Fluorinated epoxides: 5. Highly selective synthesis of diepoxides from α,ω-diiodoperfluoroalkanes. Regioselectivity of nucleophilic epoxide-ring opening and new amphiphilic compounds and monomers

An improved procedure for the radical addition of α,ω-diiodoperfluoroalkanes I–(CF2CF2)n–I (n = 2, 3) to allyl acetate that afford the corresponding bis-adducts AcOCH2CHICH2(CF2CF2)nCH2CHI–CH2OAc (2a–2b) has been developed. The primary bis-adducts 2a–2b suffered a subsequent rearrangement in the addition mixture to afford semi-rearranged adducts AcOCH2CHICH2–(CF2CF2)n–CH2CH–(OAc)CH2I (3a–3b) in an amount of ca. 15% rel. at reaction temperatures. Both adducts 2a–2b and rearranged adducts 3a–3b were converted to diepoxides CH2(–O–)CHCH2(CF2CF2)nCH2CH–(–O–)CH2 (4a–4b) with high chemoselectivity in two ways: the selectivity of the direct epoxidation of 2a–2b and/or 3a–3b with potassium hydroxide was extremely dependent on the solvent; the second method included hydrolysis of 2a–2b and/or 3a–3b to bis-iodohydrins 5a–5b and 6a–6b that were easily transformed to the diepoxides 4a–4b. Ring-opening reactions of bis-epoxides 4a–4b with hydroxy compounds in the presence of boron trifluoride etherate took place at the terminal carbon atom of both epoxide rings with complete regioselectivity. A convenient transformation of the diepoxides to the corresponding amphiphilic tetrols (14a–14b) via dioxolane intermediates was accomplished with overall yields of 57–65% . Base-catalyzed ring-opening by methacrylic acid was not completely regioselective (89% terminal attack on both oxirane rings) and afforded a mixture of regioisomeric bis-methacrylates (16a–16b and 17a–17b) bearing two hydroxyl groups. In contrast, epoxide ring-opening with morpholine was completely regioselective in both diepoxides 4a and 4b.