B. Bittner et al. / Journal of Fluorine Chemistry 182 (2016) 22–27
25
Penta-2,4-dione (1a), 3-buten-2-one (2a), 2-cyclohexene-1-one
(2b) and methyl acetoacetate (1c) were dried with CaH2 and
purified by means of fractional distillation. Methyl methacrylate
(2c) and crotonealdehyde (2d) were purified by condensation and
chemical shifts were referenced with respect to CFCl3 using the
internal standards C6F6 (ꢁ162.9 ppm) or C6H5CF3 (ꢁ63.9 ppm).
The 31P NMR chemical shifts were referenced with respect to
H3PO4 (85%) in D2O. A positive (negative) sign denotes a chemical
shift to high (low) frequency of the reference compound.
˚
dried over molecular sieves (3 A). Acrylonitrile (2e) and ethyl-2-
oxo-cyclohexanecarboxylate (1d) were dried with molecular
˚
sieves (3 A). 1-phenyl-1,3-butadione (1b) was dissolved in CH2Cl2,
3.4.2. 3-Acetylheptane-2,6-dione (3aa)
dried over MgSO4. Difluorotris(pentafluoroethyl)phosphorane,
(C2F5)3PF2, was used as delivered by Merck KGaA.
1H NMR (CDCl3), , ppm: 1.99 (dt, 3JHH = 7 Hz, 2Hc), 2.04 (s, 3He),
d
3
3
2.11 (s, 6Ha), 2.37 (t, JHH = 7 Hz, 2Hd), 3.60 (t, JHH = 7 Hz, 1Hb)
13C {1H} NMR (CDCl3), ppm: keto form: 21.6 (C4), 29.4 (C7), 30.1
(C1), 30.2 (C9), 40.6 (C5), 67.0 (C3), 204.3 (C6), 207.6 (C2), 207.7 (C8)
13C {1H} NMR (CDCl3), ppm: enol form: 21.5 (C4 or 9), 23.0 (C9 or
1), 44.1 (C5), 109.0 (C8), 191.2 (C2)
3.2. Apparatus and materials
For operations with volatile materials a glass vacuum line has
been used. The reaction vessels, constructed from FEP tubes, were
dried under dynamic vacuum for several hours prior to use.
Organic solvents were purified and dried using standard literature
methods [32].
3.3. General procedure for Michael addition reactions catalyzed by
(C2F5)3PF2
Michael donor (1a-d) was added to a solution of Michael
acceptor (2a–e) in dichloromethane (ꢂ20 g, 15 ml) at T = 20 8C.
Difluorotris(pentafluoroethyl)-phosphorane, (C2F5)3PF2 (0.5–
5 mol% calculated towards the reagent not being in excess) was
added to the solution using a syringe (Caution! Difluorotris(-
pentafluoroethyl)-phosphorane is toxic by inhalation. It
liberates HF in contact with moisture. Appropriate protections
for skin and eyes are required). The mixture was stirred for
0.1–1 h (Table 1, entries 1-4, 6), in some cases for days (Table 1,
entries 5, 7) including 6 h at 40 8C. After complete consumption of
the reactants (monitored by NMR spectroscopy) KF was added, the
suspension was washed five times with bi-distilled water (100 ml),
dried with MgSO4, filtrated and the solvent (CH2Cl2) together with
excess of reagent were distilled off under atmospheric pressure.
Product 3aa was isolated by means of fractional distillation. The
other products were isolated using column chromatography.
Detailed descriptions of the syntheses 3aa, 3ba, 3bb, 3ca, 3cb,
3da and 3db are given in Supporting Information.
3.4.3. 3-Benzoylheptane-2,6-dione (3ba)
1H NMR (CDCl3), , ppm: 1.96(s, 3Hg), 2.01 (s, 3Hh), 2.06 (m*,
d
3
3
2Hf), 2.40 (m*, 2He), 4.47 (t, JHH = 7 Hz, 1Hd), 7.36 (t, JHH = 8 Hz,
3
4
3
2Hb), 7.47 (tt, JHH = 8 Hz, JHH = 1.5 Hz, 1Ha), 7.89 (t, JHH = 8 Hz,
2Hc)
13C {1H} NMR (CDCl3), ppm: keto form: 22.4 (C8), 28.6 (C12), 29.9
(C10), 40.4 (C7), 60.9 (C6), 128.7 (C2), 128.9 (C3), 133.8 (C1), 136.1
(C4), 196.6 (C5), 203.9 (C11), 207.8 (C9)
3.4. Products characterization
3.4.1. NMR spectroscopy
Samples were measured in 3.7 mm (ØA) FEP tube placed inside a
5 mm (ØA) thin-walled precision glass NMR tube (Wilmad
537 PPT), which contained CD3CN in the annular space, or
internally in dry solvent in 5 mm (ØA) precision glass NMR tubes.
The measurements were carried out at 25 8C on a Bruker Avance III
400 MHz spectrometer equipped with a 9.3980 T cryomagnet. The
Elemental analysis:
Calculated for C14H16O3 [%]: C (72.39), H (6.94)
Experimental [%]: C (71.47), H (6.97)
1H NMR spectra were acquired using a 5 mm combination 1H/19
F
probe operating at 400.17 and 376.54 MHz, respectively. The 13C,
19F and 31P NMR spectra were obtained using a 5 mm broad-band
inverse probe operating at 100.62, 376.54 and 161.99 MHz,
respectively. Line-broadening parameters used in exponential
multiplication of the free induction decays were set equal to or less
than their respective data-point resolutions or the natural line
widths of the resonances. All line-shape functions were Lorentzian
unless specified otherwise. In some cases, the free induction
decays were multiplied by Gaussian functions for resolution
enhancement on Fourier transformation. The 1H NMR chemical
shifts were referenced with respect to tetramethylsilane (TMS)
yielding the following chemical shifts for the used solvents CDCl3
(contains CHCl3: 7.23 ppm) and CD3CN (contains CD2HCN:
1.96 ppm). The 13C NMR spectra were referenced with respect
to tetramethylsilane (TMS) using the chemical shifts for the
solvents CDCl3 (77.2 ppm) and CD3CN (118.7 ppm). The 19F NMR
3.4.4. 2-(3-Oxocyclohexyl)-1-phenylbutane-1,3-dione (3bb)
1H NMR (CDCl3),
d
, ppm: {1.29 (m) and 1.47 (m), 1.68 (m), 1.83
P
(m), 1.98 (m), 2.23 (m), 2.30 (m)} ( 8Hg ꢁ j), 2.09 and 2.11 (s, 3He),
2.86 (m, 1Hf), 4.40 (d, JHH = 10 Hz, 1Hd), 7.45 and 7.47 (dm,
3
3JHH = 7 Hz, 2Hb*), 7.58 and 7.59 (t, 3JHH = 7 Hz, 1Ha), 7.94 and 7.97
3
(d, JHH = 7 Hz, 2Hc)
13C {1H} NMR (CDCl3), ppm: keto form: 22.67 (C8), 28.11 (C11),
29.06 (C10), 38.90 (C12), 41.32 (C14), 45.76 (C9), 69.79 (C6), 128.92
(C2), 129.21 (C3), 134.30 (C1), 136.96 (C4), 195.06 (C5), 203.1 (C13),
209.4 (C7)
13C {1H} NMR (CDCl3), ppm: enol form: 22.95 (C8), 27.92 (C11),
29.66 (C10), 39.14 (C12), 41.37 (C14), 45.68 (C9), 69.37 (C6), 128.93
(C2), 129.23 (C3), 134.33 (C1), 137.00 (C4), 196.31 (C5), 203.0 (C13),
209.6 (C7)