Synthesis, characterisation and reactivity studies of chiral β-diketiminate-like supported aluminium Lewis acid complexes towards difficult Diels Alder cycloadditions.

Synthesis and characterisation of several chiral, oxazoline containing β-diketiminate type ligand supported-aluminium compounds are reported. Together with 1 equiv. of Na(BAr Cl 4 ) (Ar Cl = 3,5-Cl 2 -C 6 H 3 ), these chiral Lewis acid complexes, which possess an " achiral end" and " chiral end" have been successfully utilised as catalysts in asymmetric Diels-Alder reactions of 1,3-cyclohexadiene and several different chalcones. Systematic increase in the steric demand of the ligand's " achiral end " of these complexes resulted in enhanced enantioinduction for the cyclisation of 1,3-cyclohexadiene and chalcone. Further structural modifications of the " chiral end" clearly established that having a tert -butyl group connected to the stereogenic centre of the oxazoline fragment yielded the highest enantioselectivity value for the examined cyclisation. A substrate scope was then expanded using several different dienophiles ( i.e. chalcones) generating an enantiomeric excess range of 24-68%.