PRECISE DESIGN OF ALUMINUM REAGENTS THAT EXHIBIT STERIC AND ELECTRONIC EFFECTS

An excellent candidate as a proton substitute in man-made organic reactions is certainly a Lewis acid. Our goal is to engineer an artificial proton substitute of a special shape, which could be utilized as an effective artificial enzyme for chemical reactions, by harnessing the high reactivity of the aluminum atom toward oxygen. Such a concept was initially researched by examining the recognition ability of a specially designed organoaluminum receptors for various oxygen-containing substrates. Our initial finding on the successful discrimination between structurally very similar methyl and ethyl ethers with exceptionally bulky methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) as a highly efficient Lewis acidic receptor induced us to study the more intricate question of diastereoface differentiation for the chiral ether and carbonyl oxygens. Thus, based on our conceptually new diastereoselective activation of ether and carbonyl moieties, exceptionally bulky organoaluminum reagents, MABR and MAPH have been devised in addition to MAD. These organoaluminum receptors can be successfully utilized for various regio- and stereocontrolled organic transformations. Furthermore, electronical stabilization of aldehyde functionalities has been accomplished with MAPH by the two parallel phenyl groups of aluminum ligands.