Homochiral Amine Racemization Processes

The vast majority of early amine racemizations involve an oxidation-reduction approach, with the oxidation of the amine center removing the chirality so that subsequent reduction yields the racemate. The most efficient redox approach is achieved when the oxidized and reduced forms of the substrate are in equilibrium 

Enzyme-catalyzed racemization and racemization of Schiff base intermediates are also valuable techniques, but are generally restricted to amino acid racemiza-tions, which have been much more widely inveshgated than the topics discussed in this chapter [11, 12]. 

Racemization of chiral benzylic and aliphatic primary, secondary, and tertiary amines was recently reported by Gastaldi et al. using sulfur-based catalysts operating through a radical-based mechanism. These authors have also reported enzyme DKR of chiral amines [13]. 

Backvall later demonstrated ruthenium-catalyzed racemization of a range of primary benzyhc amines using Shvd s dimeric catalyst in toluene at 100 °C [15]. 

With the use of additives such as ammonia or 2,4-dimethyl-3-pentanol they managed to suppress dimer formation and observed complete amine racemization in 98% conversion. 

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