IMPROVING THE SCOPE AND UNDERSTANDING OF THE SYMMETRIC AND ASYMMETRIC SUZUKI COUPLING REACTION
Investigations into the Symmetric and Asymmetric Suzuki cross-coupling reaction have been described. A new reaction protocol has been developed in which isolated pre-activated sodium trihydroxyarylborate salts were employed as the organoboron coupling partner, resulting in a more convenient and stoichiometrically efficient process. This alternative protocol has been applied to symmetric Suzuki reactions employing simple electron-rich and electron-poor aryl halide partners, and to sterically challenging Suzuki reactions employing bulkier substrates. Asymmetric (atroposelective) Suzuki coupling reactions were also successfully performed using sodium trihydroxyarylborate salts as coupling substrates. The versatility of these species as general organoboron reagents was also demonstrated by their successful application in a rhodium-catalysed 1,4-addition reaction. Experimental studies of asymmetric Suzuki cross-couplings towards axially chiral biaryl products have also been detailed. Model reactions towards configurationally stable biaryl products were found to undergo a successful chiral induction with the use of chiral ferrocenyl ligand (R)-(S)-PPFA 180, with high enantiomeric excesses achieved in some cases. Investigations into the possible influences on the asymmetric induction process exerted by the electronic and steric properties of the coupling partners were carried out, involving repeat asymmetric reactions towards the biaryl product 1-(2’-nitrophenyl)-2-phenylnaphthalene 179. In these reactions, changes to the reacting moiety of the coupling substrates were tested, with an additional reaction carried out involving the reversal of the organic group borne by each substrate.
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