Synthesis of trifluormethyl substituted oxetenes by the reaction of acetylenedicarboxylate with trifluoromethyl ketone in the presence of triphenylphosphine

Article abstract of DOI:10.1016/j.jfluchem.2012.12.005

In the presence of triphenylphosphine, dialkyl acetylenedicarboxylate 2 reacted smoothly with trifluoromethyl ketone 1 in toluene at room temperature affording the 2-trifluormethyl oxetenes 3 in good yields. These products are stable on heating or in the

Full text of DOI:10.1016/j.jfluchem.2012.12.005

Journal of Fluorine Chemistry 146 (2013) 1–5
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Synthesis of trifluormethyl substituted oxetenes by the reaction of
acetylenedicarboxylate with trifluoromethyl ketone in the presence
of triphenylphosphine
b,
Huafang Fan a,b, Xiaowei Wang b, Jingwei Zhao b, Xinjin Li b, Jinming Gao a, , Shizheng Zhu
*
*
a Shaanxi Engineering Center of Bioresource Chemistry and Sustainable Utilization, College of Science, Northwest A&F University, Yangling 712100, Shaanxi, China
b Key Laboratory of Organofluorine Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
A R T I C L E I N F O
A B S T R A C T
Article history:
In the presence of triphenylphosphine, dialkyl acetylenedicarboxylate 2 reacted smoothly with
trifluoromethyl ketone 1 in toluene at room temperature affording the 2-trifluormethyl oxetenes 3 in
good yields. These products are stable on heating or in the presence of some Lewis acids, such as ZnBr2,
InCl3, and Cu(OTf)2.
Received 19 October 2012
Received in revised form 7 December 2012
Accepted 10 December 2012
Available online 20 December 2012
ß 2012 Elsevier B.V. All rights reserved.
Keywords:
Acetylenic ester
Trifluormethyl ketone
Triphenylphosphine
Oxetene
Synthesis
1. Introduction
method to synthesize a series of 5-trifluoromethyl-2,5-dihydro-
1,2-l5-oxaphosphole via the reaction of triphenylphosphine,
Oxetanes, as a class of saturated four-membered heterocyclic
compounds, have been received much more attention and widely
used as building blocks in medicinal chemistry [1]. In contrast,
oxetenes are less stable under thermal or acidic conditions (e.g.,
acetic acid) because of the increased ring strain caused by the
double bond. Several substituted oxetenes have been synthesized
[2] and Sherlin reported the first example of unsubstituted oxetene
in 1980 [3]. However, it was found that some oxetenes are unstable
on heating or in the presence of Lewis acid [4]. Asghari et al.
reported the synthesis of stable 2H-Oxetes by a cycloaddition
reaction in the presence of triphenylphosphine [5]. Recently,
Mikami et al. reported enatioselective [2 + 2] cycloaddition of
alkynes with ethyl trifluoropyruvate using chiral dicationic BINAP–
Pd complex as the catalyst [6]. In addition, the fluorinated oxetenes
derivatives were firstly prepared by Middleton in 1965 through the
reaction of hexafluoroacetone with ethoxyacetylene at low
propiolate and trifluoromethyl ketones (Scheme 2) [9]. Herein,
we will report a facile synthesis of trifluoromethyl substituted
oxetenes.
2. Results and discussion
As a test reaction, the reaction of 2,2,2-trifluoro-1-phenyletha-
none 1a and dimethyl acetylene dicarboxylate 2a was initially
studied under different reaction conditions (Table 1). According to
the results, toluene was the most suitable solvent, while PPh3 could
promote this reaction efficiently. It was also noticed that even
though the PPh3 did not involve in the final product 3a but
decrease in its amount led to decrease in the product yield sharply
(Table 1, entry 1, 2, and 4).
A series of trifluoromethyl ketones 1a–g reacted with dialkyl
acetylene dicarboxylate 2a–b in the presence of triphenylpho-
sphine in toluene at room temperature affording the stable 2-
trifluoromethyl oxetenes in moderate to good yields (Table 2). The
compound trifluoro-1-(p-tolyl)ethanone (CF3COC6H4CH3-p) could
react with diethyl acetylene dicarboxylate 2b giving best result
(Table 2, entry 8). The structure of all the CF3-oxetenes was
confirmed by the NMR, IR and MS. For example, in the 13C NMR of
3a, the quartet at 123.0 ppm (q, J = 284 Hz) and two singlets at
163.9 ppm and 161.0 ppm were assigned to CF3 and two ester
temperature and the product then rearranged to
b,b-bis(trifluor-
omethyl)acrylate at room temperature (Scheme 1) [7].
As part of our current studies on the development of new routes
to fluorinated heterocycles [8], we have recently reported a simple
* Corresponding authors. Tel.: +86 21 54925185; fax: +86 21 64166128.
E-mail address: zhusz@mail.sioc.ac.cn (S. Zhu).
0022-1139/$ – see front matter ß 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2012.12.005

2
H. Fan et al. / Journal of Fluorine Chemistry 146 (2013) 1–5
Scheme 1.
Scheme 2.
Table 1
Reaction conditions for the [2 + 2] reaction.a
Entry
Solvent
T (8C)
YR3
t (h)
Yield (%)b
1
2c
3c
4d
5
PhCH3
PhCH3
PhCH3
PhCH3
CH2Cl2
CHCl3
EtOAc
DMF
25
25
100
25
25
25
25
25
25
25
25
25
25
25
25
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PPh3
PBu3
NEt3
10
40
10
20
10
24
10
10
10
24
24
24
40
5
68
20
50
41
59
57
55
40
62
52
63
45
25
50
20
6
7
8
9
THF
10
11
12
13
14
15
Et2O
Acetone
CH3CN
n-hexane
PhCH3
PhCH3
5
a
Reactions were carried out with 1a (0.2 mmol), 2a (0.24 mmol) and PR3 (0.24 mmol) in solvent (2.0 mL) at room temperature.
Yield of the isolated product after column chromatography on silica gel.
0.04 mmol PPh3.
b
c
d
1a (0.2 mmol), 2a (0.2 mmol) and Ph3P (0.08 mmol).
Table 2
Scope of the synthesis of oxetenes.a
Entry
R1
R2
t (h)
Product
Yield (%)b
1
2
C6H5 (1a)
Me (2a)
Me (2a)
Me (2a)
Me (2a)
Me (2a)
Me (2a)
Et (2b)
Et (2b)
Et (2b)
Et (2b)
Et (2b)
Et (2b)
12
20
12
12
12
12
12
12
12
12
12
20
3a
3b
3c
3d
3e
3f
68
52
70
62
70
63
68
72
55
63
66
52
C6H4CH5CH (1b)
4-MeC6H4 (1c)
4-FC6H4 (1d)
4-ClC6H4 (1e)
4-BrC6H4 (1f)
C6H5 (1a)
3
4
5
6
7
3g
3h
3i
8
4-MeC6H4 (1c)
4-FC6H4 (1d)
4-ClC6H4 (1e)
4-BrC6H4 (1f)
2-Naphthalene (1 g)
9
10
11
12
3j
3k
3l
a
Reactions were carried out with 1 (0.2 mmol) and 2 (0.24 mmol) and PPh3 (0.24 mmol) in PhCH3 (2.0 mL) at room temperature.
Yield of the isolated product after column chromatography on silica gel.
b

H. Fan et al. / Journal of Fluorine Chemistry 146 (2013) 1–5
4. Experimental
3
4.1. General information
Purifications were achieved by flash chromatography, with
EtOAc and PE on silica gel. Petroleum ether (PE) used in this study
had boiling range 60–90 8C. IR spectra were recorded on a Perkin-
Elmer 983 spectrophotometer. 1H and 19F NMR spectra were
recorded in CDCl3 on Bruker AM-300 instruments with Me4Si and
CFCl3 (with upfield negative) as the internal and external
standards, respectively. 13C NMR spectra were recorded in CDCl3
with Bruker AMX at 100 MHz and chemical shifts were given in
ppm relative to Me4Si. High-resolution mass spectra were obtained
at Bruker ApexIII 7.0 TESLA FTMS.
4.2. General procedures for the synthesis of dimethyl 2-phenyl-2-
(trifluoromethyl)-2H-oxete-3,4-dicarboxylate
To a solution of compounds 1 (0.2 mmol) and 2 (0.24 mmol) in
toluene (1.0 mL) was added PPh3 (0.24 mmol) at room tempera-
ture. The reaction mixture was then stirred for appropriate time
(monitored by TLC). After removal of the solvent under reduced
pressure, the crude product was purified directly by column
chromatography on silica gel (PE/EtOAc = 50/1–40/1) to afford the
desired products.
Scheme 3. Plausible reaction mechanism.
carbonyl carbon atoms, respectively, while two double bond
carbon atoms are at 149.6 ppm and 131.2 ppm. The singlet at
À72.7 ppm in 19F NMR spectrum was assigned to the trifluor-
oacetyl group. And the mass spectrum of 3a showed a molecular
ion peak at m/z = 339 [M+Na]+.
4.2.1. Dimethyl 2-phenyl-2-(trifluoromethyl)-2H-oxete-3,4-
dicarboxylate (3a)
Yield: 43 mg (68%); yellowish oil; IR (CH2Cl2, film): 1793, 1728,
1648, 1453, 1388, 1185, 1010, 947, 778, 694 cmÀ1 1H NMR
;
It was noticed that this reaction did not take place without PPh3.
Despite PPh3 was recovered after the reaction, it seems to be as a
catalyst, however, the product 3 could not be isolated when using
catalytic amount of PPh3 (5 mol%). In all these reactions, its amount
should be equivalent to 2.
(300 MHz, CDCl3): d = 7.58–7.56 (m, 2H), 7.49–7.44 (m, 3H), 4.31
(s, 3H), 3.81 (s, 3H); 13C NMR (100 MHz, CDCl3): 163.9, 161.0,
149.6, 131.2, 130.0, 128.7, 126.5, 123.0 (q, J = 284.4 Hz), 120.9, 84.3
(q, J = 32.1 Hz), 60.0, 52.5; 19F NMR (282 MHz, CDCl3):
d
= À72.7 (s,
3F); MS (ESI) (m/z): 339 (M+Na+); HRMS calcd for C14H11F3O5Na:
It is reasonable to assume that in this reaction the trivalent
phosphorus nucleophile initially attacked the acetylenic ester and
then the zwitter-ion A thus formed reacted with trifluoromethyl
ketone 1a. The negatively charged oxygen atom attacked the
electron-deficient double bond carbon atom followed by loss of
PPh3 from the intermediate C to give the product oxetenes 3
(Scheme 3).
339.0456, found: 339.0451.
4.2.2. (E)-dimethyl 2-styryl-2-(trifluoromethyl)-2H-oxete-3,4-
dicarboxylate (3b)
Yield: 42 mg (61%); yellowish oil; IR (CH2Cl2, film): 1797, 1724,
1645, 1450, 1389, 1187, 1013, 973, 795, 692 cmÀ1 1H NMR
;
(300 MHz, CDCl3):
d = 7.45–7.43 (m, 2H), 7.39–7.32 (m, 3H), 6.97
All these products are stable when they are heated to 60 8C for
8 h or in the presence of some Lewis acid such as ZnBr2, InCl3 and
Cu(OTf)2, they are not decomposed or rearranged to corresponding
(d, J = 15.9 Hz, 1H), 7.17 (d, J = 16.2 Hz, 1H), 4.27 (s, 3H), 3.90 (s,
3H); 13C NMR (100 MHz, CDCl3): 163.7, 161.0, 149.0, 134.9, 129.1,
128.8, 127.2, 122.4 (q, J = 284.5 Hz), 119.7, 117.7, 82.9 (q,
a
,b
-unsaturated carbonyl compounds. It seems that the trifluor-
J = 31.8 Hz), 60.0, 52.6; 19F NMR (282 MHz, CDCl3):
d
= À77.0 (s,
omethyl group makes the bond cleavage of the C–O single bond
more difficult.
3F); MS (ESI) (m/z): 365 (M+Na+); HRMS calcd for C16H13F3O5Na:
365.0613, found: 365.0607.
4.2.3. Dimethyl 2-(p-tolyl)-2-(trifluoromethyl)-2H-oxete-3,4-
dicarboxylate (3c)
Yield: 46 mg (70%); yellowish oil; IR (CH2Cl2, film): 1793,
1727, 1648, 1452, 1387, 1182, 1008, 949, 775, 734 cmÀ1 1H
;
NMR (300 MHz, CDCl3):
d = 7.41 (d, J = 7.8 Hz, 2H), 7.22 (d,
J = 7.5 Hz, 2H), 4.27 (s, 3H), 3.78 (s, 3H), 2.37 (s, 3H); 13C NMR
(100 MHz, CDCl3): 164.0, 161.1, 149.5, 140.2, 129.6, 129.4,
126.5, 122.8 (q, J = 284.3 Hz), 120.9, 84.4 (q, J = 31.9 Hz), 60.0,
Under the same reaction conditions other ketones such as
acetophenone and benzophenone did not give corresponding
oxetenes.
52.4, 21.1; 19F NMR (282 MHz, CDCl3):
(m/z): 353 (M+Na+); HRMS calcd for C15H13F3O5Na: 353.0613,
d
= À73.7 (s, 3F); MS (ESI)
3. Conclusion
found: 353.0596.
In conclusion, a series of 2-trifluoromethyl substituted oxetenes
were prepared using acetylenedicarboxylates, trifluoromethyl
ketones and an equivalent of triphenyl phosphine at room
temperature in toluene. Compared to the oxetenes reported so
far in several literatures, these trifluoromethyl substituted
oxetenes are quite stable.
4.2.4. Dimethyl 2-(4-fluorophenyl)-2-(trifluoromethyl)-2H-oxete-
3,4-dicarboxylate (3d)
Yield: 41 mg (62%); yellowish oil; IR (CH2Cl2, film): 1797, 1727,
1648, 1453, 1389, 1186, 1011, 951, 775, 737 cmÀ1 1H NMR
;
(300 MHz, CDCl3):
d = 7.58–7.53 (m, 2H), 7.14–7.08 (m, 2H), 4.29

4
H. Fan et al. / Journal of Fluorine Chemistry 146 (2013) 1–5
(s, 3H), 3.79 (s, 3H); 13C NMR (100 MHz, CDCl3): 163.4 (d,
J = 248.5 Hz), 163.7, 161.0, 149.7, 128.9, 127.7 (d, J = 3.7 Hz), 122.7
(q, J = 283.6 Hz), 120.6, 115.8 (d, J = 21.9 Hz), 84.0 (q, J = 32.1 Hz),
4.2.10. Diethyl 2-(4-chlorophenyl)-2-(trifluoromethyl)-2H-oxete-
3,4-dicarboxylate (3j)
Yield: 48 mg (63%); yellowish oil; IR (CH2Cl2, film): 1794, 1720,
1644, 1447, 1385, 1169, 1014, 950, 791, 715 cmÀ1 1H NMR
;
60.0, 52.5; 19F NMR (282 MHz, CDCl3):
d
= À73.9 (s, 3F), À110.9 (m,
1F); MS (ESI) (m/z): 357 (M+Na+); HRMS calcd. for C14H10F4O5Na:
(400 MHz, CDCl3): d = 7.52 (d, J = 8.4 Hz, 2H), 7.41 (d, J = 8.8 Hz,
357.0362, found: 357.0357.
2H), 4.72–4.66 (m, 2H), 4.30–4.23 (m, 2H), 1.45 (t, J = 7.2 Hz, 3H),
1.26 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): 163.9, 160.5,
149.4, 136.2, 133.6, 129.9, 128.8, 128.2, 122.6 (q, J = 284.5 Hz), 84.0
(q, J = 32.0 Hz), 69.0, 61.8, 15.3, 13.8; 19F NMR (282 MHz, CDCl3):
4.2.5. Dimethyl 2-(4-chlorophenyl)-2-(trifluoromethyl)-2H-oxete-
3,4-dicarboxylate (3e)
Yield: 49 mg (70%); yellowish oil; IR (CH2Cl2, film): 1797, 1727,
1647, 1452, 1389, 1185, 1015, 950, 776, 740 cmÀ1
d
= À73.8 (s, 3F); MS (ESI) (m/z): 401 (M+Na+); HRMS calcd for
;
1H NMR
C16H14ClF3O5Na: 401.0380, found: 401.0374.
(300 MHz, CDCl3):
d = 7.49 (d, J = 7.8 Hz, 2H), 7.40 (d, J = 8.4 Hz,
2H), 4.29 (s, 3H), 3.79 (s, 3H); 13C NMR (100 MHz, CDCl3): 163.6,
160.9, 149.8, 136.3, 129.7, 128.9, 128.1, 122.6 (q, J = 284.1 Hz),
120.4, 83.9 (q, J = 32.3 Hz), 60.1, 52.5; 19F NMR (282 MHz, CDCl3):
4.2.11. Diethyl 2-(4-bromophenyl)-2-(trifluoromethyl)-2H-oxete-
3,4-dicarboxylate (3k)
Yield: 56 mg (66%); yellowish oil; IR (CH2Cl2, film): 1797, 1723,
1644, 1446, 1385, 1172, 1011, 949, 767, 734 cmÀ1 1H NMR
;
d
= À73.2 (s, 3F); MS (ESI) (m/z): 373 (M+Na+); HRMS calcd for
C14H10ClF3O5Na: 416.9561, found: 373.0067.
(300 MHz, CDCl3): d = 7.54 (d, J = 8.1 Hz, 2H), 7.42 (d, J = 8.1 Hz,
2H), 4.66 (q, J = 6.9 Hz, 2H), 4.21 (q, J = 7.2 Hz, 2H), 1.42 (t,
J = 6.9 Hz, 3H), 1.22 (t, J = 6.9 Hz, 3H); 13C NMR (100 MHz, CDCl3):
163.9, 160.5, 149.4, 133.6, 131.8, 130.5, 128.4, 124.5, 122.6 (q,
4.2.6. Dimethyl 2-(4-bromophenyl)-2-(trifluoromethyl)-2H-oxete-
3,4-dicarboxylate (3f)
Yield: 50 mg (63%); yellowish oil; IR (CH2Cl2, film): 1797, 1725,
J = 284.3 Hz), 121.1, 84.0 (q, J = 32.3 Hz), 69.0, 61.9, 15.3, 13.8; 19
F
1647, 1452, 1389, 1182, 1011, 949, 776, 695 cmÀ1
;
1H NMR
NMR (282 MHz, CDCl3):
d
= À73.8 (s, 3F); MS (ESI) (m/z): 445
(300 MHz, CDCl3):
d
= 7.54 (d, J = 8.7 Hz, 2H), 7.42 (d, J = 8.4 Hz,
(M+Na+); HRMS calcd. for C16H14BrF3O5Na: 444.9874, found:
444.9869.
2H), 4.28 (s, 3H), 3.77 (s, 3H); 13C NMR (100 MHz, CDCl3): 163.6,
160.9, 149.8, 131.9, 130.3, 128.4, 124.6, 123.0 (q, J = 282.6 Hz),
120.3, 83.9 (q, J = 31.8 Hz), 60.1, 52.5; 19F NMR (282 MHz, CDCl3):
4.2.12. Diethyl 2-(naphthalen-1-yl)-2-(trifluoromethyl)-2H-oxete-
3,4-dicarboxylate (3l)
Yield: 41 mg (52%); yellowish oil; IR (CH2Cl2, film): 1793, 1723,
1644, 1446, 1383, 1168, 1013, 970, 776, 717 cmÀ1 1H NMR
;
d
C
= À73.9 (s, 3F); MS (ESI) (m/z): 417 (M+Na+); HRMS calcd. for
14H10BrF3O5Na: 416.9561, found: 416.9556.
4.2.7. Diethyl 2-phenyl-2-(trifluoromethyl)-2H-oxete-3,4-
dicarboxylate (3g)
Yield: 47 mg (68%); yellowish oil; IR (CH2Cl2, film): 1793, 1724,
1645, 1452, 1385, 1173, 1021, 948, 762, 694 cmÀ1 1H NMR
;
(400 MHz, CDCl3): d = 7.98 (d, J = 8.0 Hz, 1H), 7.93–7.89 (m, 3H),
7.56–7.50 (m, 3H), 4.84–4.76 (m, 2H), 4.15–4.02 (m, 2H), 1.52 (t,
J = 7.2 Hz, 3H), 1.03 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
164.8, 160.5, 151.0, 134.6, 131.8, 130.9, 129.7, 128.2 (q, J = 3.7 Hz),
127.1, 125.8, 125.4, 124.2, 123.8, 123.7 (q, J = 286.5 Hz), 122.1, 87.0
(q, J = 30.5 Hz), 69.4, 61.5, 15.4, 13.5; 19F NMR (282 MHz, CDCl3):
(400 MHz, CDCl3):
d = 7.58–7.56 (m, 2H), 7.48–7.42 (m, 2H), 4.72–
4.65 (m, 2H), 4.24 (q, J = 7.2 Hz, 2H), 1.45 (t, J = 7.2 Hz, 3H), 1.23 (t,
J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3): 164.2, 160.6, 149.2,
131.4, 129.9, 128.6, 126.6, 122.8 (q, J = 284.3 Hz), 121.6, 84.5 (q,
J = 32.0 Hz), 68.9, 61.7, 15.3, 13.7; 19F NMR (282 MHz, CDCl3):
d
C
= À71.5 (s, 3F); MS (ESI) (m/z): 417 (M+Na+); HRMS calcd. for
20H17F3O5Na: 417.0926, found: 417.0920.
= À73.5 (s, 3F); MS (ESI) (m/z): 367 (M+Na+); HRMS calcd. for
Acknowledgement
d
C
16H15F3O5Na: 367.0769, found: 367.0764.
The authors thank the National Natural Science Foundation of
China (NNSFC) (Nos. 21032006 and 21102163).
4.2.8. Diethyl 2-(p-tolyl)-2-(trifluoromethyl)-2H-oxete-3,4-
dicarboxylate (3h)
Yield: 52 mg (72%); yellowish oil; IR (CH2Cl2, film): 1793, 1724,
1646, 1457, 1384, 1170, 1020, 949, 773, 734 cmÀ1 1H NMR
;
Appendix A. Supplementary data
(300 MHz, CDCl3):
d = 7.41 (d, J = 8.1 Hz, 2H), 7.21 (d, J = 8.1 Hz,
2H), 4.69–4.60 (m, 2H), 4.22 (q, J = 7.2 Hz, 2H), 2.37 (s, 3H), 1.42 (t,
J = 7.2 Hz, 3H), 1.22 (t, J = 7.2 Hz, 3H); 13C NMR (100 MHz, CDCl3):
164.3, 160.7, 149.1, 140.1, 133.6, 131.8, 129.3, 126.6, 122.9 (q,
J = 284.1 Hz), 121.8, 84.5 (q, J = 32.3 Hz), 69.8, 61.7, 21.1, 15.3, 13.7;
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jfluchem.
2012.12.005.
19F NMR (282 MHz, CDCl3):
d
= À72.8 (s, 3F); MS (ESI) (m/z): 381
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(M+Na+); HRMS calcd. for C17H17F3O5Na: 381.0926, found:
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