Maleic Anhydride → 4,4A,5,5a,6,6a-hexahydro-1H-4,6-ethenocyclopropa[f]isobenzofuran-1,3(3aH)-dione

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Furan-2,5-dione (5.32 g, 54.26 mmol) was partially dissolved in xylene (100 mL). Cyclohepta-1,3,5-triene (5 g, 54.26 mmol) was added. The reaction was stirred at 144° C. for 5 h. The mixture was allowed to cool to 25° C. and concentrated in vacuo. Purification by flash column chromatography (Teledyne Isco RediSep column; 0 to 20% ethyl acetate in hexanes) afforded the desired products, rac-(1R,2R,6S,7S,8S,10R)-4-Oxatetracyclo[5.3.2.02,6.08,10]dodec-11-ene-3,5-dione (7.46 g, 39.22 mmol, 72%) and rac-(1R,2S,6R,7S,8S,10R)-4-Oxatetracyclo[5.3.2.02,6.08,10]dodec-11-ene-3,5-dione (0.88 g, 4.63 mmol, 8%), as white solids. 1H NMR (400 MHz, CDCl3) δ: exo: 0.27-0.42 (2H, m), 1.11-1.15 (2H, m), 3.25 (2H, t, J=1.6 Hz), 3.46-3.50 (2H, m), 5.89 (2H, dd, J1=4.8 Hz, J2=3.2 Hz); endo: 0.14-0.26 (2H, m), 1.12-1.16 (2H, m), 3.09 (2H, s), 3.40-3.44 (2H, m), 5.94 (2H, dd, J1=4.8 Hz, J2=3.2 Hz). LC-MS (ESI) calcd for C11H10O3 190.20, found exo 191.0; endo 191.3 [M+H+].

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