Cobalt nanoparticles-catalyzed aerobic oxygenation and esterification of alkynes via C≡C bonds cleavage

An unprecedented efficient protocol is developed for the oxidative cleavage of C≡C bonds in alkynes to produce structure-diverse esters using heterogeneous cobalt nanoparticles as catalyst with molecular oxygen as the oxidant. A diverse set of mono- and multisubstituted aromatic and aliphatic alkynes can be effectively cleaved and converted into the corresponding esters. Characterization analysis and control experiments indicate high surface area and pore volume, as well as nanostructured nitrogen-doped graphene-layer coated cobalt nanoparticles are possibly responsible for excellent catalytic activity. Mechanistic studies reveal that ketones derived from alkynes under oxidative conditions are formed as intermediates, which subsequently are converted to esters through a tandem sequential process. The catalyst can be recycled up to five times without significant loss of activity.

Palladium-Catalyzed Cascade Carbonylation to α,β-Unsaturated Piperidones via Selective Cleavage of Carbon-Carbon Triple Bonds

A direct and selective synthesis of α,β-unsaturated piperidones by a new palladium-catalyzed cascade carbonylation is described. In the presented protocol, easily available propargylic alcohols react with aliphatic amines to provide a broad variety of interesting heterocycles. Key to the success of this transformation is a remarkable catalytic cleavage of the present carbon-carbon triple bond by using a specific catalyst with 2-diphenylphosphinopyridine as ligand and appropriate reaction conditions. Mechanistic studies and control experiments revealed branched unsaturated acid 11 as crucial intermediate.

Highly Conjugated π-Systems Arising from Cannibalistic Hexadehydro-Diels-Alder Couplings: Cleavage of C-C Single and Triple Bonds

We have investigated the cannibalistic self-trapping reaction of an ortho-benzyne derivative generated from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction. Without adding any specific trapping agent, the highly reactive benzyne is trapped by another bisdiyne molecule in at least three different modes. We have isolated and characterized the resulting products and performed high-level calculations concerning the reaction mechanism. During the cannibalistic self-trapping process, either a C≡C triple bond or an sp-sp3 C-C single bond is cleaved. Up to seven rings and nine C-C bonds are formed starting from two 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne molecules. Our experiments and calculations provide considerable insight into the variety of reaction pathways which the ortho-benzyne derivative, generated from a bisdiyne, can take when reacting with another bisdiyne molecule.

Thiazolium salt-catalyzed C-C triple bond cleavage for accessing substituted 1-naphthols via benzannulation

The first thiazolium salt-catalyzed C-C triple bond cleavage of benzene-linked allene-ynes has been established. The reaction pathway involves [2+2] cycloaddition and ring-opening of in situ generated cyclobutenes with H₂O under mild and convenient conditions, and provides practical access to substituted 1-naphthols with potentially valuable applications.

Transformations of alkynes to carboxylic acids and their derivatives via C[triple bond, length as m-dash]C bond cleavage

Alkynes are building blocks of high synthetic value and their usefulness as precursors to many chemical and biological systems is widely established. Amongst several transformations of alkynes, cleavage of the C[triple bond, length as m-dash]C bond for obtaining diverse compounds is considered to be important. This review, in particular, comprehensively assimilates the transformations of alkynes to carboxylic acids including esters, amides and nitriles resulting from the cleavage of the C[triple bond, length as m-dash]C bond either under the influence of a metal catalyst or via a metal-free approach.

PIFA-mediated esterification reaction of alkynes with alcohols via oxidative cleavage of carbon triple bonds

A metal-free esterification of alkynes via C≡C triple bond cleavage has been developed. In the presence of phenyliodine bis(trifluoroacetate), a diverse range of alkyne and alcohol substrates undergoes triple bond cleavage to produce carboxylic ester motifs in moderate to good yields. The transformation is proposed to proceed via hydroxyethanones and ethanediones as intermediates on the basis of mechanistic studies and exhibits a broad substrate scope and good functional group tolerance.

Palladium-catalyzed cleavage reaction of carbon-carbon triple bond with molecular oxygen promoted by Lewis acid

A new Lewis acid promoted and palladium-catalyzed cleavage reaction of carbon-carbon triple bond with molecular oxygen was reported, in which alkyne or 1.3-diynes is split into carboxylic ester in various alcohols.

Cleavage of a carbon-carbon triple bond via gold-catalyzed cascade cyclization/oxidative cleavage reactions of (Z)-enynols with molecular oxygen

A highly efficient carbon-carbon triple bond cleavage reaction of (Z)-enynols was developed, which offered a new route to highly substituted butenolides. The methodology is realized by a tandem reaction using a single gold(I) catalyst, which could catalyze different reactions of cyclization/oxidative cleavage in the same vessel.

Ruthenium-Catalyzed Oxidative Cleavage of Alkynes to Carboxylic Acids

We describe an efficient method for the oxidative cleavage of alkynes to carboxylic acids using a combination of RuO(2)/Oxone/NaHCO(3) in a CH(3)CN/H(2)O/EtOAc solvent system. Both internal and terminal alkynes, regardless of their electron density, can be oxidized to carboxylic acids in excellent yield (up to 99%). (1)H NMR spectroscopy and ESI-MS experiments provided evidence for alpha-diketones and anhydrides as possible intermediates in these oxidation reactions.

A new ruthenium-catalyzed cleavage of a carbon-carbon triple bond: efficient transformation of ethynyl alcohol into alkene and carbon monoxide

We report a new and efficient ruthenium-catalyzed reaction that transforms ethynyl alcohol into alkene and carbon monoxide. The most efficient catalysts are TpRu(PPh3)(CH3CN)2PF6 (10 mol %) and lithium triflate (20 mol %). The mechanism of this reaction was elucidated using an isotope-labeling experiment.

Carbon-carbon bond cleavage of diynes through the hydroamination with transition metal catalysts

The C-C bond cleavage of terminal and internal diynes takes place readily in the presence of catalytic amounts of Ru3(CO)12 or Pd(NO3)2 and of 2-aminophenol, giving the corresponding benzoxazoles and ketones in good to high yields. There are two different modes of the bond cleavage: (a) an alkyne C-C triple bond is cleaved, and (b) the C-C single bond between the two alkyne groups is cleaved.

A hydroacylation-triggered carbon--carbon triple bond cleavage in alkynes via retro-Mannich type fragmentation

The carbon-carbon triple bond in alkyne is cleaved via hydroacylation followed by retro-Mannich type fragmentation in the presence of aldehyde, which triggers a successive C-C bond cleavage.