Silver-initiated radical ring expansion/fluorination of ethynyl cyclobutanols: efficient synthesis of monofluoroethenyl cyclopentanones

A stereoselective synthesis of beta-halogenated 2-methylenecyclopentanones via silver-catalyzed formal ring expansion using water as the cosolvent is described. A variety of 2-methylenecyclopentanones with fluoro, chloro and bromo functionalities are efficiently prepared from 1-alkynyl cyclobutanols. This method offers facile access to halogenated complex molecules which are not only useful chemicals but also valuable building blocks for further derivatizations.