A Reverse Wittig Coupling with Trifluoroacetaldehyde: A Convenient One-Step Synthesis of Trifluoromethyl Alkenes

A novel, mild synthesis of aryl-3,3,3-trifluoropropenes by Wittig olefination of benzylphosphonium ylides with in-situ generated trifluoroacetaldehyde is described. The in-situ formed trifluoroacetaldehyde efficiently traps the Wittig ylides and yields trifluoromethyl alkenes without the troublesome handling. The scope of the reaction was tested in reaction of trifluoroacetaldehyde with a wide variety of benzylphosphonium ylides. The α-trifluoromethyl alkenes were isolated in good to excellent yields in a convenient one step process.