Chemoselectivity of the reactions of diazomethanes with 5-benzylidene-3-phenylrhodanine

Article abstract of DOI:10.1002/hlca.200900149

The reactions of 5-benzylidene-3-phenylrhodanine (2; rhodanine = 2-thioxo-1,3-thiazolidin-4-one) with diazomethane (7a) and phenyldiazomethane (7b) occurred chemoselectively at the exocyclic C=C bond to give the spirocyclopropane derivatives 9 and, in the

Full text of DOI:10.1002/hlca.200900149

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Helvetica Chimica Acta – Vol. 92 (2009)
Chemoselectivity of the Reactions of Diazomethanes with 5-Benzylidene-3-
phenylrhodanine
by Martin S. Seyfrieda)1), Anthony Lindena), Grzegorz Mloston´ b), and Heinz Heimgartner*a)
a) Organisch-Chemisches Institut der Universitꢀt Zꢁrich, Winterthurerstrasse 190, CH-8057 Zꢁrich
(phone: þ 41-44-6354282; fax: þ 41-44-6356812; e-mail: heimgart@oci.uzh.ch)
b
´
´
´
´
) University of Łodz, Department of Organic and Applied Chemistry, Narutowicza 68, PL-90-136 Łodz
Dedicated to Professor Valerij A. Nikolaev, Saint Petersburg, on the occasion of his 70th birthday
The reactions of 5-benzylidene-3-phenylrhodanine (2; rhodanine ¼ 2-thioxo-1,3-thiazolidin-4-one)
with diazomethane (7a) and phenyldiazomethane (7b) occurred chemoselectively at the exocyclic C¼C
bond to give the spirocyclopropane derivatives 9 and, in the case of 7a, also the C-methylated products 8
(Scheme 1). In contrast, diphenyldiazomethane (7c) reacted exclusively with the C¼S group leading to
the 2-(diphenylmethylidene)-1,3-thiazolidine 11 via [2 þ 3] cycloaddition and a ꢂtwo-fold extrusion
reactionꢃ. Treatment of 8 or 9b with an excess of 7a in refluxing CH2Cl2 and in THFat room temperature
in the presence of [Rh2(OAc)4], respectively, led to the 1,3-thiazolidine-2,4-diones 15 and 20,
respectively, i.e., the products of the hydrolysis of the intermediate thiocarbonyl ylide. On the other
hand, the reactions with 7b and 7c in boiling toluene yielded the corresponding 2-methylidene derivatives
16, 21a, and 21b. Finally, the reaction of 11 with 7a occurred exclusively at the electron-poor C¼C bond,
which is conjugated with the C¼O group. In addition to the spirocyclopropane 23, the C-methylated 22
was formed as a minor product. The structures of the products (Z)-8, 9a, 9b, 11, and 23 were established
by X-ray crystallography.
1. Introduction. – The concept of the 1,3-dipolar cycloaddition, i.e., the [2 þ 3]
cycloaddition, which has been formulated and evolved by Huisgen [1], is one of the
most powerful synthetic approaches to five-membered heterocycles [2]. The general
reactivity and the selectivities observed in the concerted reactions are nowadays well-
understood on the basis of the Frontier Molecular Orbital (FMO) theory [3]. But,
there is also an increasing number of formal 1,3-dipolar cycloadditions known, in which
the five-membered product is formed in a non-concerted, two-step mechanism [4] with
either a biradical [5] or a zwitterion [6] as the crucial intermediate.
An ideal system for the experimental and theoretical study of a concerted vs. two-
step mechanism of 1,3-dipolar cycloaddition proved to be the reactions with C¼S
dipolarophiles [7]. It has been shown that thioketones, especially aromatic thioketones,
exhibit an outstanding reactivity in cycloadditions with, e.g., nitrones [5d][8], diazo
compounds [9], and sulfines [10]. For this reason, thiocarbonyl compounds are named
ꢂsuperdipolarophilesꢃ. This high reactivity is the result of the low-lying LUMO of the
C¼S dipolarophile and the high-lying HOMO of the dipole and, therefore, is
influenced by substituents in both reaction partners [9][11].
1
)
Part of the diploma thesis of M. S. S., Universitꢀt Zꢁrich, 2005.
ꢄ 2009 Verlag Helvetica Chimica Acta AG, Zꢁrich

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In our studies on 1,3-dipolar cycloadditions with C¼S compounds, we have also
used 1,3-thiazole-5(4H)-thiones of type 1 (Fig. 1) as dipolarophiles. All reactions with
nitrile imines [12], nitrile ylides [12][13], thiocarbonyl ylides [14], carbonyl ylides [15],
azomethine ylides [16], and diazo compounds [17] occurred at the C¼S bond leading to
spirocyclic products. Similarly, organic azides and benzonitrile oxide underwent a
cycloaddition with the C¼S bond of 1, but the initially formed spirocyclic products
were not stable, and the corresponding 1,3-thiazol-5(4H)-imines [18] and 1,3-thiazol-
5(4H)-one [19], respectively, were obtained. In none of the reactions was the C¼N
bond involved.
Fig. 1. Some C¼S dipolarophiles and LUMO energies of p-bonds [3f]
Another heterocyclic C¼S compound, which in addition contains an exocyclic
C¼C and a C¼O bond, is 5-benzylidene-3-phenylrhodanine (rhodanine ¼ 2-thioxo-
1,3-thiazolidin-4-one; 2; Fig. 1). Whereas reactions with nitrile imines took place
exclusively at the C¼S group [20], thiocarbonyl ylides added onto the C¼S and C¼C
bond competitively in favor of the latter [21]. The chemoselectivity in the case of the
nitrile imines was rationalized with the low-lying LUMO of the C¼S bond [3f][20a]
(Fig. 1). Another indication of the low-lying LUMO of the C¼S group of 2 is the
chemoselectivity of the Lewis acid-catalyzed reaction with oxiranes leading to
spirocyclic products with a 1,3-oxathiolane ring [22]. However, as mentioned above,
substituents can strongly modify this general reactivity [9][11][21]. For example, it has
been shown recently that compounds 3 and 4 with conjugated C¼S groups, and diazo
compounds react selectively at the C¼S group [23], but, in the reactions with the a,b-
unsaturated thioamide 5, only dihydropyrazole-3-thiocarboxamides are formed via
addition at the C¼C bond [24]. On the other hand, the products formed in the reaction
between benzonitrile oxides and 5,5-dimethyl-3-methylidenepyrrolidine-2-thione (6),
which also possess the structure elements of an a,b-unsaturated thioamide, were
explained via initial [2 þ 3] cycloaddition at the C¼S bond and subsequent reactions
[25].
Here, we describe the results of 1,3-dipolar cycloadditions of 2 with CH2N2,
PhCHN2, and Ph2CN2.
2. Results and Discussion. – 2.1. Reactions of 2 with Diazomethanes. In analogy to
the reactions of diazo compounds with 4,4-dimethyl-2-phenyl-1,3-thiazole-5(4H)-
thione (1) [17b – d], we chose CH2N2 (7a), PhCHN2 (7b), and Ph2CN2 (7c) as 1,3-

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dipolar species for the reactions with 2 (Scheme 1). In the case of 1, all reactions took
place with the C¼S bond exclusively and were rationalized via an initial [2 þ 3]
cycloaddition leading to an unstable spirocyclic 2,5-dihydro-1,3,4-thiadiazole deriva-
tive. Subsequent elimination of N2 generated in situ reactive thiocarbonyl ylides, which
reacted further to give spirocyclic thiiranes via 1,3-dipolar ring closure (with 7b and 7c)
or the corresponding methylidene derivative (with 7a) after elimination of sulfur. On
the other hand, the [2 þ 3] cycloadducts could be isolated when 1 was reacted with 2-
diazopropane [17a] or (t-Bu)2CN2 [17c].
Scheme 1
The reaction of 2 with 7a was started by dropwise addition of a 5m solution of 7a in
Et2O to a solution of 2 in THF at ꢀ 208 under Ar. After a few min, 2 was completely
consumed, and a new product was detected by TLC. During the warming of the mixture
to room temperature, this intermediate disappeared, and two new products 8 and 9a
were formed, which were separated by column chromatography and isolated in 65 and
35% yield, respectively. Elemental analyses and mass spectra indicated that the
isomeric compounds were CH2 adducts of 2. Furthermore, the 13C-NMR spectra
evidenced that in both products the C¼S and the C¼O group were retained, i.e., the
reaction of 7a had occurred at the benzylidene group. Whereas the spectroscopic data
of the minor product were in accordance with the spirocyclic structure 9a, the major
product exhibited the signals of a Me group at 2.76 (1H) and 21.8 (13C)2) (Scheme 1).
Finally, the structures (Z)-8 and 9a were unambiguously established by X-ray
crystallography (Fig. 2). The crystal structures showed clearly that the exocyclic
The 1H-NMR spectrum of crude 8 also showed a minor signal at 2.35 ppm, which indicates the
presence of the (E)-isomer as a minor component (ca. 25%); (Z)-8 was obtained in pure form by
recrystallization from AcOEt/pentane.
2
)

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Fig. 2. ORTEP Plots [26] of the molecular structures of a) one of the two symmetry-independent
molecules of (Z)-8 and b) 9a (arbitrary numbering of the atoms; 50% probability ellipsoids)
C¼C bond of (Z)-8 is (Z)-configured, and the Ph residue on the cyclopropane ring of
9a is cis-oriented with respect to the S-atom of the 1,3-thiazolidine.
All attempts to isolate the initially formed product were in vain, although it was
stable in solution at ꢀ 208. Attempted crystallization and even concentration of the
solution by evaporation of the solvent led to the formation of 8 and 9a. The 1H-NMR
spectrum of the crude mixture showed a triplet at 3.95 ppm and a doublet at 5.28 ppm in
a ratio of ca. 1:2. These signals could be assigned to the PhCHꢀCH2 fragment of the
[2 þ 3] cycloadduct of 7a at the benzylidene group, i.e., the spirocyclic 4,5-dihydro-3H-
pyrazole 12, but not the opposite regioisomer (Scheme 2). The ratio of the two products
8 and 9a was almost independent of the temperature of the reaction. Furthermore, the
reaction in the presence of [Rh2(OAc)4], i.e., the reaction of 2 with the carbenoid, gave
the same products 8 and 9a, which were isolated in 64 and 34% yield, respectively.
In line with our expectation, the reaction of 2 with 7b was more sluggish and,
therefore, was performed in toluene at 08. No [2 þ 3] cycloadduct could be detected,
and only a single product, 9b, was obtained in 91% yield (Scheme 1). Its structure was
again determined by X-ray crystallography (Fig. 3). The orientation of the two Ph
groups on the cyclopropane ring was determined as trans.

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Helvetica Chimica Acta – Vol. 92 (2009)
Scheme 2
Surprisingly, 7c reacted with 2 in a different way. Under mild conditions, in toluene
at room temperature or at 508, no reaction with 2 was observed but only a slow
decomposition of 7c. Addition of LiClO4 or [Rh2(OAc)4] led to a faster decomposition
of 7c, but again no reaction with 2 took place. The major product in the [Rh2(OAc)4]-
catalyzed reaction was benzophenonazine (10)3), and tetraphenylethene was identified
in the mixture from the reaction with LiClO4 by 13C-NMR spectroscopy and mass
spectroscopy. Finally, a solution of 2 and 1.3 equiv. of 7c in toluene was heated under
reflux overnight. Evaporation of the solvent and washing of the residue with boiling
hexane gave 11 in 93% yield (Scheme 1). The structure was confirmed by the
13C-NMR, elemental-analysis, and MS data, and was established by X-ray crystallog-
raphy (Fig. 3). In contrast to the reactions with 7a and 7b, 7c underwent a [2 þ 3]
cycloaddition with the C¼S group of 2, followed by a ꢂtwo-fold extrusion reactionꢃ
(Barton – Kellogg reaction) [30].
Whereas the transformation 2 þ 7c ! 11 is the expected one, in which the diazo
compound reacts with the C¼S group of 2 in analogy to previously described reactions
with 1 [17], the formation of 8 and 9 deserves a comment. In reactions of 2 with
thiocarbonyl ylides, it has been observed that the C¼C bond is the preferred
dipolarophile [21]. This also holds true for the reactions with 7a and 7b. Therefore, the
spirocyclic 4,5-dihydro-3H-pyrazole 12 is a reasonable intermediate in the case of 7a,
which, via elimination of N2, could lead to 13 (Scheme 2). Ring closure via 1,3-
3
)
The formation of 10 from 7c in the presence of [Rh2(OAc)4] has been described repeatedly [27].
Because the 13C-NMR data of our compound did not correspond to those described in the literature
[28], we synthesized 10 independently from benzophenone and NH2NH2 · H2O in EtOH at 1608
according to [29] and from 7c according to the procedure described in [27b]. The 13C-NMR data
given in [28] correspond to those of benzophenone.

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Fig. 3. ORTEP Plots [26] of the molecular structures of a) 9b and b) 11 (arbitrary numbering of the
atoms; 50% probability ellipsoids)

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cyclization then yields the spirocyclic cyclopropane 9a, whereas the formation of 8 can
be rationalized by a 1,2-H shift in the intermediate 13. Alternatively, the diazo
compound could react with the benzylidene group of 2 in a Michael-type reaction to
give 14. Elimination of N2 could also lead to the intermediate 13 or directly to 8 and 9a.
2.2. Reactions of 8, 9b, and 11 with Diazomethanes. The major product of the
reaction of 2 with 7a, (Z)-84), which still offers three p-bonds as dipolarophiles, was
dissolved in CH2Cl2, and a 0.5m solution of 7a in Et2O (20 equiv.) was added
portionwise under reflux under Ar. After stirring for 24 h, chromatographic workup
gave, in addition to recovered (Z)-8, the corresponding crude 1,3-thiazolidine-2,4-
dione (Z)-15, but no cycloadduct could be detected (Scheme 3). After recrystallization
from EtOH, 34% of (Z)-155) was isolated.
Scheme 3
The analogous treatment of a solution of (Z)-84) in boiling toluene with an excess of
7b for 6 h led to a mixture of the starting material (Z)-8 (34%) and the 2-benzylidene
derivative (Z,Z)-16 as the major product (38%, Scheme 3). The 1H-NMR spectrum of
the product indicated the presence of four isomeric compounds, the ratio of which was
determined by GC/MS as 100 :30 :15 :10. Tentatively, we propose that the major isomer
is (Z,Z)-16.
Obviously, both products (Z)-15 and (Z,Z)-16 were formed via the reaction of the
diazo compound with the C¼S group of (Z)-8. The change in the reactivity from 2 to 8
can be rationalized by a steric effect, i.e., the addition onto the exocyclic C¼C bond of
8 is less favored because of the presence of an additional Me group. On the other hand,
the C¼C bond of 8 is less electrophilic, i.e., the LUMO is lying higher, and the reaction
with the diazoalkane as an electron-rich 1,3-dipole [3d] is slower. Therefore, we
propose that 7a and 7b reacted with the C¼S group of (Z)-8 in a [2 þ 3] cycloaddition
to give 17. In the case of R ¼ Ph, ꢂtwo-fold extrusionꢃ of N2 and S yielded (Z,Z)-16 as the
final product (Scheme 4). The intermediate thiirane 19 seems not to be stable under the
reaction conditions (boiling toluene). The formation of (Z)-15 is the result of the initial
capture of H2O by the thiocarbonyl ylide 18 and subsequent elimination of MeSH.
In an additional series of experiments, the reactions of 9b with 7a – 7c were studied
with the expectation that additions at the C¼S bond will occur. The reaction with 7a
(4 equiv.) was carried out at room temperature in the presence of [Rh2(OAc)4] and
4
)
)
The used material was a mixture of (Z)-8 and ca. 25% of the (E)-isomer (see Footnote 2).
According to the H-NMR spectrum, the product was also a ca. 3:1 mixture of (Z)- and (E)-15.
1
5

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Scheme 4
LiClO4 in THF. Chromatographic workup after 24 h gave the spirocyclic-1,3-
thiazolidine-2,4-dione 20 (22%, Scheme 5) and 46% of the starting material. On the
other hand, the reactions of 9b with 7b and 7c in boiling toluene gave the expected 2-
methylidene derivatives 21a and 21b in 53 and 82% yield, respectively.
Scheme 5
The structures of 21a and 21b were deduced from their MS and 13C-NMR data and,
in the case of 21b, also from elemental analysis, which all indicated the absence of the
C¼S group. The proposed (Z)-configuration of the benzylidene group of 21a could not
be confirmed unambiguously by the NOE experiment: the benzylidene H-atom
showed a NOE with an aromatic H-atom, but the latter could not be assigned with
certainty to a specific Ph group.

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Finally, the reaction of 11 with 7a in toluene at 508 yielded a mixture of the C-
methylated product (Z)-226) and the spirocyclopropane derivative 23 in a ratio of ca.
1:10 besides 39% of unchanged starting material (Scheme 6). The (Z)-configuration of
the major isomer of 22 was assigned in analogy to (Z)-8, and the structure of 23 was
established unambiguously by X-ray crystallography (Fig. 4).
Scheme 6
Fig. 4. ORTEP Plot [26] of the molecular structure of one of the two symmetry-independent molecules of
23 (arbitrary numbering of the atoms; 50% probability ellipsoids)
6
)
Mixture of two isomers.

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3. Conclusions. – The presented results of the reactions of CH2N2 (7a), PhCHN2
(7b), and Ph2CN2 (7c) with 5-benzylidene rhodanine 2, which possesses C¼S, C¼C,
and C¼O groups as potential dipolarophiles, show that the reactivities of the C¼S and
the C¼C group are quite similar, i.e., the C¼S group of 2 shows no ꢂsuperdipolar-
ophilicꢃ character. An analogous observation has been reported earlier for the C¼S
group of an a,b-unsaturated thioamide [24]. The preferred dipolarophile in the
reactions with 7a and 7b is the conjugated benzylidene group. Surprisingly, a C-
methylation leading to 8 competes with the cyclopropanation to give 9. On the other
hand, 7c reacts chemoselectively with the C¼S group of 2 yielding the 2-methylidene
derivative 11 via [2 þ 3] cycloaddition and a subsequent ꢂtwo-fold extrusion reactionꢃ.
This result indicates comparable dipolarophilicities of the C¼S and C¼C bonds of 2,
and, accordingly, the chemoselectivity of the reaction depends on the diazo compound.
It is most likely that steric as well as electronic effects play a role. This is also reflected
in the reactions of 7a and 7b with (Z)-8, which still possesses C¼S, C¼C, and C¼O
groups, the only difference to 2 being the additional Me group at the benzylidene C¼C
bond. In this case, both diazo compounds reacted with the C¼S group, leading to the 2-
benzylidene-1,3-thiazolidin-4-one (Z,Z)-16 in the reaction with 7b. With 7a, only the
product of the hydrolysis of an intermediate – most likely the thiocarbonyl ylide 18 –
was obtained. In the reactions with 9b, the C¼S group is the most reactive
dipolarophile for all three diazo compounds 7a, 7b, and 7c.
In comparison with thioketones, the C¼S groups of 2, 8, and 9b, which may be
classified as dithiocarbamates, are much less reactive, and relatively harsh conditions
are necessary for the reaction with diazo compounds. As a result, the initially formed
[2 þ 3] cycloadduct could not be isolated in any of the experiments.
We thank the analytical sections of our institute for spectra and analyses, and F. Hoffmann-La Roche
AG, Basel, for financial support.
Experimental Part
1. General. TLC: Merck 60 F254 SiO2-coated Al-plates, 0.2 mm; detection of the substances on the
TLC plates under UV light (l 254 nm) or with KMnO4 soln. Column chromatography (CC): SiO2 60, 43 –
63 mm (ZEOCHEM, Chemie Uetikon). HPLC: Varian 2510 pump and a UV detector Varian 2550; CC
250/4.6 Nucleosil 100-7 column (Macherey-Nagel); indicated are the retention time and the rel. intensity.
M.p.: Olympus microscope with TECON-Controller Series 150 instrument; uncorrected. IR Spectra:
1
Perkin-Elmer 1600 FT-IR spectrophotometer; in KBr. H- and 13C-NMR Spectra: Bruker AVX-300 or
Bruker ARX-300 instrument (300 and 75.5 MHz, resp.), in CDCl3; multiplicity of C-atoms from DEPT
spectra. MS: Finnigan MAT-95 (EI, 70 eV, or CI (NH3)) or FinniganTSQ-700 (ESI) instrument. GC/MS:
Hewlett-Packard 5890 Series II instrument. Elemental analyses were performed by the Mikroanalytisches
Laboratorium des Organisch-Chemischen Instituts der Universitꢀt Zꢁrich (Elementar Vario EL
instrument).
2. Starting Materials. CH2N2 (7a) was prepared from N-nitrosomethylurea according to [31],
PhCHN2 (7b) from benzaldehyde tosylhydrazone according to [32], and Ph2CN2 (7c) from benzophe-
none hydrazone according to [33]. The 5-benzylidene-3-phenyl-2-thioxo-1,3-thiazolidin-4-one (2) was
prepared from phenylisothiocyanate and thioglycolic acid, followed by condensation with benzaldehyde
according to [34] (see also [20b][21]): M.p.: 190 – 1948 (EtOH). IR: 3057w, 3023w, 1717vs, 1603m, 1594s,
1572w, 1492m, 1453w, 1446m, 1357s, 1316w, 1285w, 1251vs, 1185w, 1174s, 1156s, 1070w, 1036w, 1025w,
933w, 824w, 758m, 732m, 691m, 681s, 632w. 1H-NMR: 7.80 (s, ¼CH); 7.59 – 7.47 (m, 8 arom. H); 7.31 – 7.27
(m, 2 arom. H). 13C-NMR: 193.3 (s, C¼S); 167.5 (s, C¼O); 134.8, 133.3 (2s, 2 arom. C); 133.3, 130.7,
130.6, 129.6, 129.5, 129.3, 128.3 (7d, 10 arom. CH, ¼CH); 123.3 (s, C(5)).

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3. Reactions of 2 with 7a – 7c. 3.1. Reaction with 7a. To a stirred soln. of 2 (0.149 g, 0.501 mmol) in abs.
THF (ca. 6 ml) at ꢀ 208 under Ar was added dropwise 2 ml of a 0.5m soln. of 7a in Et2O. Control by TLC
showed that 2 was completely consumed, and an unstable product was formed, which, on warming the
mixture to r.t., reacted further to give two new products. The mixture was adsorbed on SiO2, and CC
(hexane/AcOEt 15 :1) gave 0.102 g (65%) of 5-[(methyl)(phenyl)methylidene]-2-thioxo-1,3-thiazolidin-
4-one (8) and 54 mg (35%) of cis-1,6-diphenyl-5-thioxo-4-thia-6-azaspiro[2.4]heptan-7-one (9a). The
products were purified by recrystallization from EtOH and hexane, resp.
Data of 8 (mixture of isomers). Yellow crystals. M.p. 165 – 1678. Rf (hexane/AcOEt 5 :1): 0.44.
HPLC (hexane/EtOH 30 :1): 5.16 (100, (Z)-8), 5.37 (33, (E)-8). IR: 1708s, 1589m, 1569w, 1496s, 1488m,
1443w, 1348s, 1318w, 1291w, 1235vs, 1177s, 1168s, 1074w, 1061w, 1026w, 983w, 865w, 762w, 727s, 698m,
1
688m, 639w. H-NMR: 7.55 – 7.27 (m, 10 arom. H); 2.76 (s, Me, (Z)-8); 2.35 (s, Me, (E)-8). 13C-NMR:
194.2 (s, C¼S); 165.8 (s, C¼O); 150.9 (s, Ph(Me)C); 142.0, 135.2 (2s, 2 arom. C); 129.7, 129.5, 129.4,
129.3, 129.0, 128.3, 128.0, 127.3, 126.6 (9d, 10 arom. C, (Z)- and (E)-8); 123.1 (s, C(5)); 21.8 (q, Me). EI-
MS: 313 (7), 312 (13), 311 (65, Mþ), 295 (9), 176 (6, [M ꢀ CSNPh]þ), 149 (13), 148 (100, [M ꢀ
CONPhCS]þ), 147 (18), 135 (9), 115 (11), 104 (8), 103 (9), 77 (11, Phþ). Anal. calc. for C17H13NOS2
(311.43): C 65.56, H 4.21, N 4.50, S 20.59; found: C 65.43, H 4.13, N 4.41, S 20.46.
Suitable crystals of (Z)-8 for the X-ray crystal-structure determination were obtained by isothermal
distillation of pentane into a soln. of 8 in AcOEt.
Data of 9a. Colorless crystals. M.p. 140 – 1428. Rf (hexane/AcOEt 5 :1): 0.38. IR: 1721vs, 1593w,
1497m, 1455w, 1424w, 1372m, 1351s, 1318w, 1241vs, 1178m, 1154w, 1129m, 1073w, 1055w, 1046w, 1030w,
976m, 834w, 777w, 757w, 728vs, 708w, 696m, 688m, 629w. 1H-NMR: 7.55 – 7.47, 7.42 – 7.33, 7.28 – 7.25, 7.25 –
7.17 (4m, 10 arom. H); 3.37 (dd, 3J(cis) ¼ 9.7, 3J(trans) ¼ 8.1, PhCH); 2.42 (dd, 2J ¼ 5.9, 3J(cis) ¼ 9.7, 1 H of
2
3
CH2); 2.08 (dd, J ¼ 5.9, J(trans) ¼ 8.1, 1 H of CH2). 13C-NMR: 199.5 (s, C¼S); 175.3 (s, C¼O); 135.2,
134.3 (2s, 2 arom. C); 129.6, 129.5, 129.0, 128.4, 128.3, 127.9 (6d, 10 arom. C); 41.4 (s, spiro-C); 34.9 (d,
PhCH); 22.7 (t, CH2). EI-MS: 313 (11), 312 (21), 311 (100, Mþ), 295 (16), 176 (35), 148 (28, [M ꢀ
CONPhCS]þ), 147 (26), 136 (10), 135 (13), 115 (47, [M ꢀ CONPhCSS]þ), 104 (13, [PhCHCH2]þ), 91
(9, [PhCH2]þ), 77 (14, Phþ). Anal. calc. for C17H13NOS2 (311.43): C 65.56, H 4.21, N 4.50, S 20.59; found:
C 65.66, H 4.16, N 4.47, S 20.35.
Suitable crystals of 9a for the X-ray crystal-structure determination were obtained by isothermal
distillation of pentane into a soln. of 9a in 1,2-dimethoxyethane.
3.2. Reaction with 7b. To a stirred suspension of 2 (0.595 g, 2.001 mmol) in toluene (ca. 10 ml) at 08
under Ar were added 80 ml of a 30 mm soln. of 7b (1.2 equiv.) in toluene. After 48 h at r.t., 2 was
completely consumed (TLC). The solvent was evaporated, and the residue was crystallized from EtOH,
yielding 0.703 g (91%) of trans-1,2,6-triphenyl-5-thioxo-4-thia-6-azaspiro[2.4]heptan-7-one (9b). Pale
yellow crystals. M.p. 222 – 2258. Rf (hexane/AcOEt 5 :1): 0.31. IR: 3057w, 1731vs, 1593w, 1495s, 1446w,
1339vs, 1316m, 1279w, 1226vs, 1197s, 1180m, 1145m, 1115m, 1075w, 1027w, 980m, 954w, 816w, 758w, 748m,
737s, 697s, 632w. 1H-NMR: 7.47 – 7.26 (m, 13 arom. H); 7.13 – 7.10 (m, 2 arom. H); 4.03 (d, 3J ¼ 8.9,
3
PhCH); 3.68 (d, J ¼ 8.9, PhCH). 13C-NMR: 198.6 (s, C¼S); 171.6 (s, C¼O); 134.9, 134.2, 132.0 (3s, 3
arom. C); 129.4, 129.3, 129.02, 128.99, 128.4, 128.3, 128.2, 128.0 (8d, 15 arom. C); 46.7 (s, spiro-C); 41.3,
37.7 (2d, 2 PhCH). EI-MS: 389 (12), 388 (26), 387 (100, Mþ), 252 (14), 251 (11), 224 (11), 223 (13, [M ꢀ
CONPhCS]þ), 218 (11), 192 (15), 191 (34, [M ꢀ CONPhCSS]þ), 178 (8), 165 (7), 147 (5), 135 (8), 91 (7,
[PhCH2]þ), 77 (7, Phþ). Anal. calc. for C23H17NOS2 (387.53): C 71.29, H 4.42, N 3.61, S 16.65; found: C
17.15, H 4.46, N 3.56, S 16.64.
Suitable crystals of 9b for the X-ray crystal-structure determination were obtained by isothermal
distillation of pentane into a soln. of 9b in 1,2-dimethoxyethane.
3.3. Reaction with 7c. To a stirred suspension of 2 (0.155 g, 0.521 mmol) in toluene (ca. 5 ml) at r.t.
under Ar were added 8 ml of a 0.1m soln. of 7c (1.3 equiv.) in benzene. After heating to reflux overnight,
the solvent was evaporated, and the residue was washed with boiling hexane to remove starting material
and side products. Yield of (Z)-5-benzylidene-2-(diphenylmethylidene)-3-phenyl-1,3-thiazolidin-4-one
(11): 0.210 g (93%). Yellow crystals. M.p. 255 – 2588. Rf (hexane/AcOEt 5 :1): 0.41. IR: 3046w, 2924w,
2852w, 1696vs, 1604vs, 1491vs, 1455w, 1442s, 1353vs, 1309w, 1287m, 1247vs, 1209w, 1175s, 1164m, 1130m,
1071m, 1051m, 1026m, 876w, 837w, 777w, 761s, 750m, 733m, 694vs, 643m, 606m. 1H-NMR: 7.61 (s, ¼CH);
7.49 – 7.28 (m, 10 arom. H); 7.12 – 6.98 (m, 5 arom. H); 6.86 – 6.81 (m, 3 arom. H); 6.75 – 6.72 (m, 2 arom.

Helvetica Chimica Acta – Vol. 92 (2009)
1811
H). 13C-NMR: 167.6 (s, C¼O); 141.5, 138.8, 136.8, 134.7, 130.9 (5s, 4 arom. C, Ph2C); 130.4, 130.1, 129.7,
128.7, 128.6, 128.2, 127.8, 127.5, 127.2, 127.1, 126.5, 126.3 (12d, 20 arom. CH, ¼CH); 123.5, 119.7 (2s, C(2),
C(5)). CI-MS (NH3): 449 (21, [M þ NH4]þ), 434 (16), 433 (34), 432 (100, [M þ H]þ). Anal. calc. for
C29H21NOS (431.55): C 80.71, H 4.90, N 3.25, S 7.43; found: C 80.58, H 5.08, N 3.15, S 7.34.
Suitable crystals of 11 for the X-ray crystal-structure determination were obtained by isothermal
distillation of pentane into a soln. of 11 in 1,2-dimethoxyethane.
4. Synthesis of Benzophenonazine (10). 4.1. Synthesis from Ph2CN2 (7c). According to [27c], to a
soln. of [Rh2(OAc)4] (4.3 mg, 9.0 mmol) in abs. THF (8 ml) at 558 were added 7.5 ml of the 0.1m soln. of 7c
(0.75 mmol). The mixture was filtered through SiO2 and recrystallized from EtOH: 159 mg (59%) of 10.
M.p. and the UV spectrum are in accordance with reported data [34]. M.p. 168 – 1698. Rf (hexane/AcOEt
5 :1): 0.53. IR: 3083w, 3056w, 3022w, 2926w, 1587m, 1564m, 1488m, 1443s, 1320s, 1294w, 1177w, 1159w,
1
1076w, 1027w, 999w, 983w, 956s, 910w, 774s, 764s, 692vs, 667m, 655s, 613w. H-NMR: 7.50 – 7.24 (m, 20
arom. H). 13C-NMR: 159.1 (s, 2 ¼CNꢀ); 138.0, 135.4 (2s, 4 arom. C); 129.6, 129.2, 128.6, 127.9, 127.8 (5d,
20 arom. CH). EI-MS: 361 (21), 360 (76, Mþ), 359 (35), 284 (21), 283 (100, [M ꢀ Ph]þ), 257 (14), 256
(13), 180 (29), 165 (25), 77 (13).
4.2. Synthesis from Benzophenone. According to [29], to a soln. of benzophenone (1.094 g,
6.003 mmol) in EtOH (ca. 15 ml), NH2NH2 · H2O (80%, 0.180 g, 2.87 mmol) and 3 drops of AcOH were
added. The mixture was heated to 1608 for 5 h in an autoclave. Evaporation to dryness and crystallization
from EtOH gave 0.203 g (20%) of 10.
5. Reaction of Some 1:1 Adducts with an Additional Diazo Component. 5.1. Reaction of 8 with 7a. A
stirred soln. of 87) (0.157 g, 0.504 mmol) in CH2Cl2 (ca. 10 ml) under Ar was heated to reflux. Within
24 h, 20 ml of the ca. 0.5m soln. of 7a (10 mmol, 20 equiv.) were added portionwise. Then, the solvent was
evaporated, the residue adsorbed on SiO2 and separated by CC (hexane/AcOEt 20 :1) to yield 8 (28%)
and crude 5-[(methyl)(phenyl)methylidene]-3-phenyl-1,3-thiazolidin-2,4-dione (15; 62 mg, 42%)8).
Crystallization from EtOH gave 34% of 15, which was still contaminated with traces of 8.
Data of 158). Colorless crystals. M.p. 117 – 1278. Rf (hexane/AcOEt 5 :1): 0.41. 1H-NMR: 7.48 – 7.25
(m, 10 arom. H); 2.69 (s, Me, (Z)-15, major product); 2.25 (s, Me, (E)-15, minor product). 13C-NMR
(signals of the major product (Z)-15): 163.7 (s, C¼O(amide)); 151.0 (s, C¼O(thiocarbamate)); 141.2,
139.4, 131.9 (3s, 2 arom. C, Ph(Me)C); 128.5, 128.3, 128.1, 128.0, 127.9, 127.5, 127.4, 127.3, 126.5, 125.7
(10d, 10 arom. CH); 115.1 (s, C(5)); 28.7 (q, Me). ESI-MS (MeOH þ NaI): 334 (20, [M(8) þ Na]þ), 318
(100, [M(15) þ Na]þ).
5.2. Reaction of 8 with 7b. A soln. of 87) (0.160 g, 0.515 mmol) in toluene (40 ml) under Ar was
heated to reflux, and 80 ml of the ca. 30 mm soln. of 7b (2.4 mmol, 4.8 equiv.) was added in 4 portions
within 6 h. After cooling to r.t., the solvent was evaporated, the residue was adsorbed on SiO2 and
separated by CC (hexane/AcOEt 20 :1). In addition to 8 (55 mg, 34%), crude 16 (73 mg, 38%) was
obtained, which was crystallized from CH2Cl2/hexane to give a mixture of diastereoisomers of 2-
benzylidene-5-[(methyl)(phenyl)methylidene]-3-phenyl-1,3-thiazolidin-4-one (16). Colorless crystals.
M.p. 84 – 878. Rf (hexane/AcOEt 5 :1): 0.41. HPLC (hexane/EtOH 25 :1): 5.27 (major product, (Z,Z)-
16), 4.82, 5.78, and 7.05 ((E,Z)-, (Z,E)-, and (E,E)-16, resp.). IR: 3059m, 2924s, 2853m, 1736vs, 1677vs,
1592vs, 1571s, 1492vs, 1454s, 1441s, 1348vs, 1290m, 1239vs, 1195vs, 1157vs, 1072m, 1028s, 1002m, 985s,
915w, 868w, 843m, 814w, 762s, 737s, 728s, 692vs, 664w, 655w, 638m, 619w, 603w. 1H-NMR: 7.58 – 7.14 (m, 15
arom. H); 2.78 (s, Me, (Z,Z)-16, major product); 2.71, 2.35, and 2.17 (3s, Me of (Z,E)-, (E,Z)-, and E,E)-
16, resp.). 13C-NMR: 164.6 (s, C¼O); 152.0, 143.5, 142.2, 135.3, 134.6, 132.8 (6s, 3 arom. C, Ph(Me)C);
129.8, 129.7, 129.4, 129.2, 129.0, 128.9, 128.9, 128.7, 128.4, 128.2, 127.6, 127.4, 126.7, 126.5, 125.7 (15d, 15
arom. C); 125.7 (s, C(5)); 120.5 (s, C(2)); 103.1 (d, ¼CH); 22.6, 20.7 (2q, Me). ESI-MS (MeOH þ NaI):
410 (10), 392 (100, [M þ Na]þ). GC/EI-MS: 14.1 – 14.4 min (10): 295 (4), 281 (14), 207 (100, [M ꢀ CO ꢀ
SCCHPh]þ), 191 (9), 148 (97, [M ꢀ CONPhCCHPh]þ), 133 (12), 114 (12), 103 (16), 96 (14), 91 (12), 77
(17, Phþ); 14.4 – 14.8 min (100): 295 (15), 281 (3), 207 (31), 191 (3), 148 (100), 133 (6), 114 (15), 103 (17),
96 (4), 91 (10), 77 (19); 15.3 – 15.5 min (15): 281 (17), 256 (22), 253 (25), 207 (100), 201 (20), 198 (10),
174 (16), 159 (14), 148 (5), 133 (17), 104 (25), 91 (18), 77 (22); 15.6 – 15.8 min (30): 281 (17), 255 (55),
7
)
)
Mixture of (Z)- and (E)-8 (ca. 3:1).
Mixture of (Z)- and (E)-15 (ca. 3:1) and contaminated with some starting material.
8

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Helvetica Chimica Acta – Vol. 92 (2009)
253 (62), 207 (100), 199 (47), 191 (8), 185 (8), 174 (39), 159 (39), 148 (9), 133 (17), 121 (10), 104 (55), 91
(63), 77 (40).
5.3. Reaction of 9b with 7a. To a mixture of 9b (0.0965 g, 0.249 mmol), 2 mg [Rh2(OAc)4 · H2O]
(4 mmol, 0.2 equiv.), and 35 mg LiClO4 (0.329 mmol, 1.3 equiv.) in THF (5 ml) under Ar was added 1 ml
of the ca. 0.5m soln. of 7a (2 mmol, 4 equiv.). After 4 h, the addition was repeated, and, after stirring for
24 h at r.t., the mixture was filtered through cotton, the solvent was evaporated, and the residue was
adsorbed on SiO2 and separated by CC (hexane/AcOEt 15 :1). Besides 9b (44 mg, 46%), trans-1,2,6-
triphenyl-4-thia-6-azaspiro[2.4]heptane-5,7-dione (20, 20 mg, 22%) was obtained and recrystallized from
CH2Cl2/hexane. Colorless crystals. M.p. 159 – 1608. Rf (hexane/AcOEt 5 :1): 0.31. IR: 3063w, 3038w,
1747s, 1722vs, 1699vs, 1602m, 1593m, 1493s, 1448m, 1424w, 1368vs, 1291w, 1245vs, 1199m, 1162vs, 1146s,
1131m, 1073w, 1026w, 1005w, 991w, 955w, 849m, 753vs, 737s, 694vs, 657w, 630w, 607w. 1H-NMR: 7.46 – 7.26
(m, 13 arom. H); 7.21 – 7.09 (m, 2 arom. H); 3.97 (d, 3J ¼ 8.9, PhCH); 3.56 (d, 3J ¼ 8.9, PhCH). 13C-NMR:
170.1, 169.6 (2s, 2 C¼O); 134.4, 132.7, 132.6 (3s, 3 arom. C); 129.3, 129.01, 128.99, 128.9, 128.4, 128.3,
128.0, 127.9, 127.1 (9d, 15 arom. C); 44.1 (s, spiro-C); 40.2, 35.9 (2d, 2 PhCH). ESI-MS (CH2Cl2/MeCN
1:1 þ NaI): 410 (10, [M(9a) þ Na]þ), 394 (100, [M(20) þ Na]þ).
5.4. Reaction of 9b with 7b. A soln. of 9b (0.101 g, 0.260 mmol) in toluene (5 ml) under Ar was
heated to reflux, and 40 ml of the ca. 30 mm soln. of 7b (1.2 mmol, 4.8 equiv.) were added portionwise
during 7 h. After cooling to r.t., the solvent was evaporated, and the residue was adsorbed on SiO2 and
separated by CC (hexane/AcOEt 15 :1). Besides 9b (37 mg, 32%), trans-(Z)-5-benzylidene-1,2,6-
triphenyl-4-thia-6-azaspiro[2.4]heptan-7-one (21a, 61 mg, 53%) was obtained, which was recrystallized
from CHCl3/hexane. Colorless crystals. M.p. 224 – 2288. Rf (hexane/AcOEt 5 :1): 0.31. IR: 3059w, 3030w,
2923w, 1753w, 1706vs, 1620vs, 1572s, 1495vs, 1446s, 1377vs, 1282w, 1233s, 1201s, 1180s, 1156m, 1120w,
1070w, 1027m, 1005w, 989w, 796m, 750s, 734s, 695vs, 630w, 616w. 1H-NMR: 7.49 – 7.07 (m, 20 arom. H);
5.73 (s, ¼CH); 3.82 (d, 3J ¼ 8.6, PhCH); 3.31 (d, 3J ¼ 8.6, PhCH). 13C-NMR: 168.6 (s, C¼O); 136.4, 135.8,
135.5, 135.2, 133.8 (5s, 4 arom. C, C(5)); 129.7, 128.9, 128.8, 128.7, 128.6, 128.5, 128.4, 128.1, 127.7, 127.4,
127.1, 125.7 (12d, 20 arom. C); 104.6 (d, ¼CH); 43.1 (s, spiro-C); 40.5, 34.8 (2d, 2 PhCH). ESI-MS
(MeOH/CH2Cl2 3 :1 þ NaI): 468 (100, [M þ Na]þ), 446 (12, Mþ).
5.5. Reaction of 9b with 7c. To a soln. of 9b (0.197 g, 0.509 mmol) in toluene (25 ml) under Ar was
added 10 ml of the ca. 0.1m soln. of 7c (1.0 mmol, 2 equiv.), and the mixture was heated to reflux. After
2 h, an additional 15 ml of the soln. of 7c (1.5 mmol, 3 equiv.) were added, and heating was continued for
2 h. Then, the mixture was cooled to r.t., the solvent was evaporated, and the residue adsorbed on SiO2.
CC gave 219 mg (82%) of trans-5-(diphenylmethylidene)-1,2,6-triphenyl-4-thia-6-azaspiro[2.4]heptan-7-
one (21b), which was recrystallized from CH2Cl2/hexane. Colorless crystals. M.p. 223 – 2258. Rf (hexane/
AcOEt 5 :1): 0.41. IR: 3060w, 3029m, 1705vs, 1597vs, 1494vs, 1452m, 1442s, 1340vs, 1309m, 1289s, 1247m,
1224vs, 1196w, 1180w, 1154m, 1127m, 1073m, 1030m, 1002w, 982w, 758vs, 730m, 698vs, 647m, 604m.
1H-NMR: 7.48 – 7.46 (m, 2 arom. H); 7.40 – 7.19 (m, 13 arom. H); 6.94 – 6.81 (m, 8 arom. H); 6.79 – 6.69
3
3
(m, 2 arom. H); 3.76 (d, J ¼ 8.4, PhCH); 3.28 (d, J ¼ 8.4, PhCH). 13C-NMR: 170.7 (s, C¼O); 141.7,
139.2, 137.0, 135.2, 134.5, 132.0 (6s, 5 arom. C, Ph2C); 130.3, 129.9, 128.9, 128.6, 128.43, 128.38, 128.2, 127.9,
127.5, 127.2, 126.9, 126.5, 126.1 (13d, 25 arom. C); 121.4 (s, C(5)); 43.8 (s, spiro-C); 40.7, 33.9 (2d,
2 PhCH). CI-MS (NH3): 539 (15, [M þ NH4]þ), 522 (100, [M þ H]þ). Anal. calc. for C36H27NOS
(521.67): C 82.88, H 5.22, N 2.68, S 6.15; found: C 82.70, H 4.99, N 2.65, S 6.02.
5.6. Reaction of 11 with 7a. A soln. of 11 (0.217 g, 0.503 mmol) in toluene (60 ml) under Ar was
heated to 508, and 16 ml of the ca. 0.5m soln. of 7a (2 mmol, 4 equiv.) were added portionwise within 24 h.
After evaporation of the solvent, the residue was extracted with boiling hexane, and 85 mg (39%) of 11
were recovered. The hexane fraction was evaporated, and the residue was adsorbed on SiO2 and
separated by CC (hexane/AcOEt 20 :1): 8 mg (4%) of 5-[(methyl)(phenyl)methylidene]-2-(diphenyl-
methylidene)-3-phenyl-1,3-thiazolidin-4-one (22) and 97 mg (43%) of cis-5-(diphenylmethylidene)-1,6-
diphenyl-6-aza-4-thiaspiro[2.4]heptan-7-one (23). The latter was recrystallized from CH2Cl2/hexane.
1
Data of 22 (impure). Colorless crystals. M.p. 160 – 1958. Rf (hexane/AcOEt 5 :1): 0.47. H-NMR:
7.45 – 7.15 (m, 10 arom. H); 7.10 – 6.89 (m, 5 arom. H); 6.83 – 6.80 (m, 3 arom. H); 6.73 – 6.67 (m, 2 arom.
H); 2.66 (s, Me, (Z)-22, major product); 2.17 (s, Me, (E)-22, minor product). 13C-NMR (signals of the
major product): 166.8 (s, C¼O); 143.6, 142.1, 141.6, 139.3, 137.4, 131.3 (6s, 4 arom. C, Ph(Me)C, Ph2C);
130.9, 130.5, 128.8, 128.5, 128.3, 127.8, 127.7, 127.6, 127.2, 126.2, 126.8, 126.0 (12d, 20 arom. C, ¼CH); 122.1,

Helvetica Chimica Acta – Vol. 92 (2009)
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Helvetica Chimica Acta – Vol. 92 (2009)
117.5 (2s, C(2), C(5)); 21.0 (q, Me). ESI-MS (MeOH þ NaI): 528 (30), 500 (13, [M þ Na þ MeOH]þ),
484 (18, [M þ K]þ), 468 (100, [M þ Na]þ).
Data of 23. Colorless crystals. M.p. 170 – 1718. Rf (hexane/AcOEt 5 :1): 0.41. IR: 3053w, 2924w,
1708vs, 1596s, 1492s, 1454m, 1442m, 1345vs, 1310w, 1287m, 1253s, 1227s, 1202w, 1178w, 1142m, 1073m,
1029w, 976w, 776w, 759m, 725m, 697vs, 643m, 605m, 589vs. 1H-NMR: 7.35 – 6.93 (m, 15 arom. H); 6.85 –
3
3
6.77 (m, 3 arom. H); 6.75 – 6.68 (m, 2 arom. H); 3.09 (dd, J(cis) ¼ 9.7, J(trans) ¼ 7.7, PhCH); 2.13 (dd,
2J ¼ 5.5, 3J(cis) ¼ 9.7, 1 H of CH2); 1.63 (dd, 2J ¼ 5.5, 3J(trans) ¼ 7.7, 1 H of CH2). 13C-NMR: 174.2 (s,
C¼O); 141.8, 139.2, 137.1; 135.5 (4s, 4 arom. C); 132.2, 119.7 (s, Ph2C, C(2)); 130.2, 130.0, 128.5, 128.4,
128.1, 128.0, 127.3, 127.2, 127.14, 127.12, 126.8, 125.9 (12d, 20 arom. C); 37.7 (s, spiro-C); 31.6 (d, PhCH);
22.1 (t, CH2). CI-MS (isobutane): 447 (31), 446 (100, [M þ H]þ), 445 (32), 365 (15), 326 (10), 312 (22),
296 (24), 282 (10), 85 (18).
Suitable crystals of 23 for the X-ray crystal-structure determination were obtained by crystallization
from CH2Cl2/hexane at ꢀ 208.
6. X-Ray Crystal-Structure Determination of (Z)-8, 9a, 9b, 11, and 23 (Table and Figs. 2 – 4)9). All
measurements were performed on a Nonius KappaCCD diffractometer [35] using graphite-monochro-
mated MoKa radiation (l 0.71073 ꢅ) and an Oxford Cryosystems Cryostream 700 cooler. The data
collection and refinement parameters are given in the Table, and views of the molecules are shown in
Figs. 2 – 4. Data reduction was performed with HKL Denzo and Scalepack [36]. The intensities were
corrected for Lorentz and polarization effects, and absorption corrections based on the multi-scan
method [37] were applied. Equivalent reflections were merged. Each structure was solved by direct
methods using SIR92 [38], which revealed the positions of all non-H-atoms. In the case of (Z)-8, the
asymmetric unit contains two symmetry-independent molecules. The atomic coordinates of the two
molecules were tested carefully for a relationship from a higher-symmetry space group using the program
PLATON [39], but none could be found. In the case of 23, only low-quality crystals could be obtained.
The asymmetric unit contains two molecules of 23 plus two partially occupied sites for CH2Cl2 molecules.
The occupation factors of these sites refined to 0.865(9) and 0.827(9). The non-H-atoms were refined
anisotropically. All of the H-atoms were placed in geometrically calculated positions and refined using a
riding model where each H-atom was assigned a fixed isotropic displacement parameter with a value
equal to 1.2 Ueq of its parent C-atom (1.5 Ueq for the Me group in (Z)-8a). The refinement of each
structure was carried out on F2 using full-matrix least-squares procedures, which minimized the function
Sw(F2o ꢀ F2c )2. A correction for secondary extinction was applied in the case of 21. In the cases of (Z)-8
and 9b, two and one reflection, resp., whose intensities were considered to be extreme outliers, were
omitted from the final refinement. Refinement of the absolute structure parameter [40] of 23 yielded a
value of 0.02(11), which suggests that the refined coordinates represent the true absolute structure,
although the precision on this parameter is low. Neutral atom-scattering factors for non-H-atoms were
taken from [41a], and the scattering factors for H-atoms were taken from [42]. Anomalous dispersion
effects were included in Fc [43]; the values for f’ and f’’ were those of [41b]. The values of the mass
attenuation coefficients are those of [41c]. All calculations were performed using the SHELXL97 [44]
program.
REFERENCES
[1] R. Huisgen, Angew. Chem., Int. Ed. 1963, 2, 565; R. Huisgen, Angew. Chem., Int. Ed. 1963, 2, 633; R.
Huisgen, in ꢂ1,3-Dipolar Cycloaddition Chemistryꢃ, Ed. A. Padwa, Wiley-Interscience, New York,
1984, Vol. 1, p. 1; R. Huisgen, Adv. Cycloadd. 1988, 1, 1; R. Sustmann, Heterocycles 1995, 40, 1.
[2] ꢂ1,3-Dipolar Cycloaddition Chemistryꢃ, Vol. 1 and 2, Ed. A. Padwa, Wiley-Interscience, New York,
1984; W. Carruthers, ꢂCycloaddition Reactions in Organic Synthesisꢃ, Pergamon, Oxford, 1990; A.
Padwa, in ꢂComprehensive Organic Synthesisꢃ, Eds. B. M. Trost, I. Fleming, Pergamon, Oxford,
9
)
CCDC-730139 – 730143 contain the supplementary crystallographic data for this article. These data
can be obtained free of charge from the Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif.

Helvetica Chimica Acta – Vol. 92 (2009)
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1991, Vol. 4, p. 1085; P. A. Wade, in ꢂComprehensive Organic Synthesisꢃ, Eds. B. M. Trost, I. Fleming,
Pergamon, Oxford, 1991, Vol. 4, p. 1134; ꢂSynthetic Applications of 1,3-Dipolar Cycloaddition
Chemistry Toward Heterocycles and Natural Productsꢃ, in ꢂThe Chemistry of Heterocyclic
Compoundsꢃ, Eds. A. Padwa, W. H. Pearson, Vol. 59, J. Wiley & Sons, New York, 2002.
[3] a) R. Hoffmann, R. B. Woodward, Acc. Chem. Res. 1968, 1, 17; b) R. B. Woodward, R. Hoffmann,
Angew. Chem., Int. Ed. 1969, 8, 781 – 853; c) K. N. Houk, J. Sims, C. R. Watts, L. J. Luskus, J. Am.
Chem. Soc. 1973, 95, 7301; d) R. Sustmann, Pure Appl. Chem. 1974, 40, 569; e) K. N. Houk, Acc.
Chem. Res. 1975, 8, 361; f) K. N. Houk, K. Yamaguchi, in ꢂ1,3-Dipolar Cycloaddition Chemistryꢃ, Ed.
A. Padwa, Wiley-Interscience, New York, 1984, Vol. 2, p. 407; g) I. Fleming, ꢂFrontier Orbitals and
Organic Chemical Reactionsꢃ, J. Wiley & Sons, New York, 1976; h) I. Fleming, ꢂPericyclic
Reactionsꢃ, Oxford University Press, Oxford, 1999; i) D. H. Ess, K. N. Houk, J. Am. Chem. Soc. 2008,
130, 10187.
[4] C. DiValentin, M. Freccero, R. Gandolfi, A. Rastelli, J. Org. Chem. 2000, 65, 6112; S. Vivanco, B.
Lecea, A. Arrieta, P. Prieto, I. Morao, A. Linden, F. P. Cossio, J. Am. Chem. Soc. 2000, 122, 6078; K.
Kaitha, P. Venuvanalingam, J. Chem. Soc., Perkin Trans. 2 2002, 2130; K. Kaitha, P. Venuvanalingam,
Int. J. Quant. Chem. 2005, 104, 64.
[5] a) R. A. Firestone, J. Org. Chem. 1968, 33, 2285; b) R. A. Firestone, J. Org. Chem. 1972, 37, 2181;
c) A. Padwa, P. H. J. Carlsen, J. Am. Chem. Soc. 1977, 99, 1514; d) R. Sustmann, W. Sicking, R.
Huisgen, J. Am. Chem. Soc. 2003, 125, 14425.
´
´
[6] R. Huisgen, G. Mloston, E. Langhals, J. Org. Chem. 1986, 51, 4087; R. Huisgen, G. Mloston, E.
´
Langhals, Helv. Chim. Acta 2001, 84, 1805; R. Huisgen, E. Langhals, G. Mloston, O. Oshima,
´
Heterocycles 1989, 29, 2069; R. Huisgen, E. Langhals, G. Mloston, O. Oshima, Helv. Chim. Acta
´
2002, 85, 2668; R. Huisgen, N. H. Langhals, J. Org. Chem. 1990, 55, 1412; G. Mloston, R. Huisgen, H.
Giera, Tetrahedron 2002, 58, 4185; V. V. Rostovtsev, L. G. Green, V. V. Vokin, K. B. Sharpless,
Angew. Chem., Int. Ed. 2001, 41, 2596; L. R. Domingo, M. T. Picher, Tetrahedron 2004, 60,
5053.
ˇ
´
[7] 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; R. Huisgen. G. Mloston, in ꢂModern Problems of
Organic Chemistryꢃ, Eds. A. A. Potekhin, R. R. Kostikov, M. S. Baird, St. Petersburg University
Press, St. Petersburg 2004, Vol. 14, pp. 23 – 45.
ˇ
[8] R. Huisgen, L. Fisera, H. Giera, R. Sustmann, J. Am. Chem. Soc. 1995, 117, 9671; R. Sustmann, W.
Sicking, R. Huisgen, J. Am. Chem. Soc. 1995, 117, 9679.
[9] R. Huisgen, E. Langhals, Tetrahedron Lett. 1989, 30, 5369; R. Huisgen, E. Langhals, Heteroat. Chem.
2006, 17, 433.
´
[10] R. Huisgen, G. Mloston, K. Polborn, R. Sustmann, W. Sicking, Liebigs Ann./Recl. 1997, 179.
[11] R. N. Butler, A. G. Coyne, P. McArdle, L. M. Sibley, L. A. Burke, Tetrahedron Lett. 2007, 48,
6687.
[12] T. Bꢁchel, R. Prewo, J. H. Bieri, H. Heimgartner, Helv. Chim. Acta 1984, 67, 534.
[13] P. Wipf, H. Heimgartner, Chimia 1984, 38, 357; P. Wipf, R. Prewo, J. H. Bieri, G. Germain, H.
Heimgartner, Helv. Chim. Acta 1988, 71, 1177; N. Bojkova, H. Heimgartner, Heterocycles 1998, 47, 781.
´
[14] G. Mloston, A. Linden, H. Heimgartner, Helv. Chim. Acta 1991, 74, 1386.
´
[15] K.-R. Meier, A. Linden, G. Mloston, H. Heimgartner, Helv. Chim. Acta 1997, 80, 1190.
´
´
[16] G. Mloston, A. Linden, H. Heimgartner, Pol. J. Chem. 1997, 71, 32; G. Mloston, A. Linden, H.
´
Heimgartner, Helv. Chim. Acta 1998, 81, 558; A. Gebert, A. Linden, G. Mloston, H. Heimgartner,
Heterocycles 2002, 56, 393; A. Gebert, H. Heimgartner, Helv. Chim. Acta 2002, 85, 2073; A. Gebert,
´
A. Linden, G. Mloston, H. Heimgartner, Pol. J. Chem. 2003, 77, 157; A. Gebert, A. Linden, G.
´
Mloston, H. Heimgartner, Pol. J. Chem. 2003, 77, 867.
´
[17] a) G. Mloston, H. Heimgartner, Helv. Chim. Acta 1992, 75, 1825; b) M. Kꢀgi, A. Linden, H.
´
´
Heimgartner, G. Mloston, Helv. Chim. Acta 1993, 76, 1715; c) G. Mloston, M. Petit, A. Linden, H.
´
Heimgartner, Helv. Chim. Acta 1994, 77, 435; d) M. Petit, A. Linden, G. Mloston, H. Heimgartner,
´
Helv. Chim. Acta 1994, 77, 1076; e) M. Kꢀgi, G. Mloston, A. Linden, H. Heimgartner, Helv. Chim.
´
Acta 1994, 77, 1299; f) M. Kꢀgi, A. Linden, G. Mloston, H. Heimgartner, Helv. Chim. Acta 1996, 79,
´
855; g) M. Kꢀgi, A. Linden, G. Mloston, H. Heimgartner, Helv. Chim. Acta 1998, 81, 285.

1816
Helvetica Chimica Acta – Vol. 92 (2009)
´
´
[18] S. Pekcan, H. Heimgartner, Helv. Chim. Acta 1988, 71, 1673; G. Mloston, J. Romanski, H.
´
Heimgartner, Helv. Chim. Acta 1995, 78, 1067; G. Mloston, H. Heimgartner, Helv. Chim. Acta 1995,
78, 1298.
[19] H. Heimgartner, Phosphorus, Sulfur Silicon Relat. Elem. 1991, 58, 281.
[20] a) H. M. Hassaneen, A. S. Shawali, D. S. Farag, E. M. Ahmed, Phosphorus, Sulfur Silicon Relat.
Elem. 1996, 113, 53; b) A. Linden, E. M. A. H. Awad, H. Heimgartner, Acta Crystallogr., Sect. C
1999, 55, 1877.
´
[21] M. S. Seyfried, A. Linden, G. Mloston, H. Heimgartner, Pol. J. Chem. 2006, 80, 1363.
[22] C. Fu, M. V. Thrane, A. Linden, H. Heimgartner, Tetrahedron 2004, 60, 5407.
[23] D. H. Egli, A. Linden, H. Heimgartner, Helv. Chim. Acta 2006, 89, 3041.
[24] D. H. Egli, A. Linden, H. Heimgartner, Helv. Chim. Acta 2006, 89, 2815.
ˇ
ˇ
´
´
[25] L. Fisera, L. Jaroskova, I. Matejkova, H. Heimgartner, Heterocycles 1995, 40, 271.
[26] C. K. Johnson, ꢂORTEP IIꢃ, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge,
Tennessee, 1976.
[27] a) P. Schwab, R. H. Grubbs, J. W. Ziller, J. Am. Chem. Soc. 1996, 118, 100; b) H. Werner, P. Schwab,
E. Bleuel, N. Mahr, P. Steinert, J. Wolf, Chem. – Eur. J. 1997, 3, 1375; c) H. Werner, P. Schwab, E.
Bleuel, N. Mahr, B. Windmꢁller, J. Wolf, Chem. – Eur. J. 2000, 6, 4461.
[28] K. C. Nicolaou, C. J. N. Mathison, T. Montagnon, J. Am. Chem. Soc. 2004, 126, 5192.
[29] E. R. Blout, V. W. Eager, R. M. Golfstein, J. Am. Chem. Soc. 1946, 68, 1983.
[30] D. H. R. Barton, B. J. Willis, J. Chem. Soc., Chem. Commun. 1970, 1225; J. Buter, S. Wassenaar,
R. M. Kellogg, J. Org. Chem. 1972, 37, 4045; R. M. Kellogg, Tetrahedron 1976, 32, 2165; F. S. Guziek
Jr., L. J. Sanfilippo, Tetrahedron 1988, 44, 6241.
[31] W. E. Bachmann, W. S. Struve, Org. React. 1942, 1, 38.
[32] D. S. Wulfman, S. Yousefian, J. M. White, Synth. Commun. 1988, 18, 2349.
[33] H. Staudinger, O. Kupfer, Ber. Dtsch. Chem. Ges. 1911, 44, 2197.
[34] R. Andreasch, A. Zipser, Monatsh. Chem. 1903, 24, 499.
[35] R. Hooft, KappaCCD Collect Software, Nonius BV, Delft, The Netherlands, 1999.
[36] Z. Otwinowski, W. Minor, in ꢂMethods in Enzymologyꢃ, Vol. 276, ꢂMacromolecular Crystallographyꢃ,
Part A, Eds. C. W. Carter Jr., R. M. Sweet, Academic Press, New York, 1997, p. 307.
[37] R. H. Blessing, Acta Crystallogr., Sect. A 1995, 51, 33.
[38] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori, M. Camalli,
SIR92, J. Appl. Crystallogr. 1994, 27, 435.
[39] A. L. Spek, PLATON, Program for the Analysis of Molecular Geometry, University of Utrecht, The
Netherlands, 2004.
[40] H. D. Flack, G. Bernardinelli, Acta Crystallogr., Sect. A 1999, 55, 908; H. D. Flack, G. Bernardinelli,
J. Appl. Crystallogr. 2000, 33, 1143.
[41] a) E. N. Maslen, A. G. Fox, M. A. OꢃKeefe, in ꢂInternational Tables for Crystallographyꢃ, Ed. A. J. C.
Wilson, Kluwer Academic Publishers, Dordrecht, 1992, Vol. C, Table 6.1.1.1, p. 477; b) D. C. Creagh,
W. J. McAuley, in ꢂInternational Tables for Crystallographyꢃ, Ed. A. J. C. Wilson, Kluwer Academic
Publishers, Dordrecht, 1992, Vol. C, Table 4.2.6.8, p. 219; c) D. C. Creagh, J. H. Hubbell, in
ꢂInternational Tables for Crystallographyꢃ, Ed. A. J. C. Wilson, Kluwer Academic Publishers,
Dordrecht, 1992, Vol. C, Table 4.2.4.3, p. 200.
[42] R. F. Stewart, E. R. Davidson, W. T. Simpson, J. Chem. Phys. 1965, 42, 3175.
[43] J. A. Ibers, W. C. Hamilton, Acta Crystallogr. 1964, 17, 781.
[44] G. M. Sheldrick, SHELXL97, Program for the Refinement of Crystal Structures, University of
Gçttingen, Germany, 1997.
Received April 30, 2009