INVESTIGADORES
BAROLO Silvia Maricel
congresos y reuniones científicas
Título:
Computational Study of reactions of 2´-halo-[1,1´-biphenyl]-2-amines: Synthesis of carbazoles by photostimulated intramolecular C-N coupling.
Autor/es:
W. D. GUERRA; S. M. BAROLO; A. B. PIERINI; R. A. ROSSI.
Lugar:
Ciudad de Piedra
Reunión:
Congreso; 10th Congress of the World Association of Theoretical and Computational Chemists; 2014
Resumen:
The Unimolecular Radical Nucleophilic Substitution
(SRN1) is a chain process that involves radicals and radical anions
as intermediates. An interesting feature of the reaction is the possibility to
obtain heterocycles by intramolecular ring closure of compounds bearing both
the leaving group and the nucleophilic center in adequate position [1].
Following this leading
idea, the possibility to obtained carbazoles by the photoinitiated reaction of
2'-halo-2-amines-biphenyls (1) was studied (eq. 1). Experimentally, the reaction of
2'-chloro-[1,1'-biphenyl]-2-amine (1a), afforded the cyclized product 2a
(9H-carbazole, 57% yield) and the
reduced product 3a (13% yield). However, 2'-chloro-N-phenyl-[1,1'-biphenyl]-2-amine (1b) gave only the product 2b (9-phenyl-9H-carbazole) in excellent yield (93%).
The experimental findings
showed in the previous equation were interpreted by density functional theory
(DFT) calculations performed with the B3LYP functional and the 6-311+G* basis
set; the solvent was simulated with the PCM continuum model. The conformations
of anions 1a- (Fig 1) and 1b- were
evaluated. In both cases de only conformer found is responsible to give, after
DET (dissociative electron transfer), the distonic radical anion 1a0?- or 1b0?-. These
intermediates afforded the conjugated radical anion 2a?- or 2b?-
respectively, by C-N cyclization. The activation energy (Eacyclization) calculated for the radical-anion coupling
was 4.55 (1a0?-) and 3.35 (1b0?-)
kcal/mol. Also, both 1a0?- and 1b0?-
could give, after internal rotations (Earotation),
the distonic radical anions 1a180?- and
1b180?-.