6708-37-8

108-31-6

1165952-91-9

6708-37-8

1,3-Cyclohexadiene (36.40 g, 0.4543 mol) and maleic anhydride (29.10 g, 0.2968 mol) were added to a 250 mL Schlenk flask equipped with a magnetic stirrer. After installing the condenser tube, the system was placed under dynamic nitrogen protection and the reaction mixture was heated to 60°C. After 5 minutes of heating, maleic anhydride was completely dissolved to form a bright yellow solution, after which reflux was initiated. 1,3-Cyclohexadiene contributed to the solidification of the reaction mixture into light yellow crystals within 25 minutes of the onset of heating. After 3 hours of continued reaction, unreacted 1,3-cyclohexadiene was removed by distillation under reduced pressure. The resulting yellow crystalline solid was recrystallized from 200 mL of standard ethanol to give Diels-Alder adduct 5 as 46.54 g of white crystalline solid (88% yield). 1H NMR (700 MHz, CDCl3, 25 °C): δ = 1.43 (d, J = 7.7 Hz, 2H, CH2 cyclohexene), 1.62 (d, J = 7.7 Hz, 2H, CH2 cyclohexene), 3.15 (t, 2H, -CH-CO), 3.25 (m, 2H, methine cyclohexene), 6.33 (dd, J = 7.7 Hz, 4.2 Hz, 3.5 Hz, 2H, -CH=CH-). 13C NMR (700 MHz, CDCl3, 25°C): δ = 22.98 (CH2, cyclohexene), 31.63 (methine cyclohexene), 44.77 (-CH-CO), 133.05 (-C=C-), 172.83 (CO). IR (cm-1): 3055 (=C-H stretch), 2980-2870 (C-H stretch), 1867-1766 (C=O stretch), 1462-1322 (C-H bend), 1238-1177 (C-O stretch), 1075-684 (C-H out-of -plane bend). LC-MS: m/z 179.07 (M+), 151.07, 147, 133, 123, 105, 79, 73.