Pyrolysis reactions of 4-methyl-tetrafluorophenyl and pentafluorophenyl prop-2-enyl ethers: Isomeric tetrahydroinden-1-ones from both intra-molecular Diels-Alder adducts of the Claisen rearrangement reaction from the 4-Me derivative - Mechanistic implicat

Article abstract of DOI:10.1016/S0022-1139(01)00503-6

Heating 4-methyl-tetrafluorophenyl prop-2-enyl ether 16 in vacuo at 170°C gives a mixture of products which includes 3-methyl-2,4,5,7-tetrafluorotricyclo[3.3.1.0^2,7]non-3-ene-6-one 18, the product of one of the two possible intra-molecular Diel

Full text of DOI:10.1016/S0022-1139(01)00503-6

Journal of Fluorine Chemistry 113 ;2002) 123±131
Pyrolysis reactions of 4-methyl-tetra¯uorophenyl and penta¯uorophenyl
prop-2-enyl ethers: isomeric tetrahydroinden-1-ones from both
intra-molecular Diels±Alder adducts of the Claisen
rearrangement reaction from the 4-Me derivative
Mechanistic implications of a thermal retro p4s ‡ p2s reaction of one of
the adducts and recyclisations by p4s ‡ p2s and/or p2s ‡ p2a routes
Andrei S. Batsanov, Gerald M. Brooke*, Alan Kenwright, Jenny L. Wood
Chemistry Department, Science Laboratories, South Road, Durham DH1 2LE, UK
Received 21 May 2001; accepted 23 August 2001
Abstract
Heating 4-methyl-tetra¯uorophenyl prop-2-enyl ether 16 in vacuo at 170 8C gives a mixture of products which includes 3-methyl-2,4,5,7-
tetra¯uorotricyclo[3.3.1.02,7]non-3-ene-6-one 18, the product of one of the two possible intra-molecular Diels±Alder reactions of the
Claisen rearrangement intermediate 17. The product of the second intra-molecular Diels±Alder reaction, 22, is proposed as the intermediate
in the formation of 6-methyl-2,5b,7,7ab-tetra¯uoro-3ab,4,5,7a-tetrahydroinden-1-one 23 in low yield ;4%) in the ¯ash vapour phase ;FVP)
pyrolysis of 16 at 410 8C; the major product is 7-methyl-2,5b,6,7ab-tetra¯uoro-3ab,4,5,7a-tetrahydroinden-1-one 27 ;38%) which is the
same as 23 but with the 6-Me and 7-F substituents interchanged. The facile formation of this unpredictable product is rationalised as
proceeding by a retro Diels-Alder reaction of 18 to the tethered 3-methyl-2,4,5-tri¯uoro-2,4-cyclohexadienylmethyl ¯uoroketene 24 which
has a choice of two intra-molecular recyclisations ;by another p4s ‡ p2s Diels-Alder reaction to 25 skeletally identical with 22, and/or a
p2s ‡ p2a route to 26) both products reacting further to 27. Under FVP conditions at 400 8C, penta¯uorophenyl prop-2-enyl ether 1 ;R=F)
gives 1,2,3,4,6-penta¯uorotricyclo[4.3.0.02,8]non-3-ene-5-one 33 ;3%), the basic structure of which is found in 26. # 2002 Elsevier
Science B.V. All rights reserved.
Keywords: Claisen rearrangement; Diels-Alder adducts; Retro Diels-Alder products; p4s ‡ p2s and/or p2s ‡ p2a cyclisations; 2,4,5-Tri¯uoro-3-
;substituent)-2,4-cyclohexadienylmethyl ¯uoroketene; Cycloaddition; Tricyclo[4.3.0.02,8]non-3-ene-5-one; X-ray crystal structures
1. Introduction
cyclobutanone derivatives readily formed 1,1-diols 6 in
three cases ;Scheme 1).
Penta¯uorophenyl and some 4-substituted-tetra¯uorophe-
nyl prop-2-enyl ethers 1 have been shown on heating to give
3, one of the two possible types of intra-molecular Diels-
Alder adduct via the Claisen rearrangement intermediates
2Ðthe result of electronically favourable conditions
whereby electron-poor ¯uorine-containing diene moieties
interact with the electron-rich alkene in the same molecule
[1±3]. Moreover, each of these Diels-Alder products is
accompanied by its skeletally rearranged isomer 5 via con-
jugatively-stabilised diradical species 4 [2±4]; the strained
The intermediacy of the alternative type of Diels±Alder
adduct 7 from the penta¯uorophenyl ether 1 via 2 ;R=F) was
®rst proposed in 1974 to account for the formation of the
penta¯uorohydroinden-1-one derivative 9 ;R=F) via another
resonance stabilised diradical 8 by ¯ash vapour-phase pyr-
olysis ;FVP) through a silica tube packed with silica wool
carried out at 480 8C at low pressure ;Scheme 2) [5].
However, when the 4-penta¯uorophenyl-tetra¯uorophenyl
ether 1 ;R=C6F5) was pyrolysed, the expected analogue of 9
;R=C6F5) was not the product isolated: what was isolated
was the hydroinden-1-one isomer 10 ;R=C6F5) in which the
7-F and the 6-C6F5 group in 9 were interchanged [2]; from
compounds 1 ;R=C6H5 and CF3) were isolated the unex-
pected isomers 10 ;R=C6H5 and CF3) and of course, 10 is
* Corresponding author. Tel.: ‡44-191-374-3109;
fax: ‡44-191-384-4737.
E-mail address: g.m.brooke@durham.ac.uk ;G.M. Brooke).
0022-1139/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 2 - 1 1 3 9 ; 0 1 ) 0 0 5 0 3 - 6

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A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
Scheme 1.
Scheme 2.
indistinguishable from 9 for R=F [5]. A remarkable depar-
ture from the expected course of reaction had obviously
occurred!
alkene moieties in 11 to give 14 via the well established
concerted p2s ‡ p2a route [9], which must then undergo
radical fission to 15, the precursor to 10 [3] ;Scheme 3).
Two rationalisations for the formation of compounds of
structure 10 have been proposed.
In the present paper, we report further attempts to gain
concrete evidence for one or both of the proposed mechan-
ism;s). We have looked for key intermediates of the type 11,
12 and 14 which might accompany the rearrangement
product 10 for R=CH3 and R=F by investigating the pyr-
olysis reactions of 4-methyl-tetra¯uorophenyl prop-2-enyl
ether 16 ;equivalent to 1 R=CH3) and re-examining that of
penta¯uorophenyl prop-2-enyl ether 1 ;R=F), respectively.
;i) Compound 12, isomeric with and having the same
carbon skeleton as 7 was the obvious precursor, which
underwent ring opening to 13 and hydrogen abstraction
as before ;Scheme 3). The formation of the unexpected
intermediate tricyclic compound 12 was rationalised by
invoking, apparently for the first time [6,7], a retro
Diels±Alder reaction of the internal Diels±Alder adduct
3 to give the cyclohexa-2,4-dienylmethyl fluoroketene
11, followed by the alternative Diels±Alder cyclisation
as shown in Scheme 3. It was noted that although these
latter p4s ‡ p2s reactions are uncommon, one intra-
molecular process has been recorded [8].
2. Results and discussion
The 4-methyl ether 16 was prepared from 4-methyl-
tetra¯uorophenol [10] by reaction with prop-2-enyl bro-
mide/K2CO3. Firstly, a static thermolysis of 16 was carried
out by heating in vacuo at170 8C for 94 h. Chromatography
;ii) The second possible explanation for the formation of 10
was the intra-molecular reaction of the fluoroketene and

A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
125
Scheme 3.
1
of the product ultimately led to four components of interest:
;i) the internal Diels±Alder adduct 18 ;equivalent to 3,
R=CH3) ;15%), the structure of which was determined by
X-ray crystallography ;Fig. 1); ;ii) the ketone 19 ;2%)
;equivalent to 5, R=CH3); ;iii) the 8,8-diol hemihydrate
20 ;3%) ;equivalent to 6, R=CH3); and ;iv) the endo
ethoxyhemiacetal 21 ;3%), the structure of which was
determined by X-ray crystallography ;Fig. 2). Compound
20 crystallised from water as a mixture of phases with
different degrees of hydration. The better-formed crystals,
suitable for X-ray crystallography, were characterised as the
sesquihydrate ;20, x ˆ 1:5) ;Fig. 3), although the elemental
analysis and H NMR spectrum of the bulk material corre-
sponds very closely to the hemihydrate, as indeed did 6
;R=F) earlier [2,4]. The presence of the small proportions of
20 and 21 in the crude product must have arisen from the
reaction of compound 19 present with water and with
adventitious ethanol, respectively, in the solvent used in
the isolation procedure. Recrystallisation of mixtures of 19
and 20 from water gave 20 while the latter on dehydration
with P2O5 gave 19. These results are summarised in
Scheme 4.
Fig. 1. Molecular structure of 18 in crystal. Henceforth double bonds are
shown in black, thermal ellipsoids at 50% probability levels.
Fig. 2. Molecular structure of 21.

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A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
Fig. 3. Asymmetric unit of 20Á1.5H2O, comprising 2 molecules of 20 and 3 of water ;hydrogen bonds are shown as - - -).
Scheme 4.
Compound 16 was subjected to FVP at 410 8C and
the magnitudes of the various JF±F) were the same as those
found in 10 ;R=C6F5, C6H5 and CF3) [2,3]. Also present in
the pyrolysis product was 4-methyl-tetra¯uorophenol ;18%)
formed from 16 by a disproportionation reaction. These
results are shown in Scheme 5 which shows the two possible
modes of formation of 27 via 24 and 25 and/or 26Ðby
analogy with Scheme 3.
The conclusion drawn from this work is that the isolation
of the tetrahydroinden-1-one derivative 23 from 16 ;the ®rst
example of the ``expected'' compound to be detected and
0.01 mmHg as before and benzotri¯uoride was added to
the crude product as an internal standard to enable the yields
of subsequently identi®ed components to be determined by
19F NMR spectroscopy. Of particular interest in this inves-
tigation was the possible presence of compounds having
resonances at very low frequenciesÐshifts more negative
than À200 ppm as found in the intra-molecular Diels±Alder
adduct 18 ;À202.5 ppm for 2-F)Ðshifts expected in com-
pounds 12/14. Compound 18 was present ;0.2%) as was its
rearrangement product 19 ;0.1%), but there were other
tantalising resonances at À202.3 and À207.8 ppm ;both
ca. 0.25%) in materials which were never ultimately iso-
lated. Two compounds only were separated by chromato-
graphy on silica. The minor component, a solid, was the
``expected'' tetrahydroinden-1-one derivative 23 ;equivalent
to 9, R=CH3) ;4%), the structure of which was determined
by X-ray crystallography ;Fig. 4). The major component
once again was the ``unexpected'' tetrahydroinden-1-one
derivative 27 ;equivalent to 10, R=CH3) ;38%), a liquid, the
structure of which was determined by a proton decoupled
19F NMR experiment; this produced a much simpli®ed
spectrum which established that the connectivities ;and
Fig. 4. Molecular structure of 23.

A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
127
Scheme 5.
isolated in this area of chemistry) does show that the original
proposal with the reaction proceeding via the simple intra-
molecular Diels±Alder addition product 22 ;7 in Scheme 2
for R=CH3) from the Claisen rearrangement product 17, is
perfectly reasonable, but that there is a much easier route to
the tetrahydroinden-1-one isomer 27 ;equivalent to 10
R=CH3), two plausible pathways being shown above.
Not having found any key intermediates of the type 11, 12
and 14 which might have accompanied the formation of the
tetrahydroinden-1-one derivatives 23 and 27 in the pyrolysis
reaction of 4-methyl-tetra¯uorophenyl prop-2-enyl ether 16,
attention was turned to a reinvestigation of work carried out
originally with penta¯uorophenyl prop-2-enyl ether 1 ;R=F)
[5,11], particularly since NMR facilities have advanced
enormously in the past 25±30 years. The ether 1 ;R=F)
was pyrolysed at 400 8C and 0.01 mmHg and the crude
product with added benzotri¯uoride as internal standard was
examined by 19F NMR spectroscopy. Five products were
readily identi®ed: the Claisen/Cope rearrangement product
4-[prop-2-enyl]-2,3,4,5,6-penta¯uoro-2,5-cyclohexadienone
29 [11] ;35%) and the penta¯uorohydroinden-1-one deriva-
tive 31 [5] ;20% yield) ;Scheme 6); and very small amounts
of the intra-molecular Diels±Alder adduct 3 ;R=F) ;0.5%)
[1], and the rearrangement product of 3, namely 5 ;R=F)
;0.1%) [4] accompanied by its 1,1-diol hemihydrate 6 ;R=F)
;0.15%) [4], ;Scheme 1). However, of particular interest in
the low frequency region of the spectrum was a material
having resonances at À180.5, À180.8 and À209.5 ppm in
the ratio 1:1:1, present in ca. 3% yield. This compound was
isolated from the complex mixture by chromatography and
sublimation to give 33, the structure of which was deter-
mined by X-ray crystallography ;Fig. 5). Two routes to 33
via the Claisen rearrangement intermediate 28 can be envi-
saged: ;i) route A by a direct formation of the four mem-
bered ring with the substituted hydrocarbon ethene moiety
of the prop-2-enyl group at C-2 of the ring, appropriately
orientated, undergoing a cycloaddition reaction with the 3,4-
di¯uoro alkene moiety of the cyclic conjugated diene, a
reaction type which is peculiar to ¯uorocarbon chemistry
proceeding in a stepwise way via the diradical 32 [12]; ;ii)
route B involves the intra-molecular Diels±Alder adduct
having the structure 30 which also cleaves homolytically and
rearranges via the same diradical 32, Scheme 6. However, it
is not possible to distinguish between these two possibilities.
Compound 33 possesses the rare tricyclo[4.3.0.02,8]no-
nane ring structure. Closely related structures have been
formed by the photochemical cyclisations of 4-methyl-4-
[prop-2-enyl]-cyclohex-2-enone and 5-methyl-5-[prop-2-
enyl]-cyclohex-2-enone [13].
The particularly interesting structural feature of com-
pound 33 is that it has the same carbon skeleton as the
intermediates 14 proposed earlier [3] when it was also
observed from molecular models that the orientation of
tethered ¯uoroketene 11a ;and now in this work, 24a)
required for the p2s ‡ p2a cycloaddition reactions are
favourable, even though the adducts are highly strained
;Scheme 3). Structure 33 lends some credence, therefore,
to the viability of the mechanism in which 14 and 26 are
invoked.
To summarise the present work leading to tetrahydroin-
den-1-one derivatives in the wider context of previous
investigations, the following points can be made.

128
A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
Scheme 6.
1. The isolation of 23 ;4% yield) from the pyrolysis of 16
shows that the simple intra-molecular Diels±Alder
adduct 22 must be involved as an intermediate, even
though its formation is not favoured.
and 10, respectively, in these reactions. The simple
intra-molecular Diels±Alder adducts 18 and 3, which are
stable, characterised compounds, must undergo the
alternative retro Diels±Alder reaction to form the
tethered fluoroketene. These thermal reactions ;as
opposed to photochemical reactions [6,7]) are to our
knowledge, the first examples of this type of reaction.
4. The final pathway from tethered fluoroketene to rear-
ranged tetrahydroinden-1-one derivatives is ambiguous
but the intermediacy of p2s ‡ p2a addition products 14
and 26 have become even more plausible with the
isolation of 33 having the same basic skeleton from the
related reaction involving 3 ;R=F).
2. Compound 27 ;36% yield), isomeric with 23, is formed
more readily from 16, but from the other ethers 1
;R=C6F5, C6H5 and CF3) only materials analogous to 10
were isolated. However, in the light of the present work,
a re-examination of the 19F NMR spectra of the crude
products from the pyrolyses of these compounds
indicates that relative to the surprise products 10 ;100
parts), the expected isomers 9 can now be seen to be
formed in smaller proportions from intramolecular
Diels±Alder adducts of general structure 7 ;27.5, 12
and 78 parts for R=C6F5, C6H5 and CF3 respectively).
3. The tethered tetrafluorocyclohexa-2,4-dienylmethyl
fluoroketene 24 and related compounds 11 are pre-
requisites for the mechanisms proposed to produce 27
Intra-molecular Diels±Alder adducts of type 3 in general
;including R=CH3, i.e. 18), available only because of the
electronic properties of ¯uorine, have enabled a general area
of chemistry to be opened up ;intra-molecular retro Diels±
Alder reactions to ketenes and dienes) in the deductive
senseÐin the way that Kimball and Roberts ®rst proposed
the existence of bromonium ions to account for the stereo-
selectivity of bromine addition to alkenes [14], their exis-
tence only to be proved many years later by the classical
work of Olah and Bollinger [15].
Compound 23 has not rearranged to 27; rather, a different
series of reactions have occurred. The wondrous thing about
Nature is that the shorter three step process from 17 ;and
analogous intermediates 2) is in fact more dif®cult than the
longer ®ve step process from 17!
3. Experimental
NMR spectra were recorded on the following instruments
at the frequencies listed: Varian Mercury 200 ;1H,
Fig. 5. Molecular structure of 33.

A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
129
199.991 MHz; 19F, 188.179 MHz) and Varian Inova 500
;1H, 499.782 MHz; 19F, 470.262 MHz). Chemical shifts are
reported using the high-frequency positive convention from
TMS and CFCl3, hence 19F resonance values are negative; J
values are in Hz); 19F COSY/proton decoupled experiments
were carried out on compounds 23, 27 and 33 to establish
connectivities. Elemental analyses were performed on an
Exeter Analytical Inc CE440 elemental analyser.
C, 54.55; H, 3.66%); dF;CDCl3) À135.3 ;s, 4-F), À176.2 ;m,
7-F), À194.5, ;m, 5-F), À202.5 ;d, 2-F); dH;CDCl3) 1.83 ;t,
3-CH3), 2.01 ;dd, 1H), 2.19 ;m, 1H), 2.85 ;m, 1H), 3.15 ;m,
1H); umax 1775 ;C=O), 1698[C;CH3)=CF] cmÀ1. ;iii) The
slowest eluting fractions ;0.238 g, 5% of the starting material)
contained mainly two components 19 and 20 in the ratio of
2:3, respectively. Recrystallisation of the mixture from water
gave 3-methyl-1,2,4,7-tetra¯uorotricyclo[3.3.1.02,7]non-3-
ene-8,8 diol hemihydrate 20 ;equivalent to 6, R=CH3, x is 0.5)
mp 65±70 8C ;Found: C, 48.36; H, 4.05. C10H11F4O2.5
requires: C, 48.59; H, 4.48%); dF;CDCl3) À115.9 ;m, 4-F),
À195.9 ;d, 1-F, 7-F), À205.9 ;s, 2-F); dH;CDCl3) 1.59 ;t, 3H),
1.75 ;t, 3-CH3), overlapping multiplets from 2.40 to 2.88
;4H), 3.82 ;broad s, 1H); umax 3334 ;shoulders at 3586, 3527)
;gem-diol and unknown amount of water of crystallisation),
1716 [C;CH3)=CF] cmÀ1. Sublimation of a mixture of 20 and
P2O5 at 50±60 8C/0.01 mmHg gave 3-methyl-1,2,4,7-tetra-
¯uorotricyclo[3.3.1.02,7]non-3-ene-8-one 19 ;equivalent to
R=CH3) mp 70.5±76 8C ;Found: C, 54.44; H, 3.65. C10H8-
F4O requires: C, 54.56; H, 3.66%); dF;CDCl3) À115.2 ;m, 4-
F), À188.1 ;d, 1-F, 7-F), À205.4 ;m, 2-F); dH;CDCl3) 1.87 ;t,
3-CH3), overlapping multiplets from 1.90 to 2.13 ;2H), 2.45
and 2.51 ;overlapping m, 2H), 2.88 ;dm, 1H); umax 1825
;C=O), 1713 cmÀ1 [C;CH3)=CF].
3.1. Preparation of 4-methyl-tetrafluorophenyl
prop-2-enyl ether 16
A mixture of 4-methyl-tetra¯uorophenol [10] ;30.95 g),
allyl bromide ;26.34 g), and potassium carbonate ;29.8 g) in
acetone ;130 ml) was heated under re¯ux for 21 h, ®ltered,
the solvent removed in vacuo at room temperature and the
residue distilled to give 4-methyl-tetra¯uorophenyl prop-2-
enyl ether 16 ;27.8 g, 73%), bp 83 8C at 10 mmHg ;Found:
C, 54.18; H, 3.62. C10H8F4O requires: C, 54.56; H, 3.66%);
dF ;CDCl3) À145.6 ;dd, 3-F, 5-F), À158.3 ;dd, 2-F, 6-F); dH
;CDCl3) 2.20 ;4-CH3), 4.67 ;d, CH2), 5.25, 5.32, 5.40 ;2
overlapping d, CH2=CH), 6.02 ;m, CH2=CH).
3.2. Static thermolysis of 4-methyl-tetrafluorophenyl
prop-2-enyl ether 16
3.3. FVP of 4-methyl-tetrafluorophenyl prop-2-enyl
ether 16 at 410 8C
The ether 16 ;4.615 g) was sealed in a 10 l round-bot-
tomed ¯ask in vacuo and heated at 170 8C for 94 h. The
products were condensed into a side arm cooled in liquid air,
washed from the opened vessel with ether which must have
contained some adventitious ethanol resulting in the forma-
tion of 21 ;see later) and the solvent evaporated to give the
crude product ;2.30 g) the 19F NMR of which showed a
complex mixture of products once again. Chromatography
of the crude product on silica using diethyl ether/light
petroleum ;bp 40±60 8C) ;40:60% v/v) as eluant gave frac-
tions which were examined by 19F NMR spectroscopy.
Three compounds of interest were identi®ed in fractions
eluting from the column: ;i) some earlier fractions ;0.145 g,
3% of the starting material) contained crystals which were
washed with cold light petroleum ;bp 40±60 8C) and then
recrystallised from light petroleum ;bp 60±80 8C) and sub-
limed at 528 at 0.01 mmHg to give 3-methyl-1,2,4,7-tetra-
¯uorotricyclo[3.3.1.02,7]non-3-ene-8-endoethoxy-8-ol 21
mp 62±66 8C, the 19F NMR of which showed the presence of
3% of compound 20 ;Found: C, 53.98; H, 5.32. C12H14F4O2
requires: C, 54.14; H, 5.30%); dF;CDCl3) À115.6 ;s, 4-F),
À193.0 ;dm, 1-F, 7-F), À205.0 ;s, 2-F); dH;CDCl3) 1.25 ;t,
CH3CH2), 1.56 ;overlapping d, 2 unassigned H), 1.74 ;t, 4-
CH3), 2.39 ;m, 2 unassigned H), 2.67 ;m, 1H), 3.35 ;d,
1 unassigned H), 3.74 ;t, CH3CH2); umax 3413 ;O±H),
1717 cmÀ1. ;ii) The next fractions of interest ;0.679 g,
15% of the starting material) were recrystallised from light
petroleum ;bp 40±60 8C)/diethyl ether to give 3-methyl-
2,4,5,7-tetra¯uorotricyclo[3.3.1.02,7]non-3-ene-6-one 18 mp
65.0±65.5 8C ;Found: C, 54.43; H, 3.63. C10H8F4O requires:
Over a period of 3.75 h, the ether 16 ;15.115 g) was
distilled in vacuo ;initially at 0.01 mmHg) from a ¯ask
heated in a water bath at ca. 60 8C through a silica tube
;510 mm  20 mm) packed in the middle 170 mm with
silica wool and heated in an oven at 410 8C, the products
of pyrolysis being collected in a trap cooled in liquid
nitrogen; the maximum pressure recorded during the experi-
ment was 0.15 mmHg. To the ;liquid) pyrolysate ;14.16 g),
was added benzotri¯uoride ;0.252 g) as an internal standard
for 19F NMR spectroscopic determination of the yields of the
materials which were subsequently identi®ed in the complex
mixture of compounds. Chromatography of the crude pro-
duct on silica ;750 g) using diethyl ether/light petroleum ;bp
40±60 8C) ;40:60% v/v) as eluant gave fractions which were
examined by 19F NMR spectroscopy. Two components of
interest were identi®ed in fractions from the column: ;i) a
liquid product ;3.67 g) isolated by distillation into a cup at
the end of a water-cooled ®nger at 0.005 mmHg/40 8C was
7-methyl-2,5b,6,7ab-tetra¯uoro-3ab,4,5,7a-tetrahydroinden-
1-one 27 ;Found: C, 54.43; H, 3.62. C10H8F4O requires: C,
54.56; H, 3.66%); dF;CDCl3) À113.7 ;d, 6-F; J5bF±6F 23.7;
J6F±7abF 3.6), À135.7 ;d, 2-F; J2F±3H 7.3, J2F±7abF 2.15),
À155.0 ;m, 7ab-F; J5bF±7abF 8.6), À189.7 ;dm, 5b-F);
dH;CDCl3) 1.88 ;m, 7-CH3), 2.12 ;m, 1 unassigned H),
2.38 ;m, 1 unassigned H), 3.32 ;dm, 1 unassigned H),
4.92 ;dm, 5a-H; J5aH±5bF 50.4), 6.89 ;m, 3H); umax 3088
;=C±H), 1744 ;C=O), 1703 [C;CH3)=CF] and 1652 cmÀ1
;CF=CH); and a slower moving component ;0.155 g); and

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A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
;ii) 6-methyl-2,5b,7,7ab-tetra¯uoro-3ab,4,5,7a-tetrahy-
droinden-1-one 23 mp 79.5±81 8C ;from cyclohexane-
toluene) ;Found: C, 54.35; H, 3.63. C10H8F4O requires:
C, 54.56; H, 3.66%); dF;CDCl3) À129.2 ;d, 7-F; J5bF±7F
2.9; J7F±7abF 29.4), À132.8 ;d, 2-F; J2F±3H 8.3, J2F±7abF 2.15),
À168.0 ;m, 7ab-F; J5bF±7abF 6.8), À186.9 ;dm, 5b-F);
dH;CDCl3) 1.85 ;t, 6-CH3), 2.16 ;m, 1 unassigned H),
2.33 ;m, 1 unassigned H), 3.44 ;dm, 1 unassigned H),
4.83 ;dm, 5a-H; J5aH±5bF 49), 6.85 ;m, 3H); umax 3064
;=C±H), 1747 ;C=O), 1703 [C;CH3)=CF] and 1639 cmÀ1
;CF=CH).
The 19F NMR spectrum of the crude reaction product
containing the internal standard ;C6H5CF3) showed the
presence of unreacted prop-2-enyl ether 16 ;0.499 g), which
indicated that 14.616 g ;15.115±0.499 g) ;97%) had been
converted to products. Other components in the mixture in
addition to the isomeric tetrahydroinden-1-one isomers 23
and 27 were the internal Diels±Alder adduct 18, its 1,3-
rearrangement product 19 and 4-methyl-tetra¯uorophenol,
with yields ;based on the 14.616 g of ether 16 consumed) of
4, 38, 0.2, 0.1 and 18%, respectively.
in the ratio 1:1:1 indicative of ¯uorines at bridgehead sites
;compound 33), and the tetrahydroinden-1-one derivative
31. A second smaller scale pyrolysis reaction of 1 ;R=F)
;3.329 g) under similar conditions gave further pyrolysate
;3.27 g), and 15.35 g of the combined materials was sepa-
rated by chromatography on silica ;750 g) using diethyl
ether/light petroleum ;bp 40±60 8C) ;40:60% v/v) as eluant.
Fractions were examined by 19F NMR spectroscopy, one of
which contained 31 and 33 ;1.0 g) which was sublimed at ca.
50 8C/0.01 mmHg and the sublimate ;0.9 g) re-chromato-
graphed on silica ;95 g) with diethyl ether/light petroleum
;bp 40±60 8C) ;30:70% v/v) as eluant. Greatly enriched
fractions of 33 ;0.19 g) were slowly sublimed at 33 8C/
0.01 mmHg to give the pure crystalline 1,2,3,4,6-penta¯uor-
otricyclo-[4.3.0.02,8]non-3-ene-5-one 33 mp 51±52.5 8C
;sealed tube) ;Found: C, 48.03; H, 2.16. C9H5F5O requires:
C, 48.23; H, 2.25%); dF;CDCl3) À127.1 ;m, 3-F; J1F±3F
16.1; J3F±4F 7.5), À153.2 ;m, 4-F; J4F±6F 10.8), À180.5 ;m,
6-F; J1F±6F 6; J2F±6F 6), À180.7 ;d, 2-F; J1F±2F 2; J2F±3F 2),
À209.5 ;m, 1-F; J1F±4F 2.5); dH;CDCl3) 2.23 ;m, 1H), 2.32
;complex d, 1H), 2.38 ;complex m, 1H), 3.02 ;m, 1H), 3.15
;complex d, 1H); umax 1728 ;C=O), 1692 cmÀ1 [CF=CF].
The 19F NMR spectrum of the pyrolysate from 12.264 g
ether 1 ;R=F) containing the internal standard showed
unreacted ether 1 ;1.281 g). Based on the amount of ether
1 consumed ;10.983 g) the yields of the tetrahydroinden-1-
one 31 and the tricyclo[4.3.0.02,8]non-3-ene-5-one 33 were
20 and 3%, respectively. Three other known compounds
identi®ed for R=F ;in very low yields) were: 3 ;0.5%), 5
;0.1%) and 6 ;0.15%), but the major product was the 2,5-
cyclohexadienone 24 ;35%); there was no C6F5OH.
3.4. FVP of pentafluorophenyl prop-2-enyl
ether 1 +R=F) at 400 8C
The ether 1 ;R=F) [5] ;12.264 g) was pyrolysed as in
Section 3.2 over 1.75 h to give 12.08 g of product; to this
was added benzotri¯uoride ;0.225 g) as the internal stan-
dard. The 19F NMR was complex, but of particular interest
was the presence of an unknown compound having low
frequency resonances at ca. À180.5, À180.8 and À209.5 ppm
Table 1
Crystal data and experimental details
Compound
18
20
21
23
33
Formula
C
10H8F4O
C10H13F4O2Á1.5H2O
265.20
C12H14F4O2
266.23
C10H8F4O
220.16
C9H5F5O
224.13
Formula weight
T ;K)
Symmetry
220.16
102
100
102
100
100
Orthorhombic
Pbca ;no. 61)
5.8604;5)
12.096;1)
24.321;2)
90
Triclinic
P1 ;no. 2)
6.712;1)
11.041;2)
15.542;5)
98.89;1)
90.51;1)
95.05;1)
1133.2;3)
4
Monoclinic
P21/c ;no. 14)
11.980;3)
7.274;2)
13.443;3)
90
Orthorhombic
P212121 ;no. 19)
6.463;1)
7.338;1)
18.659;3)
90
Orthorhombic
P212121 ;no. 19)
6.715;1)
10.753;1)
11.513;3)
90
Space group
Ê
a ;A)
Ê
b ;A)
Ê
c ;A)
a ;8)
b ;8)
g ;8)
90
100.01;1)
90
90
90
90
1724.0;3)
8
90
884.9;2)
4
90
831.3;3)
4
Ê 3
V ;A )
1153.6;5)
4
Z
Crystal size ;mm3)
Reflections total
Reflections unique
Reflections I > 2s;I)
R[I > 2s;I)]
0.12 Â 0.40 Â 0.65
9991
2195
0.07 Â 0.12 Â 0.55
13915
5921
0.15 Â 0.5 Â 0.8
13435
3038
0.09 Â 0.12 Â 0.9
0.05 Â 0.1 Â 0.3
5768
10104
1425 ;2371a)
1320 ;2197a)
0.030
1292 ;2196a)
1239 ;2121a)
0.025
2005
4625
2804
0.033
0.090
0.043
0.119
0.033
0.092
oR;F2), all data
CCDC deposition no.
0.076
0.071
163778
163779
163780
163781
163782
a Including Friedel equivalents.

A.S. Batsanovet al. / Journal of Fluorine Chemistry 113 +2002) 123±131
131
3.5. Re-examination of the 19F NMR spectra of the crude
reaction products from the pyrolyses of the prop-2-enyl
ethers 1 +R=C6F5 [2], C6H5 [3] and CF3 [3])
the Cambridge Crystallographic Data Centre, deposition
numbers CCDC-163778 to 163782.
Acknowledgements
The following compounds having structure 9 were
detected: ;i) for R=C6F5, dF;CDCl3) À112.0 ;d, 7-F; J7F±7abF
30.3), À130.9 ;d, 2-F; J2F±3H 8.3), À167.1 ;m, 7ab-F),
À182.9 ;dm, 5b-F; J5aH±5bF 49), 9 : 10 ˆ 27.5 : 100; ;ii) for
R=C6H5, dF;CDCl3) À124.7 ;d, 7-F; J7F±7abF 32.7), À134.0
;d, 2-F; J2F±3H 7.1), À160.9 ;m, 7ab-F), À176.5 ;dm, 5b-F;
J5aH±5bF 48.4), 9 : 10 ˆ 12 : 100; and ;iii) for R=CF3,
dF;CDCl3) À61.5 ;6-CF3), À108.0 ;m, 7-F), À134.5 ;d, 2-F;
J2F±3H 6.4), À161.0 ;m, 7ab-F), À177.3 ;dm, 5b-F; J5aH±5bF
48.3), 9 : 10 ˆ 78 : 100.
We thank Mrs J. Dostal for elemental analyses and
Professor J.A.K. Howard for her interest in this work.
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