Identificador: TDX:775
Autors: Yañez Rueda, Xiomara
Resum:
The Hydroacylation reaction is a rhodium-catalyzed reaction that allows to obtain ketones from the reaction of aldehydes and alkenes. The intramolecular version in order to obtain cyclopentanones has been widely studied in order to determine the mechanism and also with synthetic purposes. Cycles of 5, 6, 7 and 8 rings have been prepared using this reaction. This reaction has been made enantioselective by using chiral diphosphine ligands such as BINAP or duphos. The intermolecular hydroacylation reaction has been less studied because the importance of the competitive decarbonylation of the aldehyde, that avoids the hydroacylation reaction to proceed. Most studies have been oriented to avoid this competitive reaction, and the most successful methodology involves the formation of a quelating aldimine by reaction of the aldehyde with 3-metil-2-picoline.In this PhD work in 8 different chapters. The first one contains a review of the more relevant work in hydroacylation intra- and intermolecular. The second one describes the main objectives of the work in the context of recent bibliography. Chapters 3 and 4 study the use of Montmorillonite MK-10 in the hydroacylation intermolecular with two different purposes, to be the acid catalysts for the imine formation and ketimine hydrolysis and to the support in order to recover the catalysts. The behaviour as acid catalyst is studied in Chapter 3 concluding that MK-10 is and efficient acid catalysts that allows to replace the common organic acids in this reaction simplifying the reaction mixture. In order to support the rhodium catalyst in MK-10 is necessary to use cationic complexes. Then in the Chapter 4 is reported the synthesis of cationic rhodium complexes containing different mono and diphosphines. When these complexes were used as catalysts in the hydroacylation of 1-octene with benzaldehyde in the yields were much lower. Yields increased when chloride anion was added as BnMe3NCl. In order to know which was the role of the chloride, we performed a mechanistic studied. Studies by NMR a low temperature showed that the in the absence of the ion chloride the oxidative addition was very slow, and was very fast when the chloride ion was added. Kinetic isotopic studies and substituent effects in the reaction rate confirmed that the reductive elimination was the rate determining step when chlorine was present. We performed DFT theoretical calculations which showed that the aldimine form a four member quelate with the cationic complex avoiding the system to give the oxidative addition. This quelate is opened in the presence of chloride. That has allowed us to suggest a modification of the catalytic cycle when cationic complexes are used. In the Chapter 5 we studied the effect of bulky ligands in the control of the regioselectivity in the hydroacylation of alkynes. We observed that the starting hypothesis was correct since we observed that when bulky ligand were used an increasing percentage of product derived of introduction of acyl group in the C-1 of the alkene was observed, the product resulting of the introduction of acyl in the C-2 being the normal one with ligands with small cone angle. Unfortunately when bulky ligands were used the conversion drops dramatically.Chapter 6 reports the stereoselective synthesis of enantiomerically pure 3-hydroxy- and 2,3-dihydroxy-ciclopentanones by intramolecular cyclization of chiral 3-hydroxy-4-pentenal and 2,3-dihydroxy-4-pentenal derivatives. These substrates were obtained from 2-deoxy-ribose and ribose, respectively. The cyclization of 2,3-dihydroxy-4-pentenal derivatives required high percentage of catalysts, according to the reported for aldehydes at position 2. Chapter 7 contains the main conclusion of the work and Chapter 8 describes the experimental part of the work, including main experimental techniques used, protocols of catalysis and synthesis of compounds and data for their characterization.
Repositori URV