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Described herein is an efficient visible light mediated trifluoromethylation of (hetero)arenes using TFSP as a CF3 source. Various aromatic (hetero)cycles could undergo this protocol to give the corresponding trifluoromethylation products.

Although transition metal carbenes have found widespread applications and difluorocarbene has served as a versatile intermediate, it is still quite challenging to make use of transition-metal difluorocarbenes in synthetic chemistry due to their unpredictable reactivities. In this Highlight, we review recent developments in the transition-metal-catalyzed or -mediated transfer of difluorocarbene and the reactivies and conversions of transition-metal difluorocarbene complexes. We start with the MCF2 bonding, then provide the progress in the transfer of difluorocarbene, and finally briefly discuss the conversions of MCF2 into other metal complexes. The understanding of the interesting reactivities of MCF2 may help design the catalytic transfer of difluorocarbene for various reactions.

Ag-alloyed Cu2ZnSn(S,Se)4 kesterite semiconductors have been attracting considerable attention recently because doping with Ag can suppress the CuZn related anti-site defects, which is the main factor that limits the efficiency of kesterite solar cells. Although the performance of the thin film and the device is enhanced (for example, better crystallinity, fewer deep level defects and longer lifetime of the minority carrier) by doping a small amount of Ag in the CZTS thin film, the density of the defects remains high, and the band alignment of CdS/CZTS is not fully optimized, and the interface carrier concentration is greatly decreased. These phenomena will limit any further improvement in efficiency. In this work, to further increase the performance of the device, the interface of CdS/CZTS for an Ag-alloyed CZTS thin film solar cell was doped with In or Al. Then the properties of the thin film, interface band structure and device performance were investigated. After doping the interface with In or Al, the concentrations of the n-type and p-type carriers at the CdS/CAZTS heterojunction were boosted, and the interface band alignment was optimized, resulting in over 11% efficiency for an Ag-alloyed CZTS (with Al interface doping) thin film solar cell. Moreover, low-cost Al-doped ZnO (AZO) was used to replace indium tin oxide (ITO) as the front electrode after optimization, and more than 10% efficiency of CAZTS device without In was obtained. This study demonstrates the feasibility of controlling the doping of the interface to improve the interface performance of a heterojunction by using a simple spin coating process, and also provided a suitable experimental basis for future low-cost thin film solar cells.

For the dehydroxylation of aldoximes with 4-nitro-1-((trifluoromethyl)sulfonyl)-imidazole (NTSI), slight modifications of reaction conditions resulted in significantly different reaction paths to provide either nitriles or isonitriles. The challenging conversion of aldoximes into isonitriles was achieved under mild conditions.

Described here is the radical-mediated hydrodifluoromethylation of alkenes that occurs under transition-metal-free conditions by using the phosphonium salt [Ph3P+CF2H]Br− under the irradiation of 26 W household compact fluorescent light. The reaction lends itself to a convenient protocol for the installation of a C–CF2H bond while maintaining good functional group tolerance.

The tri- and di-fluoroethylation of alkenes with sulfonium salts, (Ph2S+CH2RF TfO−) (RF = CF3 or HCF2), by visible light photoredox catalysis to give tri-/di-fluoroethyl alkenes or methoxytri-/di-fluoroethylation products are described. It was found that varying the reaction solvent led to changes in the reaction path.

The Fe-catalyzed insertion of fluoromethylcarbenes including trifluoromethylcarbene and difluoromethylcarbene generated in situ from sulfonium salts (Ph2S+CH2CF3−OTf and Ph2S+CH2CF2H −OTf) into X–H (X = Si, C and P) bonds is described. The insertion of both carbenes into the Si–H bond occurred smoothly, and trifluoromethylcarbene could also insert into C–H and P–H bonds.

The O-difluoromethylation of 1,3-diones with S-difluoromethyl sulfonium salt is described. The sulfonium salt was previously believed to be a direct difluoromethylation reagent, but our mechanistic investigation reveals that the O-difluoromethylation reaction proceeds not only via the direct transfer of the CF2H group, but also via a difluorocarbene process. This work represents the first protocol for mild O-difluoromethylation of acyclic 1,3-diones.

The hydroperfluoroalkylation of electron-deficient olefins with perfluoroalkyl iodides promoted by a zinc/viologen system is described. Interestingly, no iodoperfluoroalkylation product was observed without the presence of a radical H-donor.

Difluoromethylation of the activated X-H bond (X = N, O and S) and aliphatic thiols, and gem-difluorocyclopropenation of alkynes with difluorocarbene generated in situ from difluoromethylene phosphobetaine (Ph3P(+)CF2CO2(-)) by decarboxylation occurred smoothly without the presence of any base or other additives.

Copper-catalyzed tandem trifluoromethylation/cyclization of internal alkynes with Umemoto's reagent leads to 3-trifluoromethyl-1,2-dihydronaphthalene derivatives in moderate to good yields. The utility of this copper-catalyzed tandem reaction was demonstrated by oxidizing and reducing the trifluoromethylated product to give naphthalene and tetrahydronaphthalene, respectively, and the development of a short route to a trifluoromethylated analogue of Nafoxidine.

Rhodium-catalyzed allylic C-F bond activation via oxidative addition was found to be a promising approach for the conversion of allylic difluoro-homoallylic alcohols into trisubstituted monofluoroalkenes in good yields with excellent stereoselectivity. The mechanism study shows that C-F bond activation via oxidative addition is involved and PPh3 is responsible for the excellent stereoselectivity.

Boron trihalide-promoted ring-opening reactions of gem-difluorocyclopropyl ketones to give the corresponding β-trifluoromethyl ketones and β-halodifluoromethyl ketones were described. It was found that boron trihalides act as both Lewis acids and nucleophiles and the proximal bond prefers to cleave in this transformation.

The CF3SO3H-promoted ring opening of gem-difluorocyclopropyl ketones prefers to undergo proximal bond cleavage and the subsequent cyclization with nitriles occurred smoothly to give 2-fluoropyrroles.

CF(3)- or -CF(2)-containing tetrahydroquinolines have been asymmetrically synthesized from the reaction of fluorinated N-arylimines with benzyl N-vinylcarbamate in the presence of a chiral phosphoric acid.

Water was found to be a suitable reaction medium for the direct asymmetric aldol reaction of various cyclic ketones with aryl aldehydes catalyzed by a primary-tertiary diamine-Bronsted acid.