Ring-opening of epoxides with boron trifluoride yielding syn-fluorohydrins was investigated using density functional methods (PBE) and two different basis sets (6-31G(d) and 6-311++G(2df,2pd), both in gas phase and simulating the bulk solvent using the PCM method. The only mechanism previously suggested for the formation of fluorohydrins from epoxides is an S-N 1-like one. We propose in this work a new mechanism, in which bond breaking in the epoxide is Coupled to fluorine transfer, yielding the fluorohydrine with retention of configuration through a single transition state. (c) 2009 Elsevier B.V. All rights reserved