The oxidation of alcohols to aldehydes and ketones by air or oxygen under mild conditions (room temperature and atmospheric pressure), catalysed by persistent and non-persistent nitroxyl radicals in combination with transition metal salts, appears to be the most convenient of the numerous processes developed for these purposes. The thermochemistry, the kinetics, and the Hammett correlations have allowed us to establish, on a quantitative basis, the fundamental difference

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The aerobic oxidation of 4,4′-diisopropyldiphenyl and 2,6diisopropylnaphthalene, catalysed by N-hydroxyphthalimide and Co(II) salts, leads to the corresponding tertiary benzyl alcohols with high conversion and selectivity under mild conditions (temperature 30-60 °C and atmospheric pressure). Solvent and temperature effects, as resulting from the pioneering work of C. Walling, and more recently from the conclusive resolution of K. U. Ingold and co-workers on a quantitative kinetic basis, strongly affect the selectivity of the aerobic oxidation. This is related to the ratio between the rate of β-scission of the alkoxyl radical, which leads to acetophenone derivatives, and the rate of hydrogen atom abstraction, leading to tertiary benzyl alcohols. These latter are efficiently converted either to diphenols for the production of liquid crystals, by reaction with H 2 O 2 , or to dienes, useful as cross-linking agents, by dehydration. The aerobic oxidation of p-hydroxyacetophenone catalysed by Mn(NO 3 ) 2 and Co(NO 3 ) 2 leads with high selectivity to p-hydroxybenzoic acid, a useful monomer for liquid crystals.

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A new process for the homolytic acylation of protonated heteroaromatic bases is described; an N-oxyl radical (PINO) generated from N-hydroxyphthalimide by air oxygen and Co(II) abstracts a hydrogen atom from an aldehyde. The resulting nucleophilic acyl radical adds to a heteroaromatic base, which is then rearomatised in a chain process. Quinazoline has an anomalous behaviour, giving 3H-quinazolin-4-one as the only reaction product.J. Heterocyclic Chem., 40, 325 (2003).The great synthetic interest of the substitution of protonated heteroaromatic bases by nucleophilic carbon-centred radicals results from the high regio-and chemoselectivity, due to polar effects, the large variety of inexpensive radical sources and the simple experimental conditions. The overall polar effect in these reactions is the result of the polarity and the polarisability of both the radicals and the substrates. While carbon-centred radicals usually do not show an extremely marked nucleophilic character, the electrophilic polarity of heteroaromatic bases is greatly increased by protonation. The strongly induced activation of heteroaromatic bases towards nucleophilic species, due to protonation, cannot be exploited with ionic nucleophiles, whose primary effect is deprotonation of the base. This problem is overcome by the use of free-radical nucleophiles, which react with protonated heteroaromatic bases in a large variety of substitutions characterised by high reactivity and selectivity. These reproduce most of the features of the FriedelCrafts aromatic substitutions, but with opposite reactivity and selectivity, so as to represent one of the main general reactions of this class of aromatic compounds [1].Because of their high reactivity (absolute rate constants in the range of 10 5 -10 8 M -1 s -1 at r.t.) the most reactive bases are effective traps for revealing the presence of carbon-centred radicals in a reaction medium. Basically any carbonyl (acyl, carbamoyl, alkoxycarbonyl) or alkyl radical not bearing electron-withdrawing groups directly bonded to the radical centre can be successfully utilised to this purpose [1].In previous works we have developed two general sources of acyl radicals, useful for the acylation of heteroaromatic bases:1. the t-BuOOH/Fe(III) redox system in the presence of aldehydes [2] (eqs. 1, 2) 2. the oxidative decarboxylation of α-ketoacids by the S 2 O 8 = Ag + redox system [3] (eqs.3, 4) In this Note we report a new homolytic acylation of heteroaromatic bases by aerobic oxidation of aldehydes, catalysed by N-hydroxyphthalimide (NHPI) and Co salts. The overall stoichiometry is given by eq. 5, [HetH 2 ] + being the protonated base.The reaction is carried out by bubbling air in a CH 3 CN or PhCN solution of the heteroaromatic base protonated by CF 3 COOH, the aldehyde, NHPI and the Co(II) salt. In the absence of NHPI no reaction occurs under the same conditions. The reactivity of acyl radicals towards protonated heteroaromatic bases is so high that, even in the case of aldehydes R-CHO where R is a tertiary alkyl gr...

Nucleophilic acyl radicals, generated by treatment of aldehydes with air, N-hydroxyphthalimide and Co(II) salts, add to protonated heteroaromatic bases furnishing C-acylated products. Quinazoline shows an anomalous reaction course furnishing quinazolinone (XIX) as the only reaction product. -(MINISCI*, F.; RECUPERO, F.; CECCHETTO, A.; PUNTA, C.; GAMBAROTTI, C.; FONTANA, F.; PEDULLI, G. F.; J.

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