Compound (R,R)-(P,P)-trans-L1

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Synthetic procedure: See article for the definitive version of this procedure and for full experimental details.

Oxalyl chloride (0.34 mL, 4.0 mmol) was added dropwise to a solution of (P,P)-trans-4 or (P,P)-cis-4 (Ref. 3) (202 mg, 0.5 mmol) in anhydrous CH₂Cl₂ (2.0 mL), anhydrous THF (2.0 mL) and one drop of DMF at 0 °C under a nitrogen atmosphere. The reaction mixture was stirred at room temperature for 2 h and subsequently concentrated to afford the crude acid chloride. The resulting acid chloride was dissolved in anhydrous CH₂Cl₂ (5.0 mL), anhydrous TEA (0.29 mL, 2.0 mmol) and the corresponding amine 2 or 3 (1.1 mmol) were added under nitrogen at 0 °C. The mixture was stirred at room temperature for 14 h. Upon completion, the solvent was evaporated in vacuo and the residue was purified by flash chromatography on silica with CH₂Cl₂/MeOH (98:2 for (P,P)-trans-L1 or (P,P)-cis-L1; 97:3 for (P,P)-trans-L2 or (P,P)-cis-L2) to provide the corresponding product as an off-white solid, 85% yield; m.p. = 189-191 °C; ¹H NMR (400 MHz, CDCl₃) δ 8.35 (d, J = 7.8 Hz, 2H), 8.19 (d, J = 7.8 Hz, 2H), 7.83 (t, J = 7.8 Hz, 2H), 7.69 (t, J = 7.7 Hz, 2H), 7.38 (d, J = 7.8 Hz, 2H), 7.32 (t, J = 5.2 Hz, 2H), 7.26 (s, 2H), 7.19 (d, J = 7.6 Hz, 2H), 4.97 – 4.75 (m, 4H), 3.00 – 2.86 (m, 2H), 2.72 – 2.57 (m, 8H), 2.54 (s, 6H), 2.31 – 2.13 (m, 8H), 1.03 (d, J = 6.4 Hz, 6H). ¹³C NMR (101 MHz, CDCl₃) δ 170.6, 158.0, 155.8, 155.1, 154.8, 144.4, 142.3, 141.7, 137.8, 137.3, 135.5, 131.4, 129.3, 127.2, 123.6, 122.2, 119.9, 118.1, 44.7, 42.1, 39.0, 24.4, 20.1, 18.7, 18.1. [α]²⁰_D = -79.4 (c 0.33, CH₂Cl₂). HRMS (ESI+, m/z) calculated for C₅₀H₅₁N₆O₂ [M + H]⁺ 767.4079; found 767.4068.