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30th June 2010 @ 10:24
No product / mixture of compounds in the previous trial: Preparation of (+/-)-BINOL-N-triflyl phosphoramide (MW39) – repetition of the experiment under similar conditions:
Preparation of a strong achiral Brønsted acid, intended for pretests for the acid-catalysed Pictet-Spengler reaction

Reaction Scheme


Table1


Start time: 5:21 PM 29/06/2010
End time: 12:15 PM 30/06/2010

Procedure: [1]
To a mixture of (+/-)-BINOL (172 mg, 600 µmol) and Et3N (585 µL, 425 mg, 4.20 mmol, 7 eq.) in DCM (3 mL) was added POCl3 (110 mg, 67 µL, 720 µmol, 1.2 eq.) and DMAP (147 mg, 1.20 µmol, 2 eq.) at 0°. The mixture was warmed to room temperature and stirred for 1 h.
- evaporated DCM, added propionitrile (3 mL) and TfNH2 MW38 (179 mg, 1.20 mmol, 2 eq.) and heated reaction mixture to 100°C for 18 h

Work-up: quenched with water, extracted with Et2O, washed with aq. NaHCO3 and 4 N HCl, dried over Na2SO4, concentrated
-TLC (ethyl acetate, 100%; stain: KMnO4): Rf = 0.26.
- purification by column chromatography (silica gel; ethyl acetate 100%; Rf = 0.26)

Result:
Product MW39-2: 224 mg pale brown solid (467 µmol, 78%);
- small impurities visible in the 1H NMR (traces of TfNH2 ?)

Analytical data:
Rf (EA, 100%) = 0.26.
1H NMR (CDCl3, 400 MHz) : δ = 2.39 (bs, 1H), 7.10-7.18 (m, 2H), 7.23-7.43 (m, 6H), 7.52-7.58 (m, 2H) 7.73-7.81 (m, 2H).
Data: 1H NMR MW39-2 (400 MHz)
13C NMR (CDCl3, 100 MHz): δ = 120.02 (q, J(CF) = 318 Hz, 1C), 120.25 (2C), 121.02, 121.46, 121.87, 125.52 (2C), 126.50, 126.57, 127.04, 127.16, 128.56 (2C), 131.14 (2C), 131.63, 131.74, 132.22, 132.30, 146.72, 146.80, 147.70, 147.80.
Data: 13C NMR MW39-2
19F NMR (CDCl3, 282 MHz): δ = -79.7.Data: 19F NMR MW39-2
31P NMR (CDCl3, 121 MHz): δ = 16.74.Data: 31P NMR MW39-2
IR (neat): nu = 1288 cm-1, 1203, 1093, 1068, 963, 875, 815, 745, 604, 560.Data: IR MW39-2
MS (ESI (-)) m/z (%): 478 [M-H]-.
HRMS (ESI (-)) Calcd. for [C21H12F3NO5PS]-: 478.0131, found: 478.0134.
C21H13F3NO5PS (479.4).

-> Testing the catalytic activity of N-triflyl phosphoramides for the acid-catalysed Pictet-Spengler reaction: MW41


References:
[1] “Design of Chiral N-Triflyl Phosphoramide as a Strong Chiral Brønsted Acid and Its Application to Asymmetric Diels-Alder Reaction", D. Nakashima and H. Yamamoto, J. Am. Chem. Soc. 2006, 128, 30, 9626–9627.
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Attached Files
19F NMR MW39-2
31P NMR MW39-2
IR MW39-2
1H NMR MW39-2
13C NMR MW39-2
13C NMR MW39-2 JCAMP-DX
1H NMR MW39-2 (400 MHz)