The general approach for the synthesis of substituted cyclobutenyl- and norbornadienyllithiums containing masked trifluoromethyl group

Article abstract of DOI:10.1016/j.tet.2010.10.024

α,β-Unsaturated trifluoromethylketones of cyclobutene number containing trimethylstannyl substituent in β-position were firstly prepared by the addition of trimethylstannyllithium to the corresponding trifluoromethylenaminoketones. The protection of carbo

Full text of DOI:10.1016/j.tet.2010.10.024

Tetrahedron 66 (2010) 9589e9595
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journal homepage: www.elsevier.com/locate/tet
The general approach for the synthesis of substituted cyclobutenyl- and
norbornadienyllithiums containing masked trifluoromethyl group
,
a
b
a
Andrey B. Koldobskii a , Ekaterina V. Solodova , Pavel V. Verteletskii , Ivan A. Godovikov ,
*
Valery N. Kalinin a
a A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Str. 28, 119991 Moscow, Russian Federation
b Department of Chemistry, Moscow State University, 119992 Moscow, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 June 2010
Received in revised form 23 September 2010
Accepted 11 October 2010
Available online 15 October 2010
a
in
,
b
-Unsaturated trifluoromethylketones of cyclobutene number containing trimethylstannyl substituent
-position were firstly prepared by the addition of trimethylstannyllithium to the corresponding
b
trifluoromethylenaminoketones. The protection of carbonyl function under basic conditions conserving
the organometallic substituent was elaborated. The generation of corresponding organolithiums by
SneLi exchange and their reactivity was studied.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Trifluoromethylenaminoketones
b
-Trimethyltin-a,b-unsaturated
trifluoromethylketones
Carbonyl group protection
Tinelithium exchange
Alkenyl organolithiums
1. Introduction
trifluoromethylated analogs stayed unknown until now. Recently
we developed unusual [2þ2]-cycloaddition reactions of 1-trifluo-
The chemistry of
cially containing leaving groups in the
a,b
-unsaturated trifluoromethylketones, espe-
roacetyl-2-halogenoacetylenes with simple alkenes to afford
substituted 1-trifluoroacetyl-2-halogeno-cyclobutenes,11 which ap-
peared to be versatile tools for further transformations including
the nucleophilic substitution of halogen atoms.12,13 The addition
of organolithiums and Grignard reagents to the available pyrro-
b-position is a fascinating and
quickly developing field of organic chemistry. This relative new class
of extremely reactive compounds is a very valuable source for the
different types of functionalization and heterocyclization reactions
frequently giving the important biologically active compounds with
a wide range of action. Owing to this reason the exhaustive and very
lidine derivatives 1aed (Fig. 1) is
-functionalization.12
Herein we report the generation of novel b-alkenyl organo-
a simple route for their
b
interesting reports, and monographs dealing with
a-fluorinated
ketones regularly appear during two last decades.1e5
lithiums with protected trifluoroacetyl group using enaminoke-
tones 1aef as the starting compounds.
An important feature of all
a
,
b-unsaturated trifluoromethyl-
ketones is the highly electrophilic character of the
b-carbon atom of
C]C bond, which is a driving force for the majority of their
transformations.
2. Results and discussion
An alternative potential approach to the novel fluorine con-
taining building blocks is an umpolung strategy to convert the
electrophilic center of the C]C bond to a strongly nucleophilic one
with preliminary protection of the carbonyl function. Although
alkenyllithums with a protected carbonyl group are widely used
synthetic intermediates,6e10 to the best of our knowledge their
2.1. The synthesis of
trifluoromethylketones
b-trimethylstannyl-a,b-unsaturated
Although trialkylstannyllithiums, sodiums, and magnesiums are
reactive and frequently used nucleophiles,14 they have never been
exploited in the reactions with conjugated enaminoketones. Re-
cently we have described a simple and preparative synthesis of
hexamethyldistannan from trimethylstannylchloride on a large
scale employing Li in THF as a coupling reagent. This method
seemed to us more convenient and gave in our hands better results
* Corresponding author. Tel.: þ7 499 135 9251; fax: þ7 499 135 6549; e-mail
address: andikineos@rambler.ru (A.B. Koldobskii).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.10.024

9590
A.B. Koldobskii et al. / Tetrahedron 66 (2010) 9589e9595
H3C
H3C
COCF3
COCF3
COCF3
COCF3
N
N
N
N
1a
1b
1c
1d
Fig. 1. The starting enaminoketones.
than traditionally used system Na in NH3. The generation of tri-
methylstannyllithium from hexamethyldistannan was also carried
out using Li in THF at ambient temperature.
It was shown that trimethylstannyllithium easily reacts with
enaminoketones 1 to give b-trimethylstannyl-a,b-unsaturated tri-
fluoromethylketones 2 in good yields after subsequent quench with
NH4Cl (Scheme 1). Interestingly, elimination of the protonated
pyrrolidine moiety from the intermediate formed upon acidifica-
tion does not require the presence of strong acid and forcing
thermal conditions, and it allows the conservation of the trime-
thylstannyl substituent. The compounds obtained can be distilled
under vacuum and exhibit moderate sensitivity to air although the
short contact is not critical.
Previously in a short preliminary communication we reported
that 1-trifluoroacetyl-2-trimethylstannylacetylene is an active dien-
ophile and easily reacts with 1,3-cyclopentadiene, and 1,3-cyclo-
hexadiene to furnish the corresponding cycloadducts 2e,f.15 Herein,
for the further investigations these compounds were prepared
according to slightly modified procedures (Scheme 2).
2.2. Protection of carbonyl group in trifluoromethylketones
2aef
Initially we expected that compounds 2aef should be useful
substrates in Stille cross-coupling and acylation reactions, however,
even thorough variation of reagents, catalysts, and conditions gave
only poor yields of coupled products, probably owing to the pow-
erful deactivating mesomeric effect of trifluoroacetyl group. In or-
der to realize an alternative approach we attempted to protect
carbonyl function followed by the generation of organolithiums via
of SneLi exchange. Our first endeavors to transform ketones 2 to
the corresponding dimethylhydrazones or dioxolanes proved to be
entirely unsuccessful since an acid, necessary as a catalyst rapidly
affected SneC bond cleavage. Another carbonyl protection meth-
odology including the addition of lithium dialkylamides to the
carbonyl group16 also failed. Eventually we found a very simple and
preparative carbonyl protection procedure that proceeds at ambi-
ent temperature under weak basic conditions and retains the tri-
methylstannyl substituent. The addition of diisopropylamine to
solutions of ketone 2 in chloroethanol results in an exothermic
reaction and the formation of corresponding dioxolanes 3 in good
COCF3
COCF3
SnMe3
1. Me3SnLi, THF
2. NH4Cl
65 –70%
N(CH2)4
1
2
Scheme 1.
Using this method the following
b-trimethylstannyl-a,b-un-
saturated trifluoromethylketones 2aed were prepared (Fig. 2).
Me
COCF3
SnMe3
COCF3
SnMe3
COCF3
COCF3
Me
SnMe3
SnMe3
2a
2b
2c
2d
Fig. 2. The target
b-trimethylstannyl-a,b-unsaturated trifluoromethylketones.
COCF3
SnMe3
86%
20 °C, 48 h
65 °C, 8 h
2e
Me3Sn
COCF3
COCF3
SnMe3
74%
2f
Scheme 2.

A.B. Koldobskii et al. / Tetrahedron 66 (2010) 9589e9595
9591
yields (Scheme 3). An elaborated protocol is possibly applicable for
the various enolizable and non-enolizable ketones, and aldehydes
having an activated carbonyl groups and different functions in-
compatible with acids. It is interesting to note that combination of
chloroethanol with K2CO3 in DMF17 gave lower yields, whereas
chloroethanol with t-BuOK in DMF18 afforded only traces of
products.
require a considerable excess of reagent and the lithiation smoothly
proceeds even at ꢀ70 ꢁC. The completion of lithiation was de-
termined by the disappearance of the starting stannylated dioxo-
lanes 3 in TLC. We have not closely studied the thermal stability of
organolithiums 4, but their acidification and reactions with chlor-
otrimethylsilan gave the corresponding products in nearly 90%
yields, being performed even at ꢀ30 ꢁC.
The organolithiums 4 were then subsequently functionalized
with DMF to afford the corresponding unsaturated aldehydes 5 in
good yields (Scheme 4). In order to extend the range of electro-
philes we also studied the interaction of organolithiums 4 gener-
ated from 3a and 3c with dimethyltrifluoroacetamide (DMTFA). It
was found that this addition proceeds much more faster than with
DMF however after work up procedure very interesting and re-
active ketones 6a,b are formed in a mixture with their hydrates. The
latter have been dehydrated by trifluoroacetic anhydride.
O
COCF3
SnMe3
O
Cl(CH2)2OH, i-Pr2NH
20 °C, 48 h
CF3
70 − 75%
SnMe3
Using this method the following aldehydes 5aef and tri-
fluoromethylketones 6a,b were prepared (Fig. 4).
2
3
The choice of DMF and DMTFA as electrophiles allowed us to
estimate the reactivity of organolithiums 4, furthermore, highly
functionalyzated compounds 5,6 bearing the unsaturated aldehyde
or trifluoromethylketone fragments and the masked trifluoroacetyl
group, should be potentially useful reagents in a variety of trans-
formations. They proved to be relatively stable compounds and can
be purified even by distillation under high vacuum. A probable
limitation of their further employment consents the necessity of
using an extremely strong Lewis or Bronsted acids for the depro-
tection of the carbonyl group adjacent to so strong inductive ac-
ceptor as trifluoromethyl substituent.1 We are currently studying
a specific mild acidolysis of dioxolanes 5 with anhydrous formic
acid via a preliminary conversion of free aldehydes 5a,b to the
corresponding dimethylhydrazones 7a,b (obtained in almost
quantitative yields). As a preliminary report, two selected examples
of this transformation are shown (Scheme 5). The dimethylhy-
drazono group itself does not undergo acidolysis at these condi-
tions. The resulting ketohydrazones 8a,b (Scheme 5) were purified
by column chromatography.
Scheme 3.
Using this method the following dioxolanes 3aef were prepared
(Fig. 3).
O
O
O
Me
O
O
O
Me
CF3
CF3
CF3
SnMe3
O
SnMe3
SnMe3
3a
3b
3c
O
O
O
O
O
CF3
CF3
CF3
3. Conclusion
SnMe3
SnMe3
SnMe3
In conclusion,
b-trimethylstannyl-a,b-unsaturated trifluoro-
3d
3e
3f
methylketones prepared in high yields by the addition of trime-
thylstannyllithium to the corresponding enaminoketones. They
proved to be relatively stable compounds, even distillable under
vacuum. The simple and effective method for protection of their
carbonyl function in mild basic conditions conserving trimethyl-
stannyl substituent was also proposed. It was subsequently dis-
covered that the resulting dioxolanes are convenient sources of
the corresponding organolithiums, that react with DMF and DMTFA
to afford unsaturated aldehydes and trifluoromethylketones of
cyclobutene and norbornadiene (also containing the masked tri-
fluoroacetyl group). Their polyfunctional structure makes them
potentially useful reagents in organic synthesis.
Fig. 3. The target trifluoromethyl dioxolanes.
Commencing the study of dioxolanes 3aef as a source of new
organolithiums 4 we expected that MeLi in ether should be the best
reagent for destannylation since the tetramethylstannan formed in
parallel with organolithiums can be easily evaporated together
with a solvent at work up stage. However, for reasons that are
unclear, the completion of destannylation requires about 50% ex-
cess of MeLi, which can interfere in the further reactions with
electrophiles. An employment of the more basic n-BuLi does not
O
O
O
O
O
O
DMF or DMTFA
78 – 84%
n-BuLi, –70 °C, 1 h
CF3
CF3
CF3
–70 – 0 °C
R = H, CF3
SnMe3
Li
COR
3
4
5, 6
Scheme 4.

9592
A.B. Koldobskii et al. / Tetrahedron 66 (2010) 9589e9595
O
O
O
Me
O
O
O
Me
CF3
CF3
CF3
COR
CHO
COR
5a (R = H), 6a (R = CF3)
5c (R = H), 6b (R = CF3)
5b
O
O
O
O
O
O
CF3
CF3
CF3
CHO
CHO
CHO
5d
5e
5f
Fig. 4. The target
a,
b-unsaturated aldehydes and trifluoromethylketones.
O
O
O
R
R
R
H N NMe
−
CF3
O
1. HCOOH, 20 °C
2. K2CO3
2
2
O
R
R
R
CF3
CF3
Et2O, 20 °C, 1 h
58 60%
−
CH=NNMe2
CH=NNMe2
CHO
5a,b
7a,b
8a,b
R, R = Me, (CH2)5
Scheme 5.
4. Experimental
4.1. General
afford 45.2 g (92%) of hexamethyldistannan as colorless liquid, bp
75 ꢁC (15 Torr), lit.19 bp 73 ꢁC (12 Torr).
4.3. General procedure for preparation of
b-trimethylstannyl-
Enaminoketones 1 have been prepared according to described
procedure.12 Diisopropylamine and chloroethanol were distilled
prior to use. Manipulations with organolithiums and organotins
were carried out under an argon atmosphere. 1H and 13C NMR
spectra were recorded in CDCl3 on ‘Bruker AMX 400’ spectrometer at
400 and 100 MHz, respectively, chemical shifts are reported in parts
per million relative to 0 for TMS. IR spectra were recorded on ‘Bruker
IFS 25’ spectrometer and are reported in terms of frequency of
absorption (cmꢀ1).
a,b-unsaturated trifluoromethylketones 2aed
To a stirred suspension of small thin strips of lithium (0.04 g,
5.7 mmol) in THF (10 mL) containing 0.05 g (0.4 mmol) of naph-
thalene, hexamethyldistannan (0.82 g, 2.5 mmol) was added in one
portion, and the reaction mixture was stirred at 25 ꢁC until disso-
lution of lithium was completed (5e6 h). The resulting solution of
organolithium was cooled to ꢀ70 ꢁC and a solution of enamino-
ketones 1aed (5 mmol) in THF (5 mL) was added dropwise. The
resulting mixture was allowed to warm to 0 ꢁC (30e40 min) and
then was quickly poured into vigorously stirred saturated solution
of NH4Cl (15 mL). After the additional 5 min of vigorous stirring the
organic layer was separated, the aqueous phase was extracted with
ether (3ꢂ10 mL), the combined organic solution was dried over
Na2SO4, and the solvent was removed under vacuum. The residue
was diluted with hexane (15 mL) and kept at 10 ꢁC for 1 h. The
insoluble material was filtered off and after solvent evaporation the
residue was distilled under high vacuum.
4.2. Preparation of hexamethyldistannan in THF
To a stirred suspension of small thin strips of lithium (2.29 g,
0.33 mol) in THF (300 mL) at 25 ꢁC a solution of Me3SnCl (59.8 g,
0.3 mol) in THF (70 mL) was added dropwise. An exothermic re-
action started after several minutes and then the addition was
performed in such a rate to maintain the internal temperature
around 30 ꢁC. The strips of lithium completely disappeared in 2 h of
stirring after which the reaction mixture was stirred for a further
2 h. The majority of the THF was distilled off under vacuum and the
residue was diluted with hexane. The resulting mixture was stirred
for 15 min, the resulting precipitate of LiCl was filtered off and after
evaporation of hexane the residue was distilled under vacuum to
4.3.1. 1-[4,4-Dimethyl-2-(trimethylstannyl)cyclobut-1-en-1-yl]-
2,2,2-trifluoroethanone (2a). From (1a). Colorless liquid, bp
60e61 ꢁC (1 Torr); yield 1.18 g (69%); Found: C, 38.9; H, 5.0; F, 16.5;
Sn, 34.7. C11H17F3OSn requires: C, 38.8; H, 5.0; F, 16.7; Sn, 34.8%; IR

A.B. Koldobskii et al. / Tetrahedron 66 (2010) 9589e9595
9593
(neat) 3004, 2995, 1700, 1605, 1245, 1175 cmꢀ1
;
dH (400 MHz,
(100.6 MHz, CDCl3) 184.8, 178.6 (q, J 38 Hz), 147.4, 133.9, 132.4, 116.9
(q, J 290 Hz), 45.0, 40.0, 24.6, 22.6, ꢀ8.4.
CDCl3) 2.74 (2H, s, CH2eC]C), 1.42 (6H, s, (CH3)2C), 0.22 (9H, s,
Me3Sn); dC (100.6 MHz, CDCl3) 178.0 (q, J 38 Hz), 172.7, 146.6, 116.9
(q, J 290 Hz), 44.1, 41.7, 28.0, ꢀ8.6.
4.5. General procedure for preparation of dioxolanes (3aef)
4.3.2. 2,2,2-Trifluoro-1-[2-(trimethylstannyl)spiro[3.5]non-1-en-1-
yl]ethanone (2b). From (1b). Yellowish liquid, bp 87e88 ꢁC (1 Torr);
yield 1.26 g (66%); Found: C, 44.3; H, 5.6; F, 14.8; Sn, 31.0%.
C14H21F3OSn requires: C, 44.1; H, 5.6; F, 15.0; Sn, 31.2%; IR (neat)
To a solution of cycloadduct 2aef (10 mmol) in 2-chloroethanol
(8 mL) diisopropylamine (1.52 g, 15 mmol) was added in one por-
tion (the solution became red and exothermic process was ob-
served) and the reaction mixture was exposed at 25 ꢁC for 48 h. The
excess of 2-chloroethanol and diisopropylamine was distilled off in
vacuum and the residue was diluted with a mixture etherehexane
1:1 (25 mL). The amine salt was filtered off and the organic solution
was consequently washed with cold solution of NaHCO3, dried over
Na2SO4 and concentrated. The residue was distilled under vacuum
to afford one of dioxolanes 3aef. Dioxolanes 3b,e,f, which crystal-
lized soon after distillation were additionally purified by low-
temperature crystallization (ꢀ20 ꢁC) from hexane.
3015, 2999, 1700, 1602, 1240, 1172 cmꢀ1
; dH (400 MHz, CDCl3) 2.76
(2H, s, CH2eC]C), 2.11e1.90 (2H, m), 1.82e1.58 (4H, m), 1.54e1.37
(4H, m) (total 10H, e(CH2)5e), 0.24 (9H, s, Me3Sn); dC (100.6 MHz,
CDCl3) 178.3 (q, J 38 Hz), 172.8, 147.0, 116.5 (q, J 290 Hz), 50.9, 47.2,
33.2, 25.5, 24.7, ꢀ8.5.
4.3.3. 2,2,2-Trifluoro-1-[7-(trimethylstannyl)bicyclo[3.2.0]hept-6-en-
6-yl]ethanone (2c). From (1c). Colorless liquid, bp 71e72 ꢁC
(1 Torr); yield 1.23 g (70%); Found: C, 40.9; H, 4.8; F, 16.2; Sn, 33.6%.
C12H17F3OSn requires: C, 40.8; H, 4.9; F, 16.2; Sn, 33.6%; IR (neat)
4.5.1. {3,3-Dimethyl-2-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]cyclo-
but-1-en-1-yl}(trimethyl)-stannane (3a). From 2a. Yellowish oil; bp
73e74 ꢁC (1 Torr); yield 3.04 g (79%); Found: C, 40.7; H, 5.6; F, 14.7;
Sn, 30.8%. C13H21F3O2Sn requires: C, 40.6; H, 5.5; F, 14.8; Sn, 30.8%;
3020, 2995, 1702, 1598, 1237, 1177 cmꢀ1
; dH (400 MHz, CDCl3) 3.58
(1H, dd, J 7.9, 3.5 Hz, HCeC]C), 3.40 (1H, dd, J 7.9, 3.5 Hz, HCeC]
C), 1.77e1.71 (2H, m), 1.70e1.64 (2H, m), 1.48e1.42 (2H, m) (total
6H, e(CH2)3e), 0.24 (9H, s, Me3Sn); dC (100.6 MHz, CDCl3) 179.0,
178.8 (q, J 39 Hz), 147.9, 116.7 (q, J 288 Hz), 56.6, 46.1, 25.2, 23.8,
22.8, ꢀ8.0.
IR (neat) 3020, 2935, 1644, 1318, 1180 cmꢀ1
; dH (400 MHz, CDCl3)
4.12e3.98 (2H, m, eCH2Oe), 3.97e3.84 (2H, m, eCH2Oe), 2.36 (2H,
s, CH2eC]C), 1.40 (6H, s, (CH3)2C), 0.16 (9H, s, Me3Sn); dC
(100.6 MHz, CDCl3) 142.6, 139.0, 122.3 (q, J 290 Hz), 104.7 (q, J
33 Hz), 65.8, 43.0, 42.2, 25.4, ꢀ7.7.
4.3.4. 2,2,2-Trifluoro-1-[8-(trimethylstannyl)bicyclo[4.2.0]oct-7-en-
7-yl]ethanone (2d). From (1d). Colorless liquid, bp 80e81 ꢁC
(1 Torr); yield 1.19 g (65%); Found: C, 42.6; H, 5.3; F, 15.4; Sn,
32.3%. C13H19F3OSn requires: C, 42.6; H, 5.2; F, 15.5; Sn, 32.3%; IR
4.5.2. Trimethyl{1-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]spiro[3.5]
non-1-en-2-yl}stannane (3b). From 2b. Yellowish solid; mp
46e47 ꢁC, bp 108e109 ꢁC (0.5 Torr); yield 3.1 g (73%); Found: C,
45.2; H, 6.1; F,13.2; Sn, 28.1%. C16H25F3O2Sn requires: C, 45.2; H, 5.9;
(neat) 3020, 2990, 1700, 1595, 1237, 1180 cmꢀ1
; dH (400 MHz,
CDCl3) 3.46 (1H, dd, J 9.6, 4.8 Hz, HCeC]C), 3.11 (1H, dd, J 9.6,
4.8 Hz, HCeC]C), 1.80e1.60 (4H, m), 1.49e1.31 (4H, m) (total 8H,
e(CH2)4e), 0.21 (9H, s, Me3Sn); dC (100.6 MHz, CDCl3) 179.5, 177.5
(q, J 38 Hz), 145.9, 117.0 (q, J 290 Hz), 44.6, 40.2, 23.2, 22.0, 17.9,
16.4, ꢀ8.3.
F,13.4; Sn, 27.9%; IR (mineral oil) 3026, 2980,1644,1320,1178 cmꢀ1
;
dH (400 MHz, CDCl3) 4.15e4.04 (2H, m, eCH2Oe), 3.96e3.85 (2H,
m, eCH2Oe), 2.39 (2H, s, CH2eC]C), 2.03e1.81 (4H, m), 1.76e1.55
(4H, m), 1.45e1.33 (2H, m) (total 10H, e(CH2)5e), 0.16 (9H, s,
Me3Sn); dC (100.6 MHz, CDCl3) 143.0,139.9,120.9 (q, J 290 Hz),105.1
(q, J 33 Hz), 66.3, 46.8, 43.4, 34.7, 25.3, 24.3, ꢀ8.0.
4.4. Preparation of bicyclic ketones (2e,f)15
4.4.1. 2,2,2-Trifluoro-1-[3-(trimethylstannyl)bicyclo[2.2.1]hepta-2,5-
dien-2-yl]ethanone (2e). To the solution of 1-trifluoroacetyl-2-
trimethylstannylacetylene11,15 (2.85 g, 10 mmol) in ether (2 mL)
freshly distilled 1,3-cyclopentadiene (1.00 g, 15 mmol) was
added in one portion and the resulting mixture was kept at 25 ꢁC
for 48 h. The solution was concentrated and the residue was
distilled to afford 2e as a yellowish liquid, bp 76e77 ꢁC (1 Torr);
yield 3.02 g (86%); Found: C, 41.2; H, 4.4; F, 16.1%. C12H15F3OSn
requires: C, 41.1; H, 4.3; F, 16.2%; IR (neat) 3035, 3000, 1700, 1610,
4.5.3. Trimethyl{7-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo
[3.2.0]hept-6-en-6-yl}stannane (3c). From 2c. Colorless oil; bp
80e81 ꢁC (1 Torr); yield 3.18 g (80%); Found: C, 42.5; H, 5.4; F,
14.3; Sn, 29.8%. C14H21F3O2Sn requires: C, 42.4; H, 5.3; F, 14.4; Sn,
29.9%; IR (neat) 3044, 2975, 1650, 1320, 1180 cmꢀ1
; dH (400 MHz,
CDCl3) 4.16e4.05 (2H, m, eCH2Oe), 4.02e3.91 (2H, m, eCH2Oe),
3.53 (1H, dd, J 7.7, 3.2 Hz, HCeC]C), 3.37 (1H, dd, J 7.7, 3.2 Hz,
HCeC]C), 1.81e1.67 (2H, m), 1.67e1.55 (2H, m), 1.49e1.38 (2H, m)
(total 6H, e(CH2)3e), 0.17 (9H, s, Me3Sn); dC (100.6 MHz, CDCl3)
145.8, 142.0, 122.4 (q, J 290 Hz), 105.7 (q, J 34 Hz), 67.5, 52.6, 48.1,
25.1, 23.7, 22.7, ꢀ8.2.
1240, 1162 cmꢀ1
; dH (400 MHz, CDCl3) 6.87 (1H, dd, J 5.6, 2,7 Hz,
HeC]C), 6.63 (1H, dd, J 5.6, 2,7 Hz, HeC]C), 4.11 (2H, m, HeC1,
HeC4), 2.20 (1H, d, J 7.5 Hz, eCH2e), 2.09 (1H, d, J 7.5 Hz,
eCH2e), 0.25 (9H, s, Me3Sn); dC (100.6 MHz, CDCl3) 195.5, 178.6
(q, J 38 Hz), 158.9, 144.0, 140.7, 117.2 (q, J 290 Hz), 72.9, 58.2,
51.4, ꢀ7.8.
4.5.4. Trimethyl{8-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo
[4.2.0]oct-7-en-7-yl}stannane (3d). From 2d. Colorless oil; bp
84e85 ꢁC (1 Torr); yield 2.92 g (71%); Found: C, 44.0; H, 5.8; F, 13.8;
Sn, 28.8%. C15H23F3O2Sn requires: C, 43.8; H, 5.6; F, 13.9; Sn, 28.8%;
4.4.2. 2,2,2-Trifluoro-1-[3-(trimethylstannyl)bicyclo[2.2.2]octa-2,5-
dien-2-yl]ethanone (2f). The solution of 1-trifluoroacetyl-2-trime-
thylstannylacetylene (2.85 g, 10 mmol) and 1,3-cyclohexadiene
(1.61 g, 20 mmol) in THF (6 mL) was heated to reflux for 6 h. The
solution was concentrated and the residue was distilled to afford 2f
as a yellowish liquid, bp 84e85 ꢁC (1 Torr); yield 2.48 g (68%);
Found: C, 43.0; H, 4.8; F,15.6%. C13H17F3OSn requires: C, 42.8; H, 4.7;
IR (neat) 3050, 2960, 1638, 1322, 1165 cmꢀ1
; dH (400 MHz, CDCl3)
4.19e4.08 (2H, m, eCH2Oe), 3.98e3.87 (2H, m, eCH2Oe), 3.39 (1H,
dd, J 9.4, 4.6 Hz, HCeC]C), 3.19 (1H, dd, J 9.4, 4.6 Hz, HCeC]C),
1.80e1.56 (4H, m), 1.54e1.36 (4H, m) (total 8H, e(CH2)4e), 0.15 (9H,
s, Me3Sn); dC (100.6 MHz, CDCl3) 146.0, 142.3, 121.9 (q, J 289 Hz),
105.3 (q, J 34 Hz), 66.9, 43.3, 40.9, 23.6, 22.6, 17.0, 15.5, ꢀ8.3.
F, 15.6%; IR (neat) 3026, 2998, 1702, 1602, 1236, 1177 cmꢀ1
;
dH
4.5.5. Trimethyl{3-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo
[2.2.1]hepta-2,5-dien-2-yl}stannane (3e). From 2e. White crystals;
mp 37e38 ꢁC; bp 87e88 ꢁC (1 Torr); yield 3.16 g (80%); Found: C,
42.7; H, 4.9; F, 14.4%. C14H19F3O2Sn requires: C, 42.6; H, 4.9; F, 14.4%;
(400 MHz, CDCl3) 6.40 (1H, t, J 6.5 Hz, HeC]C), 6.23 (1H, t, J 6.5 Hz,
HeC]C), 4.25e4.19 (2H, m, HeC1, HeC4), 1.47e1.42 (2H, m,
eCH2e), 1.40e1.33 (2H, m, eCH2e), 0.24 (9H, s, Me3Sn); dC

9594
A.B. Koldobskii et al. / Tetrahedron 66 (2010) 9589e9595
IR (mineral oil) 2985, 2908, 1312, 1174 cmꢀ1
;
dH (400 MHz, CDCl3)
(total 6H, e(CH2)3e); dC (100.6 MHz, CDCl3) 195.3, 156.0, 145.7,
6.77 (1H, d, J 5.1 Hz, HeC]C), 6.61 (1H, d, J 5.1 Hz, HeC]C),
4.18e4.04 (2H, m, eCH2Oe), 4.03e3.91 (2H, m, eCH2Oe), 3.82 (1H,
s, HeC1), 3.72 (1H, s, HeC4),1.93 (2H, d, J 5.6 Hz, eCH2e), 0.15 (9H, s,
Me3Sn); dC (100.6 MHz, CDCl3) 159.0, 157.7, 142.9, 142.1, 122.9 (q, J
290 Hz), 105.8 (q, J 34 Hz), 73.0, 66.6, 66.3, 56.1, 53.0, ꢀ8.3.
124.0 (q, J 290 Hz),106.3 (q, J 34 Hz), 67.6, 54.9, 50.6, 25.8, 23.8, 22.7.
4.6.4. 8-[2-(Trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo[4.2.0]oct-7-
ene-7-carbaldehyde (5d). From 3d and DMF. Yellowish oil, bp
79e80 ꢁC (1 Torr); yield 1.77 g (64%); Found: C, 56.7; H, 5.5; F,
20.5%. C13H15F3O3 requires: C, 56.5; H, 5.5; F, 20.6%; IR (neat) 3050,
4.5.6. Trimethyl{3-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo
[2.2.2]octa-2,5-dien-2-yl}stannane (3f). From 2f. White needles; mp
32e33 ꢁC; bp 99e100 ꢁC (1 Torr); yield 2.78 g (68%); Found: C, 44.2;
H, 5.3; F, 13.9%. C15H21F3O2Sn requires: C, 44.1; H, 5.2; F, 13.9%; IR
2996, 1670, 1604, 1360, 1177 cmꢀ1
; dH (400 MHz, CDCl3) 10.35 (1H,
s, HeCO), 4.26e4.16 (2H, m, eCH2Oe), 4.15e4.06 (2H, m, eCH2Oe),
3.44 (1H, dd, J 9.1, 4.5 Hz, HCeC]C), 3.26 (1H, dd, J 9.1, 4.5 Hz,
HCeC]C), 2.02e1.78 (4H, m), 1.74e1.51 (4H, m) (total 8H,
e(CH2)4e); dC (100.6 MHz, CDCl3) 195.1, 155.4, 142.2, 123.8 (q, J
290 Hz), 106.0 (q, J 34 Hz), 67.8, 47.7, 43.9, 25.3, 22.9, 17.0, 15.0.
(mineral oil) 3060, 2973,1298,1168 cmꢀ1
; dH (400 MHz, CDCl3) 6.35
(1H, t, J 7.0 Hz, HeC]C), 6.29 (1H, t, J 7.0 Hz, HeC]C), 4.20e4.09
(2H, m, eCH2Oe), 4.06e3.95 (2H, m, eCH2Oe), 3.92e3.80 (2H, m,
HeC1, HeC4), 1.38e1.10 (4H, m, e(CH2)2e), 0.18 (9H, s, Me3Sn); dC
(100.6 MHz, CDCl3) 149.5, 147.4, 134.3, 134.2, 123.0 (q, J 290 Hz),
105.2 (q, J 34 Hz), 66.6, 66.4, 43.1, 39.0, 24.6, 24.0, ꢀ8.0.
4.6.5. 3-[2-(Trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo[2.2.1]hepta-
2,5-diene-2-carbaldehyde (5e). From 3e and DMF. Yellow oil, bp
82e83 ꢁC (1 Torr); yield 1.95 g (75%); Found: C, 55.5; H, 4.3; F, 21.9%.
C12H11F3O3 requires: C, 55.4; H, 4.3; F, 21.9%; IR (neat) 3033, 2990,
4.6. General procedure for generation of organolithiums (4)
and for preparation of aldehydes (5aef) and
trifluoromethylketones (6a,b)
1658, 1380, 1177 cmꢀ1
; dH (400 MHz, CDCl3) 10.48 (1H, s, HeCO),
6.84 (1H, dd, J 5.3, 1.0 Hz, HeC]C), 6.64 (1H, d, J 5.3, 1.0 Hz, HeC]
C), 4.30e4.22 (2H, m, eCH2Oe), 4.20e4.11 (2H, m, eCH2Oe), 3.94
(1H, d, J 1.0 Hz, HeC1), 3.81 (1H, d, J 1.0 Hz, HeC4), 2.28 (1H, d, J
7.2 Hz, eCH2e), 2.14 (1H, d, J 7.2 Hz, eCH2e); dC (100.6 MHz, CDCl3)
195.0, 176.9, 160.9, 147.9, 144.7, 122.4 (q, J 288 Hz), 107.3 (q, J 34 Hz),
71.0, 67.5, 67.2, 58.8, 53.6.
To a stirred solution one of dioxolanes 3aef (10 mmol) in THF
(12 mL) at ꢀ70 ꢁC a solution of n-BuLi in hexane (6.9 mL of 1.6 M
solution, 11 mmol) was added dropwise and the mixture was ad-
ditionally stirred at ꢀ60 ꢁC for 1.5 h. To the resulting solution of
organolithium 4 (sometimes precipitate formation was observed)
a solution of DMF or DMTFA (14 mmol) in THF (5 mL) was added
dropwise at ꢀ70 ꢁC and the reaction mixture was allowed gradually
to warm to 0 ꢁC (about 1 h) after which it was poured into stirred
saturated NaH2PO4 (25 mL). The organic layer was separated and
the aqueous phase extracted with ether (2ꢂ20 mL). The combined
organic solution was dried over Na2SO4, concentrated, and the
residue was distilled under vacuum (in the cases of 6a,b the residue
was additionally stirred in trifluoroacetic anhydride (10 mL) for
15 min before the distillation) to afford compounds 5,6 in pre-
parative yields.
4.6.6. 3-[2-(Trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo[2.2.2]octa-
2,5-diene-2-carbaldehyde (5f). From 3f and DMF. Yellow oil, bp
94e95 ꢁC (1 Torr); yield 1.89 g (69%); Found: C, 57.1; H, 4.6; F, 20.8%.
C13H13F3O3 requires: C, 57.0; H, 4.8; F, 20.8%; IR (neat) 3038, 2990,
1665, 1600, 1380, 1177 cmꢀ1
; dH (400 MHz, CDCl3) 10.35 (1H, s,
HeCO), 6.52 (1H, t, J 6.3 Hz, HeC]C), 6.38 (1H, t, J 6.3 Hz, HeC]C),
4.34e4.25 (2H, m, HeC1, HeC4), 4.20e4.12 (2H, m, eCH2Oe),
4.03e3.92 (2H, m, eCH2Oe),1.48e1.42 (2H, m, eCH2e), 1.40e1.34
(2H, m, eCH2e);dC (100.6 MHz, CDCl3)189.0,164.1,145.7,135.9,135.2,
124.0 (q, J 290 Hz), 105.5 (q, J 34 Hz), 67.0, 66.7, 46.8, 41.0, 26.5, 24.5.
4.6.7. 1-{3,3-Dimethyl-2-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]cy-
clobut-1-en-1-yl}-2,2,2-trifluoroethanone (6a). From 3a and
DMTFA. Yellowish oil, bp 59e60 ꢁC (1 Torr); yield 2.61 g (82%);
Found: C, 45.2; H, 3.9; F, 35.6%. C12H12F6O3 requires: C, 45.3; H, 3.8;
4.6.1. 3,3-Dimethyl-2-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]cyclo-
but-1-ene-1-carbaldehyde (5a). From 3a and DMF. Yellowish oil, bp
62e63 ꢁC (1 Torr); yield 1.90 g (76%); Found C, 54.0; H, 5.9; F, 25.6%.
C11H13F3O3 requires: C, 54.1; H, 5.9; F, 25.8%; IR (neat) 3018, 1665,
F, 35.8%; IR (neat) 3010, 2985, 1700, 1602, 1277, 1170 cmꢀ1
; dH
1603, 1370, 1150 cmꢀ1
;
dH (400 MHz, CDCl3) 10.38 (1H, s, HeCO),
(400 MHz, CDCl3) 4.30e4.20 (2H, m, eCH2Oe), 4.18e4.09 (2H, m,
eCH2Oe), 2.90 (2H, s, CH2), 1.46 (6H, s, (CH3)2C); dC (100.6 MHz,
CDCl3) 178.4 (q, J 38 Hz), 155.9, 146.0, 124.3 (q, J 290 Hz), 116.6 (q, J
288 Hz), 109.4 (q, J 34 Hz), 68.9, 48.0, 44.2, 27.0.
4.29e4.19 (2H, m, eCH2Oe), 4.15e4.03 (2H, m, eCH2Oe), 2.88 (2H,
s, CH2), 1.49 (6H, s, (CH3)2C); dC (100.6 MHz, CDCl3) 192.6, 157.0,
143.8, 124.9 (q, J 290 Hz), 108.1 (q, J 32 Hz), 68.3, 49.9, 44.6, 27.0.
4.6.2. 1-[2-(Trifluoromethyl)-1,3-dioxolan-2-yl]spiro[3.5]non-1-ene-
2-carbaldehyde (5b). From 3b and DMF. Yellowish oil, bp 94e95 ꢁC
(1 Torr); yield 2.03 g (70%); Found: C, 58.0; H, 6.0; F, 19.7%.
C14H17F3O3 requires: C, 57.9; H, 5.9; F, 19.6%; IR (neat) 3045, 3000,
4.6.8. 2,2,2-Trifluoro-1-{7-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]bi-
cyclo[3.2.0]hept-6-en-6-yl}ethanone (6b). From 3c and DMTFA.
Yellowish oil, bp 64e65 ꢁC (1 Torr); yield 2.64 g (80%); Found: C,
47.1; H, 3.6; F, 34.6%. C13H12F6O3 requires: C, 47.3; H, 3.7; F, 34.5%; IR
1664, 1600, 1377, 1150 cmꢀ1
;
dH (400 MHz, CDCl3) 10.36 (1H, s,
(neat) 3026, 2990, 1700, 1277, 1184 cmꢀ1
; dH (400 MHz, CDCl3)
HeCO), 4.32e4.19 (2H, m, eCH2Oe), 4.16e4.06 (2H, m, eCH2Oe),
2.85 (2H, s, CH2C]C), 2.13e2.01 (2H, m), 1.91e1.69 (2H, m),
1.66e1.43 (2H, m) (total 10H, e(CH2)5e); dC (100.6 MHz, CDCl3)
193.3, 157.5, 140.0, 124.7 (q, J 290 Hz), 107.6 (q, J 32 Hz), 68.5, 48.3,
45.0, 33.8, 25.4, 25.1.
4.29e4.18 (2H, m, eCH2Oe), 4.17e4.07 (2H, m, eCH2Oe), 3.84 (1H,
dd, J 7.3, 3.3 Hz, HCeC]C), 3.54 (1H, dd, J 7.3, 3.3 Hz, HCeC]C),
2.02e1.88 (2H, m), 1.74e1.60 (2H, m), 1.53e1.41 (2H, m) (totally 6H,
e(CH2)3e); dC (100.6 MHz, CDCl3) 178.8 (q, J 38 Hz), 152.6, 148.5,
124.5 (q, J 290 Hz), 117.1 (q, J 288 Hz), 108.8 (q, J 34 Hz), 68.2, 68.0,
52.9, 50.9, 26.3, 24.5, 22.5.
4.6.3. 7-[2-(Trifluoromethyl)-1,3-dioxolan-2-yl]bicyclo[3.2.0]hept-6-
ene-6-carbaldehyde (5c). From 3c and DMF. Yellowish oil, bp
67e68 ꢁC (1 Torr); yield 1.91 g (73%); Found: C, 55.1; H, 5.1; F, 21.7%.
C12H13F3O3 requires: C, 55.0; H, 5.0; F, 21.7%; IR (neat) 3050, 2990,
4.7. Preparation of dimetylhydrazones 7a,b
To the stirred solution of N,N-dimethylhydazine (0.90 g,
15 mmol) and acetic acid (0.1 g) in ether (5 mL) at 20 ꢁC the alde-
hydes 5a,b (10 mmol) in ether (3 mL) was added dropwise. After 1 h
the resulting cloudy, wet solution was dried over K2CO3 and solvent
and an excess of dimethylhydrazine were removed under vacuum.
1670, 1600, 1348, 1165 cmꢀ1
; dH (400 MHz, CDCl3) 10.40 (1H, s,
HeCO), 4.26e4.15 (2H, m, eCH2Oe), 4.13e4.04 (2H, m, eCH2Oe),
3.82 (1H, dd, J 7.4, 3.6 Hz, HCeC]C), 3.54 (1H, dd, J 7.4, 3.6 Hz,
HCeC]C), 2.02e1.82 (2H, m), 1.79e1.61 (2H, m), 1.58e1.39 (2H, m)

A.B. Koldobskii et al. / Tetrahedron 66 (2010) 9589e9595
9595
The crude dimethylhydrazones 6a,b formed in almost quantitative
yield were subjected to acidolysis without further purification. For
analytical purposes they can be purified by column chromatogra-
phy (silicagel, chloroformemethanol 20: 1) although it leads to
some loss of material.
orange oil; yield 1.44 g (58%); Found: C, 53.4; H, 6.2; F, 22.9%.
C11H15F3N2O requires: C, 53.2; H, 6.1; F, 23.0%; IR (neat) 3010, 2990,
1700, 1645, 1420, 1270, 1165 cmꢀ1
; dH (400 MHz, CDCl3) 7.44 (1H, s,
HeC]N), 3.40 (6H, s, Me2N), 2.90 (2H, s, CH2), 1.55 (6H, s, (CH3)2C);
dC (100.6 MHz, CDCl3) 178.0 (q, J 39 Hz), 160.7, 156.0, 152.2, 116.5 (q, J
290 Hz), 52.8, 48.2, 43.5, 27.9.
4.7.1. 2-({3,3-dimethyl-2-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]cy-
clobut-1-en-1-yl}methylene)-1,1-dimethyl-1
l
5,2
l
5-diazyne
4.8.2. 1-{2-[(2,2-dimethyl-1l l
5,2 5-diazynylidene)methyl]spiro[3.5]
(7a). From 5a and N,N-dimethylhydrazine. Yellowish oil; yield
2.42 g (83%) after chromatography; Found: C, 53.6; H, 6.7; F, 19.4; N,
9.4%. C13H19F3N2O2 requires: C, 53.4; H, 6.6; F, 19.5; N, 9.5%; IR
non-1-en-1-yl}-2,2,2-trifluoroethanone (8b). From 7b. Yellow-or-
ange prisms, mp 40e41 ꢁC; yield 1.73 g (60%); Found: C, 58.4; H,
6.7; F, 19.7%. C14H19F3N2O requires: C, 58.3; H, 6.6; F, 19.8%; IR
(neat) 3015, 2997, 1650, 1294, 1180 cmꢀ1
;
dH (400 MHz, CDCl3) 6.95
(mineral oil) 3012, 2990, 1700, 1650, 1277, 1170 cmꢀ1
; dH (400 MHz,
(1H, s, HeC]N), 4.30e4.19 (2H, m, eCH2Oe), 4.16e4.03 (2H, m,
eCH2Oe), 2.76 (6H, s, Me2N), 2.64 (2H, s, CH2), 1.46 (6H, s, (CH3)2C);
dC (100.6 MHz, CDCl3) 144.2, 135.8, 133.7, 122.5 (q, J 290 Hz), 106.8
(q, J 32 Hz), 67.0, 46.3, 42.2, 40.7, 27.3.
CDCl3) 7.38 (1H, s, HeC]N), 3.36 (6H, s, Me2N), 2.90 (2H, s, CH2),
2.26e2.03 (2H, m), 1.82e1.60 (6H, m) (total 10H, e(CH2)5e); dC
(100.6 MHz, CDCl3) 177.2 (q, J 39 Hz), 161.1, 156.2, 152.7, 116.7 (q, J
290 Hz), 53.3, 49.0, 44.0, 33.4, 25.9, 25.3.
4.7.2. 1,1-Dimethyl-2-({1-[2-(trifluoromethyl)-1,3-dioxolan-2-yl]
spiro[3.5]non-1-en-2-yl}methy-lene)-1l l
5,2 5-diazyne (7b). From 5b
References and notes
and N,N-dimethylhydrazine. Yellowish oil; yield 2.82 g (85%) after
chromatography; Found: C, 57.9; H, 7.1; F, 17.1; N, 8.3%.
C16H23F3N2O2 requires: C, 57.8; H, 7.0; F, 17.2; N, 8.4%; IR (neat)
1. Begue, J. P.; Bonnet-Delpon, D. Tetrahedron 1991, 47, 3207e3258.
2. Nenaidenko, V. G.; Sanin, A. V.; Balenkova, E. S. Russ. Chem. Rev. 1999, 68,
437e458.
3034, 3000, 1650, 1290, 1178 cmꢀ1
; dH (400 MHz, CDCl3) 6.91 (1H, s,
3. Druzhinin, S. V.; Balenkova, E. S.; Nenaidenko, V. G. Tetrahedron 2007, 63,
7753e7808.
4. Nenaidenko, V. G.; Druzhinin, S. V.; Balenkova, E. S. Chemistry of
saturated TrifluoromethylKetones; Nova Science: New York, NY, 2007.
5. Russ. Akad. of ScienceFluorocontaining Heterocyclic Compounds, Synthesis and
Application; Furin, G. G., Ed.; Nauka: Novosibirsk, 2001.
6. Depezay, J. C.; Merrer, Y.; Saniere, M. Synthesis 1985, 766e768.
7. Nayoshi, M.; Hidenori, F.; Suguru, J.; Testuaki, T.; Chuzo, J. J. Chem. Soc., Chem.
Commun. 1994, 16, 1835e1836.
HeC]N), 4.31e4.20 (2H, m, eCH2Oe), 4.17e4.05 (2H, m, eCH2Oe),
2.75 (6H, s, Me2N), 2.66 (2H, s, CH2C]C), 2.16e1.93 (2H, m),
1.80e1.51 (6H, m) (total 10H, e(CH2)5e); dC (100.6 MHz, CDCl3)
145.0, 135.5, 134.1, 122.8 (q, J 290 Hz), 107.7 (q, J 32 Hz), 68.9, 48.4,
43.3, 41.0, 33.2, 26.0, 25.1.
a,b-Un-
4.8. Preparation of ketohydrazones 8a,b
8. Takeshi, J.; Toshiki, K.; Naoyoshi, M.; Kenji, S.; Chuzo, J. J. Chem. Soc., Chem.
Commun. 1991, 19, 1409e1411.
9. Spangler, L. A.; Swentou, J. S. J. Org. Chem. 1984, 49, 1800e1806.
10. Majetich, G.; Hull, K.; Coisares, A. M.; Khetani, V. J. Org. Chem. 1991, 56,
3958e3973.
11. Koldobskii, A. B.; Tsvetkov, N. P.; Verteletskii, P. V.; Godovikov, I. A.; Kalinin, V. N.
Izv. Acad. Nauk, Ser. Khim. 2009, 1390e1396; (Koldobskii, A. B.; Tsvetkov, N. P.;
Verteletskii, P. V.; Godovikov, I. A.; Kalinin, V. N. Russ. Chem. Bull. Int. Ed. 2009,
58, 1431e1437).
12. Koldobskii, A. B.; Tsvetkov, N. P.; Solodova, E. V.; Verteletskii, P. V.; Godovikov, I.
A.; Kalinin, V. N. Tetrahedron 2010, 66, 3457e3462.
13. Koldobskii, A. B.; Tsvetkov, N. P.; Solodova, E. V.; Kalinin, V. N. J. Fluorine Chem.
A mixture of 90%formic acid (10 mL) and acetic anhydride (2.22 g)
was kept overnight at ambient temperature. To the resulting stirred
solution one of corresponding dimethylhydrazones 7a,b (10 mmol)
was added and the mixture was stirred at 20 ꢁC for 1 h. The excess of
formic and acetic acid was removed under vacuum, the residue was
dissolved in THF (10 mL) and the resulting solution was vigorously
stirred with 10% aqueous solution of K2CO3 (10 mL) for 2 h. The or-
ganic solvent was evaporated under vacuum and the aqueous phase
was extracted with ether (3ꢂ10 mL). The ether solution was dried
over K2CO3 and concentrated in vacuum. The residual crude keto-
hydrazones 8a,b were purified by column chromatography (silicagel,
chloroformeethylacetate 5:1).
2010, 131, 852e855.
14. Pereyre, M.; Quantard, J.-P.; Alain, R. Tin in Organic Synthesis; Butterworth:
London, 1987.
15. Koldobskii, A. B.; Shilova, O. S.; Kalinin, V. N. Mendeleev Commun. 2001, 99e100.
16. Comins, D. L. SynLett 1992, 615e625.
17. Marsilje, T. H.; Hedrick, M. P.; Desharnais, J.; Tavassoli, A.; Zhang, Y.; Wilson, I.;
Bencovic, S. J.; Boger, D. L. Bioorg. Med. Chem. 2003, 11, 4487e4501.
18. Barbasiewich, M.; Makosza, M. Org. Lett. 2006, 8, 3745e3748.
19. Smith, G. F.; Kuivila, H. G.; Simon, R.; Sultan, L. J. Am. Chem. Soc. 1981, 103,
833e839.
4.8.1. 1-{2-[(2,2-dimethyl-1
thylcyclobut-1-en-1-yl}-2,2,2-trifluoroethanone (8a). From 7a. Yellow-
l l
5,2 5-diazynylidene)methyl]-4,4-dime-