Radical Cyclization and 1,5-Hydrogen Transfer in Selected Aromatic Diazonium Salts

Heterocycles ◽  
2014 ◽  
Vol 89 (1) ◽  
pp. 83 ◽  
Author(s):  
Giuseppe Daidone ◽  
Benedetta Maggio ◽  
Gianfranco Fontana ◽  
Demetrio Raffa ◽  
Francesco Ferrante
Keyword(s):  
Hydrogen Transfer ◽  
Radical Cyclization ◽  
Diazonium Salts

Cyclization of 5-hexenyl radicals from nitroxyl radical additions to 4-pentenylketenes and from the acyloin reaction

2003 ◽  
Vol 81 (6) ◽  
pp. 697-704 ◽  
Author(s):  
Huda Henry-Riyad ◽  
Thomas T Tidwell
Keyword(s):  
Ring Opening ◽  
Hydrogen Transfer ◽  
Nitroxyl Radical ◽  
Reaction Times ◽  
Major Product ◽  
Radical Cyclization ◽  
Ring Closure ◽  
Radical Ring ◽  
Intermediate Radical ◽  
Hydrocarbon Solvents

Photochemical Wolff rearrangements were used to form 5-substituted-4-pentenylketenes 1a–1d (RCH=CHCH2XCH2CH=C=O: 1a R = H, X = CH2; 1b R = Ph, X = CH2; 1c R = c-Pr, X = CH2; 1d R = H, X = O), which were observed by IR at 2121, 2120, 2119, and 2126 cm–1, respectively, as relatively long-lived species at room temperature in hydrocarbon solvents. These reacted with the nitroxyl radical tetramethylpiperidinyloxyl (TEMPO, TO·) forming carboxy-substituted 5-hexenyl radicals 3, which were trapped by a second nitroxyl radical forming 1,2 diaddition products 4a–4d. On thermolysis, 4a–4d underwent reversible reformation of the radicals 3, which underwent cyclization forming cyclopentanecarboxylic acid derivatives 6 or 11 as the major products. However, in the case of 1b, the cyclopentane derivative was formed reversibly and on prolonged reaction times the only product isolated was PhCH=CH-(CH2)4CO2H (8b) from hydrogen transfer to Cβ and cleavage of the TEMPO group. Cyclopropylcarbinyl radical ring opening in the cyclized radical 5c from 1c led to the 2-(4-N-tetramethylpiperidinyloxybut-1-enyl)cyclopentane derivative 11 as the major product. In a test for 5-hexenyl radical ring closure in the radical anion intermediate of the acyloin condensation, the ester CH2=CH(CH2)3CO2Et (12a) gave the acyloin 13a (76%) as the only observed product, while PhCH=CH(CH2)3CO2CH3 (12b) with Na in toluene gave 21% of the acyloin product 13b and 42% of 2-benzylcyclopentanol (15) from cyclization of the intermediate radical anion.Key words: ketenes, free radical cyclization, TEMPO, acyloin condensation.

ChemInform Abstract: Preparation of Polycyclic Systems by Sequential 5-exo-Digonal Radical Cyclization, 1,5-Hydrogen Transfer from Silicon, and 5-endo-Trigonal Cyclization.

ChemInform ◽  
2010 ◽  
Vol 32 (29) ◽  
pp. no-no
Author(s):  
Derrick L. J. Clive ◽  
Wen Yang ◽  
Aaron C. MacDonald ◽  
Zhongren Wang ◽  
Michel Cantin
Keyword(s):  
Hydrogen Transfer ◽  
Radical Cyclization

Effect of Niacin on Mitochondria of Allium Cepa Root Cells

1967 ◽  
Vol 25 ◽  
pp. 78-79
Author(s):  
M. Arif Hayat
Keyword(s):  
Nicotinamide Adenine Dinucleotide ◽  
Hydrogen Transfer ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Nicotinamide Adenine ◽  
Root Tips ◽  
Root Cells ◽  
Transfer Processes ◽  
Standard Procedures ◽  
A Cell ◽  
Critical Interest

Although it is recognized that niacin (pyridine-3-carboxylic acid), incorporated as the amide in nicotinamide adenine dinucleotide (NAD) or in nicotinamide adenine dinucleotide phosphate (NADP), is a cofactor in hydrogen transfer in numerous enzyme reactions in all organisms studied, virtually no information is available on the effect of this vitamin on a cell at the submicroscopic level. Since mitochondria act as sites for many hydrogen transfer processes, the possible response of mitochondria to niacin treatment is, therefore, of critical interest.Onion bulbs were placed on vials filled with double distilled water in the dark at 25°C. After two days the bulbs and newly developed root system were transferred to vials containing 0.1% niacin. Root tips were collected at ¼, ½, 1, 2, 4, and 8 hr. intervals after treatment. The tissues were fixed in glutaraldehyde-OsO4 as well as in 2% KMnO4 according to standard procedures. In both cases, the tissues were dehydrated in an acetone series and embedded in Reynolds' lead citrate for 3-10 minutes.

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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