We next probed the possibility to invert the handedness of the BTA helical catalyst under conditions similar to those used to perform the catalytic reaction. A CD spectrum of a solution containing the pre-catalytic system, i.e. all BTA monomers and the secondary phosphine ligand, was recorded at 313 K. (R)-BTA was then added to this solution leading to 50% ee in favour of the (R)-BTA monomers in the supramolecular terpolymer. The solution was stirred for 2 minutes and analyzed by CD. CD spectra before and after addition are almost mirror images (Figure and caption). These CD spectra exhibit a main CD band which belongs exclusively to BTA P since it is the only BTA monomer that absorbs in that region. We previously correlated this induced CD band to the selectivity observed in the coppercatalyzed HS reactions, i.e. the enantioselectivity (up to optimal selectivity that can be obtained by the system under study) is proportional to the intensity of this CD band. As the present BTA coassemblies contain a sufficient number of enantiopure BTA monomers to be homochiral, the inverted CD signals indicate that all BTA P monomers coordinated to copper could be positioned in opposite chiral environments as the result of a full stereochemical inversion of the handedness of the helical assemblies (from right-handed to left-handed) upon addition of (R)-BTA monomers. The exact time needed to achieve this stereochemical switch has not been determined precisely but three minutes of mixing appears reasonable to ensure full stereochemical inversion and to limit side reaction at the vinyl function.