Aerobic oxidative alkynylation

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). 

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. 

A Pd(II)-catalysed aerobic oxidative approach to 2,3-dihydro-l//-pyrrolo[l,2-u]indoles from Ai-alkynyl anilines by tandem intramolecular hydroamination and aryl C-H activation process has been reported. Molecular oxygen was the oxidant to recycle the Pd catalysis (Scheme 142). ... 

Murahashi et al. [1] reported Ru(III)-catalyzed aerobic oxidative cyanation of N,N-dimethylanilines with NaCN in 2003, and the next year Li and co-workers developed an efficient Cu(I)-catalyzed alkynylation of tertiary amines with TBHP... 

Copper(I)/TEMPO/NMI-catalyzed Aerobic Oxidation of Alcohols. A novel (bpy)Cu(I)/TEMPO/NMI system has been developed to achieve aerobic oxidation of 1° alcohols and avoid overoxidation. This system gave improved conversion relative to other aerobic oxidation protocols, demonstrating functional group tolerance for a diverse range of substrates bearing aliphatic, aryl, alkenyl, alkynyl, halides, as well as 0-, N-, and 5 -heteroatoms (eq 28). In the presence of unprotected 2° alcohols, 1° alcohols undergo selective oxidation (eq 29). ... 

Rueping M, Koenigs RM, Poschamy K, Fabry DC, Leonori D, Vila C (2012) Dual catalysis crunbination of photocatalytic aerobic oxidation and metal catalyzed alkynylation reactions—C-C bond formation using visible light. Chem Eur J 18 5170-5174... 

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. 

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