Seven-membered cyclic α-monofluorophosphonate esters such as 2-allyloxy-3-fluoro-3-phenylthio-4,7-dihydro-[1, 2]-oxaphosphinine-2-oxide were successfully synthesized in moderate total yield as 41% from open-chain allyl phosphonates having an α-arylthio group as an electroauxiliary using an alternative sequence of anodic fluorination and ring-closing olefin metathesis (RCM). On the other hand, in an