A chiral, oxidatively cleavable auxiliary in beta-lactam synthesis - Double diastereocontrol with p-methoxyphenethyl-substituted imines

A new chiral, oxidatively removable auxiliary for the Staudinger reaction i s presented. When diazo ketones 1-3 prepared from suitably protected amino acids reacted with p-methoxyphenethyl (PMPE)-substituted imines, the corres ponding trans-substituted beta-lactams 7 and 8a-h were formed. With the (S) -configured imine 5, an improvement of the selectivities is observed in com parison with achiral p-methoxybenzyl (PMB)-substituted imines by double ste reoselection; consequently, the ratio of isomers decreased with the (R)-imi ne 4. The auxiliary could be removed with cerium ammonium nitrate (CAN).