Novel endo,endo-2,5-diaminonorbonane-derived tertiary C2-symmetrical diamines were synthesized via the one-pot reductive amination of enantiomerically pure norbornane-2,5-dione. These ligands were applied to various catalytic reactions such as asymmetric deprotonation, asymmetric bromine-lithium exchange, and enantioselective addition of aryl- and allkylithium reagents to aromatic aldimines
Asymmetric bromine-lithium exchange has been successfully employed to synthesize bicoumarin chiral building blocks of (+)-isokotanin A and (-)-kotanin in good yields and with an excellent level of enantioselectivity. This is the first reported example of formal syntheses, using this direct methodology, leading to the single (M)-atropoisomer of (+)-isokotanin A and (-)-kotanin building blocks, without any resolution step.
The asymmetric bromine-lithium exchange on a series of prochiral biphenyls was investigated. As in many asymmetric organolithium reactions, the chiral ligand (here a diamine) was considered to be the enantiocontrolling element. We show here that the organolithium reagent also plays an important role.
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