Stereodivergent synthesis of β-trifluoromethyl-α- amino acids by sequential catalytic processes

In this work, a sequential organocatalytic process for the stereodivergent synthesis of β-trifluoromethyl-α-amino acids using Erlenmeyer azlactones as starting material is presented. The strategy developed consists of a sequential catalytic approach, employing two catalysts that act independently to control the absolute configuration of two different stereocenters. The first step is a catalytic asymmetric hydrogen transfer of the activated double bond of the azlactone promoted by a Jacobsen type thiourea and Hantzsch ester as hydride donor. The second step involves a nucleophilic addition of an alcohol to the carbonyl moiety controlled by a chiral bifunctional catalyst typically used in the dynamic kinetic resolution of azlactones. The catalyst structure for the second synthetic step was thoroughly investigated in order to maximize the selectivity. Both products were achieved with a good diastereoselectivity and high enantioselectivity. Taking into account the obtained result it was possible to set up an initial study for the feasibility of straightforward one-pot procedure. In conclusion, with this work it was possible to set up a synthetic strategy for the synthesis of all four diastereoisomers starting from the set of starting material.