Attilio Citterio

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—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.

ω-Iodoalkylammonium salts as permanent capillary silica wall modifiers: Comparative analysis of their structural parameters and substituent effects

Following previous work on the modification and inversion of electroendoosmotic flow (EOF) of naked silica by a cyclic diamine [1-(4-iodobutyl)-1,4-dimethylpiperazin-1-ium iodide] [J. Chromatogr. A 894 (2000) 53], the present report considerably expands previous data by describing additional compounds of the same series of omega-iodoalkylammonium salts. Four of them are able to instantaneously reverse the EOF, thus producing a cationic surface with a highly stable reverse EOF. All these compounds are believed to become covalently attached to the silica surface via alkylation occurring by nucleophilic substitution of ionized silanols on the silica wall by the omega-iodo functionality in the modifier. The unique advantage of such compounds, as compared to adsorbed polymers or oligoamine EOF quenchers, is that they are not needed any longer in the background electrolyte, after the initial conditioning step inducing the covalent bond. It is additionally demonstrated, by running a mixture of cinnamic acid compounds, that some of the omega-iodoalkylammonium salts can act as modulators of analyte migration, thus inducing separations of otherwise identical compounds, such as isomeric species. Such interactions can only occur when the analytes drift close to the silica wall, and must be rapidly reversible, since no peak tailing or broadening is experienced.

Oxidative deprotonation of carbonyl compounds by Fe(III) salts

Abstract Iron (III) salts (perchlorate and nitrate nonahydrate) in acetonitrile or acetic anhydride at 0–50°C oxidize the ∝-position of malonic esters efficiently via the corresponding radicals. In the presence of olefins and aromatics, inter- and intramolecular free radical chain or oxidative additions are observed.

Boron trichloride catalyzed ortho carbonylation of phenols: : Synthesis of 2-hydroxy-aryl-carboxyamides and -ketones.

In the presence of equimolar quantity of BCl3, phenols 1 react with isocyanates and acyl chlorides to give, usually with good-excellent yields, 2-hydroxy-aryl-carboxy-amides 2 and 2-hydroxy-aryl-ketones 3 respectively. A distinctive behaviour of BCl3 in comparison with other Lewis acids is observed.

α-Hydroxyalkylation of heteroaromatic bases by alcohols and hydroxylamine-O-sulphonic acid

Abstract The homolytic decomposition of hydroxylamine-O-sulphonic acid in alcoholic solvents was investigated in the presence or absence of protonated heteroaromatic bases and Fe(II) salt. The addition of the α-hydroxyalkyl radicals to the base and their oxidation by Fe(III) salt to the corresponding alkyl cyanide were competitive processes. A redox chain process involving the amino radical cation, NH 3 t. , is suggested and the factors affecting the yields of the homolytic substitution are discussed.

Synthesis of Aryliodides from Diazonium Tetrafluoroborate in Dimethylsulfoxide

Abstract One of the best methods for the introduction of iodine in the aromatic ring, is the reaction of arenediazonium salts with iodine ions in water1, for which a free radical mechanism was proposed2. Although the yields are generally good, numerous attempts were made to improve the method and to simplify the isolation procedure.

Electron-transfer processes: New synthesis of γ-lactones by peroxydisulfate oxidation of isopropylbenzenes and aliphatic carboxylic acids

Abstract A new synthesis of γ-lactones by peroxydisulfate oxidation of isopropylbenzenes is described. Evidence concerning the free-radical mechanism is reported; the intermediate formation of alkyl and benzyl radicals is evidenced by trapping them with quinoxaline. The role of the iron catalyst is discussed.

Hypervalent iodine as good leaving group: oxidative rearrangement of 1-IODO-2-methoxy-2-arylalkanes.

A new example of the good leaving group properties of hypervalent iodine is reported: oxidative rearrangement of 1-iodo-2-methoxy-2-arylalkanes 1 (R=alkyl) provides, via 1,2-aryl shift, alkyl benzyl ketones 3 in good yields.

Nucleophilic character of alkyl radicals. Rate constant and new methods of homolytic alkylation of 1,4-benzoquinone

Methyl-aromaten (I) reagieren mit p-Benzochinon (II) in Gegenwart von Silberpersulfat zum Produkt (III) uber diskutierte Zwischenstufen.