Diels–Alder cycloaddition: cyclopentadiene + maleic anhydride → endo-norbornene-2,3-dicarboxylic anhydride
Ready to scaleCycloaddition[4+2]
Textbook [4+2] cycloaddition. Electron-rich diene (cyclopentadiene, freshly cracked from its dimer) reacts with electron-poor dienophile (maleic anhydride) in a concerted, suprafacial, endo-selective addition. The endo product crystallises from cold toluene. Frontier-MO analysis predicts the rate (HOMO_diene/LUMO_dienophile gap) and the ortho/endo regio+stereo selectivity — see Houk, JACS 95, 4092 (1973).
Conditions
Run at 20–25 °C in toluene (~1 M substrate) for 1–4 h, or neat above maleic anhydride's mp (~52 °C) for 30 min. No catalyst required — the EDG/EWG-matched pair is fast at room temperature. Cyclopentadiene must be freshly cracked from dicyclopentadiene (170 °C distillation, used within hours).
Workup
Cool to 0 °C, filter the white crystalline endo product, wash with cold toluene, dry under vacuum.
| Compound | Role | Equiv | MW (g/mol) | ρ (g/mL) | Safety |
|---|---|---|---|---|---|
| Maleic anhydride108-31-6 · C4H2O3Maleic anhydride — recrystallised from chloroform if discoloured. | reactant | 1.0 | 98.06 | — | DangerSDS |
| Cyclopentadiene542-92-7 · C5H6Cyclopentadiene — freshly cracked from dicyclopentadiene (170 °C). Dimerises on standing; use within hours. | reactant | 1.0 | 66.10 | 0.800 | Danger |
| Toluene108-88-3 · C7H8Toluene — non-coordinating aromatic solvent; doubles as the recrystallisation medium for the product. | solvent | — | 92.14 | 0.860 | DangerSDS |
| Nadic anhydride826-62-0 · C9H8O3endo-Bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride — kinetic product. White crystalline solid, mp 165 °C; the exo isomer (mp 142 °C) is the thermodynamic product but requires heating beyond the room-temperature conditions used here. | product | — | 164.16 | — | Danger |