Cis-Cyclobutane-l,3-dicarboxylic acid

Tetraethyl butane-1,1,4,4-tetrtacarboxylate added to a soln. of Na in abs. alcohol, to the resulting soln. tetraethyl l,4-dibromobutane-l,l,4,4-tetracarboxy-late added, and heated 4 hrs. in an oil bath at no-IIS -> tetraethyl cyclobutane-1,1,2,2-tetracarboxylate (Y 75.2%) boiled with aq. HGl (1 1) at ISO-HO in an oil bath until the oily layer has dissolved after 35-40 hrs., the HGl removed by distillation, and the residue heated at 180-200° until G0.2-evolution ceases mixture of cis- and frans-cyclobutane-l,2-dicarboxylic acids (Y 97.5%) refluxed 5 hrs. at 70-90° with acetjd chloride on a water bath, excess acetyl chloride and the resulting acetic acid removed by distillation at atmospheric pressure, and the residue heated 6-7 hrs. at 160-175° in an oil bath whereby the mixed anhydride of frans-cyclobutane-l,2-dicarboxylic acid and acetic acid is converted to acetic anhydride and cis-cyclobutane-l,2-dicarboxylic acid anhydride (Y 81.2%) boiled with 2 parts of water cis-cyclobutane-l,2-di-carboxylic acid (Y ca. 100%). V. P. Gol mov and Z. P. Malevannya, 7K. 31, 665 (1961) G. A. 55, 22162b method of ring closure s. J. J. Lennon and W. H. Perkin, Soc. 1928, 1513. 

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