Enantioselective Catalysis, 120 [1] New Optically Active Pyrrole-oxazolines

W ithin the last years optically active oxazoline ligands have proven use in transition-metal catal­ ysed asymmetric synthesis. In copper-catalysed cy­ clopropanation reactions oxazolines turned out to be the ligands of choice [2, 3], Oxazolines substituted in 2-position with a heteroaromatic com pound such as pyridine [4] gave good results in many systems of asymmetric catalysis, e. g., in enantioselective hydrosilylation [5 7], However, in the coppercatalysed cyclopropanation only moderate stereo­ selectivities were obtained [8]. Therefore, we de­ cided to replace the pyridine substituent by the pyr­ role substituent [9], W hereas pyridine-oxazolines are neutral bidentate ligands, pyrrole-oxazolines af­ ter deprotonation would act in a catalyst as anionic bidentate ligands. Only a few pyrrole-oxazolines are known [ 10], none of them in optically active form. This is surprising as various chiral thiopheneoxazolines have already been synthesised [ 11].