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.
