1,3-dipolar activity in cycloadditions of an aliphatic sulfine

Article abstract of DOI:10.1021/jo9607424

2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-oxide (4) combines with diaryl thioketones at room temperature furnishing spiro-1,2,4-oxadithiolanes 6 in equilibrium reactions. Compound 6a was oxidized to the cis-S,S-dioxide 9, the structure of which was esta

Full text of DOI:10.1021/jo9607424

6570
J . Org. Chem. 1996, 61, 6570-6574
1,3-Dip ola r Activity in Cycloa d d ition s of a n Alip h a tic Su lfin e†,1
Rolf Huisgen,* Grzegorz Mloston,2 and Kurt Polborn
Institut fu¨r Organische Chemie der Universita¨t Mu¨nchen, Karlstrasse 23, D-80333 Mu¨nchen, Germany
Received April 23, 1996X
2,2,4,4-Tetramethyl-3-thioxocyclobutanone S-oxide (4) combines with diaryl thioketones at room
temperature furnishing spiro-1,2,4-oxadithiolanes 6 in equilibrium reactions. Compound 6a was
oxidized to the cis-S,S-dioxide 9, the structure of which was established by X-ray analysis. These
are the first unequivocal 1,3-cycloadditions of thione S-oxides (sulfines) which possess an allyl anion
type MO; cycloadditions to the CdS bond of sulfines as dipolarophile and dienophile had been
described before.
In tr od u ction
sulfines despite several attempts.” The lack of 1,3-dipolar
activity of sulfines, still in the early 1990s,11 was less
understandable since thiocarbonyl ylides are highly
active 1,3-dipoles12 and numerous 1,3-cycloadditions of
thiocarbonyl imines are likewise known.13
We recently presented kinetic evidence for thiones as
being superdipolarophiles.14-16 High rate constants of
cycloadditions were attributed to low π HOMO-LUMO
separations. Calculations (MP2/6-31G*, Becke3LYP/
6-31G*) for the concerted addition of the nitrone parent
to thioformaldehyde resulted in negative activation en-
thalpies.17
The first sulfine was prepared, inadvertently, by
Wedekind et al. in 1923.3 The systematic development
of this class of organosulfur compounds was largely a
fruit of the pioneering efforts of Block4 and Zwanenburg.5
Many authors use the heterocumulene formula 1 for
sulfines. However, most theoreticians do not regard the
participation of sulfur d-orbitals as high.6 Therefore, we
prefer the thione S-oxide structure 2a , due to the sulfur
and oxygen bearing a net positive and a negative charge,
respectively.7 The parent sulfine, prepared by Block et
al.,8 has a dipole moment of 2.99 D (gas phase).
We report here the first unequivocal 1,3-dipolar cy-
cloadditions of sulfines.
Resu lts a n d Discu ssion
Cycloa d d ition Equ ilibr ia of Su lfin e 4 a n d Ar o-
m a tic Th iok eton es. 2,2,4,4-Tetramethyl-3-thioxocy-
clobutanone (3) is easily available, and its S-oxide 4,
described by Zwanenburg et al.,18 is relatively thermo-
stable; we found it unchanged after 4 h at 80 °C, making
4 a suitable model sulfine.
The reaction of thiobenzophenone (5a ) and its 4,4′-
dichloro derivative (5b) with 1.1 equiv of 4 in pentane-
dichloromethane proceeded at rt in the dark; the 1,2,4-
oxadithiolanes 6a and 6b were obtained as colorless
crystals. The moderate isolated yields (62 and 55%)
reflect the ease of cycloreversion. The specimens turned
deep-blue at the melting point, the color of 5a or 5b.
The resonance hybrid 2 constitutes a 1,3-dipole;9a
sulfines are the thio analogues of carbonyl oxides, the
well-known intermediates in the ozonation of alkenes.
Zwanenburg and his group discovered the readiness
with which the CS bond of sulfines participates as 2π
reactant in Diels-Alder reactions and 1,3-dipolar cy-
cloadditions.5 Sulfines behave as dipolarophiles vs di-
azoalkanes, nitrile ylides, nitrile imines, and nitrile
oxides as well as nitrones and mu¨nchnones. However,
Zwanenburg et al.10 stated in 1967, “...we have found no
indications for 1,3-dipolar cycloaddition reactions of
† Dedicated to J u¨rgen Sauer, Regensburg, to whom cycloaddition
chemistry owes so much, on the occasion of his 65th birthday.
X Abstract published in Advance ACS Abstracts, August 15, 1996.
(1) 1,3-Dipolar Cycloadditions. 95. For part 94, see, ref 16.
(2) Present address: Department of Organic and Applied Chemistry,
University of Lodz, Poland.
(3) Wedekind, E.; Schenk, D.; Stu¨sser, R. Ber. Dtsch. Chem. Ges.
1923, 56, 633.
(4) For reviews, see: Block, E. Angew. Chem., Int. Ed. Engl. 1992,
31, 1135. Block, E. In Organic Sulfur Chemistry; Freidlina, R. Zh.,
Skorova, A. E., Eds.; Pergamon Press: Oxford, 1981; p 15.
(5) For reviews, see: Zwanenburg, B.; Lenz, B. G. In Houben-Weyl,
Methoden der Organischen Chemie; G. Thieme: Stuttgart, 1985; Vol.
E 11, 911. Zwanenburg, B. Rec. Trav. Chim. Pays-Bas 1982, 101, 1.
(6) Bent, H. A. In Organic Chemistry of Sulfur; S. Oae, Ed.; Plenum
Press: New York, 1977, p 1.
(7) Lierop, J . van; Avoird, A. van der; Zwanenburg, B. Tetrahedron
1977, 33, 539.
(8) Block, E.; Penn, R. E.; Olsen, R. J .; Sherwin, P. F. J . Am. Chem.
Soc. 1976, 98, 1264.
(11) We thank Prof. B. Zwanenburg, Nijmegen, for this private
communication.
(12) For reviews, see: (a) Kellogg, R. M. Tetrahedron 1976, 32, 2165.
(b) Huisgen, R.; Fulka, C.; Kalwinsch, I.; Xi, L.; Mloston, G.; Moran,
J . R.; Pro¨bstl, R. Bull. Soc. Chim. Belg. 1984, 93, 511.
(13) For review, see: Motoki, S.; Saito, T. Sulfur Rep. 1984, 4, 33.
(14) Huisgen, R.; Li, X. Tetrahedron Lett. 1983, 24, 4185.
(15) Huisgen, R.; Langhals, E. Tetrahedron Lett. 1989, 30, 5369.
(16) Huisgen, R.; Fisera, L.; Giera, H.; Sustmann, R. J . Am. Chem.
Soc. 1995, 117, 9671.
(9) For review, see: Huisgen R. In 1,3-Dipolar Cycloaddition
Chemistry; Padwa, A., Ed.; Wiley: New York, 1984; Vol. 1, (a) p 2, (b)
p 139.
(17) Sustmann, R.; Sicking, W.; Huisgen, R. J . Am. Chem. Soc. 1995,
117, 9679.
(10) Zwanenburg, B.; Thijs, L.; Strating, J . Rec. Trav. Chim. Pays-
Bas 1967, 86, 577.
(18) Zwanenburg, B.; Wagenaar, A.; Thijs, L.; Strating, J . J . Chem.
Soc., Perkin Trans. 1 1973, 73.
S0022-3263(96)00742-6 CCC: $12.00 © 1996 American Chemical Society

1,3-Dipolar Activity of a Sulfine
J . Org. Chem., Vol. 61, No. 19, 1996 6571
When sulfine 4 was reacted with 2 equiv of thiones 5a
or 5b in CDCl3 at rt, 1H NMR analysis after 2, 9, and 70
h indicated 96-100% of the oxadithiolanes 6a and 6b,
respectively. This allows for several conclusions: (a) the
conversion of 4 to the oxadithiolanes 6 is virtually
quantitative in the presence of an excess of thioketone;
(b) the equilibration is complete after 2 h; (c) the
equilibrium system is stable at rt.
Fresh solutions of the oxadithiolanes 6a and 6b started
to turn blue after several minutes at ambient tempera-
ture; however, the color nearly disappeared upon cooling
to -20 °C. Due to the high extinction of the long-wave
light absorption of 5, the color test is overly sensitive.
Only a small percentage of 6 is dissociated in solution at
rt. The Diels-Alder reaction of thiobenzophenone with
dimethyl acetylenedicarboxylate (DMAD) affording 719 is
slow but irreversible. Adduct 6a and 2 equiv of DMAD
1
F igu r e 1. X-ray structure of the spiro-oxadithiolane cis-
dioxide 9 (ORTEP plot).
in CDCl3 were heated to 50 °C; after 6 d the H NMR
analysis established 89% of 7, 96% of sulfine 4, and still
4% of adduct 6a . Thus, thiobenzophenone was removed
through a small equilibrium concentration by cycloaddi-
tion to DMAD.
bis-S-oxide 9 (82%). This makes the four methyl signals
in the 1H NMR spectrum of 9 nonequivalent; they spread
over a wide range (δ 0.47, 1.07, 1.72, 1.90). A sultone or
sulfone structure should have retained pairwise equiva-
lence of the methyls. The IR spectrum showed a strong
sulfoxide absorption at 1091 cm-1 and a further strong
S-O band at 1163 cm-1 for the sultine group. Benzophe-
none radical cation and benzoylium ion constitute the
most populous peaks in the MS of 9.
The degree of dissociation of oxadithiolane 6c into 4,4′-
dimethoxythiobenzophenone (5c) plus 4 is much higher
than that of 6a or 6b. Only 76% of 6c was found when
4 and 5a were reacted in 1:2 ratio under the standard
conditions described above for complete conversion to 6a
and 6b. Ground state stabilization of 5c by participation
of quinonoid resonance structures influences the cycload-
dition equilibrium. A value of Kadd ) 3.3 M-1 (CDCl3, 25
°C) for 6c was measured and corresponds to ∆G298 ) 0.70
kcal mol-1; 41% is dissociated in 1 M oxadithiolane 6c
in CDCl3.
Str u ctu r e of Cycloa d d u cts. In accord with the Cs
symmetry of 6a and 6b, the 1H NMR spectra show
pairwise identical methyl groups (δ 1.25 and 1.40,
CDCl3); formula 8 of a 1,3-dithietane S-oxide would
require four different CH3. The 13C NMR spectra allow
a complete assignment of signals.
The X-ray analysis of the monoclinic crystal revealed
the cis-S,S-dioxide 9 in an envelope conformation with
C4 as the flap (Figure 1). The sums of the bond angles
at S5 and S8 are 311° and 310°, respectively, revealing
the extent of pyramidalization. Both oxide functions are
in a pseudoaxial conformation at the 5-membered ring.
The folding angle of the cyclobutane ring amounts to
11.4°.
The bond length of 1.471 Å for the sulfoxide (S8-O4)
is nearly identical with that of DMSO (1.477 Å), and C4-
S8 with 1.823 Å compares well with 1.810 Å for C-S in
DMSO.20 The angles C4-S8-O4 (107.2°) and C7-S8-
O4 (109.8°) correspond to 106.7° for DMSO. The semi-
polar bond S5-O3 (1.447 Å) of the sultine group is
somewhat shorter than that of the sulfoxide, and the
length of the single bond S5-O6 is 1.609 Å.
Why the kinetic preference for the cis-5,8-dioxide?
After the first oxygen transfer, the sulfoxide will form a
strong hydrogen bond with the second molecule of per-
acid. As the sketch (structure 10) of the TS suggests,
the second O transfer should take place on the same face
of the 5-membered heterocycle as the first one. Sulfox-
ides are strong hydrogen bond acceptors; it may be
recalled, that proton exchange of secondary alcohols is
suppressed in DMSO, and coupling of O-H with C-H
becomes observable.21
The M+ peaks are missing in the mass spectra of 6a
and 6b; mainly those of the thioketones were observed.
Fragments coming from the sulfine part are rare, how-
ever, suggesting a fast dissociation, M+• f 5+• + 4.
Dichlorobenzophenone+ and 4-chlorobenzoylium ion (base
In 1963, it was proposed that 1,3-dipolar cycloadditions
to heteromultiple bonds are guided in a direction that
gives rise to two new strong carbon-heteroatom bonds
rather than to C-C plus the weaker heteroatom-
heteroatom bond.22 In our case, the formation of a 1,2,4-
oxadithiolane should be preferred to that of the 1,2,5-
regioisomer. However, the principle of maximum gain
of σ-bond energy22 was later discarded in favor of the
peak) point to another fragmentation pathway for 6b+•
.
Finally, in the MS of the thiofluorenone adduct 12, a peak
for M+-2CH3 was observed.
Since the thin leaflets of 6a were not suitable for single
crystal analysis, 6a was oxidized by m-CPBA to a single
(20) Dreizler, H.; Dendl, G. Z. Naturforschung 1964, 19a, 512.
(21) Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden der
Organischen Chemie, 2nd Ed.; G. Thieme: Stuttgart, 1984; p 135, 149.
(22) Huisgen, R. Angew. Chem., Int. Ed. Engl. 1963, 2, 633.
(19) Gotthardt, H.; Nieberl, S. Liebigs Ann. Chem. 1980, 867.

6572 J . Org. Chem., Vol. 61, No. 19, 1996
Huisgen et al.
perturbation MO treatment of concerted cycloadditions.9b,23
Thus, the structure of 6 was not a priori clear.
C-5 as the flap and an S-O bond length of 1.661 Å.28 In
comparison with sulfines, thioketene S-oxides reveal
markedly changed bond lengths and reactivity. No
longer does the CdS bond behave as a dipolarophile but
the CdC does; the addition of 2-diazopropane furnished
20.29
Th ioflu or en on e a s a Dip ola r op h ile. The cycload-
dition of sulfine 4 to thione 11 generated the colorless
1
needles of 12; the H and 13C NMR spectra are in accord
with a plane of symmetry in 12. Oxidation by m-CPBA
provided the S,S-dioxide 14 in analogy to the conversion
of 6a f 9.
F u r th er Obser va tion s. The dipolarophile scale for
1,3-cycloadditions of sulfine 4 is limited. No reaction was
observed with DMAD, dimethyl 2,3-dicyanofumarate,
N-sulfinylaniline, N-benzylidenemethylamine (CDCl3, 7
d at 25 °C, some hours at 60 °C). When 4 was treated
with N-isobutenylpyrrolidine (12 d, rt), the main product
was tetramethylcyclobutane-1,3-dione.
No interaction of adamantanethione S-oxide with
thiobenzophenone was monitored by the H NMR spec-
trum (CDCl3) in 14 d at rt; at 80 °C, the sulfine
disappeared in 2 d, and adamantanone occurred among
the products.
Interestingly, the yield of 12 went through a maximum
1
when the reaction with 1:2 stoichiometry at rt was
1
monitored by H NMR spectroscopy: 32% of 12 after 2
h, 54% after 9 h, and 26% after 70 h. The reason is the
irreversible dimerization of thiofluorenone furnishing 13;
the dimer was recognized as a Diels-Alder adduct by
Scho¨nberg et al.24 After 9 h (70 h), 18% (23%) of 13 was
detected; therefore, there must be further side reactions.
The “semiquantitative” evidence that thiofluorenone
reacts slower than thiobenzophenone is surprising. In
the 1,3-cycloadditions of thiobenzophenone S-methylide,
thiofluorenone exceeded thiobenzophenone 60-fold in the
rate constant.14 In the dienophilic activity vs cyclopen-
tadiene, thiofluorenone is 7100 times faster than thioben-
zophenone.25
Rela ted Cycloa d d ition s. Block et al. obtained the
(E,E)-thiosulfinate 15, in the context of his masterly
studies on the chemistry of onions, by oxidation of the
disulfide at -60 °C. The conversion to the 2-oxa-3,7-
dithiabicyclo[2.2.1]heptane derivative 17 at -40 °C was
plausibly interpreted by a thio-Claisen rearrangement
to afford 16 and a subsequent intramolecular 1,3-dipolar
cycloaddition of the (Z)-sulfine function to the thioalde-
hyde.26
Kin etic or Th er m od yn a m ic Con tr ol. Why does 4
combine with the CdS double bond but not with ole-
finic and acetylenic bonds? According to calculations
(MP4SDTQ/6-31G*//6-31G* + ZPE) by Schleyer and
Kost,30 the CS π-bond of H2CdS is 14 kcal mol-1 weaker
than the CC π-bond of ethylene. Since the σ-bond energy
of C-S is likewise lower than that of C-C, even by 19
kcal mol-1, the sulfine cycloaddition to ethylene should
be more exothermic by 5 kcal mol-1 than the addition to
thioformaldehyde. The nonreactivity of CC multiple
bonds toward sulfines is probably a kinetic phenomenon.
However, the conclusion is still shaky. Bond energies
depend on adjacent groups, and sufficient group values31
are not known for sulfur functions to calculate reliable
reaction enthalpies. Furthermore, different cycloaddition
entropies could change the picture. More information is
required.
Exp er im en ta l Section
Gen er a l Meth od s a n d In str u m en ts.16 NMR spectral
data were taken in acid-free CDCl3, stored over dry K2CO3;
assignments were based on DEPT (1H) and spectra with and
without decoupling (13C). MS evaluation of the isotope peaks
helped the assignment. Melting points are uncorrected.
2,2,4,4-Tetr am eth yl-3-th ioxocyclobu tan on e S-Oxide (4).
Thione 316 was converted to 418 by m-CPBA in ether at 0 °C;
78% of colorless crystals from pentane-CH2Cl2 1:1, mp 48-
49 °C (80%, mp 52.3-53.2 °C).18 IR (KBr): 1069 st (st means
strong) (SO), 1789 st (CdO). 1H NMR: δ 1.51 (s, 2 CH3), 1.66
(s, 2 CH3). MS (EI 70 eV, 40 °C): m/ z (proposed ion, percent
intensity) 172 (M+, 23), 156 (3+, 4%), 144 (M+ - CO, C7H12S+,
55; 13C calcd 4.3, found 4.4; 34S calcd 2.5, found 2.2), 140
(tetramethylcyclobutane-1,3-dione+, 11), 127 (C7H11S+, 25), 96
(C7H12+, 100; 13C calcd 7.8, found 7.9), 86 (dimethylthioketene+,
14), 81 (C6H9+, methylpentadienyl, 80), 70 (dimethylketene+,
Schaumann and Walter27 obtained the 3-methylene-
1,2,4-oxathiazolidine 19 from the thioketene S-oxide 18
by addition to 3,4-dihydroisoquinoline. The X-ray analy-
sis revealed an envelope structure of the heterocycle with
(23) For reviews, see: (a) Sustmann, R. Pure Appl. Chem. 1974, 40,
569. (b) Houk, K. N. In Pericyclic Reactions; Marchand, A. P., Lehr, R.
E., Eds.; Academic Press, Inc.: New York, 1977; Vol. 2, p 181. (c)
Huisgen, R. J . Org. Chem. 1976, 41, 403.
(24) Scho¨nberg, A.; Brosowski, K.-H.; Singer, E. Chem. Ber. 1962,
95, 1910.
(25) Schatz, J .; Sauer, J . Tetrahedron Lett. 1994, 27, 4767.
(26) Block, E.; Bayer, Th.; Naganathan, S.; Zhao, S.-H. J . Am. Chem.
Soc. 1996, 118, 2799.
(28) Schaumann, E.; Ehlers, J .; Behrens, U. Angew. Chem., Int. Ed.
Engl. 1978, 17, 455.
(29) Schaumann, E.; Behr, H.; Adiwidjaja, G.; Tangerman, A.;
Lammerink, B. H. M.; Zwanenburg, B. Tetrahedron 1981, 37, 219.
(30) Schleyer, P. v. R.; Kost, D. J . Am. Chem. Soc. 1988, 110, 2105.
(31) Benson, S. W. Thermochemical Kinetics; J . Wiley, Inc.: New
York, 1968; p 23.
(27) Schaumann, E.; Walter, W. Chem. Ber. 1974, 107, 3562.

1,3-Dipolar Activity of a Sulfine
J . Org. Chem., Vol. 61, No. 19, 1996 6573
85). Above 100 °C, the peak of a dimer of 4 begins to appear
and reaches a maximum at 245 °C. MS (EI, 70 eV): m/ z 344
afforded a colorless fraction of 6c. Upon evaporation of the
solvent at 0 °C, the blue color of 5c reappeared; the freshly
isolated 6c contained ca. 10% of 5c. 1H NMR: δ 1.24 (s, 2
CH3), 1.41 (s, 2 CH3), 3.80 (s, 2 OCH3), 6.84 and 7.38 (AA′XX′,
C6H4).
+
(M2 1.5; 13C calcd 0.26, found 0.28), 204 (M2 - tetramethyl-
cyclobutanedione, 2.2), 172 (M+, 51; 13C calcd 4.5, found 4.4).
We are dealing with a thermal dimerization, since M2+ did not
disappear after cooling.
(B) Equ ilibr iu m Con sta n t. Sulfine 4 (35.5 mg), thione
5c (71.6 mg), and 1,1,1,2-tetrachloroethane (57.5 mg, weight
standard) were dissolved in CDCl3 in a 2 mL volumetric flask.
1H NMR analysis (400 MHz) after 14 h (same integrals after
24 h) at rt indicated 0.0544 mmol of 6c (δ 1.24, 3.80, 7.38),
0.134 mmol of 4 (δ 1.51), and 0.245 mmol of 5c (δ 3.87, 7.7-
1,1,3,3-Tetr a m eth yl-7,7-d ip h en yl-6-oxa -5,8-d ith ia sp ir o-
[3.4]octa n -2-on e (6a ). (A) Syn th esis. Sulfine 4 (568 mg,
3.3 mmol) and thiobenzophenone (5a , 595 mg, 3.0 mmol)
reacted in 2 mL of CH2Cl2 and 6 mL of pentane for 12 h
at rt. After evaporation of the solvent, the still blue resi-
due was taken up in 1 mL of dichloromethane and 5 mL of
ethanol, concentrated at rt, and cooled to 0 °C: colorless
crystals of 6a (690 mg, 62%); from pentane at -78 °C in
thin leaflets, mp 80-81 °C (blue melt). 1H NMR: δ 1.25 (s, 2
CH3), 1.40 (s, 2 CH3), 7.2-7.6 (m, 2 C6H5). 13C NMR: δ 21.6
(q, 2 CH3), 25.2 (q, 2 CH3), 66.3 (s, C-1 and C-3), 82.7 (s, C-4),
111.8 (s, C-7), 127.4, 128.0, 128.3 (3 d, 6 aromatic CH), 142.9
(s, 2 aromatic Cq), 218.8 (s, CO). MS (EI, 70 eV, 100 °C): m/ z
198 (5a +, 94; 13C calcd 14, found 15), 182 (benzophenone+, 5),
165 (fluorenyl+, 100; 13C calcd 15, found 15), 121 (C6H5CtS+,
72; 34S calcd 3.2, found 3.3), 105 (C6H5CtO+, 10), 86 (di-
methylthioketene+, 8), 77 (C6H5+, 27). Anal. Calcd for
C21H22O2S2: C, 68.07; H, 5.99; S, 17.31. Found: C, 68.08; H,
5.99; S, 17.30.
7.85): K298 ) 3.3 M-1
.
1,1,3,3-Tetr a m eth yl-7,7-d ip h en yl-6-oxa -5,8-d ith ia sp ir o-
[3.4]octa n -2-on e 5,8-cis-Dioxid e (9). m-CPBA (345 mg, 2.0
mmol) in 5 mL of CH2Cl2 was introduced dropwise into the
stirred, ice-cooled solution of 6a (185 mg, 0.50 mmol) in 2 mL
of CH2Cl2 in 5 min. After 45 min, 20 mL of CH2Cl2 were added.
The resulting solution was washed with aqueous NaHSO3 and
then with water. The residue after evaporation gave on
trituration with ethanol 165 mg (82%) of colorless 9; after two
recrystallizations from CH2Cl2-ethanol, the melting point was
159-160 °C (gas evolution, red). IR (KBr): 780 st (SsO); 1091
st, 1163 vst (SdO), 1788 vst (CdO). The range of sulfoxide
absorptions is usually given as 1040-1060 cm-1; the value here
is somewhat higher. The S-O vibration of 5-membered
(B) 1H NMR Mon itor in g of Equ ilibr iu m . The methyl
singlets of 4 and 6a can be integrated separately; 2,6-
dimethylnaphthalene (s δ 2.43, 2 CH3) served as a weight
standard for the quantitative analysis ((5%). Sulfine 4 (0.50
mmol), thione 5a (1.00 mmol), and a standard in 1.0 mL of
CDCl3 were sealed in the NMR tube. Integration of 6a was
measured as follows: 100% (2 h), 98% (9 h), 96% (70 h at rt).
In a second series of tests, 4 (0.60 mmol) and 5a (0.50 mmol)
in 0.5 mL of CDCl3 were reacted in the sealed NMR tube. The
integration of 6a was measured as follows: 84% (2 h at rt),
96% (9 h), 91% (70 h).
sultines32 was found at 1100-1135 cm-1
.
1H NMR: δ 0.47,
1.07, 1.72, 1.90 (4 s, 4 CH3), 7.25-7.57 (m, 2 C6H5). MS (EI,
70 eV, 40 °C): m/ z 214 (C13H10OS+, probably diphenylsulfine,
4), 182 (benzophenone+, 62; 13C calcd 9.0, found 9.5), 105
(C6H5CtO+, 100; 13C calcd 7.8, found 7.4), 77 (C6H5+, 46). Anal.
Calcd for C21H22O4S2: C, 62.66; H, 5.51; S, 15.93. Found: C,
62.68; H, 5.60; S, 15.99.
X-r a y Str u ctu r e of 9.33 A crystal of 9 with an empirical
formula of C21H22O4S2 (mol wt. 402.5) was found to be
monoclinic with a space group of P21/n (No. 14). Unit cell
dimensions were determined to be a ) 8.870(2), b ) 15.530-
(4), and c ) 14.288(4) Å, â ) 95.57(2)°, Vol ) 1959 Å3, Z ) 4,
Dc ) 1.365 g/cm3, F(000) ) 848, T ) 294(1) K, and µ(Mo KR) )
(C) In ter cep tion by DMAD. Oxadithiolane 6a (78 mg,
0.21 mmol), dimethyl acetylenedicarboxylate (54 mg, 0.38
mmol), and 2,6-dimethylnaphthalene (0.079 mmol) in 0.7 mL
CDCl3 were reacted in the sealed NMR tube at 50 °C; the blue
0.283 mm-1
. Data collection was performed on a CAD4
diffractometer with a colorless crystal (size 0.4 × 0.4 × 0.27
mm) mounted in a glass capillary. Cell constants were
from 25 centered reflections using Mo KR radiation, a graph-
ite monochromator, λ ) 71.069 pm, ω scan with profile fitting,
scan width with (1.00 + 0.35 tan θ)°, and a maximum
measuring time of 60 s. The intensity of three standard
reflections were checked after every hour. In the 2θ range of
4-46° 2963 reflections with indices (h/+k/+l were measured;
2594 were unique and observed, and 2374 had I > 2σ(I). The
structure was solved with SHELXS-86, and the refinement
was done with SHELXL-93. All nonhydrogen atoms were
refined anisotropically, and hydrogens were refined with Ui
) 1.2 × Ueq of the adjacent carbon atom. A full matrix
refinement against F2 was performed. Final R1 and wR2
values were 0.0395 and 0.1139 for 2374 reflections with I >
2σ(I) and 248 variables. For all data, R1 ) 0.0434 and wR2 )
0.1183 (weights: SHELXL-93). The maximum and minimum
electron density of the final Fourier cycle were 0.396 and
-0.281 eÅ-3, respectively.
1,1,3,3-Tetr a m eth yl-2-oxo-6-oxa -5,8-d ith ia [3.4]octa n e-
7-sp ir o-9′-flu or en e (12) (A) Syn th esis. Sulfine 4 (3.3 mmol)
and 3.0 mmol of thiofluorenone (11, freshly recrystallized,
brown needles) were reacted as described for 6a ; 490 mg (44%)
of 12. Recrystallization from CH2Cl2-2-propanol at -20 °C
gave thick colorless needles, mp 116-117 °C (brown). IR
(KBr): 1786 st (CdO). 1H NMR: δ 1.47 (s, 2 CH3), 1.59 (s, 2
CH3), 7.2-7.8 (m, 8 aromatic CH). 13C NMR: δ 21.1 (q, 2 CH3),
25.9 (q, 2 CH3), 66.3 (s, C-1, C-3), 82.2 (s, C-4), 107.3 (s, C-7),
119.9, 125.6, 128.3, 130.5 (4 d, 8 aromatic CH), 139.2, 145.0
1
solution turned turquois after 6 d. The H integrals indicated
89% of 7 (s at δ 5.13, tertiary H), 96% of 4 (s, 1.66, 2 CH3), and
4% 6a (s, 1.40, 2 CH3).
1,1,3,3-Tetr a m eth yl-7,7-bis(4-ch lor op h en yl)-6-oxa -5,8-
d ith ia sp ir o[3.4]octa n -2-on e (6b). (A) Syn th esis. The
reaction of 4 (3.3 mmol) and 5b (3.0 mmol), run as described
above, provided 731 mg (55%) of 6b from ethanol, mp 95-97
°C. After thick-layer chromatography (silica gel, CH2Cl2-
pentane 1:1), colorless prisms crystallized from pentane at -20
°C, mp 105-106 °C. IR (KBr): 1786 st (CdO). 1H NMR: δ
1.25 (s, 2 CH3), 1.40 (s, 2 CH3), 7.26-7.41 (AA′BB′ of C6H4Cl);
at δ 1.51 and 1.66, 3.4% of 4 (equilibration). 13C NMR: δ 21.5
(q, 2 CH3), 25.2 (q, 2 CH3), 66.2 (s, C-1 and C-3), 83.0 (s, C-4),
110.6 (s, C-7), 128.4 and 128.7 (2 d, 8 aromatic CH), 134.6 and
141.2 (2 s, 4 aromatic Cq), 218 (s, CdO). MS (EI, 70 eV, 90
°C): m/ z 266 (5b+, 60; 268 (37Cl + 34S) calcd 42, found 42; 270
37Cl calcd 6, found 6), 250 (4,4′-dichlorobenzophenone+, 35;
37Cl calcd 22, found 23), 233 (3,6-dichlorofluorenyl+, 57), 231
(65), 155 (ClC6H4CS+, 60; 34S + 37Cl calcd 22, found 22), 139
(ClC6H5CtO+, 100; 37Cl calcd 32, found 34), 111 (ClC6H4+, 38),
86 (dimethylthioketene+, 29), 81 (C6H9+, 31). If 6b would
undergo thermal dissociation before ionization, peak 172 (4+)
and its secondary ions should appear; m/ z 172 is missing.
This suggests a splitting of M+ f 4 + 5b+. Anal. Calcd for
C21H20Cl2O2S2: C, 57.39; H, 4.59; S, 14.60. Found: C, 57.51;
H, 4.83; S, 14.64.
(B) 1H NMR Mon itor in g of Equ ilibr iu m . The cycload-
dition with 4/5b ) 1:2 (described above for 5a ) furnished 100%
6b after 2 h at rt, 97% after 9 h, and 98% after 70 h. In the
experiment with 1.2 equiv of 4, the yields of 6b amounted to
89% (2 h), 94% (9 h), and 89% (70 h).
1,1,3,3-Tet r a m et h yl-7,7-b is(4-m et h oxyp h en yl)-6-oxa -
5,8-d ith ia sp ir o[3.4]octa n -2-on e (6c). (A) Syn th esis. The
substantial equilibrium concentration of the reactants thwarted
the isolation of pure 6c. Column chromatography (silica gel,
CH2Cl2-pentane 4:1) of the equilibrium system at -20 °C
(32) Sharma, N. K.; Reinach-Hirtzbach, F. de; Durst, T. Can. J .
Chem. 1976, 54, 3012.
(33) The authors have deposited the atomic coordinates for this
structure with the Cambridge Crystallographic Data Centre. The
coordinates can be obtained, on request, from the Director, Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
U.K.

6574 J . Org. Chem., Vol. 61, No. 19, 1996
Huisgen et al.
(2 s, 4 aromatic Cq), 218.1 (CdO). MS (EI, 70 eV, 40 °C): m/ z
328 (M+ - 2CH3. 4.0; 13C calcd 0.85, found 1.05; 34S calcd 0.18,
found 0.17), 196 (11+, 100; 13C calcd 15, found 14; 34S calcd
4.4, found 4.2), 180 (fluorenone+, 5.9), 152 (biphenylene+, 25;
13C calcd 3.3, found 2.9), 96 (C7H12+, 13), 86 (dimethyl-
thioketene+, 3), 81 (C6H9+, 10). Anal. Calcd for C21H20O2S2:
C, 68.44; H, 5.47; S, 17.40. Found: C, 68,52; H, 5.34; S,
17.40.
1,1,3,3-Tetr a m eth yl-2-oxo-6-oxa -5,8-d ith ia [3.4]octa n e-
7-sp ir o-9′-flu or en e S,S-Dioxid e (14). Oxidation was as
described for the preparation of 9. After purification on a silica
gel column (CH2Cl2-acetone 98:2), 49% of 14 was obtained;
colorless crystals, mp 169-170 °C. IR (KBr): 1083, 1165 st
(SdO), 1787 st (CdO). 1H NMR: δ 1.57, 1.62, 1.75, 1.87 (4s,
4 CH3). Anal. Calcd for C21H20O4S2: C, 62.92; H, 5.03.
Found: C, 62.17; H, 5.13.
1
(B) H NMR Mon itor in g of Equ ilibr iu m . Signals were
Ack n ow led gm en t. We are grateful to the Deutsche
Forschungsgemeinschaft and the Fonds der Chemischen
Industrie for support of the project. Our thanks go to
Helmut Huber for his help in the NMR measurements
and to Reinhard Seidl for the MS spectra; Helmut
Schulz did the elemental analyses. G.M. thanks the
University of Lodz, Poland, for granting a leave of
absence.
observed at δ 1.59 (12, 2 CH3), 5.67 (13, tertiary H), and 4.43
(1,1,1,2-tetrachloroethane, weight standard). The cycloaddi-
tion reaction with 4/11 ) 1:2 furnished 39% of 12 after 2 h at
rt, 54% of 12 and 18% of 13 after 7 h, 26% of 12 and 23% of 13
after 70 h.
Dim er ic th ioflu or en on e (13);24 mp 216-217 °C (dec, 230-
232 °C 24). 13C NMR: δ 53.6 (d, aliphatic CH), 57.4 (s, aliphatic
Cq). MS (EI, 70 eV, 85 °C): m/ z 392 (M+, 9.2; 13C calcd 2.7,
found 2.7), 328 (M+ - 2S, 100; 13C calcd 26, found 25), 327
(56), 326 (40), 164 (fluorenylidene+, 10), 163 (18), 162 (11).
J O9607424