FLUORINATED SYNTHONS - REACTIVITY OF 1-R(F)-EPOXY ETHERS WITH LEWIS-ACIDS

Fluorinated epoxy ethers 2, 5, 6, and 12 react with Lewis acids to give different ring opening products, depending upon the structure and the experimental conditions. Both nucleophile-assisted and stepwise processes can occur. In all cases, except when a phenyl group stabilizes the C beta secondary carbenium ion, the C alpha-O bond is broken leading to addition, transposition, or cyclization products. EtAlCl(2) reacted with epoxy ethers 2a-c providing chlorohydrins 3a and the transposed products 4b,c and 5b,c. With epoxy ethers 6a-c aldehydes 7a-c were formed through a transposition. Epoxy ethers 9a-c underwent ring opening to the chloroketones 10a-c with EtAlCl(2) and TiCl4 and 9a gave the glycol ether 11a with Me(3)Al. Epoxy ether 12a was transformed into a mixture of chlorohydrin 13a(1) (S*R*) and the cyclized product 14a (S*R*) with TiCl4 or EtAlCl(2) at -78 degrees C. At room temperature, the cyclized products 14a (S*R*) or 15c were selectively obtained in good yields from 12a and 12c, respectively, with TiCl4.