Sintese : estrutura e reatividade de sais derivados de N-aminopiridinio e rearranjo (3,3) em sais de N-(aril) N-(metanosulfonilamino) peridino

AUTOR(ES)
DATA DE PUBLICAÇÃO

1987

RESUMO

N(aryllamino) pyridinium halides and tetrafluoroborates were synthetised according to the method of 2,4-dinitrophenylpiridinium chloride cleavage by arylhydrazines, followed by thermal cyclization. Solvent effects on the yield were verified ( acetic acid and dioxanewater). The intermediary hydrazones were characterized by means of UV, IR and mass spectroscopy, and the mechanism discussed. Reaction of pyridine N-imine derivatives (from treatment of the salts with base) with several eletrophiles led to disubstitutedsalts on the exociclic nitrogen. Some other salts were synthetised via direct amination of pyridine by O-aminosulfonic acid. Specifically, treatament of N-(aryl), N-(mesylamino) pyridinium tetrsfluoroborates with base afforded a series of new compounds (below), wich incorporates a bridged tetrahydro -a-carboline system and a boat 1,1-dioxide,1,2,4-thiadiazine, as well as all-cis ring junctions. The mechanism includes a [3,3] rearrangement, where the ene-hydrazine intermediary triggers an indolization process under very mild conditions of reaction. The strained structure of tetracycle formed does not allow rearomatization, and the dihydroindol is isolated. The rearranged structure of the product was elucidated by X-Ray diffraction and H NMR( 400MHz), irradiation experiments), in addition to the conventional spectroscopy measurements. In sn H2 atmosphere and with Raney nickel catalysis, the remaining double bond is reduced, and on reacting with metal hydrides, the product undergoes reductive cleavage to afford a 9 membered sultam ring, where the indol ring is destroyed. The piperidine nitrogen can be ethylated with triethyloxonium tetrafluoroborate and acetylated with acetyl clhoride. In addition to the experimental work, a theoretical evaluation of the N-(arylamino) pyridinium cations and their corresponding imines was inferred from MNDO calculations. The data obtained confirm some experimental results. Two brief studies were carried out: (I) On the regioselectivity in the nitration of pyridine N-oxide, pyridine N-imine and pyridine N-phenylimine; by using tools from Perturabation Theory. (II) attempts to correlate the chemical shift in C NMR and electronic densities in the carbons of the pyridinium ring.

ASSUNTO(S)

haletos compostos carbonilicos piridina

ACESSO AO ARTIGO

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