A mixture of 28.2 g (0.142 mol) of 4-(ethoxycarbonyl-amino)-thiophene-3-carboxaldehyde, 28.2 g (0.141 mol) of 4-amino-1-(1,1-dimethyl-ethoxycarbonyl)piperidine and 300 ml of toluene was refluxed using a water separator until water formation had ceased. The solvent was removed in vacuo, the residue was dissolved in 300 ml of methanol and at room temperature combined batchwise with 5.5 g (0.145 mol) of sodium borohydride. The mixture was stirred for a further hour at room temperature, then evaporated down in vacuo and the residue was distributed between water and tert. butyl-methylether. The organic phase was dried over sodium sulphate and freed from solvent in vacuo. The oily residue was further processed without purification.
