Diethyl (fluorocarbethoxymethyl)phosphonate (1), prepared from triethyl phosphite and ethyl bromofluoroacetate, reacts with n-butyllithium in THF to give the phosphonate carbanion 2.Addition of the pregenerated carbanion 2 to a THF solution of methyl or ethyl oxalyl chloride at -78 °C forms the acylated phosphonate (Et0)2P(0)CF(C0C02R)CC>2Et (3). In situ reaction of 3 with Grignard reagents affords a-fluoro-a,/3-unsaturated diesters R'(C02R)C=CFC02Et in moderate to good yields with high E-stereoselectivity. The reaction is applicable to primary, secondary, and tertiary alkyl, alkenyl, alkynyl, aryl, cyclohexyl, and perfluorinated Grignard reagents. The assignment of E and Z configuration is based on NOE experiment. The E/Z ratio of unsaturated diesters formed in the reaction varies with the metal ion and cosolvent. However, solvents and bases have little influence on the stereoselectivity.1:1 mixture of ethylenic triethyl esters (Et02CCFH)(C02-Et)C=CHC02Et and the isomerization product (Et02-CCH2)(C02Et)C=CFC02Et.8 Alkylation of (ethylphenyl)t Chung Cheng Institute of Technology.

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A reduction-olefination sequence has been used to convert esters to a-fluoro a,b-unsaturated esters. In the presence of diisobutylaluminum hydride, esters are reduced to aldehydes that react in situ with [ (EtO),P(O)-CFC(O)OEt]Zi+ to form the title compounds in good yields with high stereoselectivity. The reaction is apphcable to aliphatic, aromatic, cyclic, unsaturated, perfluorinated, and partially fluorinated esters. The E/Z ratio of unsaturated esters formed in the reaction varies with the cations present in the reaction mixture. Solvents have very little influence on stereochemistry. The sequential transformation of PhC(0)OBun to (E)-PhCH=CFC(O)OEt and then to (E,E)-PhCH=CFCH=CFC(O)OEt illustrates the scope of this methodology, which introduces a fluorine atom adjacent to an ester functionality with concomitant elongation of the chain by two carbon atoms.

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