Minisci procedure

This reaction resembles decarboxylation of carboxylates during electrode one-electron oxidation (Kolbe reaction). Kolbe reaction also consists of one-electron oxidation, decarboxylation, and culminates in dimerization of alkyl radicals just after their formation at the electrode surface. When the sulfate radical acts as a one-electron oxidant, the caboradical dimerization is hampered. The radicals can be used in preparative procedures. One typical example is alkylation of heterocyclic nitrogen bases (Minisci et al. 1983). This difference between Kolbe reaction and the reaction with the help of a dissolved electrode (the sulfate radical) deserves some explanation. The concentration of the one-electron oxidation products in the electrode vicinity is significantly higher than that in the bulk of the solution. Therefore, in the case of anode-impelled reactions, the dimerization of radicals produced from carboxylates proceeds easily. Noticeably, 864 secures the single electron nature of oxidation more strictly than an anode. In electrode reactions, radical intermediates can... 

A third approach to the generation of PINO from HPI is the one first described by Ishii and coworkers" and subsequently followed by Minisci and coworkers" for synthetically useful transformations of alcohols or other H-donor substrates into carbonyl derivatives. It entails the use of catalytic amounts of a Co(II) salt, usually Co(OAc)2, with O2 in the presence of m-Cl-benzoic acid (MCBA)". The synthetic scope of this procedure will be commented on later, but it is sufficient to point out here that PINO is produced from HPI in a catalytic cycle through a short-living Co(III) oxidizing intermediate ... 

Another method capable of inducing a TEMPO-catalysed oxidation is the one reported by Minisci and coworkers, which exploits Mn(II)-Co(II) nitrates in AcOH solution at 20-40 °C in the presence of 02 °. Primary and secondary alcohols, including aliphatic ones, are oxidized very efficiently. This procedure gave a good Hammett correlation vs. a in the oxidation of X-substituted benzyl alcohols with a large p value of —1.44... 

Minisci and coworkers followed Ishii s procedure, and implemented it in the oxidation of benzyhc alcohols to benzaldehydes in almost quantitative yields" (Table 12). A,Af-dimethylbenzylamines were converted into aldehydes in good yields, by using catalytic amounts of either HPI or A-hydroxysuccinimide (HSI) for the formation of the corresponding aminoxyl radical intermediates. Because the attempted oxidation of primary and secondary amines caused the degradation of catalyst HPI, protection of the amino group in those substrates by acetylation was considered. This led one to develop... 

Even more pronounced steric effects have been observed for the free radical alkylation of protonated N-heterocyclic bases by the procedure of Minisci ... 

In Reaction 1-100, the sulfate anion radical, and not the anode, acts as a one-electron oxidant. In this case, the caboradical dimerization is hampered. The radicals can be used in preparative procedures. One typical example is alkylation of heterocyclic nitrogen bases (Minisci et al. 1983). 

Dinitrogen tetroxide added at 0 to a soln. of cyclohexanone and acetic anhydride in CCI4, and stored ca. 57 hrs. at -10" with repeated collection of the precipitated product 2-nitroso-2-nitrocyclohexanone. Y 72%. Reactions of the product s. F. Minisci and A. Quilico, Org. Prep. Procedures 1, 5 (1969). 

An indirect approach can also be implemented in order to obtain the desired regioselectivity and improve on the yields of the alkylpyridines. For this purpose, two substrates are used simultaneously dimethylsulfoxide (DMSO) and the iodo-substituted hydrocarbon of interest (R-I). This procedure has been pioneered by Minisci and co-workers. For instance, 2- and 4-terf-adamantylpyridine can be selectively obtained by first allowing the hydroxyl radicals generated by the Gif system Fe(py)2(Pic)2/H202 (0.4 mmol/15 mmol) to react, almost exclusively, with DMSO (8.0 mL). The resulting methyl radicals... 

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