Citraconic Anhydrides → 3-Methylbicyclo[4.2.0]oct-1(6)-ene-3,4,-Dicarboxylic Anhydride

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Into a 500-mL, single-neck round bottom glass flask containing a magnetic stirring bar was weighed 96.62 grams (0.862 moles) of citraconic anhydride. The flask was then fitted with a three-neck adapter to which was attached a thermometer, a condenser and a 250-mL addition funnel. To the funnel was added 86.0 grams of a distilled dimethylenecyclobutane (DMCB) cut containing 90.2% (by GC) 1,2-isomer (77.6 grams, or 0.968 moles, of 1,2-dimethylenecyclobutane). The flask was purged with dry nitrogen. The DMCB was then added dropwise to the citraconic anhydride with stirring. No temperature increase due to reaction exotherm was evident. When the DMCB addition was complete, the mixture was allowed to stand for 53 days at room temperature to complete the reaction. At the end of this period, gas chromatography revealed that the peak corresponding to unreacted citraconic anhydride had essentially disappeared. The product was then dissolved in dichloromethane and filtered to remove insoluble gelatinous material. Dichloromethane and unreacted volatiles were removed at 60° C. on a rotary evaporator to yield a crystalline product. The crude yield was 156.18 grams (94%). 152 g of product was then recrystallized from 165 grams of cyclohexane with strong stirring. Yield of recrystallized MBODA was 132.17 grams (80%). Melting point was 64°-68° C. The 1H and 13C NMR spectra of the product were consistent with the following structure; no impurities were seen in the product by NMR except for a small amount of cyclohexane. ##STR6##

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