Synthesis of alkene, alcohols, and heterocycles containing the pentafluorosulfanyl (SF5) grouping

Article abstract of DOI:10.1080/10426507.2010.527309

Convenient and effective methods for synthesis of heterocyclic derivatives with a pentafluorosulfanyl grouping have been presented. Copyright Taylor and Francis Group, LLC.

Full text of DOI:10.1080/10426507.2010.527309

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Phosphorus, Sulfur, and Silicon and the
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Synthesis of Alkene, Alcohols,
and Heterocycles Containing the
Pentafluorosulfanyl (SF5) Grouping
Professor Valery K. Brel a
a Institute of Physiologically Active Compounds, Russian Academy of
Sciences, Chernogolovka, Moscow region, Russian Federation
Published online: 12 Jul 2011.
To cite this article: Professor Valery K. Brel (2011): Synthesis of Alkene, Alcohols, and Heterocycles
Containing the Pentafluorosulfanyl (SF5) Grouping, Phosphorus, Sulfur, and Silicon and the Related
Elements, 186:5, 1284-1287
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Phosphorus, Sulfur, and Silicon, 186:1284–1287, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.527309
SYNTHESIS OF ALKENE, ALCOHOLS,
AND HETEROCYCLES CONTAINING THE
PENTAFLUOROSULFANYL (SF5) GROUPING
Valery K. Brel
Institute of Physiologically Active Compounds, Russian Academy of Sciences,
Chernogolovka, Moscow region, Russian Federation
Abstract Convenient and effective methods for synthesis of heterocyclic derivatives with a
pentafluorosulfanyl grouping have been presented.
Keywords Fluorine; phosphorus; sulfur
INTRODUCTION
In the last several decades, much interest has been devoted to compounds with the
pentafluorosulfanyl group.1–5 The introduction of pentafluorothio groups (SF5, pentafluoro-
λ6-sulfanyl) into molecular systems can bring about substantial changes with regard to
their physical, chemical, and biological behavior. Compounds containing this group often
possess advantageous properties due to the electronegativity, high hydrolytic stability, and
steric effect of the SF5-substituent. These properties are manifested in various potential
applications such as solvents for polymers,1 energetic materials,2,3 liquid crystals,4 rocket
fuels,5 and others. Therefore, the preparation of building blocks and new organic molecules
with an SF5-group, as well as the investigation of their properties, is very important for
both theoretical and applied chemistry.
RESULTS AND DISCUSSION
As a part of our interest in the development of synthetic methods for the chemistry
of hypervalent compounds, we have initiated an investigation on the use of less explored
unsaturated pentafluorosulfanyl derivatives for the construction of cyclic, bicyclic, and
heterocyclic molecular systems. The starting compounds (3,4, 22,23; Scheme 1) were
prepared in two steps. In all cases, the first step was the photo-induced radical addition
of pentafluorosulfanyl chloride to the corresponding alkenes. Dehydrochlorination with
potassium hydroxide or potassium carbonate gave 3,4, 22,23 with good yield. The primary
alcohols 3 were oxidized by chromium trioxide to afford acid 5, obtained as a stable white
Received 29 June 2010; accepted 22 September 2010.
Work supported by the Russian Foundation for Basic Research (09-03-0099).
Address correspondence to Valery K. Brel, Institute of Physiologically Active Compounds, Russian Academy
of Sciences, Chernogolovka, Moscow region 142432, Russian Federation. E-mail: brel@ipac.ac.ru
1284

SYNTHESIS OF ALKENE, ALCOHOLS, AND HETEROCYCLES
1285
solid in 60% yield after vacuum distillation. The primary alcohol 3 was oxidized by CAN
(cerium(IV) ammonium nitrate) to afford trans-3-(pentafluoro-λ6-sulfanyl)prop-2-enal (6)
obtained as a colorless liquid in 90% yield.
Scheme 1
Compounds 5–8 participate in a Diels–Alder cycloaddition reaction to yield SF5-
containing adducts. The reaction was performed by heating a mixture of the dipolarophiles
(5–8) with cyclopentadiene (10 equiv) under a nitrogen atmosphere in closed glass ampoule
1
at 110◦C. After 10 hours, H NMR analysis showed that the reaction mixture contained
adducts 12–15 as a mixture of endo- and exo-isomers (3:1 ratio) (Scheme 2).
Scheme 2
The reaction products were then separated by preparative column chromatography.
Both endo- and exo-adducts were isolated in pure form. Reaction of 2,3-dimethylbutadiene
with 5–8 led to cycloadducts 16–19 with the pentafluorosulfanyl group attached directly
to the six-membered ring. We have also prepared cycloadducts with SF5 group con-
nected to the ring by a short spacer. For realization of this goal, we prepared methyl
4-(pentafluorosulfanyl)but-2-enoate (11) and studied its reactivity in the Diels–Alder reac-
tion. As a starting compound for the synthesis of 10, alcohol 2 was used. Analogously to the
two-step procedure above, this alcohol was transformed into 1-(pentafluorosulfanyl)but-
1-en-4-ol (4). The alcohol 4 was then oxidized by chromium trioxide to the acid 9. Its
transformation into the methyl ester 10 was performed via a standard esterification method.

1286
V. K. BREL
In the last step, we used a prototropic rearrangement that was investigated earlier on the ex-
ample of 1-(pentafluorosulfanyl)-3-chloroprop-1-ene.6 Ester 10 smoothly rearranges into
unsaturated isomer 11 under treatment with cesium carbonate. The yield of 11 is 76%.
Heating ester 11 with 2,3-dimethylbutadiene or cyclopentadiene in a sealed tube at 100◦C
for 8 h leads to cycloadducts 20,21.
The 4,5-dihydroisoxazoles with the pentafluorosulfanyl group were constructed by
a simple and efficient procedure involving preparation of the SF5-dipolarophiles and their
reaction with nitrile oxide (Scheme 3).
Scheme 3
The [3 + 2] cycloaddition of the nitrile oxides to dipolarophiles 22,23 was performed
in diethyl ether at −20◦C. In the optimized procedure, a solution of triethylamine was
added dropwise over 2 h to the mixture of arylhydroximoyl chloride and dipolarophile. The
generation of the nitrile oxide by dehydrochlorination of hydroximoyl chloride is usually
applied to the synthesis of different 3-aryl- and 3-alkylisoxazoles, but is not efficient for the
preparation of isoxazoles with functional groups. Therefore, we obtained 3-acetylisoxazoles
by another approach, the reactions of dipolarophiles 22,23 with an acetone solution of
CAN.6 When alkadienes 22,23 were refluxed in acetone with CAN for 4 h, 3-acetyl-4,5-
dihydroisoxazoles 27,28 formed in over 85% yield. For the synthesis of compounds 29,30,
we used a prototropic rearrangement of the 4,5-dihydroisoxazoles (24, 25, 28).
CONCLUSION
In conclusion, our results demonstrate a simple and efficient synthesis of novel
pentafluorosulfanyl-containing cyclic, bicyclic, and heterocyclic molecular systems. These
compounds are useful as intermediates in the preparation on of polyfunctional substations
and new materials.
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1287
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