Studies on a chiral (N,P) ligand containing a C-2-symmetric aziridine unit

As part of a program on the use of chiral aziridines in asymmetric synthesi s and catalysis, the enantiopure (N,P) ligand 1, consisting of a C-2-symmet ric chiral aziridine and a triarylphosphine unit, was prepared. The synthes is was convergent and efficient, proceeding in five steps and 37% overall y ield from 2-bromotoluene. The ligand was designed (a) for a study of the as ymmetric Pd-catalyzed allylic substitution reaction, (b) in an attempt to o btain a measure of the Irans effect of phosphorus relative to an aziridine nitrogen, and (c) to compare its performance with the corresponding chiral phosphinooxazoline species (computational studies having indicated certain similarities between the two ligand types). However, the new aziridine spec ies did not provide levels of enantioselectivity comparable to those obtain ed with the phosphinooxazoline analogs, and our results serve to underline once more the difficulties associated with the rational design of ligands f or asymmetric catalysis.