Regio- and Stereoselective Synthesis of Multisubstituted Olefins and Conjugate Dienes by Using α-Oxo Ketene Dithioacetals as the Building Blocks

Metal-Free Tunable 1,2-Difunctionalization of Terminal Alkynes: Synthesis of β-Substituted α,β-Unsaturated Ketones

A metal-free tunable 1,2-difunctionalization of the terminal alkynes showcasing a tandem installation of C-C and C-S bonds has been developed. The key enabling factor for the approach is the use of acetic acid as an acyl source to synthesize β-substituted α,β-unsaturated ketones. The reaction at room temperature leads to the regioselective acylation at the terminal carbon of alkynes, whereas at -78 °C, the acylation occurs at the more substituted carbon.

Copper(I)-Catalyzed Nitrosylation/Annulation Cascade of Enaminones with tert-Butyl Nitrite: Access to 1H-1,2,3-Triazole 2-Oxides

The direct synthesis of triazole 2-oxides has posed a challenge in the field of N-heterocyclic chemistry. A novel copper(I)-catalyzed nitrosylation/annulation cascade of enaminones provides a straightforward route to 1H-1,2,3-triazole 2-oxides by forming new C-N, N=N, and N-N bonds using noncorrosive tert-butyl nitrite (TBN) as both the N and NO sources. The synthetic protocol features easily accessible starting materials, wide substrate scopes, and good tolerance toward various functional groups while avoiding use of explosive azides.

Rhodium catalysts with superbulky NHC ligands for the selective α-hydrothiolation of alkynes

Eight rhodium complexes-including four new compounds-with the generic formula [RhCl(cod)(NHC)] (cod is 1,3-cyclooctadiene) differing by the size of their N-heterocyclic carbene (NHC) ligand were prepared, characterized, and found to be catalytically active in the hydrothiolation of terminal alkynes with aliphatic or aromatic thiols. The steric bulk of the carbene was found to markedly influence the reaction rate and selectivity. In particular, superbulky NHCs led to the almost quantitative formation of the sole α-vinyl sulfide products. The experimental conditions were optimized to allow the straightforward synthesis of a broad range of mono- and disubstituted α-adducts starting from terminal alkynes (18 examples) and thiols (5 examples). Altogether, the procedure devised in this study provides an easy access to α-vinyl sulfides with full atom economy and a low catalyst loading.

Copper(II)-Mediated Intramolecular Cyclopropanation of Ketene N,X-Acetals (X = S, O, N) under Mild Conditions

CuBr₂-mediated intramolecular oxidative cyclopropanation of α-oxo ketene N,S-acetals was efficiently achieved to afford 2-thioalkyl-3-azabicyclo-[3.1.0]hexenes under mild conditions. 2-Oxyalkyl- and 2-aminoallyl-3-azabicyclo-[3.1.0]hexenes were also obtained from the corresponding α-oxo ketene N,O- and N,N-acetals. Further C-S bond transformations led to diverse 2-aryl-substituted 3-azabicyclo[3.1.0]hexene derivatives in good to high yields.

Palladium-Catalyzed C-S Bond Cleavage with Allenoates: Synthesis of Tetrasubstituted 2-Alkenylfuran Derivatives

Palladium-catalyzed C-S cleavage of tetrasubstituted internal alkene α-oxo ketene dithioacetals was realized with allenoates as the coupling partners, efficiently affording tetrasubstituted 2-alkenylfuran derivatives with excellent regioselectivity under mild conditions. Allenoates acted as C1 synthons in the desulfurative [4 + 1] annulation.

Copper-promoted direct C–H alkoxylation of S,S-functionalized internal olefins with alcohols

Efficient copper-promoted direct C–H alkoxylation of internal olefins, α-oxo ketene dithioacetals, was achieved with alcohols as the alkoxylating reagents.

Palladium-catalyzed C–S bond activation and functionalization of 3-sulfenylindoles and related electron-rich heteroarenes

A novel palladium-catalyzed approach for constructing functionalized heteroarenes via C–S bond cleavage and C–C bond formation has been demonstrated.

Pd-Catalyzed C-S Activation/Isocyanide Insertion/Hydrogenation Enables a Selective Aerobic Oxidation/Cyclization

Unique imidoylation of thioorganics with isocyanides endows an unprecedented aerobic oxidation process. Catalyzed by Pd(Ph3P)2Cl2 in the presence of Ph3SiH under N2 then upon exposure to air, a wide range of α-acyl ketene dithioacetals react with isocyanides to afford 5-hydroxy-α,β-unsaturated γ-lactams via a C-S bond activation, isocyanide migratory insertion, hydrogenation, selective aerobic oxidation, and intramolecular nucleophilic addition sequence.

Synthesis of Multisubstituted Olefins through Regio- and Stereoselective Addition of Interelement Compounds Having B-Si, B-B, and Cl-S Bonds to Alkynes, and Subsequent Cross-Couplings

Multisubstituted olefins are fundamental motifs in organic compounds. In this account, we describe the synthesis of organic molecules bearing an olefinic moiety by the transition-metal-catalyzed regio- and stereoselective addition of a variety of interelement compounds to alkynes. Regio- and stereoselective silaboration, diborylation, and chlorothiolation have been achieved by using the transition-metal catalysts. The subsequent cross-coupling reactions of the boron-containing alkenes to install various aryl groups afforded the corresponding tri- and tetraarylated olefins. This account describes our research on the highly regio- and stereoselective synthesis of multifunctionalized olefins such as tetraarylethenes with four different aryl groups.

Copper-mediated intramolecular oxidative C-H/N-H cross-coupling of α-alkenoyl ketene N,S-acetals to synthesize pyrrolone derivatives

CuCl2 and CuBr2-mediated intramolecular oxidative C-H/N-H cross-coupling/halogenation of β-thioalkyl-substituted α-alkenoyl ketene N,S-acetals occurred efficiently, affording 4-halo-5-thioalkyl-3-pyrrolones. Tunable C-S and C-halo bond transformations of the resultant pyrrolone derivatives led to highly functionalized N-heterocyclic compounds.

An efficient desulfitative C–C cross coupling of fused thiazolidine-2-thione with boronic acids and boronic acid pinacol esters: formation of fused thiazoles

An efficient Pd(0)-catalyzed Cu(i)-mediated desulfitative C–C cross-coupling of benzo-fused thiazolidine-2-thione with boronic acids under neutral conditions and boronic acid pinacol esters under basic conditions has been demonstrated.

Vilsmeier cyclization of α-acetyl-α-aroyl ketene-N,S-acetals: direct and efficient synthesis of halogenated pyridin-2(1H)-ones

An efficient synthetic route to 3-aroyl-5-formyl-4-halo pyridin-2(1H)-ones has been developed via Vilsmeier cyclization of 2-(ethylthio(arylamino)methylene)-1-alkylbutane-1,3-dione.

Efficient synthesis of polysubstituted olefins using stable palladium nanocatalyst: applications in synthesis of tamoxifen and isocombretastatin A4

A phosphine-free stable palladium nanocatalyst was used for an efficient synthesis of polysubstituted olefins from N-tosylhydrazones and aryl iodides. This methodology was successfully utilized in the synthesis of biologically important tamoxifen and isocombretastatin A4. The nanocatalyst was easily recovered and reused without any apparent loss in size and catalytic activity.

Recent developments of ketene dithioacetal chemistry

Ketene dithioacetals are versatile intermediates in organic synthesis. Extensive research, since the last decade, has given rise to new prospects in their chemistry. The objective of this review is twofold: first, to highlight the new prospects in the chemistry of functionalized ketene dithioacetals, and second, to provide an intrinsic link between ketene dithioacetal groups and a variety of other functional groups, which has brought out many new facts that will assist in future designs.

Cyclocondensation of arylhydrazines with 1,3-bis(het)arylmonothio-1,3-diketones and 1,3-bis(het)aryl-3-(methylthio)-2-propenones: synthesis of 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity

Two efficient highly regioselective routes for the synthesis of unsymmetrically substituted 1-aryl-3,5-bis(het)arylpyrazoles with complementary regioselectivity starting from active methylene ketones have been reported. In the first protocol, the newly synthesized 1,3-bis(het)aryl-monothio-1,3-diketone precursors (prepared by condensation of active methylene ketones with het(aryl) dithioesters in the presence of sodium hydride) were reacted with arylhydrazines in refluxing ethanol under neutral conditions, furnishing 1-aryl-3,5-bis(het)arylpyrazoles 7, in which the het(aryl) moiety attached to the thiocarbonyl group of monothio-1,3-diketones is installed at the 3-position. In the second method, the corresponding 3-(methylthio)-1,3-bis(het)aryl-2-propenones (prepared in situ by base-induced alkylation of 1,3-monothiodiketones) were condensed with arylhydrazines in the presence of potassium tert-butoxide in refluxing tert-butyl alcohol, yielding 1-aryl-3,5-bis(het)arylpyrazoles 9 with complementary regioselectivity (method A). The efficiency of this protocol was further improved by developing a one-pot, three-component procedure for the synthesis of pyrazoles 9, directly from active methylene ketones, by reacting in situ generated 3-(methylthio)-1,3-bis(het)aryl-2-propenones with arylhydrazines in the presence of sodium hydride (instead of potassium tert-butoxide as base). The structures and regiochemistry of newly synthesized pyrazoles were confirmed from their spectral and analytical data along with X-ray crystallographic data of three pairs of regioisomers.