Synthesis
Anhydrous aluminum trichloride (78.8 mmol, 10.5 g, 2.3 eq.) and anhydrous dichloromethane (25 mL) were added to the flask under a protective tube of calcium chloride and the resulting suspension was stirred in an ice bath. Subsequently, a solution of anhydrous dichloromethane (15 mL) with glutaric anhydride (34.3 mmol, 3.91 g) was added slowly dropwise, keeping the reaction temperature below 7 °C. The reaction was carried out in an ice bath. After the dropwise addition was completed, stirring was continued in an ice bath for 30 min, and then bromobenzene (34.3 mmol, 5.39 g, 1.0 eq.) was carefully added. The ice bath was removed and the reaction mixture was stirred at room temperature for 19 hours. Upon completion of the reaction, the mixture was poured into ice water (15 mL) and acidified with concentrated hydrochloric acid. The aqueous layer was washed with sodium sulfate (10 mL) and the organic phase was extracted with ethyl acetate (1 × 100 mL, 2 × 50 mL). The organic phases were combined, dried with anhydrous sodium sulfate, filtered and concentrated. The crude product was dissolved in ethyl acetate and this solution was added slowly dropwise to cold hexane (1 L) with vigorous stirring. The precipitate was collected by filtration and dried to give 5-(4-bromophenyl)-5-oxovaleric acid (7.93 g, 85%) as a yellow powder with a melting point of 125-127 °C.1H NMR (300 MHz, CDCl3): δ= 2.07 (m, 2H), 2.50 (t, J = 7.2 Hz, 2H), 3.04 (t, J = 7.2 Hz, 2H), 7.60 (m, 2H). 7.60 (m, 2H), 7.82 (m, 2H).
5-(4-Bromophenyl)-5-oxovaleric acid (25.0 mmol, 6.78 g), paraformaldehyde (86.3 mmol, 2.59 g, 3.4 eq.), and piperidine (0.57 mL, 0.24 eq.) were dissolved/suspended in pyridine (42 mL) and stirred for 21 hr. at 70 °C. Upon completion of the reaction, the mixture was poured into a mixture of 1 M sulfuric acid (200 mL) and concentrated hydrochloric acid. The aqueous layer was washed with sodium sulfate (15 mL) and the organic phase was extracted with ethyl acetate (1 × 150 mL, 2 × 100 mL). The organic phases were combined, washed with half-saturated brine (300 mL), dried over anhydrous sodium sulfate, filtered and concentrated. The crude product was crystallized with ethyl acetate to give 4-(4-bromobenzoyl)pent-4-enoic acid (3.93 g, 56%) as an orange-yellow solid with a melting point of 127-128 °C. 1H NMR (300 MHz, CDCl3): δ= 2.63 (t, J = 6.9 Hz, 2H), 2.80 (t, J = 6.9 Hz, 2H), 5.67 (s, 1H) , 5.95 (s, 1H), 7.60 (m, 4H); 13C NMR (75 MHz, CDCl3): δ= 27.2, 32.6, 127.3, 127.4, 131.0, 131.6, 136.3, 145.8, 178.9, 196.6.
References
[1] Russian Journal of General Chemistry, 2014, vol. 84, # 9, p. 1825 - 1829
[2] Zhurnal Obshchei Khimii, 2014, vol. 84, # 9, p. 1825 - 1829,5
[3] Tetrahedron Letters, 2016, vol. 57, # 10, p. 1079 - 1082
[4] Heterocycles, 2005, vol. 65, # 3, p. 649 - 656
