Exploring and exploiting benzylic regioselectivity in rhodium-catalysed hydroformylation

Hydroformylation;Organometallic compounds;Rhodium catalysts;Esters

Martin, Nicola ; Clarke, Matt ; Clarke, Matt

University:University of St Andrews

Department:Chemistry (School of)

关键词: Hydroformylation;    Organometallic compounds;    Rhodium catalysts;    Esters;   

Others  :  https://research-repository.st-andrews.ac.uk/bitstream/handle/10023/1904/NicolaMartinMPhilThesis.PDF?sequence=3&isAllowed=y

来源: DR-NTU

【 摘 要 】

This project involves a study into the hydroformylation of substituted alkenes and ways to exploit “benzylic regioselectivity”. It was our aim to develop a clean, selective hydroformylation reaction which takes advantage of the tendency for benzylic regioselectivity in styrene-type molecules; in doing so, providing a potential route to important biologically active molecules. In Chapter Two, hydroformylation of methyl cinnamate is explored since we envisaged that a regioselective hydroformylation of this substrate would serve as a step in an efficient route to γ-amino acids derivatives; which are important building blocks for the synthesis of important drug molecules. Most Rh-phosphine catalysts install the formyl group α- to the ester group however, we found that certain reaction conditions and appropriate choice of phosphorus containing ligands led to highly chemoselective and regioselective hydroformylation. Regioselectivities of up to 25 : 1 favouring the benzylic aldehyde were observed. However, as will be explained, this reaction is hindered by significant hydrogenation under hydroformylation conditions. Using a novel ligand this side reaction was lowered to 5% with reasonable regioselectivity, however overall conversion to the desired aldehyde was low. As a means to synthesise γ-amino acid derivatives, enamine formation using the aldehyde products was also attempted.An alternative alkenyl arene substrate is studied in Chapter Three. High benzylic regioselectivity was observed using a variety of chiral and achiral ligands and again reaction conditions were optimised with the aim to develop an efficient process for the synthesis of γ-amino alcohol derivatives. It was found that PPh₃, tris(3,4,5-trifluorophenyl)phosphine and a phosphaadamantane cage phosphine ligand gave the most promising results with moderate to high regioselectivity observed. Asymmetric hydroformylation was not possible due to low activity using a variety of state-of-the-art chiral ligands.