Soluble-polymer-supported synthesis of beta-lactams on a modified poly(ethylene glycol)

A modified poly(ethylene glycol) (PEG) has been developed for the soluble-p olymer-supported synthesis of beta-lactams. The monomethylether of PEG (MeO PEG) with an average M-W of 5000 was used as the support, a 4-(3-propyl)phe nyl residue as the spacer, and a 4-oxyphenylamino group as the moiety with the reactive functionality. From this modified PEG representative aromatic, heteroaromatic, unsaturated, and aliphatic imines were obtained in high yi elds by different procedures. The polymer-supported imines were then employ ed to prepare several beta-lactams by enolate/imine condensation and ketene /imine cycloaddition. Examples of the control of the absolute stereochemist ry during the azetidinone ring formation are also reported. The reactions c arried out on the polymer-bound imines showed a remarkable similarity to th ose performed on nonimmobilized imines, both in terms of yields and stereos electivities. Removal of the beta-lactams from the polymer has also been ac complished to directly deliver the N-unsubstituted azetidinones.