A modular synthesis for chiral and nonsymmetrical salalen ligands (i.e., mono-reduced salens), carrying an imine and an amine functionality has been developed. The ligands can be assembled in situ by Schiff base formation of an N-(2-hydroxybenzyl)diamine with a salicylic aldehyde, thus allowing rapid and easy variation/optimization of the ligand structure. Aiming at optimal activity and enantioselectivity in the titanium-catalyzed asymmetric epoxidation of non-functionalized olefins, a positional scanning of the two ligand halves was carried out. High epoxide yields were achieved, and up to 98 % ee. The composition of the titanium complex catalysts was determined by high resolution mass spectrometry and X-ray crystallography for one selected example.
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