E.[5,11,15] Practically nothing specific is recognized concerning the mechanistic specifics of this
E.[5,11,15] Nothing specific is recognized regarding the mechanistic information of this reaction, aside from the statement that “this formal one-electron reduction on the central carbon was quite surprising”.[11] This conclusion continues to be much more convincing if one particular requires into account the absence of evident and indubitable reductants for the initial reagents. Once again, a priori, it seemed unreasonable to predict that the reaction would generate an intermediate that could play the aspect of a lowering agent. To get much better insight into mechanistic facts of this course of action, we attempted a series of reactions among triarylmethanol 6 and TFA. Some reaction situations were strictly constant together with the original protocols, whereas other people involved modifications with the reaction circumstances, as an example, the presence or absence of atmospheric oxygen in the reaction vessel plus the variation with the reaction time inside the range of 66 h. Irrespective of reaction circumstances, the crude solution was by no means a single component, but rather was two key elements conveniently observable on TLC plates (see Supporting Details). The goods had been identified as S1PR5 site trityl radical five and diamagnetic quinone methide 7 (see Scheme two), which were isolated in 526 and 139 yield, respectively (see Exp. Section). Lately, quinoide 7 was reported because the only product to outcome in the oxidative decarboxylation of trityl 5 with nicotinamide adenine dinucleotide phosphate hydride (NADPH)O2, which was catalyzed by rat, pig, and human liver microsomes,[16] plus the reaction of 5 with superoxide, which was generated by a xanthinexanthine oxide system.[16,17] The rationale for this reaction involves the attack from the O2 in the para carbon with the TAM aryl ring followed by the loss of CO2 in the resulting diamagnetic intermediate as well as a proton-catalyzed heterolytic cleavage with the O bond with the hydroperoxide group.[16,17] The absence of superoxide or the source of any other peroxide species means that the generation of quinoide 7 by the mechanism described in literature, and above, is highly improbable in our case. A plausible explanation for the simultaneous formation of trityl five and diamagnetic quinoide 7 may well comply with from what’s known in regards to the prepared reaction of sterically hindered trityl cations with nucleophiles.[18] Normally, they attack aryl rings in the para position to give 4-methylenecyclohexa-2,5-diene intermediates analogous to 9 (see Scheme 3). Really not too long ago C. Decroos et al. reported the formation of trityl radicals through an electron transfer (ET) reaction involving intermediate methylenecyclohexa-2,5-dienes and trityl cations, which had been generated in situ by oxidation of trityl 5 either by potassium hexachloroiridate(IV)[19] or hydrogen peroxide within the presence of peroxidases (horse radish peroxidase, lactoperoxidase, prostaglandin synthase, along with other MNK1 Purity & Documentation hemeproteins).[20]European J Org Chem. Author manuscript; available in PMC 2014 April 24.Rogozhnikova et al.PageThis fruitful notion of ET reactions with trityl cations participating as an oxidant provides the missing hyperlink to interpret our benefits as shown in Scheme 3. The explanation includes the reaction of cation 8 with water to yield intermediate cyclohexadiene 9. The decarboxylation of 9 followed by oxidation with cation 8 (or vice versa) provides trityl 5 and transient trityl ten. The latter should be readily oxidized by cation eight in addition to the eventual formation of quinoide 7 as well as the subsequent crop of trityl five. The overall balanced reaction fol.
