Transition Metal-Catalyzed Reactions of Methylenecyclopropanes

The transition metal-catalyzed formal 3+2 cycloaddition of methylenecyclopropanes with unsaturated compounds X=Y, such as alkenes, aldehydes, and imines, gives five-membered carbocycles or heterocycles. The Heck-type reaction of R-Pd-X with the exomethylene part of methylenecyclopropanes gives the corresponding cyclopropylcarbinylpalladium complexes which undergo further transformations through typical palladium reactions such as β-hydride elimination or reductive elimination of Pd(0). Hydrostannation, hydrosilylation, hydrocarbonation, hydroamination, and hydroalkoxylation of methylenecyclopropanes proceed through the addition of the metal hydrides (H-M) and pronucleophiles (H-Nu) to the olefinic part, and the resulting intermediates are converted to the allylic products in which the homologation by three carbon atoms takes place from M and Nu, respectively. Bismetallation produces 1,3-bimetallic derivatives through metallacyclobutane intermediates.