Hetero-diels-alder reactions of perfluoroalkyl thioamides with electron-rich 1,3-dienes: Synthesis of new 2-aminosubstituted-3,6-dihydro-2H- thiopyrans and related compounds

Article abstract of DOI:10.1016/j.tet.2012.11.086

Hetero-Diels-Alder reactions of perfluoroalkyl thioamides with electron-rich 1,3-dienes such as 2,3-dimethylbutadiene, isoprene or penta-1,3-diene gave a simple and efficient access to new 2-aminosubstituted-3, 6-dihydro-2H-thiopyrans. Three different procedures were used depending on the nature of the polyfluoroalkyl chains (R_F=CF₃, (CF ₂)_nCF₃, (CF₂)₄H) and on the nitrogen substituents of the thioamides (R¹, R²=H, p-Tol, morpholino, Ac). Moreover, cycloadditions of silyloxydienes (1- or 2-trimethylsilyloxy-1,3-butadiene and Danishefsky's diene) with N-acyl,N-tolyl trifluoromethylthioamides afforded in almost all cases the corresponding 3,6-dihydro-2H-thiopyrans or 3-oxo-tetrahydrothiopyrans. For non-symmetrical 1,3-dienes, the regio- and stereochemistry of the reactions were studied (especially using X-ray diffraction analysis) indicating a strong similarity with those reported for fluorinated thiocarboxyl derivatives. Finally, two silylated 3,6-dihydro-2H-thiopyrans underwent an unexpected base-induced ring contraction to give new 1,3-thiazolidin-4-ones.

Full text of DOI:10.1016/j.tet.2012.11.086

Tetrahedron 69 (2013) 1322e1336
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Hetero-DielseAlder reactions of perfluoroalkyl thioamides with
electron-rich 1,3-dienes: synthesis of new 2-aminosubstituted-3,6-
dihydro-2H-thiopyrans and related compounds
,
,
Oleksandr S. Kanishchev a b, Morgane Sanselme c, Jean-Philippe Bouillon a
*
a
ꢀ
ꢀ
ꢀ
Universite et INSA de Rouen, Laboratoire Chimie Organique Bioorganique Reactivite et Analyses (COBRA), UMR CNRS 6014, IRCOF, F-76821 Mont Saint Aignan Cedex, France
b Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5, Murmanska, 02094 Kiev, Ukraine
c
ꢀ
ꢀ
ꢀ
Laboratoire Sciences et Methodes Separatives (SMS), EA 3233, Universite de Rouen, IRCOF, F-76821 Mont-Saint-Aignan Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Hetero-DielseAlder reactions of perfluoroalkyl thioamides with electron-rich 1,3-dienes such as 2,3-
Received 24 September 2012
Received in revised form 23 November 2012
Accepted 26 November 2012
Available online 5 December 2012
dimethylbutadiene, isoprene or penta-1,3-diene gave
a simple and efficient access to new
2-aminosubstituted-3,6-dihydro-2H-thiopyrans. Three different procedures were used depending on the
nature of the polyfluoroalkyl chains (RF¼CF3, (CF2)nCF3, (CF2)4H) and on the nitrogen substituents of the
thioamides (R1, R2¼H, p-Tol, morpholino, Ac). Moreover, cycloadditions of silyloxydienes (1- or 2-
trimethylsilyloxy-1,3-butadiene and Danishefsky’s diene) with N-acyl,N-tolyl trifluoromethylthioamides
afforded in almost all cases the corresponding 3,6-dihydro-2H-thiopyrans or 3-oxo-tetrahydrothiopyrans.
For non-symmetrical 1,3-dienes, the regio- and stereochemistry of the reactions were studied (especially
using X-ray diffraction analysis) indicating a strong similarity with those reported for fluorinated thio-
carboxyl derivatives. Finally, two silylated 3,6-dihydro-2H-thiopyrans underwent an unexpected base-
induced ring contraction to give new 1,3-thiazolidin-4-ones.
Dedicated to Professor Charles Portella
ꢀ
(Universite de Reims Champagne Ardenne,
France) for his retirement
Keywords:
Fluorine
Sulfur
Ó 2012 Elsevier Ltd. All rights reserved.
Heterocycle
2H-Thiopyran
1,3-Thiazolidin-4-one
Thioamide
Hetero-DielseAlder reaction
Microwave
1. Introduction
The two main fluorinated thiocarbonyl derivatives are tri-
fluorothioacetaldehyde and hexafluorothioketone. The first one is
Thiocarbonyl derivatives are well known for their practical and
synthetic applications in reactions with electrophiles or nucleo-
philes, cyclizations, and cycloadditions.1 Certain derivatives bearing
an electron-withdrawing group are especially useful in hetero-
DielseAlder reactions.2 Among them, polyfluorinated thiocarbonyl
and thiocarboxyl derivatives are efficient electron-poor dien-
ophiles. Indeed, addition of perfluoroalkyl substituents to a thio-
carbonyl group substantially raises its dienophilic character
allowing reactions with electron-rich 1,3-dienes in order to syn-
thesize fluorine-containing thiopyrans.3 In this introduction, we
will focus only on hetero-DielseAlder reactions of polyfluorinated
thiocarbonyl and thiocarboxyl derivatives, respectively.
a very unstable compound, which spontaneously polymerizes even
at low temperature, but, which is a very active heterodienophile.4 It
is worth noting that perfluoroalkyl analogs (C4F9, (CF2)4H)5 are
slightly more stable and efficient in hetero-DielseAlder reactions.
Hexafluorothioacetone or its stable dimeric form reacts with
electron-rich 1,3-dienes such as substituted 1,3-butadienes, an-
thracene or furan.6aec Other polyfluorinated thioketones were
found to have similar properties.6d
Polyfluorinated thiocarboxyl derivatives belong to a large family
of compounds: thioacyl halides (chloride or fluoride),6b,7 thio-
noesters,8 dithioesters,9 and thioamides. All of those compounds
(except the latter) behave as active heterodienophiles with
electron-rich acyclic or cyclic 1,3-dienes giving fluorinated thio-
pyran derivatives.
Our interest in this field began in connection with the prepa-
ration of polyfluorodithioesters and their hetero-DielseAlder re-
actions.9 Although their syntheses required strong conditions or
* Corresponding author. Tel.: þ33 (0)2 35 52 24 22; fax: þ33 (0)2 35 52 29 59;
e-mail address: jean-philippe.bouillon@univ-rouen.fr (J.-P. Bouillon).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.11.086

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1323
expensive reagents, these dithioesters were stable compounds,
easy handled, and very efficient heterodienophiles at room tem-
perature affording good to excellent yields of cycloadducts. On the
contrary, thioamides and polyfluorinated analogs were easily pre-
pared by thionation of the corresponding amides10 but there were
only few examples of their [4þ2] cycloaddition reactions with
1,3-dienes. On the one hand, N,N-disubstituted thioformamides11
or cyano analogs12 react with both electron-poor or electron-rich
1,3-dienes yielding variously substituted dihydrothiopyrans. On
the other hand, only one example of a [4þ2] cycloaddition of
N-methyl-N-acetyltrifluorothioacetamide was described by H.G.
Viehe et al.; this result was explained by the enhancement of the
thioamide reactivity due to the introduction of the electron-
withdrawing substituent on the nitrogen atom.13
under microwave heating at 85e180 ꢀC, in the presence of WeflonÔ
(Scheme 2, Table 1: Method 1).
The choice of such conditions needs several comments: (a) the
reaction was conducted stepwise, adding new portions of 2,3-
dimethylbutadiene to the reaction mixture every 30 min in order
to diminish diene polymerization. Diene was rapidly introduced via
a syringe without opening the vial, avoiding release of chemicals
into atmosphere. The overall reaction time was 3 h and the global
quantity of 2,3-dimethylbutadiene reached 15e20 equiv; (b) NMP
as solvent was justified by its efficiency to transform electromag-
netic energy into thermal energy.19 This polar aprotic solvent al-
lows working up to 200 ꢀC without troublesome vapor and high
pressure in the tubes; (c) WeflonÔ (TeflonÔ filled with graphite)
was used in order to better transfer heat to the reaction mixture,
thus avoiding ‘hot spots’.
Using the optimized conditions (Method 1), [4þ2] cycloaddi-
tions of primary (Table 1: entry 1), secondary (entries 2 and 3), and
tertiary (entries 6e8) perfluoroalkyl thioamides 9aec,feh with
2,3-dimethylbutadiene (3) afforded moderate to good yields
(15e49%) of new 3,6-dihydro-2H-thiopyrans 10aec,feh (Scheme
2), after purification by silica gel column chromatography. Never-
theless, conversions were not complete, reaching a maximum of
83%. In addition to cycloadducts 10, polymerization products of
diene and other minor non-identified fluorinated by-products
appeared in the crude mixture. Moreover, the behavior of cyclo-
adduct 10c (Table 1: entry 3) bearing an octafluoroalkyl chain was
slightly different than the others giving a spontaneous desamina-
tion reaction into 2H-thiopyran 11 during microwave heating of the
reaction mixture (Scheme 2). This process was only observed with
(CF2)4H perfluoroalkyl chain; the CF3-analog of 11 was not detected
in the crude reaction mixture of thioamide 9b and 2,3-
dimethylbutadiene.
The main question of our study was the following: is it possible to
perform efficient [4þ2] cycloaddition reactions of polyfluoroalkyl-
containing thioamides 1 with electron-rich 1,3-dienes in order to
obtain new 3,6-dihydro-2H-thiopyrans 2 (Scheme 1).
In a recent article, we reported the first examples of hetero-
DielseAlder reactions of perfluoroalkyl thioamides with 2,3-
dimethylbutadiene under microwave heating, allowing high con-
version and moderate yields of 3,6-dihydro-2H-thiopyrans.14 Those
cycloadditions seemed to be dependent on both the nature of the
perfluoroalkyl chain and on the substituent attached to the nitro-
gen atom. In this paper, we present an expanded investigation of
hetero-DielseAlder reactions of trifluoromethyl- or poly-
fluoroalkylthioamides with various electron-rich 1,3-dienes (acy-
clic or cyclic, symmetrical or non-symmetrical), as well as the study
of their regio- and stereoselectivity.
2. Results and discussion
Our first [4þ2] cycloaddition reactions were performed with
2,3-dimethylbuta-1,3-diene (3) as a symmetrical model of alkyl-
substituted 1,3-dienes in order to find the best conditions. Then,
the optimized conditions were extended to symmetrical cyclic di-
ene (cyclohexa-1,3-diene (4)) and non-symmetrical dienes such as
isoprene (5) and penta-1,3-diene (6). Finally, the reactivity of sily-
loxy-1,3-dienes (1-(trimethylsilyloxy)butadiene (7) and Dani-
shefsky’s diene 8) was studied.
Although new cycloadducts 10aec,feh were obtained in mod-
erate to good yields (Scheme 2, Table 1), Method 1 suffered from
several drawbacks namely, only partial conversion of starting thi-
oamides, use of a large excess of diene 3 (15e20 equiv) and a few
difficulties for scaling-up the reaction. Therefore, we looked for the
possibility to enhance the dienophilic character of the per-
fluoroalkyl thioamides 9.
Literature precedent has shown that the reactivity of thioamides
can be improved by the addition of an electron-withdrawing sub-
stituent on the nitrogen atom. Indeed, a
-cyano thioamides12 react
2.1. Reactions with 2,3-dimethylbuta-1,3-diene (3) and cyclo-
hexa-1,3-diene (4)
smoothly with 2,3-dimethylbutadiene in dichloromethane solution at
room temperature; while N-acetyl thioformamide20 behaves as an
efficient dienophile with cyclohexa-1,3-diene or anthracene under
titanium tetrachloride activation. These results were explained by the
decrease in the electron-donating ability of the nitrogen lone pair. The
same type of activation was already used in the fluorinated series
regarding the unique example of [4þ2] cycloaddition with N-methyl-
N-acetyltrifluorothioacetamide with 2,3-dimethylbutadiene.13 There-
fore, these methods were combined to prepare and use N-acetyl and
The use of microwave heating has been extensively described in
the literature,15 especially in heterocyclic chemistry16 and cyclo-
additions.17 Rate enhancement, higher yields, and easier handling of
reaction mixtures are the main benefits usually mentioned for this
technology.18 Indeed, in our preliminary study,14 we have shown
that thioamides 9 reacted with an excess of 2,3-dimethylbuta-1,3-
diene (3) in N-methylpyrrolidin-2-one (NMP) in a sealed tube
R3,R4
RF
S
R3,R4
R1
R1
N
S
N
+
RF
R2
R2
1
2
R1, R2=H, Alk, Ar, Ac
R3, R4=H, Me,
OMe, OSiR5
RF=CF3, (CF2)nCF3
3
Scheme 1.

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O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
S
RF
(CF2)4H
R1
R1
Method 1 or
Method 2
N
+
N
RF
S
S
R2
R2
10a-h
9a-h
11
3
Scheme 2. Reagents and conditions. Method 1: diene (15e20 equiv), NMP, m
w 300 W, 85e180 ꢀC, 3 h. Method 2: diene (1.5e2.0 equiv), CH2Cl2, rt, 4e24 h.
Table 1
Reactions of thioamides 9aeh with 2,3-dimethylbutadiene (3)
Entry
Thioamide
R1
R2
RF
Methoda
T (ꢀC)
Conv.b (%)
Cycloadductc (%)
1
2
3
4
5
6
7
8
9a
9b
9c
9d
9e
9f
H
H
H
Ac
H
CF3
CF3
(CF2)4H
CF3
(CF2)4H
CF3
1
1
1
85
125
145
25
57
54
50
100
100
83
10a: 35
10b: 26
10c: 15d
10d: 78
10e: 69
10f: 45
10g: 49
10h: 28
p-Tol
p-Tol
p-Tol
p-Tol
2e
2f
1
Ac
25
(CH2)2O(CH2)2
(CH2)2O(CH2)2
(CH2)2O(CH2)2
180
180
180
9g
9h
CF3CF2
CF3(CF2)2
1
1
70
50
a
Method 1: diene (15e20 equiv), NMP, m
w 300 W, 85e180 ꢀC, 3 h. Method 2: diene (1.5e2.0 equiv), CH2Cl2, rt, 4e24 h.
b
c
d
e
f
Conversion was based on 19F NMR spectra of the reaction mixture.
Isolated yields. All pure cycloadducts were obtained by purification by silica gel column chromatography.
Desamination of 10c into compound 11 took place during heating of the reaction mixture under microwave irradiation.
Reaction time: 4 h.
Reaction time: 24 h.
N-benzoyl polyfluoroalkylthioamides 9d,e,i,k,l. The desired com-
pounds were obtained in almost quantitative yields by usual acylation
reactions from the corresponding thioamides 9b,c,j in the presence of
the appropriate acid chloride and triethylamine at 0 ꢀC (Scheme 3). N-
Acetyl derivatives 9d,e,k are unstable compounds and were used
immediately after isolation.
In order to compare the dienophilic character of thioamides
9bee, molecular orbital calculations were performed at the B3LYP/
6-31G** level of theory. The geometries of compounds 9bee were
first optimized and the energies of HOMO, LUMO, and their orbital
coefficients were computed using the Gaussian 0321 package of
programs. The corresponding energy values and dihedral angles
S
S
O
Et3N
CH2Cl2, 0°C
R1
R1
+
N
H
N
RF
RF
Cl
R3
O
R3
RF=CF3, R1=p-Tol, R3=Me, 9d (95%)
RF=H(CF2)4, R1=p-Tol, R3=Me, 9e (97%)
RF=CF3, R1=p-Tol, R3=Ph, 9i (95%)
RF=CF3, R1=n-Pr, R3=Me, 9k (94%)
RF=CF3, R1=p-Tol, R3=Et, 9l (95%)
9b: RF=CF3, R1=p-Tol
9c: RF=H(CF2)4, R1=p-Tol
9j: RF=CF3, R1=n-Pr
Scheme 3.
Reactions of N-acetyl thioamides 9d,e with 2,3-dimethylbut-
adiene (3) (1.5e2.0 equiv) at room temperature in dichloro-
methane solution (Table 1: Method 2: entries 4, 5) afforded the
corresponding cycloadducts 10d,e in good yields. In comparison to
non N-acetylated thioamides 10b,c (entries 2, 3), there was full
conversion of starting material and significant yield improvement
(from 26% to 78%, from 15% to 69%, respectively). Moreover, Method
2 had several advantages: the use of only a slight excess of diene
(1.5e2.0 equiv), which greatly facilitated work-up and silica gel
column chromatography; and a reaction at room temperature,
which avoided partial desamination.
between the phenyl ring and the thioamide moiety are collected in
Table 2. DielseAlder reactions are under orbital control and since
the 1,3-diene is electron-rich and the dienophiles electron-poor,
the preceding reactions are under normal control: therefore, their
reactivity was related to the energy gap between the HOMO of the
diene and the LUMO of the dienophile: ‘the lower the gap, the
easier the reaction’. Therefore, the presence of the N-acetyl
electron-withdrawing group increases the reactivity of 9d,e.
Moreover, whereas molecules 9b and 9c are quite planar (Figs. 1
and 2 and Table 2: entries 1 and 2), the introduction of an acetyl
group into molecules 9d and 9e also forces the thioamide to be out

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1325
Table 2
HOMO, LUMO energy values and dihedral angles of thioamides 9bee
Entry
Compound
EHOMO (eV)
ELUMO (eV)
Dihedral angle (ꢀ)
1
2
3
4
9b
9c
9d
9e
ꢁ6.18
ꢁ6.18
ꢁ6.31
ꢁ6.36
ꢁ1.94
ꢁ2.01
ꢁ2.45
ꢁ2.51
0.41
0.40
68.19
67.52
Fig. 4. Optimized geometry of compound 9e.
There are few examples in the literature in which cyclohexa-1,3-
diene reacts with non-symmetrical polyfluoroalkyl thiocarbonyl
derivatives;7,9d,22 and in most cases, the stereochemistry was not
discussed in detail. The outcome of this reaction for non-
fluorinated thioaldehydes has been more thoroughly studied,
showing endo selectivity during cycloadduct formation.23 In our
case, we could also reasonably assume that major isomer had an
endo configuration.
Fig. 1. Optimized geometry of compound 9b.
2.2. Reactions with isoprene (5) and penta-1,3-diene (6)
We then turned our attention on the study of regio- and ste-
reochemistry of our [4þ2] cycloaddition reactions using non-
symmetrical alkyl-substituted 1,3-dienes. It has been shown in
the literature that [4þ2] cycloadditions of perfluoroalkyl thio-
carbonyl derivatives with isoprene give a mixture of regioisomers
in equal ratio5a or with a slight excess of one isomer.9d No reaction
has been described however using penta-1,3-diene in the fluori-
nated series, but one could expect the formation of both regio- and
stereoisomers. Indeed, thioacetaldehyde reacts with penta-1,3-
diene affording a mixture (77:23) of two regioisomers.23a
Fig. 2. Optimized geometry of compound 9c.
2.2.1. Reactions with isoprene (5). In the presence of isoprene (5),
thioamides 9 were expected to give a mixture of two regioisomers.
When applying Methods 1 and 2, the same behavior described for
the reactions with 2,3-dimethylbutadiene was observed. With
thioamide 9f (R1, R2¼(CH2)2O(CH2)2), use of Method 1 led to a 19%
yield of cycloadducts 13a, 14a as a mixture (52:48) of regioisomers
(Scheme 5). Reactions with N-acetyl- and N-benzoyl thioamides 9d,
9i proceeded smoothly with isoprene at room temperature
affording good yields (76% and 67%, respectively) of the corre-
sponding cycloadducts 13b,c and 14b,c as non-separable mixtures
of regioisomers. Reaction with N-benzoyl thioamide 9i was very
slow (almost total conversion after 60 d). It is worth noting that
regioisomers 13b,c were greatly favored (85:15 mixture). This
regioselectivity, although better, was still the same as previously
observed for difluorophosphono dithioesters (60:40 mixture of
regioisomers)9d or for thiones derived from Meldrum’s acid and
malonates.24
of the plane of the phenyl ring (Figs. 3 and 4 and Table 2: entries 3
and 4). The corresponding lack of conjugation between the phenyl
ring and the thioamide leads to a significant lowering of the LUMO
energies, explaining probably the reactivity differences of mole-
cules 9b,c compared to the corresponding N-acetylated compounds
9d,e.
The major regioisomer 13b was assigned to be the 5-methyl
cycloadduct. Indeed, in 1H NMR spectrum of the mixture, the
vinylic proton was significantly shifted downfield (dH-5¼5.77 ppm)
in minor isomer 14b, compared with the major isomer 13b
Fig. 3. Optimized geometry of compound 9d.
(dH-4¼5.16 ppm). Moreover, the structure of the major regioisomer
13b was confirmed by X-ray diffraction analysis (Fig. 5).
The next step was to extend our methodology to symmetrical
cyclic 1,3-diene choosing cyclohexa-1,3-diene (4) as a model. Ap-
plying Method 1, no conversion of the starting material was ob-
served in reaction of thioamide 9b or thiomorpholide 9f. On the
contrary, N-acetyl thioamide 9d was successfully converted
(Method 2, yield: 58%) into bicyclic compound 12 as a mixture of
(0.3:1) exo/endo isomers (Scheme 4).
2.2.2. Reactions with penta-1,3-diene (6). Reactions with penta-1,3-
diene (6) were more complicated as a mixture of two regioisomers
was expected, each regioisomer being itself
diastereoisomers.
a mixture of
The first attempt with thioamide 9f using Method 1 failed; no
conversion of the starting material was observed even using a large

1326
O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
S
p-Tol
Method 2
S
N
F3C
+
CF3
Ac
N
Ac
p
-Tol
4
9d
12 (58%)
Scheme 4. Reagents and conditions. Method 2: diene (2.0 equiv), CH2Cl2, rt, 4 h: conv. 100%, mixture of (0.3:1) exo/endo isomers.
CF3
NR1R2
CF3
NR1R2
S
Method 1 or
Method 2
4
+
+
NR1R2
F3C
S
S
5
5
13a-c
14a-c
9d,f,i
a) R1,R2=(CH2)2O(CH2)2: 19% (52:48)a
b) R1=Ac, R2=p-Tol: 76% (85:15)b
c) R1=Bz, R2=p-Tol: 67% (85:15)b
Scheme 5. Reagents and conditions. aMethod 1: diene (20 equiv), NMP,
m
w 300 W, 180 ꢀC, 3 h. bMethod 2: diene (1.5 equiv), CH2Cl2, rt, 18 h to 60 d.
excess of diene and a long reaction time. On the contrary, reaction
of compound 9d with penta-1,3-diene in dichloromethane
(Method 2) led to 80% yield of cycloadducts 15 and 16 as a complex
mixture (40:24; 22:14) of regio- and diastereoisomers (Scheme 6).
The ratio of isomers was determined from 19F NMR spectra of the
crude reaction mixture. All isomers were not fully separated by
silica gel column chromatography but several enriched fractions
were obtained allowing assignment of their structures by NMR. The
structure of regioisomers was deduced from comparison of 1H NMR
signals of the protons attached to the methyl substituent. Thus, in
6-methyl isomers 16, the cyclic methine protons were significantly
shifted downfield (dH-6¼4.30, 3.79 ppm) compared with the 3-
methyl isomers (dH-3¼3.43, 3.54 ppm), due to the sulfur atom at-
tached on the same carbon. Moreover, multiplicity of the H-3
protons in the 3-methyl isomers (compound 15) was complex due
4
to an additional splitting because of the long-range JHeF coupling
with fluorine atoms of CF3-group. Cyclic methine proton (H-6) of
other regioisomers 16 appeared as
a doublet of quartet
(3JH,H¼6.8 Hz, JH,H¼6.6 Hz) due to the absence of JHeF coupling
(too long distance between H-6 and fluorine atoms). It is also worth
noting that the 3-methyl cycloadducts 15 were obtained as the
major regioisomers, this observation being in good agreement with
the literature.24,25 Unfortunately, we were not able to determine
the stereochemistry of cycloadducts 15 and 16.
3
5
Fig. 5. ORTEP representation of compound 13b (displacement ellipsoids with 50% of
probability).
S
CF3
CF3
3
p-Tol
p-Tol
p-Tol CH2Cl2, rt,
N
N
+
N
F3C
+
S
S
60h
(Method 2)
Ac
Ac
6
Ac
16
15
6
9d
80% (40:24;22:14)
Scheme 6.

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1327
2.3. Reactions with 1-(trimethylsilyloxy)butadiene (7) and
Danishefsky’s dienes 8a,b
OAc
OH
(CF2)4H
CF3
N
Ac
We then investigated the reaction of perfluoroalkyl thioamides
9 with silyloxy-1,3-dienes, especially 1-(trimethylsilyloxy)butadi-
ene (7) and Danishefsky’s dienes 8a,b to have access to new fluo-
rinated dihydro-2H-thiopyrans and 3-oxo-tetrahydrothiopyrans
(which could be valuable precursors for the synthesis of thiopyr-
anose derivatives). There are only a few examples of hetero-
DielseAlder reactions of silyloxy-1,3-dienes with polyfluorinated
thiocarbonyl or thiocarboxyl derivatives. On the one hand, per-
fluorodithioesters and 1-trimethylsilyloxy-butadiene have been
reported to proceed with low regio- and stereoselectivity to give
a mixture of four dihydro-2H-thiopyrans.9b On the other hand,
Danishefsky’s diene reacts with perfluoroalkyl thioacetaldehyde
(generated in situ from its corresponding anthracene cyclo-
adduct)26 or with phosphonodifluorodithioacetate9d affording
a mixture of regioisomers, which were then converted by acid
hydrolysis or TMSOTf treatment into dihydrothiopyranones.
NH
S
S
p-Tol
p-Tol
19
18
Fig. 6. By-products 18 and 19.
of isomers). The behavior of the cycloadduct bearing an octo-
fluorobutyl chain was different from compounds 17. Indeed, dur-
ing silica gel purification, a desilylation process followed by an
N/O acetyl group migration27 occurred giving compound 19
confirming indirectly the regiochemistry of cycloaddition reaction,
when both hydroxy and amino groups have vicinal position
(Fig. 6).
Regioisomers 20 and 21 (Table 3: entries 1 and 2) were char-
acterized in the crude mixture but spontaneously decomposed
during silica gel column chromatography. We assume that those
regioisomers containing a hemithioaminal function are less stable
to hydrolysis. A similar observation was also made in the reaction of
trifluoromethyl or octofluorobutyl dithioesters with 1-(trime-
thylsilyloxy)buta-1,3-diene.9b
Finally, as previously observed for alkyl-substituted 1,3-dienes,
thiomorpholide 9f did not react under microwave irradiation (Table
2: entry 3). Nevertheless, regioisomers 22 (mixture (67:33) of non-
separated diastereoisomers) were obtained in low 12% yield by
simple heating of 1,3-diene 7 and compound 9f (Table 3: entry 4,
Method 3).
2.3.1. Reactions with 1-(trimethylsilyloxy)buta-1,3-diene (7). Reactions
of thioamides 9 with 1-(trimethylsilyloxy)buta-1,3-diene (7) were
carried out under usual conditions (Scheme 7: Methods 1e3). The
regio- and stereoselectivity depend on the substitution pattern of
thioamides. N-Acetyl thioamide 9d was transformed (100% conver-
sion after 4 h) into a mixture of two regioisomers, each of them being
obtained as a mixture of two diastereoisomers (Table 3: entry 1). The
ratio (50:12; 24:14) of isomers was determined according to the 19F
NMR data of the reaction mixture. The separation of this mixture was
very difficult; only cycloadduct 17a was obtained as a single di-
astereoisomer after silica gel column chromatography. Unfortunately,
it was not possible to determine its stereochemistry. When
a dichloromethane solution of 17a was kept at room temperature for
several days, a spontaneous quantitative desilylation occurred lead-
ing to compound 18 (Fig. 6).
2.3.2. Reactionwith2-(trimethylsilyloxy)buta-1,3-diene(23). Reactions
were then extended to 2-(trimethylsilyloxy)buta-1,3-diene. The re-
action of thioamide 9d with 1,3-diene (23) was regioselective and led,
RF
OTMS
S
R1
RF
R1
N
R1
Method 1, 2 or 3
3
6
S
+
N
+
RF
N
R2
S
R2
R2
OTMS
OTMS
17
9d-f
7
20-22
Scheme 7. Reagents and conditions. Method 1: diene (10 equiv), NMP, m
w 300 W, 180 ꢀC, 3 h. Method 2: diene (1.5 equiv), CH2Cl2, rt. Method 3: diene (10 equiv), neat, 150 ꢀC, 3 h.
Table 3
Reaction of thioamides 9def with 1-trimethylsilyloxy-buta-1,3-diene (7)
Entry
Thio-amide
R1
R2
RF
Methoda
Conv.b (%)
Compound 17c (%)
Compounds 20e22c (%)
1
2
3
4
9d
9e
9f
Ac
Ac
p-Tol
p-Tol
CF3
(CF2)4H
CF3
2; 4 h
2; 24 h
1
3
100e
100f
w0
27
17: 17
20d
g
21d
d
(CH2)2O(CH2)2
(CH2)2O(CH2)2
d
d
9f
CF3
22: 12h
a
Method 1: diene (10 equiv), NMP, m
w 300 W, 180 ꢀC, 3 h. Method 2: diene (1.5 equiv), CH2Cl2, rt. Method 3: diene (10 equiv), neat, 150 ꢀC, 3 h.
b
c
Conversion and ratio of isomers were based on 19F NMR spectra of the reaction mixture.
Isolated yields. All pure cycloadducts were obtained after purification by silica gel column chromatography as mixtures of diastereomers.
Decomposition of cycloadducts 20, 21 was observed during purification by silica gel chromatography.
Ratio of isomers: 50:12; 24:14.
d
e
f
Ratio of isomers was not determined.
Cycloadduct was spontaneously transformed into O-acetylated derivative 19 (yield: 11%).
Ratio of diastereoisomers: 67:33.
g
h
The reaction of the octafluorobutyl thioamide 9e was more
after hydrolysis of silylated cyclodduct, to the formation of corre-
difficult (100% conversion after 24 h, Table 2: entry 2) and complex
affording O-acetylated derivative 19 (11% isolated yield) and un-
stable cycloadducts 21 (it was not possible to determine the ratio
sponding thiopyran-3-one 24 (Scheme 8). The other regioisomer was
not detected in the19F NMR spectrum of the reaction mixture. Desi-
lylation of the initially formed cycloadduct was performed by adding

1328
O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
S
CF3
TMSO
p-Tol
(i)
p-Tol
N
N
+
F3C
S
O
Ac
Ac
2
9d
23
24 (59%)
Scheme 8. Reagents and conditions. (i) (1) Method 2: diene (1.0 equiv), CH2Cl2, rt, 15 h then (2) Hþ, MeOH.
methanol containing a catalytic amount of HCl directly to the reaction
mixture. Compound 24 was then isolated in 59% yield after silica gel
column chromatography. The methylene protons of 24 appear as an
AB-system (dH-2¼2.96 ppm, 3.61 ppm) without any additional split-
ting as could be expected for other regioisomer.
analysis (Fig. 7) showing a cis relationship between the OMe and
the CF3-groups. The regioselectivity of these hetero-DielseAlder
reactions is in good agreement with those reported by E. Pfund
et al. for phosphonodifluorodithioacetate,9d but is significantly
different than what was observed for the reaction of perfluoroalkyl
thioacetaldehyde.26
2.3.3. Reactions with Danishefsky’s dienes 8a,b. The reactions with
Danishefsky’sdienes8a,bweretheninvestigatedinordertostudythe
regio- and stereochemistry of our cycloadditions. When CF3ethioa-
mide 9d reacted in the presence of 1.0 equiv of diene 8a in CH2Cl2
solution for 1 h (Scheme 9: Method 2, Table 4), only one peak of the
CF3-group was observed in the 19F NMR spectrum of the reaction
mixture, thus indicating that the reaction was totally regio- and
stereoselective. The 3-oxo-tetrahydrothiopyran 25 was obtained in
60% yieldasthe uniquediastereoisomerfromspontaneoushydrolysis
of the silyl enol ether intermediate during purification by silica gel
column chromatography. Both the methoxy group (dOMe¼3.28 ppm)
and the methine proton (dH-5¼4.81 ppm) had characteristic chemical
shifts showing them attached on the C-5 thiopyran ring.
Then, the hetero-DielseAlder reaction of Danishefsky’s diene
8a with thiomorpholide 9f was performed. When a mixture of
8a and 9f was heated at 150 ꢀC for 3 h (Method 3) directly fol-
lowed by aqueous acidic hydrolysis and subsequent flash
column chromatography (Scheme 10), cycloadducts 28 were ob-
tained in low yield as a mixture of diastereoisomers (67:33, their
stereochemistry was not determined), accompanied by
g-thio-
pyrone 29. The latter was probably formed by spontaneous
morpholine and methanol elimination starting from the corre-
sponding cycloadducts 28. It is worth noting that another syn-
thesis of compound 29 has been recently described by
decarboxylation of corresponding 4-oxo-6-trifluoromethyl-4H-
thiopyran-2-carboxylic acid.28
OMe
OMe
RO
S
RF
CF3
Method 2
p-Tol
5
p-Tol
p-Tol
+
or
TBSO
N
N
RF
N
S
S
O
Ac
Ac
Ac
OMe
25, 26
9d,e
8a,b
27
R = TMS, TBS
Scheme 9. Reagents and conditions. Method 2: diene (1.0 equiv), CH2Cl2, rt, 1 h.
Firstly, only two peaks of the CF3-groups related to the two di-
astereoisomers of compound 28 were observed in the 19F NMR
spectra of the crude reaction mixture. Moreover, 1H NMR of major
stereoisomer showed characteristic shifts for the thiopyran
‘anomeric’ MeO-group (dOMe¼3.46 ppm) and the corresponding
methine proton (dH-6¼4.92 ppm).
Table 4
Reactions of thioamides 9d,e with Danishefsky’s dienes 8a,b
Entry
Diene (R)
Thioamide
RF
Compounds
Compound
25, 26a,b (%)
27a,b (%)
1
2
3
8a (TMS)
8a (TMS)
8b (TBS)
9d
9e
9d
CF3
(CF2)4H
CF3
25: 60
26: 62
d
d
d
27: 75
Secondly, the regioselective outcome of the reaction of thio-
morpholide 9f with Danishefsky’s diene 8a is the opposite of thi-
oamides 9d,e (Scheme 9, Table 4) but the same as with 1-
(trimethylsilyloxy)buta-1,3-diene (7) (Table 3: entries 3 and 4). It
clearly shows that on the one hand, the presence of only one
electron-withdrawing substituent such as a polyfluoroalkyl group
in carboxylic acid thioamides 9feh, is not enough to overcome the
a
Quantitative conversion based on 19F NMR spectra of the reaction mixture.
Isolated yields after purification by silica gel column chromatography.
b
The hetero-DielseAlder reaction was then extended to octa-
fluorobutyl thioamide 9e. Similarly, 3-oxo-tetrahydrothiopyran 26
was obtained in 62% yield in a regio- and diastereoselective manner
(Table 4: entry 2).
In order to isolate the cycloadduct as well as to determine its
relative configuration, thioamide 9d was treated under the same
conditions with tert-butyldimethylsilyloxy-1,3-diene 8b (Scheme
9). As expected, the corresponding O-TBS silyl enol ether 27 was
more hydrolytically stable and was obtained in 75% yield, after
silica gel column chromatography (Table 4: entry 3). The relative
configuration of compound 27 was ascribed by X-ray diffraction
p-donating effect of the nitrogen atom; on the other hand, an ad-
ditional acceptor substituent, particularly one acetyl or benzoyl
group on thioamide nitrogen, is needed to reverse C]S bond po-
larization, thus making thioamides 9d,e good dienophiles in non-
catalyzed hetero-DielseAlder reactions.
2.3.4. Ring contraction to 1,3-thiazolidin-4-ones 31. As we have
mentioned above (Scheme 9), desilylation of primary cycloadducts
of type 27 using acid catalysis provided the expected deprotected

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1329
analysis was used to determine the structure and the relative
configuration of thiazolidinone 31a (Fig. 8).
Few other comments concerning the rearrangement have to be
added:
(a) First, the primary silylated cycloadduct obtained from thio-
amide 9d (Scheme 8) when treated with TBAF in CH2Cl2, pro-
duced only the derivative 24 without any rearrangement. Pure
compound 24 did not also react with TBAF.
(b) Secondly, the influence of N-acyl substituent (R2¼H, Me) on the
course of the rearrangement was also studied. The silylated
cycloadduct 30c was reacted with TBAF in CH2Cl2 in order to
obtain the corresponding 5-methyl-substituted thiazolidinone.
Unfortunately, it gave only desilylated product 32 (yield: 55%),
without any rearrangement. Pure thiopyran-3-one 32 did not
react with TBAF, CH2Cl2 or Cs2CO3, THF too.
(c) Finally, we have screened the effect of other bases on desily-
lated 3-oxo cycloadducts. For example, the rearranged product
31a was obtained from the desilylated 3-oxo thiopyran 25
using Cs2CO3 in THF (full conversion of starting material after
24 h at room temperature was monitored by 19F NMR). Using
i-Pr2NH as a base, we have also detected (by 19F NMR) the
formation of rearranged product 31a, but conversion was
low (w20%). Moreover, the usage of stronger base such as
t-BuOK or NaH in THF resulted only in decomposition of thio-
pyran ring.
Fig. 7. ORTEP representation of compound 27 (displacement ellipsoids with 50% of
probability).
CF3
S
TMSO
O
CF3
O
1) Method 3
2) (i)
N
+
+
N
F3C
S
6
O
S
O
OMe
8a
OMe
9f
28
Conv.: 70%
29
10%
10% (67:33)
Scheme 10. Reagents and conditions. Method 3: diene (2 equiv), neat, 150 ꢀC, 3 h; (i): TFA or HCl, THF/H2O.
thiopyrans 25 and 26. But it was also noticed that treatment with
TBAF for the same purpose resulted in the formation of a new
product, which had a different chemical shift in the 19F NMR
spectrum. Careful optimization of the reaction parameters allowed
us to find the correct conditions for the formation of this compound
as the major product. Thus, addition of solid TBAF trihydrate to
a dichloromethane solution of primary silylated cycloadducts 30a,b
led to the formation of the corresponding 1,3-thiazolidin-4-ones
31a,b in moderate overall yields (Scheme 11). X-ray diffraction
There are few literature examples of base-induced ring con-
traction of 3,6-dihydro-2H-thiopyrans yielding thiolanes (in one
case),29a or vinyl cyclopropanes and cyclopentenes bearing an
exocyclic sulfide function.29b,c 2,2-Disubstituted 1,3-thiazolidin-4-
ones with a CF3-group being one of the substituents at the C-2
position are also known and are usually obtained in the reaction
of thioglycolic acid or its esters with 1-aryl-1-chloro-2,2,2-
trifluoroethyl isocyanates30a,b or methyl 3,3,3-trifluoro-2-
iminopropanoate.30c
OMe
O
OMe
S
CF3
N
R1
CF3
N
R1
(i)
R1
(ii)
F3C
N
S
S
TMSO
O
O
O
R2
R2
R2
9d,k,l
30a: R1=p-Tol, R2=H
30b: R1=n-Pr, R2=H
30c: R1=p-Tol, R2=Me
31a: R1=p-Tol, R2=H (33%)
31b: R1=n-Pr, R2=H (43%)
Scheme 11. Reagents and conditions. (i): Method 2: diene 8a (1 equiv), CH2Cl2, rt, 1 h; (ii): TBAF trihydrate, rt, 15 h.

1330
O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
isoprene (5), penta-1,3-diene (6), 1- and 2- trimethylsilyloxy-1,3-
butadiene (7 and 23), and Danishefsky’s dienes 8a,b. The observed
regioselectivity is almost the same as reported in the literature for
fluorinated thiocarbonyl or thiocarboxyl derivatives. The structural
assignment of compounds 13, 17, 20e22, 24e27 was based on NMR
data or X-ray diffraction analyses. Relative configuration was usually
not determined except for cycloadducts 25e27. It was also shown
that cycloadducts 30 underwent base-induced ring contraction into
new fluorinated 1,3-thiazolidin-4-ones 31. Finally, it is worth noting
that the prepared 3,6-dihydro-2H-thiopyrans could be valuable
compounds as it was earlier demonstrated that some fluorine-
containing dihydrothiopyran derivatives possess potential cardio-
tonic activity.31
4. Experimental
Fig. 8. ORTEP representation of compound 31a (displacement ellipsoids with 50% of
probability).
4.1. General methods
In our case we can propose the following mechanism for this
ring contraction reaction (Scheme 12). Fluoride anion could attack
the silyl enol ether of compounds 30 giving first a cyclic enolate,
which could then lead to the N,O-acetal enolate 33 after a proto-
nationedeprotonation equilibrium. Finally, the latter could then
undergo a ring opening of 3,6-dihydro-2H-thiopyrandring closure
into the corresponding 1,3-thiazolidin-4-one 31 (Scheme 12).
Reagents and solvents were generally the best quality com-
mercial grade and used without further purification. Focused mi-
crowave irradiations were carried out in pressurized (0e20 bar)
sealed vessels (0e20 bar, 10 mL tubes, sealed with a septum) with
a CEM DiscoverÔ focused microwave reactor (monomode sys-
tem).18a Power input (0e400 W) was monitored by computer as
infrared measurement and continuous feedback temperature
OMe
CF3
OMe
OMe
CF3
N
CF3
N
R1
F
R1
R1
N
S
S
S
TMSO
O
O
O
O
O
33
30a,b
R1 =
-Tol, -Pr
p
n
OMe
S
O
OMe
S
CF3
N
CF3
N
R1
O
H
R1
31a,b
O
O
Scheme 12. Possible mechanism for the formation of thiazolidinones 31a,b.
3. Conclusion
control. The experiments were performed using stirring option
whereby the contents of a vessel are stirred by means of a rotating
plate located underneath the microwave cavity and a Teflon-
coated magnetic stir bar in the vessel. In all experiments a target
temperature was selected together with a power. The target tem-
perature was reached with a ramp of 2 min and the chosen mi-
crowave power stay constant to hold the mixture at this
temperature. The time of the reaction did not include the ramp
period. All reactions were followed by 19F NMR of the crude mix-
ture or by thin layer chromatography (TLC) on silica gel (Merck,
Darmstadt, Germany) and revealed using UV light or ethanolic
solution of phosphomolybdic acid. Purification of all cycloadducts
was carried out using flash silica gel column chromatography
We have described an extended investigation of hetero-
DielseAlder reactions of trifluoromethyl- and polyfluoroalkylthio-
amides with various electron-rich 1,3-dienes. The microwave-
assisted reactions (Method 1: 15e20 equiv of diene) of thioamides
9aec,feh worked quite well with 2,3-dimethylbuta-1,3-diene
affording moderate yields of cycloadducts 10aec,feh. The nature
of polyfluoroalkyl chains and substituents on the nitrogen atom of
the thioamides had a significant influence on the yields of com-
pounds 10. On the contrary, N-acetyl-thioamides 9d,e reacted
smoothly at room temperature in the presence of a slight excess of
diene (Method 2) with alkyl-substituted dienes as well as silylox-
ydienes leading to the corresponding cycloadducts in good yields.
Study of regio- and stereoselectivity was also investigated using
(70e200
mm). The purity of synthetic products was established by
NMR spectroscopic data, and MS analysis. MS: Thermo Finnigan,

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1331
LCQ Advantage Max, Electrospray Ionization, source heater
T¼220 ꢀC, capillary voltage¼33 V. High resolution mass spectra
(HRMS) were recorded with a Q-TOF Micromass Instrument in the
vessel. Thioamide 9g (0.25 g, 1 mmol), N-methylpyrrolidin-2-one
(NMP) (3 mL), and 2,3-dimethylbuta-1,3-diene (3) (0.56 mL,
5 mmol) were then added. The tube was sealed with a Teflon
septum and heated in CEM DiscoverÒ microwave reactor (reaction
positive ESI (CV¼30 V) mode. 1H (300 MHz), 19F (280 MHz), and 13
C
(75 MHz) NMR spectra were recorded on a Bruker Avance DMX
300 instrument. All the experiments were recorded using CDCl3 as
solvent. TMS signal or the residual signal of deuterated solvent was
taken as internal reference for 1H and 13C spectra and the CFCl3
signal for 19F spectra. Crystal structures of compounds 13b, 27, and
31a were determined from single-crystal X-ray diffraction analysis
parameters: standard mode, T¼180 ꢀC,
mW power: 300 W, running
time: 30 min). After one run, another portion of 1,3-diene 3
(0.28 mL, 2.5 mmol) was added with a syringe through the septum
and reaction mixture was heated again under the same conditions.
Addition of new portions of diene and heating were continued until
19F NMR of reaction mixture showed maximum conversion (total
heating time: 3 h, 1,3-diene: 15e20 equiv, see Table 1). The reaction
mixture was then poured into water (50 mL) and extracted with
CH2Cl2 (3ꢂ25 mL). The combined organic phases were washed with
water (30 mL), dried over MgSO4, evaporated under reduced
pressure, and the residue was purified by silica gel column chro-
matography (eluent: mixture petroleum ether (PE) and ethyl ace-
tate, 9:1). Combined fractions containing 10g were evaporated and
redissolved in MeOH (5e10 mL) to precipitate impurities of poly-
merized diene. After filtration and solvent evaporation, pure com-
pound 10g (0.16 g, 49%) was obtained as a colorless oil (Scheme 2,
Table 1: entry 7).
on a BrukerÓ SMART APEX diffractometer (with Mo K
0.71073 A). Data were deposited to the Cambridge Crystallographic
Data Centre.
a
1 radiation:
ꢁ
4.2. Typical procedure for the synthesis of N-acyl thioamides
9d,e,i,k (Scheme 3)
To a solution of thioamide 9b (0.66 g, 3 mmol) in CH2Cl2 (15 mL)
was added Et3N (0.46 g, 4.5 mmol). The reaction mixture was
cooled in an ice-bath, then a solution of acetyl chloride (0.32 g,
4 mmol) in CH2Cl2 (5 mL) was added dropwise. The resulting
mixture was stirred at 0 ꢀC for 1 h then evaporated in vacuo. The
residue was treated with dry Et2O and filtered. Evaporation of the
filtrate in vacuo provided N-acetyl thioamide 9d (0.75 g, 95%) as
a red oil.
4.3.2. Method 2. 2,3-Dimethylbuta-1,3-diene (0.17 mL, 1.5 mmol)
was added to a solution of thioamide 9d (0.20 g, 0.75 mmol) in 5 mL
of dry CH2Cl2. The reaction mixture was stirred at room tempera-
ture for 4 h until disappearance of the red color of the starting
thioamide, then evaporated in vacuo. The residue was purified by
silica gel column chromatography (eluent: petroleum ether/ethyl
acetate, 4:1) affording the desired product 10d (0.20 g, 78%)
(Scheme 2, Table 1: entry 4).
4.2.1. N-(2,2,2-Trifluoroethanethioyl)-N-(p-tolyl)acetamide
(9d). Mixture (70:30) of rotamers (CDCl3). 19F NMR (CDCl3,
ꢁ62.0 (s, CF3, major), ꢁ72.0 (s, CF3, minor). 1H NMR (CDCl3,
d
ppm):
ppm):
d
2.18 (s, 3H, MeCO, major), 2.30 (s, 3H, MeCO, minor), 2.36 (s, 3H, Me
p-Tol, minor), 2.41 (s, 3H, Me p-Tol, major), 6.86 (d, 3JH,H¼8.0 Hz, 2H,
3
CHAr, minor), 7.08 (d, JH,H¼8.0 Hz, 2H, CHAr, major), 7.18 (d,
4.3.3. Method 3. Thioamide 9f (0.20 g, 1 mmol) and 1-(trime-
thylsilyloxy)buta-1,3-diene (7) (1.8 mL, 10 mmol) were heated at
150 ꢀC in a 10 mL pressure vessel sealed with Teflon septum with
stirring in an oil bath for 3 h. Then, after evaporation of volatiles, the
reaction mixture was purified by silica gel column chromatography
(eluent: mixture petroleum ether and ethyl acetate, 9:1) affording
the desired product 22 (40 mg, 12%) as a mixture (67:33) of di-
astereoisomers (Scheme 7, Table 3: entry 4).
3
3JH,H¼8.0 Hz, 2H, CHAr, minor), 7.30 (d, JH,H¼8.0 Hz, 2H, CHAr
,
major). GC/MS: m/z¼219 [MþꢁAc].
4.2.2. N-(2,2,3,3,4,4,5,5-Octafluoropentanethioyl)-N-(p-tolyl)acet-
amide (9e). Yield: 97% (1.15 g). Mixture (85:15) of rotamers (CDCl3).
Red oil. Spectral data for the major rotamer is given. 19F NMR
(CDCl3,
d
ppm): ꢁ111.8 (m, CF2), ꢁ123.3 (m, CF2), ꢁ129.4 (m, CF2),
2
ꢁ137.8 (dm, JF,H¼52.0 Hz, HCF2). 1H NMR (CDCl3,
d ppm): 2.23 (s,
2
3
3H, MeCO), 2.36 (s, 3H, Me p-Tol), 6.15 (tt, JF,H¼52.0, JF,H¼5.7 Hz,
1H, HCF2), 6.86 (d, 3JH,H¼8.0 Hz, 2H, CHAr), 7.19 (d, 3JH,H¼8.0 Hz, 2H,
CHAr).
4.4. Reactions of thioamides 9aeh with 2,3-dimethylbuta-1,3-
diene (3) (Scheme 2, Table 1)
4.4.1. (4,5-Dimethyl-2-trifluoromethyl-3,6-dihydro-2H-thiopyran-2-
yl)amine (10a). Method 1. Yield: 35% (0.15 g). Oil. 19F NMR (CDCl3,
4.2.3. N-(2,2,2-Trifluoroethanethioyl)-N-(p-tolyl)benzamide(9i). Yield:
95% (0.35 g). Mixture (75:25) of rotamers (CDCl3). Yellow oil. 19F NMR
d
ppm): ꢁ81.3 (s). 1H NMR (CDCl3,
d ppm): 1.64 (s, 3H, Me), 1.67 (s,
2
(CDCl3,
(CDCl3,
d
ppm): ꢁ62.0 (s, CF3, minor), ꢁ71.4 (s, CF3, major). 1H NMR
3H, Me), 2.01 (br s, 2H, NH2), 2.20 (d, JH,H¼16.5 Hz, 1H, CHAHB),
2
2
d
ppm): 2.32 (s, 3H, Me p-Tol, major), 2.35 (s, 3H, Me p-Tol,
2.67 (d, JH,H¼16.5 Hz, 1H, CHAHB), 3.07 (d, JH,H¼16.8 Hz, 1H,
2
minor), 6.9e7.9 (m, 9H, CHAr).
SCHAHB), 3.35 (d, JH,H¼16.8 Hz, 1H, SCHAHB). 13C NMR (CDCl3,
d
ppm): 19.1 (s, CH3), 20.4 (s, CH3), 29.8 (s, SCH2), 38.6 (s, CH2), 63.7
2
4.2.4. N-(2,2,2-Trifluoroethanethioyl)-N-(propyl)acetamide (9k). Yield:
(q, JC,F¼28.5 Hz, CCF3), 123.5 (s, Cq), 124.1 (s, Cq), 126.1 (q,
1JC,F¼282.7 Hz, CF3). GC/MS: m/z¼211 [Mþ]. Anal. Calcd for
C8H12F3NS: C, 45.48; H, 5.73; N, 6.63; S, 15.18. Found: C, 45.37; H,
5.84; N, 6.51; S, 15.22.
94% (0.45 g). Mixture (85:15) of rotamers (CDCl3). Red oil. 19F NMR
(CDCl3,
d
ppm): ꢁ62.2 (s, CF3, major), ꢁ72.6 (s, CF3, minor). 1H NMR of
3
the major rotamer (CDCl3,
CH3CH2CH2), 1.72 (m, 2H, CH3CH2CH2), 2.45 (s, 3H, MeCO), 3.95 (m,
d
ppm): 0.96 (t, JH,H¼7.5 Hz, 3H,
2H, NCH2).
4.4.2. (4,5-Dimethyl-2-trifluoromethyl-3,6-dihydro-2H-thiopyran-2-
yl)(p-tolyl) amine (10b). Method 1. Yield: 26% (0.16 g). Oil. 19F NMR
4.2.5. N-(2,2,2-Trifluoroethanethioyl)-N-(p-tolyl)propionamide
(CDCl3,
d
ppm): ꢁ77.1 (s). 1H NMR (CDCl3,
d ppm): 1.70 (s, 3H, Me),
(9l). Yield: 95% (1.2 g). Mixture (55:45) of rotamers (CDCl3). Oil. 19
F
1.74 (s, 3H, Me), 2.27 (s, 3H, Me tolyl), 2.40 (d, JH,H¼17.6 Hz, 1H,
2
NMR (CDCl3,
d
ppm): ꢁ61.9 (s, CF3, major), ꢁ72.0 (s, CF3, minor).
CHAHB), 2.79 (d, 2JH,H¼18.0 Hz, 1H, SCHAHB), 2.85 (d, 2JH,H¼17.6 Hz,
2
1H, CHAHB), 3.16 (d, JH,H¼18.0 Hz, 1H, SCHAHB), 6.93 (d,
3
4.3. Typical procedure for the reactions of thioamides 9 with
1,3-dienes
3JH,H¼8.1 Hz, 2H, tolyl), 7.01 (d, JH,H¼8.1 Hz, 2H, tolyl). 13C NMR
(CDCl3,
d ppm): 19.1 (s, CH3), 20.2 (s, CH3), 20.7 (s, CH3), 30.1 (s,
SCH2), 38.4 (s, CH2), 66.7 (q, 2JC,F¼28.5 Hz, CCF3), 120.2 (s, 2ꢂCHAr),
4.3.1. Method 1. A stirring bar and one piece of WeflonÒ (WeflonÒ
is TeflonÒ filled with graphite) were placed in a 10 mL pressure
123.0 (s, Cq), 124.3 (s, Cq), 125.9 (q, JC,F¼286.4 Hz, CF3), 129.2 (s,
1
2ꢂCHAr), 131.1 (s, Cq Ar), 140.7 (s, Cq Ar). GC/MS: m/z¼301 [Mþ].

1332
O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
2
Anal. Calcd for C15H18F3NS: C, 59.78; H, 6.02; N, 4.65; S, 10.64.
Found: C, 59.92; H, 6.15; N, 4.60; S, 10.68.
ꢁ109.8 (1F, CF2, AB, JF,F¼276.1 Hz), ꢁ114.3 (1F, CF2, AB,
2JF,F¼276.1 Hz). 1H NMR (CDCl3,
d ppm): 1.72 (s, 3H, CH3), 1.75 (s, 3H,
2
CH3), 2.42 (d, JH,H¼17.4 Hz, 1H, CH2), 2.6e3.0 (m, 6H), 3.25 (d,
4.4.3. [4,5-Dimethyl-2-(1,1,2,2,3,3,4,4-octafluorobutyl)-3,6-dihydro-
2H-thiopyran-2-yl]-(p-tolyl)amine (10c). Method 1. Yield: 15%
2JH,H¼16.7 Hz, 1H, CH2S), 3.59 (m, 4H, CH2O). 13C NMR (CDCl3,
d
ppm): 19.1 (s, CH3), 20.0 (s, CH3), 31.0 (s, CH2S), 36.0 (m, CH2), 48.1
(0.13 g). Oil. 19F NMR (CDCl3,
d
ppm): ꢁ110.5 (dm, 2JF,F¼280.2 Hz, 1F,
(dd, JC,F¼4JC,F¼3.7 Hz, CH2N), 67.8 (s, CH2O), 74.1 (dd,
4
2
1
CFAFB), ꢁ112.4 (dm, JF,F¼280.2 Hz, 1F, CFAFB), ꢁ120.5 (dm,
2JC,F¼2JC,F¼21.7 Hz, Cq, CCF2), 116.4 (ddq, JC,F¼1JC,F¼266.4 Hz,
2JF,F¼291.5 Hz, 1F, CFAFB), ꢁ122.6 (dm, JF,F¼291.5 Hz, 1F, CFAFB),
2JCF¼34.6 Hz, CF2), 119.5 (qdd, 1JC,F¼288.5, 2JC,F¼2JC,F¼37.5 Hz, CF3),
123.7 (s, Cq),124.8 (s, Cq). GC/MS: m/z¼331 [Mþ], 298, 249, 229, 212,
179, 130, 86. FTIR (film, cmꢁ1): 3436, 2857, 1641, 1455, 1325, 1213,
1122, 729. HRMS (ESIþ): calcd for C13H19F5NOS m/z 332.1108, found
332.1114.
2
ꢁ130.8 (m, 2F, CF2), ꢁ138.0 (dm, JF,H¼52.2 Hz, 2F, HCF2). 1H NMR
2
(CDCl3,
d ppm): 1.71 (s, 3H, Me), 1.76 (s, 3H, Me), 2.27 (s, 3H, Me
tolyl), 2.51 (d, 2JH,H¼17.1 Hz, 1H, CHAHB), 2.81 (d, 2JH,H¼16.2 Hz, 1H,
SCHAHB), 2.93 (d, 2JH,H¼17.1 Hz, 1H, CHAHB), 3.02 (d, 2JH,H¼16.2 Hz,
1H, SCHAHB), 6.02 (tt, 2JH,F¼52.2 Hz, 3JH,F¼5.4 Hz, 1H, HCF2), 6.92 (d,
3JH,H¼8.4 Hz, 2H, tolyl), 7.00 (d, 3JH,H¼8.4 Hz, 2H, tolyl). MS (ESIþ):
m/z¼472 [MþK]. Spontaneous desamination of 10c into compound
1114 took place during heating under microwave irradiation.
4.4.8. (2-Heptafluoropropyl-4,5-dimethyl-3,6-dihydro-2H-thio-
pyran-2-yl)morpholine (10h). Method 1. Yield: 28% (0.21 g). Oil. 19
F
NMR (CDCl3,
d
ppm): ꢁ81.4 (m, 3F, CF3), ꢁ109.9 (dm, 2JF,F¼285.0 Hz,
1F, CFAFBCF3), ꢁ110.5 (dm, 2JF,F¼285.0 Hz, 1F, CFAFBCF3), ꢁ121.1 (dm,
4.4.4. N-(4,5-Dimethyl-2-(trifluoromethyl)-3,6-dihydro-2H-thio-
pyran-2-yl)-N-(p-tolyl)-acetamide (10d). Method 2. Yield: 78%
2JF,F¼287.7 Hz, 1F, CFAFB), ꢁ125.4 (dm, 2JF,F¼287.7 Hz, 1F, CFAFB). 1H
NMR (CDCl3,
d ppm): 1.73 (s, 3H, Me), 1.75 (s, 3H, Me), 2.49 (d,
(0.20 g). Oil. Rf¼0.55 (PE/EtOAc, 4:1). 19F NMR (CDCl3,
d
ppm): ꢁ71.7
2JH,H¼17.1 Hz, 1H, CHAHB), 2.7e3.0 (m, 6H, N(CH2)2þCHAHBþ-
SCHAHB), 3.25 (d, 2JH,H¼17.0 Hz, 1H, SCHAHB), 3.61 (m, 4H, O(CH2)2).
GC/MS: m/z¼381 [Mþ]. HRMS (ESIþ): calcd for C14H18F7KNOS m/z
420.0634, found 420.0641.
(s). 1H NMR (CDCl3,
d ppm): 1.40 (s, 3H, ]CCH3), 1.72 (s, 3H, MeCO),
2
1.77 (s, 3H, ]CCH3), 2.39 (s, 3H, Me p-Tol), 2.40 (d, JH,H¼15.4 Hz,
1H, CH2), 2.64 (d, 2JH,H¼15.4 Hz, 1H, CH2), 3.01 (s, 2H, CH2S), 7.0e7.2
(m, 4H, p-Tol). 13C NMR (CDCl3,
d ppm): 18.6 (s, CH3), 19.3 (s, CH3),
21.2 (s, CH3 p-Tol), 26.2 (s, CH3CO), 32.4 (s, CH2S), 38.0 (q,
3JC,F¼1.7 Hz, CH2), 73.9 (q, 2JC,F¼28.2 Hz, Cq), 125.6 (s, Cq), 126.2 (q,
1JC,F¼288.0 Hz, CF3), 129.1 (s, Cq), 129.9, 130.0, 130.6, 131.1 (s, CH p-
Tol), 138.4 (s, Cq, CAreMe), 139.1 (s, Cq, CAreN), 171.6 (s, C]O). GC/
MS: m/z¼300 [MþꢁAc], 179, 150, 107. FTIR (film, cmꢁ1): 3351, 2923,
1687, 1510, 1368, 1295, 1171. HRMS (ESIþ): calcd for C17H20F3NOSNa
m/z 366.1115, found 366.1123.
4.5. Reaction of thioamide 9d with cyclohexa-1,3-diene (4)
(Scheme 4)
4.5.1. N-(p-Tolyl)-N-(3-(trifluoromethyl)-2-thiabicyclo[2.2.2]oct-5-
en-3-yl)acetamide (12). Reaction (Method 2) of thioamide 9d
(0.20 g, 0.75 mmol) with cyclohexa-1,3-diene (4) (0.15 mL,
1.5 mmol) gave compound 12 as a mixture (1:0.3) of endo/exo
isomers (0.15 g, yield: 58%). Oil. Rf¼0.52 (PE/EtOAc, 4:1). GC/MS: m/
z¼341 [Mþ], 220, 193, 165. FTIR (film, cmꢁ1): 3436, 2945, 1683, 1511,
1366, 1312, 1278, 1174, 722. HRMS (ESIþ): calcd for C17H19F3NOS m/z
342.1139, found 342.1132. Major endo isomer 12a: 19F NMR (CDCl3,
4.4.5. N-(4,5-Dimethyl-2-(1,1,2,2,3,3,4,4-octafluorobutyl)-3,6-
dihydro-2H-thiopyran-2-yl)-N-(p-tolyl)acetamide (10e). Method 2.
Yield: 69% (0.25 g). Oil. Rf¼0.55 (PE/EtOAc, 4:1). 19F NMR (CDCl3,
2
d
ppm): ꢁ102.3 (1F, CF2, AB, JF,F¼278.0 Hz), ꢁ105.9 (1F, CF2, AB,
d
ppm): ꢁ68.6 (s). 1H NMR (CDCl3,
ppm): 1.5e2.2 (m, 4H, 2ꢂCH2),
d
2JF,F¼278.0 Hz), ꢁ121.2, ꢁ121.4 (2F, 2ꢂm, CF2), ꢁ130.1, ꢁ130.4 (2F,
1.80 (s, 3H, MeCO), 2.39 (s, 3H, Me p-Tol), 3.48 (m, 1H, CH), 5.24
2ꢂm, CF2), ꢁ137.4, ꢁ137.5 (2F, 2ꢂdm, HCF2, 2JF,H¼52.0 Hz). 1H NMR
(m, 1H, CH), 6.34 (ddd, JH,H¼8.7 Hz, JH,H¼7.5 Hz, JH,H¼1.2 Hz,
3
3
4
3
3
(CDCl3,
d
ppm): 1.36 (s, 3H, ]CCH3),1.69 (s, 3H, MeCO),1.78 (s, 3H, ]
1H, ]CH), 6.61 (dd, JH,H¼8.7 Hz, JH,H¼5.8 Hz, 1H, ]CH), 7.1e7.3
CCH3), 2.38 (s, 3H, Me p-Tol), 2.47 (d, 2JH,H¼15.3 Hz,1H, CH2), 2.88 (d,
2JH,H¼14.7 Hz, 1H, CH2S), 3.08 (m, 2H, CH2þCH2S), 6.08 (tt,
2JH,F¼52.0 Hz, 3JH,F¼5.7 Hz,1H, HCF2), 7.0e7.2(m, 4H, p-Tol).13C NMR
(m, 4H, p-Tol). 13C NMR (CDCl3,
d
ppm): 19.3 (s, CH2), 21.2 (s, CH3 p-
Tol), 27.6 (s, CH2), 27.8 (s, CH3CO), 32.1 (s, CH), 36.7 (s, CH), 83.8 (q,
1
2JC,F¼27.2 Hz, Cq, CCF3), 125.9 (q, JC,F¼287.6 Hz, CF3), 128.8 (q,
(CDCl3,
d
ppm): 18.7 (s, CH3), 19.2 (s, CH3), 21.2 (s, CH3 p-Tol), 26.7 (s,
4JCF¼3.2 Hz, ]CH), 129.3, 130.1, 132.0, 133.4 (s, CHAr), 136.0 (q,
3
CH3CO), 32.3 (s, CH2S), 37.1 (t, JCF¼3.3 Hz, CH2), 77.8 (m, Cq, CCF2,
overlapping with CDCl3), 107.9 (tt, 1JC,F¼254.0, 2JC,F¼30.1 Hz, HCF2),
104e121 (m, CF2CF2CF2),126.3,129.2 (s, Cq),129.8,129.9,131.0,131.1
(s, CHAr), 139.0 (s, Cq, CArMe), 139.2 (s, Cq, CArN), 172.5 (s, C]O). FTIR
(film, cmꢁ1): 3422, 2926, 1689, 1510, 1368, 1292, 1171, 732. HRMS
(ESIþ): calcd for C20H21F8NOSK m/z 514.0853, found 514.0846.
5JCF¼1.7 Hz, ]CH), 138.5 (s, Cq, CArMe), 141.9 (s, Cq, CArN), 172.8 (s,
C]O). Minor exo isomer 12b: 19F NMR (CDCl3,
d
ppm): ꢁ67.8 (s). 1H
NMR (CDCl3,
d
ppm): 1.5e2.2 (m, 4H, 2ꢂCH2), 1.80 (s, 3H, MeCO),
2.41 (s, 3H, Me p-Tol), 2.93 (m, 1H, CH), 3.50 (m, 1H, CH), 5.92 (dd,
3
3
3JH,H¼8.7, JH,H¼7.5 Hz, 1H, ]CH), 6.68 (dd, JH,H¼8.7 Hz,
3JH,H¼5.8 Hz, 1H, ]CH), 7.1e7.4 (m, 4H, p-Tol). 13C NMR (CDCl3,
d
ppm): 18.0 (s, CH2), 21.2 (s, CH3 p-Tol), 25.3 (s, CH3CO), 29.5
2
4.4.6. 4-(4,5-Dimethyl-2-trifluoromethyl-3,6-dihydro-2H-thiopyran-
2-yl)morpholine (10f). Method 1. Yield: 45% (0.13 mg). Oil. Rf¼0.37
(s, CH2), 34.7 (s, CH), 37.7 (s, CH), 78.4 (q, JC,F¼25.7 Hz, Cq,
CCF3), 120e127 (CF3 not visible), 126.9 (s, CHAr), 129.7 (q,
4JC,F¼3.5 Hz, ]CH), 129.8, 130.4, 130.7 (s, CHAr), 137.9 (s, Cq, CArMe),
(PE/EtOAc, 9:1). 19F NMR (CDCl3,
d
d
ppm): ꢁ71.3 (s). 1H NMR (CDCl3,
ppm): 1.71 (s, 3H, Me), 1.75 (s, 3H, Me), 2.44 (d, 2JH,H¼17.5 Hz, 1H,
138.4 (q, JC,F¼1.0 Hz, ]CH), 138.6 (s, Cq, CArN), 173.3 (s, C]O).
5
2
CHAHB), 2.69 (m, 2H, NCH2), 2.79 (d, JH,H¼16.4 Hz, 1H, SCHAHB),
2
2.83 (d, JH,H¼17.5 Hz, 1H, CHAHB), 3.13 (m, 2H, NCH2), 3.23 (d,
4.6. Reactions of thioamides 9d,f,i with isoprene (5) (Scheme 5)
2JH,H¼16.4 Hz, 1H, SCHAHB), 3.59 (m, 4H, O(CH2)2). 13C NMR (CDCl3,
d
ppm): 18.9 (s, CH3), 20.0 (s, CH3), 30.4 (s, CH2S), 35.2 (q,
4.6.1. 4-(5- or 4-Methyl-2-(trifluoromethyl)-3,6-dihydro-2H-thio-
pyran-2-yl)morpholine (13a) or (14a). Compounds 13a and 14a
were obtained (Method 1) as a mixture (52:48) of regioisomers
from thioamide 9f (0.20 g, 1 mmol) and isoprene (5) (2.5 mL,
25 mmol). They were not separated by silica gel column chroma-
tography (eluent: mixture petroleum ether and ethyl acetate, 9:1);
analyses were done on the mixture. Yield: 19% (50 mg). Oil. Rf¼0.38
3JC,F¼1.1 Hz, CH2), 47.2 (s, CH2N), 68.1 (s, CH2O), 71.0 (q,
2JC,F¼24.9 Hz, CCF3), 122.5 (s, Cq), 123.9 (s, Cq), 126.6 (q,
1JC,F¼293.1 Hz, CF3). GC/MS: m/z¼281 [Mþ]. HRMS (ESIþ): calcd for
C
12H18F3KNOS m/z 320.0698, found 320.0692.
4.4.7. 4-(4,5-Dimethyl-2-(pentafluoroethyl)-3,6-dihydro-2H-thio-
pyran-2-yl)morpholine (10g). Method 1. Yield: 49% (0.16 mg).
(PE/EtOAc, 9:1). 19F NMR (CDCl3,
CF3). 1H NMR (CDCl3,
d
ppm): ꢁ71.1 (s, CF3), ꢁ71.2 (s,
Rf¼0.35 (PE/EtOAc, 9:1). 19F NMR (CDCl3,
d
ppm): ꢁ78.5 (3F, m, CF3),
d ppm): 1.74 (s, 3H, CH3), 1.77 (s, 3H, CH3),

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1333
2.4e3.4 (m, 16H, CH2NþCH2þCH2S), 3.5e3.6 (m, 8H, CH2O), 5.39
TolþCqPhþCqHet), 172.1 (s, C]O). HRMS (ESIþ): calcd for
(m, 1H, HC¼), 5.63 (m, 1H, ]CH). 13C NMR (CDCl3,
d
ppm): 23.6,
C21H20F3NONaS m/z 414.1115, found 414.1124. Selected data for mi-
24.3 (s, CH3), 25.5 (s, CH2), 29.1 (s, CH2), 29.5 (s, CH2), 33.7 (s, CH2),
47.2, 47.3 (s, CH2N), 68.2, 68.3 (s, CH2O), 70.1, 70.7 (q, 2JC,F¼25.1 Hz,
Cq, CCF3), 117.3, 117.9 (s, ]CH), 126.7, 126.9 (q, 1JC,F¼293.5 Hz, CF3),
130.6, 131.6 (s, Cq, CMe). MS (ESIþ): m/z¼268 [Mþ], 234. FTIR (film,
cmꢁ1): 3402, 2852, 1684, 1646, 1451, 1260, 1147, 935, 727. HRMS
(ESIþ): calcd for C11H17F3NOS m/z 268.0983, found 268.0988.
nor isomer (4-methyl) 14c: 19F NMR (CDCl3,
NMR (CDCl3, ppm): 5.81 (br s, 1H, ]CH).
d
ppm): ꢁ71.8 (s). 1H
d
4.7. Reactions of thioamide 9d with penta-1,3-diene (6)
(Scheme 6)
4.7.1. N-(3- and 6-Methyl-2-trifluoromethyl-3,6-dihydro-2H-thio-
pyran-2-yl)-N-(p-tolyl)-acetamides (15) and (16). Compounds 15
and 16 were obtained (Method 2) as a mixture of two regioisomers
(each regioisomer being a mixture of two diastereoisomers) (40:24;
22:14) from thioamide 9d (0.55 g, 2.1 mmol) and penta-1,3-diene
(6) (0.3 mL, 2.9 mmol). Isomers were not fully separated by silica
gel column chromatography (eluent: PE/EtOAc, 6:1); but several
enriched fractions with certain isomers were obtained allowing
structural assignment of regioisomers by NMR. Yield: 80% (0.26 g).
GC/MS (m/z)¼329 [Mþ]. HRMS (ESIþ): calcd for C16H18F3NONaS m/z
352.0959, found 352.0963. 3-Methyl regioisomer: major di-
astereoisomer 15a: Colorless solid. Mp¼123e125 ꢀC (from hexane).
4.6.2. N-(5- and 4-Methyl-2-trifluoromethyl-3,6-dihydro-2H-thio-
pyran-2-yl)-N-(p-tolyl)-acetamides (13b) and (14b). Compounds
13b and 14b were obtained (Method 2) as a mixture (85:15) of
regioisomers from thioamide 9d (0.55 g, 2.1 mmol) and isoprene (5)
(0.30 mL, 2.9 mmol). They were not separated by silica gel column
chromatography (eluent: PE/EtOAc, 4:1). Yield: 76% (0.52 g).
Rf¼0.55 (PE/EtOAc, 4:1). On standing the major isomer 13b was
spontaneously crystallized out from the mixture. Major isomer (5-
methyl) 13b: Colorless crystals. Mp¼63e64 ꢀC (from hexane). 19F
NMR (CDCl3,
d
ppm): ꢁ72.5 (s). 1H NMR (CDCl3,
d ppm): 1.71 (s, 3H,
2
MeCO), 1.87 (s, 3H, ]CCH3), 2.28 (dm, JH,H¼15.4 Hz, 1H, CHAHB),
2
3
2.41 (s, 3H, Me p-Tol), 2.63 (dd, JH,H¼15.4 Hz, JH,H¼6.6 Hz, 1H,
CHAHB), 2.80 (d, 2JH,H¼14.7 Hz, 1H, SCHAHB), 3.14 (d, 2JH,H¼14.7 Hz,
1H, SCHAHB), 5.16 (br s,1H, ]CH), 7.06e7.24 (m, 4H, p-Tol). 13C NMR
Rf¼0.42 (PE/EtOAc, 6:1). 19F NMR (CDCl3,
d
ppm): ꢁ72.9 (s). 1H NMR
3
(CDCl3,
d
ppm): 1.36 (d, JH,H¼7.2 Hz, 3H, CH3), 1.71 (s, 3H, MeCO),
2.27 (dm, 2JH,H¼15.5 Hz, 1H, CHAHB), 2.41 (s, 3H, Me p-Tol), 2.67 (dd,
3
(CDCl3,
d
ppm): 21.0 (s, CH3), 22.2 (s, CH3), 25.8 (s, CH3), 30.7 (q,
2JH,H¼15.5 Hz, JH,H¼6.8 Hz, 1H, CHAHB), 3.43 (m, 1H, CHMe), 5.45
3
3
3JC,F¼2.0 Hz, CH2), 31.3 (s, SCH2), 74.2 (q, 2JC,F¼28.1 Hz, CCF3), 119.5
(m, 1H, ]CH), 6.08 (dt, JH,H¼9.0 Hz, JH,H¼3.0 Hz, 1H, ]CH),
7.07e7.30 (m, 4H, p-Tol). Selected data for minor diastereoisomer
1
(s, CH]CCH3), 126.2 (q, JC,F¼287.6 Hz, CF3), 129.6, 129.7, 130.2,
130.8 (s, CH Ar), 138.6, 138.8, 139.2 (3ꢂs, 2ꢂCq ArþCq Het), 171.3 (s,
C]O). MS (ESIþ): m/z¼352 [MþNaþ], 330 [Mþ]. X-ray crystal
structure determination of 13b. C16H18F3NOS, M¼329.37, mono-
15b: Rf¼0.24 (PE/EtOAc, 6:1). 19F NMR (CDCl3,
d
ppm): ꢁ70.6 (s). 1H
NMR (CDCl3,
d ppm): 3.54 (m, 1H, CHMe). 6-Methyl regioisomer:
major diastereoisomer 16a: Rf¼0.48 (PE/EtOAc, 6:1). 19F NMR (CDCl3,
ppm): ꢁ67.7 (s). 1H NMR (CDCl3,
d
ppm): 1.36 (d, 3JH,H¼6.6 Hz, 3H,
ꢁ
ꢁ
ꢁ
clinic, P21/c (Nr 14), a¼14.304(1)A, b¼8.2377(6)A, c¼15.921(1) A,
d
3
ꢁ
ꢀ
b
¼118.432(5) , V¼1649.7(2)A , Z¼4, dcalcd¼1.326. A total of 12,633
CH3), 1.74 (s, 3H, MeCO), 2.41 (s, 3H, Me p-Tol), 2.94 (dm,
2
reflections were collected at room temperature using a three-circle
2JH,H¼17.1 Hz, 1H, CHAHB), 3.43 (d, JH,H¼17.1 Hz, 1H, CHAHB), 4.30
goniometer of a Bruker SMART APEX diffractometer equipped with
(dq, 3JH,H¼6.8 Hz, 3JH,H¼6.6 Hz, 1H, CHMe), 5.69 (dm, 3JH,H¼10.5 Hz,
1H, ]CH), 5.83 (dd, 3JH,H¼10.5, 3JH,H¼6.8 Hz, 1H, ]CH), 7.1e7.3 (m,
4H, p-Tol). Selected data for minor diastereoisomer 16b: Rf¼0.30 (PE/
ꢁ
a CCD area detector and Mo K
a
radiation (
l¼0.71069 A). The
structure was solved by direct methods with SHELXS-9732 and re-
fined by least square using F2 values and anisotropic thermal pa-
rameters for non-hydrogen atoms with SHELXL-9733 available with
the WinGX34 package. The hydrogen atoms were located by
Fourier-difference synthesis and fixed geometrically according to
their environment with a common isotropic temperature factor.
The final cycle of full matrix least square refinement on F2 was
based on 3362 observed reflections and 203 variable parameters
and converged with unweighted and weighted agreement factors
EtOAc, 6:1). 19F NMR (CDCl3,
d
ppm): ꢁ63.7 (s). 1H NMR (CDCl3,
d
ppm): 3.79 (m, 1H, CHMe).
4.8. Reactions of thioamides 9def with 1-trimethylsilyloxy-
buta-1,3-diene (7) (Scheme 7, Table 3)
4.8.1. N-(2-(Trifluoromethyl)-3- and 6-(trimethylsilyloxy)-3,6-dihydro-
2H-thiopyran-2-yl)-N-(p-tolyl)acetamide (17) and (20). Compounds
17 and 20 were obtained (Method 2) as a mixture of two
regioisomers (each regioisomer being itself a mixture of two di-
astereoisomers (crude mixture: 50:12; 24:14)) from thioamide 9d
(0.2 g, 0.75 mmol) and 1-trimethylsilyloxy-buta-1,3-diene (7)
(0.26 mL, 1.5 mmol). The single diastereoisomer 17a was obtained as
the major product after silica gel column chromatography (eluent:
PE/EtOAc, 4:1). Regioisomers 20a,b were characterized in the crude
mixture but spontaneously decomposed during silica gel purifica-
tion. 3-Trimethylsilyloxy regioisomer: major diastereoisomer 17a:
Yield: 17% (50 mg). Yellow solid. Mp¼72e75 ꢀC. Rf¼0.55 (PE/EtOAc,
of R1¼0.0454, wR2¼0.1224 for 2876 reflections with I>2
sI and
R1¼0.0520, wR2¼0.1282 for all data. The data have been deposited
to the Cambridge Crystallographic Data Centre (Nr CCDC 811996).
ORTEP representation of compound 13b is given in Fig. 5. Selected
data for minor isomer (4-methyl) 14b: Oil. 19F NMR (CDCl3,
d ppm):
ꢁ71.2 (s). 1H NMR (CDCl3,
d ppm): 5.77 (br s, 1H, ]CH).
4.6.3. N-(5- and 4-Methyl-2-trifluoromethyl-3,6-dihydro-2H-thio-
pyran-2-yl)-N-(p-tolyl)-benzamides (13c) and (14c). Compounds
13c and 14c were obtained (Method 2) as a mixture of regioisomers
(85:15) from thioamide 9i (0.16 g, 0.5 mmol) and isoprene (5)
(0.1 mL, 1 mmol). They were not separated by silica gel column
chromatography (eluent: PE/EtOAc, 9:1); analyses were done on
the mixture. Yield: 67% (0.13 g). Oil. Rf¼0.25 (PE/EtOAc, 9:1). Major
4:1). 19F NMR (CDCl3,
d
ppm): ꢁ62.5 (s). 1H NMR (CDCl3,
d ppm): 0.14
(s, 9H, SiMe3), 1.71 (s, 3H, MeCO), 2.39 (s, 3H, Me p-Tol), 2.83 (ddd,
3
4
2JH,H¼16.5 Hz, JH,H¼3.6 Hz, JH,H¼1.2 Hz, 1H, CH2), 3.17 (ddd,
3
4
2JH,H¼16.5 Hz, JH,H¼3.6 Hz, JH,H¼1.2 Hz, 1H, CH2), 5.87 (d,
isomer (5-methyl) 13c: 19F NMR (CDCl3,
d
ppm): ꢁ72.5 (s). 1H NMR
3JH,H¼5.1 Hz, 1H, CHOTMS), 5.98 (dd, 3JH,H¼10.2 Hz, 3JH,H¼5.4 Hz, 1H,
3
3
(CDCl3,
d
ppm): 1.82 (s, 3H, ]CCH3), 2.25 (s, 3H, Me p-Tol), 2.41 (dm,
]CH), 6.06 (dt, JH,H¼10.2 Hz, JH,H¼3.9 Hz, 1H, ]CH), 7.0e7.3 (m,
2JH,H¼15.4 Hz, 1H, CHAHB), 2.82 (d, 2JH,H¼14.6 Hz, 1H, SCHAHB), 2.95
4H, CHAr). 13C NMR (CDCl3,
d ppm): 0.4 (s, SiMe3), 21.3 (s, Me p-Tol),
(dd, 2JH,H¼15.4 Hz, 3JH,H¼6.8 Hz, 1H, CHAHB), 3.17 (d, 2JH,H¼14.7 Hz,
26.4 (s, CH2), 27.1 (s, MeCO), 63.5 (s, CHOTMS), 77.9 (q, 2JC,F¼25.5 Hz,
Cq), 125.0 (q, 1JC,F¼289.2 Hz, CF3), 126.3 (s, ]CH), 129.3, 129.5, 130.1,
130.4 (s, CHAr), 131.0 (q, 4JC,F¼1.8 Hz, ]CH),138.8 (s, Cq, CArMe), 139.3
(s, Cq, CArN), 172.6 (s, C]O). MS (ESIþ): m/z¼404 [MþH]þ, 332, 314.
FTIR (film, cmꢁ1): 3412, 2959,1674,1511,1368,1253,1182, 887. HRMS
(ESIþ): calcd for C18H24F3NO2SSiNa m/z 426.1147, found 426.1138.
1H, SCHAHB), 4.95 (br s, 1H, ]CH), 6.96e7.20 (m, 9H, p-TolþPh). 13
C
NMR (CDCl3,
d ppm): 21.0 (s, CH3), 22.3 (s, CH3), 31.2 (q,
3JC,F¼2.2 Hz, CH2), 31.5 (s, SCH2), 75.2 (q, 2JC,F¼28.0 Hz, CCF3), 119.6
(s, CH]CCH3), 126.4 (q, 1JC,F¼287.1 Hz, CF3),127.5,127.7,128.9,129.0
(4ꢂs, CHp-TolþCHPh), 137.5, 138.0, 138.3, 138.7 (4ꢂs, Cq
p-

1334
O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
Selected data for minor diastereoisomer 17b: 19F NMR (CDCl3,
ꢁ67.3 (s). 6-Trimethylsilyloxy regioisomer: selected data for major di-
astereoisomer 20a: 19F NMR (CDCl3,
ppm): ꢁ71.6 (s). Selected data
for minor diastereoisomer 20b: 19F NMR (CDCl3,
ppm): ꢁ72.3 (s).
d
ppm):
(0.31 g, 1.2 mmol) in 5 mL of dry CH2Cl2. The reaction mixture was
stirred at room temperature for 15 h. 19F NMR spectra of the re-
action mixture showed full conversion of 9d into primary silylated
cycloadduct (dF¼ꢁ72.2 ppm). HCl (1 mL of 0.5%) in MeOH solution
was then added to the resulting mixture and it was stirred at room
temperature for 6 h (19F NMR of the reaction mixture showed full
conversion of silylated cycloadduct into thiopyranone 24). The
solvent was then evaporated in vacuo and the residue was purified
by silica gel column chromatography (eluent: mixture petroleum
ether and ethyl acetate, 2:1) yielding compound 24 (0.24 g, 59%).
d
d
When a dichloromethane solution of 17a was kept at room
temperature for several days, a spontaneous quantitative desilyla-
tion occurred leading to compound 18 (Fig. 6). Colorless solid.
Mp¼130e131 ꢀC.19F NMR (CDCl3,
d
ppm): ꢁ66.1 (s). 1H NMR (CDCl3,
d
ppm): 1.83 (s, 3H, MeCO), 2.42 (s, 3H, Me p-Tol), 2.84 (dd,
2JH,H¼17.3 Hz, 3JH,H¼3.6 Hz,1H, CH2), 3.34 (d, 2JH,H¼17.3 Hz,1H, CH2),
4.97 (br s, 1H, CHOH), 5.86e6.04 (m, 2H, CH]CH), 7.11 (d,
Mp¼115e117 ꢀC. Rf¼0.6 (PE/EtOAc, 2:1). 19F NMR (CDCl3,
d ppm):
3JH,H¼8.1 Hz, 1H, CHAr), 7.18 (d, JH,H¼8.1 Hz, 1H, CHAr), 7.26 (d,
ꢁ75.0 (s). 1H NMR (CDCl3,
d ppm): 1.78 (s, 3H, MeCO), 2.12e2.23 (m,
2H, CH2), 2.32e2.41 (m, 1H, CH2), 2.42 (s, 3H, Me p-Tol), 2.63e2.74
3
3JH,H¼8.1 Hz, 2H, CHAr). HRMS (ESIþ): calcd for C15H16F3NO2NaS m/z
2
354.0752, found 354.0761.
(m, 1H, CH2), 2.96 (d, JH,H¼15.5 Hz, 1H, SCHAHB), 3.61 (d,
2JH,H¼15.5 Hz, 1H, SCHAHB), 7.18e7.28 (m, 4H, CHAr). 13C NMR
4.8.2. N-(2-(1,1,2,2,3,3,4,4-Octafluorobutyl)-3- and 6-(trimethylsily-
loxy)-3,6-dihydro-2H-thiopyran-2-yl)-N-(p-tolyl)acetamide (19) and
(21). Cycloadducts 19 and 21 were obtained (Method 2) as a com-
plex mixture of two regioisomers (each regioisomer being a mixture
of two diastereoisomers whose ratio was not possible to determine
in the crude mixture) from thioamide 9e (0.4 g, 1 mmol) and 1-
trimethylsilyloxy-buta-1,3-diene (7) (0.35 mL, 2 mmol). After silica
gel column chromatography (eluent: PE/EtOAc, 4:1), the single di-
astereoisomer 19 was obtained as the result of a desilylation and an
acetyl group migration. Regioisomers 21a,b were characterized in
the crude mixture but spontaneously decomposed during silica gel
purification. Compound 19: Yield: 11% (50 mg). Mp¼60e62 ꢀC.
(CDCl3, d ppm): 21.0 (s, Me p-Tol), 25.5 (s, MeCO), 26.6 (s, CH2), 33.6
2
(s, CH2), 37.8 (s, CH2), 69.6 (q, JC,F¼29.6 Hz, Cq), 126.3 (q,
1JC,F¼287.6 Hz, CF3),130.0,130.1,130.3,130.5 (4ꢂs, 4ꢂCHAr),137.2 (s,
Cq, CArMe), 139.9 (s, Cq, CArN), 172.3 (s, COMe), 203.9 (s, C]Ocyclic).
HRMS (ESIþ): calcd for C15H16F3NO2SNa m/z 354.0752, found
354.0750.
4.10. Typical procedure for reactions of thioamides 9d,e with
Danishefsky’s dienes 8a,b (Scheme 9, Table 4)
Compound 25 (0.46 g, yield: 60%) was obtained (Method 2) as
only one diastereoisomer from thioamide 9d (0.55 g, 2.1 mmol) and
Danishefsky’s diene 8a (0.4 mL, 2.1 mmol), after desilylation under
neutral conditions and silica gel column chromatography (eluent:
PE/EtOAc, 2:1).
Rf¼0.55 (PE/EtOAc, 4:1).19F NMR (CDCl3,
ppm): ꢁ108.0 (1F, CF2, AB,
d
2JF,F¼289 Hz), ꢁ109.4 (1F, CF2, AB, 2JF,F¼289 Hz), ꢁ122.6, ꢁ122.9 (2F,
2ꢂm, CF2), ꢁ130.2, ꢁ130.3 (2F, 2ꢂm, CF2), ꢁ137.5 (2F, dm, HCF2,
2JF,H¼52.1 Hz).1H NMR(CDCl3,
d ppm):2.16 (s, 3H, MeCO), 2.28 (s, 3H,
Me p-Tol), 2.84 (ddd, JH,H¼17.8 Hz, JH,H¼5.3 Hz, JH,H¼1.2 Hz, 1H,
2
3
4
4.10.1. N-(5-Methoxy-6-trifluoromethyl-3-oxo-tetrahydrothiopyran-
6-yl)-N-(p-tolyl)-acetamide (25). Solid. Mp¼146e147 ꢀC. Rf¼0.4
CH2), 3.02 (ddd, 2JH,H¼17.9 Hz, 3JH,H¼5.2 Hz, 4JH,H¼2.6 Hz, 1H, CH2),
3
4.31 (br s, 1H, NH), 5.47 (d, JH,H¼5.5 Hz, 1H, CHOAc), 5.98 (tt,
(PE/EtOAc, 2:1). 19F NMR (CDCl3,
d
ppm): ꢁ66.3 (s). 1H NMR (CDCl3,
2JH,F¼52.1 Hz, 3JH,F¼5.7 Hz, 1H, HCF2), 5.98e6.04 (m, 1H, HC]), 6.13
d ppm): 1.76 (s, 3H, MeCO), 2.42 (s, 3H, Me p-Tol), 2.70 (dd,
3
(m, 1H, ]CH), 7.02 (d, JH,H¼8.0 Hz, 2H, 2ꢂCHAr), 7.13 (d,
2JH,H¼17.4 Hz, 3JH,H¼4.9 Hz, 1H, CHAHB), 2.93 (d, 2JH,H¼15.6 Hz, 1H,
3JH,H¼8.0 Hz, 2H, 2ꢂCHAr). 13C NMR (CDCl3,
d
ppm): 20.6 (s, MeCO),
SCHAHB), 2.97 (dd, 2JH,H¼17.4 Hz, JH,H¼1.7 Hz, 1H, CHAHB), 3.28 (s,
3
21.0 (s, CH3 p-Tol), 25.3 (s, CH2), 68.7 (t, 2JC,F¼24.9 Hz, Cq, CCF2), 70.5
3H, CH3O), 3.74 (d, JH,H¼15.6 Hz, 1H, SCHAHB), 4.81 (dd,
2
(s, CHOAc), 107.8 (tt, 1JC,F¼254.2 Hz, JC,F¼30.0 Hz, HCF2), 105e120
3JH,H¼4.9 Hz, 3JH,H¼1.7 Hz, 1H, CHOMe), 7.12e7.28 (m, 4H, CHAr). 13
C
2
(m, CF2CF2CF2), 117.9 (s, ]CH), 125.8 (s, ]CH), 127.7 (s, Cq, CArMe),
129.4, 130.1 (s, CHAr), 140.8 (s, Cq, CArN), 169.2 (s, C]O). GC/MS :
m/z¼403 [MþꢁOAc]. FTIR (film, cmꢁ1): 3423, 2925,1755,1686,1517,
1372, 1224, 1174, 1129. HRMS (ESIþ): calcd for C18H17F8NO2SNa m/z
486.0750, found 486.0764.
NMR (CDCl3, d ppm): 21.0 (s, Me p-Tol), 26.1 (s, MeCO), 37.7 (s, CH2),
2
39.1 (s, CH2), 58.0 (s, CH3O), 74.2 (q, JC,F¼28.0 Hz, Cq), 77.5 (s,
1
CHOMe), 125.4 (q, JC,F¼289.3 Hz, CF3), 129.9, 130.2, 130.3, 130.4
(4ꢂs, 4ꢂCHAr), 137.8 (s, Cq, CArMe), 139.7 (s, Cq, CArN), 172.5 (s,
COMe), 202.0 (s, C]Ocyclic). HRMS (ESIþ): calcd for C16H18F3NO3SNa
m/z 384.0857, found 384.0847.
4.8.3. 4-(2-(Trifluoromethyl)-6-trimethylsiloxy-3,6-dihydro-2H-thio-
pyran-2-yl)morpholine (22). Compounds 22a,b were obtained
(Method 3) as a mixture (67:33) of diastereomers from thioamide
9f (0.2 g, 1.0 mmol) and 1-trimethylsilyloxy-buta-1,3-diene (7)
(1.8 mL, 10 mmol). They were not separated by silica gel column
chromatography (eluent: PE/EtOAc, 9:1); analyses were done on
the mixture. Yield: 12% (40 mg). Oil. Rf¼0.31 (PE/EtOAc, 9:1). 19F
4.10.2. N-(5-Methoxy-6-(1,1,2,2,3,3,4,4-octafluorobutyl)-3-oxo-tetra-
hydrothiopyran-6-yl)-N-(p-tolyl)acetamide (26). Yield: 62% (0.30 g).
Oil. Rf¼0.4 (PE/EtOAc, 3:1). 19F NMR (CDCl3,
ppm): ꢁ98.0 (1F, CF2,
d
AB, 2JF,F¼278.0 Hz), ꢁ103.2 (1F, CF2, AB, 2JF,F¼278.0 Hz), ꢁ120.2 (1F,
CF2, AB, 2JF,F¼295.1 Hz), ꢁ121.9 (1F, CF2, AB, 2JF,F¼295.1 Hz), ꢁ129.7
2
(2F, m, CF2), ꢁ137.0 (1F, dm, HCF2, JF,H¼51.2 Hz), ꢁ137.6 (1F, dm,
2
NMR (CDCl3,
d
ppm): ꢁ71.2 (s, CF3, major), ꢁ71.4 (s, CF3, minor). 1H
HCF2, JF,H¼51.2 Hz). 1H NMR (CDCl3,
d ppm): 1.76 (s, 3H, MeCO),
NMR (CDCl3,
d
ppm): 0.2 (s, 18H, 2ꢂSiMe3), 2.5e3.2 (m, 12H,
2.40 (s, 3H, Me p-Tol), 2.92 (m, 1H, CH2), 2.94 (s, 2H, CH2), 3.43 (m,
CH2NþCH2), 3.6 (m, 8H, CH2O), 5.35 (br s, 1H, CHOTMS, major), 5.60
(br s, 1H, CHOTMS, minor), 5.7e5.8 (m, 2H, ]CH), 5.8e5.9 (m, 2H,
]CH). FTIR (film, cmꢁ1): 3402, 2855, 1723, 1614, 1453, 1288, 1119,
844, 726. HRMS (ESIþ): calcd for C13H23F3NO2SSi m/z 342.1171,
found 342.1174.
1H, CH2), 3.45 (s, 3H, OMe), 5.59 (br s, 1H, CHOMe), 6.09 (tt,
3
2JH,F¼51.2 Hz, JH,F¼5.6 Hz, 1H, HCF2), 7.18e7.34 (m, 4H, CHAr). 13
C
NMR (CDCl3, d ppm): 21.3 (s, CH3 p-Tol), 27.3 (s, MeCO), 37.5 (s, CH2),
40.0 (s, CH2), 57.7 (s, OCH3), 75.0 (s, CHOMe), 78.7 (m, Cq), 129.7,
129.8, 130.3, 130.7 (4ꢂs, 4ꢂCHAr), 139.1 (s, Cq, CArMe), 140.5 (s, Cq,
CArN), 173.4 (s, COMe), 202.0 (s, COcyclic). GC/MS: m/z¼493 [Mþ],
350, 318, 250, 149, 100. FTIR (film, cmꢁ1): 3430, 2932, 1725, 1689,
1509, 1369, 1294. HRMS (ESIþ): calcd for C19H20F8NO3S m/z
494.1036, found 494.1033.
4.9. Reaction of thioamide 9d with 2-trimethylsilyloxy-buta-
1,3-diene (23) (Scheme 8)
4.9.1. N-(6-Trifluoromethyl-3-oxo-tetrahydrothiopyran-6-yl)-N-(p-
tolyl)-acetamide (24). 2-(Trimethylsilyloxy)buta-1,3-diene (23)
(0.22 mL, 1.2 mmol) was added to a solution of thioamide 9d
4.10.3. N-(3-Methoxy-2-trifluoromethyl-5-(tert-butyldimethylsily-
loxy)-3,6-dihydro-2H-thiopyran-2-yl)-N-(p-tolyl)acetamide

O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
1335
3
(27). Yield: 75% (0.67 g). Colorless crystal. Mp¼116e118 ꢀC. Rf¼0.4
(CDCl3,
d
3
ppm): 7.12 (d, JH,H¼10.3 Hz, 1H, CH), 7.35 (s, 1H, CH),
(PE/EtOAc, 9:1). 19F NMR (CDCl3,
d
ppm): ꢁ62.9 (s). 1H NMR
7.81 (d, JH,H¼10.3 Hz, 1H, CH). GC/MS: m/z¼180 [Mþ], 152, 133.
(CDCl3,
d ppm): 0.21 (s, 3H, SiCH3), 0.25 (s, 3H, SiCH3), 0.96 (s, 9H,
SiBu-t), 1.71 (s, 3H, MeCO), 2.40 (s, 3H, Me p-Tol), 2.56 (d,
4.12. Typical procedure for the rearrangement of cyclo-
adducts 30 into 1,3-thiazolidin-4-ones 31 (Scheme 11)
2
4
2JH,H¼15.6 Hz, 1H, SCHAHB), 3.11 (dd, JH,H¼15.6 Hz, JH,H¼1.2 Hz,
3
1H, SCHAHB), 3.29 (s, 3H, CH3O), 5.18 (dd, JH,H¼6.4 Hz,
3
4JH,H¼1.2 Hz, 1H, C]CH), 5.45 (d, JH,H¼6.4 Hz, 1H, CHOMe), 7.00
Danishefsky’s diene 8a (0.45 mL, 2.3 mmol) was added to
a solution of thioamide 9d (0.6 g, 2.3 mmol) in 10 mL of dry
CH2Cl2. The reaction mixture was stirred at room temperature for
24 h. 19F NMR spectra of the reaction mixture showed full con-
version of 9d into cycloadduct 30a (dF¼ꢁ62.9 ppm). Then, solid
TBAF$3H2O (1.45 g, 4.6 mmol) was added to the solution, which
was stirred at room temperature for 15 h (19F NMR of the reaction
mixture showed full conversion of cycloadduct 30a into thiazoli-
dinone 31a). Solvent was evaporated in vacuo and the residue was
purified by silica gel column chromatography (eluent: mixture
petroleum ether and ethyl acetate, 2:1) affording 31a (0.27 g,
33%).
3
3
(d, JH,H¼8.1 Hz, 1H, CHAr), 7.14 (d, JH,H¼8.1 Hz, 1H, CHAr), 7.21 (d,
3JH,H¼8.1 Hz, 2H, 2ꢂCHAr). 13C NMR (CDCl3,
d
ppm): ꢁ4.8 (s,
SiCH3), ꢁ4.4 (s, SiCH3), 18.0 (s, Cq t-Bu), 21.2 (s, Me p-Tol), 25.5 (s,
CH3 t-Bu), 26.9 (s, MeCO), 28.8 (s, CH2), 56.3 (s, CH3O), 73.9 (s,
2
CHOMe), 76.4 (q, JC,F¼27.5 Hz, Cq), 101.9 (s, CH]C), 125.0 (q,
1JC,F¼289.8 Hz, CF3), 129.3, 129.5, 130.0, 130.8 (4ꢂs, 4ꢂCHAr), 138.8
(s, Cq, CArMe), 139.3 (s, Cq, CArN), 151.2 (s, Cq, ]COTBS), 172.1 (s,
C]O). HRMS (ESIþ): calcd for C22H32F3NO3SSiNa m/z 498.1722,
found 498.1718. X-ray crystal structure determination of 27.
ꢁ
C
22H32F3NO3SSi, M¼475.64, triclinic, P-1 (Nr 2), a¼11.314(1)A,
ꢁ
ꢁ
b¼11.538(1)A, c¼12.048(2)A,
a
¼109.675(2)ꢀ,
b
¼111.281(2)ꢀ,
3
ꢁ
ꢀ
g
¼104.073(2) , V¼1254.6(3)A , Z¼2, dcalcd¼1.259. A total of 10,105
reflections were collected at room temperature using a three-
circle goniometer of Bruker SMART APEX diffractometer
equipped with CCD area detector and Mo radiation
4.12.1. 2-(1-Methoxy-3-oxobutyl)-3-(p-tolyl)-2-(trifluoromethyl)
thiazolidin-4-one (31a). Solid. Mp¼146e147 ꢀC. Rf¼0.3 (PE/EtOAc,
a
a
K
a
2:1). 19F NMR (CDCl3,
d
ppm): ꢁ69.6 (s). 1H NMR (CDCl3,
d ppm):
(
l
¼0.71069 A). The structure was solved by direct methods with
2.31 (s, 3H, MeCO), 2.39 (s, 3H, Me p-Tol), 2.98 (d, 2JH,H¼18.1 Hz, 1H,
ꢁ
SHELXS-9732 and refined by least square using F2 values and an-
isotropic thermal parameters for non-hydrogen atoms with
SHELXL-9733 available with the WinGX34 package. The hydrogen
atoms were located by Fourier-difference synthesis and fixed
geometrically according to their environment with a common
isotropic temperature factor. The final cycle of full matrix least
square refinement on F2 was based on 5071 observed reflections
and 288 variable parameters and converged with unweighted and
weighted agreement factors of R1¼0.0491, wR2¼0.1343 for 4049
CHAHB), 3.21 (dd, JH,H¼18.1 Hz, JH,H¼8.3 Hz, 1H, CHAHB), 3.31 (s,
2
3
2
3H, CH3O), 3.65 (d, JH,H¼15.8 Hz, 1H, SCHAHB), 3.87 (d,
2JH,H¼15.8 Hz, 1H, SCHAHB), 4.48 (m, 1H, CHOMe), 6.95 (d,
3JH,H¼8.1 Hz, 2H, CHAr), 7.25 (d, JH,H¼8.1 Hz, 2H, CHAr). 13C NMR
3
(CDCl3, d ppm): 21.3 (s, Me p-Tol), 31.0 (s, SCH2), 31.3 (s, MeCO), 46.6
2
(s, CH2), 60.0 (s, CH3O), 76.6 (q, JC,F¼28 Hz, Cq), 76.6 (s, CHOMe),
125.2 (q, 1JC,F¼287.0 Hz, CF3), 128.8 (s, 2ꢂCHAr), 130.5 (s, 2ꢂCHAr),
132.9 (s, Cq, CArMe), 139.9 (s, Cq, CArN), 172.9 (s, C]O cyclic),
205.6 (s, C]O). HRMS (ESIþ): calcd for C16H18F3NO3SNa m/z
384.0857, found 384.0862. X-ray crystal structure determination
reflections with I>2
s
I and R1¼0.0605, wR2¼0.1433 for all data.
ꢁ
The data have been deposited to the Cambridge Crystallographic
Data Centre (Nr CCDC820012). ORTEP representation of com-
pound 27 is given in Fig. 7.
of 31a. C16H18F3NO3S, M¼361.37, triclinic, P-1 (Nr 2), a¼7.929(1)A,
ꢁ
ꢁ
3
b¼10.355(1)A,
c¼11.316(1)A,
a
¼90.714(2)ꢀ,
b
¼98.565(2)ꢀ,
ꢀ
ꢁ
g
¼106.499(2) , V¼879.4(1)A , Z¼2, dcalcd¼1.365. A total of 7005
reflections were collected at room temperature using a three-circle
4.11. Typical procedure for reaction of thioamide 9f with
Danishefsky’s diene 8a (Scheme 10)
goniometer of a Bruker SMART APEX diffractometer equipped with
ꢁ
a CCD area detector and Mo K
a
radiation (
l
¼0.71069 A). The
structure was solved by direct methods with SHELXS-9732 and re-
fined by least square using F2 values and anisotropic thermal pa-
rameters for non-hydrogen atoms with SHELXL-97.33 The hydrogen
atoms were located by Fourier-difference synthesis and fixed geo-
metrically according to their environment with a common isotropic
temperature factor. The final cycle of full matrix least square re-
finement on F2 was based on 3518 observed reflections and 220
variable parameters and converged with unweighted and weighted
agreement factors of R1¼0.0525, wR2¼0.1419 for 2714 reflections
Thioamide 9f (0.25 g, 1.25 mmol) and Danishefsky’s diene 8a
(0.55 mL, 2.5 mmol) were heated at 150 ꢀC in a 10 mL pressure
vessel sealed with Teflon septum with stirring in an oil bath for
5 h (Method 3). After evaporation of the volatiles, the residue was
dissolved in THF (15 mL) and 1.5 mL of TFA or HCl (large excess)
was added. The reaction mixture was stirred at room tempera-
ture for 20 h, and evaporated in vacuo. 19F NMR spectra of the
crude mixture revealed significant conversion of starting com-
pound 9f into cycloadducts but the latter were mainly decom-
posed during purification by silica gel column chromatography
(eluent: mixture petroleum ether and ethyl acetate, 3:1) afford-
ing a mixture of compound 28 (40 mg, yield: 10%, mixture
(67:33) of diastereoisomers) and the product 29 (40 mg, yield:
10%).
with I>2
s
I and R1¼0.0665, wR2¼0.1537 for all data. The data have
been deposited to the Cambridge Crystallographic Data Centre (Nr
CCDC816987). ORTEP representation of compound 31a is given in
Fig. 8.
4.12.2. 2-(1-Methoxy-3-oxobutyl)-3-propyl-2-(trifluoromethyl)thia-
zolidin-4-one (31b). Yield: 43% (0.28 g). Colorless crystals.
4.11.1. 6-Methoxy-2-morpholino-2-trifluoromethyl-3,6-dihydro-2H-
thiopyran-4(3H)-one (28). Oil. Rf¼0.32 (PE/EtOAc, 3:1). Only anal-
Mp¼88e90 ꢀC. Rf¼0.35 (PE/EtOAc, 2:1). 19F NMR (CDCl3,
d ppm):
3
ꢁ72.4 (s). 1H NMR (CDCl3,
d
ppm): 0.87 (t, JH,H¼7.5 Hz, 3H,
yses of major diastereoisomer are given. 19F NMR (CDCl3,
d
ppm):
CH3CH2CH2), 1.49e1.69 (m, 2H, CH3CH2CH2), 2.23 (s, 3H, MeCO),
ꢁ70.4 (s). 1H NMR (CDCl3,
d
ppm): 2.8e2.9 (m, 4H, 2ꢂCH2N), 2.87
2.45 (dd, JH,H¼18.0 Hz, JH,H¼1.7 Hz, 1H, CHAHB), 2.95 (m, 1H,
2
3
2
(d, JH,H¼15.0 Hz, 1H, CHAHBCq), 2.9 (m, 2H, CH2CO), 3.27 (dd,
NCHAHB), 3.01 (dd, 2JH,H¼18.0 Hz, 3JH,H¼8.0 Hz,1H, CHAHB), 3.22 (m,
2JH,H¼15.0 Hz, JH,H¼1.2 Hz, 1H, CHAHBCq), 3.46 (s, 3H, OCH3), 3.70
1H, NCHAHB), 3.40 (s, 3H, CH3O), 3.43 (d, JH,H¼15.5 Hz, 1H,
4
2
(m, 4H, 2ꢂCH2O), 4.92 (dd, 3JH,H¼3JH,H¼3.6 Hz,1H, CHOMe). GC/MS:
m/z¼299 [Mþ].
SCHAHB), 3.65 (d, JH,H¼15.8 Hz, 1H, SCHAHB), 4.64 (dd, 1H,
2
3JH,H¼8.0 Hz, 3JH,H¼1.7 Hz, CHOMe). 13C NMR (CDCl3,
d ppm): 11.4 (s,
CH3CH2CH2), 20.0 (s, CH3CH2CH2), 30.8 (s, SCH2), 31.1 (s, MeCO),
4.11.2. 2-Trifluoromethyl-4H-thiopyran-4-one (29).28 Oil. Rf¼0.25
45.5 (s, NCH2), 46.6 (s, CH2), 59.9 (s, CH3O), 75.6 (q, JC,F¼28.5 Hz,
2
(PE/EtOAc, 3:1). 19F NMR (CDCl3,
d
ppm): ꢁ64.2 (s). 1H NMR
Cq), 75.8 (s, CHOMe), 125.5 (q, JC,F¼286.5 Hz, CF3), 172.3 (s, C]O
1

1336
O.S. Kanishchev et al. / Tetrahedron 69 (2013) 1322e1336
cyclic), 205.6 (s, C]O). HRMS (ESIþ): calcd for C12H18F3NO3SNa m/z
336.0857, found 336.0860.
Lett. 2002, 43, 5809e5812; (f) Timoshenko, V. M.; Tkachenko, A. V.; Shermolo-
vich, Yu. G. J. Fluorine Chem. 2005, 126, 369e372.
10. For preparation of thioamides, see: (a) Bauer, W.; Kuchlein, K. Houben-Weyl’s
€
Methoden der Organischen Chemie; Georg Thieme: Stuttgart, New York, NY,1985;
Vol. E5; 1218e1279; (b) Timoshenko, V. M.; Shermolovich, Yu. G.; Grellepois, F.;
Portella, C. J. Fluorine Chem. 2006, 127, 471e475.
4.12.3. N-(5-Methoxy-6-trifluoromethyl-3-oxo-tetrahydrothiopyran-
6-yl)-N-(p-tolyl)-propionamide (32). Yield: 55% (0.19 g). Solid.
11. Padwa, A.; Gareau, Y.; Harrison, B.; Rodrigues, A. J. Org. Chem. 1992, 57,
3540e3545.
12. (a) Friedrich, K.; Zamkanei, M. Tetrahedron Lett.1997, 25, 2139e2140; (b) Friedrich,
K.; Zamkanei, M. Chem. Ber. 1979, 112, 1867e1872.
13. Laduron, F.; Nyns, C.; Janousek, Z.; Viehe, H. G. J. Prakt. Chem./Chem.-Ztg. 1997,
339, 697e707.
14. Mikhailichenko, S.; Bouillon, J.-P.; Besson, T.; Shermolovich, Yu. G. Tetrahedron
Rf¼0.5 (PE/EtOAc, 2:1). 19F NMR (CDCl3,
d
ppm): ꢁ69.6 (s). 1H NMR
3
(CDCl3,
d
ppm): 1.14 (t, JH,H¼7.3 Hz, 3H, CH3CH2CO), 2.38 (s, 3H,
p-Tol), 2.58 (q, 3JH,H¼7.3 Hz, 2H, CH3CH2CO), 2.91 (d, 2JH,H¼17.7 Hz,
2
3
1H, CHAHB), 3.18 (dd, JH,H¼17.7 Hz, JH,H¼8.7 Hz, 1H, CHAHB), 3.29
2
(s, 3H, CH3O), 3.65 (d, JH,H¼15.7 Hz, 1H, SCHAHB), 3.86 (d,
2JH,H¼15.7 Hz, 1H, SCHAHB), 4.50 (d, 3JH,H¼8.7 Hz, 1H, CHOMe), 6.97
(d, 3JH,H¼8.1 Hz, 2H, CHAr), 7.25 (d, 3JH,H¼8.1 Hz, 2H, CHAr).
Lett. 2010, 51, 990e993.
15. For recent reviews, see: (a) Caddick, S.; Fitzmaurice, R. Tetrahedron 2009, 65,
3325e3355; (b) Kappe, C. O.; Dallinger, D. Mol. Divers. 2009, 13, 71e193; (c) De
la Hoz, A.; Diaz-Ortiz, A.; Moreno, A. Chem. Soc. Rev. 2005, 34, 164e178.
ꢀ
Acknowledgements
16. Besson, T.; Thiery, V. Top. Heterocycl. Chem. 2006, 1, 59e78.
17. Rodriquez, M.; Taddei, M. Top. Heterocycl. Chem. 2006, 1, 213e266.
18. For description of instrument and methodology, see: (a) Ferguson, J. D. Mol.
Divers. 2003, 7, 281e286; (b) Microwaves in Organic Synthesis; Loupy, A., Ed.;
Wiley-VCH: Weinhein, 2006.
The authors thank Ambassade de France at Kiev (Institut de
ꢀ
Cooperation Franco-Ukrainienne) for financial support (O.S.K.), Pr.
19. For recent examples of the use of NMP under microwaves, see: Lamazzi, C.;
Dreau, A.; Bufferne, C.; Flouzat, C.; Patrick Carlier, P.; ter Halle, R.; Besson, T.
Tetrahedron Lett. 2009, 50, 5402e5405.
G. Dupas for theoretical calculations, Pr. Y.G. Shermolovich and T.
Besson for interesting discussion, Dr. D. Harakat for HRMS analyses
ꢀ
and Dr. K. Ple for English polishing. We also thank the Centre de
20. For use of N-acyl thioamides in [4þ2] cycloaddition reactions, see: Arnaud, R.;
ꢀ
Chavant, P.-Y.; Molvinger, K.; Vallee,Y.J. Chem. Soc., Chem. Commun.1995,1897e1898.
Ressources Informatiques de Haute-Normandie (CRIHAN) for soft-
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21. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman,
J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.;
Iyengar, S. S.; Tomasi, J.; Barone Mennucci, V. B.; Cossi, M.; Scalmani, G.; Rega, N.;
Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li,
X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
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