In 1966, Nozaki et al. described the asymmetric cyclopropane formation catalyzed by the (salicylaldiminato)copper(II) complex 1 (salicylaldiminato ligand = [C-(2-oxidophenyl-)tO)methanimine-tcN]) [ 11. This was one of the first enantioselective chemical transformations using catalytic amounts of homogeneous chiral metal complexes. Since then, a large number of efficient metal catalysts with bi-or multidentate Schzjjf bases, derived from substituted salicylaldimine derivatives, were developed. Modifications of the ligand led to high enantioselectivities in a variety of 1 2 3 reactions. E.g., optically active Cu" complexes were used in the synthesis of cyclopropanes [2], asymmetric epoxidation of simple alkenes was achieved with (sa1en)manganese complex 2 [3], and enantioselective cyclization was catalyzed by an analogous (sa1en)cobalt complex [4]. The general concept is based on the conformational rigidity induced by the metal-N bonds which creates an appropriate three-dimensional structure for chiral recognition of the substrate. I) ' )
Part of the projected Ph. D. thesis, Universitat Basel.
Visiting student from the Technische Hochschule Aachen, Germany.