Regio- and stereo-controlled synthesis of bicyclic α-methylene-γ-butyrolactones containing a fluorine via halofluorination-radical cyclization

Abstract

3-Alkoxycycloalkenes undergo regio- and stereoselective halofluorination with pyridinium poly(hydrogen fluoride) and 1,3-dibromo-5,5-dimethylhydantoion or N-iodosuccinimide to give (1 S*,2 S*,3 S*)-1-alkoxy-3-fluoro-2-halocycloalkanes in good yields. Among the halofluorides, the 3-(2-propynyloxy) derivatives are in turn converted into bicyclic α-methylene-γ-butyrolactons containing a fluorine via radical cyclization followed by oxidation, leading to a stereospecific synthesis of (±)-4-fluoro-l- epi-damsin.