PdCl(2)-promoted reactions of diaryl-substituted methylenecyclopropanes.

The PdCl(2)-promoted reactions of methylenecyclopropanes (MCPs) 1 bearing diaryl substituents on the terminal double bond were carefully investigated. The solvents employed significantly affected the reaction outcomes. It was found that dimeric allylpalladium(ii) complexes 2a-2f can be obtained as the sole products in acceptable to good yields under mild reaction conditions with THF as the solvent, while dimeric allylpalladium(ii) complexes 2a-2f along with another type of dimeric allylpalladium(ii) complexes 4a-4e can be obtained in good to high total yields if N,N-dimethylacetamide (DMAc) was used as the solvent. Moreover, using N,N-dimethylformamide (DMF) as the solvent in the presence of water, it was found that water can also participate in the reaction to form another type of dimeric allylpalladium(ii) complex 6 as the minor product. All of these dimeric allylpalladium(ii) complexes reported in the paper have been characterized by X-ray crystal structure diffraction.