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.
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