Boric anhydride (0.49 g, 7.0 mmol) was combined with 3-benzyl-2,4-pentanedione (8, 1.90 g, 10.0 mmol) and stirred for 48 hr at room temperature under a nitrogen atmosphere. A solution of dry ethyl acetate (10 ml), benzaldehyde (1b, 2.05 ml, 20.2 mmol) and tributyl borate (11.0 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 filtered to afford a solid. The crude solid was triturated with methanol to give 2.30 g (63%) of a yellow solid: mp 162-164° C. [expected mp 156-158° C.]; 1H NMR: δ 3.99 (s, 2H), 6.99 (d, 2H, J=15.6 Hz), 7.34 (m, 15H), 7.77 (d, 2H, J=15.2 Hz); 13C NMR: δ 31.8, 109.3, 120.8, 126.5, 127.8, 128.1, 128.8, 130.0, 135.3, 140.5, 141.9, 183.6.
