Gold-Catalyzed Hydrofluorination of Internal Alkynes Using Aqueous HF

Abstract

The gold-catalyzed hydrofluorination reaction of internal alkynes using hydrofluoric acid is reported. Notably, those conditions use one of the most economical sources of HF and are free of additional additives. Both symmetrical and unsymmetrical internal alkynes can be utilized, and the use of alkynes bearing a fluorinated group at the propargylic position as substrates allowed for a regioselective hydrofluorination reaction.

A HF Loaded Lewis‐Acidic Aluminium Chlorofluoride for Hydrofluorination Reactions

“…Various reports demonstrate catalytic hydrofluorination reactions of alkynes, using transition metal complexes and different HF sources . HF sources including adducts such as DMPU/HF, Et 3 N⋅3 HF, and pyridine⋅(HF) x have been used for fluorination, as for instance, demonstrated by Olah in the hydrofluorination of alkynes using pyridinium poly(hydrogenfluoride) .…”

Stereodivergent Alkyne Hydrofluorination Using Protic Tetrafluoroborates as Tunable Reagents

“…It is noteworthy that in hydrofluorination reactions employing alkyl aryl acetylenes,t he vinyl fluoride products were delivered exclusively with C À Fb ond formation taking place adjacent (a)t ot he aryl group.T hese results complement Au-catalyzed hydrofluorination procedures,w hich deliver the fluorine to the carbon atom adjacent to the alkyl group, b to the aryl group. [7][8][9][10][11][12] This divergence likely stems from the ability for the aryl group to stabilize both an adjacent positive charge in the case of the current metal-free process and an adjacent C(sp 2 ) À Au bond in case of the Au-catalyzed protocols to give the a-a nd b-fluorinated regioisomers, respectively.…”

“…When direct comparisons were available (for 75, 77, 82), the regioisomeric ratios (15:1 to > 20:1) exceeded those previous reported for the Au-catalyzed transformation (2:1 to 4.3:1). [12]…”

“…[6] As an alternative to the aforementioned approaches,t he hydrofluorination of alkynes represents aparticularly general and atom-economical synthesis of vinyl fluorides,e specially considering the broad range of alkyne substrates that are easily accessed from inexpensive,c ommercially available building blocks.S everal metal-catalyzed systems for the hydrofluorination of alkynes have been developed in recent years. [7][8][9][10][11][12][13][14][15] Following the initial disclosure of aA u-catalyzed process by Sadighi and co-workers, [7] an umber of coinage metal complexes have been employed as catalysts for the hydrofluorination of alkynes using Lewis-base adducts of hydrogen fluoride as the fluorinating reagents (Scheme 1B). [7][8][9][10][11][12][13] In the Au-catalyzed systems, Z-vinyl fluorides are formed with high stereoselectivity,a nd for aryl alkyl alkynes,the major regioisomer formed is the one in which the fluorine is delivered to the carbon atom adjacent to the alkyl group (b to the aryl group,S cheme 1Ba).…”

“…[7][8][9][10][11][12][13][14][15] Following the initial disclosure of aA u-catalyzed process by Sadighi and co-workers, [7] an umber of coinage metal complexes have been employed as catalysts for the hydrofluorination of alkynes using Lewis-base adducts of hydrogen fluoride as the fluorinating reagents (Scheme 1B). [7][8][9][10][11][12][13] In the Au-catalyzed systems, Z-vinyl fluorides are formed with high stereoselectivity,a nd for aryl alkyl alkynes,the major regioisomer formed is the one in which the fluorine is delivered to the carbon atom adjacent to the alkyl group (b to the aryl group,S cheme 1Ba). Since the initial report of Au-catalyzed alkyne hydrofluorination in 2007, the scope of this process has seen considerable expansion and now includes alkynes bearing either electron-withdrawing groups or directing groups,a sw ell as terminal alkynes.…”