E.[5,11,15] Nothing specific is known in regards to the mechanistic facts of this
E.[5,11,15] Nothing particular is identified in regards to the mechanistic details of this reaction, aside from the statement that “this formal one-electron reduction of the central carbon was pretty surprising”.[11] This conclusion is still extra convincing if a single takes into account the absence of evident and indubitable reductants for the initial reagents. Again, a priori, it seemed unreasonable to predict that the reaction would create an intermediate that could play the component of a reducing agent. To get much better insight into mechanistic specifics of this process, we attempted a series of reactions between triarylmethanol six and TFA. Some reaction situations had been strictly constant together with the original protocols, whereas other people involved modifications with the reaction conditions, by way of example, the presence or absence of atmospheric oxygen in the reaction vessel and also the variation of the reaction time in the array of 66 h. Regardless of reaction conditions, the crude item was by no means a single element, but as an alternative was two key elements easily observable on TLC plates (see Supporting Information). The items had been identified as trityl radical five and diamagnetic quinone methide 7 (see Scheme 2), which have been isolated in 526 and 139 yield, respectively (see Exp. Section). Lately, quinoide 7 was reported because the only item to result in the oxidative decarboxylation of trityl 5 with nicotinamide MMP-10 medchemexpress 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 method.[16,17] The rationale for this reaction entails the attack from the O2 at the para carbon of the TAM aryl ring followed by the loss of CO2 in the resulting diamagnetic intermediate and a proton-catalyzed heterolytic cleavage with the O bond from the hydroperoxide group.[16,17] The absence of superoxide or the supply of any other peroxide species indicates that the generation of quinoide 7 by the mechanism described in literature, and above, is extremely improbable in our case. A plausible explanation for the simultaneous formation of trityl 5 and diamagnetic quinoide 7 may stick to from what is identified regarding the ready reaction of sterically hindered trityl cations with nucleophiles.[18] Usually, they attack aryl rings in the para position to provide 4-methylenecyclohexa-2,5-diene intermediates analogous to 9 (see Scheme 3). Quite not too long ago C. Decroos et al. reported the formation of trityl radicals via an electron transfer (ET) reaction in between intermediate methylenecyclohexa-2,5-dienes and trityl cations, which were generated in situ by oxidation of trityl five either by potassium hexachloroiridate(IV)[19] or hydrogen peroxide within the presence of peroxidases (horse radish peroxidase, lactoperoxidase, prostaglandin synthase, and also other hemeproteins).[20]European J Org Chem. Author manuscript; available in PMC 2014 April 24.Rogozhnikova et al.PageThis fruitful idea of ET reactions with trityl cations participating as an oxidant delivers the missing link to interpret our results as shown in Scheme 3. The explanation requires the reaction of NPY Y4 receptor web cation 8 with water to yield intermediate cyclohexadiene 9. The decarboxylation of 9 followed by oxidation with cation 8 (or vice versa) gives trityl five and transient trityl ten. The latter need to be readily oxidized by cation 8 in conjunction with the eventual formation of quinoide 7 plus the subsequent crop of trityl 5. The overall balanced reaction fol.