Difluoromethyl Radical Triggered Tandem Reaction of N-Allyl Amides to Difluoromethylated ß-Amino Alcohols by Photoredox Catalysis.

An elegant tandem reaction process for transferring N-allyl amide into CF2H-ß-amino alcohol is described. This approach proceeded smoothly under visible light irradiation in the presence of a 3 mol % Ir complex, exhibiting a broad substrate scope and functional group tolerance, and a variety of CF2H-ß-amino alcohols were readily accessed in good to excellent yields under mild conditions. The reliable mechanistic studies revealed that sequential difluoromethyl radical addition/carbocation trap/rearrangement is involved.

Visible-Light-Driven Difluoromethylation of Isocyanides with S-(Difluoromethyl)diarylsulfonium Salt: Access to a Wide Variety of Difluoromethylated Phenanthridines and Isoquinolines.

A highly efficient approach of visible-light-driven radical difluoromethylation of isocyanides to access a wide variety of difluoromethylated phenanthridines and isoquinolines is herein described. Electrophilic S-(difluoromethyl)diarylsulfonium salt proved to be a good difluoromethyl radical precursor under photoredox catalysis. A broad range of isocyanides were tolerated to furnish the corresponding difluoromethylated phenanthridines, isoquinolines, furo[3,2-c]pyridine, and pyrido[3,4-b]indole in moderate to excellent yields under mild conditions. A plausible mechanism was also proposed.

Difluoromethylation of Phenols and Thiophenols with the S-(Difluo-romethyl)sulfonium Salt: Reaction, Scope, and Mechanistic Study.

A facile and practical approach for the difluoromethylation of phenols and thiophenols was described. Making use of the recently developed bench-stable S-(difluoromethyl)sulfonium salt as the difluorocarbene precursor, a wide variety of diversely functionalized phenols and thiophenols were readily converted to their corresponding aryl difluoromethyl ethers in good to excellent yields in the presence of lithium hydroxide. Chemoselectivity of various O,S-nucleophiles toward difluorocarbene was systematically studied, suggesting the reactivity order ArS- > RS-, ArO- > ROH > RO-, ArSH, ArOH, RSH.

Facile difluoromethylation of aliphatic alcohols with an S-(difluoro-methyl)sulfonium salt: reaction, scope and mechanistic study.

A facile and practical approach for the difluoromethylation of aliphatic alcohols with an S-(difluoromethyl)sulfonium salt was developed. A wide variety of alcohols with broad functional groups are compatible to furnish the corresponding alkyl difluoromethyl ethers in good to excellent yields under mild reaction conditions. Control experiments and DFT computational studies suggest that the difluoromethylation of alcohols mainly proceeds via a difluorocarbene pathway involving a five-membered transition state with the participation of water, whose crucial role in this reaction was also elucidated by control experiments.

Air- and Light-Stable S-(Difluoromethyl)sulfonium Salts: C-Selective Electrophilic Difluoromethylation of ß-Ketoesters and Malonates.

Air- and light-stable electrophilic difluoromethylating reagents, S-(difluoromethyl)- S-phenyl- S-(2,4,6-trialkoxyphenyl) sulfonium salts were successfully developed, and the introduction of intramolecular hydrogen bonds plays a crucial role for the stabilities and reactivities of these reagents. C-selective difluoromethylation of a broad range of ß-ketoesters and malonates proceeded smoothly under mild reaction conditions to give good to excellent yields with excellent C/O regioselectivities.

Efficient endo Cycloisomerization of Terminal Alkynols Catalyzed by a New Ruthenium Complex with 8-(Diphenylphosphino)quinoline Ligand and Mechanistic Investigation.

Several new ruthenium complexes supported by the P,N-donor ligand 8-(diphenylphosphino)quinoline (DPPQ) were synthesized, including [RuCl2 (DPPQ)2 ] (1), [Ru(µ-Cl)(DPPQ)2 ]2 (BPh4 )2 (2), and [RuCl(DPPQ)2 Py](BF4 ) (3). Complex 2, with only 1 mol % loading, was found to be catalytically active for the endo cycloisomerization of various terminal alkynols to endo-cyclic enol ethers in moderate to excellent yields. In particular, the 7- and 8-endo heterocyclization can be achieved efficiently to give the seven-membered 3-benzoxepine and eight-membered 3-benzo[d]oxocine derivatives. The stoichiometric reactions of 2 with various alkynol substrates have been carried out to investigate the mechanism, which led to a series of seven-, six-, and five-membered oxacyclocarbene ruthenium complexes including [RuCl(DPPQ)2 {=CCH2 C6 H4 CH2 CH2 O}](BPh4 ) (12) and [RuCl(DPPQ)2 {=CCH2 (CH2 )n CH2 O}](BPh4 ) (n=3, 12'; n=2, 13; n=1, 14). The quantitative transformation of oxacyclocarbene 12 into catalyst 2 and 3-benzoxepine 5 a as well as the efficient catalytic activity of 12 for the endo-cyclization of 2-(2-ethynylphenyl)ethanol (4 a) demonstrated that 12 is a key intermediate involved in the catalytic cycle. Moreover, comparative studies on the modeling reactions and catalytic activity of the series of oxacyclocarbene complexes indicated that the different catalytic activity of 2 for the endo-cycloisomerization of different types of alkynols can be related to the reactivity of the respective ruthenium oxacyclocarbene intermediates.

Metal-free (Boc)2O-mediated C4-selective direct indolation of pyridines using TEMPO.

Direct metal-free C-4-selective indolation of pyridines is achieved for the first time using TEMPO and (Boc)2O. A variety of substituents on both indoles and pyridines are tolerated to give 3-(pyridin-4-yl)-1H-indole derivatives in moderate to excellent yields. This finding provides a novel approach for developing metal-free C-H functionalization of pyridines.

Cu(II)-catalyzed highly regio- and stereoselective construction of C-C double bonds: an efficient method for the ketonization-olefination of indoles.

A general and efficient method for the cross-coupling of indoles with ß-keto esters by using TEMPO/CuSO4·5H2O in air as oxidant has been developed. This reaction features high functional-group compatibility and an excellent selectivity. This methodology provides an alternative approach for the ketonization-olefination of indoles in moderate to good yields.

Metal-free catalyzed oxidative trimerization of indoles by using TEMPO in air: a biomimetic approach to 2-(1H-indol-3-yl)-2,3'-biindolin-3-ones.

A simple, convenient and efficient metal-free catalyzed oxidative trimeric reaction of indoles toward a variety of 2-(1H-indol-3-yl)-2,3'-biindolin-3-one derivatives in moderate to excellent yields has been developed. This transformation proceeds via a tandem oxidative homocoupling reaction by using TEMPO in air as an environmentally benign oxidant. This methodology provides an alternative approach for the direct generation of all-carbon quaternary centers at the C3 position of indoles.