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18th June 2010 @ 07:56
Starting material for the synthesis of N-triflyl phosphoramides - strong chiral Brønsted acid catalysts for asymmetric Pictet-Spengler reactions [1] [data=size:400x100]214[/data] [data=size:500x150]216[/data] Start time: 3:05 PM 18/06/2010 End time: 4:50 PM 18/06/2010 [b]Procedure:[/b] [2] Ammonia gas (30 mL liquid, 25.4 g, 212 mmol, 15 eq.) was condensed in 3-neck-flask fitted with a dry ice condenser at -78°. Trifluoromethanesulfonic acid (2.4 mL, 4.00 g, 14.2 mmol) was added dropwise over a period of 45 min. . The excess of ammonia was evaporated by allowing the reaction to warm to room temperature. The colorless and solid remain was purified by sublimation under vacuum: - first sublimation with a cold finger wasn’t successful – bumping mixture - Second trial: two flasks connected with a distillation bridge, oil bath temperature: 130 °C, pressure ~ 1mbar [b]Result:[/b] Product [b]MW38-1[/b]: 1.41 g (9.47 mmol, 67%) colorless crystalline solid; yield reference: 89% [1] [b]Analytical data:[/b] m.p. 118.5-120°C. ref IR (neat): nu = 3388 cm-1, 3279, 1519, 1352, 1147, 943, 611. [b]References:[/b] [url=http://dx.doi.org/10.1021/ja062508t][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, [i]J. Am. Chem. Soc.[/i] [b]2006[/b], [i]128[/i], 30, 9626–9627. [/url] [url=http://dx.doi.org/10.1016/j.jfluchem.2004.05.009][2] "Synthesis of 3,6-dioxa-Δ7-4-trifluoromethyl perfluorooctyl trifluoromethyl sulfonimide: bis[(perfluoroalkyl)sulfonyl] superacid monomer and polymer", B. H. Thomas, G. Shafer, J. Ji Ma, M.-H. Tu and D. D. DesMarteau, [i]J. Fluorine Chem.[/i] [b]2004[/b], [i]125[/i], 8, 1231-1240. [/url] [url=http://www.rsc.org/Publishing/Journals/JR/article.asp?doi=JR9570002574][3] "500. Fluorinated sulphonic acids. Part I. Perfluoro-methane-, -octane-, and -decane-sulphonic acids and their simple derivatives", J. Burdon, I. Farazmand, M. Stacey and J. C. Tatlow, [i]J. Chem. Soc.[/i] [b]1957[/b], 2574 - 2578, DOI: 10.1039/JR9570002574.[/url] [b]Procedure from reference:[/b] [2] [i]4.7. Preparation of CF3SO2NH2 (11)[/i] Into a specially fabricated addition funnel which could be evacuated was placed 61.74 g (218.8 mmol) of (CF3SO2)2O. To a 250 mL two-necked round bottom flask was condensed 115 g (6.7 mol) of anhydrous ammonia. The flask was removed from the vacuum line and fitted with the addition funnel containing (CF3SO2)2O, a magnetic stirrer, and a drying tube to exclude moisture. The reaction mixture was placed in a -78 °C bath and the anhydride was added dropwise over a 2 h period. The excess ammonia was removed by allowing the reaction to warm to room temperature, leaving a white solid. The product was purified by sublimation at 80 8C under vacuum to give 28.96 g (194.3 mmol) of white crystalline product (89% yield). 19F NMR (CD3CN) d(CF3) -79.4 (3F,s); 1H NMR (CD3CN) d (NH2) 6.6 (2H,s); IR (solid, KBr pellet) 3379 (s); 3372 (s); 1511 (m); 1348 (s); 1232 (m); 1185 (s); 1155 (m).
Attached Files
Reaction Scheme
Table1
Reaction Scheme correction
Table1 correction