Hidroformilação de terpenos e propenilbenzenos de ocorrência natural para a síntese de produtos de química fina

Abstract

In the present work, the rhodium catalyzed hydroformylation of naturally occurring terpenes and 2-propenylbenzenes was studied using organometallic complexes modified by phosphorus ligands. The hydroformylation was a key step in four studies: in the transformation of naturally occurring terpenes not yet explored through this methodology, in tandem transformations, as a synthetic step in a multi-step protocol and in a biphasic system with catalyst recovery. The products obtained show a great potential as fragrances and pharmaceuticals. The hydroformylation of the sesquiterpene valencene was studied in a homogeneous system. Although the proven potential of this compound as a fragrance precursor, its hydroformylation was never reported before. Temperature, ligand nature and P/Rh molar ratio were evaluated. At the best conditions, a monocarbonylated product was selectively obtained in 100% yield. In harsher conditions, a dicarbonylated product was obtained with a yield of 62%. These are novel aldehydes never reported before. The tandem hydroformylation/acetalization cocatalyzed by acid of the monoterpene limonene in the presence of neopentyl glycol, 2-ethyl-1,3-hexanediol or 1,3-butanediol in order to obtain cyclic acetals used as fragrances was also studied. With neopentyl glycol, the influence of temperature, diol excess, acid concentration and solvent were evaluated, as well as a comparison between the tandem and the multi-reactor protocols. Acetals were obtained with up to 97% yield. The products derived from 2-ethyl-1,3-hexanediol and 1,3-butanediol are novel compounds. In another study, 2-propenylbenzenes were transformed through a cross-metathesis/dehydrochlorination/hydroformylation sequence. The two first steps transform a terminal olefin into a terminal conjugate diene. Some reaction parameters for the hydroformylation were evaluated, such as ligand nature, temperature, solvent and substrate nature. Branched aldehydes were obtained with up to 92% yield. After carbonylation of one of the double bonds, a fast isomerization/hydrogenation of the remaining double bond can occur. The hydrogenation can be inhibited by the simple change of ligand and temperature. At least 9 novel compounds were obtained. Finally, the 2-propenylbenzene estragole was hydroformylated in an aqueous biphasic system containing a rhodium catalyst anchored in a phosphine functionalized core-cross-linked micelle nanoreactor (Rh/TPP@CCM). A methodology for an efficient application and recycling of the catalyst was developed. At the best conditions, the catalyst was efficiently recycled four times, with no loss in aldehyde chemoselectivity.