1,5-Dipolar electrocyclizations of thiocarbonyl ylides bearing C=N groups: Reactions of N-[(dimethylamino)methylene]thiobenzamide and 2-(dimethylhydrazono) -1-phenylethane-1-thione with diazo compounds

Article abstract of DOI:10.1002/hlca.200790025

The reactions of thiobenzamide 8 with diazo compounds proceeded via reactive thiocarbonyl ylides as intermediates, which underwent either a 1,5-dipolar electrocyclization to give the corresponding five membered heterocycles, i.e., 4-amino-4,5-dihydro-1,3-

Full text of DOI:10.1002/hlca.200790025

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1,5-Dipolar Electrocyclizations of Thiocarbonyl Ylides Bearing C=N Groups:
Reactions of N-[(Dimethylamino)methylene]thiobenzamide and
2-(Dimethylhydrazono)-1-phenylethane-1-thione with Diazo Compounds
by Daniel H. Egli1), Anthony Linden and Heinz Heimgartner*
Organisch-chemisches Institut der Universität Zürich, Winterthurerstr. 190, CH-8057 Zürich
(phone: +41446354282; fax: +41446356812; e-mail: heimgart@oci.unizh.ch)
The reactions of thiobenzamide 8 with diazo compounds proceeded via reactive thiocarbonyl ylides
as intermediates, which underwent either a 1,5-dipolar electrocyclization to give the corresponding five
membered heterocycles, i.e., 4-amino-4,5-dihydro-1,3-thiazole derivatives (i.e., 10a, 10b, 10c, cis-10d, and
trans-10d) or a 1,3-dipolar electrocyclization to give the corresponding thiiranes as intermediates, which
underwent a SNi’-like ring opening and subsequent 5-exo-trig cyclization to yield the isomeric 2-amino-
2,5-dihydro-1,3-thiazole derivatives (i.e., 11a, 11b, 11c, cis-11d, and trans-11d). In general, isomer 10
was formed in higher yield than isomer 11. In the case of the reaction of 8 with diazo(phenyl)methane
(3d), a mixture of two pairs of diastereoisomers was formed, of which two, namely cis-10d and trans-
10d, could be isolated as pure compounds. The isomers cis-11d and trans-11d remained as a mixture.
In the reactions of the thioxohydrazone 9 with diazo compounds 3b and 3d, the main products were
the alkenes 18 and 23, respectively. Their formation was rationalized by a 1,3-dipolar electrocyclization
of the corresponding thiocarbonyl ylide and subsequent desulfurization of the intermediate thiiran. As
minor products, 2,5-dihydro-1,3-thiazol-5-amines 21 and 24 were obtained, which have been formed by
1,5-dipolar electrocyclization of the thiocarbonyl ylide, followed by a 1,3-shift of the dimethylamino
group.
1. Introduction. – The concept of the 1,5-dipolar electrocyclization as a tool for the
synthesis of five-membered heterocycles has been proposed 25 years ago [1][2]. Since,
we have shown that thiocarbonyl ylides, which bear a C=O group at the C(a)-atom,
undergo this cyclization to give 1,3-oxathioles [3][4] (see also [5][6]). These thiocar-
bonyl ylides were generated in situ by the reaction of thiocarbonyl derivatives with
a-diazo carbonyl compounds. Very recently, we reported on the reaction of a-thioxo-
carbonyl derivatives with diazo compounds [7]. We were mostly interested in systems,
in which the conjugated p-system consisted of a C=O or a C=S group, i.e., in reactions
of a-thioxo ketone 1 and a-thioxo thioamide 2 (Scheme 1).
The reactions with diazo compounds 3 all followed the same pathway: 1,3-dipolar
cycloaddition to give a 2,5-dihydro-1,3,4-thiadiazole, N2 elimination by cycloreversion
to produce thiocarbonyl ylides 4, and 1,5-dipolar electrocyclization. The resulting prod-
ucts are either 1,3-oxathioles 5 or 1,3-dithioles 6, respectively. Some thiirane side prod-
ucts, which were formed by a competing 1,3-dipolar electrocyclization, were unstable,
and elimination of sulfur led to the corresponding alkenes, e.g., 7.
1
)
Part of the Ph.D. thesis of D. H. E., University of Zürich, 2006.
ꢀ 2007 Verlag Helvetica Chimica Acta AG, Zürich

Helvetica Chimica Acta – Vol. 90 (2007)
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Scheme 1
With the aim of extending the scope of this reaction, we used thiocarbonyl com-
pounds that possess a conjugated system containing a N-atom. Since N-[(dimethylami-
no)methylidene]thiobenzamide (8; cf. Scheme 2) is not only readily available, but also
stable, and thus allows for a precise calculation of the yield2), we used it as a starting
material in the present work. Because we were interested in systems with the N-
atom in different positions, reactions of 2-(dimethylhydrazono)-1-phenylethane-1-thi-
one (9; cf. Scheme 7) were also investigated. Although 9 showed a few drawbacks con-
cerning stability and yield calculation, we used it because of the relatively simple four-
step synthesis. The results of the reactions with 8 and 9 are presented below.
2. Results and Discussion. – 2.1. Reactions with N-[(Dimethylamino)methylidene]-
thiobenzamide (8). In 1989, Danion-Bougot et al. [8a] showed that the reaction of 8 with
diazomethane (3a) in Et2O in the dark led to three products, 10a, 11a, and 12 (Scheme
2; see also [8b]). The correlation of the spectroscopic data with the corresponding struc-
tures was supported by the conversion of 10a with phenyl isothiocyanate in refluxing
benzene to give the known 1,3-thiazole 13 and N,N-dimethyl-N’-phenylurea 14
(Scheme 2).
Scheme 2
2
)
Because of unstable starting materials, it was a problem to calculate correct yields for the reactions
described in [7].

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On closer inspection of this result, we became convinced that the correlation of the
structures and data requires verification, because an additional structure also corre-
sponds to the given data. Instead of 11a, the isomeric structure 10a’ (Fig. 1) could be
generated by a 1,3-H shift in 10a. The corresponding data of 10a’ and 11a are expected
to be quite similar, but the results of NOE experiments by irradiation of the Me2N
group would be distinctive. Whereas 10a and 11a should show a positive NOE, no
NOE would be observed in the case of 10a’ (Fig. 1).
Fig. 1. NOE Signals of 10a, 10a’, and 11a
Therefore, we repeated the experiment with 8 and 3a in Et2O and obtained two iso-
meric dihydro-1,3-thiazoles in accordance with [8a] (ratio ca. 1:1). Both products
showed a positive NOE of the methine H-atom on irradiation of Me2N, i.e., both mol-
ecules contain the structure fragment CHÀNMe2, and, therefore, the assignment made
by Danion-Bougot et al. is correct indeed. The formation of 10a’ can be excluded.
However, the reaction pathway proposed by Danion-Bougot et al., in which 10a and
11a are formed via an intermediate thiirane 15a, is not in accordance with the general
experience for such reactions. We assume that the intermediate thiocarbonyl ylide 16a
is the origin of both compounds 10a and 11a (Scheme 3). Whereas the formation of 11a
can be explained via a 1,3-dipolar electrocyclization to give 15a, followed by a SNi’-like
ring opening and subsequent 5-exo-trig cyclization, as proposed by Danion-Bougot
et al., 10a is formed via a 1,5-dipolar electrocyclization of 16a. This pathway seems to
be much more reliable, as there is no CÀC-bond cleavage of the thiirane ring known
to give thiocarbonyl ylides. Rather, thiocarbonyl ylides are the usual intermediates of
reactions of thioketones with diazo compounds [5][6].
Scheme 3

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The reaction of 8 with diazo(diphenyl)methane (3b) was carried out in CH2Cl2 at
room temperature in the presence of a catalytic amount of Rh2(OAc)4 and yielded
two products. Based on previous experiences from experiments with thiocarbonyl
ylides [7], we assumed that the reaction would lead to an intermediate thiocarbonyl
ylide 16b, which would undergo either a 1,3-dipolar electrocyclization to give the thiir-
ane 15b and, by subsequent SNi’ ring opening and 1,5-cyclization, the 2,5-dihydro-1,3-
thiazole 11b, or a 1,5-dipolar electrocyclization to yield the corresponding 4,5-dihy-
dro-1,3-thiazole 10b (Scheme 4).
Scheme 4
The 13C-NMR spectra of the two isolated products showed that we could exclude
structure 15b, because the expected d for the amidine C-atom at ca. 155 ppm was miss-
ing (see Exper. Part). The spectra of both compounds again were very similar with only
small deviations of 5–10 ppm for some signals. The NOE experiment showed that the
Me2N group in 10b has to be close to the H-atom, which absorbed at 6.84 ppm. In the
case of 11b, the NOE experiment showed the analogous response of an H-atom bonded
to the heterocycle, therefore, an isomer of type 10a’ (Fig. 1) can be excluded. By ꢁinad-
equate-NMR measurementsꢂ of 10b, it has been shown that CHNMe2 is connected
directly to another C-atom of the ring. In compound 11b, no such coupling would be
observed. Unfortunately, it was not possible to crystallize the two products, as they
remained as oily substances. Obviously, the 1,5-dipolar electrocyclization is preferred
to a 1,3-dipolar electrocyclization, since the yield of 10b (49%) is significantly higher
than that of 11b (30%).
Similar to the reaction of 8 with 3b, treatment with diazocyclohexane (3c) led to two
products 10c and 11c (Scheme 5). The latter proved to be unstable and could not be iso-
lated in pure form. In contrast to the previous experiments, the reaction takes place
spontaneously, and, therefore, there was no need of Rh catalyst. In the crude NMR
spectrum, the products showed the already known pattern of the 10a/11a mixture,
but the ratio of 10c to 11c rose to 3 :1 (Scheme 5).
The next diazo compound selected for the reaction with 8 was diazo(phenyl)me-
thane (3d). In Et2O/toluene at room temperature, a spontaneous reaction occurred,
which, after 5 d, led to a mixture of four isomeric products, but only three of them,

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Scheme 5
namely cis-10d, cis-11d, and trans-11d, could be isolated after chromatographic workup
(SiO2; hexane/AcOEt/Et3N; Scheme 5). The analogous reaction of 8 with 3d in THF,
catalyzed by Rh2(OAc)4, and workup without using Et3N as an additive led only to
one product, namely the fourth isomer, i.e., trans-10d, of the reaction described
above (see Exper. Part). The reasons for the different results are not clear. A possible
explanation could be that, under acidic workup conditions (SiO2 without Et3N), the iso-
mers cis-11d and trans-11d decomposed, and cis-10d isomerized to trans-10d. With
respect to the thermodynamic stability, the trans-product should be more stable than
the cis-isomer.
The assignment of the structures of the four isomers was achieved on the basis of the
following data. First, 2D-NMR studies (HMBC) have shown a coupling between Me2N
and both H-atoms of the heterocycle, namely HÀC(4) and HÀC(5), of trans-10d. On
the other hand, only one coupling (Me2N, HÀC(2)) was observed in cis-11d and
trans-11d. Second, the cis- and trans-isomers could be distinguished on the basis of
their H,H-coupling constants. As a rule, the cis coupling in five-membered heterocycles
is larger than the trans coupling [9]. Therefore, the smaller J(4,5) value of 4.4 Hz of
trans-10d (cis-10d, 7.6 Hz) indicates the trans-configuration.
An explanation of the formation of the thermodynamically less favored cis-10d is
based on the selectivity rules for pericyclic reactions (see, e.g., [10][11]). For steric rea-
sons, the preferred structure of the thiocarbonyl ylide formed from 8 and 3d should be
16d, which is in equilibrium with 16d’ (Scheme 6). The disrotatory ring closure of the
latter then yields cis-10d. The more stable trans-10d could be formed under the condi-
tions of the acidic workup via a reversible 1,3-H shift.
Surprisingly, the reaction of ethyl diazoacetate (3e) with 8 did not lead to the
expected thiazole derivative. The only product, which could be isolated in traces, was
17, the ꢁtrimerꢂ of the starting diazo compound (Scheme 5). Its structure was established
by X-ray crystallography (Fig. 2). In the crystal structure, the two ester groups at the

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91
Scheme 6
adjacent stereogenic centres have the trans-configuration. The NH group forms an
intermolecular H-bond with one of the ester carbonyl O-atoms of an adjacent molecule
and thereby links the molecules into extended chains, which run parallel to the [100]
direction and can be described by a graph set motif [12] of C(6).
Fig. 2. ORTEP Plot [13] of the molecular structure of 17 (50% probability ellipsoids, arbitrary num-
bering of atoms)
The described results obtained with 8 show that this starting material is relatively
unreactive, and, therefore, the reaction with less reactive diazo compounds has to be
catalyzed by Rh2(OAc)4, or the reaction time has to be increased. Whereas, in the reac-
tion of 8 with 3a, 46% of the products (10a+11a) could be isolated, no reaction took
place with 3b without addition of catalyst. In the case of 3e, no formation of a thiocar-
bonyl ylide was observed. Instead, dimerization of the generated carbenoid yielded
diethyl fumarate [14], which underwent a 1,3-dipolar cycloaddition with 3e to give 17.

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2.2. Reactions with 2-(Dimethylhydrazono)-1-phenylethane-1-thione (9). The reac-
tion of 9 with 3b in benzene at room temperature gave two products. The first one
was identified as N,N-dimethyl-N’-(2,3,3-triphenylprop-2-enylidene)hydrazine (18;
Scheme 7). The reaction mechanism of its formation, in analogy with previous cases,
is proposed as follows: 1,3-dipolar cycloaddition and elimination of N2 yields the thio-
carbonyl ylide of type 19’, which undergoes a 1,3-dipolar electrocyclization to give the
corresponding thiirane 20. Finally, desulfurization of the latter leads to 18 (cf. [7]). The
second product was isolated in small yields and turned out, surprisingly, to be 2,5-dihy-
dro-N,N-dimethyl-2,2,5-triphenylthiazol-5-amine (21). It apparently results from a
rearrangement of the primarily formed intermediate 1,3-thiazol-3-amine 22 (R=Ph).
In this case, unlike in the reactions with 8, the Me2N group is bound to the N(3)-
atom. A 1,3-shift of the amino substituent then leads to the 2,5-dihydro-1,3-thiazole
21 (Scheme 7).
Scheme 7
The structures of 18 and 21 have been established by X-ray crystallography (Fig. 3).
The conjugated p-system in 18 from C(1) to N(4), including N(5), C(7), C(13), and
C(19) is almost planar. All Ph substituents in compound 18 are twisted out of this
plane because of steric reasons (torsion angles C(2)ÀC(1)ÀC(7)ÀC(8) 52.7(2)8,
C(2)ÀC(1)ÀC(13)ÀC(18) 44.08, and C(1)ÀC(2)ÀC(19)ÀC(20) 55.1(2)8). In the case
of 21, the asymmetric unit contains two symmetry-independent molecules, each of
which is disordered by inversion of the entire molecule about its centre of gravity.
The ratio of the major orientation of each molecule to the minor orientation is ca.
93 :7. The crystals are also inversion twins.
The analogous reaction of 9 with 3d gave a complex mixture of products, which con-
sisted of two pairs of diastereoisomers at least. The (E/Z)-isomers of N,N-dimethyl-N’-
(2,3-diphenylprop-2-enylidene)hydrazine (23) and the cis/trans-isomers of 2,5-dihydro-
N,N-dimethyl-2,5-diphenylthiazol-5-amine (24a and 24b) are the likely products, which
could be separated partially by CC and MPLC. The structures were elucidated on the

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Fig. 3. ORTEP Plot [13] of the molecular structure of a) 18 and b) one of the independent molecules
of 21 (50% probability ellipsoids, arbitrary numbering of atoms)
basis of the NMR and mass spectra. Furthermore, one of the diastereoisomers of 24, i.e.,
trans-24, could be crystallized, and the X-ray crystal structure was determined success-
fully (Fig. 4). In the crystal, the heterocyclic ring has a shallow envelope conformation
with S(3) as the envelope flap. The Ph substituents are cis-oriented.
The reactions of 9 with 3b and 3d, respectively, showed that the intermediate thio-
carbonyl ylide 19 reacts only to a minor extent to the five-membered ring. The prefer-
red reaction of 19 is the 1,3-dipolar electrocyclization, which leads to an intermediate
thiirane 20, and subsequent desulfurization yields the alkenes.
3. Conclusions. – The presented results show that the two thiocarbonyl compounds
8 and 9 with a conjugated C=N group react with diazo compounds 3 to give the corre-
sponding thiocarbonyl ylides of type 16 and 19, respectively, with an extended p-sys-
tem. In the case of 8 and the less reactive 3b, the reaction has to be catalyzed by
Rh2(OAc)4. Whereas, in the non-catalyzed reaction, a 1,3-dipolar cycloaddition to
give the corresponding 2,5-dihydro-1,3,4-thiadiazole and subsequent N2 elimination
is the likely reaction mechanism of the formation of the thiocarbonyl ylide, an initial
Rh-catalyzed N2 elimination to give a carbenoid, which adds to the C=S group, leads
to the intermediate 1,3-dipoles in the catalyzed reactions [5][6]. The thiocarbonyl
ylides of type 16, which have been generated from 8, undergo competitive 1,5- and
1,3-dipolar electrocyclizations, and yield dihydrothiazole and thiirane derivatives,
respectively. On the other hand, the main reaction of the isomeric thiocarbonyl ylides
19 is the 1,3-dipolar electrocyclization, which leads to thiiranes 20.

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Fig. 4. ORTEP Plot [13] of the molecular structure of trans-24 (50% probability ellipsoids, arbitrary
numbering of atoms)
We thank the analytical units of our institute for spectra and analyses, and the Swiss NationalScience
Foundation and F. Hoffmann-La Roche AG, Basel, for financial support.
Experimental Part
1. General. See [7]. M.p.: Büchi B-540. IR Spectra: in KBr unless otherwise stated. 1H- and 13C-NMR
Spectra: Avance DRX-500 (500 and 125 MHz, resp.), and Avance DRX-600 (600 and 150 MHz, resp.).
2. Starting Materials. All thiocarbonyl derivatives and their precursors, and all diazo compounds were
prepared according to known protocols: diazomethane (3a) [15], diazo(diphenyl)methane (3b) [16], di-
azocyclohexane (3c) [17], diazo(phenyl)methane (3d) [18], N-[(dimethylamino)methylidene]thioben-
zamide (8) [19], 2-(dimethylhydrazono)-1-phenylethane-1-thione (9) [20][21]. All other reagents are
commercially available.
3. Yields. As 9 and almost all diazo compounds are only stable in soln., and the diazo compounds
were often used in excess, the yields of the corresponding reactions were approximated. They are
based on experience [7] or on the volume of N2 evolved.
4. GeneralProcedure A (GP A). To a soln. of a thiocarbonyl compound (1.8–5.2 mmol) in CH2Cl2,
Et2O, or THF (20–100 ml), the diazo compound (3–8 mmol) in toluene, benzene, or Et2O (30–150 ml)
was added in several portions by means of a dropping funnel, or, in the case of 3a, by means of a Pasteur
pipette. After total conversion of the thiocarbonyl compound, monitored either by TLC(treated during
3
20 s with a soln. of Et2O and 1% of Et3N), color change or evolution of N2 ), the solvent was evaporated,
and the mixture was analyzed and purified by chromatography using silica gel, which had been treated
with 3% Et3N. Furthermore, the solvent was doped with 1% of Et3N.
3
)
The evolution of N2 was determined volumetrically with a gas burette attached to the reaction vessel.

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5. Reaction of 8 with Diazoalkanes. 5.1. 4,5-Dihydro-N,N-dimethyl-2-phenyl-1,3-thiazol-4-amine
(10a) and 2,5-Dihydro-N,N-dimethyl-4-phenyl-1,3-thiazol-2-amine (11a). According to GP A, a soln. of
8 (772 mg, 4 mmol) in Et2O (30 ml) and 3a (ca. 6 mmol) in Et2O (30 ml) were used. After 3 d at r.t. in
the dark, the mixture was separated by CC (hexane/AcOEt 5 :1) to give 173 mg (ca. 21%) of 10a and
206 mg (ca. 25%) of 11a.
Data of 10a. Yellowish oil. IR (neat): 3081w, 3060m, 3028m, 2970vs, 2939vs, 2864vs, 2829vs, 2784s,
1688w, 1607vs, 1578s, 1490s, 1473s, 1448vs, 1358vs, 1297vs, 1272vs, 1233vs, 1196s, 1177m, 1156m, 1119s,
1
1073vs, 1042vs, 999vs, 949vs, 766vs, 690vs, 624s. H-NMR: 7.88–7.85 (d-like, 2 arom. H); 7.47–7.38 (m,
3 arom. H); 5.56 (dd, J=6.7, 2.4, HÀC(4)); 3.51 (dd, J=9.1, 2.7, 1 H of CH2); 3.28 (dd, J=6.7, 5.1, 1
H of C H); 2.44 (s, Me2N). 13C-NMR: 167.0 (s, C(2)); 133.1 (s, 1 arom. C); 131.2, 128.3, 128.3 (3d, 5
2
arom. CH); 97.3 (d, C(4)); 40.4 (t, C H); 34.5 (q, Me2N). CI-MS (NH3): 207 (100, [M+1]+), 162 (36,
2
[MÀMe2NH]+), 104 (17).
Data of 11a. Yellowish crystals. M.p. 64–678. IR: 3126w, 3058m, 3032w, 2922m, 2805w, 1726m,
1683m, 1644vs, 1579m, 1489s, 1445s, 1414s, 1354m, 1274m, 1254m, 1226m, 1185m, 1159w, 1116m, 1061s,
1042s, 1030s, 1009m, 775s, 746s, 732s, 696s. 1H-NMR: 7.95–7.92 (d-like, 2 arom. H); 7.49–7.40 (m, 3
arom. H); 7.08 (dd, J=5.2, 1.9, HÀC(4)); 4.34 (dd, J=16.3, 1.9, 1 H of CH2); 4.22 (dd, J=16.3, 5.2, 1
H of C H); 2.25 (s, Me2N). 13C-NMR: 168.9 (s, C(2)); 133.1 (s, 1 arom. C); 131.4, 128.5, 128.5 (3d, 5
2
arom. CH); 107.3 (d, C(4)); 41.3 (t, C H); 39.0 (q, Me2N). CI-MS (NH3): 206 (18, M+), 174 (100,
2
[MÀS]+), 161 (94, [MÀMe2N]+), 134 (82, [MÀNHCHNMe2]+), 103 (58, PhCN+).
When the chromatographic workup was carried out without addition of Et3N as described in [8], only
11a was isolated.
5.2. 4,5-Dihydro-N,N-dimethyl-2,5,5-triphenyl-1,3-thiazol-4-amine (10b) and 2,5-Dihydro-N,N-
dimethyl-4,5,5-triphenyl-1,3-thiazol-2-amine (11b). According to GP A, a suspension of 8 (360 mg, 1.87
mmol) in CH2Cl2 (20 ml) and a soln. of 3b (ca. 2.5 mmol) in benzene (20 ml) were used. To the stirred
mixture at r.t., a cat. amount (20 mg) of Rh2(OAc)4 was added. After ca. 16 h, the mixture was separated
by CC (hexane/AcOEt 20 :1 to 5 :1): 328 mg (0.92 mmol, 49%) of 10b and 200 mg (0.56 mmol, 30%) of
11b.
Data of 10b. Yellowish oil. Rf (hexane/AcOEt 8 :1) 0.5. IR: 3057m, 3027m, 2935s, 2865s, 2831s,
2786m, 1805w, 1733w, 1596s, 1575s, 1491vs, 1472m, 1445vs, 1311m, 1275s, 1227s, 1176m, 1156m, 1083s,
1062vs, 1040vs, 994vs, 944vs, 920m, 901m, 888m, 828m, 765vs, 752vs, 723vs, 694vs, 632m, 623s. 1H-
NMR: 7.87–7.84 (q-like, 2 arom. CH); 7.43–7.07 (m, 13 arom. CH); 6.01 (s, HÀC(2)); 2.19 (s, Me2N).
13C-NMR: 166.1 (s, C(4)); 149.1, 140.1, 133.2 (3s, 3 arom. C); 131.4, 129.9, 128.5, 128.3, 128.3, 127.3,
126.9, 126.9, 126.4 (9d, 15 arom. CH); 100.9 (d, C(2)); 74.4 (s, C(5)); 41.3 (q, Me2N). CI-MS (NH3):
359 (100, [M+1]+), 314 (39, [MÀMe2NH]+), 224 (37).
Data of 11b. Yellowish oil. Rf (hexane/AcOEt 8 :1) 0.3. IR: 3056m, 3028w, 2977m, 2942m, 2860m,
2825m, 2779m, 1807w, 1734w, 1680w, 1624s, 1599s, 1545m, 1489s, 1470s, 1445vs, 1352s, 1289m, 1257s,
1205m, 1179s, 1152m, 1081s, 1067s, 1043s, 1023vs, 1002s, 932m, 908w, 852s, 824w, 772s, 758s, 742vs,
1
695vs, 639m. H-NMR: 7.52–7.49 (d-like, 2 arom. H); 7.40–7.35 (t-like, 4 arom. H); 7.21–7.00 (m, 9
arom. H); 6.84 (s, HÀC(4)); 2.27 (s, Me2N). 13C-NMR: 171.2 (s, C(2)); 143.1, 142.8, 133.2 (3s, 3 arom.
C); 130.5, 130.2, 129.4, 129.0, 128.0, 127.8, 127.7, 127.0, 126.9 (9d, 15 arom. CH); 101.5 (d, C(4)); 78.3
(s, C(5)); 39.8 (q, Me2N). CI-MS (NH3): 359 (10, [M+1]+), 327 (100, [MÀS+1]+), 314 (5
[MÀMe2NH]+), 193 (22).
5.3. N,N-Dimethyl-2-phenyl-1-thia-3-azaspiro[4.5]dec-2-en-4-amine (10c). According to GP A, a sus-
pension of 8 (384 mg, 2 mmol) in CH2Cl2 (10 ml) and a soln. of 3c (ca. 2.5 mmol) in CH2Cl2 (40 ml) were
used. After 1 d at r.t., the mixture was separated by CC (hexane/AcOEt 10 :1 to 5 :1): 360 mg (67%) of
10c, and 120 mg (22%) of a mixture of 10c and N,N-dimethyl-4-phenyl-1-thia-3-azaspiro[4.5]dec-3-en-2-
amine (11c)4).
Data of 10c. Yellowish oil. IR (neat): 3061m, 3027w, 2930vs, 2855vs, 2833vs, 2790s, 2669w, 1808w,
1756w, 1688w, 1595vs, 1577s, 1491m, 1473s, 1447vs, 1404w, 1377m, 1295s, 1266vs, 1246vs, 1229s, 1212m,
1176m, 1156m, 1135m, 1091s, 1074s, 1042vs, 1025vs, 993vs, 958s, 940s, 909m, 858s, 766vs, 690vs, 625m.
4
)
It was not possible to isolate 11c in pure state.

96
Helvetica Chimica Acta – Vol. 90 (2007)
1H-NMR: 7.91–7.88 (d-like, 2 arom. H); 7.45–7.36 (m, 3 arom. H); 4.92 (s, HÀC(4)); 2.48 (s, Me2N);
2.04–1.32 (m, 10 H, cyclohexane). 13C-NMR: 167.4 (s, C(2)); 133.8 (s, 1 arom. C); 131.0, 128.3, 128.1
(3d, 5 arom. CH); 101.5 (d, C(4)); 66.6 (s, C(5)); 42.3 (br. q, Me2N); 40.9, 32.2, 26.3, 25.5, 24.2 (5t, 5
CH2, cyclohexane). EI-MS: 275 (10), 274 (47, M+), 230 (7, [MÀMe2N]+), 171 (28), 160 (100,
[MÀC6H10S]+), 138 (18), 121 (11), 103 (24), 57 (84).
1
Data of 11c (from a ca. 1:3 mixture of 10c/11c). H-NMR: 7.48–7.38 (m, 5 arom. H); 6.76 (s, HÀ
C(2)); 2.31 (s, Me2N); 1.93–1.59 (m, 10 H, cyclohexane). 13C-NMR: 176.8 (s, C(4)); 135.0 (s, 1 arom.
C); 129.0, 128.2, 127.9 (3d, 5 arom. CH); 100.3 (d, C(2)); 72.7 (s, C(5)); 39.3 (s, Me2N); 38.1, 36.9,
25.2, 25.0, 24.5 (5t, 5 C H, cyclohexane).
2
5.4. cis-4,5-Dihydro-N,N-dimethyl-2,5-diphenyl-1,3-thiazol-4-amine (cis-10d) and cis/trans-2,5-Dihy-
dro-N,N-dimethyl-4,5-diphenyl-1,3-thiazol-2-amine (cis-11d and cis/trans-11d). According to GP A, a
soln. of 8 (1 g, 5.2 mmol) in dry Et2O (30 ml) and 3d (ca. 8 mmol) in toluene (150 ml) were used.
After 4 d at r.t. in the dark, the mixture was separated by CC (hexane/AcOEt 3 :1) and MPLC (Et2O/
hexane 1:5): 362 mg (ca. 24%) of cis-10d (colorless oil), and 616 mg (ca. 43%) of a mixture of cis- and
trans-11d (yellowish oil).
Data of cis-10d. IR (neat): 3061m, 3028m, 2941s, 2866s, 2833m, 2786m, 2771m, 1680w, 1600s, 1577s,
1531m, 1493s, 1471m, 1447vs, 1420m, 1366m, 1312s, 1269s, 1226m, 1177m, 1155m, 1068s, 1040s, 988s,
1
943m, 910m, 896m, 765vs, 731s, 694vs. H-NMR: 7.96–7.93 (d-like, 2 arom. H); 7.49–7.23 (m, 8 arom.
H); 5.20 (d, J=7.6, HÀC(4)); 5.05 (d, J=7.6, HÀC(5)); 2.30 (s, Me2N). 13C-NMR: 166.2 (s, C(2));
137.5, 133.4 (2s, 2 arom. C); 131.4, 128.5, 128.4, 128.3, 128.2, 127.6 (6d, 10 arom. CH); 99.2 (d, C(4));
57.4 (d, C(5)); 42.8 (q, Me2N). CI-MS (NH3): 281 (8), 238 (100, [MÀMe2NH+1]+), 148 (20).
Data of the Mixture of cis-11d and trans-11d5): IR (neat): 3060m, 3027m, 2978m, 2944s, 2862s, 2825s,
2779m, 1635vs, 1599m, 1577m, 1494s, 1471s, 1448vs, 1355s, 1337m, 1317m, 1279vs, 1213m, 1177s, 1067vs,
1046vs, 1037vs, 1024vs, 1001m, 886s, 853s, 763vs, 729vs, 693vs, 630s, 585m, 546s. 1H-NMR (cis-11d):
7.82–7.74 (m, 2 arom. H); 7.35–7.15 (m, 8 arom. H, HÀC(4)); 5.88 (d, J=4.8, HÀC(5)); 2.32 (s,
Me2N). 13C-NMR (cis-11d): 169.7 or 169.2 (s, C(2)); 141.7, 132.7 or 132.4 (2s, 2 arom. C); 130.9, 130.8,
129.7, 129.5, 129.4, 129.1, 128.9, 128.3, 128.0, 127.5, 127.4, 127.2 (12d, 10 arom. CH); 105.7 (d, C(4));
1
61.6 (d, C(5)); 39.3 (q, Me2N). H-NMR (trans-11d): 7.82–7.74 (m, 2 arom. H); 7.35–7.15 (m, 8 arom.
H); 7.10 (d, J=2.6, HÀC(4)); 5.97 (d, J=2.6, HÀC(5)); 2.38 (s, Me2N). 13C-NMR (trans-11d): 169.7 or
169.2 (s, C(2)); 141.8, 132.7 or 132.4 (2s, 2 arom. C); 130.9, 130.8, 129.7, 129.5, 129.4, 129.1, 128.9,
128.3, 128.0, 127.5, 127.4, 127.2 (12d, 10 arom. CH); 105.2 (d, C(4)); 60.8 (d, C(5)); 39.8 (q, Me2N).
CI-MS (NH3): 281 (6), 251 (100, [MÀS+1]+), 238 (70, [MÀMe2NH+1]+), 148 (29).
5.5. trans-4,5-Dihydro-N,N-dimethyl-2,5-diphenyl-1,3-thiazol-4-amine (trans-10d). According to GP
A, a soln. of 8 (592 mg, 3 mmol) in dry THF (20 ml) and 3d (ca. 4 mmol) in toluene (80 ml) were used. To
the stirred mixture at r.t., a cat. amount (20 mg) of Rh2(OAc)4 was added. After 4 d, the mixture was sep-
arated by CC (hexane/AcOEt 4 :1 to 1:4)6): 258 mg (ca. 41%7)) of trans-10d. Yellowish-oily crystals. M.p.
could not be determined. IR (neat): 3083m, 3061s, 3028s, 2972s, 2940vs, 2866s, 2833s, 2788s, 1808w, 1754w,
1716w, 1687w, 1608vs, 1600vs, 1579s, 1492vs, 1473s, 1449vs, 1361s, 1293s, 1272s, 1253s, 1228s, 1177m, 1158s,
1075s, 1040vs, 997vs, 960s, 936s, 865m, 766vs, 751m, 690vs. 1H-NMR: 7.95–7.92 (d-like, 2 arom. H);
7.52–7.40 (m, 3 arom. H); 7.32–7.23 (m, 5 arom. H); 5.53 (d, J=4.4, HÀC(4)); 4.80 (d, J=4.4, HÀ
13
C(5)); 2.45 (s, Me2N). C-NMR: 167.3 (s, C(2)); 142.7, 131.5 (2s, 2 arom. C); 133.1, 128.9, 128.68),
127.6, 127.4 (5d, 10 arom. CH); 106.2 (d, C(4)); 55.7 (d, C(5)); 40.5 (q, Me2N). CI-MS (NH3): 284
(21), 283 (100, [M+1]+), 238 (45, [MÀMe2NH+1]+), 148 (21).
5.6. Experiment with EthylDiazoacetate (3e). According to GP A, a suspension of 8 (380 mg, 2
mmol) in THF (20 ml) and a soln. of 3e (ca. 4 mmol) in CH2Cl2 (40 ml) were used. To the stirred mixture,
5
)
On the basis of 2D-NMR experiments (HMBC), some signals could be assigned to the structures of
cis-11d and trans-11d. The signals of the aromatic C-atoms and the quaternary C-atoms could not be
correlated.
In the workup procedure, no Et3N was used.
Ca. 160 mg of the starting material 8 were recovered.
6
7
8
)
)
)
The intensity of this signal indicates absorption of 4 arom. CH.

Helvetica Chimica Acta – Vol. 90 (2007)
97
a cat. amount (ca. 20 mg) of Rh2(OAc)4 was added. After 10 d at r.t., the mixture was separated by CC
(hexane/AcOEt 4 :1): 450 mg of a complex mixture of products resulting from decomposition and ca.
15 mg of triethyl trans-4,5-dihydro-1H-pyrazole-3,4,5-tricarboxylate (17).
Crystals suitable for the X-ray crystal-structure determination were grown from CH2Cl2/pentane by
slow evaporation of the solvent.
6. Reactions of 9 with Diazoalkanes. 6.1. N,N-Dimethyl-N’-(2,3,3-triphenylprop-2-enylidene)hydra-
zine (18) and 2,5-Dihydro-N,N-dimethyl-2,2,5-triphenyl-1,3-thiazol-5-amine (21). To a soln. of freshly
prepared 9 (ca. 1.6 mmol) in benzene (10 ml), a purple soln. of 3b (ca. 2.5 mmol) in benzene (20 ml)
was added dropwise. After stirring for 1 h at r.t., purification of the crude mixture by CC (hexane/
AcOEt 15 :1) and MPLC(hexane/MeOH 90 :5) afforded a mixture of two products, which were sepa-
rated by crystallization from hexane/AcOEt/Et2O affording 234 mg of 18 (30%) and 60 mg (7%) of 21.
Data of 18. Pale-brownish crystals. M.p. 176–1778. IR: 3056w, 3027w, 2992w, 2970w, 2947m, 2867m,
2828m, 2783w, 1805w, 1664m, 1596w, 1580w, 1558w, 1488s, 1467m, 1445vs, 1175m, 1082m, 1073m, 1033m,
1
1009vs, 932m, 923m, 902s, 873m, 758vs, 697vs, 648s, 637s. H-NMR: 7.36–6.85 (m, 15 arom. H, and 1
=CH); 2.72 (s, Me2N). 13C-NMR: 142.8, 142.4, 139.5 (3s, 3 arom. C); 137.8 (s, 1 =C); 136.5 (br. s, 1
=C , 1=CH); 131.7, 131.0, 130.9, 127.9, 127.2, 127.1, 126.2, 126.0 (8d, 15 arom. CH); 42.6 (q, Me2N).
CI-MS (NH3): 327 (100, [M+1]+), 284 (16, [MÀMe2N+1]+), 203 (12), 178 (19), 160 (15), 158 (13).
Crystals suitable for the X-ray crystal-structure determination were grown from hexane/AcOEt/
Et2O by slow evaporation of the solvent.
Data of 21. Colorless crystals. M.p. 135–1378. IR: 3063w, 3026w, 2992w, 2970m, 2946m, 2868m,
2828m, 2783w, 1956w, 1804w, 1664m, 1595m, 1580w, 1487s, 1467s, 1445vs, 1031m, 1009vs, 932m, 923m,
901vs, 873m, 757vs, 697vs, 661m, 648s, 637s, 615m. 1H-NMR: 7.75 (d-like, 2 arom. H); 7.68–7.64 (d-
like, 2 arom. H); 7.35–7.15 (m, 11 arom. H, HÀC(4)); 2.09 (s, Me2N). 13C-NMR: 162.7 (d, HÀC(4));
146.2, 145.2, 139.8 (3s, 3 arom. C); 128.7, 128.5, 128.3, 127.9, 127.1, 127.1, 126.9, 126.5 (8d, 15 arom.
CH); 106.7 (s, C(2)); 97.5 (s, C(5)); 41.2, 41.1 (2q, Me2N). CI-MS (NH3): 358 (5, M+), 327 (10, [MÀ
Me2N+NH4]+), 314 (28, [MÀMe2N]+), 178 (100).
Crystals suitable for the X-ray crystal-structure determination were grown from CDCl3 by slow evap-
oration of the solvent.
6.2. (E/Z)-N,N-Dimethyl-N’-(2,3-diphenylprop-2-enylidene)hydrazine (23) and 2,5-Dihydro-N,N-
dimethyl-2,5-diphenyl-1,3-thiazol-5-amine (24). To a soln. of freshly prepared 9 (ca. 5 mmol) in a mixture
of hexane and AcOEt (300 ml, 10 :1), a soln. of 3d (ca. 6 mmol) in toluene (150 ml) was slowly added at
r.t. Purification of the crude mixture after 1 h by CC (hexane/AcOEt 10 :1 to 3 :1) and MPLC (hexane/
AcOEt 90 :5) afforded 3 almost pure compounds: 163 and 54 mg, resp., of the (E)- and (Z)-isomer of 23
(i.e., 23a and 23b)9), and 75 mg of one of the diastereoisomers of 24.
Data of 23a. Yellowish oil. IR: 3019m, 2950m, 2851m, 2824m, 2786m, 1626m, 1593m, 1551s, 1491s,
1469s, 1446s, 1266s, 1129m, 1077m, 1043vs, 896m, 862m, 760s, 750s, 698vs, 607m. 1H-NMR: 7.96 (s,
CH=N); 7.88–7.59 (m, 10 arom. H); 7.06 (s, C H=C); 3.24 (s, Me2N). 13C-NMR: 161.9 (d, C H=N);
141.2, 139.6, 137.5 (3s, 2 arom. C, 1 =C); 132.1, 130.2, 129.3, 127.8, 127.6, 127.2, 126.9 (7d, 10 arom.
CH, 1 =CH); 42.6 (q, Me2N). CI-MS (NH3): 252 (20), 251 (100, [M+1]+), 210 (16, [MÀMe2N2 +NH4]+),
209 (99, [MÀMe2N2 +NH3]+).
Data of 23b: Colorless oil. IR: 3055m, 3022m, 2951m, 2854m, 2784m, 1595m, 1553s, 1444s, 1361m,
1272s, 1133s, 1040vs, 918m, 897m, 849m, 778m, 756vs, 703vs, 632m, 601s. 1H-NMR: 7.70–7.54 (m, 5
arom. H); 7.53 (s, C H=N); 7.46–7.39 (m, 3 arom. H); 7.29–7.26 (m, 2 arom. H); 7.06 (s, C H=C); 3.21
(s, Me2N). 13C-NMR: 140.2, 139.1, 138.1 (3s, 2 arom. C, 1 =C); 137.0 (d, C H=N); 129.9, 129.8, 129.4,
128.2, 127.8, 127.0, 126.5 (7d, 10 arom. CH, 1 =CH); 42.7 (q, Me2N). CI-MS (NH3): 252 (19), 251 (100,
[M+1]+), 223 (11, [MÀMe2N+NH4]+).
Data of trans-24. Colorless crystals. M.p. 86–888. IR: 3080w, 3058m, 3024m, 2986m, 2959m, 2897w,
2843w, 2816s, 2772s, 1655s, 1595w, 1580w, 1488s, 1469m, 1451vs, 1427m, 1253m, 1235s, 1154m, 1095m,
1082m, 1064s, 1042m, 1028m, 996vs, 979s, 943m, 923s, 911s, 857m, 844s, 780w, 754vs, 732vs, 695vs,
1
633vs, 613s. H-NMR: 8.02–8.00 (d-like, 2 arom. H); 7.99–7.50 (m, 6 arom. H); 7.49 (d, J=2.9, HÀ
9
)
It was not possible to assign the spectra to (E)- and (Z)-23 on the basis of the present information.

98
Helvetica Chimica Acta – Vol. 90 (2007)
C(4)); 7.48–7.37 (m, 2 arom. H); 6.79 (d, J=2.9, HÀC(2)); 2.39 (s, Me2N). 13C-NMR: 165.7 (d, C(4));
141.0, 140.4 (2s, 2 arom. C); 128.7, 128.5, 128.5, 128.2, 127.9, 126.7 (6d, 10 arom. CH); 106.7 (s, C(5));
83.5 (d, HÀC(2)); 40.6 (q, Me2N). CI-MS (NH3): 283 (10, [M+1]+), 251 (12, [MÀS+1]+), 238 (100,
[MÀMe2N]+), 178 (88, [MÀPhCN]+).
Table. Crystallographic Data of Compounds 17, 18, 21, and trans-24
17
18
21
trans-24
Crystallized from
CH2Cl2/pentane hexane/AcOEt/Et2O CDCl3
CH2Cl2/hexane
C17H18N2S
282.40
Empirical formula
Formula weight [g molÀ1
Crystal color, habit
Crystal dimensions [mm]
Temp. [K]
Crystal system
Space group
Z
C12H18N2O6
286.28
C23H22N2
326.44
C23H22N2S
358.50
]
colorless, prism colorless, prism
0.22”0.25”0.32 0.10”0.15”0.22
colorless, prism colorless, prism
0.10”0.15”0.25 0.20”0.22”0.30
160(1)
orthorhombic
P212121
4
160(1)
160(1)
monoclinic
Cc
8
160(1)
monoclinic
P21/n
triclinic
ꢀ
P1
2
4
Reflections for cell
determination
2q Range for cell
determination [8]
14502
4028
5653
34463
4–55
4–55
4–60
4–60
Unit cell parameters a [Š] 7.8473(2)
b [Š] 10.3424(2)
9.9323(3)
9.9977(3)
10.4338(3)
62.635(2)
84.408(1)
78.997(1)
903.16(5)
1.200
12.9159(1)
15.0573(2)
20.1476(2)
90
106.6416(6)
90
3754.16(7)
10.9672(2)
6.0702(1)
22.4345(4)
90
91.248(1)
90
1493.18(5)
1.256
0.208
c [Š] 17.3424(5)
a [Š] 90
b [8]
90
g [Š] 90
V [Š3] 1407.51(6)
1.351
Dx [g cmÀ3
]
1.268
0.181
w
m(MoKa) [mmÀ1
Scan type
]
0.109
f and w
55
0.0703
f and w
55
f and w
60
2qmax [8]
60
Transmission factors (min;
max)
0.816; 0.925
–
–
0.870; 0.961
Total reflections measured
Symmetry-independent
reflections
20739
1867
21209
4105
52142
10265
38665
4378
Reflections with I>2s(I)
Reflections used in
refinement
1679
1866
2953
4102
8259
10257
3218
4376
Parameters refined; restraints 189; 0
229; 0
0.0483
0.1375
684; 1266
0.0421
0.1000
184; 0
0.0449
0.1166
R (on F; I>2s(I) reflections) 0.0390
wR (on F2; all indept.
0.1050
reflections)
Weighting parameters [a, b]a): 0.0578; 0.3696 0.0785; 0.0696
0.0506; 0.966
1.024
–
0.0533; 0.4053
1.062
0.069(4)
Goodness-of-fit
Secondary extinction
coefficient
1.066
0.032(6)
1.045
0.040(8)
Final Dmax/s
D1 (max; min) [e Š
0.001
0.28; À0.24
0.001
0.25; À0.22
0.001
0.24; À0.27
0.001
0.30; À0.27
À3
]
a) wÀ1 =s2(F2o)+(aP)2 +bP, where P=(Fo2 +2F2c )/3.

Helvetica Chimica Acta – Vol. 90 (2007)
99
Crystals suitable for the X-ray crystal-structure determination were grown from CH2Cl2/hexane by
slow evaporation of the solvent.
7. X-Ray Crystal-Structure Determination of 17, 18, 21, and trans-24 (Table and Figs. 1–3)10). All
measurements were performed on a Nonius KappaCCD diffractometer [22] using graphite-monochro-
mated MoKa radiation (l 0.71073 Š) and an Oxford Cryosystems Cryostream 700 cooler. The data col-
lection and refinement parameters are given in the Table, and views of the molecules are shown in Figs.
1–3. Data reduction was performed with HKL Denzo and Scalepack [23]. The intensities were corrected
for Lorentz and polarization effects, and an absorption correction based on the multi-scan method [24]
was applied in the cases of 17 and trans-24. Equivalent reflections were merged with the exception of the
Friedel pairs of 21. The structures were solved by direct methods using SHELXS97 [25] (for 17) and
SIR92 [26] (for 18, 21, and trans-24), which revealed the positions of all non-H-atoms. In the case of
21, there are two symmetry-independent molecules in the asymmetric unit. The atomic coordinates of
the two molecules were tested carefully for a relationship from a higher symmetry space group using
the program PLATON [27], but none could be found. In addition, both molecules are disordered by
inversion of each entire molecule about its center of gravity. Refinement of constrained site occupation
factors for the two orientations of each molecule yielded values of 0.934(1) and 0.935(1) for the major
conformation of molecules A and B, resp. An extensive series of similarity restraints was applied in
order to keep the chemically equivalent bond lengths and angles about all atoms in the minor compo-
nents to be similar to those of the major components. Furthermore, neighboring atoms within and
between each disordered orientation were restrained to have similar atomic displacement parameters.
The non-H-atoms of the major orientations were refined anisotropically, while those of the minor orien-
tations were refined isotropically. The non-H-atoms of 17, 18, and trans-24 were refined anisotropically.
The amine H-atom of 17 was placed in the position indicated by a difference electron density map, and its
position was allowed to refine together with an isotropic displacement parameter. All remaining H-atoms
of 17 and all of the H-atoms of 18, 21, and trans-24 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 any Me group). The refinement of each
structure was carried out on F2 using full-matrix least-squares procedures, which minimized the function
Sw(F2o ÀF2c )2. Corrections for secondary extinction were applied, except in the case of 18. In 17, 18, 21,
and trans-24, 1, 3, 8, and 2 reflections, resp., whose intensities were considered as extreme outliers,
were omitted from the final refinement. Refinement of the absolute structure parameter [28] for 21
yielded a value of 0.45(4), which indicates that the structure is an inversion twin. For 17, the space
group permits the compound to be enantiomerically pure, but the absolute configuration could not be
determined. The enantiomer used in the refinement model was chosen arbitrarily. Neutral atom scatter-
ing factors for non-H-atoms were taken from [29a], and the scattering factors for H-atoms were taken
from [30]. Anomalous dispersion effects were included in Fc [31]; the values for f ’ and f ’’ were those
of [29b]. The values of the mass attenuation coefficients are those of [29c]. All calculations were per-
formed using the SHELXL97 [32] program.
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100
Helvetica Chimica Acta – Vol. 90 (2007)
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Received August 10, 2006