Highly efficient induction of chirality in intramolecular [2+2] cycloadditions between ketenimines and imines

Highly stereocontrolled, intramolecular [2 + 2] cycloadditions between kete nimines and imines leading to 1,2-dihydroazeto[2,1-b]quinazolines have been achieved. The source of stereocontrol is a chiral carbon atom adjacent eit her to the iminic carbon or nitrogen atom. In the first case, the stereocon trol stems from the preference for the axial conformer in the first transit ion structure. In the second case, the origin of the stereocontrol lies on the two-electron stabilizing interaction between the C-C bond being formed and the sigma* orbital corresponding to the polar C-X bond, X being an elec tronegative atom. These models can be extended to other related systems for predicting the stereochemical outcome in this intramolecular reaction.