Oscillation experiment (a) showing selectivity for salicyl aldehyde (8) over p-hydroxybenzaldehyde (15) contrasted with a control experiment in flow in the absence of oscillations (b). These competition experiments were carried out using conditions and starting ingredient concentrations that result in peak/steady-state concentrations of piperidine of 22 1/19 1 mM (mean plus s.d.; Supplementary Fig. 33). In the oscillating conditions (a) the concentrations of 8 (pink) and the associated product 3-(methoxycarbonyl)coumarin (10, orange) were found to oscillate, whereas the concentrations of 15 (teal) and its associated product dimethyl (p-hydroxybenzylidene)malonate (16, brick red) remain nearly constant with less than 6% conversion of 15 to 16. By contrast, in the non-oscillating control experiment with steady concentrations of piperidine (b) that equal the peak concentration in their oscillating counterpart, the reaction of 8 (pink) to 10 (orange) reaches nearly full conversion whereas that of 15 (teal) to 16 (brick red) reaches a conversion of around 18%. All reactions were carried out in CSTR at 60 C in DMSO and were monitored using in situ infrared spectroscopy (Supplementary Fig. 34) and 1 H-NMR spectroscopy of samples taken every 30 min.
