Photochemical and photophysical behavior of 2-halo-N, N-diphenylaniline in photostimulated intramolecular arylation reactions. Synthesis of carbazoles.

MICAELA D. HEREDIA; MARÍA EUGENIA BUDÉN; JAVIER I. BARDAGÍ; MARCELO PUIATTI; ROBERTO A. ROSSI

Carlos Paz

Encuentro; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología (XIII ELAFOT); 2017

Recently we reported an efficient strategy to afford a family of 9-H-carbazoles by a photosubstitution intramolecular N -arylation reaction from biphenyl amines (Radical Nucleophilic Substitution Unimolecular, SRN 1). In contrast to C-N bond formation strategies to obtain carbazoles, C-C bond forming route from 2-halo-N,N-arylaniline, has been less explored. More recently, the reactions of 2-iodo and 2-bromodiarylanilines (3a and 3b) with KOtBu in presence of ethylene glycol or 1,10-phenanthroline provide carbazoles in moderate to excellent yields by Base-promoted Homolytic Aromatic Substitution. In contrast to iodide and bromide substrates (3a and 3b), chloride derivative 3c exhibit lower reactivity. In our case, when we did the photostimulated reaction (using visible light) of 3c (R 2 = H) in presence of KO t Bu (3 equiv) in DMSO we succesfully obtained 2b in 85% yield. Under this super-basic conditions, dimsyl anion is formed from a strong base (KO t Bu) and DMSO (solvent). Preliminar results reveal that no Charge Transfer Complex (CTC) interaction could be detected by the UV-Vis absorption spectrum between the dimsyl anion and 3. Previous studies showed that dimsyl anion is responsible for inducing the initiation by a photo-BHAS process on alkyl and aryl halides [3]. This posibilitty was analized, however there was not change in fluorescence intensity of 3c increasing concentrations of KO t Bu, what is more a new maxima of the emission spectra was detected. In the present work we study the photophysical properties (UV-Vis, steady state fluorescence and time-resolved fluorescence) from 2-halo- N , N -diarylaniline and photochemical aspects in the mechanism (varying the reaction conditions) of these photosubstitution reactions. Also, computational modelling will be use to evaluate the proposed hypothesis.