Synthesis and exploration of chiral aza-bis(oxazolines) and organocatalysts in asymmetric reactions

Aza-bis(oxazolines) (azabox) were introduced by our group in 20001 as structural hybrids of bis(oxazolines) and aza-semicorrins. The attractive features of these ligands are their facile attachment to organic and inorganic supports through alkylation of the central nitrogen, thus, arriving at recyclable catalysts, and the higher electron density than the corresponding bis-(oxazolines), which has been found to be advantages for some reactions, for example in Co catalyzed conjugate reduction of alpha, beta-unsaturated carbonyl compounds or in Pd catalyzed allylations. In order to further utilize the great potential of azabox ligands, their immobilization on various polymeric supports (MeOPEG, Tentagel, Polystyrene, Dendrimer, Fluorous metrials, etc)26 via click reaction was studied, offering both an easy way to recover precious chiral catalysts and improving on reactions through unusual solvation effects. The obtained yield and enantioselectivities were equal or comparable to the non-immobilized ligands.