with longitudinal eddy current delay (LED)23 on 1H and 19F
nuclei was used.
Notes and references
‡1H chemical shifts are given in italics, 13C in ordinary font, 15N in
bold face, the chemical shifts of acetonitrile are in fact those of its
mixture with the protonated form, the signals are averaged through rapid
exchange of both forms on the NMR time scale.
The ESI mass spectra were recorded for m/z 100–3000. For
the mixture CH3CN–TfOH 4 : 1 additionally ESI mass spectra
from m/z 200 to 10 000 were recorded. A hybrid QTOF (quadru-
pole-time-of-flight) mass spectrometer with an electrospray inter-
face (micrOTOF-Q, Bruker Daltonics) was utilized. Nitrogen
1 I. D. Gridnev and N. A. Gridneva, Russ. Chem. Rev., 1995, 64, 1021–
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was used as a drying gas at 220 °C and at flow of 4 L min−1
.
2 P. Savu, in Kirk-Othmer Encyclopedia of Chemical Technology, John
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Nebulizer pressure was set to 1.0 bar. The capillary voltage was
set at −4.0 kV in the positive scan mode. Sample solutions were
infused into the ESI source by LC Agilent 1200 at FIA mode
(Flow Injection Analysis, 2–5 μL at a flow rate of CH3CN
0.1 mL min−1).
4 J. Umezawa, O. Takahashi, K. Furuhashi and H. Nohira, Tetrahedron:
Asymmetry, 1994, 5, 491–498.
CH3CN Panreac (HPLC-gradient grade, 99.9%), CD2Cl2 was
dried over molecular sieves 4 Å, TfOH reagent grade, 98% was
purchased from Aldrich and used without further purification.
All the mixtures under study contained 20% (v/v) of CD2Cl2
(for field-frequency lock). Special experiments showed that the
usage of freshly distilled TfOH and adding CD2Cl2 to the reac-
tion mixtures did not influence the products composition.
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Preparation of acidic solutions
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TfOH (50–670 mg, 0.33–4.5 mmol), CD2Cl2 (0.1 mL), and
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such portions to obtain the ratio CH3CN–TfOH needed (from
1 : 14 to 20 : 1). The tube closed and the three-layered mixture
shook under cooling with cold water just before the NMR
spectra registration. For ESI-MS determination a drop (approx.
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Acknowledgements
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We thank the Russian Academy of Sciences (Project No. 5.1.4)
for financial support. Helpful remarks by Dr S. Nagy are greatly
appreciated.
2288 | Org. Biomol. Chem., 2012, 10, 2282–2288
This journal is © The Royal Society of Chemistry 2012