Monofluorinated epoxides were successfully prepared through the O-cyclization reaction between a-fluorosulfoximines and ketones. The obtained fluoroepoxides were found to readily undergo an interesting ring-opening process (involving both a C À F bond cleavage and another C À F bond formation) in the presence of titanium tetrafluoride or pyridinium poly(hydrogen fluoride) to afford afluorinated ketones. The later process constitutes a formal catalytic 1,2-fluorine shift reaction.Keywords: epoxides; fluorine; fluorine shift; ringopening; sulfoximines Due to the high electronegativity and small size of the fluorine atom, the replacement of hydrogen atom(s) by fluorine in organic compounds often results in a profound change in their physical, chemical and biological properties.[1] As a consequence, over the past decade, organofluorine compounds have found broad applications in both life sciences and materials science.[2] To date, many endeavours have been made to develop new efficient synthetic methods for the selective introduction of fluorine atom(s) or fluorinated moieties into organic molecules.[2] Although epoxides are highly useful building blocks in organic synthesis, the reports on the preparation and synthetic utilizations of monofluorinated epoxides are scarce. [3][4][5] Monofluorinated epoxides are usually prepared by the epoxidation of monofluoroolefins, [3] the treatment of fluorohalohydrins with a base, [4] or the Darzens reaction between a ketone and dibromo(tertbutyldimethylsililyl)fluoromethane [5] (or ethyl dibromofluoroacetate [6] ). Fluorinated epoxides are known to be relatively unstable, and tend to undergo a variety of ring-opening reactions with nucleophiles.[3c,7,9] When monofluoroepoxides were treated with fluoride ion, a-fluorinated carbonyl compounds were obtained through a ringopening process involving both a C À F bond cleavage and another C À F bond formation. [3a,8] This type of transformation also proceeded smoothly in the presence of triethylamine-tris(hydrogen fluoride) [9] or boron trifluoride [10] . Futhermore, the acid-catalyzed isomerizations of polyfluorinated epoxides into the corresponding ketones have been previously documented. [7] As part of our efforts to develop new synthetic approaches for organofluorine compounds, [11] we recently developed some unique synthetic methods for the preparation of di-and monofluorinated compounds by using fluorinated sulfoximine reagents. [12,13] In particular, the a-difluoromethylsulfoximine was used as a novel and efficient difluorocarbene reagent, [12] and the a-fluorosulfoximines could readily react with simple nitrones to give monofluoroalkenes with excellent Z/E stereocontrol. [13] In this paper, we wish to report another interesting synthetic application of fluorinated sulfoximines, that is, the efficient synthesis of a-monofluorinated epoxides derived from a-fluorosulfoximines and ketones, and the subsequent ringopening reaction of the monofluoroepoxides by using TiF 4 or pyridinium poly(hydrogen fluoride) (Olahs reage...
