Fluorinative Rearrangements of Substituted Phenylallenes Mediated by (Difluoroiodo)toluene: Synthesis of α-(Difluoromethyl)styrenes

Phenylallenes undergo fluorinative rearrangement upon the action of (difluoroiodo) toluene in the presence of 20 mol% BF3 center dot OEt2 to yield alpha-difluoromethyl styrenes. This unprecedented reaction was entirely chemoselective for the internal allene pi bond, and showed remarkable regioselectivity during the fluorination event. Substituted phenylallenes, phenylallenes possessing both phenyl- and alpha-allenyl substituents, and diphenylallenes were investigated, and good functional-group compatibility was observed throughout. The ease with which allenes can be prepared on a large scale, and the operational simplicity of this reaction allowed us to rapidly access fluorine-containing building blocks that have not been accessed by conventional deoxyfluorination strategies.