Sistemas catalíticos tandem para a funcionalização de arilpropenos de origem natural

Abstract

This work presents the advances made in the development of tandem catalytic systems highly efficient in converting allyl and propenyl benzenes of renewable sources into products of proved or potential interest as fine chemicals. The reactions studied were: cross-metathesis/hydrogenation; hydroaminomethylation; and hydroformylation / Knoevenagel condensation / hydrogenation. In the first part of the work, the cross-metathesis of the propenyl benzenes isoeugenol, anethole and isosafrol with methylacrylate were performed employingGrubbs-type catalysts. The addition of phenols (2-tert-butyl or 4-tert-butyl) leaded to the increase both in stability of the catalyst and selectivity for the desired cross metathesis products. Under optimal conditions, yields around 95% were obtained with 2,8 mol% of RuCl2(IMes)(CH2Ph) in dichloroethane at 70oC. If desired, the C=C of the formed cinammates and ferulates can be hydrogenated employing the residualruthenium complexes by adding 30 bar of molecular hydrogen and reacting for 3h at 70 oC with quantitative yield. In the second part of the work, the hydroaminomethylation of eugenol or isoeugenol with di-n-butylamine promoted by bis [(1,5-cyclooctadiene) (ì-methoxy)rhodium (I)] (Rh-1) was studied. In the absence of phophorus ancillaries, the system promoted the complete conversion of the substrate into amines, but the regioselectivity was low. On one hand phophine-type ligands reduce the competitive isomerization and improve the regioselectivity for the linear product. On the other hand, the addition ofsuch kind of ligands hampers the enemine hydrogenation step and make the intermediate aldehydes and enamines accumulate. Employing triflic acid as a promoter, the catalytic system becomes highly efficient and regioselective. Under optimalconditions the corresponding linear amine is obtained in 93% employing 0.05 mol% ofthe above-mentioned Rh complex NAPHOS as ancillary.In the third part of the work the tandem sequence hydroformylation / Knoevenagel condensation / hydrogenation was employed having eugenol as substrate and acetoacetone, methylmalonate or ethylacetoacetate as condensation counterparts.The reaction was performed in water as solvent employing the Rh-1, tris(3-sulfonatophenyl)phosphine, trisodium salt (TPPTS), piperidynium acetate and cetyltrimethylammonium chloride (CTAC). Under optimal conditions, yields up to 83% were obtained. It was possible to recycle the catalyst by reusing the aqueous phase, although it caused some loss in selectivity