SYNTHESIS OF BETA-LACTAMS BY CONDENSATION OF TITANIUM ENOLATES OF 2-PYRIDYLTHIOESTERS WITH IMINES - INFLUENCE OF THE IMINE STRUCTURE ON THE TRANS/CIS STEREOSELECTIVITY

The condensation of the titanium enolates of C-2 alkyl substituted 2-pyridylthioesters with imines affords beta-lactams in trans/cis ratios that largely depend on the structure of the C-imine residue. Bulky and non-chelating heteroatom-containing groups lead to the formation of trans p-lactams, while sterically non-requiring or chelating groups favour the formation of the cia-products. On the basis of NMR evidences a rationale is proposed to account for the observed stereoselectivity.