Scheme 2. Modular assembly of enantioselective switchable catalysts 1 and 2. Reagents and conditions: (i) 6 or 7, Pd(PPh3)4, THF, 2 M Na2CO3, 60 °C, 4 days. (ii) p-Toluenesulfonic acid, THF, H2O, 50 °C, 3 h. (iii) 3- or 4-Nitrobenzohydrazide, aniline, CH2Cl2, r.t., 16 h. (iv) CF3CO2H, CH2Cl2, r.t., 1 h. (v) 4 or 5, DMF, Et3N, MeOH, r.t., 16 h.
