Alkynes aerobic oxidation

Novel practical methods using various reagents, such as [Co(OAc)Br],1355 sulfur trioxide,1356 or ds-dioxoruthenium complexes,1357 were developed to transform alkynes to 1,2-diketones. Radical-catalyzed aerobic oxidation using A-hydro-xyphthalimide combined with a transition metal (Co, Cu, or Mn) affords a,P-acetylenic ketones in good yields.1358 Oxidation by the HOF. acetonitrile complex yields diketones, ketoepoxides, or cleavage products.1359 Ozonolysis of acetylenes combined with trapping techniques affords to isolate various derivatives.1360,1361 New information for the ozonolysis of acetylene was acquired by quantum-chemical investigatons.1362... 

Various benzylic alcohols, as well as cinnamyl alcohol and cyclohexanol, were dehydrogenated using large amounts of GiO under sonication [71] or GeO [72]. Despite the high GeO loadings (200 wt%), the material acted as an aerobic oxidation catalyst, since hardly any reaction occurred under nitrogen and the material could be recycled many times. Interestingly, GiO acted as a multifunctional tandem alcohol oxidation-alkyne hydration-aldol condensation catalyst for chal-cone formation directly from phenylacetylenes and benzyl alcohols [73]. 

Terminal alkynes undergo oxidative coupling in the presence of the GuGl-TMEDA catalytic system in [G4GiIm]PF6 under aerobic conditions to produce 1,3-diynes. " Intermolecular Pauson-Khand reactions of strained alkenes with alkynes and Go2(GO)g were performed in [G4GiIm]PF6 either thermally or in the presence of... 

Efficient and regioselective iron-catalyzed aerobic oxidative reactions afforded 3,5-disubstituted isoxazoles 5 from homopropargylic alcohols 4, r-BuONO as the nitrogen source, and H2O under mild conditions (140L6298).A transition metal-free one-pot synthesis of 3,5-disubstituted isoxazoles used terminal alkynes by treatment with -BuLi, then aldehydes and iodine to afford intermediate a-alkynyl ketones 6 converted into isoxazoles 7 with hydroxylamine (14JOC2049). 

Ru2(II,II) complexes are known to catalyze hydrogenation of alkenes and alkynes [235], cross-metathesis of alkenes [198], and intermolecular insertion of diazo compounds into 0-H bond [236]. Ru2(II,III) complexes catalyze the oxidative transformation of secondary amines to imines [237], aerobic oxidations of alcohols... 

SFs-anilines, aldehydes, and arylacetylenes (15EJ01415). This method was inspired by the Fe(III)-catalyzed aerobically oxidative synthesis of quinoHnes developed by Tu and coworkers (09CEJ6332). Both 3- and 4-SF5-anihnes (39 and 11), various aldehydes—aromatic, heterocyclic, formaldehyde, trifluoroacetaldehyde ethyl glyoxylate, and aromatic alkynes can serve as reaction components to provide access to a series of 2-aryl substituted 6(7)-SF5-quinolines 104a—s (Scheme 26). Flowever, cyclization products were not observed when aliphatic alkynes were used under the reported conditions. 

The CDC between A-f-butyl nitrones and terminal alkynes to form alkynylated nitrones in good to excellent yields, catalysed by zinc trifiate, was achieved using 3,3, 5,5 -tetra-tertbutyldipheno-quinone and O2 as oxidants. The alkynylated nitrones were transformed to regioisomerically pure 3,5-disubstituted isoxazoles. Experimental and DFT computational studies of Pd(OAc)2/pyridine-catalysed intramolecular aerobic oxidative amination of alkenes supported a stepwise mechanism that involved (i) the formation of a Pd(ll)-amidate-alkene chelate with release of 1 equiv. of pyridine and AcOH from the catalyst centre, (ii) insertion of alkene into a Pd—N bond. 

In 2008, the Stahl group published the first copper-catalyzed aerobic oxidative amidation of terminal alkynes [200]. An extensive screening of various copper sources, Br0nsted bases, and solvents led to the optimal conditions shown in Scheme 4.51. 

Huang X, Li X, Jiao N (2015) Copper-catalyzed direct transformation of simple alkynes to alkenyl nitriles via aerobic oxidative nincorporation. Chem Sci 6 6355-6360... 

The di-copper-substituted y-Keggin-type silicotungstate [y-H2SiWio036Cu2(/i-l, 1-N3)2]" could act as an efficient reusable homogeneous catalyst for the aerobic oxidative alkyne homocouplmg [125-127]. Various kinds of structurally diverse... 

Ag-catalyzed in situ generation of azomethine ylides from alkynyl A-benzylidene glycinates 35 and their reaction with electron-deficient alkynes 36 were demonstrated by Su and Porco (Scheme 16.17) [26]. This reaction is supposed to be initiated by cycloisomerization of alkynyl imines 35 to isoquinolinium species A with the assistance of AgOTf. Subsequent proton transfer would afford azomethine ylides B with regeneration of Ag(I). 1,3-Dipolar cycloaddition with alkynes 36 followed by aerobic oxidation may furnish pyrroloisoquinoline products 37. It is worth noting that various types of electron-deficient alkynes, irrespective of internal and terminal alkynes, are applicable to this reaction. 

Pries P, Halter D, Kleinschek A, Hartung J. Functionalized tetrahydrofurans from alkenols and olefins/alkynes via aerobic oxidation-radical addition cascades. / Am Chem Soc. 2011 133 3906-3912. 

Chu L, Qing FL. Copper-mediated aerobic oxidative trifluoromethylation of terminal alkynes with MesSiCFs. J. Am. Chem. Soc. 2010 132 7762-7763. 

Addition funnel pressure reactor, 201 Adjustable pressure relief valve, 200 Aerial oxidation, 64 Aerobic product transfer, 193 Aerosol pressure vessel, 198 Air-sensitive materials decomposition, 147 HPLC analysis, 24 recovering, 193 synthesis and handling, 34 Alkyne electron density, 287 Alkyne ligand, 282 Alkyne it donor orbitals, 287 Alkyne levels, 285 Ambient pressure flow cell, 238-244 Ammonia synthesis, 182 Anaerobic column chromatography, 17-18/ Anaerobic transfer, 144 Anionic polymerization, 182 Apparatus design philosophy, 117 Arc lamp... 

Attention is also drawn to other reactions in which a single atom of oxygen from H20 is involved. Hydratases that catalyze the addition of the elements of H20 to activated bonds are involved in the P-oxidation of long-chain alkanoates by yeasts (Section 4.4.4), in aerobic degradation of N-heterocyclic compounds (Chapter 6, Section 6.3.1.1), and both the aerobic and the anaerobic degradation of alkynes (Chapter 6, Sections 6.1.4 and 6.7.1). 

The aerobic dehydrogenative annulation of 2-aryl-substituted pyrroles and indoles for a variety of alkynes, using the system ruthenium(Il) catalyst with oxidant Cu(0Ac)2.H20, was then reported. The reaction was now performed under ambient air as the ideal sacrificial oxidant, thus only 10 mol% of Cu (0Ac)2.H20 could be used for efficient transformations of indoles [(Eq. 89)] [178]. This method could also be applied to synthesize pyrrolo[2,l-a]isoquinolines from 2-arylpyrroles with dialkyl-, diaryl-, or alkylarylacetylenes with an excellent regioselectivity. The competition experiments showed that an electron-deficient alkyne favours this reaction and that the more acidic C-H bond activation is favoured [(Eq. 89)] [178]. 

Another example of ruthenium(II)-catalysed double inserticm of alkynes into C-H and O-H bonds was reported by Lee. The C-H bond oxidative cyclizations of phosphonic acid monoesters or phosphinic acids with alkynes lead to a wide range of phosphaisocoumarins with excellent yields up to 97%. The catalyst was prepared from [RuCl2(p-cymene)]2/KPF6, with 1 equiv. of Ag2C03 and of AgOAc in t-BuOH, under aerobic conditions [(Eq. 101)] [194]. 

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