Syntheses of optically active α-amino nitriles by asymmetric transformation of the second kind using a principle of O.!Dimroth

A mixture of solids A(s) and B-s in equilibrium with the dissolved compounds A(1) and B-1 is transformed completely into one pure solid, say B-s, if the dissolved compounds A(1)reversible arrow B-1 are equilibrating in solution. This is applied to transform 1 : 1 mixtures of solid diastereomeric amygdalates (2-hydroxy-2-phenylacetates; mandelates) (R,R)-3 + (S,R)-3 prepared from racemic alpha-amino nitriles (R,S)-1 with (R)-mandelic acid 2 into stereochemically pure single diastereomers (R,R)-3, or (S,R)-3 (de > 97%) ('asymmetric transformation of the second kind by application of Dimroth's principle'). Decomposition of the amygdalates (R,R)-3, or (S,R)-3, with aqueous base affords the enantiomerically pure alpha-amino nitriles (R)-1, or (S)-1 (ten examples). The chiral auxiliary (R)mandelic acid is recovered almost quantitatively. The optically active alpha-amino nitriles are hydrolyzed to amides 6, and further to alpha-N-alkylamino acids 7. N-Benzylamino acids 7 are hydrogenated to alpha-amino acids 8. Some of the optically active alpha-amino nitriles 1 are reduced to optically active 1,2-diamines 9. In most cases, absolute configurations could be assigned by comparison of the specific rotations observed with those of authentic compounds.