SYNTHESIS OF BETA-LACTAMS BY CONDENSATION OF THE TIN ENOLATES OF 2-PYRIDYLTHIOESTERS WITH IMINES - A COMPARISON BETWEEN TITANIUM AND TIN ENOLATES

Addition of tricthylamine to a mixture of 2-pyridylthioesters and SnCl4 or SnBr4 affords the corresponding tin(IV) enolates that add to imines to give beta-lactams in fair to good yields and with various degree of trans/cis stereoselectivity. Examples of highly diastereofacially selective reactions carried out on a chiral thioester and on a chiral imine are also reported. The results are compared with those obtained in the condensations promoted by TiCl4 and TiBr4.