Bench‐Stable Electrophilic Fluorinating Reagents for Highly Selective Mono‐ and Difluorination of Silyl Enol Ethers

Abstract

Efficient methods for the synthesis of fluorinated compounds have been intensively studied, recently. Development of practical fluorinating reagents is indispensable for this purpose. Herein, bench‐stable electrophilic fluorinating reagents were synthesized as N‐fluorobenzenesulfonimide (NFSI) substitutes. Reagents obtained by replacing one of the NFSI sulfonyl groups with an acyl group led to the highly selective monofluorination of silyl enol ethers with suppression of undesired overreaction, that is, difluorination. On the other hand, reagents bearing electron‐withdrawing substituents at NFSI benzenesulfonyl groups efficiently facilitated the difluorination of silyl enol ethers under base‐free conditions. Thus, both mono‐ and difluorinated target materials were prepared from the same substrate.

Conversion of a AuI Fluorido Complex into an N‐Fluoroamido Derivative: N−F versus Au−N Reactivity

“…Complex 2 exhibits a doublet in the 31 P{ 1 H} NMR spectrum at 36.9 ppm with a coupling constant to the nitrogen-bound fluorine of 3 J FP = 7 Hz. In the 19 F NMR spectrum a doublet at À 89.6 ppm was observed with the same coupling constant. FSO 2 Ph was identified by the singlet in the 19 F NMR spectrum at 65.5 ppm, which is in agreement with previously reported values in the literature.…”

“…[21] We were able to produce the anion The compound [Au(SPhos)(CNtBu)][N(F)SO 2 Ph] ( 5) is not stable in solution and the elimination of FtBu was observed over the course of hours to days. The latter is revealed by a decet in the 19 F NMR spectrum at À 130.3 ppm ( 3 J FH = 21 Hz) as well as the corresponding doublet in the 1 H NMR spectrum at 1.35 ppm. [28] In addition to FtBu, the cyanido complex [Au(CN)(SPhos)] ( 6) was obtained, which was also synthesized independently by treatment of [Au(F)-(SPhos)] ( 1) with NaCN (Scheme 3) A doublet at 157.4 ppm in the 13 C{ 1 H} NMR spectrum with a coupling constant of 2 J CP = 120 Hz was observed for the metal-bound carbon atom, whereas the IR spectrum showed an absorption band at 2142 cm À 1 .…”

“…The N1À F1 bond length in 2 of 1.445(3) Å is longer as the one in NFSI (1.422(3) Å), [18] but comparable to separations in other organic molecules bearing N(F)SO 2 Ph groups (1.417( 2)-1.432(3) Å). [19] The N1 atom is located 0.45 Å above the Au1/S1/F1 plane with the sum of angles at N1 being 339°, which suggests an arrangement between trigonal-pyramidal and trigonal-planar.…”

“…This is in good agreement with data for [Au(SIPr)(CNtBu)] + , which shows a band at 2244 cm À 1 . [27] In the 19 F NMR spectrum of 5, a singlet at À 140.7 ppm was observed, which is assigned to the anion [N(F)SO 2 Ph] À . As mentioned above, Dond et al reported on an equilibrium of KF with NFSI, forming FSO 2 Ph as well as K[N(F)SO 2 Ph], and characterized the species HN(F)SO 2 Ph after acidic workup.…”

An N-Fluorinated Imide for Practical Catalytic Imidations

“…40−43 This current situation is hardly surprising since the reagent was repurposed from a fluorination reagent that had not considered its use as a nitrogen-based building block; additionally, the development of new N-fluorinated imides is a nontrivial task under ordinally laboratory settings, requiring access to fluorine gas. 44 Consequently, catalytic imidations with NFSI remain academic pursuits, despite their potential for expedient derivatization of feedstock chemicals into valuable nitrogen-containing materials.…”