Anomalous fluorinations of 3-aryl-2-hydroxypropanoic esters by diethylaminosulfur trifluoride (DAST)

Abstract

Treatment of 3-aryl-2-hydroxypropanoic esters 8 with diethylaminosulfur trifluoride (DAST) gives considerable amounts of rearranged 2-aryl-3-fluoropropanoic esters 12 together with the expected products 11. The extent of rearrangement is dependent on solvent and on the substitution pattern of the aryl ring; the mechanism of rearrangement probably involves anchimeric assistance by the aryl group in the S_N1 component of the reaction pathway. Recation of the isomeric 3-hydroxy-2-phenylpropanoic ester 13 shows much less rearrangement under similar conditions, and an elimination product 21 is also obtained.