Methylenecyclobutane-1,2-dicarboxylate

METHYLENECYCLOBUTANE-l,2-DICARBOXYLATE (3-MethylenecycIobutane-l,2-dicarboxylic acid, dimethyl ester)... 

The crude anhydride is carefully fractionated through a 13-mm. x 1.2-m. Nester still at a pressure of 25 mm. (Note 4) and a reflux ratio of at least 10 1. After a fore-run of maleic anhydride, b.p. 50-100°/25 mm., and a small intermediate fraction, there is obtained 75-90 g. (22-26%) of 3-methylenecyclobutane-l,2-dicar-boxylic anhydride b.p. 155-159°/25 mm. 1.4935-1.4952 (Note 5). This material is of sufficient purity for most uses, but it contains approximately 2-5% of propargylsuccinic anhydride. Redistillation through the Nester still gives 65-80 g. (19-23%) of 3-methylenecyclobutane-l,2-dicarboxylic anhydride b.p. 155°/25 mm. 1.4946-1.4955. 

B. Dimethyl 3-methylenecyclobutane-l,2-dicarboxylate. One liter of methanol is added cautiously with occasional shaking to 276 g. (2.00 moles) of 3-methylenecyclobutane-l,2-dicarboxylic anhydride ( d 1.4946-1.4955 Note 6) and 5 g. of />-toluenesulfonic acid in a 2-1. three-necked flask fitted with a thermometer, a condenser, and a dropping funnel. Refluxing starts after about two-thirds of the methanol has been added. The remainder is added at a rate that maintains vigorous boiling. The solution is refluxed for 30-40 hours with the pot temperature increasing... 

Since 3-methylenecyclobutane-l,2-dicarboxylic anhydride is easily converted to 3-methyl-2-cydobutene-l,2-dicarboxylic acid, it is an intermediate to a variety of cyclobutenes. The dimethyl ester of 3-methylenecyclobutane-l,2-dicarboxylic acid is also a versatile compound on pyrolysis it gives the substituted allene, methyl butadienoate, and on treatment with amines it gives a cyclobutene, dimethyl 3-methyl-2-cyclobutene-l,2-di-carboxylate. ... 

The reaction of propargyl carbonate 187 with 2,5-hexanedione-3,4-dicarboxylate (203) for 7 h catalyzed by [Pd2(dba)3] and dppe afforded methylenecyclobutane 204 by double C-alkylation, and 3-methylenedihydropyran derivative 205 by C- and O-alkylations, in 52% and 42% yields, respectively (Scheme 11-54). The cyclobutane 204 is a product of a... 

The pyrolysis tube is flushed with nitrogen, the lower section is heated to 600° and the upper section to 300° (Note 1), and the pressure is regulated at 25 mm. Then 184 g. (1.00 mole) (Note 2) of dimethyl 3-methylenecyclobutane-l,2-dicarboxylate is admitted over a period of 3,hours (Note 3). The product, which amounts to 172-177 g., collects in the traps. It is distilled through a 13-mm. x 1.2-m. Nester spinning-band still. First... 

Dimethyl 3-methylenecyclobutane-l,2-dicarboxylate passed during 3 hrs. at 300-600°/25 mm through a vertical N2-flushed Vycor-glass tube packed with glass ringsmethyl butadienoate (Y 40-44%) and methyl acrylate (Y 48-55%). H. B. Stevenson and W. H. Sharkey, Org. Synth. 43, 71 (1963). 

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