[CH3:1][C:2](=[O:7])[CH2:3][C:4](=[O:6])[CH3:5].[CH:8](=O)[C:9]1[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1.B(OCCCC)(OCCCC)O[CH2:18][CH2:19][CH2:20]C.[CH2:32](N)[CH2:33][CH2:34][CH3:35].Cl>C(OCC)(=O)C>[C:9]1([CH:8]=[CH:1][C:2](=[O:7])[CH2:3][C:4](=[O:6])[CH:5]=[CH:35][C:34]2[CH:20]=[CH:19][CH:18]=[CH:32][CH:33]=2)[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1
Boric anhydride (0.49 g, 7.0 mmol) was combined with 2,4-pentanedione (2, 1.05 ml, 10.0 mmol) and stirred for 18 hr at room temperature under a nitrogen atmosphere. A solution of dry ethyl acetate (10 ml), benzaldehyde (1b, 2.05 g, 20.2 mmol) and tributyl borate (11.00 ml, 40.5 mmol) was added and the mixture stirred for 15 min at room temperature. Butylamine (0.20 ml, 2.0 mmol) was added dropwise over 30 min and stirring was continued for 18 hr at room temperature. Hydrochloric acid (15 ml, 0.4 N) was warmed to 60° C., added to the mixture and stirring was continued for 1 hr. The resulting mixture was extracted into ethyl acetate, washed with saturated sodium chloride, dried over magnesium sulfate, filtered and evaporated to afford a solid. The crude solid was triturated with methanol to give 0.90 g (33%) of a yellow solid: mp 140-142° C. [expected mp 139-140° C.]; 1H NMR: δ 5.84 (s, 1H), 6.62 (d, 2H, J=15.7 Hz), 7.39 (m, 6H), 7.54 (dd, 4H, J=7.4, 4.0 Hz), 7.66 (d, 2H, J=15.9 Hz), 15.85 (s, 1H); 13C NMR: δ 101.6, 124.1, 128.0, 128.9, 130.0, 135.0, 140.5, 183.2.
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