C-C Bond Activation of Cyclopropanes Enabled by Phosphine-Catalyzed Formation of High-Strain Methylenecycopropane Intermediate.

An effective strategy for the ring-opening/elaboration of cyclopropanes by phosphine catalyst is documented, providing the 2,4-pentadiene sulfonamides and isoindolines in moderate to good yields. The key to the success of this reaction is phosphine-catalyzed introduction of a trigonal center into cyclopropanes, which results in the formation of higher ring strain cyclopropylidenemethyl phosphonium salt. Moreover, this methodology is employed as the key step for the synthesis of bioactive molecules.