Synthesis of 2-Chlorocyclopropene-Tethered Diazocarbonyl Compounds and Their Cyclization to Form Poly-Substituted...

Herein, we disclose a dual C─F bond functionalization of gem-difluorocyclopropenes using a catalytic amount of TiCl₄. The reaction proceeds through a sequential nucleophilic addition of chloride and silyl diazoenolates to the nonsymmetric cyclopropenium cations generated by the fluoride abstraction. The preferential monofluorocyclopropenium-titanate(IV) salts enable an efficient halogen transfer within the ion pairs, thus providing the opportunity to accept the addition of another type of nucleophiles. A stable [(PhC₃HCl)⁺]₂[Ti₄Cl₁₂F₆]^2- salt was isolated, and its structure was confirmed by X-ray crystal diffraction. The chemo- and regioselective addition of two different nucleophiles gives vicinal substitution products regardless of the electronic properties of substituents on the gem-difluorocyclopropenes and the sizes of nucleophiles. Various 2-chlorocyclopropene-tethered diazocarbonyl compounds were prepared with the tolerance of a wide range of functional groups. The synthetic utility of the resultant products was demonstrated by the discovery of a new poly-substituted phenol synthesis via a Rh(II)-catalyzed cyclization reaction.