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

Abstract

An improved procedure for the radical addition of α,ω-diiodoperfluoroalkanes I–(CF 2CF 2) n –I ( n = 2, 3) to allyl acetate that afford the corresponding bis-adducts AcOCH 2CHICH 2(CF 2CF 2) n CH 2CHI–CH 2OAc ( 2a– 2b) has been developed. The primary bis-adducts 2a– 2b suffered a subsequent rearrangement in the addition mixture to afford semi-rearranged adducts AcOCH 2CHICH 2–(CF 2CF 2) n –CH 2CH–(OAc)CH 2I ( 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 CH 2(–O–)CHCH 2(CF 2CF 2) n CH 2CH–(–O–)CH 2 ( 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.