O-Quinoneimine

Nickel carbonyl reacts with o-quinoneimine with displacement of all the carbonyl groups to form Ni(N2C H4)2 (XCII) 41), and Fe(CO)5 reacted with aminotropone imines to form (XCIII R = Me, Et, Ph, p-MeC6H4). 

Scheme 2.38 Lewis acid-promoted annulation of o-quinoneimine dibenzimides 266 with...

However, the ZnCl2-catalyzed reaction of o-quinoneimine dibenzimide 266a (R = = H) and allylstannane 264 resulted in the formation of ring-allylated... 

The most frequently studied systems involving interposed dehydration are those in which p- or o-hydroxylamino phenol is dehydrated to the corresponding quinoneimine. This reaction is interposed in the reduction of o- and -nitrophenols, which follows scheme (88) (35) ... 

At present, many coordination compounds, which contain ligands capable of participating in easy and reversible one-electron redox processes, are known. Nitroxyl radicals, spatially hindered o-quinones, quinoneimines, and phenoxazinone systems are examples of such ligands. 

The BF3-catalyzed reaction of a-aminoaldehydes with 10 is valuable for highly stereoselective synthesis of 2,3,5-trisubstituted pyrrolidines with all -cis configurations (Equation (50)).197 The stereochemical outcome like chelation-controlled stereochemistry might result from the inherent conformational arrangement of the aldehyde-BF3 complex. />-Quinoneimines, o-quinones, and a-alkoxyhydroperoxides undergo similar types of [3 + 2]-cycloadditions with allylsilanes to afford dihydro indoles, dihydrobenzofurans, and 1,2-dioxolanes, respectively.164,175,198... 

Coupling carbonyl compounds with aromatic amines bearing amino, hydroxy, or thiol groups in o -positions is known to be a general method for the synthesis of 1,3-benzazoles, with the intermediate formation of the respective 2,3-dihydro derivatives. No heterocyclization occurs, however, in the reaction of o-phenylene-diamines or o-aminophenols with /i-quinones. In these cases, the reaction stops at the stage of formation of the deeply colored quinoneimine 105 which is similar to that obtained by the previously studied reaction of a variety of / -substituted anilines with derivatives of p -bcn/oquinonc.6 Compounds 10 do not undergo cyclization under heating or irradiation of its solution (Scheme 4). 

Prominent examples are the redox pairs o- or p-quinones/hydroquinones, the corresponding quinoneimines, the diimines and the azobenzenes and disulfides [68]. V. Stackelberg [69] has pointed out that the exclusive formation or cleavage of 0-H, N-H, S-H, or S-S bonds is a necessary precondition for reversible organic redox partners. This can be clearly recognized in the case of the quinone/hydroquinone redox reaction (cf. Eq. (13)). Only O -H bonds are formed or cleaved. In contrast, in the case of the acetone/isopropanol redox system, 0-H and C-H bonds participate. 

Table 3 lists the dose and incidence of the hepatotoxicity for various drugs, some of which have been withdrawn as a result of these findings. Some of the drugs show effects on liver function earlier than the actual onset of liver toxicity, with serum aminotransferase levels raised by threefold the upper limit of normal (ULN). The incidence of this is much higher and can show a classical dose response for instance, tolcapone, a catechol-O-methyltransferase inhibitor used as an adjunct to levodopa in Parkinson s disease, produces threefold the ULN in 1-3% of patients receiving 100 mg TID and 3.7% of patients receiving 200 mg TID (Olanow and Watkins 2007). Tolcapone, an o-nitrocatechol, is metabohzed to reactive intermediates - o-quinone or quinoneimine species - by human fiver microsomes (Smith et al. 2003). 

Willstatter and collaborators discovered o-benzoquinone (I) by oxidising a solution of catechol in ether by silver oxide, and prepared />-quinoneimine (II) and diimine (III) by the similar oxidation of />-aminophenol and p-phenylenediamine ... 

---