Influence of reaction conditions on products of the Pictet–Spengler condensation

The Pictet–Spengler reaction with N-protected α-amino aldehydes was found to be very sensitive to reaction conditions. The outcome of the reaction can be controlled mainly by choice of solvent. Tetrahydro-β-carbolines were obtained in apolar solvents, while in polar media octahydro-bipyrroloindoles were the main compounds. Temperature, amount of acid and reaction time also influenced the final results of the PS reaction. Depending on conditions, products with opposite configuration of stereogenic centre, descended from amino aldehydes, were formed as byproducts.