Síntese, elucidação estrutural e propriedades ópticas de 1,3,2-oxazaborininos diflúor-substituídos

Abstract

The present work presents the synthesis, spectroscopic structural characterization, microbiological and photophysical properties evaluation of new series of diflúoro-organoboro compounds, BODIPYs analogous, from β-enamino-α-keto ester precursors. Initially, following a methodology already reported in the literature, the synthesis of the (Z)-4-(4-bromophenyl)-4-methoxy-2-oxobut-3-enoate (1) precursor was carried out through the acylation reaction of the acetal derived from 4-bromoacetophenone with ethyloxalyl chloride in the presence of pyridine. Then, the synthesis of a novel series of eight β-aminovinyl-α-keto esters, namely (Z)-4-(arylamino)-4-(4-bromophenyl)-2-oxobut-3-ethyl-enoates (3a-h) was carried out from reaction between ethyl (Z)-4-(4-bromophenyl)-4-methoxy-2-oxobut-3-enoate (1) and different substituted primary arylamines (2a-h) in yields from 63-92%, where aryl = phenyl (a), 4-methoxyphenyl (b), 4-nitrophenyl (c) , 4-bromophenyl(d), 2-naphthyl (e), 2-anthracenyl (f), 9H-fluoren-2-yl (g) e 1-pyrenyl (h). In a subsequent reaction step, these β-enamino-α-keto esters 3 were employed as precursor blocks (NCCCO) in the synthesis of new complexes ethyl 3-aryl-4-(4-bromophenyl)-2,2-diflúoro-2H-1,3λ4,2λ4-oxazaborinino-6-carboxylates (4) in reaction with BF3.OEt2 (BF2 source). Thus, a novel series of eight BF2-complexes could be isolated in 60-80% of yield. The series 3, 4 had their antibacterial activity evaluated with negative results for the microorganism strains Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Streptococcus mutans, Enterococcus faecalis, Klebsiella pneumonie, Proteus mirabilis, Candida albicans) e Chromobacterium violaceum. Lastly, the BF2-complexes 4a-h compounds were also subjected to evaluation of their absorption and emission photophysical properties (UV-Vis). It was found that all the complexes 4 showed no luminescence (emission) in solution, independently of the solvents used in the tests.