Synergistic Homogeneous Asymmetric Cu Catalysis with Pd Nanoparticle Catalysis in Stereoselective Coupling of Alkynes with Aldimine Esters

Understanding the nature of a transition-metal-catalyzed process, including catalyst evolution and the real active species, is rather challenging yet of great importance for the rational design and development of novel catalysts, and this is even more difficult for a bimetallic catalytic system. Pd(0)/carboxylic acid combined system-catalyzed allylic alkylation reaction of alkynes has been used as an atom-economical protocol for the synthesis of allylic products. However, the asymmetric version of this reaction is still rather limited, and the in-depth understanding of the nature of active Pd species is still elusive. Herein we report an enantioselective coupling between readily available aldimine esters and alkynes using a synergistic Cu/Pd catalyst system, affording a diverse set of α-quaternary allyl amino ester derivatives in good yields with excellent enantioselectivities. Mechanistic studies indicated that it is most likely a synergistic asymmetric molecular Cu catalysis with Pd nanoparticle catalysis. The Pd catalyst precursor is transformed to soluble Pd nanoparticles in situ, which are responsible for activating the alkyne to an electrophilic allylic Pd intermediate, while the chiral Cu complex of the aldimine ester enolate provides chiral induction and works in synergy with the Pd nanoparticles.

One-Pot, Metal-Free Synthesis of Allyl Sulfones in Water

A one-pot dehydration cross-coupling reaction between allyl alcohols and sodium sulfinates that provides allyl sulfones in good to excellent yields is presented. Its broad substrate scope includes symmetrical and asymmetrical α,α-diaryl- and α-aryl-substituted allylic alcohols and aryl and alkyl sodium sulfinates. For asymmetrical allylic substrates, the E isomer predominates with examples of excellent stereoselectivity. Control experiments provide the basis for a proposed radical-mediated mechanism. The metal-free procedure applies cheap and commercially available tetrabutylammonium tribromide as the catalyst and H2O as the solvent. Notable features of this simple, efficient, weakly toxic, and environmentally benign strategy include mild and convenient operating conditions and readily accessible starting materials.

Pd/Brønsted acid catalysed intramolecular N-allylation of indoles and pyrroles with alkynes for the synthesis of N-fused heterocycles

We, herein, report a Pd(0) and Brønsted acid-catalyzed redox-neutral intramolecular N-allylation of indoles and pyrroles with alkynes for the synthesis of biologically important imidazolidinone-fused N-heterocycles. The allylation is completely atom-economical and is applicable to a wide range of substrates. The methodology eliminates the use of a leaving group or an oxidizing agent, often employed for the allylation of nucleophiles. To the best of our knowledge, N-allylation of indoles and pyrroles with alkynes has not been reported to date.

Rhodium-Catalyzed Regio- and Enantioselective Allylic Sulfonylation from Sulfonyl Hydrazides

A highly regio- and enantioselective allylic sulfonylation has been developed with rhodium and bisoxazolinephosphine (NPN*) ligands from racemic branched allylic carbonates and readily available sulfonyl hydrazides under neutral conditions. Branch-selective allylic sulfones with a >20:1 branch:linear ratio and >99% ee could be synthesized in ≤96% yield. Both Z and E linear allylic carbonates could also be converted into the same chiral branched allylic sulfones with high regio- and enantioselectivities.

Ligand-Enabled Gold-Catalyzed C(sp2)-S Cross-Coupling Reactions

Herein we report C(sp²)-S cross-coupling reactions of aryl iodides and arylsulfonyl hydrazides under ligand-enabled, Au(I)/Au(III) redox catalysis. This strategy operates under mild reaction conditions, requires no prefunctionalized aryl coupling partner, and works across several aryl iodides. The utility of this protocol is highlighted through the synthesis of various medicinally relevant biaryl sulfones. The reaction mechanism is supported with control experiments, mass spectrometry, and NMR studies.

Visible-Light-Induced Tandem Reaction of Allenes with Selenesulfonates Leading to (E)-2,3-Disulfonylpropene Derivatives

A visible-light-induced tandem reaction of allenes with selenesulfonates was developed, providing (E)-2,3-disulfonylpropene derivatives in moderate to good yields. This reaction was featured with simple operation, good regioselectivity and stereoselectivity, and wide functional group tolerance. Photoinduced radical additions via energy transfer were proposed.

Palladium-catalyzed dearomative allylation of indoles with cyclopropyl acetylenes: access to indolenine derivatives

A palladium-catalyzed redox-neutral allylic alkylation of indoles with cyclopropyl acetylenes has been disclosed. Various 1,3-diene indolenine framework bearing a quaternary stereocenter at the C3 position were synthesized straightforwardly in good to excellent yields with high regio- and stereoselectivities. The reaction could be further expanded to the dearomatization of naphthols to synthesize functionalized cyclohexadienones with 1,3-diene motifs. The reaction exhibited high atom economy and good functional group tolerance.

Palladium nanoparticles as efficient catalyst for C-S bond formation reactions

The development of green, economical and sustainable chemical processes is one of the primary challenges in organic synthesis. Herein, we report an efficient and heterogeneous palladium-catalyzed sulfonylation of vinyl cyclic carbonates with sodium sulfinates via decarboxylative cross-coupling. Both aliphatic and aromatic sulfinate salts react with various vinyl cyclic carbonates to deliver the desired allylic sulfones featuring tri- and even tetrasubstituted olefin scaffolds in high yields with excellent selectivity. The process needs only 2 mol% of Pd2(dba)3 and the in situ formed palladium nano-particles are found to be the active catalyst.

Rhodium-catalyzed regio- and enantioselective allylic alkylation of pyrazol-5-ones with alkynes

An atom-economical, regio- and enantioselective allylic alkylation of pyrazol-5-ones with alkynes was developed under rhodium catalysis.

Palladium-NHC-Catalyzed Allylic Alkylation of Pronucleophiles with Alkynes

The palladium-N-heterocyclic carbene (NHC)-catalyzed allylic alkylation of various pronucleophiles with alkynes has been accomplished under mild conditions. The protocol exhibits broad functional group compatibility and high atom economy. Moreover, the catalytic process avoids the use of external oxidants and acid as additives.

A regioselectivity switch in Pd-catalyzed hydroallylation of alkynes

By exploiting the reactivity of a vinyl-Pd species, we control the regioselectivity in hydroallylation of alkynes under Pd-hydride catalysis. A monophosphine ligand and carboxylic acid combination promotes 1,5-dienes through a pathway involving isomerization of alkynes to allenes. In contrast, a bisphosphine ligand and copper cocatalyst favor 1,4-dienes via a mechanism that involves transmetalation. Our study highlights how to access different isomers by diverting a common organometallic intermediate.

Palladium-catalyzed allylation of aminophenol with alkynes to construct C-N bonds

A method for the allylic alkylation of aminophenol with alkynes was developed using a palladium-catalysed allylation reaction with 100% atom economy. A series of structurally diverse N-allylic substituted allylamines were synthesized in good yields with high chemo-, regio-, and stereoselectivities under mild conditions.

Synthesis of multisubstituted arylsulfones via a one-pot, three-component [3 + 3] benzannulation reaction

A one-pot, three-component [3 + 3] benzannulation reaction of α,β-unsaturated carbonyl compounds, bromoallylic sulfones, and sodium sulfinates provided multisubstituted arylsulfones with moderate to good yields.

Photoinduced synthesis of allylic sulfones using potassium metabisulfite as the source of sulfur dioxide

Synthesis of allylic sulfones through a photoinduced three-component reaction of aryl/alkyl halides, potassium metabisulfite, and allylic bromides under ultraviolet irradiation at room temperature is developed. Diverse allylic sulfones are generated in moderate to good yields.

Visible-light-induced cascade sulfonylation/cyclization of N-propargylindoles with aryldiazonium tetrafluoroborates via the insertion of sulfur dioxide

A simple and efficient visible-light-catalyzed cascade sulfonylation/cyclization of N-propargylindoles with K₂S₂O₅ and aryldiazonium tetrafluoroborates for the construction of 2-sulfonyl-substituted 9H-pyrrolo[1,2-a]indoles is developed.

Alkynes as Electrophilic or Nucleophilic Allylmetal Precursors in Transition-Metal Catalysis

Diverse late transition metal catalysts convert terminal or internal alkynes into transient allylmetal species that display electrophilic or nucleophilic properties. Whereas classical methods for the generation of allylmetal species often form stoichiometric by-products, the recent use of alkynes as allylmetal precursors enables completely atom-efficient catalytic processes to be carried out, including enantioselective transformations.

Accessing 1,3-Dienes via Palladium-Catalyzed Allylic Alkylation of Pronucleophiles with Skipped Enynes

An unprecedented palladium-catalyzed allylic alkylation of pronucleophiles with unactivated skipped enynes has been developed. This method provides a straightforward access to a wide array of 1,3-dienes without the need to preinstall leaving groups or employ extra oxidants. The reaction exhibited high atom economy, good functional group tolerance, excellent regioselectivities, and scalability. With D₂O as cosolvent, deuterium could be incorporated in high efficiency.

Palladium-catalyzed allylation of tautomerizable heterocycles with alkynes

A method for the allylic amidation of tautomerizable heterocycles was developed by a palladium catalyzed allylation reaction with 100% atom economy. A series of structurally diverse N-allylic substituted heterocycles can be synthesized in good yields with high chemo-, regio-, and stereoselectivities under mild conditions.

Synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles by cascade annulation of 2-alkynyl-N,N-dialkylanilines

Divergent synthesis of N-alkyl-3-sulfonylindoles and N-alkyl-3-sulfanylindoles from 2-alkynyl-N,N-dialkylanilines and sulfonyl hydrazides has been described.

Palladium-catalyzed tandem cyclization/sulfonylation of homoallenyl amides with sodium sulfinates

A palladium-catalyzed cyclizative sulfonylation of homoallenyl amides has been developed using sodium sulfinates as the sulfonylation reagent and PhI(O₂CCF₃)₂ as the oxidant, providing a facile access to 2-amino-5-sulfonylmethylfurans in good to excellent yields.