Abstract
AbstractThe anion [(EtO)2P(O)CFCO2Et]−Li+, pregenerated from its precursor diethyl (carboethoxyfluoromethyl)phosphonate (EtO)2P(O)CFHCO2Et and n‐butyllithium, was added via syringe to a THF solution of ethyl oxaiyl chloride to yield an acylated phosphonate (EtO)2P(O)CF(COCO2Et)CO2Et. In situ reaction with Grignard reagents RMgX produces the α‐fluorodiesters (E,Z)‐R(CO2Et)C=CFCO2Et in good yields. In contrast, addition of ethyl oxalyl chloride to a THF solution of diethyl (carboethoxyfluoromethyl)phosphonate anion gives an isolated intermediate (EtO)2P(O)CFCO2Et(CO2Et)C=CFCO2Et. Subsequent reaction of this isolated intermediate with Grignard reagents also affords a one‐pot synthesis of the α‐fluorodiesters with high E‐stereoselectivity. The E‐stereoselectivity increases when HMPT or DMPU is used as a cosolvent in the preparation of diethyl 2‐fluoro‐3‐phenylfumarate (E,Z)‐Ph(CO2Et)C=CFCO2Et.
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