Oxidation and Dimerization

Mixed cuprates of the type LiCuR R are oxidized to homo-coupled (R 2 and R 2) and/or cross-coupled (R R ) dimers 259, 300). Oxidation of a mixture of two cuprates containing a considerable excess of one affords the cross-coupled dimer in high yield 61, 292, 297). Oxidation 

The thermal decomposition of aryl- and vinylcopper compounds is an alternative method of obtaining dimeric products from organocopper compounds. Both methods have been used extensively by Kauffmann and co-workers 153-164). Thermal decomposition of organocopper compounds of the type ZN=C(R)—CHRCu affords suitable precursors for a variety of 1,4-diketones. Thermal decomposition is not applicable to all organocopper compounds (see Section III,B,3). Various oxidations and dimerizations are listed in Table V. 

Copper compound Conditions Temp. Oxidant (°C) Dimer yield (%) References 

The reaction of 2,2 -dilithiobiphenyl, or the analogous Grignard reagent, with excess copper(II) chloride gave a mixture of products from which biphenylene and o-tetraphenylene were isolated 235, 304). Other products were tetra- and octaphenyls. The reaction was explained in terms of the formation of a copper(II) ate complex (IX) which, under the influence of further Cu ions, oxidatively couples to give a 60% 

---

Fig. 6. One-electron oxidation and dimerization where (21a) is a dye, (21b) a radical cation, and (21c) a dimer.

Scott was able to leverage the same type of methodology in an impressive display in which /V-methyltryptamine was dimerized directly to afford chimonanthine (7) (Scheme 9.2b) [9c]. Deprotonation of the indole 1H proton with methyl Grignard followed by treatment with FeCl3 accomplished the singleelectron oxidation and dimerization of the indole moiety. The racemic and meso stereoisomeric products were obtained as a mixture in 19 % and 7 % yields, respectively. Takayama later found hypervalent iodine to be a superior oxidant, affording yields of 17 % and 30 %, respectively [9j]. In both cases, however, as in the case of Hendrickson s example, stereocontrol could not be achieved. 

The reaction of 2-mercaptopyridine (PYSH) (7), with di-iodine in a molar ratio of 1 2 led to the oxidation and dimerization of the ligand and produced (PYS-PYSH)+... 

Isomerization, Oxidation, and Dimerization of Radical Cations of Stiibene Derivatives... 

The initial attack in the anodic oxidation of papaverine73 probably involves a similar attack further oxidation and dimerization leads to the isolated product, 12,12 -bis-(2,3,9,10-tetramethoxyindolo[2,l-a])isoquin61yl. The electrooxidation of a tetramethoxy substituted 2-methyl-l-phenethyl-1,2,3,4-tetrahydroisoquinoline to a dibenzoquinolizinium derivative is analogous.76... 

The third step in the process involves cooling the reaction gases below their dew point, so that a liquid phase of weak nitric acid is formed. This step effectively promotes the state of oxidation and dimerization (Reactions 3 and 4), and removes water from the gas phase. This in turn increases the partial pressure of the nitrogen peroxide component. 

Should the data concerning carbamazepine be of more general validity, estuarine areas, and even more the deltas because of their shallower water, could be important locations for the photochemical transformation of pollutants transported by river water. Also note that carbamazepine underwent oxidation and dimerization in the presence of Fe(III) + chloride, and chlorination only to a... 

The initial attack in the anodic oxidation of papaverine [75] probably involves a similar attack further oxidation and dimerization leads to the isolated product, 12,12 -bis-(2,3,9,10-tetramethoxyindolo[2,l-fl]isoquinolyl). An analogous reaction is the electrooxidation of a tetramethoxy-substituted 2-methyl-l-phenethyl-l,2,3,4-tetrahydroisoquinoline to a dibenzoquinolizinium derivative [76] and the oxidation of A,A -triphenyl-( -phenyle-nediamine to 9,10-diphenylphenazine [77]. Intramolecular Michel addition of nitrogen in a tetrahydroquinoline derivative to an o-quinone moity have resulted in the formation of a 5,6-dihydrodibenz[6,d]indolizine derivative [78]. A similar ring closure occurs during the oxidation of various catecholamines [79] and similar compounds [79] to indoles. Cyclic a-carbonylazo compounds, generated by anodic oxidation of the hydrazines, may be trapped by reaction with dienes to the expected heterocycles [80]. 

D Annibale and his colleagues [99] performed experiments on VA oxidation using MnP from Lentinus edodes. They demonstrated two different types of reactions occurring in the presence and absence of GSH. When GSH was not included in the reaction mixture of MnP, Mn +, VA, H2O2 and chelator, aromatic ring cleavage, side chain oxidization and dimerization of VA were detected. (The main metabolite was y-muconolactone (58%), and three dimerization products were also observed [31] 2.3 and 1.8%, respectively). However, with the addition of GSH, veratraldehyde was the only metabolite formed. Veratryl alcohol oxidation was 32 and 14% in nonthiol and thiol mediated reactions, respectively. Under both conditions, oxidation depended strictly on the presence of both Mn + and H2O2. 

Yields of 3-chloroindoles reach 90% while performing the reaction under nitrogen and decrease considerably in acetic acid in the presence of oxygen. Under these conditions together with chloroindoles the products of oxidation and dimerization are formed (Scheme 49). 

Pasternak, M. and A. Morduchowitz. 1983. Photochemical oxidation and dimerization of alkylbenzenes. Selective reactions of the alkyl side groups. Tetrahedron Lett. 24, 4275-4278. 

The mechanistic foundations of indole nitration have been well established <72HC 25-2)539>. While the 3-position is the preferred site for electrophilic attack, nitration of indole itself is complicated by oxidation and dimerization. In strongly acidic solution, the 3-position is protonated and reaction takes place at the 5-position under the directing influence of the iminium moiety (Scheme 114). 

---