Selecting reactions and reactants using a switchable rotaxane organocatalyst with two different active sites† †Electronic supplementary information (ESI) available: Synthetic procedures and characterisation data. See DOI: 10.1039/c4sc03279a Click here for additional data file.

Synthetic catalysts have previously been developed where a stimulus can be used to turn the catalytic activity ‘on’ or ‘off’ or to change the stereochemical outcome of a reaction. Here we report on an articial system that can switch between two different modes of organocatalysis, each promoting a different chemical transformation. The result is a molecular catalyst that can be used to produce different reaction outcomes from a mixture of building blocks (Fig. 1). The switchable catalyst employed is a [2]rotaxane in which the position of the macrocycle can be changed to block one or other of two organocatalytic active sites. The rotaxane (1/1-H$CF3CO2 , Fig. 2) features a thread bearing dibenzylamine/dibenzylammonium and squaramide units as the catalytic centres. The activities of the organocatalytic sites are based