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Conformational switching between diastereoisomeric atropisomers of arenedicarboxamides induced by complexation with Lewis acids

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Microsoft Word - b716105k.doc Supporting information: experimental data for 1b, 1c, 2a and syn/anti-2c; cif files of anti-2c and syn-2c. N,N,N’,N’-Tetraisopropyl-3,6-bis(trimethylsilyl)-9,9-dimethyl-9H-xanthene-4,5-dicarboxamide 1b O O N O N TMSTMS To a solution of N,N,N’,N’-tetraisopropyl-9,9-dimethyl-9H-xanthene-4,5-dicarboxamide 1a (502 mg, 1.08 mmol) in dry THF (20 mL) was added N,N,N’,N’-tetramethylethylenediamine (0.81 mL, 5.37 mmol) and the solution was cooled at -78ºC under nitrogen and stirred for 5 min. n-Butyllithium (2.4 mL, 5.52 mmol, 2.3 M in hexanes) was added and the mixture was stirred for 1 h. Freshly distilled trimethylsilyl chloride (2 mL) was added and the mixture was allowed to warm to room temperature. The mixture was partitioned between AcOEt and H2O and the organic phase was washed with H2O, dried, filtered and the solvent was removed under reduced pressure. The crude product was purified by flash chromatography (Petrol to petrol:AcOEt 30%) to yield 1b (461 mg, 70%), followed by mono-silylated 1b’ (103 mg, 18%). M.p. 190-192 ºC. ¹H-NMR (CDCl3, 300 MHz) δ 0.31 (s, 18H), 0.99 (d, J = 6.9 Hz, 6H), 1.03 (d, J = 6.9 Hz, 6H), 1.53 (d, J = 6.9 Hz, 6H), 1.54 (d, J = 6.9 Hz, 6H), 1.62 (s, 6H), 3.39 (septet, J = 6.9 Hz, 2H), 4.30 (septet, J = 6.9 Hz, 2H), 7.28 (d, J = 7.8 Hz, 2H), 7.37 (d, J = 7.8 Hz, 2H). ¹³C-NMR (CDCl3, 75.5 MHz) δ 0.7 (CH3), 21.5 (CH3), 21.8 (CH3), 21.9 (CH3), 22.2 (CH3), 32.9 (CH3), 33.8 (Cq), 45.7 (CH), 49.6 (CH), 124.9 (CH), 129.7 (CH), 130.1 (Cq), 131.9 (Cq), 137.0 (Cq), 145.8 (Cq), 167.7 (Cq). IR (film) 1634 cm⎯¹. HRMS Calcd for C35H57O3N2Si2: 6.9.3902. Found: 609.3903. N,N,N’,N’-Tetraisopropyl-3-trimethylsilyl-9,9-dimethyl-9H-xanthene-4,5-dicarboxamide 1b’ O O N O N TMS ¹H-NMR (CDCl3, 300 MHz) δ 0.308 (s, 9H), 0.95 (d, J = 6.9 Hz, 3H), 1.08 (d, J = 6.9 Hz, 3H), 1.16 (d, J = 6.9 Hz, 3H), 1.17 (d, J = 6.9 Hz, 3H), 1.44 (d, J = 6.9 Hz, 3H), 1.46 (s, 3H), 1.53 (d, J = 6.9 Hz, 6H), 1.60 (d, J = 6

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