title: Ruthenium-catalyzed C-H activation/cyclization for the synthesis of phosphaisocoumarins.
abstract: An efficient and cost-effective ruthenium-catalyzed oxidative cyclization of phosphonic acid monoesters or phosphinic acids with alkynes has been developed for the synthesis of a wide range of phosphaisocoumarins in good to excellent yields under aerobic conditions. A multitude of arylphosphonic acid monoesters and arylphosphinic acids having electron-donating and -withdrawing groups were oxidatively cyclized. Various diarylacetylenes, dialkylacetylenes, and alkylarylacetylenes effectively underwent the ruthenium-catalyzed oxidative cyclization. A substrate possessing benzoic acid as well as a phenylphosphonic monoester moiety was smoothly cyclized with hex-3-yne to afford a compound having both isocoumarin and phosphaisocoumarin moieties. Alkenylphosphonic monoester afforded phosphorus 2-pyrone through oxidative cyclization with alkyne. Competition experiments between diaryl- and dialkylalkynes and between diarylacetylenes having p-methoxy and p-chloro groups gave results which showed that the present oxidative cyclizations were not affected by the electronic effects of alkynes. Mechanistic studies revealed C-H bond metalation to be the rate-limiting step.
authors.affiliation: Department of Chemistry, Kangwon National University , Hyoja-2-dong, 192-1, Chuncheon 200-701, Republic of Korea.
authors.forename: Youngchul
authors.initials: Y
authors.lastname: Park
authors.forename: Incheol
authors.initials: I
authors.lastname: Jeon
authors.forename: Seohyun
authors.initials: S
authors.lastname: Shin
authors.forename: Jiae
authors.initials: J
authors.lastname: Min
authors.forename: Phil Ho
authors.initials: PH
authors.lastname: Lee