Radical addition reactions of fluorinated species. Part 8. Regioselectivity of radical additions to perfluoroalkylethylenes and quantum chemical calculations. Highly selective two-step synthesis of 4-(perfluoroalkyl)butane-1,2-diols

Perfluoroalkylethylenes RF–CHCH2 (RF = C4F9,C6F13,C8F17) added easily nucleophilic radicals generated from alkanols, oxolane and 2,2-dimethyl-1,3-dioxolane. The additions were initiated photochemically in the presence of acetone or by dibenzoyl peroxide and were completely regioselective and almost completely chemoselective with preparative yields up to 90%. 4-Fluoroalkylated dioxolanes obtained (5a–5c) were deprotected by methanolysis in acid media to afford 4-perfluoroalkyl-1,2 butanediols (15a–15c) that were converted to the corresponding bis-methacrylates (16a–16c). 2,2,4-Trimethyl-1,3-dioxolane (17) reacted at two centers to yield 84:16 regioisomeric mixture of fluoroalkylated dioxolanes with preferential attack of the adduct-radical to the more sterically hindered tertiary C–H bond in 17. The complete regioselectivity of the additions to perfluoroalkylethenes is discussed in relation to the “tail effect” of perfluoroalkylated chain and energies of intermediate adduct-radicals calculated using PM3 and ab initio quantum chemical methods.