Phthalimide N-oxyl

A new reagent, AMiydroxyphthalimide combined with Co(acac)n (n = 2,3), transforms alkylbenzenes to ketones, whereas methylbenzenes give the corresponding carboxylic acids.1121 Phthalimide N-oxyl was found to be the key intermediate. Novel oxoperoxo Mo(VI) complexes mediate the cost-effective and environmentally benign oxidation of methylbenzenes to carboxylic acids.1384 Similar green oxidation of p-xylene to terephthalic acid was reported by using a Ru-substituted heteropolyanion.1385... 

The radical C-H transformation of ethers is generally initiated by a-hydrogen abstraction with highly reactive radicals generated from such initiators as peroxides [3a, g], photo-activated carbonyl compounds [3b—d], metallic reagents [3i, j], and redox systems [3f, h[. Various combinations of ethers, radical initiators, and radical acceptors (e.g. carbon-carbon multiple bonds) may be used as the reaction components [6], Several notable means of direct C-C bond formation via the radical a-C-H transformation of ethers involve the use of triflon derivatives [7], the phthalimide-N-oxyl (PINO) radical [8], 2-chloroethylsulfonyl oxime ethers [9], and N-acyl aldohydrazones [10],... 

The mechanism of the aerobic oxidation of alcohols depends on the particular catalyst used. Two general mechanisms can be considered (1) the direct oxygenation of alcohols by 02 through a free-radical chain process initiated by the catalyst, and (2) the direct oxidation of the alcohol by the catalyst, which is then regenerated by 02. Both mechanisms are well illustrated [6] by the aerobic oxidations catalyzed by the persistent tetramethylpiperidine-N-oxyl (TEMPO) radical 1 and the nonpersis-tent phthalimide-N-oxyl (PINO) radical 2. 

Recently, we have developed an innovative strategy for the catalytic generation of a type of carbon radical from hydrocarbons. This is a phthalimide N-oxyl (PIN O) radical generated in situ from N-hydroxyphthalimide (NHPI) and molecular oxygen in the presence (or absence) of a cobalt ion under mild conditions. The carbon radicals, derived from a variety of hydrocarbons under the influence of molecular oxygen, lead to oxygenated products like alcohols, ketones, and carboxylic acids in good yields. The development of NHPI-catalyzed reactions has been reported in review papers [7]. 

Benzyl ethers may be converted into their corresponding benzaldehyde derivatives by oxidation with nitric oxide (NO) in the presence of catalytic (V-hydroxyphthaUmide (NHPl). NO reacts with the catalyst to give phthalimide N-oxyl (PINO), which abstracts the benzylic hydrogen atom from the substrate to generate a radical, which reacts in turn with NO to give a carbocation. Nucleophilic attack of water to the cationic species gives the aldehyde via a hemiacetal intermediate. ... 

Ishii et al. also found that phthalimide N-oxyl 94 generated by cocatalyzed oxidation of N-hydroxyphthalimide under O2 atmosphere abstracts a hydrogen atom of C-H moiety in secondary alcohol. They also expanded Ms reaction to y-lactone synthesis through this radical generation from cyclopentanol 92 followed by radical addition to acrylates (Scheme 42) [65]. 

Another typical example for the direct oxidative transformation of methyl arenes were developed by Wang and co-workers [118]. In this palladium catalyzed reaction, tert-butyl nitrite (TBN) was employed as both nitrogen source and oxidant N-hydroxyphthalimide (NHPI) was used as precursor of the active phthalimide N-oxyl (PINO) radical, which initiates the reaction to give benzylic radical A by grabbing hydrogen atom from the substrate. In the interaction between TBN and NHPI, TBN decomposes to NO radical and tert-butyl alcohol. NO radical would trap benzylic radical A to give nitrosomethyl benzene B, which isomerizes to aldoxime C [119]. Finally, nitrile product would be generated fitom C by palladium catalysis (Scheme 4.21). 

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