Theoretical studies of the conformers of rac-6,6′,7,7′-tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-bisisoquinoline and its N-acyl and N-alkyl derivatives

The low-energy structures and internal rotation about the C₁-C₁^′ bridging bond of rac-6,6′,7,7′-tetramethoxy-1,1′,2,2′,3,3′,4,4′-octahydro-1,1′-bisisoquinoline, its N-alkyl and N-acyl derivatives were studied using the DFT B3LYP method. The global minimum (gauche) of 1,1′-bisisoquinoline was found to be different from the reported crystal structure (trans), which indicated the important of environment on the compound conformation and hence it catalytic potential. Our calculations also indicated that the global minima of 1,1′-bisisoquinoline and its derivatives are dynamically stable along their internal rotation potential energy surface. The stable conformations of the tetrahydroisoquinoline groups of N-acyl derivatives are different from their parent molecule and there is a dependency of their structures on the N-substituents for N-acyl derivative.