copper trifluoromethanesulfonate in 1,2-dichloro-ethane
T=20°C; Cycloaddition; Cyclopropanation; Product distribution; Further Variations:also in the presence of various ligands;
Wiberg, Kenneth B.; Wasserman, David J.; Martin, Eric J.; Murcko, Mark A.
Journal of the American Chemical Society, 1985 , vol. 107, # 21 p. 6019 - 6022