S.-T. Lin et al. / Tetrahedron 64 (2008) 5103–5106
5105
y = 6.8931x - 0.6111
2
3,3-difluoro-2-chlorocyclopropene (186 mg, 1 mmol), and phenyl-
acetylene (110 mg, 1.1 mmol) were added against a stream of
nitrogen followed by addition of Pd(OAc)2. After the mixture was
stirred at room temperature for 2 h, it was filtered and solvent was
removed under reduced pressure. Next, the residue was purified by
flash chromatography on a silica gel column to give 163 mg the
cross-coupling compound. Yield is given below.
3
2
R
= 0.8941
1
y = 3.3706x - 0.1346
2
0
R
= 0.9584
-1
-2
-3
-4
y = -0.9684x - 0.0418
2
R
= 0.9258
4.2.1. 1-Phenyl-3,3-difluoro-2-phenylethynylcyclopropene (3a)
Yield 65%; yellow solid; mp 36–37 ꢁC; 1H NMR d 7.79 (dd, 2H, J¼8,
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0
0
2 Hz, C2,6-H), 7.69 (dd, 2H, J¼8, 2 Hz, C2 ,6 -H), 7.58–7.64 (m, 3H,
Hammett's constants (σ)
0 0 0
C
3,4,5-H), 7.40–7.51 (m, 3H, C3 ,4 ,5 -H); 13C NMR d 73.3, 100.9 (t,
J¼279 Hz), 105.3, 108.8 (t, J¼12 Hz), 121.7, 129.7, 130.1 (t, J¼10 Hz),
Figure 1. The correction between SCS (Cb
constants (s).
(
), Cg
(
), C3
(
)) versus Hammett’s
130.4, 130.9, 131.4, 133.1, 133.2; 19F NMR d ꢀ107.6; IR 2204, 1768
ꢂ
(nC]C) cmꢀ1; MS m/z (%) 252 (Mþ , 80.5), 251 (100.0), 233 (20.9),
resonance effect on C3 by the aryl group (slope¼þ3.37) through
four bonds is characteristic for this system. The contribution of
resonance between the triple bond and double bond enhances the
resonance effect for the cyclopropene ring leading to a larger r
value of 6.89 as compared to the value of 4.50 found for compound
1 series. On the other hand, the substituent effect on Cg is reduced
(r¼ꢀ0.97 compared with ꢀ1.63 for compound 1).9
202 (69.2), 200 (32.2); calcd for C17H10F2: C, 80.94; H, 4.00; found: C,
81.02; H, 4.06.
4.2.2. 1-(30-Tolyl)-3,3-difluoro-2-phenylethynylcyclopropene (3b)
Yield 66%; yellowsolid;mp 38–39 ꢁC; 1H NMR d7.68 (dd, 2H, J¼8,
0
0
0
0
0
2 Hz, C2 ,6 -H), 7.59 (br, 1H, C2-H), 7.45–7.54 (m, 6H, C3,4,5, C3 ,4 ,5 -H),
2.42 (s, 3H, CH3); 13C NMR d 21.0, 73.3, 101.0 (t, J¼279 Hz), 105.2,
108.4 (t, J¼12 Hz), 121.6, 124.0, 129.7, 130.1 (t, J¼10 Hz), 130.3,
131.2, 131.4, 133, 134.0, 140.4; 19F NMR d ꢀ108.3; IR 2204, 1768
3. Conclusion
ꢂ
(nC]C) cmꢀ1; MS m/z (%) 266 (Mþ ,100), 265 (46), 251 (96), 216 (63),
The difluorocyclopropene compounds have a unique character,
i.e., activated the carbon–chlorine bond for the Sonogashira re-
action and transmitted the electron from a phenyl ring through the
acetylene moiety. This behavior is attributed to the aromaticity of
215 (72), 189 (20); calcd for C18H12F2: C, 81.19; H, 4.52; found: C,
81.17; H, 4.40.
4.2.3. 1-(40-Tolyl)-3,3-difluoro-2-phenylethynylcyclopropene (3c)
Yield 71%; yellow solid; mp 40–42 ꢁC; 1H NMR d 7.70 (d, 2H,
cyclopropene resulting from the low-lying antibonding s orbitals
*
of the C–F s-bonds, which are capable of accepting p-electrons
from an adjacent carbon.
0
0
J¼8 Hz, C2,6-H), 7.67 (dd, 2H, J¼8, 2 Hz, C2 6 -H), 7.42 (d, 2H, J¼8 Hz,
0 0 0
C
3,5-H), 7.45–7.54 (m, 6H, C3,4,5-H, C3 ,4 ,5 -H), 2.43 (s, 3H, –CH3); 13C
NMR d 21.7, 73.5, 101.0 (t, J¼279 Hz), 104.8, 107.4 (t, J¼12 Hz), 121.4,
121.8, 129.7, 130.0 (t, J¼10 Hz), 131.0, 131.1, 131.3, 133.0, 144.2; 19F
4. Experimental
4.1. General
ꢂ
NMR d ꢀ107.8; IR 2203,1766 (nC]C) cmꢀ1; MS m/z (%) 266 (Mþ , 92),
265 (42), 251 (100), 216 (71), 215 (87); calcd for C18H12F2: C, 81.19;
H, 4.52; found: C, 81.14; H, 4.47.
2,2-Difluorostyrenes were prepared from the corresponding
aldehydes and ClCF2CO2Na in the presence of triphenylphosphine
in dry diglyme solution at 180 ꢁC.12 1-Aryl-2-chloro-3,3-difluoro-
cyclopropenes were prepared from the reaction of 2,2-difluoro-
styrene and chloroform in the presence of NaOH.9 The preparation
of phenylethynylcyclopropenes was performed under a dry nitro-
gen atmosphere. 1H NMR, 13C NMR, and 19F NMR spectra were
recorded at 400, 100, and 376 MHz on Bruker Advance 400 spec-
trometer, respectively, at ambient temperature. Chemical shifts
for samples in CDCl3 solution are reported in d units relative to TMS
(1H and 13C) and trifluoromethylbenzene (at ꢀ63.9 ppm, 19F). For
the SCS study, the 13C NMR data of 0.03 g analyte in 0.3 mL of CDCl3
solution were recorded at 100 MHz. The digital resolution was
generally 0.02 ppm. Mass spectra were obtained from GC/MS
(Fisons 8000 series coupled with Finnigan MD-800) at an ioniza-
tion potential of 70 eV. IR spectra were recorded from a film on KBr
plate on a Perkin–Elmer System 2000 FT-IR spectrometer. Ele-
mental analyses were performed at the Instrumental Analytic
Center at National Chung-Hsing University.
4.2.4. 1-(30-Anisyl)-3,3-difluoro-2-phenylethynylcyclopropene (3d)
Yield 69%; yellow solid; mp 38–40 ꢁC; 1H NMR d 7.69 (dd, 2H,
0
0
0
0
0
J¼8, 2 Hz, C2 6 -H), 748–7.55 (m, 4H, C5-H, C3 ,4 ,5 -H), 7.37 (d, 1H,
J¼8 Hz, C6-H), 7.20 (dd, 1H, J¼8, 2 Hz, C4-H), 3.90 (s, 3H, OCH3); 13
C
NMR d 55.9, 73.3, 100.9 (t, J¼279 Hz), 105.5, 109.1 (t, J¼12 Hz),
115.4, 119.4, 121.7, 123.3, 125.2, 129.8, 130.0 (t, J¼10 Hz), 131.5,
131.6, 133.1, 161.2; 19F NMR d ꢀ107.5; IR 2204, 1768 (nC]C) cmꢀ1; MS
ꢂ
m/z (%) 282 (Mþ ,100), 267 (62), 251 (45), 238 (71), 232 (42), 202
(25), 189 (35); calcd for C18H12F2O: C, 76.59; H, 4.28; found: C,
76.48; H, 4.28.
4.2.5. 1-(40-Anisyl)-3,3-difluoro-2-phenylethynylcyclopropene (3e)
Yield 70%; yellow solid; mp 71–73 ꢁC; 1H NMR d 7.74 (d, 2H,
0
0
J¼8 Hz, C2-H), 7.68 (dd, 2H, J¼8, 2 Hz, C2 ,6 -H), 7.48–7.52 (m, 3H,
3 ,4 ,5 -H), 7.16 (d, 2H, J¼8 Hz, C3,5-H), 3.91 (s, 3H, OCH3); 13C NMR
0
0
0
C
d 56.1, 73.6, 101.1 (t, J¼279 Hz), 105.9, 106.2 (t, J¼12 Hz), 115.9, 116.7,
121.9, 129.7 (t, J¼10 Hz), 129.7, 131.2, 132.9, 133.0, 163.9; 19F NMR
ꢂ
d ꢀ107.6; IR 2205, 1766 (nC]C) cmꢀ1; MS m/z (%) 282 (Mþ , 100), 267
(40), 251 (24), 238 (63), 217 (49), 189 (57); calcd for C18H12F2O: C,
76.59; H, 4.28; found: C, 76.57, H, 4.25.
4.2. Preparation of 1-aryl-3,3-difluoro-2-phenylethynyl-
cycloropenes via Sonogashira coupling reaction
4.2.6. 1-(30-Chlorophenyl)-3,3-difluoro-2-phenylethynylcyclo-
propene (3f)
Typical procedure: Under a nitrogen atmosphere, Pd(OAc)2
(6.6 mg, 0.03 mmol) and K2CO3 (0.42 g, 3 mmol) were placed in
a 10 mL side-armed Pyrex tube using a magnetic stirring bar. The
system was evacuated when heated at 60 ꢁC for 30 min to remove
the moisture and oxygen molecule. After the system was refilled
with nitrogen, CH3CN (5 mL), HMPA (11 mg, 0.06 mmol), 1-phenyl-
Yield 63%; yellow solid; mp 49–51 ꢁC; 1H NMR d 7.81 (br, 1H,
0
0
C2-H), 7.70–7.81 (m, 1H, C6-H), 7.68 (dd, 2H, J¼8, 2 Hz, C2 ,6 -H),
7.58–7.65 (m, 2H, C4,5-H), 7.47–7.55 (m, 3H, C3 ,4 ,5 -H); 13C NMR
d 73.0, 100.5 (t, J¼280 Hz), 106.4, 110.7 (t, J¼12 Hz), 121.4, 125.8,
128.6 (t, J¼10 Hz), 129.4, 129.8, 130.2, 131.6, 132.2, 133.0, 133.2,
0
0
0