Thiyl Radical Mediated Racemization of Benzylic Amines

Thiyl radical mediated reversible H abstraction from the stereogenic center α to the nitrogen atom is a mild method to racemize benzylic amines. Owing to the sensitivity of atom‐transfer reactions to enthalpic effects, a knowledge of both the S–H and the α‐C–H bond dissociation energies is fundamental to select the thiol that is appropriate to abstract the hydrogen atom from a given amine. In the absence of experimental data, theoretical calculations supply a useful predictive tool. The experiments described here are helpful in delineating the optimal conditions that have to be fulfilled for the racemization to proceed in a reasonable time in the presence of either a stoichiometric or a catalytic amount of thiol. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)