Halogenation of fluorinated 1,3,5-triketones

Article abstract of DOI:10.1002/hlca.200790043

The behavior of linear and cyclic fluorinated 1,3,5-triketones and their metal derivatives towards common halogenating agents was examined, and optimal reaction conditions for the straightforward synthesis of mono-, di-, and tetrahalogenated products were

Full text of DOI:10.1002/hlca.200790043

Helvetica Chimica Acta – Vol. 90 (2007)
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Halogenation of Fluorinated 1,3,5-Triketones
by Dmitri V. Sevenard*a), Olesya Kazakovaa), Dmitri L. Chizhovb), Danil S. Yachevskiib), Enno Lorka),
Jçrn Poveleita), Valery N. Charushinb), and Gerd-Volker Rçschenthalera)
a) Institute of Inorganic & Physical Chemistry, University of Bremen, Leobener Str., D-28334 Bremen
(phone: +49-421-218-3435; fax: +49-421-218-4267; e-mail: sevenard@chemie.uni-bremen.de)
b) Institute of Organic Synthesis, Russian Academy of Sciences, Ural Branch, S. Kovalevskoy Str. 22,
620219 Ekaterinburg, Russia
The behavior of linear and cyclic fluorinated 1,3,5-triketones and their metal derivatives towards
common halogenating agents was examined, and optimal reaction conditions for the straightforward syn-
thesis of mono-, di-, and tetrahalogenated products were found (Schemes 1–3). An aromatization
through a double HBr elimination from an a,a’-dibrominated cyclohexanone was shown to be a prom-
ising synthetic route to 1,1’-(2-hydroxy-1,3-phenylene)bis[2,2,2-trifluoroethanones] (=2,6-bis(trifluoro-
ACHTREUNGacetyl)phenols; Scheme 4). Additionally, the 1,3,5-triketones prepared add readily H2O or alcohols to
produce novel bridged 2,6-dihydroxypyran-4-ones (Scheme 2). The structure of the obtained compounds
6a and 7a was confirmed by X-ray structure analysis.
Introduction. – Due to their polyfunctional nature and high reactivity, 1,3,5-trike-
tones are versatile reaction partners in a variety of organic transformations [1], as
well as valuable tridentate ligands in coordination chemistry [2]. The methods of prep-
aration and synthetic applications are well documented [1–3]. However, little effort
has been devoted to F-containing 1,3,5-triketones, although incorporation of F-atoms
or fluorinated groups into organic compounds is known to induce dramatic consequen-
ces on their chemical reactivity, physical properties, and biological activity [4]. An
excellent example of such a ꢀtransformationꢁ are fluorinated 1,3-dicarbonyl compounds.
In this case, a significant change of the electron-density distribution results in peculiar
tautomeric features (keto–enol, enol–enol) and in an unexpected behavior in the
course of chemical reactions, when compared to nonfluorinated analogs [5]. Continu-
ing our long-standing interest in the chemistry of fluorinated 1,3-diketones and 1,3-keto
esters [6], we have started a research program dealing with related 1,3,5-triketones [7].
Given the synthetic importance of fluorinated 1,3-dicarbonyl compounds bearing an
additional halogen atom in position 2 [8][9], we have explored reactions of
bis(trifluoroACHTREUmNG ethyl) triketones 1 and metal derivatives 2 with halogenating agents.
The results obtained are presented herein.
Results and Discussion. – In spite of advances in the halogenation of 3-(polyfluoro-
ACHTREUNGalkyl)-substituted 1,3-keto esters [9], only scattered reports concerning related reac-
tions of 1,3-diketones were published [10]. Elemental Br2 was found to be unsuitable
for selective bromination of 2-(trifluoroacetyl)cyclohexanone [10f][11]. On the other
hand, N-bromosuccinimide (NBS) was efficient for the a-bromination of 4,4,4-tri-
ꢂ 2007 Verlag Helvetica Chimica Acta AG, Zürich

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Helvetica Chimica Acta – Vol. 90 (2007)
fluoro-1-phenylbutane-1,3-dione [10d]. Therefore, it was reasonable to employ this
reagent for our initial experiments.
Treatment of noncyclic 1,3,5-triketone 1a with a 4-fold excess of NBS in CHCl3
resulted in a complete bromination of both methylene moieties to afford 3 in a virtually
quantitative yield (Scheme 1, Entry 1). Reactions of cyclohexanone derivative 1b with 2
equiv. of NBS in CH2Cl2 and CHCl3 proceeded smoothly to give 2,4-dibrominated
1,3,5-triketone 4a as a mixture of cis- and trans-isomers (Scheme 1, Entry 2).
Attempts to convert 1a with elemental Br2 furnished only complex mixtures of sev-
eral products – whatever molar amount of Br2 was used (Entry 3). Tetrabrominated tri-
ketone 3 could be detected by 19F-NMR spectroscopy in any case (d(F) ꢀ67.2), but its
yields were not satisfactory. By contrast, a,a’-dibromination of 1b could be performed
successfully with 2 equiv. of Br2 in anhydrous CHCl3 – similarly to the bromination of
diethyl 2-oxocyclohexane-1,3-dicarboxylate [12]. The reaction (Scheme 1, Entry 4) pro-
ceeded with marked stereoselectivity in comparison to the brominations by NBS (Entry
2), the exclusive formation of cis-4a being observed (19F-NMR monitoring of the reac-
tion mixture). Use of the bis(lithium enolate) 2a instead of the corresponding 1,3,5-tri-
ketone 1b in this reaction appeared to be more convenient. In this case, evolution of
gaseous HBr (Entries 3 and 4) did not take place, the only by-product was LiBr, and
simple evaporation of the volatile materials allowed to isolate cis-4a in fair yield and
purity (Scheme 1, Entry 5)
Chlorination of 1b was also studied. Upon treatment with elemental Cl2 or refluxing
in SO2Cl2, a,a’-dichlorination was achieved (Scheme 1, Entries 6 and 7). Both transfor-
mations proceeded with similar stereoselectivity, the cis-4b being the predominant iso-
mer. Noteworthy, in the case of SO2Cl2, the chemoselectivity can be directed easily.
Carried out with 1b in CH2Cl2 at room temperature, the reaction produced the
mono-chlorinated 1,3,5-triketone 5b in quantitative yield (Scheme 1, Entry 8). In con-
trast, the bromination of 1b with 1 equiv. of Br2 was not selective yielding both the
monoACHTERbUNG rominated product 5a and the dibromo derivative 4a in a ratio of 81:10
(Scheme 1, Entry 9). I-Containing reagents were investigated to no avail. The 1,3,5-tri-
ketone 1b and I2 failed to react, and in the reactions with IBr and ICl, only intractable
reaction mixtures were formed.
1
)
In the General Part, 1,3,5-triketones 1 are depicted as their major U-bis-enol tautomeric form [7].

Helvetica Chimica Acta – Vol. 90 (2007)
371
Scheme 1
In spite of the high electrophilicity of the terminal carbonyl groups (note, four or
five halogen atoms are in a positions2), pure 3 and cis-4a are stable, nonhygroscopic
substances and do not undergo any detectable hydration even after exposure for sev-
eral days in an open flask, as confirmed by NMR spectroscopy. After dissolving in
wet CHCl3 and concentration of the solution, cis-4a remained unchanged, too. In this
context, the result obtained from the repeated reaction of cyclohexanone 1b with 2
equiv. of Br2 seemed to be somewhat surprising. Instead of the expected 4a, the bridged
pyran-4-one 6a was isolated in 49% yield after evaporation of the reaction mixture
without vacuum (Scheme 2, Entry 10). From the structural point of view, compound
6a can be considered as a cyclic hydrate of triketone cis-4a (related fluorinated
cyclic/bridged compounds are described in [14]). Our initial assumption was that the
solvent CHCl3 was not dry enough, causing the hydration and cyclization of intermedi-
ary cis-4a already in the reaction vessel. However, during the reaction both in CHCl3
2
)
The tendency of the highly halogenated ketones to add H2O is well known [13], with hexafluoro-
acetone [13c] and methyl trifluoropyruvate (=methyl 3,3,3-trifluoro-2-oxopropanoate) [13d] as
excellent examples.
AHCTREUNG

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Helvetica Chimica Acta – Vol. 90 (2007)
distilled from P2O5 and in CHCl3 of commercial quality (Scheme 2, Entries 10 and 11),
only cis-4a was detected in the reaction mixture by 19F-NMR spectroscopy (d(F)
ꢀ69.7). Its transformation to 6a took place in both experiments only on the final evap-
oration of the reaction mixture under air. This fact suggests strongly that air moisture is
responsible for the hydration step in CHCl3 solution saturated by HBr, a by-product of
the double bromination. Compound 4b obtained by using either Cl2 or SO2Cl2 behaves
the same way, furnishing the pyran-4-one 6b in 71 and 77% yield from 1b, respectively
(Scheme 2, Entries 12 and 13). The copper(II) complex 2b appeared to be also reactive
under the conditions described, giving rise to the corresponding bridged 3,5-dibromo-
pyran-4-one 6a in 83% yield, with CuBr2 as by-product (Scheme 2, Entry 14). All the
reactions (Entries 10–14) occur highly regioselectively, only one diastereoisomer
could be observed, within the limits of NMR detection.
Scheme 2

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373
To pursue this point a little further, the dibromo derivative cis-4a (pre-generated
from 1b and Br2) was treated in situ with an excess of dry MeOH. Subsequent concen-
tration of the reaction mixture in vacuo gave the corresponding bridged adduct 7a in
28% yield (Scheme 2, Entry 15). Interestingly, upon recrystallization of the crude prod-
uct from wet toluene, both 6a and 7a could be isolated (Scheme 2, Entry 16). Formation
of 6a can be explained via a partial hydrolysis of 7a. Indeed, for the MeOH and propan-
1-ol adducts 7a,b obtained in situ (established by 19F-NMR spectros
ACHTREcUNG opy), the complete
conversion into 6a was observed on exposure of the reaction mixture to atmospheric
moisture (Scheme 2, Entries 17 and 18). It is worthy of mention that halogenation of
cyclohexanones 1b,c in the presence of EtOH also allowed to trap the intermediary
cis-a,a’-dihalogenated compounds 4 (Scheme 2, Entries 19 and 20). Like the pyran-4-
ones 6, all the compounds 7 were formed as sole diastereoisomer.
Obviously, besides the enhanced electrophilicity of the terminal carbonyl moieties
in 4, there are two factors being critical for the cyclizations into compounds 6 or 7. The
first one is the necessity of an acid catalysis (HBr, HCl, or CuBr2) for a double AN
sequence (addition of H2O or alcohol followed by the pyran ring closure). The behavior
of cis-4a in CHCl3 solution acidified by 12% hydrochloric acid supports this last
assumption. An equilibrium cis-4a
6a was detected by 19F-NMR spectroscopy
G H
(mol-ratio 64 :36, respectively, after 16 h at room temperature). On the other hand,
as mentioned, 3 and cis-4a did not add H2O in a pure state. The second point is a sterical
factor, where two requirements have to be fulfilled: a) a cis-structure of 4, as well as b)
the proximity of the terminal carbonyl groups in 4 are required for the successful cyc-
lization. The importance of the second factor is clearly demonstrated by the reaction of
cyclopentanone 1d where the monocyclic bis(geminaldiol) derivative 8a was formed as
a sole product after the double bromination and hydration of the intermediary cis-4d
(Scheme 3). Similarly, methanolysis of the reaction mixture resulted in an exclusive for-
mation of monocyclic bis(hemi)ketal 8b (Scheme 3). Additionally, no conversion was
observed for the tetrabrominated compound 3 in a CHCl3/aqueous HCl solution
(Scheme 3), although transformation of starting 1a into the corresponding 2,6-dihy-
droxypyran-4-one 9 was found to proceed smoothly (Scheme 3) [7][15]. There is little
reason to doubt that the unfavorable structural features of the deduced product 10 are
responsible for the lack of cyclization of 3 (Scheme 3). Indeed, two Br-atoms (van-der-
Waals radii 190 pm) occupy inevitably the axial positions in 10 increasing significantly
the conformational energy of the molecule (when ꢀchairꢁ conformation is favored, sim-
ilarly to 6a and 7a (see below, C(1)ꢀC(5) distance ca. 251 pm), and other tetrahydro-
4H-pyran-4-one [16] derivatives).
X-Ray single-crystal investigation of compounds 6a and 7a revealed ꢀchairꢁ confor-
mations for both connected cycles (Figure, Table). In 6a, the C(9) and O(3) atoms devi-
ate from the plane of the other pyran-ring atoms by ꢀ73.9 and 57.1 pm, respectively;
deviations of the C(9) and C(7) atoms from the plane of the other cyclohexanone-
ring atoms are ꢀ74.2 and 60.5 pm, respectively. In 7a the C(9) and O(3) atoms deviate
from the plane of the other pyran-ring atoms by ꢀ75.0 and 57.2 pm, respectively; devi-
ations of C(9) and C(7) atoms from the plane of the other cyclohexanone-ring atoms
are ꢀ73.3 and 63.2 pm, respectively. The CF3 substituents at the pyran ring of both
compounds are equatorial and cis arranged, whereby the OH and MeO groups occupy
axial positions (torsion angles C(9)ꢀC(1)ꢀC(2)ꢀO(1) ꢀ68.6(3)8, C(9)ꢀC(1)ꢀC(2)ꢀ

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Helvetica Chimica Acta – Vol. 90 (2007)
Scheme 3
C(10) 169.4(3)8 (for 6a), and C(9)ꢀC(1)ꢀC(2)ꢀO(1) 65.4(3)8, C(9)ꢀC(1)ꢀC(2)ꢀ
C(11) ꢀ170.8(2)8, C(9)ꢀC(5)ꢀC(4)ꢀO(2) ꢀ72.4(3)8, C(9)ꢀC(5)ꢀC(4)ꢀC(10)
167.4(2)8 (for 7a)). In 6a, one of the OH H-atoms is involved in intramolecular H-
bonds to the second OH O-atom (O···O 280.4(4) pm, ffOꢀHꢀO 125(5)8). In its
turn, this second OH group forms an intermolecular H-bond to the C=O O-atom of
the adjacent molecule (O(1)···O(4)’ 287.1(3) pm, ffOꢀHꢀO 146(6)8). In 7a, the proton
of the OH group is involved in an intermolecular H-bond to the C=O O-atom of an
adjacent molecule (O(1)···O(4)’ 281.1(3) pm, ffOꢀHꢀO 153(2)8). These intermolecu-
lar O(1)ꢀH···O(4)’ interactions cause the formation of molecular dimers in crystals of
both 6a and 7a.
Table. Principal Bond Lengths [pm] and Angles [8] for 6a and 7a. For numbering, see Figure.
6a
7a
C(1)ꢀC(9)
C(1)ꢀC(2)
C(2)ꢀO(3)
152.9(4) C(9)ꢀC(1)ꢀC(8)
155.8(4) C(9)ꢀC(1)ꢀC(2)
107.2(3)
106.1(2)
C(1)ꢀC(9) 152.9(4) C(9)ꢀC(1)ꢀC(8) 107.3(2)
C(1)ꢀC(2) 156.6(4) C(9)ꢀC(1)ꢀC(2) 104.5(2)
141.5(3) C(9)ꢀC(1)ꢀBr(1) 108.09(19) C(2)ꢀO(3) 142.1(3) C(9)ꢀC(1)ꢀBr(2) 109.67(19)
O(3)ꢀC(2)#1a) 141.5(3) O(1)ꢀC(2)ꢀO(3)
111.2(2)
O(3)ꢀC(4) 142.6(3) O(2)ꢀC(4)ꢀO(3) 112.9(2)
C(2)ꢀO(1) 137.8(3) O(2)ꢀC(4)ꢀC(10) 104.2(2)
C(2)ꢀC(11) 155.3(4) C(7)ꢀC(8)ꢀC(1) 113.2(3)
C(9)ꢀO(4) 119.7(3) C(2)ꢀO(3)ꢀC(4) 119.1(2)
C(1)ꢀBr(2) 195.0(3) F(3)ꢀC(10)ꢀC(4) 109.4(2)
C(10)ꢀF(1) 132.7(4) C(2)ꢀO(1)ꢀC(12) 119.8(2)
C(2)ꢀO(1)
C(2)ꢀC(10)
C(9)ꢀO(4)
C(1)ꢀBr(1)
C(10)ꢀF(1)
138.1(3) O(1)ꢀC(2)ꢀC(10) 105.8(2)
155.0(4) C(7)ꢀC(8)ꢀC(1)
113.3(3)
119.8(5) C(2)#1ꢀO(3)ꢀC(2) 119.2(3)
195.9(3) F(3)ꢀC(10)ꢀC(2) 109.8(2)
133.2(3) F(3)ꢀC(10)ꢀF(2) 107.7(3)
a) #1 x, ꢀy+12, z.
Multinuclear NMR data of compounds 6 and 7, collected for CDCl3 and
(D6)acetone solutions, are consistent with the bridged bicyclic structure. 13C-NMR
Spectra are especially informative, with the signals for C(2) and C(4) found at d ca.

Helvetica Chimica Acta – Vol. 90 (2007)
375
Figure. Molecular structures of compounds 6a and 7a. Thermal ellipsoids with 50% probability; arbi-
trary numberings. For 6a, symmetry transformations used to generate equivalent atoms: #1 x, ꢀy+12,
z. For the principal bond lengths and bond angles, see the Table.
101, indicating their (hemi)ketal character. Only one set of signals was observed in all
1
measured H-, 13C-, and 19F-NMR spectra verifying the presence of only one diaster-
eoisomer. We were not able to detect any ring–chain transformations for compounds
6 and 7 in CDCl3 and (D6)acetone solutions using NMR techniques. Obviously, the rea-
son for such a stability of the cyclic hemiketal form (being reported earlier for other
pyran derivatives with CF3 and OH moieties in 2(6) positions [6d][7][14a–g]) is an
electron-withdrawing influence of the CF3 group [13]. Striking features of the NMR
5
4
spectra of compounds 7a,c,d are the J(H,F) and J(C,F) couplings which are helpful
for the signal assignment. The NMR data of compound 5b require special comments.
1
In this case, only one tautomeric form, namely the enol, was obvious in the H-, 13C-,
and 19F-NMR spectra (CDCl3 solution, 228), as established by the OH resonance at
d(H) 14.05, as well as by the d(C) values of the nuclei of the hydroxyenone backbone
4
(d 175.1, 104.7, and 182.8 for C(1), C(6) and CF3C, resp.). Based on the J(C,F) and
5J(F,H) splittings observed, the U-structure of this backbone is suggested.
Pyran-4-ones 6a,b are stable compounds. Being heated to 1508 at 0.1 Torr for 30
min, they could be recovered without any detectable change. However, an attempt
with pyridine resulted in a strong tarring. On the other hand, upon treatment of 4a
with Et3N, 1,1’-(2-hydroxy-1,3-phenylene)bis[2,2,2-trifluoroethan-1-one] (=2,6-bis(tri-
fluoroacetyl)phenol; 11) was obtained in 31% yield (Scheme 4). The product is a valua-
ble fluorinated building block being difficult to synthesize otherwise. Of course, reac-
tion conditions have to be optimized; nevertheless, 4 and 5 are promising reaction part-
ners, and this encouraging result stimulates us to continue the investigation.
Conclusion. – The halogenation of linear and cyclic F-containing 1,3,5-triketones
and their metal salts was studied. Reaction conditions for the preparation of mono-,
di-, and tetrahalogenated products were established. These compounds added H2O
and alcohols readily, and the subsequent cyclization provided novel bridged 2,6-dihy-

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Helvetica Chimica Acta – Vol. 90 (2007)
Scheme 4
droxy-4H-pyran-4-one derivatives. This ring closure is controlled by a complex inter-
play of electrophilicity of the terminal carbonyl moieties, their mutual sterical arrange-
ment, and acid catalysis. A synthetic route to 2,6-bis(trifluoroacetyl)-substituted phe-
nols via double HBr elimination from the a,a’-dibrominated cyclohexanone was dis-
covered. Further evaluation of the synthetic potential of the obtained 1,3,5-triketones
is under way, and the results will be published elsewhere.
We gratefully acknowledge the generous gift of chemicals from Dr. M. Braun, Solvay Fluor und De-
rivate GmbH, Hannover, Germany, and Dr. J. Barten, Hansa Fine Chemicals GmbH, Bremen, Germany.
Mrs. D. Kemken and Dr. T. Dülcks, Institute of Organic Chemistry, University of Bremen, Germany, are
thanked for the recording of mass spectra. We are gratefull to Mr. P. Brackmann, Institute of Inorganic &
Physical Chemistry, University of Bremen, Germany, for the X-ray diffraction measurements.
Experimental Part
1. General. All chemicals are commercially available and were used as purchased unless otherwise
specified. Reactions in dried solvents (CH2Cl2 and CHCl3 distilled from P2O5, MeOCH2CH2OMe and
THF from sodium/benzophenone ketyl) were performed in oven-dried glassware under a static N2
atmosphere. Column chromatography (CC): Silica gel 60, 320–630 mesh (MP Biomedicals Germany
GmbH). M.p. and b.p.: uncorrected. NMR Spectra: Bruker DPX-200 spectrometer; at 200.1 (1H), 50.3
(13C), or 188.3 MHz (19F); d in ppm, J in Hz, Me4Si (1H and 13C) and CCl3F (19F) scales; d(H) referenced
to d(H) 7.25 of residual CHCl3 or to d(H) 2.05 of the central line of (D6)acetone; d(C) referenced to d(C)
77.0 (CDCl3) and 29.9 ((D6)acetone) of the central line of the solvent signal; d(F) referenced to d(F)
ꢀ162.23 of hexafluorobenzene as internal standard; 19F-NMR monitoring of samples from the reaction
mixtures dissolved in CHCl3 containing hexafluorobenzene as an internal reference (without lock);
assignments of d(H) and d(C) of 6 and 7 by INEPT and DEPT135 experiments and by the 5J(H,F)
and 4J(C,F) splittings; assignments of d(F) of compounds 7 by comparison with d(F) of the symmetrical
6. MS (m/z, intensity (%)): EI (70 eV), Finnigan MAT-8200 and MAT-95 spectrometers; CI (NH3 as reac-
tant gas) and DCI (8 mA/s, NH3 as reactant gas), MAT-8200 spectrometer; ESI, Bruker Esquire-LC spec-
trometer. HR-MS: peak matching method, Finnigan MAT-95 spectrometer. Elemental analyses: Mikro-
analytisches Beller Labor, Gçttingen, Germany.
X-Ray single-crystal determination for compounds 6a and 7a at ꢀ100(2)8, Siemens-P4 diffractome-
ter with a graphite monochromated MoKa radiation (l 71.073 pm) and the low-temperature device LT2.
The structures were solved by direct methods and refined by full-matrix least-squares at F2 with the
SHELXL-97 program package [17]. All non-H-atoms were refined anisotropically, the OH protons
were refined isotropically, the positions of the other H-atoms were calculated as a riding model. For
both compounds, absorption correction was carried out by using an empirical (DIFABS) method.

Helvetica Chimica Acta – Vol. 90 (2007)
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2. Starting 1,3,5-Triketones and Metal Derivatives. Compounds 1 were prepared by a double conden-
sation of the corresponding ketone and ethyl trifluoroacetate with LiH as a base (1a and 1d: in MeOCH2-
CH2OMe as a solvent, according to [7] and [18a], resp.; 1b [18] and 1c: in THF as a solvent, according to
[19]).
2.1. 4-(tert-Butyl)-2,6-bis(trifluoroacetyl)cyclohexanone (1c). Yield 77%. Yellow liquid. B.p.
128–1328/20 Torr. In CDCl3 at 228, 75 :14 :11 mixture of the bis-enol, mono-enol, and monohydrate
1
(i.e., geminaldiol RꢀC(OH)2CF3), resp. (by H-NMR; for details about tautomerism of fluorinated 1,3,
5-triketones, see [7]). EI-MS: 346 (13, M+), 331 (7, [MꢀMe]+), 327 (4, [MꢀF]+), 289 (6,
[MꢀC4H9]+); 277 (16, [MꢀCF3]+), 57 (100, C4Hþ9 ), and other fragments. HR-MS: 346.1009
(C14H16F6Oþ3 , M+; calc. 346.1004); ꢀ1.5 ppm (10.0), ꢀ0.5 mu (10.0), Rꢁ10000.
t
Data of Bis-enol 1c: 1H-NMR (CDCl3): 0.94 (s, Bu); 1.22–1.56 (m, 1 H); 2.01–2.15 (m, 2 H);
2.74–2.81 (m, 2 H); 14.58 (q, 4J(H,F)=1.9, 2 OH). 13C-NMR (CDCl3): 27.0 (s, Me); 24.2 (q, 4J(C,
F)=2.83), C(3), C(5)); 32.4 (s, Me3C); 43.3 (s, C(4)); 109.0 (s, C(2), C(6)); 119.2 (q, 1J(C,F)=278.3,
2
CF3); 160.4 (q, J(C,F)=35.3, CF3C); 195.9 (s, C(1)). 19F-NMR (CDCl3): ꢀ68.73 (s).
Data of Mono-enol 1c: 1H-NMR (CDCl3): 0.91 (s, tBu); 4.09 (t, 3J(H,H)=7.1, HꢀC(6)); 14.2 (br. s,
OH); overlap of the other alicyclic CH signals by the corresponding resonances of the predominant tau-
tomer. 19F-NMR (CDCl3): ꢀ76.88 (s, 3 F, (C=O)CF3); ꢀ73.90 (s, 3 F, =C(OH)CF3).
Data of Mono-hydrate 1c·H2O: 19F-NMR (CDCl3): ꢀ78.55 (s, C(OH)2CF3); ꢀ73.67 (s, =C(OH)-
CF3).
2.2. 2,6-Bis(trifluoroacetyl)cyclohexanone Dilithium Salt (2a). According to [19]: 51% yield. Yellow
powder. M.p. 2508 (dec.). 1H-NMR ((D6)acetone): 1.51–1.68 (m, CH2, 2 H); 2.34–2.51 (m, 2 CH2, 4 H).
19F-NMR ((D6)acetone): ꢀ68.9 (t, 5J(F,H)=1.93)). ESI-MS (MeCN): 585 (100, [2 C10H6F6O3 +Li+2
H]ꢀ), 289 (80, [C10H6F6O3 +H]ꢀ), and other fragments.
2.3. Bis[2,6-bis(trifluoroacetyl)cyclohexanone] Dicopper(2+) Salt (2b). Dilithium salt 2a (5.0 g, 16.6
mmol) was added to a sat. aq. Cu(OAc)2 soln. (100 ml). The mixture was stirred for 24 h at r.t. The pre-
cipitated copper(2+) salt was filtered off, washed with H2O (3”50 ml), and dried in vacuo. The solid was
washed with hot CHCl3 (3”20 ml), recrystallized from MeOH, and dried for 10 h at ca. 1108: 2b (3.9 g,
66%). Dark green powder. M.p. >2508 (dec.). Anal. calc. for C20H12F12O6Cu2 (703.38(3)): C 34.15, H 1.72,
F 32.4; found: C 33.98, H 1.84, F 32.3.
3. Brominations with Br2 (Entries 3–5 and 9). 3.1. cis-2,6-Dibromo-2,6-bis(trifluoroacetyl)cyclohex-
anone cis-4a; Entries 4 and 5). 3.1.1. Entry 4: Br2 (0.64 g, 4.0 mmol) was added dropwise to a well stirred
soln. of 1b (0.52 g, 1.8 mmol) in dried CHCl3 (8 ml). The mixture was stirred in a stoppered flask for 12 h
at r.t. After opening the flask (caution, slight internal pressure due to HBr vapors), the volatile materials
were removed in vacuo. The solid residue was recrystallized: cis-4a (0.67 g, 83%). Colorless crystals. M.p.
67–698 (petroleum ether (100–1408)). 1H-NMR (CDCl3): 2.07–2.19 (m, CH2); 2.28–2.41 (m, 2 H);
2.85–2.98 (m, 2 H). 13C-NMR (CDCl3): 19.6 (s, C(4)); 39.6 (s, C(3), C(5)); 65.2 (s, C(2), C(6)); 115.4
1
2
(q, J(C,F)=292.0, CF3); 180.9 (q, J(C,F)=35.8, CF3C); 188.3 (s, C(1)). 19F-NMR (CDCl3): ꢀ69.7 (s).
EI-MS: 446 (18, M+), 367 (24, [M–Br]+), 218 (100, [MꢀCF3 ꢀ2 BrꢀH]+), 191 (60, [MꢀCF3COꢀ
2 Br]+), 69 (74, CFþ3 ), and other fragments. HR-MS: 445.8600 (M+, C10H679Br2F6O3; calc. 445.8588);
ꢀ2.8 ppm (10.0), ꢀ1.3 mu (10.0), Rꢁ10000.
3.1.2. Entry 5: Br2 (3.2 g, 20 mmol) was added carefully to a well stirred suspension of 2a (3.0 g, 10
mmol) in dried CHCl3 (30 ml) causing an exothermic reaction. The mixture was stirred in a stoppered
flask for 12 h at r.t. Petroleum ether (58–628) (20 ml) was added to the suspension formed, the mixture
cooled to ꢀ308, and the precipitated LiBr filtered off. The filtrate was concentrated, and the solid residue
recrystallized: cis-4a (3.3 g, 74%).
3.2. Entry 3: Br2 (0.32 g, 2.0 mmol; 0.70 g, 4.3 mmol; 1.3 g, 8.1 mmol) was added dropwise to a well
stirred soln. of 1a (0.50 g, 2.0 mmol) in CHCl3 (10 ml). The mixture was stirred in a stoppered flask for
40 h at r.t. After opening the flask (caution, slight internal pressure due to HBr vapors), the volatile mate-
3
)
Confirming the U-structure of the C(O)ꢀCꢀC(O)ꢀCꢀC(O) or C(O)ꢀCꢀC(O) fragment.

378
Helvetica Chimica Acta – Vol. 90 (2007)
rials were evaporated. 19F-NMR Investigation of the yellow oily residue revealed a complex mixture of
products, with 3 as the only identifiable product (d(F) ꢀ67.2 (s), see below, 4.1.), at the complete conver-
sion of starting 1a.
3.3. Entry 9: Br2 (0.07 g, 0.45 mmol) was added to a well stirred soln. of 1b (0.13 g, 0.45 mmol) in
CHCl3 (2 ml). The mixture was stirred in a stoppered flask for 10 h at r.t. After opening the flask (caution,
slight internal pressure due to HBr vapors), the mixture was analyzed by 19F-NMR to reveal 5a (d(F)
ꢀ71.1 (s, 3 F), ꢀ73.9 (s, 3 F)), and cis-4a (d(F) ꢀ69.7 (s)) as the only identifiable products, at 87% con-
version of starting 1b.
4. Brominations Using NBS (Entries 1 and 2). 4.1. 3,3,5,5-Tetrabromo-1,1,1,7,7,7-heptafluoroheptane-
2,4,6-trione (3; Entry 1). NBS (0.88 g, 4.9 mmol) was added to a stirred soln. of 1a (0.30 g, 1.2 mmol) in
CHCl3 (15 ml). After the mixture was stirred in a stoppered flask for 18 h at r.t., the volatile materials
were evaporated in vacuo, and the solid residue was carefully washed with hot petroleum ether
(58–628) (2”20 ml). The combined liquid phases were concentrated to afford 3 (0.55 g, 81%) as a
white solid. An anal. sample was obtained by recrystallization from petroleum ether (58–628): Colorless
crystals. M.p. 83–848. 13C-NMR (CDCl3): 52.3 (s, C(3), C(5)); 114.6 (q, 1J(C,F)=292.4, C(1), C(7)); 174.4
(q, 2J(C,F)=37.3, C(2), C(6)); 181.8 (s, C(4)). 19F-NMR (CDCl3): ꢀ67.24 (s). EI-MS: 562 (<1, M+), 465
(<1, [MꢀCF3CO]+), 295 (40, CF3C(O)CBr2CO+), 267 (32, CF3C(O)CBr2þ), 97 (14, CF3CO+), 69 (100,
CFþ3 ), and other fragments. Anal. calc. for C7Br4F6O3 (565.68(2)): C 14.86, H 0.0, F 20.2; found: C
14.92, H <0.30, F 20.0.
4.2. cis/trans-2,6-Dibromo-2,6-bis(trifluoroacetyl)cyclohexanone (cis/trans-4a mixture; Entry 2).
NBS (0.29 g, 1.6 mmol) was added to a stirred soln. of 1b (0.23 g, 0.8 mmol) in CHCl3 (10 ml) or
CH2Cl2 (5 ml). The mixture was stirred in a stoppered flask (in CHCl3 for 4 h; in CH2Cl2 for 14 h) at
r.t. 19F-NMR Investigation of the pale yellow liquid revealed two products: cis-4a (d(F) ꢀ69.7 (s)) and
trans-4a (d(F) ꢀ70.2 (s)), ratio 40 :60, at complete conversion of starting 2b.
5. Chlorinations (Entries 6–8). 5.1. cis/trans-2,6-Dichloro-2,6-bis(trifluoroacetyl)cyclohexanone (cis/
trans-4b mixture; Entries 6 and 7). 5.1.1. Entry 7: The 1,3,5-triketone 1b (1.0 g, 3.4 mmol) was dissolved in
freshly distilled SO2Cl2 (6 ml) and the soln. heated to reflux for 16 h. The volatile materials were removed
in vacuo: anal. pure cis/trans-4b 82 :18 (by 19F-NMR) (1.2 g, 97%). Colorless needles. M.p. 37–428. 1H-
NMR (CDCl3): 1.92–2.91 (m). EI-MS: 358 (2, M+), 262 (24, [MꢀCF3CO+H]+), 227 (16,
[MꢀCF3COꢀCl+H]+), 165 (100, [Mꢀ2 CF3CO+H]+), 129 (28, [Mꢀ2 CF3COꢀCl]+), 69 (46, CF3þ),
and other fragments. HR-MS: 357.9596 (M+, C10H635Cl2F6O3þ ; calc. 357.9598); 0.5 ppm (10.0), 0.2 mu
(10.0), Rꢁ10000.
Data of cis-4b: 13C-NMR (CDCl3): 16.5 (s, C(4)); 37.9 (s, C(3), C(5)); 71.3 (s, C(2), C(6)); 115.1 (q,
1J(C,F)=291.5, CF3); 183.3 (q, 2J(C,F)=36.3, CF3C); 194.2 (s, C(1)). 19F-NMR (CDCl3): ꢀ71.08 (s).
Data of trans-4b: 13C-NMR (CDCl3): 17.9 (s, C(4)); 38.7 (s, C(3), C(5); 72.6 (s, C(2), C(6)); 115.3 (q,
1J(C,F)=292.0, CF3); 180.7 (q, 2J(C,F)=37.7, CF3C); 189.2 (s, C(1)). 19F-NMR (CDCl3): ꢀ71.13 (s).
5.1.2. Entry 6: A soln. of 1b (0.26 g, 0.9 mmol) in dried CHCl3 (6 ml) was placed in a thick-walled
glass ampoule equipped with a Teflon tap. Then Cl2 (0.14 g, 2.0 mmol) was condensed into the evacuated
ampoule at liq.-N2 temp. The mixture was gradually allowed to warm and stirred for 16 h at r.t. The
formed pale yellow soln. was analyzed by 19F-NMR to reveal two products: cis-4b and trans-4a, ratio
82 :18, at complete conversion of starting 1b.
5.2. 2-Chloro-2,6-bis(trifluoroacetyl)cyclohexanone (5b; Entry 8). Freshly distilled SO2Cl2 (0.74 g, 5.5
mmol) was added dropwise to a stirred soln. of 1b (0.73 g, 2.5 mmol) in dried CH2Cl2 (15 ml). The mixture
was stirred for 40 h at r.t., the volatile materials were removed in vacuo: anal. pure 5b (0.79 g, 97%). Pale
yellow oil. 1H-NMR (CDCl3): 1.92–2.16 (m, 2 H); 2.20–2.42 (m, 2 H); 2.46–2.64 (m, 1 H); 2.67–2.84 (m,
1 H); 14.05 (s, 1 H, OH). 13C-NMR (CDCl3): 17.6 (s, C(4)); 21.0 (q, 4J(C,F)=2.93)), C(5)); 33.5 (s, C(3));
1
1
71.2 (s, C(2)); 104.7 (s, C(6)); 115.4 (q, J(C,F)=292.9, CF3); 116.5 (q, J(C,F)=287.2, CF3); 175.1 (s,
C(1)); 182.8 (q, 2J(C,F)=36.0, CF3C); 184.0 (q, 2J(C,F)=35.5, CF3C). 19F-NMR (CDCl3): ꢀ74.06 (t,
5J(F,H)=1.13)), C(OH)CF3); ꢀ71.69 (s, C(O)CF3). EI-MS: 324 (60, M+), 289 (48, [MꢀCl]+), 255 (68,
[MꢀCF3]+), 227 (80, [MꢀCF3CO]+), 191 (100, [MꢀCF3COꢀClꢀH]+), 69 (64, CFþ3 ), and other frag-
ments. HR-MS: 323.9985 (M+, C10H735ClF6O3þ ; calc. 323.9988); 1.0 ppm (10.0), 0.3 mu (10.0), Rꢁ10000.
6. Bridged Pyran-4-ones 6 and 7. 6.1. (1RS,2SR,4RS,5SR)-1,5-Dibromo-2,4-dihydroxy-2,4-bis(tri-
fluoromethyl)-3-oxabicyclo[3.3.1]nonan-9-one (6a; Entries 10, 11, 14, 17, and 18). 6.1.1. Entries 10 and

Helvetica Chimica Acta – Vol. 90 (2007)
379
11: Br2 (0.16 g, 1.00 mmol) was added dropwise to a well stirred soln. of 1b (0.13 g, 0.45 mmol) in CHCl3
(2 ml; dried (Entry 10) or of commercial quality (Entry 11)). The mixture was stirred in a stoppered flask
for 14 h at r.t. After opening the flask (caution, slight internal pressure due to HBr vapors) the content
was concentrated without vacuum. The solid residue was recrystallized: 6a (Entry 10: 0.10 g, 49%; Entry
1
11: 0.17 g, 81%). Off-white crystals. M.p. 112–1168 (toluene). H-NMR (CDCl3): 1.55–1.75 (m, 1 H);
2.38–2.50 (m, 3 H); 2.94–3.10 (m, 2 H); 4.1 (br. s, 2 OH). 13C-NMR (CDCl3): 23.0 (s, C(7)); 42.6 (s,
2
1
C(6), C(8)); 70.1 (s, C(1), C(5)); 100.6 (q, J(C,F)=33.1, C(2), C(4)); 120.6 (q, J(C,F)=289.9, CF3);
188.8 (s, C(9)). 19F-NMR (CDCl3): ꢀ78.69 (s). EI-MS: 446 (4, [MꢀH2O]+), 367 (3, [MꢀH2OꢀBr]+),
349 (19, [MꢀH2OꢀCF3CO]+), 270 (100, [MꢀBrꢀCF3COꢀH2O]+), 69 (58, CFþ3 ), and other fragments.
DCI-MS (pos.): 482 (4, [M+NH4]+), 210 (100, [MꢀCF3COꢀ2 Br+H]+), 69 (24, CFþ3 ), and other frag-
ments. DCI-MS (neg.): 463 (12, [MꢀH]ꢀ), 385 (19, [MꢀBr]ꢀ), 367 (29, [MꢀBrꢀH2O]ꢀ), 113 (100), 79
(12, Brꢀ), and other fragments. HR-MS: 445.8597 ([MꢀH2O]+, C10H679Br2F6Oþ3 ; calc. 445.8588); ꢀ1.9
ppm (10.0), ꢀ0.9 mu (5.0), Rꢁ10000.
X-Ray Crystal-Structure Analysis of 6a4). Single crystal, crystallized from toluene. Colorless prisms;
C10H8Br2F6O4 (465.98); 0.35”0.35”0.3 mm3, orthorombic Pnma with a=704.60(10), b=1541.1(3),
c=1207.8(2) pm; V=1.3115(4) nm3, D=2.360 g·cmꢀ3, Z=4; difference electron density 0.565 and
ꢀ0.888 e·Šꢀ3. Index range ꢀ9ꢂhꢂ1, ꢀ20ꢂkꢂ20, ꢀ15ꢂlꢂ15, 2q range 2.64 to 27.508, reflections
measured 6823, unique reflections 1557 (R(int)=0.0383). Completeness to qmax =27.508: 99.9%, data/
restraints/parameter 1557/2/117. Goodness-of-fit on F2 1.087; final R values (I>2s(I)): R1 =0.0315,
wR2 =0.0693; R value (all reflections): R1 =0.0467, wR2 =0.0754.
6.1.2. Entry 14: A soln. of Br2 (1.61 g, 10.1 mmol) in CHCl3 (5 ml) was added in one portion to a well
stirred suspension of 2b (1.76 g, 2.5 mmol) in CHCl3 (10 ml). The mixture was stirred in a stoppered flask
for 12 h at r.t. Then the mixture was treated with Et2O (20 ml), the aq. phase extracted with Et2O (3”10
ml), the combined extract concentrated without vacuum, and the solid residue recrystallized to afford 6a
(1.93 g, 83%).
6.1.3. Entries 17 and 18: Br2 (0.64 g, 4.0 mmol) was added dropwise to a well stirred soln. of 1b (0.52
g, 1.8 mmol) in dried CHCl3 (8 ml). The mixture was stirred in a stoppered flask for 12 h at r.t. After
opening the flask (caution, slight internal pressure due to HBr vapors), the content was treated with
dried MeOH (8 ml, Entry 17) or propan-1-ol (2 ml, Entry 18). After stirring at r.t. (Entry 17: for 4 h;
Entry 18: for 20 h), the mixture was analyzed by 19F-NMR to reveal the corresponding alcohol adducts
7a,b as the only products (7a: d(F) ꢀ78.7 (s, CF3) and ꢀ71.4 (s, CF3); 7b: d(F) ꢀ78.3 (s, CF3) and
ꢀ71.4 (s, CF3)). The soln. was concentrated without vacuum, and the solid residue recrystallized from
toluene: 6a (Entry 17: 0.34 g, 39%; Entry 18: 0.50 g, 58%).
6.2. (1RS,2SR,4RS,5SR)-1,5-Dichloro-2,4-dihydroxy-2,4-bis(trifluoromethyl)-3-oxabicyclo[3.3.1]-
nonan-9-one (6b; Entries 12 and 13). 6.2.1. Entry 12: A soln. of 1b (0.26 g, 0.9 mmol) in dried CHCl3
(6 ml) was placed in a thick-walled glass ampoule equipped with a Teflon tap, and then Cl2 (0.14 g, 2.0
mmol) was condensed into the evacuated ampoule at liq.-N2 temp. The mixture was gradually allowed
to warm and stirred for 16 h at r.t. The resulting pale yellow soln. was concentrated without vacuum,
and the solid residue was recrystallized to afford 6b (0.24 g, 71%). Off-white crystals. M.p. 1408 (toluene).
1
1H-NMR (CDCl3): 1.56–1.99 (m, 1 H); 2.18–2.53 (m, 3 H); 2.79–2.97 (m, 2 H); 4.3 (br. s, 2 OH). H-
NMR ((D6)acetone): 1.79–1.91 (m, 1 H); 2.27–2.46 (m, 3 H); 2.89–3.24 (m, 2 H); 7.4 (br. s, 2 OH).
13C-NMR (CDCl3): 21.0 (s, C(7)); 41.0 (s, C(6), C(8)); 76.0 (s, C(1), C(5)); 100.5 (q, 2J(C,F)=33.4,
C(2), C(4)); 120.5 (q, 1J(C,F)=289.2, CF3); 189.6 (s, C(9)). 13C-NMR ((D6)acetone): 22.0 (s, C(7));
2
1
42.2 (s, C(6), C(8)); 77.2 (s, C(1), C(5)); 101.6 (q, J(C,F)=32.5, C(2), C(4)); 122.3 (q, J(C,F)=289.6,
CF3); 190.2 (s, C(9)). 19F-NMR (CDCl3): ꢀ79.16 (s). 19F-NMR ((D6)acetone): ꢀ77.78 (s). EI-MS: 262
(14, [MꢀCF3COOH]+), 227 (10, [MꢀCF3COOHꢀCl]+), 165 (100, [MꢀCF3COOHꢀCF3CO]+), 129
4
)
CCDC-618481 and CCDC-618480 contain the supplementary crystallographic data (excluding struc-
ture factors) for the structures 6a and 7a, resp. These data can be obtained free of charge via
www.ccdc.cam.ac.uk/data_request/cif from the Cambridge Crystallographic Data Centre.

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Helvetica Chimica Acta – Vol. 90 (2007)
(27, [MꢀCF3COOHꢀCF3COꢀHCl]+), 69 (44, CF3þ), and other fragments. CI-MS (neg.): 375 (14,
[MꢀH]ꢀ), 261 (10, [MꢀCF3COOHꢀH]ꢀ), 227 (100, [MꢀCF3COOHꢀCl]ꢀ), and other fragments.
Anal. calc. for C10H8Cl2F6O4 (377.06(7)): C 31.85, H 2.14; found: C 31.74, H 2.24.
6.2.2. Entry 13: The 1,3,5-triketone 1b (0.40 g, 1.4 mmol) was dissolved in freshly distilled SO2Cl2 (2
ml). After heating to reflux for 1 h, the mixture was concentrated under air, and the solid residue was
recrystallized: 6b (0.40 g, 77%).
6.3. (1RS,2SR,4RS,5SR)-1,5-Dibromo-2-hydroxy-4-methoxy-2,4-bis(trifluoromethyl)-3-oxabicyclo-
[3.3.1]nonan-9-one (7a; Entries 15 and 16). 6.3.1. Entry 15: Br2 (0.16 g, 1.0 mmol) was added dropwise
to a well stirred soln. of 1b (0.13 g, 0.45 mmol) in dried CHCl3 (2 ml). The mixture was stirred in a stop-
pered flask for 12 h at r.t. After opening the flask (caution, slight internal pressure due to HBr vapors),
dry MeOH (2 ml) was added, and the mixture was stirred for additional 4 h at r.t. The volatile materials
were removed in vacuo. The resulting oily residue was dissolved in dry toluene (1 ml) and the soln. left to
crystallize at ꢀ358. The precipitate formed was filtered off and dried: 7a (60 mg, 28%). Colorless prisms.
M.p. 116–1228 (toluene). 1H-NMR (CDCl3): 1.54–1.70 (m, 1 H); 2.31–2.52 (m, 3 H); 2.97–3.14 (m,
5
2 H); 3.52 (q, J(H,F)=2.6, Me); 3.79 (s, OH). 13C-NMR (CDCl3): 23.1 (s, C(7)); 42.9 (s, C(8)); 43.4
4
4
2
(q, J(C,F)=3.3, C(6)); 54.8 (q, J(C,F)=2.9, Me); 69.9 (s, C(1)); 73.1 (s, C(5)); 99.9 (q, J(C,F)=33.1,
C(2)); 102.5 (q, 2J(C,F)=31.4, C(4)); 120.7 (q, 1J(C,F)=289.5, CF3ꢀC(2)); 120.7 (q, 1J(C,F)=294.0,
CF3ꢀC(4)); 188.2 (s, C(9)). 19F-NMR (CDCl3): ꢀ78.65 (s, CF3ꢀC(2)); ꢀ71.38 (q, J(F,H)=2.6, CF3ꢀ
5
C(4)). EI-MS: 446 (2, [MꢀMeOH]+), 409 (1, [MꢀCF3]+), 367 (4, [MꢀMeOHꢀBr]+), 350 (8, [MꢀCF3-
COOMe]+), 285 (36, [MꢀCF3COOHꢀBr]+), 271 (100, [MꢀCF3COOMeꢀBr]+), 69 (40, CFþ3 ), and
other fragments. CI-MS (pos.): 496 (23, [M+NH4]+), 382 (28, [MꢀCF3CO+H]+), 208 (100), 69 (51,
CFþ3 ), and other fragments. CI-MS (neg.): 557 (6, [M+Br]ꢀ), 478 (4, Mꢀ), 477 (4, [MꢀH]ꢀ), 446
(1, [MꢀMeOH]ꢀ), 399 (5, [MꢀBr]ꢀ), 365 (14, [MꢀCF3COO]ꢀ), 349 (8, [MꢀCF3COOMeꢀH]ꢀ),
286 (100, [MꢀCF3COOꢀBr]ꢀ), 79 (21, Brꢀ), and other fragments. HR-MS: 556.8029 ([M+Br]ꢀ,
C11H1079Br3F6Oꢀ4 ; calc. 556.8033); 0.8 ppm (10.0), 0.5 mu (10.0), Rꢁ3600.
X-Ray Crystal-Structure Analysis of 7a4). Single crystal, crystallized from toluene. Colorless prisms;
C11H10Br2F6O4 (480.01); 0.5”0.4”0.4 mm3, monoclinic P21/c with a=1217.9(2), b=776.30(10),
c=1645.7(2) pm, b=109.760(10)8; V=1.4643(4) nm3, D=2.177 g·cmꢀ3, Z=4; difference electron den-
sity 0.515 and ꢀ0.536 e·Šꢀ3. Index range ꢀ1ꢂhꢂ15, ꢀ10ꢂkꢂ1, ꢀ21ꢂlꢂ21, 2q range 2.63 to 27.508,
reflections measured 4408, unique reflections 3331 (R(int)=0.0231). Completeness to qmax =27.508:
99.3%, data/restraints/parameter 3331/0/213. Goodness-of-fit on F2 1.034; final R values (I>2s(I)):
R1 =0.0321, wR2 =0.0643; R value (all reflections): R1 =0.0483, wR2 =0.0695.
6.3.2. Entry 16: Br2 (0.16 g, 1.0 mmol) was added dropwise to a well stirred soln. of 1b (0.13 g, 0.45
mmol) in dried CHCl3 (2 ml). The mixture was stirred in a stoppered flask for 11 h at r.t. After opening
the flask (caution, slight internal pressure due to HBr vapors), dry MeOH (4 ml) was added, and the mix-
ture was stirred for additional 8 h at r.t. The volatile materials were removed in vacuo, and 7a (10 mg,
5%) and 6a (30 mg, 15%) were obtained by a fractional recrystallization of the solid residue from tolu-
ene.
6.4.
(1RS,2SR,4RS,5SR)-1,5-Dichloro-4-ethoxy-2-hydroxy-2,4-bis(trifluoromethyl)-3-oxabicyclo-
ACHTREUNG[3.3.1]nonan-9-one (7c; Entry 19). A mixture of 1b (0.26 g, 0.9 mmol), dried EtOH (0.10 g), and dried
CHCl3 (6 ml) was placed in a thick-walled glass ampoule equipped with a Teflon tap, and then Cl2
(0.14 g, 2.0 mmol) was condensed into the evacuated ampoule at liq.-N2 temp. The mixture was gradually
allowed to warm and stirred for 14 h at r.t. The resulting colorless soln. was concentrated without vac-
uum, and the solid residue was recrystallized from toluene to afford a mixture of two kinds of crystals
who could be easily separated mechanically: 6b (30 mg, 10%; off-white crystals) and 7c (130 mg, 36%;
colorless prisms). 7c: M.p. 130–1508. 1H-NMR (CDCl3): 1.12 (t, 3J(H,H)=6.8, Me); 1.68–1.85 (m, 1
H); 2.09–2.53 (m, 3 H); 2.80–3.02 (m, 2 H); 3.70–3.88 (m, 1 H, CH2O); 3.85 (s, OH); 3.90–4.08 (m, 1
4
H, CH2O). 13C-NMR (CDCl3): 14.5 (s, Me); 21.0 (s, C(7)); 41.2 (s, C(8)); 41.8 (q, J(C,F)=3.3, C(6));
63.0 (q, 4J(C,F)=2.8, CH2O); 99.6 (q, 2J(C,F)=33.0, C(2)); 102.3 (q, 2J(C,F)=32.5, C(4)); 120.8 (q,
1
1J(C,F)=289.2, CF3ꢀC(2)); 120.8 (q, J(C,F)=293.9, CF3ꢀC(4)); 189.3 (s, C(9)); probably, the signals
of C(1) and C(5) are overlapped by the resonance of the solvent. 19F-NMR (CDCl3): ꢀ79.20 (s, CF3ꢀ
C(2)); ꢀ72.00 (m, CF3ꢀC(4)). EI-MS: 262 (15, [MꢀCF3COOC2H5]+), 227 (11,
[MꢀCF3COOC2H5 ꢀCl]+),
165
(100,
[MꢀCF3COOC2H5 ꢀCF3CO]+),
129
(12,

Helvetica Chimica Acta – Vol. 90 (2007)
381
[MꢀCF3COOC2H5 ꢀCF3COꢀHCl]+), 69 (15, CF3þ), 29 (34, C2Hþ5 ), and other fragments. CI-MS (pos.):
422 (100, [M+NH4]+), 386 (9, [M+NH4 ꢀHCl]+), 308 (30, [M+NH4 ꢀCF3COOH]+), and other frag-
ments. Anal. calc. for C12H12Cl2F6O4 (405.12(0)): C 35.58, H 2.99; found: C 35.70, H 2.89.
6.5. (1RS,2SR,4RS,5SR)-1,5-Dibromo-7-(tert-butyl)-4-ethoxy-2-hydroxy-2,4-bis(trifluoromethyl)-3-
oxabicyclo[3.3.1]nonan-9-one (7d) and (1RS,2SR,4RS,5SR)-1,5-Dibromo-7-(tert-butyl)-2,4-dihydroxy-
2,4-bis(trifluoromethyl)-3-oxabicyclo[3.3.1]nonan-9-one (6c; Entry 20). Dried EtOH (2 ml) was added
to a soln. of 1c (0.50 g, 1.4 mmol) in CHCl3 (15 ml), followed by Br2 (0.51 g, 3.2 mmol). The mixture
was stirred in a stoppered flask for 18 h at r.t. The volatile materials were evaporated, and 7d (40 mg,
5%) and 6c (60 mg, 8%) were obtained by fractional recrystallization of the solid residue from tolu-
ene/petroleum ether (100–1408) 1:5.
1
t
3
Data of 7d: Colorless crystals. M.p. 161–1628. H-NMR ((D6)acetone): 0.92 (s, Bu); 1.06 (t, J(H,
H)=6.8, Me); 2.12–2.37 (m, 2 H); 2.41–2.61 (s, 1 H); 2.86–3.11 (m, 2 H); 3.65–3.83 (m, 1 H, CH2O);
3.95–4.10 (m, 1 H, CH2O); 7.89 (s, OH). 13C-NMR ((D6)acetone): 14.9 (s, MeCH2); 27.2 (s, Me3C);
4
4
33.1 (s, Me3C); 43.6 (s, C(7)); 45.4 (s, C(8)); 45.8 (q, J(C,F)=3.3, C(6)); 63.3 (q, J(C,F)=1.9, CH2O);
71.8 (s, C(1)); 72.3 (s, C(5)); 101.9 (q, 2J(C,F)=32.0, C(2)); 102.9 (q, 2J(C,F)=30.6, C(4)); 122.2 (q,
1J(C,F)=294.3, CF3ꢀC(4)); 122.3 (q, 1J(C,F)=290.1, CF3ꢀC(2)); 188.5 (s, C(9)). 19F-NMR
((D6)acetone):
ꢀ77.93
(s,
CF3ꢀC(2));
ꢀ71.84
(s,
CF3ꢀC(4)).
EI-MS:
327
(14,
[MꢀCF3COOC2H5 ꢀBr]+), 247 (5, [MꢀCF3COOC2H5 ꢀBrꢀHBr]+), 69 (7, CF3þ), 57 (100, C4Hþ9 ),
and other fragments. CI-MS (pos.): 566 (55, [M+NH4]+), 452 (10, [MꢀCF3CO+H]+), 372 (4,
[MꢀCF3COꢀBr]+), 355 (7, [MꢀCF3COꢀBrꢀOH]+), 264 (10, [MꢀC2H5 ꢀCF3COꢀ2 Br]+), and
other fragments. CI-MS (neg.): 627 (3, [M+Br]ꢀ), 548 (2, Mꢀ), 547 (2, [MꢀH]ꢀ), 423 (22,
[MꢀBrꢀC2H5OH]ꢀ), 388 (75, [Mꢀ2 HBr]ꢀ), 342 (100, [Mꢀ2 HBrꢀC2H5OH]ꢀ), 331 (95, [Mꢀ2
HBrꢀC4H9]ꢀ), 322 (45, [Mꢀ2 HBrꢀC2H5OHꢀHF]ꢀ), 113 (40, CF3COOꢀ), 79 (76, Brꢀ), and other
fragments. HR-MS: 327.0219 ([MꢀCF3COOC2H5 ꢀBr]+, C12H1579BrF3O2þ ; calc. 327.0208); ꢀ3.6 ppm
(10.0), ꢀ1.2 mu (10.0), Rꢁ10000.
Data of 6c: Colorless prisms. M.p. 130–1318. 1H-NMR ((D6)acetone): 0.93 (s, tBu); 2.17–2.37 (m, 2
H); 2.45–2.68 (s, 1 H); 2.84–3.03 (m, 2 H); 7.37 (s, 2 OH). 13C-NMR ((D6)acetone): 27.2 (s, Me3C); 33.2
2
(s, Me3C); 43.6 (s, C(7)); 45.1 (s, C(6), C(8)); 71.3 (s, C(1), C(5)); 101.8 (q, J(C,F)=32.5, C(2), C(4));
122.3 (q, 1J(C,F)=289.6, CF3); 189.2 (s, C(9)). 19F-NMR ((D6)acetone): ꢀ78.51 (s). EI-MS: 406 (1,
[MꢀCF3COOH]+), 327 (9, [MꢀCF3COOHꢀBr]+), 309 (2, [MꢀCF3COOHꢀCF3CO]+), 69 (6, CFþ3 ),
57 (100, C4Hþ9 ), and other fragments. CI-MS (pos.): 538 (5, [M+NH4]+), 425 (55, [MꢀCF3CO+H]+),
344 (90, [MꢀCF3COꢀBr]+), 264 (90, [MꢀCF3COꢀ2 BrꢀH]+), and other fragments. CI-MS (neg.):
519 (1, [MꢀH]ꢀ), 405 (16, [MꢀHꢀCF3COOH]ꢀ), 326 (35, [MꢀCF3COOHꢀHBr]ꢀ), 113 (100,
CF3COOꢀ), 79 (62, Brꢀ), and other fragments. HR-MS: 327.0216 ([MꢀCF3COOHꢀBr]+, C12H1579BrF3-
Oþ2 ; calc. 327.0208); ꢀ2.6 ppm (10.0), ꢀ0.8 mu (10.0), Rꢁ10000.
7. Cyclopentanone Derivatives 8. 7.1. cis-2,5-Dibromo-2,5-bis(2,2,2-trifluoro-1,1-dihydroxyethyl)cy-
clopentanone (8a). A soln. of Br2 (1.61 g, 10.1 mmol) in CHCl3 (5 ml) was added in one portion to a
well stirred soln. of 1d (1.38 g, 5.0 mmol) in CHCl3 (5 ml). The mixture was stirred in a stoppered
flask for 24 h at r.t. After opening the flask (caution, slight internal pressure due to HBr vapors), the con-
tent was slowly concentrated without vacuum. The solid residue was recrystallized: 8a (1.74 g, 74%). Col-
orless crystals. M.p. 105–1108 (CHCl3). 1H-NMR (CDCl3): 2.39–2.50, 2.86–2.96 (2m, 2”2 H, 2 CH2); 3.8,
2
5.3 (2 br. s, 2”2 H, 4 OH). 13C-NMR (CDCl3): 33.4 (s, C(3), C(4)); 60.1 (s, C(2), C(5)); 93.8 (q, J(C,
F)=32.3, CF3C); 121.4 (q, 1J(C,F)=288.3, CF3); 206.5 (s, C(1)). 19F-NMR (CDCl3): ꢀ80.31 (s). EI-
MS: 468 (9, M+), 432 (15, [Mꢀ2 H2O]+), 370 (42, [MꢀH2OꢀHBr]+), 353 (35, [Mꢀ2 H2OꢀBr]+),
325 (78, [Mꢀ2 H2OꢀBrꢀCO]+), 273 (100, [MꢀH2OꢀHBrꢀCF3CO]+), and other fragments. Anal.
calc. for C9H8Br2F6O5 (469.95 (7)): C 23.00, H 1.72, F 24.3, Br 34.01; found: C 23.02, H 1.74, F 24.2, Br
34.04.
7.2. cis-2,5-Dibromo-2,5-bis(2,2,2-trifluoro-1-hydroxy-1-methoxyethyl)cyclopentanone (8b). A soln.
of Br2 (0.58 g, 3.63 mmol) in dried CHCl3 (3 ml) was added in one portion to a well stirred soln. of 1d
(0.5 g, 1.81 mmol) in dried CHCl3 (3 ml). The mixture was stirred in a stoppered flask for 24 h at r.t.
After opening the flask (caution, slight internal pressure due to HBr vapors), dry MeOH (5 ml) was
added, and the mixture was stirred for additional 12 h at r.t. The volatile materials were removed in
vacuo. The solid residue was recrystallized: 8b (0.39 g, 43%). White crystals. M.p. 144–1458 (hexane).

382
Helvetica Chimica Acta – Vol. 90 (2007)
5
1H-NMR (CDCl3): 2.32–2.41, 2.88–2.97 (2m, 2”2 H, 2 CH2); 3.53 (q, J(H,F)=1.2, 2 MeO); 5.05 (q,
4J(H,F)=1.0, 2 OH). 13C-NMR (CDCl3): 33.0 (m, C(3), C(4)); 52.4 (q, 4J(C,F)=1.7, MeO); 60.7 (s,
C(2), C(5)); 95.4 (q, 2J(C,F)=31.6, CF3C); 121.8 (q, 1J(C,F)=291.1, CF3); 208.1 (s, C(1)). 19F-NMR
(CDCl3): ꢀ76.55 (m). Anal. calc. for C11H12Br2F6O5 (498.01(0)): C 26.53, H 2.43, F 22.9, Br 32.09;
found: C 26.58, H 2.47, F 22.9, Br 32.10.
8. 1,1’-(2-Hydroxy-1,3-phenylene)bis[2,2,2-trifluoroethan-1-one] (=2,6-Bis(trifluoroacetyl)phenol;
11). Dry Et3N (0.24 g, 2.3 mmol) was added dropwise at ꢀ508 to a soln. of 4a (0.35 g, 0.8 mmol) in
dried CH2Cl2 (5 ml). The mixture was allowed to reach r.t. After stirring for 24 h, H2O (40 ml) was
added, and the mixture was acidified with 12% HCl soln. to pH 1 and extracted with CH2Cl2 (5”10
ml). The combined org. phase was dried (MgSO4) and concentrated and the crude product purified by
CC (CHCl3): 11 (70 mg, 31%). Yellow oil (19F-NMR: containing ca. 20% of mono-hydrate), i.e., geminal
diol RꢀC(OH)2CF3. EI-MS: 286 (16, M+), 217 (100, [MꢀCF3]+), 147 (46, [Mꢀ2 CF3 ꢀH]+), and other
fragments. HR-MS: 286.0069 (M+, C10H4F6O3; calc. 286.0065); ꢀ1.4 ppm (10.0), ꢀ0.4 mu (10.0),
Rꢁ10000.
Data of 11. 1H-NMR (CDCl3): 7.18 (t, 3J(H,H)=7.8, HꢀC(4)); 8.10 (d, HꢀC(3), HꢀC(5)); 11.90 (s,
1
OH). 13C-NMR (CDCl3): 115.9 (q, J(C,F)=290.1, CF3); 118.7 (s, C(4)); 120.0 (s, C(2), C(6)); 138.5 (q,
4J(C,F)=2.83), C(3), C(5)); 164.1 (s, C(1)); 182.8 (q, 2J(C,F)=37.2, C=O). 19F-NMR (CDCl3): ꢀ72.78 (s).
Data of Mono-hydrate 11·H2O: 1H-NMR (CDCl3): 2.1, 4.8 (2 br. s, 2”1 H, 2 OH); 7.17 (t,
3J(H,H)=7.8, HꢀC(4)); 7.96 (dm, 1 H); 8.10 (m, 1 H); 12.19 (s, 1 H, OH). 13C-NMR (CDCl3): 93.5 (q,
2J(C,F)=33.9, C(OH)2); 122.8 (q, 1J(C,F)ꢁ290, CF3); 120.7 (s, C(2)); 133.0 (q, 3J(C,F)=3.8, C(6));
135.0 (q, 4J(C,F)=2.83), C(3)); 139.9 (s, C(5)); 161.1 (s, C(1)); 185.2 (q, 2J(C,F)=36.7, C=O); the signals
of the second CF3 group and C(4) could not be found. 19F-NMR (CDCl3): ꢀ85.97 (s, CF3C(OH)2);
ꢀ70.68 (d, 5J(F,H)=2.03), CF3C=O).
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Received October 10, 2006