Catalyst-Free Hydrodefluorination of Perfluoroarenes with NaBH₄

Abstract

Presented is an economical means of removing fluorine from various highly fluorinated arenes using NaBH4. The procedure was adapted for different classes of perfluoroarenes. A novel isomer of an emerging class of organic dyes based on the carbazole phthalonitrile motif was succinctly synthesized in two steps from tetrafluorophthalonitrile, demonstrating the utility of the hydrodefluorination procedure. Initial exploration of the dye shows it to be photoactive and capable of facilitating contrathermodynamic styrenoid E/Z isomerization.

Regioselective Transfer Hydrogenative Defluorination of Polyfluoroarenes Catalyzed by Bifunctional Azairidacycle

“…In the HDF of 3-chloro-2,4,5,6-tetrafluoropyridine (8a) under standard conditions, the carbon-fluorine bond at the 4-position was specifically cleaved to yield 3chloro-2,5,6-trifluoropyridine (9a) quantitatively without the erosion of the chlorine substituent (Entry 9). The monodefluorination in preference to dechlorination is a peculiar feature of the nucleophilic aromatic substitution mechanism [51], in contrast with the In contrast, the regioisomeric tetrafluorophthalonitrile (5b) can be reduced stepwise to give mono-and di-defluorinated products, as investigated in our previous work [33].…”

“…In the HDF of 3-chloro-2,4,5,6-tetrafluoropyridine (8a) under standard conditions, the carbon-fluorine bond at the 4-position was specifically cleaved to yield 3-chloro-2,5,6-trifluoropyridine (9a) quantitatively without the erosion of the chlorine substituent (Entry 9). The monodefluorination in preference to dechlorination is a peculiar feature of the nucleophilic aromatic substitution mechanism [51], in contrast with the trend of aromatic hydrodehalogenation involving electron-transfer radical anion fragmentation, in which the heavier halogen favors undergoing fragmentation [52]. The reaction was also compatible with 4-cyano-2,3,5,6-tetrafluoropyridine (8b) possessing a non-fluorine substituent at the 4-position, leading to the formation of 4-cyano-2,5-difluoropyridine (9b) in a 98% yield via double defluorination with 2 equiv of HCOOK (Entry 10).…”

C-F bond activation under transition-metal-free conditions

“…In analogy to previous protocols which utilized i Bu 2 AlH or LiGaH 4 (vide supra), Weaver and co-workers [62] reported the HDF of perfluoroarenes with NaBH 4 (Scheme 20). The advantage of this reaction is that it is compatible with both EDG and EWG substituted substrates (103)(104)(105)(106)(107)(108)(109)(110)(111)(112)(113)(114).…”

“…Using pyrene-based photocatalyst (PC1), N,N-diisopropylethylamine (DIPEA) as the base, common polyfluoroaromatics including hexafluorobenzene (HFB, 55), pentafluorobenzene (PFB, 56), pentafluoropyridine (57), and octafluoronaphthalene (58) could be successfully converted in good yields. And this catalytic system is compatible with an array of functional groups such as ester (59), CF 3 (60), ether (61), and aryl (62). Notably, the 1,2,4,5-TFB (56) is also possible to be synthesized directly from HFB via one-pot di-HDF when a twofold base was used (see ref.…”

Fluoride-Triggered Synthesis of 1-Aryl-2,2-difluoroalkenes via Desilylative Defluorination of (1-Aryl)-2,2,2-trifluoroethyl-silanes

“…Derivatizations of gem -difluoroalkene motifs by additions of a nucleophile are numerous and often lead to the substitution of the fluorine and the creation of C–C bonds. ,, For instance, catalyst-free hydrodefluorination was attempted using LiAlH 4 leading to corresponding monofluoroalkenes 6 in moderate yields (Scheme ). , An excess of LiAlH 4 was necessary to get complete conversion into products 6b and 6c . ( Z )-1-Benzylidene­perfluoro­alkanes 5a – b underwent hydro­de­fluorin­ation to afford the corresponding ( E )-β-(per­fluoro­alkyl)­styrene derivatives 6 with excellent yield and complete stereoselectivity.…”