Several novel 2-aryl-1,3-oxazinane and 2-aryl-1,3-oxazolidine derivatives were synthesized from N-benzyl-2-piperidineethanols and N-benzyl-2-piperidinemethanols, respectively, by using electrooxidative methods in methanol. For these reactions, the yields of the corresponding cyclized compounds were significantly increased by using catalytic amounts of iodide ions. In contrast, 3-dialkylamino-1-phenylpropanols afforded the expected cyclic 6-phenyl-1,3-oxazinane derivatives using only a small excess of base.

A range of 1,7-diarylheptane-1,7-diones were electrooxidized in the presence of iodide ions and a base in a mixture of methanol and toluene as the reaction solvents to give the corresponding cyclized 1,2-diaroylcyclopentanes in moderate to good yields. The reactions were carried out under extremely mild reaction conditions for which the optimal amount of electrolytic current varied from 2.05-3.17 F·mol -1 depending on the substrates. The reaction presumably proceeds through a two-electron oxidation process in which the iodide ion plays an important role as the electron carrier.The formation of carbon-carbon bonds is indispensable for the construction of organic compounds, and typically involves well-known classical chemical reactions. In certain situations, however, a more effective synthetic strategy can be provided by the electrooxidative method. Moreover, such electrooxidations can be carried out under very mild reaction conditions, without the use of special, and often harsh, reagents. The use of electrooxidations for carbon-carbon bond formations in the syntheses of various organic compounds has been described in numerous reports, 1 including those from our laboratories. 2 During our investigations, we have discovered that 1,7-diarylheptane-1,7-diones 1 can be converted through intramolecular cyclization into the corresponding 1,2-diaroylcyclopentanes 2, as shown in Scheme 1.Although there are a few reports that describe the conversion of 1,7-diarylheptane-1,7-diones or their derivatives into the corresponding products through classical chemical methods, 3 the electrooxidative cyclization of such compounds is, to the best of knowledge, novel. On a related note, we have previously described the electrooxidative formation of 1,2-diaroylcyclopropanes. 4Initially, the optimal reaction conditions for the anodic cyclization were determined in methanol using 1,7-diphenylheptane-1,7-dione (1a, X = H) as the model substrate. Various combinations of the supporting electrolytes (mediators and bases) are listed in Table 1, along with the yields of the resulting cyclized product 2a (X = H) and recoveries of unreacted substrate 1a. Whereas the use of NaOMe was ineffective (2% yield, Table 1, entry 2), and the use of KI gave a yield of 48% (entry 1), the presence of both KI and NaOMe (1.0 equivalent with respect to substrate 1a) was effective in increasing the yield to 60% (entry 3). Although substituting KI with NaI gave a comparable yield (59%, entry 12), significantly lower yields were observed when KI was substituted with KBr (4%, entry 7) or KCl (3%, entry 8), with nearly full recoveries of 1a. These results indicate that the yield of 2a is strongly affected by the presence of the iodide ion. Lower yields were also observed with the use of a neutral salt such as NaClO 4 (38% yield, entry 9), a weaker base such as NaOAc (42% yield, entry 10), or a strong base such as t-BuOK (47% yield, entry 11).During the early stages of the electrooxidation, the yield of 2a increased in proportion to the amount of current passed (41%...

NISHIKAWA, S.; YAMAMORI, H.; OHASHI, K.; OKIMOTO*, M.; HOSHI, M.; YOSHIDA, T.; Synth. Commun. 43 (2013) 13, 1766-1771, http://dx.

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The reactivity of gangliosides with superoxide anion (O2(•-)) and hydroxyl radical (HO(•)) was evaluated by ESR spin-trapping using 5,5-dimethyl-1-pyrroline-N-oxide under physiological conditions (1/15 M phosphate buffer, pH 7.4). Gangliosides proved to react with HO(•) but not with O2(•-). The second order rate constants for various gangliosides with HO(•) ranged from 5 × 10(9) M(-1)s(-1) to 16 × 10(9) M(-1)s(-1). The rate constant for tetrasialoganglioside, GQ1b, was about three times higher than that of monosialoganglioside, GM1. The reactivity of gangliosides and asialo-GM1 with HO(•) was in the order: GQ1b >GT1b >GD1a >GD1b = GM1 ≫ asialo-GM1. The observed high reactivity of gangliosides probably involves the sialyl residues, since sialic acid was shown to be more reactive with HO(•) than d-glucose under the same conditions.