,3-dithiolanes 4A/5A and 4B/
5B, thus reflecting the diphenylmethyl-type stabilization.
In the MS of the dithiolanes described here, m/z 165 oc-
curs as a substantial peak. It was established by Schumann
et al., that thiobenzophenone+. (and related radical cations)
break down into the 9-fluorenyl cation (24, m/z 165) + HS·,
and a reasonable mechanism was proposed.[31] We observed
that the peaks of thiobenzophenone S-alkylides+. have a
steady companion, which possesses one mass unit less, and
a conversion of diphenylmethyl to fluorenyl is supposed.
One of the two H-atoms set free reduces the alkylidene
group, e.g., the sulfonium structure 25 is tentatively as-
signed to m/z 225 (39%). The competing loss of EtS· con-
verted 22 to the fluorenyl cation 24 (38%).
In the MS of the positional isomer 5Ab, m/z 226 is like-
wise base peak (+ m/z 225, 40%), and radical cations 15
and 21 are also present. Despite having many peaks in com-
mon, different intensities and specific fragments support the
non-identity of the MS of 4Ab and 5Ab. Some ‘mixing’ of
fragments also appeared in the MS of 4Ba/5Ba, but it is not
general.
Radical cations of cyclobutanones and cyclobutanes un-
dergo 2+2 cycloreversions. The loss of dimethylketene from
the spiro-tetramethylcyclobutanones of type 4C/5C+. and
isobutene elimination from 4D/5D+. are taking place side
by side with the 3+2 cycloreversions. In the MS of 4C and
4D, a fragmentation is preferred which corresponds to path
c of Scheme 6, whereas the radical cations of 5C/5D favored
initial expulsion of RЈ2C=S, followed by 2+2 cyclorever-
sion, to give thiirane 27 as product of an intramolecular
substitution (Scheme 7).
glass plates, usually with a 2 mm layer of Merck silica gel 60PF254
.
In the description of the NMR spectra, the structural assignments
of the signals are based on a spectroscopic synopsis of numerous
2,5-dihydro-1,3,4-thiadiazoles, thiiranes, and 1,3-dithiolanes; those
of this paper and preceding ones[6,8,10] were involved. To facilitate
the comparison, the position numbering of the monocyclic hetero-
rings is retained for the spiro-compounds. For each of the three
heterocycles, one example shows the procedure, and the others fol-
low with formula numbers and brief spectroscopic and analytical
characterization. In the interpretation of the MS, the proposed for-
mulae may not be the structures of the cationic fragments, but
rather illustrate fragmentation pathways.
New 2,5-Dihydro-1,3,4-thiadiazoles and Thiiranes
2,5-Dihydro-5,5-dimethylspiro[(1,3,4)-thiadiazole-2,2Ј-adamantane]
(2Ac): Freshly sublimed adamantanethione[32] (1A, 498 mg,
3.0 mmol) in pentane (5 mL) at 0 °C was dropwise treated with the
red 2-diazopropane,[33] until the red color of 1A just faded. After
1 h at –78°, the lustrous leaflets of 2Ac were filtered: 634 mg (89%);
the m.p. 59–60 °C (dec.) did not change after recryst. from pentane.
1H NMR: δ = 1.72 (s, 2 Me), 1.77–2.2 (m, 12 H), 2.57–2.85 (m, 2
H) ppm. IR (KBr): ν = 990, 1449 cm–1 st; 1583 m (N=N) cm–1.
˜
MS (30 °C), m/z (%): 2.35 (0.1) [M+– 1], 208 (44) [M+ – N2], 176
(46) [208 – S]+, 166 (100) [1A+], 135 (40) [C10H15+], 91 (50), 79 (34).
C13H20N2S (236.37): calcd. C 66.05, H 8.53, N 11.85, S 13.57;
found C 66.13, H 8.58, N 11.80, S 13.60.
Selected for discussion is the further degradation of 27
(m/z 252) which is a common fragment in the MS of all
members of the 5C/5D family. Either it forms 28 on ring-
opening or loses a sulfur atom to give m/z 220 which –
formally – could be the allene derivative 26. Even more
2Ba: This dihydro-1,3,4-thiadiazole and is 1,2,3-regioisomer were
formed in the ratio 87:13[34] by the reaction of diisopropyl thioke-
tone (1B)[35] with gaseous diazomethane in pentane at 0 °C. M.p.
1
–12 to –10 °C (MeOH). H NMR: δ = 0.90, 0.97 (2 d, J = 6.5 Hz,
2×2 Me), 2.60 (sept, J = 6.5 Hz, 2 H of iPr2), 5.62 (s, 5-H2) ppm.
populated were the products of further methyl loss, the cat- IR (KBr plates): ν = 1383 m, 1469 br.; 1577 m (N=N) cm–1. MS
˜
Eur. J. Org. Chem. 2005, 1519–1531
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R. Huisgen, G. Mloston, H. Giera, E. Langhals, K. Polborn, R. Sustmann
FULL PAPER
(30 °C), m/z (%): 172 (Ͻ 0.1) [M+], 144 (100) [M+ – N2], 129 (14)
2Ha. Colorless needles (MeOH), m.p. 64–65 °C. 1H NMR: δ = 1.15
[144 – Me]+, 111 (32), 101 (57) [144 – iPr]+, 97 (45), 83 (50), 74
(s, 6 Me), 5.54 (s, 5-H ) ppm. IR (KBr): ν = 946 br. m, 1368 s, 1391
˜
2
(50). C8H16N2S (172.29): calcd. C 55.77, H 9.36, N 16.26, S 18.61; s; 1576 m (N=N) cm–1. MS (20 °C), m/z (%): 200 (0.2) [M+], 172
found C 55.82, H 9.09, N 16.26, S 18.59.
(14) [M+ – N2], 143 (10) [M+ – tBu], 140 (2) [172 – S]+, 111 (25)
[143 – S]+, 83 (31) [140 – tBu]+, 70 (57), 57 (100) [tBu+]. C10H20N2S
(200.34): calcd. C 59.95, H 10.06, N 13.98, S 16.01; found C 60.22,
H 9.99, N 13.96, S 16.05.
2Fb: 2,2,5,5- Tetramethylcyclopentanethione (1F)[36,37] and diazo-
ethane (1.4 equiv.) were reacted in Et2O at –10 °C. The pale-yellow
oil (74%) crystallized from pentane at –78 °C and was obtained as
1
2Ja: 2,2,6,6-Tetramethylcyclohexanethione (1J)[38,40] and diazo-
methane in pentane at –10 °C; twice recryst. from pentane, 2Ja
a colorless oil at room temp. H NMR: δ = 0.65, 0.76, 1.13, 1.15
(4 s, 4 Me), 1.75 (d, J = 6.9 Hz, 5-Me), 1.90–2.20 (m, 3Ј-H2, 4Ј-
H2), 5.77 (q, J = 6.9 Hz, 5-H) ppm. 13C NMR: δ = 22.0, 24.8, 25.0,
29.8 (4 q, 1:1:1:2, 5 Me), 38.0, 38.2 (2 t, C-3Ј, C-4Ј), 46.8, 47.8 (2
1
(72%) showed m.p. 104–105 °C (dec.). H NMR: δ = 0.54, 1.21 (2
s, 2×2 Me), 1.51–2.14 (m, 6 ring-H), 5.58 (s, 5-H2) ppm. 13C NMR:
δ = 19.0 (t, C-4Ј), 27.2, 28.1 (2 q, 2×2 Me), 38.6 (t, C-3Ј + C-5Ј),
41.1 (s, C-2Ј + C-6Ј), 83.9 (t, C-5), 121.1 (s, C-2) ppm. IR (KBr):
s, C-2Ј, C-5Ј), 93.7 (d, C-5), 130.7 (s, C-2) ppm. IR (KBr plates): ν
˜
= 1015 s, 1366 s, 1381 s, 1465 br.; 1570 m, 1594 m (N=N) cm–1.
MS (90 °C), m/z (%): 212 (3.5) [M+], 211 (10), 185 (38) [C11H21S;
ν = 1379 s, 1385 s; 1578 m (N=N) cm–1. MS (40 °C), m/z (%): 212
˜
13C 4.7/4.7, 13C2 + 34S 1.7/1.7], 156 (16) [C9H16S+, 1F+], 141 (26)
(3) [M+], 184 (76) [M+ – N2], 169 (34) [184 – Me]+, 152 (13) [184 –
S, C11H20+], 137 (93) [152 – Me]+, 123 (84) [C9H15+], 109 (47)
[C8H13+], 95 (82), 82 (100) [C6H10+], 81 (77), 69 (62). C11H20N2S
(212.34): calcd. C 62.21, H 9.49, N 13.19, S 15.10; found C 62.47,
H 9.57, N 13.43, S 15.10.
+
[1F+
–
Me], 138 (30), 123 (100) [C9H15
,
probably
tetramethylcyclopentenyl+], 109 (31), 95 (12), 81 (22), 69 (35)
[C5H9+]. C11H20N2S (212.35): calcd. C 62.21, H 9.49, N 13.19;
found C 62.72, H 9.64, N 12.97.
2Fc: The reaction of 1F with 2-diazopropane in Et2O furnished
67% of pure 2Fc, crystalline in pentane at –78 °C, and at room
2Jb: Thione 1J and diazoethane in Et2O at –10 °C; 70% of isolated
2Jb, m.p. 71–72 °C (pentane). H NMR: δ = 0.55, 0.64, 1.18, 1.23
(4 s, 4 Me), 1.79 (d, J = 6.9 Hz, 5-Me), 1.50–2.03 (m, 6 H), 5.69
(q, J = 6.9 Hz, 5-H) ppm. 13C NMR: δ = 19.0 (t, C-4Ј), 20.6, 27.08,
27.23, 27.71, 29.0 (5 q, 5 Me), 38.2, 38.6 (2 t, C-3Ј, C-5Ј), 39.9, 41.4
1
1
temp. colorless oil. H NMR: δ = 0.75, 1.10 (2 s, 2×2 Me at C-2Ј,
C-5Ј), 1.75 (s, 2 Me at C-5), 1.88–2.31 (m, 3Ј-H2, 4Ј-H2) ppm. 13C
NMR: δ = 25.1, 29.9, 30.5 (3 q, 3×2 Me), Ϸ 38.1 (11 lines, higher
order, C-3Ј, C-4Ј), 47.4 (s, C-2Ј + C-5Ј), 103.7 (s, C-5), 130.8 (s, C-
(2 s, C-2Ј, C-6Ј), 94.3 (d, C-5), 130.0 (s, C-2) ppm. IR (KBr): ν =
˜
1585 m (N=N) cm–1. MS (40 °C), m/z (%): 211 (5) [M+ – Me], 198
2) ppm. IR (KBr plates): ν = 1365 s, 1381 s, 1457 s br.; 1588 m
˜
(N=N) cm–1. MS (25 °C), m/z (%): 211 (19) [M+ – Me], 198 (23)
(28) [M+ – S; 13C 3.7/3.6, 13C2 0.23/0.26, no S], 169 (19), 137 (16),
[M+ – N2], 183 (11) [198 – Me]+ (13C 1.4/1.2), 123 (55) [C9H15
;
+
+
123 (100) [C9H15
,
trimethylcyclohexenyl+ or tetramethyl-
13C
5.5/6.1,
no
S],
109
(100)
[C8H13
,
probably
+
cyclopentenyl+], 121 (13) [C9H13+], 95 (23), 81 (43) [C6H9+], 79 (11),
69 (15), 67 (16). C12H22N2S (226.38):, calcd. C 63.67, H 9.80, N
12.37, S 14.16; found C 63.85, H 9.70, N 12.39, S 14.15.
trimethylcyclopentenyl+], 107 (19), 95 (22), 81 (15), 67 (13).
C12H22N2S (226.38): calcd. C 63.67, H 9.80, N 12.37, S 14.16;
found C 64.15, H 9.54, N 12.20, S 14.21.
Extrusion of N2 from 2,5-Dihydro-1,3,4-thiadiazoles (2): The condi-
tions for the in situ reactions of thiocarbonyl ylides 3 have to be
adapted to the half-life of 2. For studying cycloadditions of 3, low
stationary concentrations are desirable. A half-life of the precursor
2 in the range of 1 h and 6–8 half-lives as reaction time are fitting.
The rate measurement by the nitrometric technique[4] is described
and supplemented by a list of further half-lives.
2Gb: Reaction of 1,1,3,3-tetramethylindanthione (1G)[36,38] with di-
azoethane in Et2O at –10 °C, 78% yield. M.p. 64–66 °C (pentane).
1H NMR: δ = 0.95, 1.06, 1.36, 1.39 (4 s, 4 Me), 1.81 (d, J = 6.8 Hz,
5-Me), 5.93 (q, J = 6.8 Hz, 5-H), 7.19 (br. s, 4 arom. H). 13C NMR:
δ = 22.0, 22.26, 22.41, 31.0, 31.3 (5 q, 5 Me), 50.0, 50.7 (2 s, C-1Ј,
C-3Ј), 95.0 (d, C-5), 122.46, 122.55, 127.4 (3 d, 1:1:2, 4 arom. CH),
131.6 (s, C-2), 148.3 (s, 2 arom. C ) ppm. IR (KBr): ν = 759 s
˜
q
2Ac: The vigorously stirred soln. of pure 2Ac (472 mg, 2.00 mmol)
in toluene (10 mL) was brought into a bath of 80 1 °C and con-
nected with a 100 mL nitrometer. Time and N2 volume after 15 min
are defined as zero values, and Vϱ was measured after 7 h. The
first-order evaluation with k1t = ln (Vϱ/Vϱ – Vt) and linear re-
gression of 17 volume readings (up to 83% reaction) afforded 104k1
(arom. out-of-plane deform.), 1454 m, 1468 m, 1479 m, 1574 w,
1581 w, 1604 w (arom. ring vibr., N=N) cm–1. MS (40 °C), m/z (%):
245 (2) [M+ – Me], 232 (16) [M+ – N2; 13C2
+
34S 0.9/0.8], 185
(20) [C14H17+], 172 (100) [C13H16+, probably tetramethylindene+ or
trimethylnaphthalene+; 13C 14/13, 13C2 1.0/0.7, no S], 171 (23), 157
(85) [C12H13+], 155 (15), 141 (22), 128 (14) [C10H8+, naphthalene+],
115 (12). C15H20N2S (260.39): calcd. C 69.18, H 7.74, N 10.76, S
12.32; found C 69.33, H 7.74, N 10.89, S 12.31.
= 2.45 [s–1] (t = 47.2 min) and a correlation coefficient r = 0.9992;
½
reproducibility 4%.
Further Rate Data (often mean values of several determinations):
2Gc: Reaction of 1G with 2-diazopropane in Et2O at –10 °C gave
1
Values below refer to the formula numbers in Scheme 3, t in min
90% yield. M. p. 117–118 °C (pentane). H NMR: δ = 1.03, 1.33,
½
1.81 (3 s, 3×2 Me), 7.18 (br. s, 4 arom. H) ppm. 13C NMR: δ =
22.6, 30.6, 31.3 (3 q, 3×2 Me), 50.4 (s, C-1Ј + C-3Ј), 105.3 (s, C-
5), 122.5, 127.3 (2 d, 2×2 arom. CH), 131.8 (s, C-2), 148.3 (s, 2
(solvent, temp. in °C): 2Aa 25.7 (xylene, 50), 77.5 (xylene, 40), 90.3
(THF, 40), 108 (MeCN, 40); 2Ab 37.4 (xylene, 50); 2Ac 124 (xylene,
50); 2Ba 23.9 (toluene, 70); 2Ca 17.8 (xylene, 50); 2Cb 19.1 (xylene,
50); 2Cc 120 (xylene, 50); 2Da 97.1 (xylene, 40), 101 (THF, 40), 163
(MeCN, 40); 2Ea 16.5 (toluene, 52); 2Fa 111 (xylene, 40); 2Fb 31.8
(xylene, 50); 2Fc 91.7 (xylene, 100); 2Ga 0.718 (xylene, 100), 68.4
(xylene, 50); 2Gb 65.6 (xylene, 50); 2Gc 20.0 (xylene, 100); 2Ha 29.2
(xylene, 100); 2Ja 15.6 (xylene, 100); 2Jb 20.8 (xylene, 100).
arom. C ) ppm. IR (KBr): ν = 765 + 768 s, 990 s, 1360 m, 1375
˜
q
m, 1451 s, 1479 m, 1594 m cm–1. MS (50 °C), m/z (%): 246 (11)
[M+ – N2], 231 (8) [246 – Me]+, 199 (16) [231 – S]+, 189 (15) [1G+
Me, C12H13S+], 172 (68) [C13H16+], 157 (100) [C12H13
trimethylindenyl+], 156 (28), 149 (15), 142 (27) [C11H10
–
+
,
,
+
methylnaphthalene+], 115 (24), 111 (15). C16H22N2S (274.42):
calcd. C 70.03, H 8.08, N 10.21, S 11.69; found C 70.32, H 7.96,
N 10.44, S 11.72.
Thiiranes 7 as Products of Electrocyclization of 2: With increasing
steric demands of thiocarbonyl ylides 2, the electrocyclization com-
petes with the in situ cycloadditions, and the analysis of thiiranes
in the reaction mixtures is required. The example of 7Fb is sup-
plemented by the brief description of further new thiiranes. Some-
2Ha: Di-tert-butyl thioketone (1H)[39] (δ(1H) = 1.45, s, 6 Me) and
diazomethane in Et2O at 0 °C. 1H NMR analysis indicated 97% of
1526
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Aliphatic Thiocarbonyl Ylides and Thiobenzophenone
FULL PAPER
times, a symmetry-allowed 1,4-H shift competes with the electrocy-
clization; the thioenol ethers formed will not be dealt with here.[34]
7Jb: N2 elimination from 2Jb (octane, 130 °C, 1 h) provided 89%
1
of 7Jb (1H NMR analysis). M.p. 65–66 °C (pentane). H NMR: δ
= 0.86, 1.08, 1.22, 1.31 (4 s, 4 Me at C-2, C-6), 1.38–1.60 (m, 3×2
H), 1.73 (d, J = 6.4 Hz, 3Ј-Me), 2.94 (q, J = 6.4 Hz, 3Ј-H) ppm.
13C NMR: δ = 19.0 (t, C-4), 17.7, 26.4, 28.7, 31.2, 36.1 (5 q, 5 Me),
36.8, 38.3 (2 s, C-2, C-6), 39.1 (d, C-3Ј), 40.3, 43.9 (2 t, C-3, C-5),
65.9 (s, C-1) ppm. C12H22S (198.36): calcd. C 72.66, H 11.18, S
16.17; found C 72.35, H 11.03, S 16.17.
2,2,3Ј,5,5-Pentamethylspiro[cyclopentane-1,2Ј-thiirane] (7Fb): 2,5-
Dihydro-1,3,4-thiadiazole 2Fb (970 mg, 4.57 mmol) in benzene
(5 mL) was refluxed for 2 h. After removal of the solvent, the H
1
NMR analysis with sym-C2H2Cl4 in CDCl3 indicated 100% of 7Fb
(q, 2.86). The thiirane crystallized from MeOH at –78 °C and was
filtered at low temp., m.p. 58–60 °C. 1H NMR: δ = 0.83, 1.06, 1.23
(3 s, 1:2:1, 4 Me), 1.55–1.64 (m, 3-H2, 4-H2), 1.60 (d, J = 6.0 Hz,
3Ј-Me), 2.86 (q, J = 6.0 Hz, 3Ј-H) ppm. 13C NMR (100 MHz,
DEPT): δ = 19.3, 27.3, 29.6, 31.3, 32.2 (5 Me), 38.2 (C-3Ј), 39.0,
41.7 (C-3, C-4), 43.5, 43.9 (C-2, C-5), 74.0 (C-2Ј) ppm. MS (25°),
Reactions with Thiobenzophenone: Table 1 presents the reaction
conditions for the thermolysis of dihydro-1,3,4-thiadiazoles 2 in the
presence of thiobenzophenone as well as the product yields deter-
mined by 1H NMR analysis with weight standard. The example
2Ab (key to formula numbers in Scheme 3) illustrates the pro-
cedure.
m/z (%): 184 (22) [M+], 152 (10) [M+ – S], 137 (54) [C10H17+, 152 –
+
Me], 123 (33) [C9H15+], 109 (100) [C8H13
,
probably
trimethylcyclopentenyl+], 96 (33) [C7H12+], 95 (42) [109 – Me]+, 81
(55) [C6H9+]. C11H20S (184.34): calcd. C 71.76, H 10.94, S 17.39;
found C 71.93, H 10.90, S 17.35.
Adamantanethione S-Ethylide (3Ab): Spiro compound 2Ab[41]
(444 mg, 2.00 mmol) and freshly distilled thiobenzophenone (6,
436 mg, 2.20 mmol) in abs. THF (4 mL) were magnetically stirred
in a 60 °C bath for 6 h. After evaporation, quantitat. 1H NMR
analysis indicated 57% of 4Ab (t δ = 4.55 ppm) and 38% of 5Ab
(t, 3.57). The solvent was removed, and the residue subjected to
PLC (petroleum ether/CH2Cl2 8:2). The first fraction afforded 5Ab
(120 mg, 15%) from CHCl3/acetone as colorless prisms. Renewed
PLC of the second fraction gave 4Ab as colorless oil (175 mg, 25%)
which soon crystallized.
7Cb: N2 extrusion from 2Cb[41] (toluene, 50 °C, 4 h) and distillation
at 99–94 °C (bath)/12 mm furnished 7Cb as colorless oil; yield 81%
(1H NMR analysis). 1H NMR: δ = 1.07, 1.20, 1.25, 1.37 (4 s, 4 Me
at C-2, C-4), 1.61 (d, J = 6.0 Hz, 3Ј-Me), 3.19 (q, J = 6.0 Hz, 3Ј-
H) ppm. IR (NaCl plates): ν = 999, 1030, 1459; 1782 vs, 1810 m
˜
(C=O). C10H16OS (184.29): calcd. C 65.17, H 8.75, S 17.40; found
C 65.20, H 8.67, S 17.39.
1
1
4Ab: M.p. 115–117 °C (CHCl3/EtOH). H NMR: δ = 1.17 (d, J =
7Fc: After N2 elimination from 2Fc (octane, 130°, 1 h), H NMR
6.5 Hz, Me), 1.42–2.42 (m, 14 H), 4.55 (q, J = 6.5 Hz, 5-H), 7.06–
7.50 (m, 10 arom. H) ppm. 13C NMR: δ = 19.3 (q, Me), 26.3, 26.4,
41.6, 42.9 (4 d, 4 CH of adamantane), 35.7, 35.9, 37.1, 37.4, 37.6
(5 t, 5 CH2 of adamantane), 52.8 (d, great residual 1JR, C-5), 73.7,
75.9 (2 s, C-2, C-4), 126.3, 126.7, 127.3, 127.7, 127.8, 129.4 (6 d,
1:1:2:2:2:2, 10 arom. CH), 143.0, 146.2 (2 s, 2 arom. Cq) ppm. MS
(EI, 100 °C), m/z (%): 392 (52) [M+], 332 (82) [M+ – MeCHS, 21],
analysis in CDCl3 showed 85% of 7Fc. M.p. 131–133 °C (MeOH).
1H NMR: δ = 1.06, 1.29 (2 s, 4 Me at C-2, C-5), 1.68 (s, 2 Me at
C-3Ј), 1.55–1.70 (br. s, 3-H2, 4-H2) ppm. MS: the fragmentation
cascade is similar to that observed for the precursor 2Fc (see
above). C12H22S (198.36): calcd. C 72.66, H 11.18, S 16.17; found
C 72.09, H 11.03, S 16.02.
331 (12), 226 (100) [M+ – 1A, Ph2C–S=CHMe+, 22], 225 (39)
7Gb: After thermolysis in the closed NMR tube (CDCl3, 80 °C, 1
h), 1H NMR analysis indicated 94% of 7Gb. M. p 53–54 °C
+
[C15H13S+, 25], 198 (27) [C10H14S2
;
13C2 + 34S2 calcd. 1.84/found
1
2.2], 194 (80) [C10H14–S=CHMe]+, 166 (56) [C10H14S+ = 1A+], 165
(38) [9-fluorenyl+, 24], 133 (31) [C10H13+], 91 (41) [C7H7+].
C25H28S2 (392.61): calcd. C 76.48, H 7.19, S 16.34; found C 76.50,
H 7.25, S 16.30.
(MeOH). H NMR: δ = 1.11, 1.38, 1.40, 1.52 (4 s, 4 Me at C-1, C-
3), 1.75 (d, J = 6.2 Hz, 3Ј-Me), 3.02 (q, J = 6.2 Hz, 3Ј-H), 7.15 (br.
s, 4 arom. H) ppm. 13C NMR: δ = 19.0, 28.3, 30.3, 32.1 (4 q,
1:1:1:2, 5 Me), 36.8 (d, C-3Ј), 46.9, 47.7 (2 s, C-1,C-3), 73.6 (s, C-
2), 121.9, 122.2, 127.09, 127.27 (4 d, 4 arom. CH), 148.6, 150.3 (2
s, 2 arom. Cq) ppm. MS: similar to that of 2Gb above. C15H20S
(232.38): calcd. C 77.52, H 8.68, S 13.80; found C 77.54, H 8.57, S
13.77.
5Ab: M.p. 195–196 °C (dec) (CH2Cl2/EtOH). 1H NMR: δ = 1.47
(d, J = 6.3 Hz, Me), 1.0–3.45 (m, 14 H), 3.57 (q, J = 6.3 Hz, 2-H),
7.0–8.12 (3 m, 6:2:2, 10 arom. H) ppm. 13C NMR: δ = 19.7 (q,
Me), 26.4 (2 x), 38.9, 40.0 (3 d, 4 CH of C10H14), 33.3, 33.5, 37.6,
1
1
7Gc: H NMR analysis with sym-C2H2Cl4 showed quantitat. for-
39.3, 42.1 (5 t, 5 CH2), 35.9 (d, high JR, C-2), 78.5, 79.6 (2 s, C-
mation of 7Gc in the thermolysis of 2Gc (toluene, 120 °C, 5 h).
M.p. 93–94 °C (MeOH, 89%, colorless needles). 1H NMR: δ =
1.41, 1.53 (2 s, 4 Me at C-1 and C-3), 1.85 (s, 2 Me at C-3Ј), 7.14
(s, 4 arom. H) ppm. 13C NMR: δ = 28.4, 30.8, 31.3 (3 q, 3×2 Me),
48.6 (s, C-1 + C-3), 48.8 (s, C-3Ј), 78.5 (s, C-2), 121.9, 127.2 (2 d,
2×2 arom. CH), 149.9 (s, 2 arom. Cq) ppm. C16H22S (246.40):
calcd. C 77.99, H 9.00, S 13.01; found C 78.28, H 8.93, S 13.01.
4, C-5), 126.0, 127.6 (2 d, 2 arom. p-CH), 127.1, 127.6, 131.0, 132.3
(4 d, 8 arom. o-CH, m-CH), 143.0, 145.4 (2 s, 2 arom. Cq) ppm.
MS (100 °C), m/z (%): 392 (3) [M+], 332 (10) [M+ – MeCHS, 21],
300 (77) [Ph2C=C10H14]+, 226 (100) [Ph2C=S–CHMe]+, 225 (40)
[C15H13 S+], 211 (32) [226 – Me]+, 194 (18) [C10H14 = S–CHMe]+,
166 (32) [1A+], 165 (43) [9-fluorenyl+], 91 (40) [C7H7+], 77 (11)
[C6H5+]. C25H28S2 (392.61): calcd. C 76.48, H 7.19, S 16.34; found
C 76.54, H 7.22, S 16.36.
7Ha: 73% (1H NMR analysis). Distillation at 50 °C (bath)/10 mm
and PLC (pentane) gave 7Ha as colorless liquid. 1H NMR: δ =
1.15 (s, 6 Me), 2.35 (s, 3Ј-H2) ppm. C10H20S (177.33): calcd. 69.69,
H 11.70, S 18.61; found C 69.87, H 11.46, S 18.58.
Adamantanethione S-Isopropylide (3Ac): The first fraction of PLC
crystallized from EtOH: 4Ac (55%). 5Ac was enriched in the sec-
ond fraction (separation failed).
7Ja: After N2 elimination from 2Ja (xylene, 100 °C, 2 h, 99%) and
Kugelrohr distillation, 7Ja crystallized from Et2O. M.p. 77–78 °C.
1H NMR: δ = 0.93, 1.15 (2 s, 2×2 Me), 1.30–1.75 (m, 6 ring-H),
2.43 (s, 3Ј-H2) ppm. 13C NMR: δ = 19.0 (t, C-4), 28.5, 30.4 (2 q,
2×2 Me), 29.1 (t, C-3Ј), 37.0 (s, C-2 + C-6), 41.7 (t, C-3 + C-5),
63.2 (t, C-1) ppm. C11H20S (184.34): calcd. C 71.67, H 10.94, S
17.39; found C 71.66, H 10.80, S 17.45.
4Ac: M.p. 153–155 °C. 1H NMR: δ = 1.55 (s, 2 Me), 1.57–2.25 (m,
14 H), 7.0–7.25 (2 m, 6:4, 10 arom. H) ppm. 13C NMR: δ = 28.9
(q, broadened, 2 Me), 26.0, 26.2, 42.4 (3 d, 1:1:2, 4 CH of C10H14),
36.3, 36.4, 37.5 (3 t, 2:2:1, 5 CH2 of C10H14), 62.4 (s, C-5), 70.9,
77.6 (2 s, C-2, C-4), 126.2, 126.9, 130.1 (3 d, 1:2:2, 10 arom. CH),
145.6 (s, 2 arom. Cq) ppm. MS (100 °C), m/z (%): 406 (5) [M+],
332 (100) [M+ – Me2CS, 21], 331 (18), 240 (15) [C16H16S+, Ph2C–
Eur. J. Org. Chem. 2005, 1519–1531
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1527

R. Huisgen, G. Mloston, H. Giera, E. Langhals, K. Polborn, R. Sustmann
FULL PAPER
S=CMe2+], 208 (42) [C10H14=S–CMe2]+, 193 (18) [C15H13+], 166 m/z calcd./found (%): 368.1263/368.1276 (0.1) [M+], 298.0846/
(58) [C10H14S+ = 1A+], 165 (35) [9-fluorenyl+], 115 (25), 91 (46) 298.0857 (43) [C18H18S2+, M+ – C4H6O], 212.0657/212.0672 (13)
[C7H7+], 77 (13) [C6H5+]. C26H30S2 (406.63): calcd. C 76.79, H 7.44,
S 15.77; found C 76.89, H 7.47, S 15.76.
[C14H12S+, Ph2C=S–CH2+], 211.0597/211.0586 (15) [C14H11S+, 9-
+
(methylsulfanyl)fluorenyl+], 180.0936/180.0954 (100) [C14H12
,
+
Ph2C=CH2
;
13C 15.6/15.4; 13C2 1.14/1.15, no S], 179.0858/
5Ac: From spectrum of mixture by subtraction. 1H NMR: δ = 1.42
(s, 2 Me) ppm. 13C NMR: δ = 29.0 (q, br., 2 Me), 26.7, 27.0, 34.8
(3 d, 1:1:2, 4 CH of C10H14), 33.6, 39.2, 39.5 (3 t, 2:2:1, 5 CH2 of
C10H14), 50.8 (s, C-2), 80.7, 81.1 (2 s, C-4, C-5), 126.5, 132.6 (2 d,
8:2, 10 arom. CH), 146.8 (s, 2 arom. Cq) ppm.
179.0864 (38) [C14H11+], 178.0780/178.0796 (36) [C14H10+],
+
165.0702/165.0704 (47) [C13H9
, 24), 152.0624/152.0629 (8)
[C12H8+], 86.0189/86.0189 (25) [Me2C=C=S+], 70.0417/70.0425 (9)
[Me2C=C=O+]. C22H24OS2 (368.54): calcd. C 71.69, H 6.56; found
C 71.19, H 6.54.
Diisopropyl Thioketone S-Methylide (3Ba):[19] By-product (Ϸ 10%)
was a thioenol ether formed from 3Ba by 1,4-hydrogen shift.[34]
From EtOH 50% of 5Ba; PLC of the mother liquor (pentane/
CH2Cl2 8:2) afforded 4Ba (12%).
2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-Ethylide (3Cb): The
dependence of the product composition on the reaction temp.
(Table 1) is noteworthy. The 45 °C experiment afforded 4Cb (40%)
and 11% of 5Cb by fractional crystallization from EtOH. Dithiol-
ane 12b (q, 4.09) was identified with the product obtained from
thiobenzophenone S-ethylide and 6.[4] Thiirane 7Cb was analyzed
by q at 3.19.
4Ba: M.p. 93–94 °C (MeOH). 1H NMR: δ = 0.98 (d, J = 6.6 Hz, 4
Me), 2.20 (sept, J = 6.6 Hz, 2 H of iPr2), 3.72 (s, 5-H2), 7.05–7.57
(2 m, 6:4, 2 Ph) ppm. 13C NMR: δ = 19.7, 20.0 (2 q, 2×2 diastereo-
topic Me), 37.5 (d, 2 CH of iPr2), 49.0 (t, C-5), 74.1, 84.1 (2 s, C-
2, C-4), 126.5, 127.9 (2 d, 4:1, 10 arom. CH), 145.8 (s, 2 arom. Cq)
ppm. MS (60 °C), m/z (%): 342 (2) [M+], 299 (100) [M+ – iPr], 211
4Cb: M.p. 170–171 °C (CH2Cl2/EtOH), fine needles. 1H NMR: δ
= 0.92, 1.04, 1.32, 1.42 (4 s, 4 Me), 1.16 (d, J = 6.5 Hz, 5-Me), 4.35
(q, J = 6.5 Hz, 5-H), 7.0–7.5 (m, 2 Ph) ppm. 13C NMR: δ = 20.2
(s, probably 5-Me), 22.6, 23.3, 24.1, 24.4 (4 q, 4 Me at C-2Ј, C-4Ј),
54.0 (d, C-5), 65.3, 67.7, 71.9 (3 s, C-2Ј, C-4Ј, C-2), 76.4 (s, C-4),
126.7, 127.0 (2 d, 2 arom. p-CH), 127.6, 127.7, 128.4, 128.8 (4 d, 8
arom. o,m-CH), 142.4, 145.8 (2 s, 2 arom. Cq), 220.6 (s, C=O) ppm.
MS (30 °C), m/z (%): 382 (0.03) [M+], 312 (37) [M+ – C4H6O; 13C
(11)
[C14H11S+,
9-(methylsulfanyl)fluorenyl+],
180
(13)
[Ph2C=CH2+], 87 (59) [iPrCϵS+]. C21H26S2 (342.55): calcd. C
73.63, H 7.65, S 18.72; found C 73.82, H 7.58, S 18.75.
1
5Ba: M.p. 138–140 °C (EtOH). H NMR: δ = 0.92, 1.32 (2 d, J =
6.6 Hz, 2 × 2 diastereotopic Me), 2.60 (sept, J = 6.6 Hz, 2 H of
iPr2), 3.63 (s, 2-H2), 7.45–7.70 (2 m, 6:4, 2 Ph) ppm. 13C NMR: δ
= 22.1, 25.1 (2 q, 2 × 2 Me), 30.3 (t, C-2), 35.0 (d, 2 × CH of iPr2),
78.0, 80.0 (2 s, C-4, C-5), 126.5, 127.0, 129.9 (3 d, 1:2:2, 10 arom.
CH), 144.4 (s, 2 arom. Cq) ppm. MS (80 °C), m/z (%): 342 (0.4)
[M+], 299 (10) [M+ – iPr; 13C 2.0/2.1], 257 (21) [299 – C3H6]+, 221
7.7/7.8], 226 (10) [Ph2C=S–CHMe+; 13C2 + 34S 0.59/0.51], 225 (9),
+
194 (100) [Ph2C=CHMe+; 13C2 1.3/1.1, no S], 193 (33) [C15H13
,
probably 9-(ethylsulfanyl)fluorenyl+], 179 (14) [194 – Me]+, 165 (13)
[fluorenyl+], 115 (15), 86 (13) [Me2C=C=S]+. C23H26OS2 (382.57):
calcd. C 72.20, H 6.85, S 16.76; found C 72.53, H 6.79, S 16.78.
(11) [C17H17+, probably 9-isobutylfluorenyl+; HR 221.134/221.131],
5Cb: M.p. 126–128 °C (CH2Cl2/pentane). 1H NMR: δ = 1.30, 1.37,
1.67 (3 s, 1:1:2, 4 Me), 1.35 (d, J = 6.5 Hz, 2-Me), 3.87 (q, J =
6.5 Hz, 2-H), 6.95–7.65 (2 m, 6:4, 10 arom. H) ppm. 13C NMR: δ
= 21.1 (d, 2-Me), 25.4, 26.0, 26.9 (3 q, 1:2:1, 4 Me), 38.9 (d, C-2),
68.0, 68.5 (2 s, C-2Ј, C-4Ј), 77.7, 79.7 (2 s, C-4, C-5), 126.76, 126.88
(2 d, 8 arom. o,m-CH), 130.5, 131.4 (2 d, 2 arom. p-CH), 144.6 (s,
br., 2 arom. Cq), 220.5 (s, C=O) ppm. C23H26OS2 (382.58): calcd.
C 72.20, H 6.85, S 16.76; found C 72.04, H 6.93, S 16.77.
+
212 (100) [Ph2C–S=CH2
; +
13C2 34S 5.6/6.1; HR 212.0657/
212.0644], 211 (88) [C14H11S+, 9-methylsulfanylfluorenyl+; HR
211.0579/211.0574], 198 (61) [6+; 13C 8.9/9.6, 13C2
+
34S 3.3/3.2],
+
197 (21) [C13H9S+], 180 (24) [Ph2C=CH2
;
13C 3.8/3.5], 179 (26)
[C14H11+, 9-methylfluorenyl+], 165 (98) [fluorenyl+; 13C 14.1/15.1,
+
HR 165.070/165.068], 152 (10) [C12H8
,
biphenylene+; HR
152.0624/152.0623], 144 (18) [C8H16S+, iPr2C=S–CH2
;
13C2 + 34S
+
0.87/0.86], 130 (13) [iPr2CS+], 121 (49) [PhCϵS+; 13C2
+
34S 2.3/
2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-Isopropylide (3Cc): (a)
2.7], 87 (23) [iPrCϵS+], 77 (14) [Ph+]. C21H26S2 (342.55): calcd. C
1
After reaction (THF, 60 °C, 6 h) of 2Cc[43] with 1.2 equiv. of 6, H
73.63, H 7.65, S 18.72; found C 73.36, H 7.56, S 18.78.
NMR analysis in CDCl3 at 102 °C (closed tube) with dibenzyl as
weight standard indicated the 1,3-dithiolanes 4Cc, 5Cc, and 12c
(Table 1) as well as 18% of thiirane 7Cc (s, 1.67),[43] and 18% of
2,2,4,4-tetramethyl-3-[(1-methylethenyl)sulfanyl]cyclobutanone (2
s, 3.35, 4.70) as product of 1,4-H shift.[43] (b) PLC (pentane/
CH2Cl2, 7:3) gave the red thione 1C (13%) from the first fraction
and 12c (12%) from the second fraction. Renewed PLC (pentane/
Et2O 95.5) of the third fraction furnished 18% each of pure 4Cc
and 5Cc.
2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-Methylide (3Ca): (a)
In addition to the 80 °C-experiment of Table 1, 2Ca[42] and 2 equiv.
of 6 in C6D6 were reacted in an NMR tube at 80 °C for 15 min
and furnished 19% of 4Ca (s, δ = 3.78 ppm), 70% of 5CA (s, 3.33),
and 10% of 12a (s, 3.68). (b) The low solubility allowed isolation
of 12a from CHCl3/MeOH, m.p. 198–200 °C (blue), identified with
authentic 12a[4] (m.p. 203–204 °C) by 1H NMR and IR spectra. (c)
The preparative experiment furnished 5Ca (31%, m.p. 123–126 °C,
from MeOH, identical with the product obtained from thiobenzo-
phenone S-methylide + 1C[6] in mixed m.p. and NMR spectra. The
mother liquor contained 4Ca/5Ca 7:3, and separation was achieved
by PLC (petroleum ether/ethyl acetate, 98:2); the second fraction
gave 4Ca which crystallized from hexane and little CH2Cl2.
1
4Cc: M.p. 136–138 °C (MeOH). H NMR (100 °C): δ = 1.03, 1.30,
1.58 (3 × 2 Me), 7.00–7.75 (2 m, 6:4, 2 Ph) ppm. 1H NMR (30 °C):
two signals are broadened by coalescence: 0.97 (half-width 16 Hz,
2 Me), 7.35–7.80 (4 arom. H) ppm. 13C NMR (32 °C): δ = 22.7 (q,
4 Me), 24.3 (br., 2 Me), 62.8 (s, C-5), 66.8 (s, C-2Ј + C-4Ј), 68.8 (s,
C-2), 78.3 (s, C-4), 126.6 (d, 2 arom. CH), 127.1, 130.0 (2 d, 2 × 4
4Ca: M.p. 85–86 °C (CH2Cl2/hexane). 1H NMR (400 MHz): δ =
1.21, 1.27 (2 s, 2 × 2 Me), 3.83 (s, 5-H2), 7.23–7.32 (m, 6 arom. H), arom. CH), Ϸ 145 (br., 2 arom. Cq), 221.3 (s, C=O) ppm. IR (KBr):
7.46–7.48 (m, 4 arom. H) ppm. 13C NMR (100 MHz, DEPT): δ =
22.7, 24.4 (2 × 2 Me), 49.7 (C-5), 66.7 (C-2Ј + C-4Ј), 73.7, 77.2 (C-
ν = 1779 cm–1 (C=O) cm–1. MS (30 °C), m/z (%): 326 (65) [M+
–
˜
C4H6O; 13C2 + 34S 7.3/7.0], 252 (20) [326+ – Me2CS, C17H16S+, 28],
2, C-4), 127.1 (2 arom. p-CH), 127.87, 128.08 (4 m-CH, 4 o-CH), 251 (38) [C17H15S+], 240 (7) [C16H16S+, Ph2C–S=CMe2+], 239 (14),
144.1 (2 arom. C ), 220.6 (C=O) ppm. IR (KBr): ν = 695 s, 748 m
237 (65) [C16H13S+; 13C 11.6/12.0], 208 (100) [Ph2C=CMe2+], 207
(arom. out-of-plane deform.), 1446, 1458, 1492 m, 1597 w (arom. (14), 193 (31) [208 – Me]+, 178 (31) [208 – 2 Me]+, 165 (36)
ring vibr.), 1781 vs. (C=O) cm–1. MS (20 °C, MAT 95Q, CMASS), [fluorenyl+], 159 (21), 129 (15), 115 (28), 86 (22) [Me2C=C=S+], 70
˜
q
1528
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2005, 1519–1531

Aliphatic Thiocarbonyl Ylides and Thiobenzophenone
FULL PAPER
(14) [Me2C=C=O+]. C24H28OS2 (396.60): calcd. C 72.68, H 7.12, S
16.17; found C 72.62, H 7.06, S 16.18.
(354.56): calcd. C 74.52, H 7.39, S 18.09; found C 74.43, H 7.31, S
18.08.
1
5Cc: M.p. 148–149 °C (MeOH). H NMR (100 °C): δ = 1.30, 1.37,
2,2,5,5-Tetramethylcyclopentanethione S-Methylide (3Fa), Methyl-
ene Transfer: Dihydro-1,3,4-thiadiazole 2Fa[37] (0.49 mmol) and 6
(0.99 mmol) in CDCl3 (0.5 mL) were reacted in a NMR tube 15 h
at 40 °C. After addition of sym-C2H4Cl2, the 1H NMR analysis
revealed 98% of thione 1F (s, 1.90, 4 H), and 95% of 12a (s, 3.70,
2 H). In a preparative experiment, 12a was isolated and identified.
1.72 (3 s, 3 × 2 Me), 6.95–7.23, 7.37–7.63 (2 m, 6:4, 10 arom. H)
ppm. H NMR (30 °C): 1.30 (s, half-width 18 Hz, 4 Me), 1.71 (s,
1
2 Me), 7.03–7.23 (m, sharp, 6 arom. H), 7.33–7.67 (br. hump, 4
arom. H) ppm. 13C NMR (32 °C): δ = 26.4, 26.8, 33.0 (slightly
broadened, q not resolved, 3 × 2 Me), 51.1 (s, C-2), Ϸ 69 (very br.,
C-2Ј + C-4Ј), 79.9, 80.7 (2 s, C-4, C-5), 126.85 (d, sharp, 4 arom.
CH), 127.06 (d, 2 arom. CH), 131.6 (br., d not resolved, 4 arom.
2,2,5,5-Tetramethylcyclopentanethione S-Ethylide (3Fb): Reaction
of 2Fb with 2.6 equiv. of 6 in CDCl3 (0.5 mL) in a closed NMR
CH), Ϸ 147 (br., 2 arom. C ), 220.9 (s, C=O) ppm. IR (KBr): ν =
˜
q
1
tube. H NMR analysis as above indicated 99% of 12b (d, 1.65; q,
1779 cm–1 (C=O) cm–1. MS (80 °C), m/z (%): 326 (34) [M+
–
4.09), and the signals of 1F appeared.
C4H6O], 322 (48) [M+ – Me2CS; 13C 11.2/11.6, 13C2 + 34S 3.4/3.7],
; +
13C2 34S 4.1/4.3],
+
252 (67) [322 – C4H6O, Me2C=C=S–CPh2
2,2,5,5-Tetramethylcyclopentanethione S-Isopropylide (3Fc): The re-
action of 2Fc with 3.3 equiv. of 6 in toluene at 100 °C in 1 h pro-
vided thiirane 7Fc (90%, s, 1.06).
237 (100) [C16H13S+, 29, 30, or 31; 13C 17.8/17.9], 220 (38)
+
+
[C17H16
,
26], 205 (34) [C6H13
,
probably 9-(1-propenyl)
fluorenyl+], 165 (23) [fluorenyl+], 111 (11). C24H28OS2 (396.60):
calcd. C 72.68, H 7.12, S 16.7; found C 72.71, H 7.11, S 16.17.
1,1,3,3-Tetramethylindan-2-thione S-Methylide (3Ga): Methylene
transfer was observed when dihydrothiadiazole 2Ga[37] and 5 equiv.
of 6 in CDCl3 (1 mL) were reacted 15 min at 80 °C. 1H NMR
analysis indicated 96% of 12a (s, 3.70) besides the signals of thione
1G.
12c: M.p. 161–163 °C (blue). 1H NMR: δ = 1.57 (br. s, 2 Me),
6.75–7.47 (2 m, 6:4, 4 Ph) ppm. 13C NMR (32 °C, some signals
broadened): δ = 32.8 (q, 2 Me), 54.2 (s, C-2), 81.7 (s, C-4 + C-5),
126.2, 132.1 (2 d, 16 arom. o,m-CH), 126.5 (d, 4 arom. p-CH), 144.0
1,1,3,3-Tetramethylindan-2-thione S-Ethylide (3Gb): Dihydrothiadi-
azole 2Gb and 2.1 equiv. of 6 were reacted under the same condi-
(s, 4 arom. C ) ppm. IR (KBr): ν = 699 s, 729 m (arom. out-of-
˜
q
plane deform.), 1441 m, 1490 m, 1597 w (arom. ring vibr.) cm–1.
MS (125 °C), m/z (%): 438 (Ͻ 1) [M+], 332 (4) [Ph2C=CPh2+], 240
(18) [C16H16S+, Ph2C=S–CMe2+], 239 (10), 225 (16) [240 – Me]+,
208 (22) [C16H16+, Ph2C=CMe2+], 198 (22) [Ph2C=S+], 193 (11)
[208 – Me]+, 165 (100) [9-fluorenyl+], 129 (12) [C10H9+], 121 (84)
[PhCϵS+], 115 (48), 91 (27) [C7H7]+, 77 (59) [Ph+]. C29H26S2
(438.63): calcd. C 79.40, H 5.98, S 14.62; found C 79.25, H 5.87, S
14.61.
1
tions and provided 12b (98%, H NMR analysis, s, 4.08). The iso-
lated crystals, m.p. 174–176 °C (blue), were compared with authen-
tic 12b[4] (m.p. 172–174 °C, dec., blue).
1,1,3,3-Tetramethylindan-2-thione S-Isopropylide (3Gc): The N2 ex-
trusion from the more stable 2Gc in the presence of 2.1 equiv. of 6
1
in toluene required 5 h at 130 °C. The H NMR analysis (CDCl3)
disclosed 93% of thiirane 7Gc (s, 1.84).
Di-tert-butyl Thioketone S-Methylide (3Ha):[19] The 1H NMR
analysis used s, 3.70 for 12a (67%), s, 1.45 for thioketone 1H (75%),
and s, 2.34 for thiirane 7Ha (13%); 12a was isolated and identified.
2,2,4,4-Tetramethylcyclobutanethione S-Methylide (3Da): After the
reaction (40 °C, 12 h) of 2Da[15] (13.7 mmol) with 6 (15.0 mmol) in
THF (20 mL), 5Da (38%) crystallized from EtOH; CC on silica gel
(cyclohexane) afforded 5Da (9%) as the first fraction and 4Da (5%)
as last fraction.
2,2,6,6-Tetramethylcyclohexanethione S-Methylide (3Ja): After re-
action of 2Ja and 2.7 equiv. of 6 (Table 1), the analysis with sym-
C2H2Cl4 indicated 73% of 12a (s, 3.68) and 18% of thiirane 7Ja (s,
2.41).
4Da: M.p. 52 °C (pentane). 1H NMR: δ = 1.14, 1.28 (2 s, 2 × 2
Me), 1.60 (s, 3Ј-H2), 3.69 (s, 5-H2), 7.06–7.50 (m, 10 arom. H) ppm.
13C NMR: δ = 28.8, 30.0 (2 q, 2 × 2 Me), 42.8 (s, C-2Ј + C-4Ј),
47.4, 49.6 (2 t, C-3Ј, C-5), 73.1 (s, C-2), 80.9 (s, C-4), 126.6 (d, 2
arom. p-CH), 127.82, 127.88 (2 d, 8 arom. o,p-CH), 144.9 (s, 2
2,2,5,5-Tetramethylcyclohexanethione S-Ethylide (3Jb): The condi-
tions for N2 extrusion from 2Jb were the same as for 2Ja. The
analysis established 12b (q, 4.09, 61%), thiirane 7Jb (q, 2.90, 28%),
and an unknown compound (q, 3.68, 8%). The isolated crystals of
12b, m.p. 168–169 °C, were identified.
arom. Cq) ppm. MS (40 °C), m/z (%): 354 (0.6) [M+], 298 (100)
+
[M+ – C4H8, C18H18S2
;
13C 20/21, 13C2 + 34S2 10.8/10.3], 212 (16)
[C14H12S+, Ph2C–S=CH2
;
13C 2.5/2.9], 211 (12), 180 (98)
+
+
[Ph2C=CH2
;
13C 15/14, 13C2 1.1/1.2, no S], 179 (30) [C14H11+],
Thermolysis Reactions of Some 1,3-Dithiolanes
178 (29), 174 (12) [probably C8H14S2+], 165 (32) [9-fluorenyl+], 86
(20). C22H26S2 (354.56): calcd. C 74.52, H 7.39, S 18.09; found C
74.90, H 7.31, S 18.11.
(a) 4,4,5,5-Tetraphenyl-1,3-dithiolane (12a): In a closed NMR tube,
12a (46 μmol) in PhCN (0.4 mL) was heated to 140 °C for 110 min;
the blue solution contained 12a (s, 3.68) and 1,1-diphenylethylene
(13a, s 5.38) in 1:1 ratio. After 12 h at 140 °C, 12a had disappeared
and 46% of 13a were present; several signals of unknown products
at δ = 1.98–2.63 were integrated and corresponded to 49% of CH2
group of the initial concentration of 12a. In a second experiment,
12a (103 μmol) in CDCl3 was heated to 135 °C for 35 h; besides 13a
(66%), again signals at 2.0–2.6 showed up. UV/Vis spectroscopy
indicated 6 (103 μmol, 100%).
1
5Da: M.p. 106–107 °C (EtOH). H NMR: δ = 1.26, 1.58 (2 s, 2 ×
2 Me), 1.34, 1.80 (AB, J = 10.6 Hz, 3Ј-H2), 3.26 (s, 2-H2), 7.0–7.3
(m, 10 arom. H) ppm. 13C NMR: δ = 25.4 (t, C-2), 30.2, 32.6 (2 q,
2 × 2 Me), 45.6 (s, C-2Ј + C-4Ј), 47.9 (t, C-3Ј), 78.8, 79.2 (2 s, C-
4, C-5), 126.2 (d, 2 arom. p-CH), 126.7, 130.8 (2 d, 8 arom. o,m-
CH), 145.1 (s, 2 arom. Cq) ppm. MS (30 °C), m/z (%): 308 (8) [M+ –
CH2S, C21H24S+; 13C 1.9/1.7, 13C2 + 34S 0.58/0.46], 298 (56) [M+
–
+
+
C4H8, C18H18S2
; ;
13C 11.2/11.5], 276 (14) [308+– S, C8H14 = CPh2
13C2 0.36/0.30, no S], 276 (14) [C21H24+], 252 (9) [298+ – CH2S, 28],
237 (32) [C16H13S+], 233 (26) [C18H17+], 220 (92) [276+ – C4H8, 26],
(b) 2,2-Dimethyl-4,4,5,5-tetraphenyl-1,3-dithiolane (12c): The more
thermolabile 12c (80 μmol) and sym-C2H2Cl4 (116 μmol) in CDCl3
219 (31) [C17H15+], 212 (23) [Ph2C-S=CH2+], 211 (29), 205 (100) (0.5 mL) were heated in a closed tube at 100 °C (bath). The smooth
[C16H13
;
13C 17.8/18.0, 13C2 1.5/1.8, no S], 198 (22) [Ph2C=S+], conversion of 12c (s, 1.56) to 1,1-diphenylisobutene (13c, s, 1.79,
+
180 (34) [Ph2C=CH2+], 179 (32) [C14H11+], 178 (40), 165 (67)
[fluorenyl+], 121 (22) [Ph-CϵS+], 86 (39) [Me2C=C=S+]. C22H26S2 91 (65), 99 (110); identification with an authentic specimen.
no side products) amounted to% (after h): 6 (4), 28 (19.5), 42 (74),
Eur. J. Org. Chem. 2005, 1519–1531
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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R. Huisgen, G. Mloston, H. Giera, E. Langhals, K. Polborn, R. Sustmann
FULL PAPER
Table 4. X-ray crystallographic data of 1,3-dithiolanes.
Compound
4Cc
5Ca
5Da
Molecular formula
Molecular mass
Crystal size [mm]
Crystal system
Space group, Z
Unit cell parameters
a [Å]
C24H28OS2
396.58
0.10×0.17×0.26
monoclinic
P21/c, 8
C22H24OS2
368.53
0.53×0.40×0.20
monoclinic
P21/c, 4
C22H26S2
354.55
0.50×0.40×0.23
monoclinic
P21/n, 4
15.8285(4)
22.8286(4)
11.9030(2)
101.0855(8)
4220.8(2)
1.248
15.465(5)
8.806(3)
13.994(3)
96.86(2)
1892.1(10)
1.294
10.775(2)
16.174(3)
11.052(2)
93.233(12)
1923.0(6)
1.225
b [Å]
c [Å]
β [°]
Volume [Å3]
Dcalcd. [g cm–3]
F(000)
)
1696
784
760
Index range
–17 Յ h Յ 18
–26 Յ k Յ 26
–12 Յ l Յ 13
3.17–24.06
200(2)
39517
6640
0 Յ h Յ 17
–10 Յ k Յ 0
–16 Յ l Յ 15
2.65–23.97
295(2)
3072
2953
0 Յ h Յ 12
–18 Յ k Յ 0
–12 Յ l Յ 12
2.23–23.97
295(2)
3189
3015
θ range [°]
Temperature [K]
Reflections collected
Reflections unique
Reflections obsd. [Ͼ 2σ(I)]
Rint
5066
0.0621
2511
0.0261
2594
0.0082
Parameters
Final R [I Ͼ 2σ(I)]
Final wR2
487
0.0478
0.1077
230
0.0352
0.0854
221
0.0353
0.0880
Residual electron dens. [e/Å]
Goodness of fit
CCDC deposition no.
0.274, –0.292
1.059
249169
0.165, –0.192
1.077
249170
0.202, –0.209
1.098
249171
(c) Spiro Compound 5Da: When 5Da (172 μmol) and 6 (187 mmol)
in PhCN (0.5 mL) were heated at 140 °C for 5 h, the 1H NMR
spectrum indicated dithiolane 12a (s, 3.68), 1,1-diphenylethylene
(13a, s, 5.38), and unconsumed 5Da (s, 3.13) in the ratio 39:25:36,
and thione 1D (s, 2.18) occurred in an amount equivalent to 12a +
13a. On further heating, 12a and 5Da disappeared; after 20 h at
140 °C, 1H NMR analysis with as-C2H2Cl4 provided 13a (86 μmol)
and 1D (97 μmol); not identified signals pointed to side products.
Acknowledgments
We express our gratitude to the Fonds der Chemischen Industrie,
Frankfurt, for continued support. G. M. is indebted to the Alexan-
der von Humboldt Foundation for a stipend. Our thanks are going
to Dr. Peter Mayer and Wenwei Lin for their help in the X-ray
measurements. We sincerely thank Helmut Huber for his help in
NMR spectroscopy, to Reinhard Seidl for providing the mass spec-
tra, to Helmut Schulz and Magdalena Schwarz for the numerous
elemental analyses, and to Malgorzata Celeda (University of Lodz)
for some supplementary experiments.
X-ray Diffraction Analyses of 1,3-Dithiolanes (Table 4, Figure 1,
Figure 2): All crystals were sealed in glass capillaries and mounted
on the goniometer head of a Nonius KappaCCD aera detector
(4Cc) or a Nonius MACH3 four-circle diffractometer (5Ca and
5Da) operating with Mo-Kα radiation and a graphite monochroma-
tor. The unit cell dimensions were calculated using a least-squares
refinement of a variable amount of setting angles. In case of the
KappaCCD measurement a sphere was measured using a φ/ω scan
with a scan step of 0.9° and a scan time of 60 s per degree. In the
case of the MACH3 diffractometer, a quadrant was measured using
an intensity-dependent ω/2Θ scan with a width of [0.81 + 0.47
tanΘ]° (5Ca) or [0.62 + 0.47 tanΘ]° (5Da). The usual corrections
were applied. The structures were solved by SHELXS-86 and re-
fined by SHELXL-93.[44] All non-hydrogen atoms were refined an-
isotropic, all hydrogen atoms were calculated as riding atoms with
an isotropic temperature factor. The molecules were drawn using
ZORTEP[45] on the basis of 30% probability ellipsoids. CCDC-
249169 ... -249171 contain the supplementary crystallographic data
(excluding structure factors) for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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Eur. J. Org. Chem. 2005, 1519–1531

Aliphatic Thiocarbonyl Ylides and Thiobenzophenone
FULL PAPER
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Received: October 26, 2004
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© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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