Preparation and thermal behavior of 3,3,4,4-tetrafluorocyclobutane-1,2-diols: A new family of cyclobutane-1,2-diols

Article abstract of DOI:10.1246/cl.2000.1366

Thermal dimerization of 2,2-difluoro enol silyl ethers led to 3,3,4,4-tetrafluorocyclobutanes. The [2+2] cycloaddition proceeded in a "head-to-head" fashion to afford the cyclobutanes containing the trans and cis stereoisomers. The cyclobutanes were trans

Full text of DOI:10.1246/cl.2000.1366

1366
Chemistry Letters 2000
Preparation and Thermal Behavior of 3,3,4,4-Tetrafluorocyclobutane-1,2-diols:
A New Family of Cyclobutane-1,2-diols
Satoru Kobayashi, Youko Yamamoto, Hideki Amii,* and Kenji Uneyama*
Department of Applied Chemistry, Faculty of Engineering, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530
(Received September 5, 2000; CL-000833)
Thermal dimerization of 2,2-difluoro enol silyl ethers led
to 3,3,4,4-tetrafluorocyclobutanes. The [2+2] cycloaddition pro-
ceeded in a “head-to-head” fashion to afford the cyclobutanes
containing the trans and cis stereoisomers. The cyclobutanes
were transformed to tetrafluorocyclobutane-1,2-diols by desily-
lation.
Fluorine containing cyclobutanes are interesting precursors
for bioactive compounds or functionalized polymers.1–3
Thermal [2+2] cycloaddition is one of the well-known methods
to produce cyclobutanes from α,α-difluoroolefins.4–7 However,
there is no report on tetrafluorocyclobutanediol. Herein, we
report the thermal dimerization of 2,2-difluoro enol silyl ethers
2 to give 3,3,4,4-tetrafluorocyclobutane-1,2-diols derivatives 3,
which are considered to be promising bifunctional molecules
possessing two silyl-protected hydroxyl functionalities.
Recently, we have reported Mg(0)-promoted selective
defluorination of readily available trifluoromethyl ketones 1 in
the presence of chlorotrimethylsilane by means of a process
involving C−F bond cleavage (Scheme 1),8,9 which provides an
easy access to a variety of 2,2-difluoro enol silyl ethers 2.
The enol ethers 2 that possess either electron-withdrawing
(entry 2) and electron-donating (entry 3) on the aryl ring pro-
vided 3 in good yields. In all cases, the cyclobutanes 3 were
obtained as a mixture of trans and cis isomers in an approxi-
mate ratio 1:1. The diastereomeric mixture of 3 was separable
by column chromatography on silica gel.11 When the enol silyl
ether 2a was heated at 150 °C for 6 h, trans and cis-3a were
obtained in 54% yield in a ratio of 10:1, indicating that thermal
decomposition of cis-3a took place. In fact, the compounds of
trans- and cis-3a showed different thermal stability at high tem-
perature. On thermogravimetric analysis (TGA) for each iso-
mers under nitrogen atmosphere, the weight loss of cis-3a start-
ed at 115 °C, whereas no weight loss up to 150 °C in the case of
The preparation procedure of cyclobutanes 3 from 2 is very
simple. Heating neat 2a under an Ar atmosphere at 110 °C for
6 h10 gave a mixture of trans and cis isomers of 3a in good
yield (Table 1). On heating 2 in air at the same temperature,
however, a complex mixture of no fluorine containing com-
pounds was obtained as strong yellow and high viscous oil.
The intermolecular [2+2] cycloaddition of 2 proceeded pre-
dominantly in a head-to-head fashion. It is well-known that the
thermal [2+2] cycloaddition reactions of fluoroolefins proceed
via radical intermediates.5–7 The preference for the head-to-
head adduct formation can be explained by assuming that the
ring open-chain biradical intermediates generated from radical
coupling at the 2-positions (head-to-head coupling) of 2, are
much more stable than that of head-to-tail coupling due to the
stabilization of both of the radical centers of the intermediates
by the aromatic and siloxy group.
Other examples of formation of 3 are given in Table 1.
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1367
Okayama University for 19F NMR analysis, the Venture
Business Laboratory of Graduate School of Okayama
University for X-ray crystallographic analysis, and Central
Glass Co. Ltd. for TGA.
trans-3a.
Besides the thermograms, the X-ray crystal structure analy-
ses of trans- and cis-3b12 also suggest the weakness of
C(1)–C(2) bond since the bond lengths of C(3)–C(4) (1.52 Å
(trans-3b) and 1.52 Å (cis-3b)) are shorter and the lengths of
C(1)–C(2) (1.60 Å (trans-3b) and 1.63 Å (cis-3b)) are longer
as compared with the reported average bond lengths of cyclobu-
tanes (1.55 Å). As shown in Figure 1, cis-3b has a more
strained 4-membered ring structure than trans-3b; the bond
length of C(1)–C(2) of cis-3b (1.63 Å) is slightly longer than
that of trans-3b (1.60 Å), and the longer C(1)–C(2) bond length
in cis-3b would result in potentially reducing the thermal stabil-
ity of cis-3.
Compound 3 could be converted into diol 4 (Scheme 2).
Desilylation for 3a with tetrabutylammonium fluoride (TBAF)
was achieved at –80 °C for 2 h.13 Different reactivity on this
reaction was observed for trans and cis-3a. Desilylation with
TBAF for cis-3a was faster than trans-3a. The higher reactivity
of cis-3a is consistent with the result of TGA and X-ray analy-
ses. Furthermore, ketone 5 was obtained from diol cis-4a (63%
isolated yield) by treating with silica gel and Na2SO4 in Et2O at
room temperature for 12 h.14 On the other hand, diol trans-4a
was scarcely converted to 5 under such conditions.
References and Notes
1
2
W. H. Sharkey, Fluorine Chem. Rev., 2, 1 (1968).
D. A. Babb, “Fluoropolymers 1,” Kluwer Academic/
Plenum Publishers, New York (1999), pp. 25–50.
D. W. Smith, Jr., D. A. Babb, H. V. Shah, A Hoeglund, R.
Traiphol, D. Perahia, H. W. Boone, C. Langhoff, and M.
Radler, J. Fluorine Chem., 104, 109 (2000).
E. E. Lewis and M. A. Naylor, J. Am. Chem. Soc., 69,
1968 (1947).
3
4
5
J. D. Park, H. V. Holler, and J. R. Lacher, J. Org. Chem.,
25, 990 (1960).
6
7
G. Fuller and J. C. Tatlow, J. Chem. Soc., 1961, 3198.
P. D. Bartlett, L. K. Montgomery, and B. Seidel, J. Am.
Chem. Soc., 86, 616 (1964).
8
9
K. Uneyama, G. Mizutani, K. Maeda, and T. Kato, J. Org.
Chem., 64, 6717 (1999).
H. Amii, T. Kobayashi, Y. Hatamoto, and K. Uneyama,
Chem. Commun., 1999, 1323.
10 Generally, intermolecular [2+2] cycloaddition of α,α-diflu-
oroolefins occurs when heating at 100–700 °C, see ref 1.
11 19F NMR (CDCl3, 188 MHz, C6F6 as an internal standard)
of trans-3a: δ (ppm) 40.8 (2 F, d, J = 201 Hz), 43.5 (2 F, d,
J = 201 Hz). 19F NMR (CDCl3, 188 MHz) of cis-3a: δ
(ppm) 41.1 (2 F, d, J = 217 Hz), 42.4 (2 F, d, J = 217 Hz).
12 Crystal Data for trans-3b: C22H26Cl2F4O2Si2, MW =
525.52, monoclinic, space group C2/c (#15), a =
12.4317(7), b = 13.7899(8), c = 14.3406(6) Å, β =
90.077(3)°, V = 2629.9(2) Å3, Z = 4, Dc = 1.327 g·cm–3, R
= 0.0469, Rw = 0.0603. Crystal Data for cis-3b:
C22H26Cl2F4O2Si2, MW = 525.52, triclinic, space group P1
(#2), a = 10.732(1), b = 13.022(2), c = 9.974(1) Å, α =
89.986(5)°, β = 100.734(7)°, γ = 105.270(9)°, V = 1319.42
Å3, Z = 2, Dc = 1.323 g·cm–3, R = 0.0569, Rw = 0.0620.
These structures were solved and refined with teXsan pro-
gram package.
In summary, we have prepared tetrafluorocyclobutanes by
thermal [2+2] dimerization of difluoro enol silyl ethers. The
dimers were consisting of trans and cis stereoisomers. TMS
deprotection of the dimers led to diols that could be derived to a
wide range of 4-membered ring containing materials.
13 19F NMR (CDCl3, 188 MHz, C6F6 as an internal standard)
of trans-4a: δ (ppm) 37.9 (2 F, d, J = 205 Hz), 39.3 (2 F, d,
J = 205 Hz). 19F NMR (CDCl3, 188 MHz) of cis-4a: δ
(ppm) 35.2 (2 F, d, J = 218 Hz), 40.2 (2 F, d, J = 218 Hz).
14 We have found that ketone 5 was also obtained from 2,2-
difluoro enol silyl ethers 2 by oxidative dimerization.
This work was financially supported by Mitsubishi
Chemical Corporation Fund and Ministry of Education,
Science, Sports and Culture of Japan (Scientific Research (B),
No. 12450356). We thank the SC-NMR laboratory of