F. Minisci

Nucleophilic character of alkyl radicals—VI : A new convenient selective alkylation of heteroaromatic bases

Abstract A new method of homolytic alkylation of heteroaromatic bases is described, in which the silver-catalysed oxidative decarboxylation of acids by peroxydisulphate is used as a source of alkyl radicals. The method is particularly noteworthy because of the good yields and the high selectivity obtained, due to the nucleophilic character of the alkyl radicals; for synthetic interest it is comparable to electrophilic alkylation in the homocyclic series.

Efficient Mn–Cu and Mn–Co–TEMPO-catalysed oxidation of alcohols into aldehydes and ketones by oxygen under mild conditions

Abstract A catalytic amount of Mn(II)–Co(II) or Mn(II)–Cu(II) nitrates in combination with TEMPO allows the selective oxidation of primary and secondary alcohols to aldehydes and ketones by oxygen under very mild conditions. Mechanistic aspects are discussed. The catalyst can be considered the cheapest and the most effective for the selective aerobic oxidation of alcohols.

Polar effects in free-radical reactions: new synthetic developments in the functionalization of heteroaromatic bases by nucleophilic radicals

The synthetic interest of the direct substitution of protonated heteroaromatic bases by nucleophilic carbon-centered radicals is furtheron developed by the following new achievements: i) utilization of the redoc system in several solvents; ii) utilization of benzoyl peroxide in alcohols; iii) carbamoylation by HCONH2 and H2O2 in the presence of catalytic amounts of Fe(II). These systems allow to obtain either substitution till now tried without success or reactions of industrial interest. Polar effects play a dominant role in determining reactivity, selectivity and synthetic applications; in particular the role of the strongly nucleophilic intermediate radicals of pyridinyl type in the rearomatization step is emphasized.

Nucleophilic character of alkyl radicals—V: Selective homolytic α-oxyalkylation of heteroaromatic bases

Abstract The direct introduction of α-oxyalkyl groups into heteroaromatic bases has been achieved by means of various oxidising agents: hydrogen peroxide, t-butyl-hydroperoxide, ammonium peroxy-disulphate, sodium perborate and bis-(4-t-butylcyclohexyl)-peroxydicarbonate. The good yields and the complete selectivity obtained are due to the nucleophilic character of the α-oxyalkyl radicals. A quantitative study concerning the nucleophilic character of the dioxanyl radical, carried out by measuring the relative rates of attack on 4-substituted quinolines; revealed in detail all the features of nucleophilic substitutions.

Nucleophilic character of alkyl radicals—VII : Substituent effects on the homolytic alkylation of protonated heteroaromatic bases with methyl, primary, secondary and tertiary alkyl radicals

Abstract The relative rates of the homolytic alkylation of protonated 4-substituted pyridines with methyl, n-propyl, n-butyl, sec-butyl and t-butyl radicals, obtained by the silver-catalyzed decarboxylation of acids with ammonium peroxydisulphate, are reported. This is the first time that the reactivities of the main alkyl radicals have been compared using the same reagent model in a homolytic aromatic alkylation. The alkylation takes place exclusively in the 2 position and the chemical reactivity parameters correlate well with the chemical shifts, but not with the Hammett σ m constants because of an enhanced conjugation of the electron-releasing substituents. The influence of the polar characteristics on the t-butyl radical is very striking. The results are discussed in terms of a π-complex transition state.

Nucleophilic character of alkyl radicals—II : Selective alkylation of pyridine, quinoline and acridine by hydroperoxides and oxaziranes

Abstract Homolytic alkylation of pyridine, quinoline and acridine by redox systems is a selective process as regards orientation and reactivity. The synthetic aspects and the mechanism of the reduction of oxaziranes and homolytic substitution are discussed.

A novel and mild source of carbon-centered radicals by iodosobenzene diacetate (IBDA) and sodium azide from alcohols, ethers, aldehydes, amides and alkyl iodides

Abstract A radical process for the thermal decomposition of IBDA in the presence of sodium azide; by this method, carbon centered radicals can be generated either by hydrogen abstraction from the solvent (an alcohol, an ether, an aldehyde or formamide) or by iodine abstraction from alkyl iodides.

Nucleophilic character of alkyl radicals—XIII: Absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate

Abstract The absolute rate constants for the addition of alkyl radicals to acrylonitrile and methyl acrylate are determined by evaluating the ratio of ligand-transfer oxidation and addition to the double bond. Secondary alkyl radi c als appear to be more reactive than primary alkyl radicals, despite the less favourable energetics. The classical selectivity : reactivity relationship is reversed owing to the nucleophilic character of the alkyl radicals.

A new general method of homolytic alkylation of protonated heteroaromatic bases by carboxylic acids and iodosobenzene diacetate

Abstract A new general, simple and mild procedure is reported in this communication, based on the photochemically induced decarboxylation of carboxylic acids by iodosobenzene diacetate to obtain the substitution of bases by nucleophilic alkyl radicals.

New general and convenient sources of alkyl radicals, useful for selective syntheses

Abstract Alkyl radicals are obtained from alkyl icdides under very simple conditions and with cheap reagents: i) H 2 O 2 and DMSO; ii) H 2 O 2 and acetone; iii) t-BuOOH. The alkyl radicals can be utilized for selective syntheses, mainly selective formation of carbon-carbon bonds.