The development of organolead reagents in organic synthesis
This thesis describes the synthesis of novel lead(IV) tetracarboxylates and the development of their use in carbon-carbon bond formation processes, with a particular emphasis on the construction of chiral, quaternary centres. Organolead(IV) tricarboxylates have been widely used in the functionalisation of a range of β-dicarbonyl compounds, and the available evidence suggests that these reactions occur by a ligand coupling mechanism. For this reason, by using chiral lead(IV) compounds, it may be possible to achieve a transfer of asymmetry in the bond formation reaction. A variety of achiral and chiral dicarboxylic acid ligands were synthesised, either by reaction of phthalic or camphoric anhydride with a range of diols, or by elaboration of the camphoric acid skeleton directly. A range of novel lead(IV) compounds were constructed using these ligands, both as bis-complexes and as mixed ligand complexes. The complexes were characterised by a combination of IR and NMR techniques, including 207Pb NMR spectroscopy, and elemental analysis. The reactivity of some of the complexes was demonstrated via reaction with allyltributyltm. The lead(IV) complexes were used in the α-phenylation of a range of β-dicarbonyl substrates. Yields ranged from poor to excellent, but in all cases the enantiomeric excesses of the reactions were found to be no greater than 12%. Studies of these complexes by 207Pb NMR spectroscopy revealed that each complex was present as more than one species in solution, which is thought to be the reason for the poor overall transfer of chirality in the phenylation reactions. The arylation procedure uses catalytic mercury(II) acetate, which can in turn introduce further potential ligands to the exchanging system. It was found that alternative catalysts, such as mercury(II) chloride, could be used successfully in the α-phenylation reaction.