Interpretation of the Diastereoselectivity of the Cyclopropane Formation Involving π-Allyl Palladium Complexes Based on Molecular Mechanics Calculations

The diastereoselectivity of the base-induced cyclization of 2-amino-4-chlorobutyronitrile derivatives and of the palladium (0) catalyzed tandem alkylation and cyclization of (E)- and (Z)-1,4-dichlorobut-2-enes, providing suitable precursors of asymmetric 2,3-methanoamino acids, was interpreted by means of molecular mechanics calculations based on the MM2 force field. The dummy atom concept for the construction of η3-allyl palladium complexes and a new parameter set for the calculation have been used. The observed diastereoselectivity which resulted from simple kinetic or thermodynamic control, can be however altered in some cases by the palladium-induced reversibility of the three-membered ring formation.