The stereo-divergent functionalization of alkynes: a comprehensive review

Alkynes are central in crafting pharmaceuticals, agrochemicals, and materials owing to their reactivity and linear geometry. This review unveils cutting-edge advancements in the stereo-divergent functionalization of alkynes, transforming them into invaluable tools for synthesizing stereochemically defined alkenes and alkanes. The review highlights ground-breaking methodologies that achieve exceptional E- and Z-selectivity using innovative catalysts like cobalt, nickel, and palladium through hydrogenation, hydroboration, and hydrosilylation. Recent breakthroughs such as dual-catalytic systems and energy transfer catalysis enable unprecedented stereocontrol. Sustainable strategies including water as a hydrogen source and recyclable catalysts align with green chemistry principles, paving the way for eco-friendly synthesis. This synthesis of cutting-edge techniques and their applications inspire new avenues in synthetic chemistry, offering transformative tools for creating complex molecular architectures with precision and sustainability.

Dehydrogenative Coupling of Terminal Alkynes with O/N-Based Monohydrosilanes Catalyzed by Rare-Earth Metal Complexes

Newly synthesized rare-earth metal alkyl complexes bearing a tripyrrolyl ligand act as excellent precatalysts for the cross-dehydrogenative coupling between various terminal alkynes and O/N-based monohydrosilanes of HSi(OEt)₃/HSi(NMe₂)₃, leading to the formation of a variety of alkoxysilylalkyne and aminosilylalkyne derivatives in good to high yields. The precatalysts LRE(CH₂SiMe₃)(thf)₂ (RE = Y(1a), Er(1b), Yb(1c), L = 2,5-[(2-C₄H₃N)CPh₂]₂(C₄H₂NMe), thf = tetrahydrofuran) were easily prepared in high yields via the reactions of RE(CH₂SiMe₃)₃(thf)₂ with the proligand H₂L in a single step. Mechanistic studies reveal that treatment of 1 with phenylacetylene could generate the active catalytic species: dinuclear rare-earth metal alkynides (L(thf)_n[RE(μ-C≡CPh)]₂L) (RE = Y(5a), n = 1; Yb(5c), n = 0), which could react with HSi(OEt)₃ to produce the coupling product 4aa and the dinuclear rare-earth metal hydrides (L (thf)[RE(μ-H)]₂L) (RE = Y(6a); Yb(6c)). By contrast, prior treatment of 1c with HSi(OEt)₃ proceeds via cleavage of the Si-O bond to produce the dinuclear ytterbium alkoxide (LYb(μ-OEt))₂ 7c, which is inert in the dehydrogenative coupling reaction. The results of the mechanistic studies are consistent with the observation that the reaction is greatly influenced by the addition sequence of precatalyst/alkynes/silanes.

Stereodivergent Catalysis

This review covers diastereo- and enantiodivergent catalyzed reactions in acyclic and cyclic systems using metal complexes or organocatalysts. Among them, nucleophilic addition to carbon-carbon and carbon-nitrogen double bonds, α-functionalization of carbonyl compounds, allylic substitutions, and ring opening of oxiranes and aziridines are considered. The diastereodivergent synthesis of alkenes from alkynes is also included. Finally, stereodivergent intramolecular and intermolecular cycloadditions and other cyclizations are also reported.

Pd@[nBu₄][Br] as a Simple Catalytic System for N-Alkylation Reactions with Alcohols

Palladium nanoparticles, simply and briefly generated in commercial and cheap onium salts using supercritical carbon dioxide, have been found to be an effective catalytic system for additive free N-alkylation reaction using alcohols via cascade oxidation/condensation/reduction steps.