1,3-Dithiolanes from cycloadditions of alicyclic and aliphatic thiocarbonyl ylides with thiones: Regioselectivity

Article abstract of DOI:10.1002/chem.200204659

The regiochemistry of 1,3-di-thiolanes obtained from thiocarbonyl ylides 9 and thiones 10 shows a striking dependence on substituents. Previously and newly performed experiments indicate that sterically hindered cycloalkanethione S-methylides and dialkylt

Full text of DOI:10.1002/chem.200204659

FULL PAPER
1,3-Dithiolanes from Cycloadditions of Alicyclic and Aliphatic Thiocarbonyl
Ylides with Thiones: Regioselectivity**
Rolf Huisgen,*[a] Grzegorz Mloston,[b] Kurt Polborn,[a] and Reiner Sustmann[c]
Dedicated to Emanuel Vogel on the occasion of his 75th birthday
Abstract: The regiochemistry of 1,3-di-
thiolanes obtained from thiocarbonyl
ylides 9 and thiones 10 shows a striking
dependence on substituents. Previously
and newly performed experiments indi-
cate that sterically hindered cycloal-
kanethione S-methylides and dialkyl-
thioketone S-methylides react with ali-
cyclic and aliphatic thiones to give the
2,2,4,4-tetrasubstituted 1,3-dithiolanes
11 exclusively. Aryl groups in one or
both reactants lead to a preference for,
or even complete formation of, 4,4,5,5-
tetrasubstituted 1,3-dithiolanes 12. Sev-
eral mechanisms appear to be involved,
but the paucity of experimental criteria
is troubling. Quantum-chemical calcula-
tions (see preceding paper) on the cyclo-
addition between thioacetone S-methyl-
ide and thioacetone furnish lower acti-
vation energies for the concerted
process than for the two-step pathways
via C,S- or C,C-biradicals; the favoring
of the 2,4-substituted 1,3-dithiolanes
over the 4,5-substituted type would be
expected to increase with growing bulk
of substituents. Aryl groups stabilize
intermediate biradicals. Experimental
criteria for the differentiation of regio-
isomeric dithiolanes are discussed. Thio-
carbonyl ylides 9 are prepared by 1,3-
cycloadditions between diazomethane
and thioketones and subsequent N2
elimination from the usually isolable
2,5-dihydro-1,3,4-thiadiazoles 17; differ-
ent ratios of the two rate constants lead
to divergent product formation scenar-
ios.
Keywords: cycloaddition
¥
1,3-di-
thiolanes ¥ reaction mechanisms ¥
regioselectivity ¥ thiocarbonyl ylides
diazomethane, and identified the primary adduct as 2,5-
dihydro-1,3,4-thiadiazole 2;[3] the ™white solid∫ (no analyses)
lost nitrogen on warming and furnished thiirane 5 (Scheme 1).
Treatment of 1 with 0.8 equivalents of diazomethane provided
some 1,3-dithiolane 4 as well as 5, but the intermediacy of the
thiocarbonyl S-methylide 3 remained unrecognized.
Introduction
1,3-Cycloadditions between diazoalkanes and thioketones
and subsequent N2 elimination offer the most convenient
and variable pathway to thiocarbonyl ylides (reviews:[1, 2]). In
1970, Diebert studied the reaction between the easily
accessible 2,2,4,4-tetramethyl-3-thioxocyclobutanone (1) and
[a] Prof. R. Huisgen, Dr. K. Polborn
Department of Chemistry
Ludwig-Maximilians-Universit‰t
Butenandtstrasse 5 13 (Haus F)
81377 M¸nchen (Germany)
Fax (‡49)89-2180-77717
E-mail: rolf.huisgen@cup.uni-muenchen.de,
kvp@cup.uni-muenchen.de
[b] Prof. G. Mloston
Section of Heteroorganic Compounds
University of Lodz
Narutowicza 68, 90-136 Lodz (Poland)
E-mail: gmloston@krysia.uni.lodz.pl
[c] Prof. R. Sustmann
Institut f¸r Organische Chemie der Universit‰t
Universit‰tsstrasse 5, 45117 Essen (Germany)
E-mail: reiner.sustmann@uni-essen.de
Scheme 1. Thiocarbonyl ylides and thiones: classic examples of differing
regioselectivity.
[**] 1,3-Dipolar Cycloadditions, Part 127. Part 126: R. Huisgen, G. Mlos-
ton, E. Langhals, T. Oshima, Helv. Chim. Acta 2002, 85, 2668 2685.
2256
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/chem.200204659
Chem. Eur. J. 2003, 9, 2256 2263

2256 2263
Thiocarbonyl ylides such as 3 cannot be isolated, but can be
intercepted with suitable dipolarophiles. Cycloadditions be-
tween the sterically hindered 3, an electron-rich 1,3-dipole,
and acceptor-substituted ethylenes have served as a model
system to probe the borderline crossing from the concerted
mechanism to the two-step process via zwitterionic intermedi-
ates.[4, 5]
mechanisms with C,S and C,C biradicals as intermediates as
well as the concerted cycloaddition.[11] The outcome of
transition state (TS) calculations is to be compared with
experimental results in several publications, and this first set
presents thiocarbonyl ylides ‡ thiones with alicyclic and
aliphatic substituents.
In 1930/31, two groups reported the formation of 4,4,5,5-
tetraphenyl-1,3-dithiolane (8), produced in high yield from
thiobenzophenone and diazomethane at 08C.[6, 7] The mech-
anism, involving 2,2-diphenyl-2,5-dihydro-1,3,4-thiadiazole
(6) and thiobenzophenone S-methylide (7) as intermediates,
was established 50 years later.[8] This clarification led to the
insight that thiones are ™superdipolarophiles∫, with respect
not only to thiocarbonyl ylides, but also to diazoalkanes,
nitrones, and other 1,3-dipoles (review:[9]). Rate measure-
ments on Diels Alder reactions similarly revealed the
™superdienophilic∫ character of thiones.[10]
Results and Discussion
According to the calculations for thioformaldehyde S-meth-
ylide (9, R ˆ H; Scheme 2), concerted cycloaddition to ethene
has to overcome a well-defined barrier lower than the
A fascinating problem of regioselectivity emerges: thio-
carbonyl ylide 3 ‡ thione 1 gave rise to the 2,2,4,4-
tetrasubstituted dithiolane 4, whereas 7 and thiobenzophe-
none exclusively afforded the 4,4,5,5-tetrasubstituted type 8.
Reactant pairs with other sets of substituents followed one or
the other path, or furnished mixtures of regioisomers.
Undoubtedly, several mechanisms are participating in dithio-
lane formation, but experimental criteria are scarce. The
Scheme 2. Regiochemistry of 1,3-dithiolane formation and conceivable
biradical intermediates.
retention of dipolarophile configuration–so informative for
[4]
ˆ
ˆ
additions to C C bonds –is not applicable to C S bonds.
All the more welcome, therefore, were the quantum-
chemical calculations reported in the preceding paper, which
brought to light that account has to be taken of two-step
activation energy of biradical formation.[11, 12] In contrast, the
concerted addition between 9 and thioformaldehyde (10, R' ˆ
H) shows no sign of a potential energy barrier. Starting from
the energy level of the reactants, the energy of the four-center
reaction complex goes down, and–a rare feature–no TS can
be defined on the route to 1,3-dithiolane. Two-center reac-
tions lead to C,S and C,C biradicals, formed via barriers of
‡3.4and 4.7 kcalmol À1, respectively.
Abstract in German: Die Regiochemie der 1,3-Dithiolan-
Bildung aus Thiocarbonyl-yliden 9 and Thionen 10 zeigt eine
auffallende Abh‰ngigkeit vom Substitutionsmuster. Alte und
neue Experimente lehren, da˚ sich sterisch gehinderte Cycloal-
kanthion-S-methylide und Dialkylthioketon-S-methylide mit
alicyclischen und aliphatischen Thionen ausschlie˚lich zu
2,2,4,4-tetrasubstituierten 1,3-Dithiolanen 11 vereinigen. Aryl-
reste in einem oder beiden Reaktanten f¸hren vorzugsweise
oder gar vollst‰ndig zu 4,4,5,5-tetrasubstituierten 1,3-Dithiola-
nen 12. Mehrere Mechanismen scheinen beteiligt zu sein, aber
der Mangel an experimentellen Kriterien ist schmerzlich.
Quantenchemische Rechnungen (vorstehende Arbeit) zur
Cycloaddition des Thioaceton-S-methylids mit Thioaceton
ergeben niedrigere Aktivierungsenergien f¸r den konzertierten
Proze˚ als f¸r die zweistufigen Wege ¸ber C,S- und C,C-
Biradikale; der Vorzug der 2,4-substituierten 1,3-Dithiolane
vor den 4,5-substituierten Typen sollte mit zunehmender
Substituentengrˆ˚e steigen. Arylreste stabilisieren intermedi‰re
Biradikale. Experimentelle Kriterien f¸r die Unterscheidung
der regioisomeren 1,3-Dithiolane werden diskutiert. Thiocar-
bonyl-ylide 9 bereitet man durch 1,3-Cycloaddition des Dia-
zomethans an Thioketone und anschlie˚ende N2-Abspaltung
aus den meist isolierbaren 2,5-Dihydro-1,3,4-thiadiazolen 17;
unterschiedliche Verh‰ltnisse der beiden Geschwindigkeits-
konstanten beeinflussen Reaktionsablauf und Produktspiegel.
For the reaction between thioacetone S-methylide (9, R ˆ
Me) and thioacetone (10, R' ˆ Me), the second model used for
calculation, two addition directions produce 1,3-dithiolanes 11
and 12. The formation of 11 is 5 kcalmolÀ1 more exothermic
than that of 12, reflecting steric hindrance by the adjacent
gem-dimethyl groups in 12. Now the concerted processes for
the formation of 11 and 12 (R ˆ R' ˆ Me) show small
activation barriers: 3.1 and 4.4 kcalmolÀ1, respectively. In
the framework of the two-step pathways, C,S biradical 13 and
C,C biradical 14 lead to 11, whereas the cyclizations of 15 and
16 give rise to 12. The activation energies of biradical
formation are still higher than those of the four-center
cycloadditions.[11]
Generally, the substituents in 9 and 10 (Scheme 2) will
influence the energy profile of cycloaddition in several
respects: 1) substituents lose conjugation energy present in
the reactants, 2) conjugation may stabilize the terminal
carbon atom(s) of biradicals, and 3) steric hindrance in TSs
and products will increase. The expectation that aryl sub-
stitution should work in favor of the biradical pathways is
borne out by further calculations.[13]
All experimentally studied systems of 9 ‡ 10 bear
substituents R and R' larger than Me. The difference of
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2257

R. Huisgen et al.
FULL PAPER
1.3 kcalmolÀ1 in the activation energies of the two concerted
paths leading to 11 and 12 (R ˆ R' ˆ Me) will increase with
growing steric interference in the TS in favor of formation of
11.
Table 1. Formation of 2,4-substituted 1,3-dithiolanes 11 from thiocarbonyl
ylides 9 and thiones 10; for symbols A G see Scheme 3.
Reactants
1,3-Dithiolane 11
Ref.
9, R2 10, R'2
Formula Yield[%] M.p. [8C]
d(13C) of C5
The mechanism via the C,S-biradical 13, which requires
bonding of the reactants between CH2 and CR'2, likewise
produces 11. The formation of 13 (R ˆ R' ˆ Me) passes
through a TS at 7.1 kcalmolÀ1: 4.0 kcalmolÀ1 higher than the
TS of the concerted pathway to 11. However, with increasing
steric demands of R and R', this energy difference should
diminish because the TS(concerted) would be expected to rise
more rapidly than the TS(C,S biradical). The two pathways to
11 should therefore become competitive, and the change of
mechanism may even go unnoticed. (U)B3LYP calculations
with the aliphatic and alicyclic residues R2 and R'2 employed
experimentally (A I in Scheme 3) are not yet feasible.
A
A
A
A
A
A
A
B
B
B
B
B
B
F
A
B
11AA
11AB
86
80
64
85
89
81
94oil
88
73
87
84oil
85
66,b
39
29
165 166
128 129
43 45
122 51.9244
108 110
230 231
45.5
41.9
48.2
[16]
55.9
48.2
[16]
[16]
[16]
Me, SMe
(SPh)2
ˆ ˆ
S C
19A
20A
[16]
[16]
19A
D
11AD
11BA
11BB
11BC
11BD
11BE
20B
7.8
4
[17]
[17]
A
B
C
D
139 141
159 161
108 109
47.0
43.4
49.1
[14][a]
[3, 14][a]
[17]
8.7
4
E
123 81.5244
132 13450.2
oil
[17]
44.3
[a]
ˆ ˆ
S C
F
G
11FF
11GG
[15][a]
[18]
G
b.p. 143 144
[a] This paper. [b] In dilute solution (0.005m 17B in CS2) 30% 19B ‡ 16%
20B.
that the intramolecular reaction course is less hindered than
the intermolecular one.
Carbon disulfide is a weaker dipolarophile towards 9A than
its monoadduct 19A (Scheme 4). The high yield of 19A (89%
in Table 1) was observed in dilute CS2 solution (0.005m 17A);
ˆ
19A (now in the role of R'2C S) reacted >300 times more
Scheme 3. The dithiolane formation reaction scheme and the substituents
employed.
Clearly, 1,3-dithiolanes 11 are the only cycloadducts found
for combinations of non-aromatic reactants published to date
(Table 1). Most examples use thiocarbonyl S-methylides 9
(Scheme 3) derived from adamantanethione (A) or 2,2,4,4-
tetramethyl-3-thioxocyclobutanone (B). The selection of
thiones 10 is broader and includes 1,3-thiazole-5(4H)-thiones
C
E. The yields of the spirocyclic adducts in Table 1 are
1
based on H NMR analysis with weight standard. Since the
corresponding regioisomers 12 are unknown, small amounts
may have escaped the analysis. In cases of moderate yields in
Table 1, side products have been analyzed. A preliminary
communication on some cycloadducts of 9B[14] is supplement-
ed here by spectroscopic and analytical data.
Scheme 4. Carbon disulfide reacts ™normally∫, but aromatic and olefinic
unsaturation change the regiochemistry.
Competing with the cycloaddition is the electrocyclization
of 9, which irreversibly furnishes thiiranes 18. Increasing
yields of 18 signal weak dipolarophilic activity (e.g., 30% of
18F along with 39% of 11FF in the example with two
diisopropyl groups[15]). The sterically most demanding thio-
carbonyl ylides, 9H and 9I, no longer react with thione 1
(ˆ 10B); quantitative yields of thiiranes 18H and 18I indicate
rapidly than CS2 with 9A.[16] The chiral bisadduct 20A shows
equivalent adamantane systems, due to the presence of a
C2 axis; both dithiolane rings belong to type 11. When 9B was
treated with carbon disulfide (as solvent), the corresponding
monoadduct 19B and bisadduct 20B were identified by
1H NMR spectroscopy, but only the latter compound was
isolated pure and crystalline. Four 1H and four 13C signals for
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Regioselectivity of 1,3-Dithiolane Formation
2256 2263
eight methyl groups in the NMR spectra of 20B testify to
C2 symmetry. Should the pathway via the attractive C,S-
biradical 21 be discussed? This is not clear because the extra
in pentane at À308C to give 17A,[21] the less reactive ethyl
diazoacetate required 2 h at 608C for the addition, which was
immediately followed by N2 extrusion from 26. Thiocarbonyl
ylide 27 combined with a second molecule of 10A and
provided the dispirodithiolane 29 in 87% yield (Scheme 5);
although the ratio of reactants was 1:1, two molecules of 10A
ˆ ˆ
stabilization of S C S (like that of CO2) lowers the reactivity.
The dithiocarboxylic esters (methyl dithioacetate), dithio-
lactones 19, 1,3-thiazole-5(4H)-thiones 10C 10E, and di-
phenyl trithiocarbonate in Table 1 correspond to aliphatic or
alicyclic thioketones in their regiochemical behavior, afford-
ing 1,3-dithiolanes 11. However, 9A reacts with methyl
dithiobenzoate to give the regioisomers 22A and 23A,[16] so
the presence of one phenyl group among the four substituents
is sufficient to bring out the biradical pathway,[13] at least
partially (Scheme 4).
In the reaction between the unsaturated thioketone 24 and
diazomethane, Metzner obtained 25 (meso ‡ dl) in 85%
yield.[19] Dithiolane 25 corresponds to type 12, the vinylic
unsaturation in both reactants probably sharing the phenyl
group×s capacity to stabilize an intermediate C,C biradical of
type 16.
Direct measurements of cycloaddition rates of 9 are not
obtainable, since the rate-determining step is always the loss
of N2 from the precursor 2,5-dihydro-1,3,4-thiadiazole 17. The
solvent dependence of rate constants is also not accessible,
thus further diminishing the applicable mechanistic criteria.
However, it is not necessary to dispense completely with
structure/rate relationships, which are a valuable mechanistic
criterion. Competition constants between pairs of dipolaro-
philes with thiobenzophenone S-methylide (7) have provided
relative rates and indicated the superiority of thiones as
dipolarophiles.[20]
Scheme 5. ∫Schˆnberg reaction∫: cycloreversion (N2 extrusion) of 2,5-
dihydro-1,3,4-thiadiazole is faster than its formation.
entered into the formation of 29, and 0.5 equivalents of ethyl
diazoacetate remained unconsumed. When the reaction was
repeated at room temperature and at À288C, the disappear-
ance of the red color of thione 10A required 12 h and six
weeks, respectively, and NMR monitoring did not bring any
26 to light.
The reaction shown in Scheme 5 corresponds to that in
Scheme 3, consisting of two 1,3-dipolar cycloadditions sepa-
rated by a 1,3-dipolar cycloreversion (extrusion of N2), but the
rate ratio of the first two steps is reversed here. The
cycloaddition of ethyl diazoacetate is rate-determining, and
only the 1:2 product 29 can be isolated. We have proposed the
term ™Schˆnberg reaction∫ for this 1:2 stoichiometry[8] to
honor the pioneer of thione chemistry, who studied the
formation of dithiolane 8 in the reaction between diazo-
methane and thiobenzophenone.[7] Two differences are nota-
ble, however: 2,2-diphenyl-2,5-dihydro-1,3,4-thiadiazole (6)
was isolable at À788C, and eliminated N2 at À458C
(Scheme 1).[8] The second difference lies in the regiochemis-
try: 8 and 29 belong to dithiolane types 12 and 11, respectively.
The highly hindered 8 may originate from a pathway with a
C,C biradical intermediate of type 16.[13] In contrast, 29 could
well be the result of a concerted cycloaddition, although a
path via a C,C biradical of type 14 with the carboxylate as
stabilizing substituent is also conceivable.
The tools allowing the assignments of structures 11 and 12
are mentioned briefly:
Symmetry: The 13C NMR spectrum of the 4,4,5,5-tetraphenyl-
1,3-dithiolane (8) shows only one set of Ph signals, due to
C2v symmetry. In the regioisomer 11 (R ˆ R' ˆ Ph), only one s
plane is left, and two different phenyl spectra would be
expected. The dithiolane 11AA similarly belongs to the point
group Cs. The two adamantane residues are different, but both
reveal the presence of the mirror plane through a reduction in
the number of 13C signals. For the same reason, 11BB meets
the same expectation, with four NMR signals for eight methyl
groups, and not two signals, as would be expected for the
(unknown) 12BB.
Matched pairs: Reactants 9A ‡ 10B and 9B ‡ 10A give
different 2,4-substituted thiolanes (11AB and 11BA), where-
as regioisomers 12AB and 12BA would be identical.
In the concerted elimination of N2 from 17, the substituents
gain conjugation when the thiocarbonyl ylide 9 is formed.
Thus, the rate constants of the first-order N2 elimination
reflect the stabilizing influence of substituents in 9. The
spirothiadiazolines 17A and 17B lose N2 with half-reaction
times of 89 and 86 min at 408C (THF),[5b, 21] respectively, while
the formation of 7 from 6 (t1/2 ˆ 56 min at À458C in THF)[8b]
profits from the incipient phenyl conjugation. The carboxylate
group should stabilize the anionic charge of thiocarbonyl ylide
27, but the rate constant of N2 extrusion from 26 is not
accessible, for reasons given above.
13C chemical shift of ring-CH2: The triplet for C5 in 11 appears
at higher frequencies (d ˆ 42 56 ppm in Table 1) than that of
C2 in 12 (d ˆ 28 31 ppm).[16] The deshielding effect exerted
by the quaternary C4on C5 of 11 is stronger than that of the
second thioether function acting on C2 of 12. For example, C5
signal in 22A was found at d ˆ 28.1, and the C2 signal of 23A
at d ˆ 47.3 ppm (Scheme 4).
The 2,5-dihydro-1,3,4-thiadiazoles (i.e., the cycloadducts of
diazoalkanes and thiones) are not always isolable. Whereas
adamantanethione (10A) rapidly reacted with diazomethane
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R. Huisgen et al.
FULL PAPER
On slow addition of phenyldiazomethane to adamantane-
thione, decolorization and N2 evolution took place simulta-
neously. The formation of 92% of thiirane 28 shows that
electrocyclic ring-closure won over the cycloaddition. Corre-
spondingly, the ™Schˆnberg reaction∫ failed for interaction
between thione 1 and ethyl diazoacetate or phenyldiazo-
methane. The thiiranes 30 (93%) and 31 (93%) were
obtained instead of the cycloadducts.
Dithiolane 29 may be singled out for a brief structural
comment. As a consequence of the chirality, the 13C NMR
shows 20 signals for the 20 C atoms of two adamantane
systems. We have previously discussed the mass spectra of 1,3-
dithiolanes[16] and assumed an open-chain structure–here 32
(Scheme 6)–for the molecular ion. Splitting of radical cation
Figure 1. Structure of 1,3-dithiolane 4 (ZORTEP plot; thermal ellipsoids
at 30% probability level) showing the envelope conformation of the
À
À
heterocycle. Selected bond lengths [ä]: C4 S5 1.817(2), S5 C6 1.826(2),
À
À
À
À
C6 S10 1.813(2), S10 C11 1.793(2), C11 C41.526(3), C3 C41.598(2),
À
À
À
À
À
C6 C9 1.601(3); bond angles [8]: C4 S5 C6 100.37(9), S5 C6 S10
À
À
À
À
À
À
106.4(1), C6 S10 C11 95.04(9), S10 C11 C4106.7(1), C11 C4 S5
À
104.3(1); dihedral angles [8] within heterocycle at: C4 S5 À27.6(2),
À
À
À
À
S5 C6 À4.9(1), C6 S10 29.8(1), S10 C11 À51.5(1), C11 C451.4(1).
Scheme 6. Suggested pathway of mass spectral fragmentation of
dithiolane 29.
À
C4 C11 (1.526 ä) in the dithiolane ring, probably as a
consequence of van der Waals pressure.
The puckering angle of cyclobutane (288)[30] is reduced in
cyclobutanone (gas phase) to 10.4 Æ 2.78[31] or 11.58;[32] its
evaluation by electron diffraction, microwave, or IR data is
rendered difficult by a low inversion barrier. Possibly, lattice
forces contribute to the planarization of the four-membered
rings in the crystal of 4.
‡
32 leads to C10H14S2 as base peak, together with an olefinic
‡
compound (m/z 220, C14H20O2 ). The first fragment is
tentatively assigned the structure (34) of a distonic ion;
distonic species are those with separate centers of charge and
spin density.[22, 23] Scheme 6 outlines a plausible pathway. 1,3-
Dipoles related to 34 are thiocarbonyl S-sulfides.[24, 25]
A
second, minor mode of fragmentation follows the cyclo-
‡
‡
addition path: 27 (m/z 252, 12%) and 10A (m/z 166, 11%),
so both fragments can bear the positive charge.
Conclusions
We determined the X-ray structure of 4 (ˆ 11BB) to learn
about the influence of the space-filling spiro-annulated
substituents on the conformation of the 1,3-dithiolane ring.
Whereas the X-ray analysis of 2,2'-bis(1,3-dithiolane) re-
vealed a half-chair,[26] the hetero ring of 4 shows a pronounced
envelope conformation (Figure 1). The dihedral angle at C4-
S5-C6-S10 (ˆ À4.98) defines a quasi-plane, and C11 as a
™flap∫ is located 0.78 ä above that plane. The puckering
displacement of the cyclopentane envelope amounts to 0.46 ä
(gas-phase electron diffraction).[27] The bond angle at the
bivalent S atom is smaller than that at sp3-hybridized carbon
and easier to deform. Previous NMR studies indicate that 1,3-
dithiolanes are more strongly puckered than 1,3-dioxolanes.[28]
Five-membered rings such as 1,3-dithiolanes have ten
conformers each for half-chair and envelope in the pseudo-
rotation circuit. Bulky substituents may strongly confine
favorable conformations.[29] The envelope structure resembles
that observed for the cycloadduct obtained from 9A and 10
(R ˆ Ph).[16]
The formation of 2,2,4,4-tetrasubstituted 1,3-dithiolanes 11 in
1,3-dipolar cycloadditions between alicyclic or aliphatic
thiocarbonyl ylides 9 and thiones 10 is in accordance with
the concerted pathway indicated by quantum-chemical TS
calculations as most favorable for R ˆ R' ˆ Me, the barrier
height being 3.1 kcalmolÀ1. Two biradical pathways similarly
furnish dithiolanes 11. The activation energies for biradical
formation were calculated, and were found to be
7.1 kcalmolÀ1 for C,S biradical 13 and 9.1 kcalmolÀ1 for C,C
biradical 14 (R ˆ R' ˆ Me).[11] It is to be expected that all these
barriers should increase for more voluminous substituents R
and R', probably to a higher extent for the sensitive concerted
process than for the two-center reactions leading to biradicals.
Since computer resources prohibit calculations on the larger
systems, there remains an uncertainty about the extent to
which one- and two-step processes contribute to the favored
formation of dithiolanes 11. Free of this ambiguity, however,
are reactions of type 9 ‡ 10 (R ˆ R' ˆ Ph).[13]
The two four-membered rings in 4 are virtually planar, as
the sums of the intracyclic bond angles (359.48, 360.08)
demonstrate. The intracyclic angles at the carbonyl C atoms
Experimental Section
À
are compressed to 95.68 and 95.98. The C C bond length for
General: IR spectra were recorded on Perkin Elmer 125 or Beckmann
FT model IFS 45 instruments. NMR spectra were taken on Bruker
À
C1 C4in the cyclobutanone ring (1.598 ä) exceeds that of
2260
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
Chem. Eur. J. 2003, 9, 2256 2263

Regioselectivity of 1,3-Dithiolane Formation
2256 2263
1
WP80CW (80 MHz) for H and WP80DS (20 MHz) for 13C (multiplicities
63.5, 66.4(C1 ‡ C3, C7 ‡ C9), 71.6, 73.6 (C4, C6), 219.9, 220.3 (2 Â
by comparison of 1H decoupled with off-resonance spectra), or Varian
XR400S for 1H (400 MHz) and 13C (100 MHz) with DEPT. Solvent was
acid-free CDCl3, stored over dry K2CO3, if not otherwise stated. As weight
C O) ppm; IR (KBr): nÄ ˆ 1030m, 1461s, 1775vs (C O), 2926m, 2968s
ˆ
ˆ
‡
‡
(C H) cmÀ1; MS (308C): m/z (%): 326 (0.4) [M] , 298 (0.6) [M À CO] (13C
À
0.11/0.12), 256 (34) [M À C4H6O] (13C 5.0/5.3; 13C2 ‡ 34S 3.4/3.3), 186 (100)
‡
1
‡
standard for quantitative H NMR analysis (usually Æ4%, relative), sym-
[C9H14S2, M À 2  dimethylketene] (13C 10/11; 13C2 ‡ 34S 9.3/9.3), 171 (9)
‡
‡
tetrachloroethane (d ˆ 5.92 ppm) or trichloroethylene (d ˆ 6.70 ppm) were
used. The MS are EI spectra with 70 eV, recorded on AET 909 or Finnigan
MAT 90 machines; intensities of isotope peaks are reported as, for
example, 13C% calcd/%found; HR ˆ high-resolution (by peak-matching
with perfluorokerosine). CC ˆ column chromatography; PLC ˆ prepara-
tive layer chromatography: 20 Â 20 cm glass plates, 2 mm Merck silica gel
[186 À Me] , 86 (12) [C4H6S; dimethylthioketene] , 85 (5), 70 (3)
‡
[C4H6O] ; elemental analysis calcd (%) for C17H26O2S2 (326.51): C 62.53,
H 8.03, S 19.64; found: C 62.51, H 8.03, S 19.69.
2,2,4,4-Tetraisopropyl-1,3-dithiolane (11FF): Thiadiazoline 17F (517 mg,
3.00 mmol) and thione 10F (568 mg, 3.30 mmol) in THF (3 mL) were
stirred at 658C for 6 h. 1H NMR analysis of the s at d ˆ 3.05 indicated 39%
of 11FF and about 30% of thiirane 18F. 2,4-Dimethyl-3-methylthio-2-
pentene, the second product of 17F thermolysis,[36] was also present, but
could not be quantified. After separation by PLC (pentane/Et2O), the
colorless oil (318 mg) crystallized from MeOH at À788C. Rapid filtering
and dissolving in pentane (3 mL) allowed the isolation of pure 11FF, m.p.
ꢀ20 228C; 1H NMR (80 MHz): d ˆ 1.07, 1.10, 1.12, 1.20 (4  d, 6 lines
visible, 24H; 4 pairs of diastereoisotopic Me), 2.32 (sept, 3J ˆ 7.0 Hz, 4H;
CH of 4  iPr), 3.05 (s, 2H; 5-H2) ppm; 13C NMR (20.2 MHz): d ˆ 20.3, 20.5
(2 Â q; 2 Â 2Me), 20.9 (q; 4 Â Me), 35.3, 37.6 (2 Â d; 2 Â CH of 4 Â iPr), 44.3
60PF254
.
Preparation of 2,5-dihydro-1,3,4-thiadiazoles
Compound 17A:[21]
Compound 17B: This compound was described by Diebert[3] without m.p.
and elemental analyses; it was later characterized[33] (m.p. 40 428C) and
keeps well in the deep-freeze.
Compound 17H:[34]
2,2-Diisopropyl-2,5-dihydro-1,3,4-thiadiazole (17F): Treatment of 2,4-di-
methylpentane-3-thione (10F)[35] with diazomethane in Et2O at 08 fur-
nished 17F and the regioisomeric 4,5-dihydro-1,2,3-thiadiazole in 85:15
ratio.[36] Colorless prisms of 17F crystallized from the crude product in
MeOH at À788C, m.p. À12 to À108C; 1H NMR (80 MHz): d ˆ 0.90, 0.97
(t; C5), 77.0, 81.2 (2  s; C2, C4) ppm; IR (film): nÄ ˆ 1382m, 1462m,
‡
1477m; 2963s (C H) cmÀ1; MS (608C): m/z (%): 274(2) [ M] , 231 (100)
À
‡
‡
[M À iPr] , 187 (1) [231 À C3H8, C9H15S2] , 133 (3), 129 (5) [C7H13S, 10F À
‡
‡
‡
‡
À
H] , 111 (19) [C8H15] , 97 (4), 87 (26) [C4H7S, iPr CS] , 43 (10) [iPr] , 4 1
‡
3
3
(15) [allyl] ; elemental analysis calcd (%) for C15H30S2 (274.52): C 65.62, H
(2  d, J ˆ 6.5 Hz; 4  Me), 2.60 (sept., J ˆ 6.5 Hz; 2  CH), 5.62 (s, 2H;
5-H2) ppm; IR (KBr): nÄ ˆ 1577 m (N N) cmÀ1; MS: m/z (%): 172 (<1)
11.02, S 23.36; found: C 65.81, H 10.68, S 23.20.
ˆ
‡
‡
[M] , 144 (100) [M À N2] , 129 (14) [144 À Me], 111 (32), 101 (57), 97 (45);
elemental analysis calcd (%) for C8H16N2S (172.29): C 55.77, H 9.36, N
16.26, S 18.61; found: C 55.82, H 9.09, N 16.26, S 18.59.
1,1,4,4-Tetramethyl-6-thioxo-5,8-dithiaspiro[3,4]octane-2-one (19B) and
1,1,3,3,9,9,11,11-octamethyl-5,7,12,15-tetrathia-trispiro[3.1.1.3.2.2]pentade-
cane-2,10-dione (20B): a) Thiadiazoline 17B (396 mg, 2.0 mmol) in CS2
(10 mL, 166 mmol) was stirred in a bath at 458C for 6 h; after evaporation,
1H NMR analysis in CDCl3 with weight standard indicated 66% of 20B
(doublet at d ˆ 3.32 ppm, 2H) and 21% of thiirane 5 (singlet at d ˆ
2.29 ppm, 2H). The colorless bisadduct 20B (240 mg, 58%) crystallized
6,6,10,10-Tetramethyl-4-thia-1,2-diazaspiro[4,5]dec-1-ene (17I): Analo-
gously, 2,2,6,6-tetramethylcyclohexanethione[37] (dark red oil, b.p. 848C/
12 Torr) was converted with diazomethane into 17I, which was isolated as
1
colorless crystals (72%), m.p. 104 105 8C; H NMR (80 MHz): d ˆ 0.54,
1
from methanol, m.p. 132 1348C; H NMR (80 MHz): d ˆ 1.29, 1.35, 1.39,
1.21 (2 Â s, 12H; 2 Â 2Me), 1.5 2.2 (m, 6H; 3 Â CH2), 5.60 (s, 2H;
3-H2) ppm; 13C NMR (20.2 MHz): d ˆ 19.0 (t; C8), 27.2, 28.1 (2  q; 2 Â
1.43 (4  s; 8  Me), 3.32, 3.62 (AB, 2J ˆ 12.2 Hz; 13-H2 ‡ 14-H2) ppm;
13C NMR (20 MHz, Tesla BS 687): d ˆ 21.9, 22.2, 24.7, 25.1 (4  2Me), 50.2
(C13, C14), 65.4, 67.9 (C1, C3, C9, C11), 75.7 (C6), 83.8 (C4, C8), 219.1 (2 Â
2Me), 38.6 (t; C7, C9), 41.1 (s; C6, C10), 83.9 (t; C3), 129.6 (s; C5) ppm; IR
(KBr): nÄ ˆ 1576m (N N) cmÀ1; MS (208C): m/z (%): 212 (3) [M] , 184(76)
‡
ˆ
C O) ppm; IR (KBr): nÄ ˆ 1026m, 1459s; 1778vs (C O) cmÀ1; MS (508C):
‡
‡
ˆ
ˆ
[M À N2] , 169 (34) [184 À Me], 152 (13) [184 À S, C11H20] , 137 (93)
‡
‡
‡
‡
‡
‡
‡
m/z (%): 346 (0.4) [M À C4H6O] , 276 (50) [M À 2 Â C4H6O; C11H16S4]
[C10H17] , 123 (84) [C9H15] , 109 (47) [C8H13] , 95 (82) [C7H11] , 82 (100)
34
(13C 6.1/7.3, 13C2 ‡ S 9.26/9.26), 158 (100) [276 À Me2C CS2; C7H10S2]
‡
‡
ˆ
[C6H10] , 81 (77) [C6H9] , 69 (69), 55 (49); elemental analysis calcd (%) for
C11H20N2S (212.35): C 62.21, H 9.49, N 13.19, S 15.10; found: C 62.47, H 9.47,
N 13.43, S 15.10.
‡
‡
(13C2 ‡ 34S 9.1/8.4), 157 (78) [C7H9S2] , 143 (16) [C6H7S2] (13C2 ‡ 34S 1.4/
13
‡
1.6), 86 (14) [Me2C C S] ( C2 ‡ 34S 0.63/0.67), 85 (10), 71 (11) [C4H7O] ,
ˆ ˆ
‡
ˆ ˆ
70 (10) [Me2C C O] ; elemental analysis calcd (%) for C19H28O2S4
1,3-Cycloadditions and electrocyclizations
(416.69): C 54.76, H 6.77, S 30.78; found: C 54.74, H 6.75, S 30.76.
1,1,3,3-Tetramethylcyclobutane-2-spiro-2'-1,3-dithiolane-4'-spiro-2''-ada-
mantane (11BA): Freshly recrystallized thiadiazoline 17B (396 mg,
2.00 mmol) and adamantanethione[38] (10A, 365 mg, 2.20 mmol) in abso-
lute THF (4mL) were heated in a 40 8C bath for 8 h; a gas burette indicated
the liberation of N2 (2 mmol). After removal of the solvent under vacuum,
the residue was subjected to 1H NMR analysis in CDCl3 with weight
standard, and the integral of the singlet at d ˆ 3.12 ppm indicated 88% of
cycloadduct 11BA. Twice crystallized from EtOH, pure 11BA (463 mg,
69%) was obtained as lustrous leaflets, m.p. 139 1418C; 1H NMR
(80 MHz): d ˆ 1.31 (s, br., 12H; 4  Me), 1.62 2.32 (m, 14H), 3.12 (s,
2H; 5'-H2) ppm; 13C NMR (20.2 MHz): d ˆ 22.4, 24.7 (2  q; 2  2Me),
26.8, 27.4, 37.9 (3 Â d, 1:1:2; 4 Â CH of adamantane), 34.8, 36.9, 38.2 (3 Â t,
1:2:2; 5 Â CH2 of adamantane), 47.0 (t; C5'), 66.1 (s; C1, C3), 73.5, 74.3 (2 Â
b) After N2 elimination from 17B (2.0 mmol) in CS2 (400 mL, 6.64 mol) at
458C, 1H NMR analysis with the standard showed 25% of 5, 16% of 20B,
and 30% of 19B (s, 4.09, 2H). The red semisolid contained monoadduct
19B, the isolation of which failed because it decomposed on silica gel
during PLC. 1H NMR (80 MHz): d ˆ 1.42, 1.48 (2  2Me), 4.09 (s, ring CH2,
assigned in analogy to 4.17 for CH2 of 19A[16]).
Ethyl
dispiro[1,3-dithiolane-2',2;4',2''-bis(adamantane)]-5'-carboxylate
(29): a) Adamantanethione (10A, 333 mg, 2.00 mmol) and ethyl diazoace-
tate (228 mg, 2.00 mmol) in THF (4mL) were allowed to react at 60 8C.
After 2 h, the red color of 10A had disappeared, and only the faint yellow
of the excess of ethyl diazoacetate persisted; 27 mL of N2 were evolved.
1H NMR analysis in CDCl3 established 87% of 29 (s, d ˆ 4.37). Crystals
(255 mg, 61%) from EtOH, m.p. 150 1518C. 1H NMR (80 MHz): d ˆ 1.25
ˆ
ˆ
s; C2', C4'), 220.6 (s; C O) ppm; IR (KBr): nÄ ˆ 1777s (C O), 2855m,
3
(t, J ˆ 7.0 Hz, 3H; Me), 1.50 2.87 (m, 28H), 4.10, 4.15 (2  q, 3J ˆ 7.0 Hz,
‡
2913s, 2978s (C H) cmÀ1; MS (608C): m/z (%): 336 (8) [M] , 266 (100)
À
2H; diastereotopic H of Et), 4.37 (s, 1H; 5'-H) ppm; 13C NMR (20.2 MHz):
d ˆ 14.1 (q; Me), 26.17 (2  ), 26.81, 27.23, 34.01, 34.47, 34.62, 36.14, 36.20,
36.38, 36.47, 37.13, 37.56, 37.92, 38.19, 38.38, 41.31, 44.89 (18C of two
nonequivalent adamantane systems), 59.1 (d; C-5'), 60.8 (t; OCH2), 73.9,
‡
‡
‡
[M À dimethylketene, C15H22S2] , 188 (15) [C8H12OS2] , 180 (8) [C11H16S ,
‡
‡
18A] , 148 (15) [C11H16, 2-methyleneadamantane] , 86 (53%) [C4H6S,
‡
‡
dimethylthioketene] , 71 (9), 70 (9) [C4H6O, dimethylketene] ; elemental
analysis calcd (%) for C19H28OS2 (336.55): C 67.80, H 8.39, S 19.06; found: C
67.75, H 8.18, S 19.05.
ˆ
76.5 (2  s; C2', C4'), 171.3 (s; C O) ppm; IR (KBr): nÄ ˆ 1098m, 1147s
(C O), 1736s (C O), 2854s, 2987vs (C H) cmÀ1; MS (1008C), m/z (%):
À
ˆ
À
1,1,3,3,7,7,9,9-Octamethyl-5,10-dithiadispiro[3.1.3.2]undecane-2,8-dione
(4; ˆ 11BB): The crude product, obtained analogously from 17B and 1,[39]
contained 73% of 11BB according to 1H NMR analysis of the singlet at d ˆ
3.17 ppm; thiirane 5 was a side product. Dithiolane 11BB (442 mg, 68%)
crystallized from EtOH, m.p. 159 1618C after recrystallization. Diebert[3]
obtained 31% with m.p. 162 1648C. 1H NMR (400 MHz): d ˆ 1.305, 1.308,
1.35, 1.36 (4 Â s, 12H; 8 Â Me), 3.22 (s, 2H; 11-H2) ppm; 13C NMR
(100 MHz, DEPT): d ˆ 19.8, 21.8, 25.14, 25.24 (4  2Me), 43.5 (CH2; C11),
‡
‡
‡
418 (27) [M] , 345 (2) [M À CO2Et] , 252 (12) [C14H20O2S, M À 10A] , 220
‡
‡
ˆ
À
(3) [C14H20O2, C9H14CH CH CO2Et] , 198 (100) [C10H14S2] (34; HR
‡
calcd 198.0537, found 198.0544), 166 (11) [10A] , 133 (22) [C10H13, 10A À
‡
‡
SH] , 91 (15) [C7H7] , 79 (8); elemental analysis calcd (%) for C24H34O2S2
(418.64): C 68.85, H 8.19, S 15.32; found: C 69.00, H 8.09, S 15.35.
b) The reaction was also run at lower temperatures. According to the color
test and 1H NMR monitoring, the completion required about 12 h at 258C,
Chem. Eur. J. 2003, 9, 2256 2263
www.chemeurj.org
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2261

R. Huisgen et al.
FULL PAPER
6 d at ‡58C, and six weeks at À288C. Dithiolane 29 was the only defined
with I > 2s(I) and 198 variable and 1 restraint. R1 ˆ 0.0285 and wR2 ˆ
0.0696 for all data. Weight: SHELXL-93. Absolute structure parameter:
À0.03(6). Maximum and minimum of the final difference Fourier synthesis
0.176 and À0.149 eäÀ3. ZORTEP plot.[44] CCDC-192837 contains the
supplementary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 IEZ, UK; fax: (‡44)1223 336 033; email:
deposit@ccdc.cam.ac.uk).
product.
3-Phenyl-[thiirane-2-spiro-2'-adamantane] (28):[40] Thione 10A (365 mg,
2.2 mmol) in CDCl3 (2 mL) was treated dropwise with phenyldiazo-
methane[41] in pentane at room temperature until the orange-red color
faded; N2 was immediately set free. 1H NMR analysis indicated 92% of
thiirane 28 (s, d ˆ 3.91 ppm). Evaporation and trituration with MeOH gave
crystalline 28 (413 mg, 73%); recrystallization from pentane, m.p. 67
688C (oil[40]): 1H NMR (80 MHz): d ˆ 1.2 2.1 (m, 14H), 3.91 (s, 3-H),
7.1 7.5 (m, 5H; Ph) ppm; IR (KBr): nÄ ˆ 702s, 754s (arom. out-of-plane
deform.), 1447s, 1492m, 1599w (arom. ring vibr.), 2849s, 2910vs
(C H) cmÀ1; elemental analysis calcd (%) for C17H20S (256.40): C 79.63,
À
Acknowledgements
H 7.86, S 12.51; found: C 79.81, H 7.86, S 12.48.
We are greatly indebted to the Fonds der Chemischen Industrie, Frankfurt,
for the support of our research program. G. M. thanks the Alexander von
Humboldt Foundation for the prolongation of a stipend. Sincere thanks are
expressed to Helmut Huber for his help in NMR spectroscopy, to Reinhard
Seidl for the mass spectra, as well as to Helmut Schulz and Magdalena
Schwarz for the elemental analyses.
Ethyl 4,4,6,6-tetramethyl-5-oxo-1-thiaspiro[2.3]hexane-2-carboxylate (30):
a) Thione 1 (2.0 mmol) and ethyl diazoacetate (2.2 mmol) in CDCl3 (2 mL)
were magnetically stirred at room temperature; after 10 h, 48 mL N2
(2.0 mmol) had evolved; 1H NMR analysis: 93% of 30. CC (silica gel,
CH2Cl2) gave 30 (328 mg, 68%) as a colorless oil, and Kugelrohr distillation
at 808C/0.05 Torr furnished the analytical sample; 1H NMR (80 MHz): d ˆ
1.11, 1.25, 1.30, 1.32 (4  s, 12H; 4Me), 1.40 (t, 3J ˆ 7.0 Hz, 3H; Me of Et),
3.50 (s; 2-H), 4.19 (q, 3J ˆ 7.0 Hz, 2H; OCH2) ppm; IR (KBr): nÄ ˆ 1027s,
À
ˆ
ˆ
1180s, 1275m, br. (C O), 1724s, 1746s (C O, ester), 1788vs (C O,
[1] R. Huisgen, C. Fulka, I. Kalwinsch, X. Li, G. Mloston, J. R. Moran, A.
Prˆbstl, Bull. Soc. Chim. Belg. 1984, 93, 511 532.
‡
ketone), 2929m, 2967s (C H) cmÀ1; MS (1308C): m/z (%): 242 (5) [M] ,
À
‡
‡
210 (3) [M À S] , 197 (8) [M À OEt] , 182 (40) [197 À Me], 172 (25)
[2] G. Mloston, H. Heimgartner, in The Chemistry of Heterocyclic
Compounds, Vol. 59, Synthetic Applications of 1,3-Dipolar Cyclo-
addition Chemistry Toward Heterocycles and Natural Products (Eds.:
A. Padwa, W. H. Pearson), Wiley, New York, 2002, pp. 360.
[3] C. E. Diebert, J. Org. Chem. 1970, 35, 1501 1505.
[4] a) R. Huisgen, G. Mloston, E. Langhals, J. Am. Chem. Soc. 1986, 108,
6401 6402; b) G. Mloston, E. Langhals, R. Huisgen, Tetrahedron Lett.
1989, 30, 5373 5376; c) R. Huisgen, G. Mloston, H. Giera, E.
Langhals, Tetrahedron 2002, 58, 507 519.
[5] a) R. Huisgen, G. Mloston, E. Langhals, J. Org. Chem. 1986, 51, 4085
4087; b) R. Huisgen, G. Mloston, E. Langhals, Helv. Chim. Acta 2001,
84, 1805 1820.
[6] E. Bergmann, M. Magat, D. Wagenberg, Ber. Dtsch. Chem. Ges. 1930,
63, 2576 2584.
[7] a) A. Schˆnberg, D. Cernik, W. Urban, Ber. Dtsch. Chem. Ges. 1931,
64, 2577 2581; b) A. Schˆnberg, B. Kˆnig, E. Singer, Chem. Ber. 1967,
100, 767 777.
[8] a) I. Kalwinsch, X. Li, J. Gottstein, R. Huisgen, J. Am. Chem. Soc.
1981, 103, 7032 7033; b) R. Huisgen, I. Kalwinsch, X. Li, G. Mloston,
Eur. J. Org. Chem. 2000, 1685 1694.
[9] L. Fisera, R. Huisgen, I. Kalwinsch, E. Langhals, X. Li, G. Mloston, K.
Polborn, J. Rapp, W. Sicking, R. Sustmann, Pure Appl. Chem. 1996, 68,
789 798.
‡
‡
[C8H12O2S; M À dimethylketene] , 169 (100) [M À CO2Et] , 141 (27), 126
‡
(79), 107 (16), 99 (20) [169 À C4H6O], 81 (11), 70 (12) [C4H6O] ; elemental
analysis calcd (%) for C12H18O3S (242.33): C 59.47, H 7.49, S 13.23; found: C
59.13, H 7.42, S 13.37. b) An experiment at À288C was completed after
three weeks; 1H NMR monitoring did not reveal signals of the intermediate
dihydrothiadiazole derivative.
4,4,6,6-Tetramethyl-2-phenyl-1-thiaspiro[2.3]hexane-5-one (31): Thione 1
was treated with phenyldiazomethane as described for 30; 96% N2
evolution. 1H NMR analysis indicated 93% of 31 (s, d ˆ 4.17 ppm); crystals
(67%) from MeOH, m.p. 90.5 92.58C; 1H NMR (80 MHz): d ˆ 0.60, 1.17,
1.25, 1.35 (4 Â s, 12H; 4 Â Me), 4.17 (s; 2-H), 7.1 7.3 (m; Ph) ppm; IR
(KBr): nÄ ˆ 703, 762m (arom. out-of-plane deform.), 1456s, 1493w (arom.
ring vibr.), 1780vs (C O), 2925m, 2965s (C H) cmÀ1; elemental analysis
calcd (%) for C15H18OS (246.36): C 73.13, H 7.37, S 13.02; found: C 73.16, H
7.47, S 13.07.
ˆ
À
2,3-Dihydro-1,1,3,3-tetramethylspiro[1H-indene-2.2'-thiirane]
(18H):
Thiadiazoline 17H (150 mmol) and thione (402 mmol) in CDCl3
1
(0.5 mL) were heated at 808C in an NMR tube for 10 min. After the
sample had cooled and dibenzyl had been added (s, d ˆ 2.92 ppm),
1H NMR analysis showed 100% of 18H (s, d ˆ 2.54ppm); [42] 1H NMR:
identical with a sample prepared without 1.[34]
4,4,8,8-Tetramethyl-1-thiaspiro[2.5]octane (18I): The analogous experi-
ment with 1 and 17I in octane (15 min at 1308C) provided 100% of 18I[42]
(i.e., thiocarbonyl ylide 9I likewise refused to undergo cycloaddition with
1). In a preparative experiment, 18I was obtained from Et2O as needles,
m.p. 78 798C. 1H NMR (80 MHz): d ˆ 0.93, 1.15 (2  s, 12H; 4  Me),
1.30 1.75 (m, 6H), 2.43 (s, 2H; 2-H2) ppm; 13C NMR (20.2 MHz): d ˆ 19.0
(t, C6), 28.5, 30.4(2 Â q, 2 Â 2Me), 29.1 (t, C2), 37.0 (s, C4, C8), 41.7 (t, C5,
[10] a) J. Sauer, J. Schatz, Tetrahedron Lett. 1994, 35, 4767 4770; b) J.
Breu, P. Hˆcht, U. Rohr, J. Schatz, J. Sauer, Eur. J. Org. Chem. 1998,
2861 2874; c) U. Rohr, J. Schatz, J. Sauer, Eur. J. Org. Chem. 1998,
2875 2883.
[11] See preceding paper: R. Sustmann, W. Sicking, R. Huisgen, Chem.
Eur. J. 2003, 9, 2245 2255.
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11494.
‡
C7), 63.2 (s, C3) ppm; MS (208C): m/z (%): 184(18) [ M] , 169 (9) [M À
‡
‡
‡
Me] , 152 (16) [M À S] , 137 (44) [152 À Me], 123 (14), 109 (45) [C8H13] ,
‡
‡
‡
96 (46), 95 (43) [C7H11] , 82 (100) [C6H10] , 69 (34) [C5H9] , 55 (28)
[C4H7] ; elemental analysis calcd (%) for C11H20S (184.34): C 71.67, H
‡
10.94, S 17.40.
X-ray diffraction analysis of 4 (Figure 1): monoclinic, space group P21,
no. 4. Unit cell dimensions: a ˆ 8.0034(12), b ˆ 11.691(2), c ˆ 9.571(3) ä,
b ˆ 96.39(2)8, Vˆ 890.0(4) ä3, Z ˆ 2, 1calcd ˆ 1.218 MgmÀ3, F(000) ˆ 352,
Tˆ 295(2) K, m(MoKa) ˆ 0.301 mmÀ1. Data collection: Nonius MACH3
diffractometer, colorless block (0.27 Â 0.47 Â 0.53 mm), mounted in a glass
capillary, cell constants from 25 centered reflections. MoKa radiation,
l ˆ 0.71073 ä, graphite monochromator, w-2q scan, scan width (0.66
‡0.55 tanq)8, maximum measuring time 60 s, intensity of three standard
reflections checked every 2 h, q range 2.56 23.968 for all Æh, Æk, Æl
reflections, 3277 reflections measured, 2785 unique, and 2659 reflections
with I > 2s(I). Lorentz, polarization, and absorption corrections (Tmin/Tmax
0.8960 and 0.9984). Structure solution by SHELXS-86 and refinement by
SHELXL-93.[43] Final R1 ˆ 0.0263 and wR2 ˆ 0.0673 for 2659 reflections
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2262
¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Regioselectivity of 1,3-Dithiolane Formation
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Received: December 10, 2002 [F4659]
Chem. Eur. J. 2003, 9, 2256 2263
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¹ 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2263