Lanthanide‐mediated Defluorinative Transformations of Trifluoromethylated Benzofulvenes: Access to Functionalized Difluoroalkenes and Mechanistic Insights.

Accessing difluorinated organic molecules via selective C‐F bond activation in CF3‐containing substrates has become a valuable synthetic pathway. The combination of lanthanide metals (lanthanum, dysprosium) with Lewis acids (AlCl3, LaI3) allows the efficient regio‐ and stereoselective transformation of CF3‐benzofulvenes into a range of versatile difluoroalkenes proceeding via ε,ε‐difluoropentadienyl lanthanide or aluminium species. The reaction of these organometallic intermediates towards ketones and nitroalkenes is herein reported and analyzed in relation to previous studies on aldehydes. The influence of steric and electronic factors of the organic substrates but also of the lanthanide metals and Lewis acids on the regio and stereoselective reaction is highlighted and corroborated by in‐depth DFT studies. The resulting difluorinated homoallylic alcohols and nitroalkanes were further functionalized to new benzofulvenes and their reactivity explored.