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Diels–Alder cycloaddition: cyclopentadiene + maleic anhydride → endo-norbornene-2,3-dicarboxylic anhydride

Diene + Dienophile →[4+2] cyclic adduct

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.

Expected yield: 80–95 %
Expected duration: 1–4 h at 20–25 °C in toluene; 30 min neat above 52 °C

Mechanism reference ↗

Anchor reagent — fix this amount, scale everything else Substrate concentration · M

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Reactants

Reactants for Diels–Alder cycloaddition: cyclopentadiene + maleic anhydride → endo-norbornene-2,3-dicarboxylic anhydride: stoichiometric quantities derived from the anchor amount.
Reagent	Equiv	Moles · mmol	Mass · g	Volume · mL
Cyclopentadiene 542-92-7 · C5H6	1.0	10.00	0.661	0.83
Maleic Anhydride 108-31-6 · C4H2O3	1.0	10.00	0.981	0.66

Solvent

Solvent for Diels–Alder cycloaddition: cyclopentadiene + maleic anhydride → endo-norbornene-2,3-dicarboxylic anhydride: stoichiometric quantities derived from the anchor amount.
Reagent	Equiv	Moles · mmol	Mass · g	Volume · mL
Toluene SDS 108-88-3 · C7H8	—	186.67	17.200	20.00

Product

Product for Diels–Alder cycloaddition: cyclopentadiene + maleic anhydride → endo-norbornene-2,3-dicarboxylic anhydride: stoichiometric quantities derived from the anchor amount.
Reagent	Equiv	Moles · mmol	Mass · g	Volume · mL
826-62-0 826-62-0 · C9H8O3	1.0	10.00	1.642	1.16

Expected isolated yield

What you should actually weigh out of the recrystallisation flask, scaled from the limiting reactant via the canonical-procedure yield window.

Product: 826-62-0 826-62-0 · C9H8O3
Theoretical max: 1.64 g (10.00 mmol)
Expected isolated · 80–95 % yield: 1.31 – 1.56 g

Stoichiometry: moles_X = (moles_anchor / equiv_anchor) × equiv_X. Mass = moles × MW; volume = mass / ρ. Solvent volume = total reactant moles ÷ substrate concentration.

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Stoichiometry Calculator Limiting reagent, theoretical yield, and reaction quantities with full unit propagation. Molar Mass Calculator Molecular weight and percent composition to weigh out each reagent. Chemical Equation Balancer Balance the reaction before you scale it. Fractional Distillation Predictor Plan the work-up — predict which fractions distil and where azeotropes bite.