Formation of unsaturated bicyclic γ-butyrolactone by oxidative dimerization of 2-methyl-2-ethynylcyclopropanecarboxylic acid

Conclusions The oxidative dimerization of a mixture of the trans and cis isomers of 2-methyl-2-ethynylcyclopropanecarboxylic acid in the presence of CuCl and NH₄Cl gives, along with bis(trans-1-methyl-2-carboxyl-1-cyclopropyl)diacetylene (53% yield), also the corresponding dilactone, and specifically bi(1-methyl-4-oxo-3-oxabicyclo[3.1.0]-2-hexalidene)methyl (14% yield), which is probably formed via the intramolecular cyclization of the intermediately formed bis(cis-1-methyl-2-carboxy-1-cyclopropyl) diacetylene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1164–1166, May, 1981.