Synthesis of β-lactams by condensation of titanium enolates of 2-pyridylthioesters with imines. Influence of the imine structure on the trans/cis stereoselectivity

Article abstract of DOI:10.1016/S0040-4020(01)87005-8

The condensation of the titanium enolates of C-2 alkyl substituted 2-pyridylthioesters with imines affords β-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 β-lactams, while sterically non-requiring or chelating groups favour the formation of the cis-products. On the basis of NMR evidences a rationale is proposed to account for the observed stereoselectivity.