Fluorinated Butanolides and Butenolides. Part 10. Convenient Synthesis of 3-Fluoro-4,5-diphenylfuran-2(5H)-one (V) from Benzoin Ethers (I). Novel and Efficient Z—E Isomerization and Cyclization of 2-Fluoroalkenoate Precursors, Substitution of Vinylic Fluorine.