Novel organoalanes in organic synthesis and mechanistic insight in conjugate addition

This thesis describes the development of novel aluminium hydrides (HAlCl2•Ln) and organoalanes(Cl2AlCH=CHR and ClMeAlCH=CHR) for organic synthesis, as well as exploring the mechanism by which copper-catalysed conjugate addition proceed with diethylzinc and triethylaluminium. In Chapter 1, the mechanism of copper-catalysed conjugate addition of diethylzinc to cyclohexenone and nickelcatalysed 1,2-addition of trimethylaluminium to benzaldehyde has been studied. The kinetic behaviour of the systems allows insight into which metal to ligand ratio provides the fastest rest state structure of the catalyst to enter the rate determining step. The ligand order in these reactions (derived from these ligand optimisation plots) provides information about the molecularity within the transition state. In Chapter 2, the synthesis of somewhat air-stabilised aluminium hydrides and their subsequent use in palladiumcatalysed cross-coupling is described. Stabilised aluminium hydrides of the type HAlCl2•Ln, [HAl(OtBu)2] and [HAl(NiBu2)]2 were synthesised. The hydroalumination of terminal alkynes was optimal using bis(pentamethylcyclopentdienyl) zirconocene dichloride, resulting in a highly regio- and stereo3 chemical synthesis of alkenylalanes which undergo highly efficient palladium catalysed cross-coupling with a wide range of sp2 electrophiles. Chapter 3, describes conjugate addition chemistry of ClXAlCH=CHR (X = Cl or Me) under phosphoramidite/ copper(I) conditions (X = Me). Highly enantioselective additions to cyclohexenones (89-98+% ee) were attained. A highly efficient racemic addition of the alkenylalanes (X = Cl) to alkylidene malonates occurs without catalysis. Finally, Chapter 4 includes all the experimental procedures and the analytical data for the compounds prepared in the subsequent chapters.