Rate constant for hydroxylation of a primary alkyl radical by induced decomposition of an alpha hydroperoxyalkyl diazene

Abstract

Rate constants for induced decomposition of 5-hexenyl(1 -hydroperoxy -1 -methylethyl) diazene ((CH3)2C(OOH)N=N-(CH2),CH=CH2, 2) have been estimated. Thermolysis of 2 at 50°C affords 5-hexenyl radicals which abstract the hydroxyl group from 2 in competition with cyclization of 5-hexenyl to cyclopentylmethyl radicals. The known rate constant (kc) for that cyclization was used to clock the bimolecular hydroxyl abstraction process. For reaction in hexafluorobenzene at 50°C, the rate constant for abstraction of hydroxyl from 2 (koH) was found to be dependent on the concentration of 2. For example, at [2] = 0.4 M, koH = 3.2 X lo6 M-I S K I whereas, at [2] = 0.10 M, koH = 1.8 X lo7 M-I s-l. The concentration dependence of koH is attributed to the effects of intermolecular hydrogen bonding and the large absolute values of koH are ascribed to concerted induced decomposition, the 0-0 bond being broken in concert with scission of the nearest C-N bond of the azo function. The relevance of the results, to synthetic application of a-hydroperoxyalkyl diazenes in hydroxyalkylation reactions, is discussed.CHANDRA LAKHANI, LUKOSE MATHEW et JOHN WARKENTIN. Can. J. Chem. 65, 1748Chem. 65, (1987.On a CvaluC les constantes de vitesse pour la dCcomposition induite de I'hextne-5 yl (hydroperoxy-1 methyl-1 Cthyl) diazkne ((CH3)2C(OOH)N=N(CH2)4CH=CH2, (2). La thermolyse du composC 2, 50°C, conduit a des radicaux hexkne-5 yles qui enlkvent le groupernent hydroxyle du compose 2; cette rCaction est en compttition avec la cyclisation de I'hexkne-5 yle en radical cyclopentylmCthyle. On a utilist la constante de vitesse (kc) de cyclisation qui est connue comme chronomktre pour mesurer la vitesse du processus d'enltvement bimoltculaire de I'hydroxyle. Dans le cas de la reaction dans I'hexafluorobenzkne, a 50°C, on a trouvk que la constante de vitesse pour I'enlkvement de I'hydroxyle du composC 2 (kOH) depend de la [Traduit par la revue]

Diastereoselective sp3 C–O Bond Formation via Visible Light-Induced, Copper-Catalyzed Cross-Couplings of Glycosyl Bromides with Aliphatic Alcohols

“…The coupling product 44 was, however, observed in the reaction, and no cyclization product was isolated. Kochi and co-workers have previously demonstrated that carbon radicals can be oxidized rapidly by copper complex to generate alkyl copper intermediates; , therefore, it is possible that oxidation of anomeric C1-radical by a copper­(II) complex to form alkylcopper­(III) complex is faster than a radical 5- exo -trig cyclization. , Next, we hypothesize that if C–O bond formation occurs through out-of-cage, addition of TEMPO (5 equiv) to the reaction mixture would lead to the formation of a TEMPO adduct. As can be seen in Scheme B, the TEMPO-trapping product 45 was not detected in the coupling reaction, suggesting that electron transfer and subsequent interactions with anomeric radical intermediate are likely to take place within the same solvent cage.…”