Diels-Alder reactions of β-trifluoroacetylvinylsulfones

Article abstract of DOI:10.1016/S0040-4020(00)00980-7

Diels-Alder reactions of β-trifluoroacetylvinylsulfones with 1,3-dienes in CH₂Cl₂ afforded corresponding mono- and polycycloadducts. A possibility of stereo- and regioselective cycloaddition was investigated. Elimination of sulfonyl group from cycloadducts leads to α,β-unsaturated trifluoromethylketones in good yields.

Full text of DOI:10.1016/S0040-4020(00)00980-7

TETRAHEDRON
Pergamon
Tetrahedron 57 (2001) 201±209
Diels±Alder reactions of b-tri¯uoroacetylvinylsulfones
*
Arkady L. Krasovsky, Valentine G. Nenajdenko and Elizabeth S. Balenkova
Department of Chemistry, Moscow State University, 119899 Moscow, Russia
Received 27 July 2000; revised 26 September 2000; accepted 12 October 2000
AbstractÐDiels±Alder reactions of b-tri¯uoroacetylvinylsulfones with 1,3-dienes in CH2Cl2 afforded corresponding mono- and poly-
cycloadducts. A possibility of stereo- and regioselective cycloaddition was investigated. Elimination of sulfonyl group from cycloadducts
leads to a,b-unsaturated tri¯uoromethylketones in good yields. q 2000 Elsevier Science Ltd. All rights reserved.
1. Introduction
In recent years, Diels±Alder reactions of vinylsulfones have
attracted considerable attention.1±19 The sulfonyl group is a
versatile and ¯exible functionality that enjoys increasing
popularity as an activating group in organic synthesis. It is
also convenient, the elimination of sulfonyl group can be
easily accomplished resulting in alkene3±9 or allene10 forma-
tion and the adducts can be transformed into the correspond-
ing anion which can be alkylated.1 Moreover the sulfonyl
Scheme 1.
group may undergo desulfonylation11±14 and oxidative
desulfonylation with the formation of the corresponding
ketones.15,16
very reactive electrophiles, reacting with heteroarenes such
as pyrrole, indole and furan. It has been shown that
b-tri¯uoroacetylvinylsulfones 2a,b easily add water to
form gem-diols. The preparation of pure ketones 2a,b
demands water-free conditions, whereas oxidation of 1a,b
in aqueous tri¯uoroacetic acid yields diols 3a,b (Scheme 1).
Introduction of electron-withdrawing substituents in the a
or b positions decrease the LUMO energy level and increase
the dienophilicity. The addition of dienes to a compound in
which the double bond was activated by both a sulfonyl and
a carbonyl group has also been reported,9,17±19 but although
b-tri¯uoroacetylvinylsulfones are expected to be good
dienophiles, their reactivity in Diels±Alder cycloadditions
have previously not been described in the literature.
We now report the investigation of the reactivity of
b-tri¯uoroacetylvinylsulfones and their hydrated forms in
reaction with 1,3-dienes. We found that both b-tri¯uoro-
acetylvinylsulfones and the corresponding hydrates are
highly reactive dienophiles. Their reactions with cyclic
and linear dienes proceed easily even at room temperature
in CH2Cl2 to form cycloadducts 4±8 in high yield. Only in
the case of reaction with 9,10-dimethylanthracene is
prolonged re¯ux in CH2Cl2 required.
2. Results and discussion
In recent work20 we have prepared some b-tri¯uoroacetyl-
vinylsulfones by oxidation of the readily available sul®des
1a,b. We have found that these alkenes 2a,b and 3a,b are
We started our investigation from interaction of the diols
Scheme 2.
Keywords: Diels±Alder cycloaddition reaction; sulfones; tri¯uoromethylketone.
* Corresponding author. Tel.: 17-95-939-2276; fax: 17-95-932-88-46; e-mail: nen@acylium.chem.msu.ru
0040±4020/01/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(00)00980-7

202
A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
Scheme 3.
Scheme 4.
Table 1. Yields and diastereomeric ratio of cycloadducts 7a,8a
reaction of diol 3a with cyclopentadiene and cyclo-
hexadiene. A mixture of three isomers was isolated
(Scheme 4, Table 1).
Product
Ratio of isomers (%)
Yield (%)
endo±exo
exo±endo
endo±endo
The diol 3b is a much less reactive dienophile compared
with diol 3a. Interaction of dienes with diol 3b at room
temperature proceeds very slowly. For instance, the reaction
of 3b with 1,3-cyclohexadiene (2 equiv.) in CH2Cl2 at room
temperature afforded 50% conversion after 10 days. Re¯ux
in CH2Cl2 accelerates the reaction and leads to the stereo-
speci®c formation of cycloadducts 4b±9b. Only trans
substituted cyclohexenes are formed in reaction of diol 3b.
7a (nˆ1)
8a (nˆ2)
34
33
46
45
20
22
78
89
because they are more easily handled. Reaction of 1,3-buta-
diene and 2,3-dimethylbutadiene with the diol 3a results in
formation of cycloadducts 4a, 5a as mixture of cis and trans
isomers. Preferentially trans substituted cyclohexenes are
formed. We believe that the low stereoselectivity is due to
diol 3a existing as a mixture of cis and trans isomers
(Scheme 2).
The stereochemistry of compounds 4±8 was established by
1H NMR spectroscopy. Those cycloadducts 4±6 having a
trans arrangement of CH±COCF3 and CH±SO2R
groups, have J3HH of 10.3±11.0 Hz, while those with a cis
arrangement have J3HH of 4±5 Hz. In bicyclic products 7,8
JHexo±Hendo is in the range 5±7 Hz. However, if the sulfonyl
group is exo arranged a signi®cant difference between
signals CHa and CHb protons in 1H NMR spectra is
observed, contrary to the compounds with sulfonyl group
in endo position which have close shifts of CHa and CHb
To study the regiochemistry of the cycloaddition we investi-
gated the reaction of diol 3a with isoprene. We found that a
mixture of the four possible cycloadducts 6a (trans/cis) and
6a0 (trans/cis) is formed (Scheme 3).
The cis/trans isomers ratio for cycloadducts 4a±6a
precisely correspond to the ratio of the isomers in the initial
diol 3a. Low stereoselectivity is also observed in the case of
1
protons in H NMR spectra21 (Scheme 5, Table 2).
Scheme 5.
We supposed that the cycloaddition using the keto form of
reagents might proceed more selectively since both ketones
2a,b exist in the trans form. In the Diels±Alder reaction of
sulfones 2a,b with linear dienes, only trans isomers of 4,5
were formed in good yield. In the case of the unsymmetrical
diene±isoprene, we have obtained a mixture of regioisomers
6a/6a0 in 2/1 and 6b/6b0 in 2.5/1 ratio, preferentially para
COCF3 substituted isomers are formed. In the case of cyclic
dienes such as cyclopentadiene and 1,3-cyclohexadiene
Table 2. Proton chemical shifts and coupling constants in cycloadducts 7,8
Product
3JHH, Hz
dHa2dHb, ppm
7 (nˆ0)
exo SO2R
endo SO2R
endo±endo
exo SO2R
endo SO2R
endo±endo
5.1
5.5
Overlap
6.2
6.7
0.59
0.07
0.28
0.52
Overlap
0.09
8 (nˆ1)
10.6

A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
203
mixture of exo and endo cycloadducts were formed. So
tri¯uoroacetyl and sulfonyl substituents have similar
orientation ability (Scheme 6, Table 3).
Alder reactions. We have calculated LUMO energy of
reagents 2a,b as well as for analogous CH3CO-compounds.
There is a dramatical difference between LUMO energies of
CF3-containing and non-¯uorinated alkenes. The presence
of the CF3 group in the molecule results in a signi®cant
decrease in the LUMO energy, and CF3 ketones are much
more electron-de®cient and reactive species (Table 4).
We also investigated the in¯uence of a series of Lewis acids,
such as BF3, TiCl4, Eu(fod)3 and ZnCl2 on the regio- and
stereochemistry of cycloaddition. In some cases addition of
Lewis acid leads to some increase of yield (5±10%), but
does not signi®cantly affect the regioisomers ratio. We
believe that this can be attributed to the possibility of
coordination with both carbonyl and sulfonyl groups with
nearly equal probability due to low nucleophilicity of the
CF3CO carbonyl group.
Regio and stereoselectivity of the reactions of 2a,b with
dienes can be explained using the LUMO orbital coef®-
cients. The preferential formation of the para-COCF3-
isomers in the case of reaction with isoprene is in good
agreement with `large±large' molecular orbitals over-
lapping in the transition state (Scheme 7).
We used semiempirical PM3 calculations to explain the
observed reactivity of the reagents 2,3. Frontier molecular
orbital theory is one of the most successful approaches in the
prediction of the regio- and endo±exo selectivity for Diels±
As we have found in the reaction with cyclic 1,3-dienes the
cycloadducts have a preference for an endo-oriented
tri¯uoroacetyl moiety. As is shown in Table 4, LUMO
Scheme 6.
Table 3. Reaction of sulfones 2a,b with dienes; a,a0 RˆPh, b,b0 RˆMe
pRatio of regioisomer was con®rmed by the product of oxidative aromtaization

204
A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
Table 4. LUMO coef®cients at the atoms
RˆPh
RˆMe
RˆPh
RˆCH3
R0ˆCF3
R0ˆCH3
R0ˆCF3
R0ˆCH3
S (1)
C (2)
C (3)
C (4)
O (5)
LUMO, eV
0.0986
0.5614
0.4644
0.4708
0.4420
0.1818
0.5420
0.5469
0.3302
0.3120
20.83
0.0956
0.5641
0.4773
0.4645
0.4396
21.80
0.1712
0.5777
0.6141
0.3249
0.3036
20.83
0.1798
0.4728
0.4951
0.0941
±
0.1588
0.6308
0.6930
0.1191
±
21.67
20.85
20.92
desirable product. We found that elimination of the sulfonyl
group with DBU whilst open to the air leads to instant
oxidative aromatization of the product-1,4-dienes to the
corresponding tri¯uoroacetylbenzenes 15±17 (Scheme 8).
However, under an argon atmosphere 1,4-cyclohexadiene
derivatives 10±12 can be obtained in quantitative yields.
The elimination reaction to form the enone 14 proceeds
with high yield, however, prolonged re¯ux of about 12 h
in CH2Cl2 is required.
Scheme 7.
orbital coef®cients for ¯uorinated alkenes are considerably
greater for the carbonyl group compared with CH3CO
analogues. We suppose that the endo-COCF3 selectivity is
connected with the secondary p-orbital interaction between
the p-system of the dienes and the p-system of the carbonyl
groups of the reagents 2a,b. Having greater LUMO coef®-
cients at the carbonyl group than at the sulfonyl group,
secondary p-orbital interactions in the transition state are
more probable between the C(4) carbon of the reagents
and the p-system of the diene resulting in preferable
endo-COCF3 stereochemistry. However the regioselectivity
of the cycloaddition was not high, both in the case of
b-tri¯uoroacetylvinylsulfones and in the case of the non-
¯uorinated analogues.9
Elimination of the sulfonyl group from cycloadduct 8 yields
bicyclic tri¯uoroacetyl substituted diene 13 in quantitative
yield. In contrast, our attempts to prepare the corresponding
diene from cyclopentadiene derivatives 7 were unsuccess-
ful, probably due to instability of the forming diene
connected with its high strain and the basic conditions of
reaction (Scheme 9; Table 5).
The elimination of the sulfonyl group is rather convenient
for preparation of tri¯uoroacetyl substituted derivatives of
1,4-cyclohexadiene 10±12, and new polycyclic adducts
13,14. Moreover both pure trans isomer 4±6 and the
mixture of cis±trans isomers give the same product.
These products are good building blocks to construct new
fused tri¯uoromethyl substituted heterocycles.
We also investigated the possibility of sulfonyl group
removal from cycloadducts. A number of bases, namely
NaH, NaHCO3, NaOEt, Et3N, Et(i-Pr)2N and DBU were
been used to study the elimination. Best results were
obtained for DBU, in dry CH2Cl2, which is probably
connected with its high basicity and low nucleophilicity.
Other bases resulted in formation of tars, or low yield of
3. Conclusion
We have investigated b-tri¯uoroacetylvinylsulfones in
Diels±Alder reactions. The dienophiles are conveniently
prepared reagents which were proven to be good
Scheme 8.
Scheme 9.

A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
205
Table 5. Elimination of sulfonyl group by DBU from 4±9; RˆPh, Me
4.1. Preparation of Diels±Alder cycloadducts 4±9
To a solution of vinylsulfone 2a,b and 3a,b (1 mmol) in
CH2Cl2 (5 ml) the corresponding diene (2 mmol) was
added. The mixture was stirred at room temperature (in
the case of the reaction with anthracenes reactions were
carried out at 408C with stirring). Removal of the solvent
under reduced pressure afforded products, which were puri-
®ed by column chromatography over silica gel using hexane
as eluent.
Scheme 10.
synthetic equivalents of 1,1,1-tri¯uoro-3-butyn-2-ones
(Scheme 10).
4.1.1. trans-2,2,2-Tri¯uoro-1-[6-(phenylsulfonyl)-3-cyclo-
hexen-1-yl]ethanone (4a). Yield (274 mg, 86%), colourless
oil; [Found: C, 52.59; H, 4.19. C14H13F3O3S requires C,
52.83; H, 4.12%]; nmax (®lm) 1770 cm21; dH (400 MHz,
CDCl3) 7.88±7.84 (2H, m, arom.), 7.72±7.67 (1H, m,
arom.), 7.62±7.55 (2H, m, arom.), 5.69 (2H, br s, 2CHv),
3.81 (1H, ddd, Jˆ6.3, 10.6, 4.6 Hz, CH-6), 3.58 (1H, ddd,
Jˆ5.9, 10.6, 4.5 Hz, CH-1), 2.64-2.50 and 2.30±2.19 (4H,
m, 2CH2); dC (100 MHz, CDCl3) 192.3 (Jˆ35.4 Hz), 137.2,
134.2, 129.4, 128.5, 128.5, 123.3, 115.6 (Jˆ291.8 Hz),
61.2, 38.8, 28.5, 24.3.
It was found that the cycloaddition with various dienes take
place in mild condition. Stereochemistry of reaction was
studied.
4. Experimental
All solvents used were dried and distilled according to stan-
dard procedures. Silica gel Merck 60 and Merck 60F254
plates were used for conventional and analytical (TLC)
chromatography, respectively.
The reaction of 3a with 1,3-butadiene gave a mixture of
trans- and cis-isomers Ð (77/23), after puri®cation, yield

206
A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
(277 mg, 87%), colourless oil; [Found for mixture of
isomers: C, 52.57; H, 4.17. C14H13F3O3S requires C,
52.83; H, 4.12%]; minor isomer cis-2,2,2-tri¯uoro-1-[6-
(phenylsulfonyl)-3-cyclohexen-1-yl]ethanone: nmax (®lm)
1770 cm21; dH (400 MHz, CDCl3) 7.88±7.84 (2H, m,
arom.), 7.72±7.67 (1H, m, arom.), 7.62±7.55 (2H, m,
arom.), 5.76±5.50 (2H, m, 2CHv), 3.78±3.70 (1H, m,
CH-6), 3.60±3.54 (1H, m, CH-1), 2.84±2.76 and 2.58±
2.42 (4H, m, 2CH2); dC (100 MHz, CDCl3) 188.7
(Jˆ35.2 Hz), 137.3, 134.2, 129.3, 128.6, 125.2, 122.0,
115.6 (Jˆ292.0 Hz), 61.7, 36.3, 26.5, 23.5.
nyl)-3-cyclohexen-1-yl]ethanone (6a) and trans-2,2,2-
tri¯uoro-1-[3-methyl-6-(phenylsulfonyl)-3-cyclohexen-1-
yl]ethanone (6a0)Ð(2/1), after puri®cation, yield (289 mg,
87%), colourless oil; [Found for mixture of isomers: C,
54.47; H, 4.43. C15H15F3O3S requires C, 54.21; H,
4.55%]; nmax(®lm) 1765 cm21; dH (400 MHz, CDCl3) 7.85
(2H, m, arom.), 7.67 (1H, m, arom.), 7.56 (2H, m, arom.),
5.40 (1H, m, CHv, 6a), 5.34 (1H, m, CHv, 6a0), 3.90±3.45
(2H, m, CH-1, CH-6), 2.60±2.05 (4H, m, 2CH2), 1.70±1.61
(3H, br s, CH3); dC (100 MHz, CDCl3) for major isomer
(6a): 192.6 (Jˆ35.2 Hz), 137.4, 134.2, 131.1, 129.4,
128.5, 117.5, 115.6 (Jˆ290.0 Hz), 62.0, 38.9, 28.9, 22.7,
18.3.
4.1.2. trans-2,2,2-Tri¯uoro-1-[6-(methylsulfonyl)-3-cyclo-
hexen-1-yl]ethanone (4b). Yield (226 mg, 88%), white
solid; mp 110±1158C; [Found: C, 42.35; H, 4.12.
C9H11F3O3S requires C, 42.19; H, 4.33%]; nmax (®lm)
1775 cm21; dH (400 MHz, CDCl3) 5.78 (2H, br s,
2CHv), 3.75 (1H, ddd, Jˆ8.2, 10.3, 2.1 Hz, CH-6), 3.52
(1H, ddd, Jˆ5.6, 10.3, 4.7 Hz, CH-1), 2.93 (3H, s, CH3),
2.65±2.20 (4H, m, 2CH2); dC (100 MHz, CDCl3) 192.3
(Jˆ35.0 Hz), 123.6, 123.4, 115.4 (Jˆ290.0 Hz), 59.6,
40.2, 39.0, 28.5, 24.7.
The reaction of 3a with isoprene gave a mixture of isomers
cis1trans (6a), and cis1trans (6a0), yield (282 mg, 85%),
colourless oil; [Found for mixture of isomers: C, 54.35; H,
4.49. C15H15F3O3S required C, 54.21; H, 4.55%]; nmax (®lm)
1768 cm21
.
The reaction of 2b (or 3b) with isoprene gave a mixture of
regioisomers trans-2,2,2-tri¯uoro-1-[4-methyl-6-(methyl-
sulfonyl)-3-cyclohexen-1-yl]ethanone (6b) and trans-
2,2,2-tri¯uoro-1-[3-methyl-6-(methylsulfonyl)-3-cyclo-
hexen-1-yl]ethanone (6b0)Ð(2.5/1) after puri®cation,
yield (230 mg, 85%), white solid; mp 105±1108C; [Found
for mixture of isomers: C, 44.70; H, 4.80. C10H13F3O3S
4.1.3. trans-1-[3,4-Dimethyl-6-(phenylsulfonyl)-3-cyclo-
hexen-1-yl]-2,2,2-tri¯uoroethanone (5a). Yield (295 mg,
85%), colourless oil; [Found C, 55.61; H, 4.91.
C16H17F3O3S requires C, 55.48; H, 4.95%]; nmax (®lm)
1770cm21; dH (400 MHz, CDCl3) 7.83 (2H, m, arom.),
7.68 (1H, m, arom.), 7.57 (2H, m, arom.), 3.80 (1H, ddd,
Jˆ6.4, 10.7, 4.5 Hz, CH-6), 3.56 (1H, ddd, Jˆ6.1, 10.7,
3.5 Hz, CH-1), 2.60±2.00 (4H, m, 2CH2), 1.58 (6H, br s,
2CH3); dC (100 MHz, CDCl3) 192.5 (Jˆ35.3 Hz), 137.3,
134.1, 129.3, 128.5, 122.8, 122.7, 115.5 (Jˆ290.0 Hz),
62.1, 39.8, 34.7, 30.3, 18.4, 18.1.
required C, 44.44; H, 4.85%]; nmax (®lm) 1775 cm21
.
Major isomer (6b): dH (400 MHz, CDCl3) 5.45 (1H, br s,
CHv), 3.69 (1H, ddd, Jˆ7.5, 10.6, 3.1 Hz, CH-6), 3.47
(1H, ddd, Jˆ5.9, 10.6, 4.4 Hz, CH-1), 2.90 (3H, s,
CH3SO2), 2.60±2.20 (4H, m, 2CH2), 1.75 (3H, s, CH3). dC
(100 MHz, CDCl3) 192.7 (Jˆ35.1 Hz), 131.2, 117.2, 115.3
(Jˆ290.0 Hz), 59.6, 39.5, 38.9, 32.9, 24.7, 22.4.
The reaction of 3a with 2,3-dimethyl-1,3-butadiene gave a
mixture of trans and cis isomersÐ(78/22), after puri®ca-
tion, yield (302 mg, 87%), colourless oil; [Found for
mixture of isomers: C, 55.58; H, 4.89. C16H17F3O3S requires
C, 55.48; H 4.95%]; minor isomer cis-1-[3,4-dimethyl-6-
(phenylsulfonyl)-3-cyclohexen-1-yl]-2,2,2-tri¯uoroetha-
none: nmax (®lm) 1770 cm21; dH (400 MHz, CDCl3) 7.83
(2H, m, arom.), 7.68 (1H, m, arom.), 7.57 (2H, m, arom.),
3.70 (1H, ddd, Jˆ6.4, 4.6, 4.5 Hz, CH-6), 3.56 (1H, ddd,
Jˆ6.1, 4.6, 3.5 Hz, CH-1), 2.80±2.00 (4H, m, 2CH2), 1.58
(3H, s, CH3), 1.50 (3H, s, CH3); dC (100 MHz, CDCl3)
192.5 (Jˆ35.2 Hz), 137.6, 134.4, 129.2, 128.6, 124.3,
121.4, 115.7 (Jˆ290.0 Hz), 62.5, 37.5, 32.2, 29.1, 18.5,
18.2.
Minor isomer (6b0): dH (400 MHz, CDCl3) 5.45 (1H, br s,
CHv), 3.79 (1H, ddd, Jˆ6.7, 10.5, 3.7 Hz, CH-6), 3.47
(1H, ddd, Jˆ5.7, 10.5, 4.8 Hz, CH-1), 2.91 (3H, s,
CH3SO2), 2.60±2.20 (4H, m, 2CH2), 1.80 (3H, s, CH3); dC
(100 MHz, CDCl3) 192.8 (Jˆ35.1 Hz), 131.0, 117.6, 115.3
(Jˆ290.0 Hz), 60.2, 40.0, 38.9, 28.9, 28.7, 22.6.
The reaction of 2a with cyclopentadiene gave a mixture of
stereoisomers 1-[3-(endo-phenylsulfonyl)bicyclo[2.2.1]-
hept-5-en-2-yl]-exo-2,2,2-tri¯uoro-ethanone (7a) and 1-
[3-(exo-phenylsulfonyl)bicyclo[2.2.1]hept-5-en-2-yl]-endo-
2,2,2-tri¯uoro-ethanone (7a0)Ð(3/4) after puri®cation,
yield (251 mg, 76%), colourless oil; [Found for mixture of
isomers: C, 54.70; H, 3.85. C15H13F3O3S required C, 54.54;
4.1.4. trans-1-[3,4-Dimethyl-6-(methylsulfonyl)cyclohex-
3-en-1-yl]-2,2,2-tri¯uoroethanone (5b). Yield (242 mg,
85%), white solid; mp 115±1208C; [Found: C, 46.13; H,
5.47. C11H15F3O3S requires C, 46.27; H, 5.32%]; nmax
(®lm) 1775 cm21; dH (400 MHz, CDCl3) 3.73 (1H, ddd,
Jˆ6.4, 10.4, 4.0 Hz, CH-6), 3.47 (1H, ddd, Jˆ5.6, 10.4,
5.2 Hz, CH-1), 2.90 (3H, s, CH3SO2), 2.60±2.15 (4H, m,
2CH2), 1.69 (3H, s, CH3), 1.65 (3H, s, CH3); dC (100 MHz,
CDCl3) 192.9 (Jˆ35.0 Hz), 123.3, 122.9, 115.5
(Jˆ290.0 Hz), 60.5, 40.5, 40.3, 34.7, 30.5, 18.6, 18.3.
H, 3.97%]; nmax (®lm) 1765 cm21
.
(7a): dH (400 MHz, CDCl3) 7.90±7.50 (5H, m, arom.), 6.44
(1H, dd, Jˆ2.8, 5.6 Hz, CHv), 6.41 (1H, dd, Jˆ3.0, 5.6 Hz,
CHv), 4.19 (1H, dd, Jˆ3.1, 5.5 Hz, CH-3), 3.34 (1H, br s,
CH), 3.28 (1H, br s, CH), 3.24 (1H, br d, Jˆ5.5 Hz, CH-2),
1.55 (1H, br d, Jˆ9.5 Hz, CH-7), 1.48 (1H, br d, Jˆ9.5 Hz,
CH-7).
(7a0): dH (400 MHz, CDCl3) 7.90±7.50 (5H, m, arom.),
6.33 (1H, dd, Jˆ3.3, 5.6 Hz, CHv), 5.95 (1H, dd, Jˆ2.8,
5.6 Hz, CHv), 3.84 (1H, dd, Jˆ3.4, 5.1 Hz, CH-3), 3.52
(1H, br s, CH), 3.48 (1H, dd, Jˆ1.7, 5.1 Hz, CH-2), 3.37
The reaction of 2a with isoprene gave a mixture of regio-
isomers trans-2,2,2-tri¯uoro-1-[4-methyl-6-(phenylsulfo-

A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
207
(1H, br s, CH), 2.25 (1H, br d, Jˆ9.2 Hz, CH-7), 1.66 (1H,
br d, Jˆ9.2 Hz, CH-7); dC (100 MHz, CDCl3) for mixture of
isomers: 189.5 (Jˆ34.8 Hz), 188.5 (Jˆ34.4 Hz), 138.9,
138.5, 135.6, 135.5, 134.7, 134.2, 134.0, 133.9, 129.4,
129.3, 127.9, 127.8, 115.3 (Jˆ292.2 Hz), 115.2
(Jˆ292.3 Hz), 66.2, 64.7, 49.0, 48.9, 48.7, 47.9, 47.0,
46.4, 44.9, 44.7.
CH-3), 3.48 (1H, br d, Jˆ6.7 Hz, CH-2), 3.16 (1H, br s,
CH), 3.07 (1H, br s, CH), 1.6±1.2 (4H, m, CH2).
(8a0): dH (400 MHz, CDCl3) 7.90±7.50 (5H, m, arom.),
6.43 (1H, dd, Jˆ7.4, 7.4 Hz, CHv), 5.98 (1H, dd, Jˆ7.4,
7.4 Hz, CHv), 3.62 (1H, br d, Jˆ6.2 Hz, CH-3), 3.58 (1H,
dd, Jˆ6.2 Hz, CH-2), 3.20 (1H, br s, CH), 3.17 (1H, br s,
CH), 2.43 (1H, m, CH2), 1.91 (1H, m, CH2), 1.6±1.2 (2H, m,
CH2). dC (100 MHz, CDCl3) for mixture of isomers 189.2
(Jˆ35.0 Hz), 188.9 (Jˆ35.1 Hz), 138.2, 137.0, 136.0,
134.0, 133.9, 132.8, 132.2, 131.7, 130.3, 129.4, 129.1,
128.6, 115.4 (Jˆ292.1 Hz), 115.2 (Jˆ292.2 Hz), 63.2,
61.5, 47.7, 46.3, 32.7, 31.9, 29.4, 29.0, 25.0, 24.9, 24.4,
24.2.
The reaction of 3a with cyclopentadiene gave a mixture of
stereoisomers 1-[3-(endo-phenylsulfonyl)bicyclo[2.2.1]-
hept-5-en-2-yl]-exo-2,2,2-tri¯uoro-ethanone (7a) and 1-
[3-(exo-phenylsulfonyl)bicyclo[2.2.1]hept-5-en-2-yl]-endo-
2,2,2-tri¯uoro-ethanone (7a0) and 1-[3-(endo-phenylsulfo-
nyl)bicyclo[2.2.1]hept-5-en-2-yl]-endo-2,2,2-tri¯uoro-
ethanoneÐ(34/46/20) after puri®cation, yield (258 mg,
78%), colourless oil. [Found for mixture of isomers: C,
54.67; H, 3.89. C15H13F3O3S required C 54.54, H 3.97%];
The reaction of 3a with cyclohexa-1,3-diene gave a mixture
of stereoisomers 1-[3-(endo-phenylsulfonyl)bicyclo[2.2.2]-
oct-5-en-2-yl]-exo-2,2,2-tri¯uoro-ethanone (8a) and 1-[3-
(exo-phenylsulfonyl)bicyclo[2.2.2]oct-5-en-2-yl]-endo-2,2,2-
tri¯uoro-ethanone (8a0) and 1-[3-(endo-phenylsulfonyl)bi-
cyclo[2.2.2]oct-5-en-2-yl]-endo-2,2,2-tri¯uoroethanoneÐ
(33/45/22) after puri®cation, yield (306 mg, 89%), colour-
less oil. [Found for mixture of isomers: C, 55.99; H, 4.30.
C16H15F3O3S requires C, 55.81; H, 4.39%]; nmax (®lm)
nmax (®lm) 1770 cm21
.
Minor isomer endo±endo: dH (400 MHz, CDCl3) 7.90±7.50
(5H, m, arom.), 6.35 (1H, dd, Jˆ3.1, 5.6 Hz, CHv), 6.14
(1H, dd, Jˆ2.8 Hz, Jˆ5.6 Hz, CHv), 1.86 (1H, br d,
Jˆ9.0 Hz, CH-7,), 1.58 (1H, br d, Jˆ9.0 Hz, CH-7).
1
Other H NMR, 13C NMR signals are overlapped by the
signals of major isomer.
1770 cm21
.
The reaction of 2b (or 3b) with cyclopentadiene gave a
mixture of stereoisomers 1-[3-(endo-methylsulfonyl)bi-
cyclo[2.2.1]hept-5-en-2-yl]-exo-2,2,2-tri¯uoro-ethanone
(7b) and 1-[3-(exo-methylsulfonyl)bicyclo[2.2.1]hept-5-
en-2-yl]-endo-2,2,2-tri¯uoro-ethanone (7b0)Ð(2/3), after
puri®cation, yield (215 mg, 80%), colourless oil; [Found for
mixture of isomers: C, 44.68; H, 4.31. C10H11F3O3S requires
Minor isomer endo±endo: dH (400 MHz, CDCl3) 7.90±7.50
(5H, m, arom.), 6.35 (1H, dd, Jˆ7.3, 7.3 Hz, CHv), 6.11
(1H, dd, Jˆ7.3, 7.3 Hz, CHv), 3.94 (1H, br d, Jˆ10.6 Hz,
CH-3), 3.58 (1H, dd, Jˆ10.6 Hz, CH-2), 2.94 (1H, br s,
CH), 2.85 (1H, br s, CH), 1.6±1.3 (4H, m, CH2). 13C
NMR signals are overlapped by the signals of major isomer.
C, 44.77; H, 4.13%]; nmax (®lm) 1770 cm21
.
The reaction of 2b (or 3b) with cyclohexa-1,3-diene gave a
mixture of stereoisomers 1-[3-(endo-methylsulfonyl)bi-
cyclo[2.2.2]oct-5-en-2-yl]-exo-2,2,2-tri¯uoro-ethanone
(8b) and 1-[3-(exo-methylsulfonyl)bicyclo[2.2.2]oct-5-en-
2-yl]-endo-2,2,2-tri¯uoro-ethanone (8b0)Ð(38/62), after
puri®cation, yield (243 mg, 86%), white solid; mp 78±
808C; [Found for mixture of isomers: C, 46.66; H, 4.39.
C11H13F3O3S requires C, 46.80; H, 4.64%]; nmax (®lm)
(7b): dH (400 MHz, CDCl3) 6.45±6.38 (2H, m, CHv), 3.84
(1H, dd, Jˆ3.2, 5.1 Hz, CH-3), 3.49 (1H, br s, CH), 3.38
(1H, br s, CH), 3.27 (1H, br d, Jˆ5.1 Hz, CH-2), 2.85 (3H, s,
CH3SO2), 1.64 (1H, br d, Jˆ9.5 Hz, CH-7), 1.55 (1H, br d,
Jˆ9.5 Hz, CH-7).
(7b0): dH (400 MHz, CDCl3) 6.41 (1H, dd, Jˆ3.1, 5.4 Hz,
CHv), 6.06 (1H, dd, Jˆ2.6, 5.4 Hz, CHv), 3.88 (1H, dd,
Jˆ3.6, 4.8 Hz, CH-3), 3.64 (1H, br s, CH), 3.49 (1H, br s,
CH), 3.24 (1H, br d, Jˆ4.8 Hz, CH-2), 2.91 (3H, s,
CH3SO2), 2.20 (1H, br d, Jˆ9.5 Hz, CH-7), 1.68 (1H, br
d, Jˆ9.5 Hz, CH-7). dC (100 MHz, CDCl3) for mixture of
isomers 189.4 (Jˆ34.8 Hz), 188.7 (Jˆ34.6 Hz), 139.8,
136.0, 135.3, 134.8, 116.0 (Jˆ292.4 Hz), 115.8 (Jˆ
292.4 Hz), 64.2, 62.4, 48.6, 48.0, 47.9, 47.2, 46.5, 46.2,
44.6, 44.5, 40.7, 40.4.
1760 cm21
.
(8b): dH (400 MHz, CDCl3) 6.56±6.47 (2H, m, CHv), 3.81
(1H, br d, Jˆ6.8 Hz, CH-3), 3.38 (1H, br d, Jˆ6.8 Hz,
CH-2), 3.29 (1H, br s, CH), 3.19 (1H, br s, CH), 2.80 (3H,
s, CH3SO2), 1.8±1.2 (4H, m, CH2).
(8b0): dH (400 MHz, CDCl3) 6.44 (1H, dd, Jˆ7.5, 7.3 Hz,
CHv), 6.11 (1H, dd, Jˆ7.5, 7.4 Hz, CHv), 3.63 (1H, br d,
Jˆ6.0 Hz, CH-3), 3.58 (1H, br d, Jˆ6.0 Hz, CH-2), 3.27
(1H, br s, CH), 3.19 (1H, br s, CH), 2.84 (3H, s, CH3SO2),
2.27 (1H, m, CH2), 1.88 (1H, m, CH2), 1.8±1.2 (2H, m,
CH2). dC (100 MHz, CDCl3) for mixture of isomers 189.5
(Jˆ34.8 Hz), 189.2 (Jˆ35.2 Hz), 135.5, 132.4, 132.3,
130.3, 115.2 (Jˆ292.2 Hz), 115.1 (Jˆ292.2 Hz), 62.1,
59.6, 47.1, 46.2, 40.5, 38.6, 32.1, 31.5, 29.4, 29.3, 25.1,
24.7, 22.2, 17.9.
The reaction of 2a with cyclohexa-1,3-diene gave a mixture
of stereoisomers 1-[3-(endo-phenylsulfonyl)bicyclo-
[2.2.2]oct-5-en-2-yl]-exo-2,2,2-tri¯uoro-ethanone
(8a)
and 1-[3-(exo-phenylsulfonyl)bicyclo[2.2.2]oct-5-en-2-yl]-
endo-2,2,2-tri¯uoro-ethanone (8a0)Ð(3/4), after puri®ca-
tion, yield (279 mg, 81%), colourless oil; [Found for mixture
of isomers: C, 55.95; H, 4.37. C16H15F3O3S requires C, 55.81;
H, 4.39%]; nmax(®lm) 1760 cm21.
4.1.5. trans-1-[1,8-Dimethyl-16(phenylsulfonyl)tetracy-
clo-[6.6.2.02,7.09,14]-hexadeka-2,4,6, 10,12,14-hexaen-15-yl]-
2,2,2-tri¯uoro-1-ethanone (9a). Yield (329 mg, 70%),
yellow solid; mp 150±1538C; [Found: C, 66.22; H, 4.61.
(8a): dH (400 MHz, CDCl3) 7.90±7.50 (5H, m, arom.),
6.39±6.30 (2H, m, CHv), 3.84 (1H, br d, Jˆ6.7 Hz,

208
A. L. Krasovsky et al. / Tetrahedron 57 (2001) 201±209
C26H21F3O3S requires C, 66.37; H, 4.50%]; nmax (®lm)
1758 cm21; dH (400 MHz, CDCl3) 7.80±7.10 (13H, m,
arom.), 3.96 (1H, d, Jˆ7.2 Hz, CH), 3.82 (1H, d,
Jˆ7.2 Hz, CH), 2.20 (3H, s, CH3), 2.10 (3H, s, CH3). dC
(100 MHz, CDCl3) 192.8 (Jˆ36.1 Hz), 140.0±108.0 (18C,
arom.), 116.0 (Jˆ291.0 Hz), 74.4, 53.9, 46.0, 43.0, 18.5,
16.0.
4.2.3. 2,2,2-Tri¯uoro-1-(4-methylcyclohexa-1,4-dien-1-
yl)ethanone (12a). nmax(®lm) 1720 cm21; dH (400 MHz,
CDCl3) 7.10 (1H, br s, CHv), 5.42 (1H, br s, CHv),
2.95±2.65 (4H, m, 2CH2), 1.60 (3H, s, CH3). dC
(100 MHz, CDCl3) 181.4 (Jˆ33.6 Hz), 146.5, 137.1,
131.0, 118.7, 117.1 (Jˆ291.0 Hz), 32.5, 28.9, 22.6.
4.2.4. 2,2,2-Tri¯uoro-1-(5-methylcyclohexa-1,4-dien-1-
yl)ethanone (12b). nmax(®lm) 1710 cm21; dH (400 MHz,
CDCl3) 7.10 (1H, br s, CHv), 5.3 (1H, br s, CHv),
2.95±2.65 (4H, m, 2CH2), 1.65 (3H, s, CH3). dC
(100 MHz, CDCl3) 181.4 (Jˆ33.6 Hz), 146.0, 137.1,
129.6, 118.7, 117.0 (Jˆ291.0 Hz), 32.5, 28.1, 22.0.
The reaction of 3a with 9,10-dimethylanthracene gave a
mixture of trans and cis isomers (77/23), after puri®cation;
yield (339 mg, 72%), yellow solid; mp 141±1448C. [Found:
C, 66.30; H, 4.66. C26H21F3O3S requires C, 66.37; H,
4.50%]; nmax (®lm) 1758 cm21
.
4.2.5. 1-Bicyclo[2.2.2]octa-2,5-dien-2-yl-2,2,2-tri¯uoro-
ethanone (13). White solid; mp 78±808C; [Found: C,
59.25; H, 4.47. C10H9F3O requires C, 59.41; H, 4.49%];
Minor isomer cis-1-[1,8-dimethyl-16(phenylsulfonyl)-
tetracyclo[6.6.2.02,7.09,14]-hexadeka-2,4,6,10,12,14-hexaen-
15-yl]-2,2,2-tri¯uoro-1-ethanone: dH (400 MHz, CDCl3)
7.80±7.10 (13H, m, arom.), 3.93 (1H, d, Jˆ3.6 Hz, CH),
3.83 (1H, d, Jˆ3.6 Hz, CH), 2.20 (3H, s, CH3), 2.10 (3H, s,
CH3). dC (100 MHz, CDCl3) 192.7 (Jˆ36.1 Hz), 140.0±
108.0 (18C, arom.), 115.9 (Jˆ291.0 Hz), 74.5, 53.7, 46.5,
43.3, 18.5, 15.9.
n
max(®lm) 1715 cm21; dH (400 MHz, CDCl3) 7.66 (1H, m,
CHv), 6.41 (1H, m, CHv), 6.32 (1H, m, CHv), 4.37 (1H,
br s, CH), 3.90 (1H, br s, CH), 1.50±1.15 (4H, m, 2CH2); dC
(100 MHz, CDCl3) 176.8 (Jˆ34.2 Hz), 154.2, 140.6, 134.4,
132.9, 116.5 (Jˆ291.6 Hz), 38.5, 34.9, 24.1, 24.0.
4.2.6. 1-[1,8-Dimethyl-16-en-tetracyclo[6.6.2.02,7.09,14]-
hexadeka-2,4,6,10,12,14-hexa en-15-yl]-2,2,2-tri¯uoro-
1-ethanone (14). Yellow solid; mp 102±1078C; [Found:
C, 73.23; H, 4.51. C20H15F3O requires C, 73.16; H,
4.60%]; nmax (®lm) 1715 cm21; dH (400 MHz, CDCl3)
7.81 (1H, s, CHv), 7.40±67.0 (8H, m, arom.), 2.48 (3H,
s, CH3), 2.26 (3H, s, CH3); dC (100 MHz, CDCl3) 177.9
(Jˆ34.1 Hz), 163.8, 147.8, 146.2, 146.0, 145.2, 143.8,
125.2, 125.1, 124.9, 124.8, 122.3, 121.1, 120.7, 120.4,
116.0 (Jˆ293.3 Hz), 50.7, 49.9, 15.2, 14.4.
4.1.6. trans-1-[1,8-Dimethyl-16(methylsulfonyl)tetra-
cyclo[6.6.2.02,7.09,14]-hexadeka-2,4,6,10,12,14-hexaen-15-
yl]-2,2,2-tri¯uoro-1-ethanone (9b). Yield (294 mg, 72%),
yellow solid; mp 130±1358C; [Found: C, 61.60; H, 4.47.
C21H19F3O3S requires C, 61.75; H, 4.69%]; nmax (®lm)
1760 cm21; dH (400 MHz, CDCl3) 7.6±6.7 (8H, m,
arom.), 3.71 (1H, d, Jˆ7.3 Hz, CH), 3.50 (1H, d,
Jˆ7.3 Hz, CH), 2.37 (3H, s, CH3), 2.27 (3H, s, CH3); dC
(100 MHz, CDCl3) 192.6 (Jˆ36.0 Hz), 140.0±108.0 (12C
arom.), 114.9 (Jˆ292.7 Hz), 74.4, 53.9, 45.8, 43.4, 42.0,
18.5, 16.0.
Compounds 15±17 was obtained from corresponding
cycloadducts 4±6 in air conditions. The product was puri-
®ed by column chromatography over silica gel using hexane
as eluent. The proton NMR data were in agreement with the
literature.22
4.2. General procedure for the elimination of sulfonyl
group
To a solution of cycloadduct (1 mmol) in CH2Cl2 (5 ml),
DBU (1.1 mmol) was added. The mixture was stirred at
room temperature. The product was puri®ed by column
chromatography over silica gel using hexane as eluent.
Acknowledgements
The research described in this publication was supported by
Russian Fundamental Investigation Foundation (Grant N
00-03-32760a and N 00-03-32763a).
4.2.1. 1-Cyclohexa-1,4-dien-1-yl-2,2,2-tri¯uoroethanone
(10). Colourless oil; nmax (®lm) 1715 cm21; dH (400 MHz,
CDCl3) 7.12 (1H, br s, CHv), 5.75±5.68 (1H, m, CHv),
5.60±5.54 (1H, m, CHv), 3.00±2.65 (4H, m, 2CH2); dC
(100 MHz, CDCl3) 189.2 (Jˆ33.8 Hz), 146.2, 144.1,
128.2, 122.6, 117.3 (Jˆ291.2 Hz), 33.5, 29.0.
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