Synthesis of 3-fluorofuran-2(5H)-ones based on Z/E photoisomerisation and cyclisation of 2-fluoro-4-hydroxybut-2-enoates

Mixtures of some (E)- and (Z)-2-fluoroalk-2-enoates prepared from the corresponding 2-hydroxycarbonyl compounds and ethyl 2-(diethoxyphosphoryl)-2-fluoroacetate have been transformed in high conversions into the target 3-fluoro-furan-2(5H)-ones by an efficient Z/E photoisomerisation of noncyclisable Z isomers followed by acid-catalysed cyclisation. In contrast, the acid-catalysed deprotection of ethyl (E)- and (Z)-4-[tert-butyl(dimethyl)silyloxyl-2-fluoro-4-phenylbut-2-enoates resulted in the displacement of vinylic fluorine, affording ethyl (E)-2-oxo-4-phenylbut-3-enoate. 3Fluoro-4-phenylfuran-2(5H)-one was transformed into 2[tert-butyl(dimethyl)silyloxy]-3-fluoro-5-methylfuran as a novel fluorinated building block. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)