Atropisomeric Properties of 7-, 8-, and 9-Membered-Ring Dibenzolactams: Conformation, Thermal Stability, and Chemical Reactivity

The atropisomeric enantiomers of 7-, 8-, and 9-membered-ring dibenzolactams were separated by using chiral H PLC, and their stereochemistries were clarified by using X-ray crystallographic analysis. The atropisomers showed high stereochemical stability with the 8-membered ring being the most stable. In 7- and 8-membered dibenzolactams, highly stereoselective C7-methylation proceeded from the lower side of the ring to provide the products with a C7-methyl group in the pseudoaxial orientation, which converted to thermodynamically more stable isomers with the pseudoequatorial C7-methyl group. In 9-membered dibenzolactam, C7-methylation occurred from the opposite (upper) side of the ring to provide a thermodynamically stable product with the pseudoequatorial C7-methyl group.