Quaternary centres bearing a nitrogen atom are found in natural products and therapeutic agents but they represent a remarkably challenging synthetic motif to access when stereochemical control is required. This thesis details investigations into the development of an innovative approach that â by combining biocatalysis with organolithium chemistry â allows the synthesis of enantioenriched Î±-tertiary amines. The strategy relies on the initial enzymatic asymmetric synthesis of amines. Two complementary pathways were identified: deracemisation with amine oxidases or enantioselective reduction with imine reductases. The enantioenriched amines were converted to the corresponding N-benzyl-Nâ-aryl ureas and subsequent organolithium-mediated stereospecific aryl migration developed in the Clayden group were carried out to obtain Î±-tertiary amines. Various scaffold were investigated: 1,1-disubstituted 1,2,3,4-tetrahydroisoquinoline, 2,2-disubstituted azepane and 1,1-disubstituted 2,3,4,5-tetrahydro-1H-benzo[c]azepine derivatives were successfully synthesised. The methodology was extended to acyclic systems, giving 3-pyridyl-derived Î±-tertiary amines.