Marino Poloni

Chemical and electrochemical synthesis of quinoneimine n-oxides from indolinone-3-arylimino nitroxide radicals

Abstract 2,2-Diphenyl-3-arylimino-indoline-1-oxyls are efficiently converted to the corresponding isomeric 5- and 7-quinoneimine N-oxides either by chemical (cerium ammonium nitrate) or electrochemical oxidation in aqueous acetonitrile. The electrochemical studies indicate that mono-electronic oxidation of the starting compounds leads to the corresponding oxoammonium ions. These are stable in anhydrous acetonitrile, as indicated by cyclic voltammetry, but in non-anhydrous conditions undergo rapid nucleophilic attack by water molecule followed by further oxidation to the final products. The relative economic and practical advantages of the electrochemical unvs the chemical process are discussed. The ESR parameters for the new nitroxide radicals involved in the present investigation are also reported.

IPSO-substitutions. Reactions of 3-substituted indoles with benzoylperoxide

Abstract 3-substituted indoles with benzoylperoxide led to the 3-benzoyloxy derivative. The react i on is discussed in terms of homolytic ipso -substitution.

Electrophilic ipso-substitutions. Part 3. Reactions of 3-substituted indoles,4-substituted N,N-dimethylanilines, and 1- and 3-substituted indolizines with nitrous acid

Reactions of 3-substituted indoles, N,N-dimethylanilines, and 1- and 3-substituted indolizines with nitrous acid yield products of ipso-substitutions, essentially the corresponding nitro-derivatives. An electron transfer process is proposed for the initial step, on the basis of reaction products, e.s.r. evidence, and substrate oxidation potentials.

A correlation between half-wave and ionization potentials for indoles and indolizines

Half-wave oxidation potentials (E1/2), in acetonitrile at a platinum electrode, and gas-phase ionization potentials (P) have been measured for a number of indole and indolizine derivatives, variously substituted on the five-membered ring. Except for a few compounds, a linear correlation of P vs. E1/2 was found. Deviations from linearity are discussed in terms of conformation differences between the two phases and P value uncertainties in those cases where the vibrational fine structure was resolved.

Stereoselective reduction of indoline nitroxide radicals

1,2-Dihydro-2-alkyl-2-phenyl-3H-indol-3-one 1-oxyls (1) and the corresponding amines (6) undergo stereoselective reduction with NaBH4 giving respectively a pair of diastereoisomeric hydroxylamines (2),(3) and the corresponding amines (7),(8) Both lead to nitroxide radicals (4) and (5), by oxidation; the quantitative ratio of diastereoisomers was determined by means of liquid–liquid chromatography. The configurations of the isomers are tentatively assigned on the basis of 1H n.m.r. and e.s.r. data, as well as on the stereochemistry of the reaction.

Radical cations. Part 2. Oxidative dimerization of indolizines: a chemical and electrochemical investigation

3-Unsubstituted indolizines undergo oxidative dimerization in the presence of catalytic amounts of FeIII and oxygen. Although much experimental evidence apparently indicates that FeII is reoxidised to FeIII by oxygen, a chain mechanism cannot be envisaged. A chain sequence can be proposed only in the case where a stoicheiometric amount of FeIII is used.

Electrophilic ipso-substitutions. Part 2. Reactions of 3-substituted indoles and 4-substituted NN-dimethylanilines with arenediazonium ions

3-Substituted indoles and 4-substituted NN-dimethylanilines react with arenediazonium ions to form 3-arylazoindoles and 4-arylazo-NN-dimethylanilines, respectively. The formation of the σ-complex intermediate was interpreted both as electrophilic ipso-attack and as coupling of two radicals deriving from an electron transfer process. Both mechanisms are discussed on the basis of the experimental evidence and on the substrate oxidation potentials. The leaving abilities of the substituents are discussed on the basis of the experimental results.

Acid-catalysed rearrangements. Specific syntheses of 2,3-disubstituted indoles and N-hydroxyindoles

Diastereoisomeric 2-alkyl-(or phenyl)-2-phenyl-3-hydroxy-2,3-dihydroindoles in an acid medium undergo elimination of water and transposition of the group having the major migratory power from C-2 to C-3. The stereochemistry of these compounds and the substituent at the nitrogen atom does not affect the final products, which are the same for the two diastereoisomeric indolines. The migratory power follows the sequence benzyl > phenyl > alkyl. The resulting 2,3-disubstituted indoles and N-hydroxyindoles were obtained in quantitative yield.

Electrophilic ipso-substitutions. Part 1. Reaction of 3-substituted indoles with nitronium and nitrosonium ions

3-Substituted indoles react with nitronium and nitrosonium ions to yield 3-nitroindole. In both cases the reaction was interpreted as an electrophilic ipso-substitution. The reaction mechanism is interpreted by hypothesizing the formation of a σ-complex-like intermediate, which is some cases is preceded by an electron-transfer process. An order for the leaving abilities of the different electrofugal groups is discussed.

Stereospecific reduction of 3-hydroxy-3H-indoles and of their corresponding N-oxides with NaBH4 and LiAIH4. Synthesis of true 1-hydroxy-2,3-disubstituted indoles. Crystal and molecular structure of 3-hydroxy-2,3-diphenylindoline

3-Hydroxy-3H-indoles (1) and their corresponding N-oxides (5) undergo stereospecific reduction at the double CN bond giving the indoline derivatives (2) and (6) respectively, which, in acidic medium, lose water to give the 2,3-disubstituted indoles (3) and (7) whose physical and spectroscopic data are not in agreement with those reported previously. The structure of 3-hydroxy-2,3-diphenylindoline, one of the reduction products, was determined by X-ray diffraction, and it was shown that hydrogen adds at C-2 cis to the hydroxy-group on C-3. 3,3-Disubstituted-3H-indoles with two organic radicals on C-3 give a mixture of stereoisomers.