[28096-33-5] · C19H16FP · Fluoromethylenetriphenylphosphorane · (MW 294.32)
(can function for the introduction of =CFH into organic compounds)
Alternate Name: triphenylphosphonium fluoromethylide [28096-34-6].
Preparative Methods: fluoromethylenetriphenylphosphorane is prepared in situ by the dehalogenation of fluoroiodomethyltriphenylphosphonium iodide with Zinc/Copper Couple in DMF,1 or pregenerated by the dehydrohalogenation of fluoromethyltriphenylphosphonium iodide with n-Butyllithium1 or Phenyllithium2 at -78 °C. The precursor fluoromethyltriphenylphosphonium salt is prepared by the reaction of Triphenylphosphine with iodofluoromethane,1 by the reaction of Methylenetriphenylphosphorane with FClO3,2 or by the reaction of hydroxymethyltriphenylphosphonium tetrafluoroborate with N,N-Diethylaminosulfur Trifluoride (DAST).3
Reaction of the pregenerated ylide, fluoromethylenetriphenylphosphorane, with aldehydes and ketones at -78 °C gives the corresponding alkenes, RRīC=CHF, in 16-45% yields (eq 1). From aldehydes and asymmetrical ketones a mixture of trans and cis isomers was obtained in a 1:1 ratio.2 A modification employs additional Potassium t-Butoxide in the above reaction sequence to achieve higher yields (28-69%) of RRīC=CHF.1 Fluoromethylenetriphenylphosphorane could also be generated in situ. For example, treatment of fluoroiodomethyltriphenylphosphonium iodide with zinc-copper couple and aldehydes or fluorinated ketones in DMF gives the alkenes, RRīC=CHF, in 54-80% yields (eq 2).1
Donald J. Burton & Weiming Qiu
University of Iowa, Iowa City, IA, USA