Chiral diamines. 1. Relative energies of (-)-sparteine conformers, interconversion barriers, and alkyllithium complexes

The structures of the four lower energy sparteine complexes were examined at several theoretical levels including B3P86/6-31G* and B3PX6/6-311+G*. The transition states for interconverting two pairs of conformers were determined using the synchronous transit guided quasi-Newton procedure. Complexes with lithium hydride and propyllithium also were examined. The bidentate complexes formed from conformer Ib and propyllithium had two conformations with essentially the same energy. This may account for the low enantioselectivity observed in the reaction of alkyllithium-sparteine complexes with carbonyl compounds. (C) 2000 Elsevier Science B.V. All rights reserved.