Catalytic Electrophilic Thiocarbocyclization of Allenes.

An efficient approach via catalytic electrophilic thiocarbocyclization of allenes to construct indene-based sulfides with excellent regioselectivities is disclosed. The reactions were carried out at low temperatures by selenide catalysis in the presence of TMSOTf. Not only electrophilic arylthio reagents but also electrophilic alkylthio reagents worked well under these conditions. Furthermore, the method could be applied to intermolecular azidothiolation of allenes.

Chalcogenide-Catalyzed Intermolecular Electrophilic Thio- and Halofunctionalization of gem-Difluoroalkenes: Construction of Diverse Difluoroalkyl Sulfides and Halides.

Thio- and halodifluoromethylated compounds are an important class of compounds in medicinal chemistry and organic synthesis. Herein, we report a facile method for the construction of these compounds via chalcogenide-catalyzed intermolecular electrophilic thio- and halofunctionalization of gem-difluoroalkenes. Simple treatment of gem-difluoroalkenes with electrophilic sulfur/halogen reagents and various O- or N-nucleophiles affords diverse multifunctionalized thio- and halodifluoromethylated compounds. This reaction features a relatively broad substrate scope, good functional group tolerance, and mild reaction conditions.

Enantioselective Construction of Axially Chiral Amino Sulfide Vinyl Arenes by Chiral Sulfide-Catalyzed Electrophilic Carbothiolation of Alkynes.

The enantioselective construction of axially chiral compounds by electrophilic carbothiolation of alkynes is disclosed for the first time. This enantioselective transformation is enabled by the use of a Ts-protected bifunctional sulfide catalyst and Ms-protected ortho-alkynylaryl amines (Ts=tosyl; Ms=mesyl). Both electrophilic arylthiolating and electrophilic trifluoromethylthiolating reagents are suitable for this reaction. The obtained products of axially chiral vinyl-aryl amino sulfides can be easily converted into biaryl amino sulfides, biaryl amino sulfoxides, biaryl amines, vinyl-aryl amines, and other valuable difunctionalized compounds.

Chiral selenide-catalyzed enantioselective synthesis of trifluoromethylthiolated 2,5-disubstituted oxazolines.

Chiral selenide-catalyzed enantioselective trifluoromethylthiolation of 1,1-disubstituted alkenes is disclosed. By this method, a variety of chiral trifluoromethylthiolated 2,5-disubstituted oxazolines were obtained in good yields with high enantioselectivities. This work not only provides a new pathway for the synthesis of chiral oxazolines, but also expands the library of chiral trifluoromethylthiolated molecules.

PIDA-Mediated Formal Olefinic C=C Bond Cleavage of α-Oxo-Ketene N,N-Acetals toward Substituted Oxazolines.

The hypervalent iodine reagent PhI(OAc)2 (PIDA) mediated the formal oxidative C=C bond cleavage and subsequent cyclization of internal olefins, that is, α-oxo-ketene N,N-acetals, which afforded substituted oxazolines. Isothiazoline derivatives were obtained from the reactions of α-thioxo-ketene N,N-acetals with PIDA under the same conditions. Hydrolysis of the resultant oxazoline derivatives led to highly functionalized oxazolones. A plausible mechanism was proposed based upon the formation of isothiazoline-type intermediates.

α,ß-Unsaturated N-Acylindoles: An Alternative Class of Michael Acceptors and Their Application in Asymmetric Borylation.

Copper(I)-catalyzed enantioselective borylation of α,ß-unsaturated N-acylindoles as well as N-acylpyrroles was efficiently achieved by means of bis(pinacolato)diboron (B2pin2), affording the enantioenriched products in excellent yields with up to 99% ee. The present work provides an alternative class of Michael acceptors, that is, α,ß-unsaturated N-acylindoles, for potential asymmetric transformations.

Copper-Catalyzed Asymmetric Borylation: Construction of a Stereogenic Carbon Center Bearing Both CF3 and Organoboron Functional Groups.

Copper-catalyzed borylation of ß-trifluoromethyl-α,ß-unsaturated ketones was efficiently achieved by means of bis(pinacolato)diboron (B2pin2), affording the enantioenriched products in good yields with high enantioselectivities. CuI and (R,S)-Josiphos consist of the most efficient catalyst system under mild conditions. In the absence of the chiral ligand, the reactions could be performed more efficiently to form ß-ketone derivatives which were directly borylated and indirectly trifluoromethylated at the ß-carbon atom of the α,ß-unsaturated ketone substrates. The present protocol provides a promising method to access a stereogenic carbon center bearing both CF3 and organoboron functional groups.

Rhodium(iii)-catalyzed sp(2) C-H bond addition to CF3-substituted unsaturated ketones.

Rhodium(iii)-catalyzed conjugate addition of aromatic and olefinic C-H bonds to CF3-substituted unsaturated ketones was efficiently achieved. Both arene and olefin substrates bearing a chelate assisted-directing group were coupled with a variety of ß-trifluoromethyl-α,ß-unsaturated ketones with excellent atom-economy, high yields, and broad substrate scopes.

Brønsted acid activation strategy in transition-metal catalyzed asymmetric hydrogenation of N-unprotected imines, enamines, and N-heteroaromatic compounds.

Asymmetric hydrogenation plays an important role in organic synthesis, but that of the challenging substrates such as N-unprotected imines, enamines, and N-heteroaromatic compounds (1H-indoles, 1H-pyrroles, pyridines, quinolines, and quinoxalines) has only received increased attention in the past three years. Considering the interaction modes of a Brønsted acid with a Lewis base, Brønsted acids may be used as the ideal activators of C=N bonds. This Minireview summarizes the recent advances in transition-metal-catalyzed, Brønsted acid activated asymmetric hydrogenation of these challenging substrates, thus offering a promising substrate activation strategy for transformations involving C=N bonds.