Regio- and π-facial selective Lewis acid interceded Diels–Alder reactions of α-dienyl-β-lactams: an indepth analysis

The regio-, diastereo-, and π-facial selective Lewis acid mediated Diels–Alder reactions of cis/trans-3-butadienyl-2-azetidinones with unsymmetrical dienophiles viz. methyl acrylate, dimethyl fumarate, and acrolein leading to the synthesis of diastereomerically pure and biologically potent 1,3,4-trisubstituted-2-azetidinones are reported. Theoretical calculations at HF/6-31G∗∗ and 6-31G∗∗/DFT levels have been performed to support the observed π-facial selectivity. The formation of diastereomerically pure ‘endo’ adducts is supported by the X-ray diffraction studies.