NOVEL CONCEPTS IN DIRECTED BIARYL SYNTHESIS .39. THE INFLUENCE OF ALUMINUM TRICHLORIDE ON A CONFIGURATIVELY LABILE LACTONE-BRIDGED BIARYL -QUANTUM-CHEMICAL CALCULATIONS AND OPTICAL SPECTROSCOPY

Semiempirical and ab initio calculations on the binding properties of the AlCl3 complex of 1,3-dimethylbenzo[b]naphtho[1,2-d]pyran-6-one are reported. Compounds of this type are key intermediates in the stereos elective synthesis of axially chiral biaryl systems. Semiempirical (MN DO, PM3) and ab initio (STO-3G, 3-21G) calculations give important inf ormation about conformational changes that occur by complexing the fre e lactone with AlCl3: the calculations predict a significant influence on the lengths of the (C=O)exo and (C-O)endo bonds, and a distinct pl anarization of the heterocyclic lactone part of the complexed benzonap hthopyranone. IR and Raman spectroscopy was applied in order to confir m the theoretical predictions. The good agreement of results obtained by semiempirical frequency calculations with the experimental data sup ports the assignment of vibrational bands affected on coordination. Th e highest shift caused by coordination (- 152 cm-1) is observed for nu (C=O).